Bridgeport J-Head Series User manual

Bridgeport J-Head Series I Mill Rebuild
Document Number: BPJ1RBLD_002
Document Version: 2.0.01
Document Version Date: January 31, 2011
Prepared By: Hoffman Mechatronics
496 Albrough Blvd.
Colonial Beach, Va 22443
[e-mail]

Hoffman Mechatronics Bridgeport Mill J1 Rebuild
Table of Contents
1.0 Document Information .....................................................................................................6
1.1 Disclaimer..........................................................................................................................................6
1.2 Notes from the Author........................................................................................................................6
1.3 Copyright............................................................................................................................................6
1.4 Document Organization.....................................................................................................................7
1.5 Change History..................................................................................................................................7
1.6 Dedications and Acknowledgements.................................................................................................7
2.0 Mill Overview.....................................................................................................................8
2.1 Mill Description ..................................................................................................................................8
2.2 Repair Estimates ...............................................................................................................................8
2.3 Why would I do this?..........................................................................................................................9
2.4 Isn’t it too old?....................................................................................................................................9
2.5 Disassembly/Reassembly Suggestions...........................................................................................10
3.0 Motor and Drive Section ................................................................................................12
3.1 Motor Removal, Inspection, & Reassembly (RIR)...........................................................................12
3.1.1 Motor Removal..........................................................................................................................12
3.1.2 Motor Inspection........................................................................................................................12
3.1.3 Motor Reassembly ....................................................................................................................13
3.2 Motor Replacement .........................................................................................................................13
3.3 Drive Housing Section.....................................................................................................................14
3.3.1 Drive Housing Removal ............................................................................................................14
3.3.2 Drive Housing Inspection..........................................................................................................16
3.3.3 Drive Housing Reassembly.......................................................................................................17
4.0 J-Head Section................................................................................................................18
4.1 J-Head R & R...................................................................................................................................19
4.1.1 J-Head Removal........................................................................................................................19
4.1.2 J-Head Reassembly..................................................................................................................20
4.2 Quill Pinion Shaft RIR......................................................................................................................20
4.2.1 Quill Pinion Shaft Removal .......................................................................................................20
4.2.2 Quill Pinion Shaft Inspection.....................................................................................................21
4.2.3 Quill Pinion Shaft Reassembly..................................................................................................22
4.3 Quill Stop and Quill Indicator RIR....................................................................................................22
4.3.1 Quill Stop and Quill Indicator Removal.....................................................................................22
4.3.2 Quill Stop Inspection.................................................................................................................23
4.3.3 Quill Stop Reassembly..............................................................................................................23
4.4 Quill and Spindle Removal ..............................................................................................................23
4.4.1 Quill and Spindle Inspection......................................................................................................24
4.4.2 Spindle Bearing Reassembly/Replacement..............................................................................25
4.5 On Machine Spindle Extraction .......................................................................................................28
4.6 Feed Driving Gear Assembly RIR ...................................................................................................28
4.6.1 Feed Driving Gear Assembly Removal.....................................................................................29
4.6.2 Feed Driving Gear Assembly Inspection...................................................................................30
4.6.3 Feed Driving Gear Assembly Reassembly...............................................................................30
4.7 Feed Reverse Gear Assembly RIR.................................................................................................30
4.7.1 Feed Reverse Gear Assembly Removal...................................................................................30
5.0 Turret Section .................................................................................................................31
5.1 Ram Adapter RIR ............................................................................................................................32
5.1.1 Ram Adapter Removal..............................................................................................................32
5.1.2 Ram Adapter Inspection............................................................................................................32
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5.1.3 Ram Adaptor Reassembly........................................................................................................32
5.2 Ram RIR..........................................................................................................................................33
5.2.1 Ram Removal............................................................................................................................33
5.2.2 Ram Inspection .........................................................................................................................33
5.2.3 Ram Reassembly......................................................................................................................34
5.3 Turret RIR........................................................................................................................................35
5.3.1 Turret Removal..........................................................................................................................35
5.3.2 Turret Inspection .......................................................................................................................36
5.3.3 Turret Reassembly....................................................................................................................36
6.0 Table Section ..................................................................................................................38
