Mill-Drill Conversion

Conversion of a Grizzly G1005 Mill/Drill to CNC

MillconvertedS

Go HERE for the Ball Screw Conversion

Please click on the links for photos and captions.

I have owned a Grizzly G1005 mill/drill since 1991. Interesting to note I paid about $1200 back then and the same model is now listed in the Grizzly catalog for $895.

Since 1996 I had been gathering information and considering converting it to some kind of CNC operation. My plans were put on hold for a while when I had to move and put the mill in storage. During that time I was fortunate to have a CNC knee mill at my employer’s shop that I had full use of.

In 2001 I decided I was going to convert the mill/drill at the lowest possible cost. I was not immediately concerned with accuracy, and just wanted to play with it. I had three Slo-Syn stepper motors with IBM part numbers I picked up for almost nothing at a junk store that was closing. I had also recently torn apart a couple old copy machines so I had a bunch of timing belts and pulleys. Software and stepper motor drivers were still needed.

After realizing I could not find any free drivers, I decided to buy the 5 Amp driver kits sold by Dan Mauch. They were the lowest cost 5 Amp drivers I could find. I enjoyed assembling them and testing them but the documentation was somewhat lacking. As a contribution to the home CNC hobby, I rewrote the documentation and sent it to Dan. I don’t know if he ever used it. The three drivers were assembled and mounted along with my homegrown power supply in an old mid tower PC case. (My first usable milled product is the airflow slots in the front and back cover plates.)

Stepper Drivers

I looked at several software options and decided to start with the trial version of Master5CNC. The setup seemed easy enough, and the trial version was free. The trial version is limited to 500 program steps and the special features like photo engraving and dxf file processing are turned off. This would allow me to at least see if the conversion would work without regretting a software purchase.

I decided to mount the stepper motors on the mill/drill in such a way as to not cause any irreversible damage, in case I decided to scrap the project. The X-axis motor and pulleys are mounted to the feed screw on the “free” end of the screw. This is the end without the thrust bearings. I removed the hand wheel mount, machined off the end closest to the table, and mounted a plastic timing pulley to it. The motor is mounted to a ¼” x 4″ piece of aluminum flat bar. The flat bar is then bolted to the face of the screw support.

X and Y Drives

The Y-axis motor is mounted in much the same way. Instead of modifying the hand wheel mount; I made an aluminum hub for a large timing pulley. The hub mounts to the feed screw with setscrews. Three tapped holes on the front of the hub allow the hand wheel to be attached for manual operation.

The Z-axis required a different approach. I removed the fine feed hand wheel, and the travel indicator/bearing retainer behind it. I tapped three holes in the rim of the bearing mount casting to mount the motor mount. A spacer and clip was required to keep the bearing in position. A timing pulley was mounted on the shaft leaving enough shaft to remount the hand wheel.

Z Axis Drive

My first attempts at running the mill were a bit frustrating. I was running Master5CNC on a Celeron 433 in an ABIT BE6 motherboard and could not get a smooth pulse train to the stepper drivers. This caused the motors to freeze up or miss a bunch of pulses. I switched to an old Pentium 233 in a cheap motherboard, and everything seemed to smooth out.

 

So now I had a rather crude CNC Mill. It had 0.017″ backlash in the X and Y axes and a lot of slop in the Z. Master5CNC has backlash compensation for linear moves but none in circular interpolation. This made for a really ugly circular cut. I decided to try using EMC instead of Master5CNC. It should be noted that this was my first attempt at using Linux. My friend John helped me get the EMC Brain Dead Install loaded on a separate hard drive. My brain must not be dead yet because without John’s help I would not have gotten it installed. John raves about Linux being so stable it never locks up. My experience was not the same as his. Linux might be great, but it’s not yet ready for the masses. EMC was more difficult to configure, and presented more problems than I was willing to deal with, so I abandoned it.

I knew I would not be satisfied with anything made on the mill until it had zero backlash. At this point I used the mill quite a lot in “push button” mode. Basically using the jog keys instead of turning hand wheels. I like this so much, the hand wheels were never reinstalled on the mill.

At some point, one axis quit working. It turned out one of the stepper drivers had gone bad (shorted output transistors, and possibly one or both the IC’s). One IC is a programmable chip, and the other is basically un-obtainable according to Dan. I also found the pin on my parallel port connected to that driver was dead. My solution was to scrap that driver and get a Gecko Drive that I had read so much about on various sites and groups. Master5CNC is very easy to configure an alternate parallel port pin for the one that got fried.

I bought a Gecko G210 micro stepping drive for $129. And installed it in my drive box. The drive is a very nice package and makes for a much cleaner installation than the original drive. I think the only configuration differences are that an external resistor is required to limit the current, and the enable signal is backwards from the Dan Mauch drivers. The micro stepping functionality makes for much smoother operation. The Gecko drives also have optical isolation so they won’t fry your parallel port if they have a problem. I will not hesitate to replace the other drives with Geckos if I have a problem with them.

The Quest for Zero Backlash

I have had a lot of fun with the whole CNC and ball screw conversion project and would highly recommend doing it if you have any interest.   As you can see from my project, you don’t have to be an expert at anything, and you don’t have to spend thousands of dollars.  

The end result is a CNC mill/drill that can mill out a ¼” diameter circular pocket with accuracy of about +/- 0.001″.   This is fine for my tinkering.

See some First Cuts with zero backlash.