My Benchmaster CNC Mill

I currently have many tools in my shop.  My favorite one is the CNC mill I built from an old 1954 Benchmaster mill.  It’s heavy duty and very rigid.  It works excellent and I run it with Mach3.

Original mill before CNC conversion

The mill is old and uses worn out ACME lead screws.  This is not ideal for a CNC machine so I had to upgrade the lead screws to ball screws.  I bought a length of 5/8 ball screw rod and two Thomson ball screws from Mcmaster Carr.

Thomson Ball Screws

I had to make an aluminum adapter to attach the ball nut to the table.  So far it works fine and aluminum seems to hold up well.  The nuts did not fit well in this mill.  I had to modify the mill table by machining off about 0.250 inch from the underside to allow for clearance for the nut.

Ball Screw Adapter

Connecting the ball screws to my existing handles and using my existing table bushing was important so I machined an adapter that is identical to the fitting on the end of my ACME lead screw.  I used two set screws and clamped down on the ball screw.  This was my cheap alternative to buying the very expensive ball nut mounts.  So far I have had no problems with this setup and it has minimal backlash.  Some day if I ever wear out the bushings I will just CNC a bearing block.
Ball screw Installed

Steppers with a 2:1 gear reduction

Now that the ball screws are all installed I had to buy some stepper motors.  I bought 3 Keling stepper motors from Dan Mauch who owns  Camtronics.  He helped me pick the correct size steppers for my machine.  Dan was a great help and gave me a lot of advise on my setup.  The X & Y axis ended up with two 385 oz-in steppers with a 2:1 gear reduction and the Z axis has a 495 oz-in with a 2:1 gear reduction.  They are plenty strong enough and I can get 50in/min rapids with ease on the x-y and about 20in/min on the Z.  That’s fast enough for me.  I also extended the shaft so I could attach my original handles.  Now I can still use it as a manual mill just like before.
I had to make all the mounts and I bought the timing belt and pulleys from McMaster Carr.  I decided to go with belts and not direct drive because belts are very forgiving on the install.  Belts still work very well even if you make crooked mounts and your holes are not perfect.  It also allowed me to use smaller (hence cheaper) stepper motors.   There are lots of places online that sell motors.
Here are a couple pictures of the Z-Axis mount. There was no real place to drill hols so I made a clamp to clamp onto the Z-Axis shaft support. It works great.

Z Axis Mount
Z Axis Mount
Z Axis mount
Z Axis mount
Making the stepper standoff mounts
Mill Fully Converted to CNC

Now that the mill is fully converted.  I needed a way to control it.  I ended up buying a Gecko G540 controller complete with box & 36v power supply.

Back of Controller
Front of Controller (I added the labels)

The controller was complete with power supply, cooling fan, power switch, & motor disengage switch.  It works perfect and was worth every penny.

CNC Mill complete with Controller & PC running Mach3

I currently run a demo version of Mach3 to control the CNC.  It is a really nice piece of software.  I also tried EMC2 which runs on Linux and can be downloaded free at  EMC2  also is nice and does not have the 500 line limit that demo version of Mach3 has.   I have not played with it too much but you can run it off a CD-ROM without installing Linux permanently.  I plan on using it more this year.

Here is a video of it engraving.

Finished tool with engraving.

Here is the finished engraving.
Here is the complete McMaster Carr  parts list:
14 Tooth Acetal Pulley  (3)         57105K14
28 Tooth Acetal Pulley  (3)         57105K24
Urethane Timing belt (3)             1679K21
5/8 Ball Nut  (2)                            5966K16
5/8 Ball Screw  (2 feet)                 5966K261
The motor mounts are all homemade out of 1/4″ Aluminum Plate.  I also did not use the expensive ball nut mounts.  I used the standard bushings that were in the mill table and the standard anti backlash nut.

Added pulley covers and a light.
Added pulley covers and a light.

Here is an updated picture of my mill. I added a light and I covered the belts since I was getting chips in between the belt and pulley.
I have been asked what my travel is so I measured it. I have 4.1 inches “Y” travel, 12 inches “X” travel and about 6″ “Z” travel. I could get another 1/2 inch on the “Y” if I removed my rubber cover that keeps chips out of the ways. So far I have not needed it.

Update 02-14-14:
I added thrust washers between the lash nuts and the table which was an awesome upgrade recommended from someone reading my page.   Thanks Blaine!  My backlash on the X & Y is now 0.001 inch max.    Make sure and pack them with some lithium grease or equivalent bearing grease.
McMaster part numbers:
These cover the X, Y, and Z axis.  I did not install them on my Z axis since I have a very tight Z and did not need them.

Thrust Washer
Thrust Washer
Installed Thrust Washer
Installed Thrust Washer

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