6.1 Lead Screw Bearings & Brackets RIR.............................................................................................38
6.1.1 Lead Screw Bearings & Brackets Removal..............................................................................38
6.1.2 Lead Screw Bearings & Brackets Inspection............................................................................39
6.1.3 Lead Screw Bearings & Brackets Reassembly.........................................................................39
6.2 Table X&Y-Axis Gib RIR..................................................................................................................40
6.2.1 Table X&Y-Axis Gib Removal...................................................................................................41
6.2.2 Table X&Y-Axis Gib Inspection.................................................................................................41
6.2.3 Table X&Y-Axis Gib Reassembly..............................................................................................42
6.3 Table RIR.........................................................................................................................................42
6.3.1 Table Removal..........................................................................................................................42
6.3.2 Table Inspection........................................................................................................................43
6.3.3 Table Reassembly ....................................................................................................................44
7.0 Saddle Section................................................................................................................45
7.1 Saddle Section Removal .................................................................................................................45
7.2 Saddle Section Inspection...............................................................................................................46
7.3 Saddle Section Reassembly............................................................................................................47
8.0 Knee Section...................................................................................................................48
8.1 Knee Section Removal....................................................................................................................48
8.2 Knee Section Inspection..................................................................................................................50
8.3 Knee Section Reassembly...............................................................................................................51
9.0 Tramming the Mill...........................................................................................................52
9.1 Bridgeport Method...........................................................................................................................52
9.2 Bearing Race Method......................................................................................................................53
9.3 Tramming to the Vice.......................................................................................................................53
10.0 Maintenance & Lubricants.............................................................................................54
10.1 Backlash Adjustment.......................................................................................................................54
10.2 Feed Trip Adjustment ......................................................................................................................55
10.3 Spindle Lubricant.............................................................................................................................55
10.4 Way Lubricant..................................................................................................................................56
11.0 Troubleshooting .............................................................................................................57
11.1 Quill does not go more than 3-4 inches down.................................................................................57
11.2 Quill feed does not disengage when the quill stop is hit..................................................................57
11.3 I try to install a gib and it stops short. It feels like it is hitting something.........................................57
11.4 My quill keeps falling down, I have to lock the quill in place for it to stay up...................................57
12.0 CNC Conversion.............................................................................................................57
12.1 Why would you convert to CNC?.....................................................................................................57
12.2 Where do you start? ........................................................................................................................58
12.3 Phase 1 – The Ball Screws..............................................................................................................58
12.4 Phase 2 – The Electronics...............................................................................................................59
12.4.1 Open Loop System ...................................................................................................................59
12.4.2 Closed Loop System.................................................................................................................61
12.5 Phase 3 – The X and Y Axes ..........................................................................................................61
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12.6 Phase 4 – The Z Axis ......................................................................................................................63
12.7 Phase 5 – The Planetary Gearhead for Z Axis................................................................................64
12.8 Software packages..........................................................................................................................65
12.9 The Moral of the Story.....................................................................................................................65
13.0 Reference Documents and Websites............................................................................67
13.1 Documents.......................................................................................................................................67
13.2 Websites..........................................................................................................................................67
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Table of Figures
Figure 1 - Mill ID Plate................................................................................................................................8
Figure 2 - J Head Figure 3 - Table and Knee ......................................................................................9
Figure 4 - Grub Screws, note the hollow locking screw...........................................................................11
Figure 5 - Motor Nuts................................................................................................................................12
Figure 6 - Drive Housing Assembly..........................................................................................................14
Figure 7 - Power Head Mounting .............................................................................................................15
Figure 8 - Drive Housing Timing Belt .......................................................................................................15
Figure 9 - Bolts Fastening Drive Housing Together.................................................................................16
Figure 10 - Drive Housing Inspection.......................................................................................................16
Figure 11 - Gear Housing Cover..............................................................................................................17
Figure 12 - J-Head....................................................................................................................................18
