Being the impatient sort, I did NOT clean the garage all the way…instead I cleared a section of the workbench and used that as my CNC building point. This granted me the instant satisfaction I craved, without actually cleaning more than a 4×3 space off. I still need/want to clean the garage, as I would like to have more room, but that isn’t fun!
The first step was to take the Mini-Mill out of the attic, blow the dust off, and evaluate why exactly I gave up on it before. I remembered having issues with the Z axis (up and down movement). This was a struggle because of the material type I used…cutting board instead of plexiglass or MDF…just doesn’t slide as smoothly. I also tried to cut some corners when making the bearing tension arms. Overall the results were dismal, and I was never able to get the accuracy I needed.
I decided to shorten the Y axis, as I was getting a lot of flex in that direction, and to completely rebuild the Z axis. The Y axis was not that hard, I cut the motor support down, realigned it, and added a better axis guide to keep the table running true. I cannot find any more slop in the table, other than some that still exists in the motor when it changes direction. I believe I can brace this using the other 2 motor mount point and a 90 degree support…pictures will show it better once I figure out a better way to take them…my phone/camera is great but it syncs what/when it wants and it frustrates me!
For the Z axis, I opted to strip it down and use some 16” drawer slides I had from my workbench project. The original workbench plans had a little door that slide out and held screwdrivers etc….not practical or needed in my setup, and I never returned the slides to Lowes. I used one on each side, with a plate in between them holding the router tool, and another at the top for the motor to connect to. Figuring out a better way to connect the threaded rod to the motors was a bigger struggle. I went through 4-5 iterations before I landed on a short section of 3/16” brake like into the coupler, then a piece of fuel hose clamped tight to it I used a piece of PVC over the hose to adapt up to ¼” inch for the threaded rod. I made my own clamps from a couple square sections of cutting board with a hole drilled for the hose, and a slot to allow them to tighten to a smaller diameter. Pretty ingenious I thought…then I realized after the fact that I could have just used a hose clamp…sometimes the simple answer eludes you!
With the Z axis all hooked up, I was anxious to try it out! It was at this point that the length from my workbench to my computer became a problem…I had 9 feet of parallel printer cable (after hooking 2 together), but 20 feet of cable needed. I may not be a genius, but I knew that wasn’t going to work, so I used my portable worktable ($15 Lowes after Christmas clearance) to hold it closer to the computer while I began the process of dialing everything in.
I managed to find the original paperwork that came with the CNC controller kit I bought/built 3 years ago. I re-read this to remember what I had built. Turns out I am using ½ steps, took me about 20 minutes to decipher that…waiting 3 years is tough!
Next I had to decide which CNC software to try and learn. MACH3 seems to be the more popular on the EasyCNC forum group, and so I started with that. I printed/read their 14 page “how to get started” manual, and learned a few things:
- I don’t have any limit switches. This is bad. I need to be able to tell the software when to stop trying to move the table!
- I don’t have an emergency stop button. This could also be bad….everyone needs a big red button to push
- I don’t have home buttons. These are usually tied into the limit switches somehow…need to learn more
- My math skills suck. I followed their formula to figure out how many revolutions of the motor it takes to move 1 unit (1” to me). 2000 steps per revolution, at ½ step per is 4,000 steps. 4,000 * 18 threads per inch is 7200 steps per inch. This was fine until as I was falling asleep I remembered that ¼” rod is 20 TPI. No wonder it wasn’t very accurate!
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Although I didn’t have that accuracy down, I was able to figure out the right feed rates for the X/Y/Z axis, fast enough to be useful, but not to fast that the motor would lockup and squeal like a pig being chased for bacon…
Oh yeah…It took me ½ hour to figure out why the X axis moved to the right only…even when I told it to move left. Turned out I had a selection wrong and kept missing it. Frustration.
Toward the end of my testing I started having problems with my X axis. I think it was out of alignment, and because it was direct connected without any flex, it got into a bind and nothing I could do would make it better. I am going to rebuild the connection like I did my Z axis and see if that helps. I also have to redo the way the rod mounts to the Axis…I might try an anti-backlash assembly I saw on the net, currently I am using ¼” rod couplers instead of nuts, and they seem ok for backlash…might be low enough that I can program it out via the software.
For now that it is…to-do’s now are:
- Fix X axis
- Manually try some foam carving (cheap and won’t damage anything if something goes terribly wrong)
- Begin to learn Google Sketchup, as I hear that CAD drawings can be translated into GCode files via a plugin (don’t know which one, or how, but that is what I need to learn!)