Ed,
You were so helpful when I was trying to troubleshoot my Voccell Laser Engraver that I thought you would appreciate knowing how it ended up. You will recall that I was getting “slippage” in the x direction when printing in fill mode. It did not always occur, but when it did, it resulted in characters that were slanted to the right, and the x-zero would be significantly shifted by the end of the run. The belt had been recently replaced and increasing the belt tension had no impact, suggesting that the belt was not slipping. I also checked to confirm that the drive pulley was not slipping on the shaft. This led me to believe that the “slippage” must be in the stepper motor.
Following your suggestions, I found that the X stepper motor appeared to be electrically sound with 2.4 ohms of resistance on each phase, but there seemed to be much more resistance to turning than for the y-axis motor which is about the same physical size with only a slightly different model number (and shafts on both ends). I surmised that there must be a bad bearing in the x-axis motor that was causing the motor to “skip beats.” But, on removing the motor we found that the resistance was uniform throughout a full revolution and the resistance to turning felt more magnetic than mechanical. It didn’t feel like a bad bearing. After a lot of web searches and emails to China and even Spain, I did have offers to sell me a motor which they promised was exactly what I needed. but they would never provide detailed specs on their motor, and they wanted to be paid in bitcoin. I did finally find what appeared to be a replacement for my motor but where I ended up finding it was on Amazon. I decided that a cheap motor from Amazon might actually be my safest option. It was only $12 compared to the $100 that the “bitcoin” sellers wanted so even if it didn’t last very long, it wasn’t a huge gamble.
However, when working on the motor I noticed that the x-axis belt, which had recently been replaced by a colleague, was a little different than the y-axis belts (the old x-axis belt was no longer available). The tooth spacing was the same (2mm) but the new belt is 10mm wide whereas the belts on the y-axis only measured about 9.5mm. More significantly, on closer inspection, the tooth shape was different. The teeth on the new belt were rounded but those on the y-axis belts were square, as were those on the x-axis drive pulley. I think my colleague had probably concluded that the difference was due to excessive wear on the old belt which was in pretty bad shape. I found a comparable 3/8” wide timing belt with square teeth at McMaster-Carr and ordered it.
And the result was that when I replaced the belt, my x-axis slippage went away. I never did put in the new motor I had bought because everything works fine. It was apparently belt slippage all the time. Why it was so consistent when it was slipping, I don’t understand, but I am happy to report that my problem is solved. Your advice was extremely helpful as without it, I probably would have given up. Our club had already decided that we were probably going to have to buy a new laser, but now it looks like maybe we can squeeze a little more out of this one.
Thanks again for your invaluable help and also that of others who offered suggestions.
Happy New Year