Figure 13 - J-Head Mounting....................................................................................................................19
Figure 14 - Overload Lever Plunger and Spring ......................................................................................21
Figure 15 - Overload Clutch Ring and Circlip...........................................................................................21
Figure 16 - Ball Reverse Lever, and Quill Stop Trip Lever.......................................................................22
Figure 17 - Homemade Spanner Nut Wrench..........................................................................................24
Figure 18 - Note the Axial Alignment Asterisk and the Bearing Orientation ............................................25
Figure 19 - Note the alignment marks on outer races preparing for next step.........................................26
Figure 20 - Aligning with Nosepiece Screw Hole .....................................................................................27
Figure 21 – Homemade Spanner Nut Wrench.........................................................................................27
Figure 22 - Worm Gear Cradle Assembly................................................................................................29
Figure 23 - Feed Driving Gear Assembly.................................................................................................29
Figure 24 - Reverse Feed Gear Assembly...............................................................................................30
Figure 25 - Reverse Feed Gear Removal................................................................................................31
Figure 26 - Ram Adapter..........................................................................................................................32
Figure 27 - Ram Assembly.......................................................................................................................33
Figure 28 - Turret Base and Ram Lock....................................................................................................33
Figure 29 - Ram Installation .....................................................................................................................34
Figure 30 - Ram Sliding Fixture................................................................................................................35
Figure 31 - Turret Bolts and Cross Member.............................................................................................36
Figure 32 - Turret Reassembly.................................................................................................................36
Figure 33 - Turret Cross Member.............................................................................................................37
Figure 34 - Table Handle, Dial and Nut....................................................................................................38
Figure 35 - Broken Bracket.......................................................................................................................39
Figure 36 - Bearing Bracket with Bearings Installed................................................................................40
Figure 37 - Gib Adjusting Screw...............................................................................................................40
Figure 38 - Gib Parallels...........................................................................................................................40
Figure 39 - Y-Axis Chip Wiper Cover.......................................................................................................41
Figure 40 - Y-Axis Gib and Adjusting Screw............................................................................................41
Figure 41 - Table Nearly Ready for Removal...........................................................................................43
Figure 43- Saddle.....................................................................................................................................45
Figure 44- Lead Screw Nut.......................................................................................................................45
Figure 45- Lead Screw Nut Bracket .........................................................................................................46
Figure 46- Knee Gib Area.........................................................................................................................48
Figure 47– Removing/Reinstalling the Knee............................................................................................49
Figure 48 - After the Crank and Dial have been Removed......................................................................49
Figure 49 - Knee Elevating Bevel Gears..................................................................................................50
Figure 50 - Elevating Screw Bearing Retainer Ring.................................................................................50
Figure 53 - Feed Nut Bracket...................................................................................................................54
Figure 54 - Feed Trip Lever......................................................................................................................55
Figure 55 - Spindle and Back Gear Lube Cups........................................................................................55
Figure 56 - Way Lube Fittings ..................................................................................................................56
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Figure 57 - Knee Lube Fittings.................................................................................................................56
Figure 58 – CNC Electronics....................................................................................................................60
Figure 59 – X Axis Drive Tube .................................................................................................................62
Figure 60 – Y Axis Drive Tube .................................................................................................................62
Figure 62 – Z Axis Installation..................................................................................................................64
Figure 63 – Z Axis Planetary Gearbox Installation...................................................................................65
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1.0 Document Information
1.1 Disclaimer
Milling machines are industrial pieces of equipment meant to be operated by trained personnel.
The maintenance and rebuild procedures for these machines are also meant to be carried out by
trained personnel. This manual is provided merely to provide information to authorized persons,
and the author assumes no liability for any damage or injury from the information and
procedures that are documented within. These machines are heavy, powerful, and dangerous to
those not trained in their operation or maintenance. I want to emphasize that you should exercise
EXTREME CAUTION when working on or with these machines to minimize or eliminate the
possibility of personal injury.
1.2 Notes from the Author
This document was created during the rebuild of my personal 1963 Bridgeport Series I J-Head,
Stepped Pulley Mill. Much of the information presented in this document is from my own
personal experiences, and all of the images that are located throughout the document were taken
by me using a Nikon Coolpix 4300 and a Nikon D70s. For those images where I have included
drawings, they were created using either TurboCADCAM or SolidWorks.
So why would I take the time to try and document this? First of all, because I could not find the
information I needed to complete this rebuild and I thought that others may want some of the
same information. Secondly, I wanted to give something back to the home machining
community that has provided so much useful information to me. Where possible I have included
acknowledgements/references for the assistance I have received. If I have missed anyone, please
feel free to let me know. I certainly could not have compiled and reviewed all of this information
by myself, nor do I want people to think that I have. There are many trained personnel out there
willing to devote their time and machines and I want to make sure that have I given everyone
their fair share of credit.
