Hoffman Mechatronics
Bridgeport Mill J1 Rebuild
12.2 Where do you start?
You start by evaluating your need for a CNC machine and the costs involved. I am going to save
you a lot of time here by letting you know exactly what I had to change, the exact prices I paid,
and the contact information for each manufacturer. Why am I doing this? Because I want to give
something back. I have only changed the price of this document once in the 5 years I have been
producing it, and now that I have added the CNC data, I have no intention of changing the price.
I decided to convert my machine in stages or phases. This allowed me to actually use the
machine itself to help me advance from one stage to another thus minimizing the manual labor
required to complete the process. Phase 1 of the project included the replacement of the lead
screws with ballscrews, Phase 2 included the electronics, Phase 3 the stepper motors for the X
and Y axes, Phase 4 included the stepper motor and mount for the Z-Axis, and finally Phase 5
included the addition of a Planetary Gearhead for the Z-Axis.
If you are curious of the overall cost, I spent approximately $2000 to get to Phase 3 on this
conversion. For Phase 5, the prices were dependant upon what I could find on eBay, and I was
able to add all planetary to the Z-Axis for less than $100. I have since been able to regularly find
planetary gearheads on the online auctions for around $129-200. Obviously if you start with a
machine that already has ballscrews you are well ahead of the game. There are a lot of surplus
mills out there, do not be shy about grabbing an older CNC mill that has a bad controller. There
are people in the CAMS group that have taken older Bridgeport CNC machines and converted
them to use the Gecko drives and Mach3 software with the existing stepper motors. There are
others that have had to replace the existing drive systems completely. The bottom line is that
starting with a machine that was designed for CNC but may not be working, just saves you
money.
12.3 Phase 1 – The Ball Screws
My machine was old enough that it still had the ACME lead screws installed. I had checked my
backlash before disassembling the machine and knew that something would have to be done.
Knowing that the end result of this machine was a CNC conversion, I bit the bullet and ordered
new ball screws from Rockford Ballscrew Company. The Rockford Ballscrew company has ball
screws for all Bridgeport Mills, and their clones. The gentleman I spoke with was very
knowledgeable and very helpful with ensuring that I ordered the correct parts for my table.
Please note that the part numbers and prices in the table below were for my specific mill. The
part numbers may change slightly for your mill depending upon the X and Y dimensions of your
table.
Part #
Manual Desc
Vendor
Qty
Price
Units
BRP2209
Y-Axis Ballscrew 9” Table Depth
Rockford Ballscrew
1
$262.50 Each
BRP2236
X-Axis Ballscrew 36” Table Width
Rockford Ballscrew
1
$168.75 Each
B2350
Ballscrew Feednut Bracket
Rockford Ballscrew
1
$87.05 Each
7204
Bridgeport XY Ballscrew Bearing Kit
Rockford Ballscrew
1
$127.88 Each
As for the installation of the ball screws, it pretty much follows the installation of the lead screws
with a couple minor exceptions. You never remove the ball screw from the feednut, and the
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January 31, 201111