In my tests and trials on the Maslow, I have been trying to optimize the feeds and speeds.
I am a CNC programmer for a large cabinet manufacturer in my area, so I have some experience doing this on production machines. There are two types of bits we use most, 1/4" downshear and 3/8" compression. The 1/4" downshear bits spin at 18000rpm, 6000 mm/min, 10mm in one pass. The 3/8" compression bits spin at 18000rpm, 16000 mm/min, 19+ mm in one pass. Now, I know that trying to run the Maslow at the same sort of speeds isn’t going to work, since it’s not nearly as powerful as these gantry-style production machines.
I used this speed calculator I came up with at work to help do the optimization of the Maslow:
The lowest RPM available to me on my router in 10K, so I lowered the spindle speed on the calculator and came up with an optimal feed of 2500 mm/min. I made up a couple of test programs, and was surprised to see the machine wasn’t actually running at that speed. Okay, I didn’t measure the actual speed, but it certainly looked like it was slower than it should be. Also, the bit was squealing. It was ear-piercingly loud, which usually means that something’s off.
I did a little digging. I remembered seeing somewhere a mention of a maximum feedrate hardcoded into the machine. When I opened up the firmware, I found the value under CNC_Functions:
In the spirit of experimentation, I tried increasing the value to 3000 just to see what would happen. I will admit, I was a little nervous I was going to overheat and fry the motor controller. However, in running a couple of test cuts, the machine hadn’t let the smoke out yet. I ran two tests. First, I tried cutting 4 straight, horizontal lines, each at different speeds. The sound did improve when it got to the 2500mm/min line. Also, I ran my calibration test, and circle within a square. I definitely didn’t expect the results:
The straight line test is at the bottom, cut into one of my original square calibration tests. I’m not entirely sure what caused it, but the lines deviated quite a bit from what I programmed. The circle in the square test above that is even further off. Some of that may have been the sled drifting, but I saw the motors trying to adjust their position as the sled made it back to the correct location. It almost looks like one of the encoders wasn’t keeping up with the other. Or maybe the interval of the PID tuning is too long? The only programming I know is G-Code and a little scripting so I’m not entirely sure how to fix this issue. If anyone has any ideas, I’d like to try them out.
I’m also going to see if making some tooling changes solves my problem for now. I ordered some 1 flute upshear bits from the Maslow store. According to my calculations, the idea feedrate for that bit is 1000mm/min (see the above feedrate table, the bit in question is 2 rows down from the highlighted one), so it should work pretty well at the Maslow’s top speed of 900. I will also try plunging my 2 flute bit deeper into the plywood and see if that helps.
I made the switch over to a pantograph sled just after I ran these tests, so I first have to get the machine dialed back in