Where possible I have taken pictures of every phase of the assembly and tuning of this wonderful
machine. Most of the information I have is from doing, not from being taught, so if you find
something in error, I beg of you … please let me know. This document can only improve if
people like you are willing to say “Mike is full of crap, I better let him know!”
What is the benefit for telling me that I am full of crap? Well, not only the personal pleasure of
doing so, but I will place your name in the acknowledgements section, and send you a revised
copy of the manual.
1.3 Copyright
Hoffman Mechatronics (a.k.a. Mike Hoffman) maintains the copyright to this document. If this
document is sold without my permission, then that is a violation of my copyright. I have decided
to release this document into the public domain, which means if you paid for it, you have been
ripped off, and someone else is profiting from my work.
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1.4 Document Organization
You will quickly note that I have tried to organize this document to the corresponding parts of
the Bridgeport Mill. I believe it will make this document easier to follow should someone be
trying to solve a specific problem. It also tends to follow the order of disassembly if someone is
starting to completely disassemble their mill for the first time. One of the last sections of the
document deals with troubleshooting. Although this portion is rather small now, I am hoping that
I can add to this as more and more people provide questions, and solutions to common and not so
common problems.
NOTES: are included in the document where I think something bears bringing attention to.
CAUTIONS: are highlighted where someone may be injured if proper safety precautions are not
taken.
1.5 Change History
Revision Date Changed By Change Description
Draft 8/29/2005 M. Hoffman Initial draft
Draft 0.01 10/15/2005 M. Hoffman More images, callouts, and tense corrections.
1.0.00 8/22/2006 M. Hoffman More images, more text, and review of all figures
1.6 Dedications and Acknowledgements
First and foremost I want to dedicate this manual to my wife who has put up with my insane
hobbies and business ideas for some 21 years. She is the one who carries me to the hospital when
I do stupid things, and then cares for me at home until I am once again able to do more stupid
things.
Secondly I want to thank my brother for showing me this amazing machine, and putting the idea
in my head that I could rebuild it and make it new again.
I also wanted to send out a special thanks to the Chesapeake Area Metalworking Society
(CAMS). From the very beginning they have supported my efforts and offered to help with
everything. Sorry guys, I won’t be bringing the finished mill in for “Show n Tell”, but I will
bring pictures!
The following people have helped me considerably along the way, and this document would be
so much less without their inspiration and guidance.
Kirk Burns & Machinist Preston (Burns Machine Shop, King George, Va)
Gary Gelts (Hardinge/Bridgeport)
Jonathan Gavel (CAMS)
Eric Hoffmeyer (CAMS)
Leigh Basset (CAMS)

Hoffman Mechatronics Bridgeport Mill J1 Rebuild
2.0 Mill Overview
I decided to write this section to provide you with an idea of the condition of the mill as I was
evaluating it for purchase and refurbishment. I also wanted to provide a description of the
amount of work that went into the mill to make it operational again.
2.1 Mill Description
The mill that I am rebuilding throughout this document is a 1963 Bridgeport Series I J-Head
Mill. The mill was identified by a brass plate in Figure 1 below that was installed by the US
Navy. This plate identifies this mill as Model# J60526, Serial# BR69063. If you don’t have the
nice Navy placard on your mill you can also find the model number of the older mills on the
door to the pedestal, the face of the J-Head, and on the knee.
Figure 1 - Mill ID Plate
This mill came equipped with a 9” x 36” Table, 9” knee and a Geared Power Feed unit. I paid
$300 for the machine after it was purchased from a Government Surplus by my brother for $400.
That’s right; my brother gave it to me for less than his cost. Yes, I have a great brother!!!
2.2 Repair Estimates
After my initial look at the mill I estimated that it would cost about $1000 to get the mill
operational again, and based on the articles I have read in the forums I estimated that it would be
another $1200 to $1300 to convert this machine to Computer Numeric Controlled (CNC).
What follows is a quick summary of the visible items that helped me to make this estimation: the
spindle bearings were stuck, the table was stuck, the knee was stuck, the turret in/out axis was
stuck, and the entire machine was covered in rust and metal shavings. The spindle bearing felt
protector was missing and metal shavings were covering the upper spindle bearing. From this I
assumed that the bearings were not merely just stuck, but would be unsalvageable. Some of the
components from the J-Head had already been removed and put in boxes, and many items looked
as though they were broken and/or bent from the mill being dropped or mishandled. There were
also a great many parts that were not damaged at all, just stuck because of years of dried up
grease, or the friction from surface rust. Based on the age of the machine and the condition of the
spindle bearings, I decided all bearings would most likely need to be replaced. As you can see
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from Figures 2 and 3 below it barely looked like a mill at all. You can see in the figures that the
Y-Axis handle is bent, the Reverse Feed Knob has been sheered off, and many of the 1” Balls
that were on the selector shafts have been sheared off as well.
Figure 2 - J Head Figure 3 - Table and Knee
2.3 Why would I do this?
So why would I tackle such a huge undertaking? There are several reasons, but the most
compelling reason for me was that I needed a mill, and why should I buy a mill that is advertised
as a Bridgeport Clone, when I could have a Bridgeport? My decision to rebuild this mill was
quickly justified after a 5pm telephone call one evening from a technician at Hardinge Tools.
I had called Hardinge Tools to see if I might get more information about disassembling part of
the mill. I was working to disassemble the J-Head and ran into a stumbling block removing the
reverse feed gear assembly. Since I did not want to break any additional parts, I called Hardinge,
fully expecting them to brush me off because I am a home user with a 42 year old machine. I left
a voicemail message and went about trying to find the information I needed elsewhere. Imagine
my surprise when I received a phone call from Gary Gelts, a Hardinge Bridgeport Service
Technician, on his way to a trouble call. He said he had heard my voicemail and wanted to help
me out. After we had talked for a couple minutes, he pulled off the road, extracted his manuals,
and talked me through the procedure of removing the reverse feed gear assembly. After
removing the assembly and thanking Gary for his time, I sat there thinking about the entire
phone call, the level of professionalism, the enthusiasm, and the willingness to help someone
without the least expectation of payment. Yes, a Bridgeport was definitely the way to go.
2.4 Isn’t it too old?
Not really. As you can expect, many of the older machines were designed to very strict
tolerances for accuracy, ease of maintenance, and durability. The machines were so popular and
so durable that many of them are still in operation today, and more and more of these mills are
finding their way into the home market. They are showing up on Online Auctions and
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Government Auctions all of the time, and parts are still readily available from several vendors.
To this date I have been able to purchase every single replacement part I have needed for this
mill.
The only real downside to the machine for home use (besides the size and weight), is that the
motors on the machines are designed for 3-phase AC Power. While this is not an insurmountable
challenge, it does require that the user start to thinking about Electronic Phase Converters,
Rotary Phase Converters or Variable Frequency Drives (VFD) which I will not cover in this
manual. There are already reams of information out there on those. As far as power for my mill
is concerned, I started by sharing a VFD between my mill and my South Bend Lathe. Since my
ultimate goal was to convert this machine for CNC use, I purchased a very nice 1 ½ HP DC
Motor, a DC Motor control and have since converted my mill to use this very nice motor. The
controller that I am using allows changing direction by flipping a toggle switch, and speed is
controlled through the use of a 5KOhm potentiometer. A perfect addition of the mill as my next
goal is to convert this mill for CNC use.
2.5 Disassembly/Reassembly Suggestions
Whenever I take something apart I take lots of pictures. I am only 47 years old, but knowing the
exact location of every screw is well beyond my instant memory recall. I also tend to use a lot of
the cheap zipper sandwich bags, and boxes from the local super market. I find that I can throw a
note or drawing inside the bag with the parts, and it will keep things together until I am ready to
assemble them. You will see me refer to “baggies” throughout this document, and it is these
zipper bags that I am talking about. It is also helpful to come up with a numbering scheme if you
intend to disassemble something. Fortunately, Bridgeport has already provided this for us.
I also tend to make notes and draw pictures of things that I find “very interesting”. With regards
to the Bridgeport, one of the items that I marked as “very interesting” was the type of grub
screws they used for securing parts, then securing the grubs. I had never quite seen an
arrangement like this, so I noted it with pictures and notes. In fact, I found this one feature of the
Bridgeport so compelling to talk about, that I started the discussion here before you have even
started to read the disassembly instructions. The reason for this is two fold, one for information,
and also so that you do not break anything during the disassembly.
The grub screw and its hollow locking screw are shown below in Figure 4. What makes these
parts interesting is that since the locking grub is hollow, you can actually insert your allen
wrench through the locking screw into the grub that is locked, and this will prevent you from
being able to break it loose. In some cases I placed masking tape around the allen wrench to keep
the allen wrench from going too deep through the hollow locking screw and into the main grub
screw.
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Figure 4 - Grub Screws, note the hollow locking screw.
Whenever you take something apart, whether it be something you intend to repair or not, you
should think about how you would reassemble it, and figure out how it worked. I have learned so
much by paying attention to the engineers who traveled before me. Something that was
innovative 50 or even 100 years ago might still be considered innovative today.
When I disassembled this machine I worked in sections, and I compared everything to the
manuals and drawings that I had been able to acquire both from other people and on the web. I
looked for missing parts, broken parts, and places where the manuals had not been updated to
reflect the machine. As I continued through the disassembly, I started documenting the items I
would need to complete the rebuild. This list of parts helped me tremendously, because during
the teardown I began to see Bridgeport parts that I needed on the online auctions. I would
venture to say that I have saved about $200 on the rebuild of this machine by finding items
online for much less than the replacement costs.
I also made a note of the broken parts that I thought I myself could fabricate. Many of the
gearshift plungers that were broken could be easily built on my small Craftsman Lathe, so I was
able to save money by fabricating the parts myself. In some cases it is cheaper to purchase the
replacement parts than to expend the labor to build them. I will leave this decision to you. I
prefer to make what I can and hone my skills.
Where parts can get away from you, or be easily overlooked, I have tried to make notes
throughout the document to warn the reader. There are some springs in this machine, and if care
is not taken when removing some parts, you may find yourself on your hands and knees scouring
the garage floor for a 3/16 ball bearing that flew out unexpectedly. By the way, hardware stores
sell individual 3/16 ball bearings in their rack sections for 10 cents (Thank goodness!).
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3.0 Motor and Drive Section
The motor on this old style Series I J-Head mill is a “Pancake Style” 3-Phase motor capable of
operating at 220VAC, or 440VAC at a speed of 1750 RPMs. Power to the spindle is supplied
through a “Stepped” pulley arrangement that provides for four different spindle speeds. This mill
is also equipped with a back gear arrangement that doubles the number of spindle speeds to 8.
For most home users this motor is more than sufficient. Larger motors are available for the mill
from various vendors, but unless you are turning some extremely large tools (flycutters, etc),
have about $600 to spend, or looking for some extreme RPMs, the ½ HP motor will do just fine.
Since I had to disassemble most of my motor for cleaning and painting, I have detailed many
aspects of the motor, from the wiring to the sheet metal.
3.1 Motor Removal, Inspection, & Reassembly (RIR)
The motor on my mill is a ½ horsepower 3-phase Pancake Style motor. In 1963 the ½
horsepower motor was considered a powerful motor, and many of the larger surfacing bits were
not being used. I would recommend that you attempt to work with the motor that you have
before considering a replacement. Many home machinists will simply not use all of the
capabilities of the machine. If you are going to be using some large bits, or working some
extremely hard metals, you may want to consider a larger more powerful motor.
CAUTION : Before attempting to remove the motor, disconnect the power to the mill.
3.1.1 Motor Removal
The motor on a Bridgeport mill is fairly easy to remove. You need to release the nuts that secure
it to the drive housing portion of the mill as shown in Figure 5 below, remove the belt,
disconnect any power cables, and lift the motor off the unit. This motor weighs about 30 pounds
and was very easy for me to manage.
Figure 5 - Motor Nuts
3.1.2 Motor Inspection
These motors are extremely durable. My motor, manufactured in 1963 did not have any
problems other than the fact that the outer housing was covered in rust. It ran fine, had plenty of
power, and continues to work well for most of my applications. The only real thing that bears
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inspection on the motor is the motor bearings. Once the motor has been removed from the mill,
you should be able to easily turn the motor shaft with your hand. The operation should be smooth
and uniform. If you feel any “gritty” or “jerky” motion, then your bearings are most likely bad
and will need to be replaced.
Replacement of the bearings starts with the removal of the step pulley. Remove all grub screws
securing the step pulley to the motor shaft, and use a gear puller capable of reaching to the
bottom of the step pulley to extract it from the shaft. Do not attempt to use a gear puller on the
pulley face surfaces as these will break easily.
With the pulley removed, you should have easy access to the bearing retainer bolts. These bolts,
once removed, allow the bearing retainer to be removed exposing the bearings for replacement. I
found it easiest to remove the motor cover, and to press the motor shaft out through the motor
casing. The bearings could then easily be removed from the motor casting. Before pressing the
motor shaft out through the casing ensure that the shaft is clean and lubricated. If you feel any
resistance stop pushing and find the cause of the binding.
3.1.3 Motor Reassembly
For reassembly, you will start by installing new bearings into the motor casing. In some cases
people have told me that this is easier to do with the motor shaft in place. Others have put the
new bearings in, put the bearing plate in a press and pressed the motor shaft onto the bearings.
Since the motors differ slightly among the models you should do what works best for your
motor.
Once the bearings have been installed, and the motor has been reassembled, you can loosely
install the step pulley and place the motor back on the mill. The reason for leaving the step
pulley loose is so that is may be aligned with the matching step pulley in the motor housing.
Failure to align the pulleys will reduce belt life and make for a noisy drive system. Alignment is
accomplished simply with the use of a straight edge aligning the faces of the pulleys. Once you
have the pulleys aligned, tighten the grub screws for the motor pulley.
3.2 Motor Replacement
I have had several people ask me why I would consider a motor replacement for my mill, and
what I generally tell them is that the reasons for me were that I want to control spindle speed
through CNC controls, and that I would like to be able to operate at speeds outside the range of
the existing motor.
To that end, I happened to be looking on the online auctions for parts when I happened across a
new 1½ hp DC motor with a 5/8” shaft made by Pacific Scientific. I couldn’t resist, so I bought
the motor and a controller for it. The controller I purchased allows controlling spindle direction
with a toggle switch (or relays with my CNC Controller), and speed is currently controlled with a
5KOhm Potentiometer, or a voltage source 0-9VDC. Being a computer software/hardware
person I intend to build a control that contains a small microprocessor that will allow me to set
the Spindle Rotations Per Minute (RPMs). By reading an optical reflector that will be connected
to the spindle pulley or the motor, the microprocessor will be able to control the Pulse Width
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Modulation (PWM) to the motor to maintain the selected RPMs even under load. I have done
this before in my line of work at 12 and 24VDC. I am just hoping that I don’t kill myself with the
90-110VDC that this motor requires.
The advantage to a system like this is that I no longer require 3-phase, and I will have precise
control of spindle speed. Since this motor has a max rated speed of 3800 RPMs, it will also allow
me to drive the spindle at slightly higher speeds which may be required for some CNC
operations.
3.3 Drive Housing Section
The Drive Housing Section, shown in figure 6 below, houses the stepped pulley assembly,
spindle brake assembly, and all of the spindle drive components for the mill including the back
gear. Within this assembly, the power from the motor is transmitted to the spindle through a
stepped pulley and v-belt system, and a timing belt arrangement. Power to the spindle may also
be directed through the back gear which provides a gear reduction unit that will allow spindle
speeds as low as 80 rotations per minute (RPMs).
Figure 6 - Drive Housing Assembly
3.3.1 Drive Housing Removal
You should first follow the steps for removing the motor. Once the motor has been removed, you
can remove the Drive Housing Assembly by removing the 3 bolts sown in Figure 7 below that
secure it to the J-Head and slide the assembly up and over the spindle.
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Power Head
Mountin
g
Nu
t
Power Head
Mountin
g
Nu
t
Power Head
Mountin
g
Nu
t
Figure 7 - Power Head Mounting
I found it easier to separate the drive housing cases by removing the timing belt from the larger
timing belt pulley first. There may be several ways of doing this, but the most effective for me
was to remove the 4 flat head screws from the timing pulley that secure the top portion of the
timing pulley as shown in Figure 8 below. You can then slide the timing belt up and over the top
of the pulley. You will not be able to remove the belt at this time, but at least it will be out of the
way.
These screws secure the top
portion of the pulley.
Removing them makes
timing belt removal easier.
Figure 8 - Drive Housing Timing Belt
Once you have freed up the belt, you can then turn the unit over and remove the six bolts that
fasten the two halves of the Drive Housing together as shown in Figure 9 below. There are two
alignment pins that align the two halves of the casing together. Once you have separated the
cases enough to clear these pins, the cases should slide apart easily. If not, check to be sure that
the timing belt is not hampering your movements.
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Drive Housing Bolts Alignment Pin
Alignment Pin
Back Gear Shifter
Figure 9 - Bolts Fastening Drive Housing Together
3.3.2 Drive Housing Inspection
There are several sets of bearings in the drive housing that should be inspected prior to placing
the drive housing back in service. Two sets of these bearings are shown in Figure 10 below. The
Spindle Bull Gear Bearings are located beneath the Spindle Bull Gear Assembly. To remove the
Bull Gear Bearings you will have to remove the Bull Gear Assembly by removing the spanner
nut located on the opposite side and the circlip that retains the bearings in the housing. The Back
Gear Bearings are located one in each of the gear casings. To remove the Back Gear Bearing
from the lower casing you will need a slide hammer puller much like those used for pilot
bushings.
Back Gear
Bearin
g
Spindle Bull
Gea
r
Bearin
g
s
Figure 10 - Drive Housing Inspection
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3.3.3 Drive Housing Reassembly
As you can see from Figure 10 above, you will want to grease all of the bearings very well
during reassembly. Ensure that you grease the shift linkage as well. Check all items for freedom
of movement and then reassemble the gear housing cover as shown in the Figure 11 below.
Figure 11 - Gear Housing Cover
You will note in Figure 11 above that the short shaft is awaiting the woodruff key, and the large
timing belt pulley. Once you have installed the timing belt pulley, you can start prepping the
upper portion of the drive housing by placing the v-belt on the upper most stepped pulley. I
found that it made the installation easier if I clamped the v-belt around the pulley using a cable
tie. You can then slide the timing belt over the spindle drive timing pulley. You are now ready to
start assembling the drive housing. As you move the two housings together you will have to
check the belts several times to ensure that they are not getting stuck beneath the pulleys, or by
the cases.
Some people have indicated that the oil cup in the figure above should preclude the need for
grease inside the gear housing and that it should be instead filled with oil. What I have found
after tearing the mill down to inspect after a years worth of hard service as a CNC machining
center is that the oil supplements the grease and fills the areas where the grease was unable to
penetrate. Virtually no wear is visible in this section, and the bearings are all running free and
true. I will leave the final decision here up to the user, although I do appreciate any feedback.
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4.0 J-Head Section
This by far is the most important and most complex portion of the mill. The J-Head houses the
Quill and Spindle which are the main moving parts responsible for the milling operations. The
spindle holds the bits that you will use in your milling operations, and the quill provides for the
vertical movement, and bearing surfaces for the spindle. The J-Head mill has a wide variety of
options and functions that may be controlled, such as: quill feed speeds, quill feed directions,
quill feed engagement, and quill lock. Figure 12 below shows all the major parts of the J-Head.
Quill Feed Handle
Automatic Quill
Feed En
g
a
g
emen
t
Feed Rate Selector
Quill Pinion Shaft
Assembly
Quill Stop
Micrometer Nut
and Screw
Feed Reverse
Overload Clutch
Housin
g
Clockwork Spring
Feed Engagement
Leve
r
Quill Lock
Quill Nosepiece Spindle
Figure 12 - J-Head
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In this section of the document I will attempt to clarify the disassembly and reassembly of the
various subassemblies that make up the J-Head. The order of disassembly allows someone to
fully disassemble and categorize their parts on a subassembly basis.
Before attempting to work on any portion of the J-Head, remove power from the machine.
4.1 J-Head R & R
The J-Head as shown in Figure 13 below is secured to the front of the Ram Adaptor using 4 large
bolts and nuts that ride in a T-Track on the Ram Adaptor. As you can see from this figure, I have
removed the motor and drive assembly before attempting to remove the J-Head. This makes the
unit more manageable and much lighter.
J-Head
Mountin
g
Bolts
J-Head
Mountin
g
Bolts
J-Head
Mountin
g
Bolts
J-Head
Mountin
g
Bolts
Figure 13 - J-Head Mounting
4.1.1 J-Head Removal
You should be sure to support the J-Head before loosening the 4 bolts that secure it to the Ram
Adaptor. The J-Head weighs in the neighborhood of 60-70 pounds and is very awkward due to
the length of the spindle shaft, and the rotation of the spindle. You may think you have a good
grip, then something will spin and this unit will go flying out of your hands. You can remove the
J-Head from the unit with the Power Head attached, but keep in mind that this makes the unit
another 50-60 pounds heavier.
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