Hi folks. I’m cutting tab slots in a 1/2" plywood panel (32" x 18"). I’m zeroing to the bottom left corner using BitZero. Works fine, returns exactly to position using Rapid Position - Return to XY + 6mm Z.
The tabs on the left side of the panel are perfectly in position (1" from the left edge), but as we move to the right, pockets are not in the correct X position (Y seems OK). By the time we get to the tab pockets on the far right side (should be exactly 30" from outer edge to outer edge with the left side tabs), we’re 3/16" off (at 29 13/16", not far enough right). You can also see the large pocket in the middle of the image is about 1/16" off already at the midpoint.
So, it looks like precision is dropping with distance from X’s zero. Is this a loose/tight belt issue? Something else?
Attached image to hopefully help understand my explanation. Sadly, the notes on the board say “right of target” – I meant “left of target” (not far enough to the right side).
Looks like an SO3 or a 4. The right hand limit is limited by the homing position. Jog your cutter all the way to the right and see if you can jog past where your slots are in the picture. If you are lined up with them you are simply hitting the hard limit on the right side.
If you are at the limit on the right you can increase the limit on the left side by modifying your shapeoko.json file. The stock parameters are “safe” and not the maximum you could jog to. Jogging is limited to the parameters set during the setup procedure. You cannot change the right side but you can likely increase the left and get a slightly bigger cutting area. During the running of a .c2d file and/or gcode there is no limit but you have physical limits. The physical limits are when the Z axis hits the left side rail. The only limits are when jogging but not when running gcode.
You can modify your shapeoko.json file to get a little bit more movement to the left and you modify the file a few mm at a time until you physically hit the wall and then back up some for a safety cushion. The way to modify shapeoko.json file is to open CC and then Help and Open Data Directory. In the CM directory is the shapeoko.json file. You can modify the file with a text editor like Notepad. Just save the file as text. What to modify is:
Do not copy the numbers above because I have an XXL and HDZ. The number is negative because they are measuring in MM from the homing position. After modifying the file and saving you have to close CM and restart it because the file is only read on the startup of CM. You may need to power cycle the Shapeoko itself. If you ever run the setup again it will revert to the stock settings.
What the above does is gives you slightly more cutting room from right to left. The right cannot increased but the left side can be increased giving you a little bit more cutting capacity. Just dont increase your X travel too much because you can slam into the left side rail and that would likely make you lose steps.
Thanks guys. I will check all these things in the morning. I appreciate the links to instructions.
The one thing that I think is interesting is the “drift” seems to be proportional to the distance from zero (only ~1/16th at mid bed, 3/16ths by far right edge).
feeds and speeds — make sure that they match the tooling being used
toolpaths — make sure that they don’t result in excessive tooling engagement (avoid slotting) or rubbing (cutting deeper than the cutting flutes against a vertical wall)
should only be necessary to achieve parts fit when rotation comes into play, it shouldn’t be necessary for general machine operation and it is only a tiny minority of customers who do it.
I’m starting in on testing all the things mentioned here. A bit more data:
I wanted to eliminate the limit issue suggested by Guy. In Carbide Create, I moved the side slot that is in the upper right of my image over 1/2" (immediately bordering the slot that is cut already). I re-BitZeroed everything and ran a job that would just cut a shallow pocket. It didn’t hit a limit (looked like there was still space to the right on the gantry - not touching a sensor) and the slot aligned perfectly with the right edge of the existing (incorrectly placed) slot. Also, the BitSetter is more right than either of these cuts and the CNC has no problem getting perfectly centered on it. So I don’t think it’s a limit/constriction issue.
I’m trying to find a video/tutorial on the pulley set screws that Will mentions. There are some other posts with links but maybe the tutorial has moved? A current link would be helpful.
It’s 1/2" plywood with a new-ish 1/4" bit (18,000 rpm) and a 1/2" wide slot. Just using the stock #201 feeds and speeds for Softwood, no overrides, so I don’t think this is the issue.
OK, I think I’m back in business. Thanks everyone for the good suggestions. Here’s what I ended up doing.
As mentioned above, I started by making sure I wasn’t hitting an X-axis limit.
I checked all the belt tensions, cleaned things up on the belt rails. All in all, it still seemed pretty good. I don’t have that many hours on the machine even though I’ve owned it for 3 years. I never did figure out how to check the X-axis pulleys. It looked like I would need to pull the stepper motor out and I wasn’t ready to do that until I exhausted some other options.
I liked the calibration suggestion as the inaccuracy seemed pretty consistent and proportional across the workbed - not like what you might see, at least in my mind, with a loose belt or slipping pulley. I found this video from Sunridge Studio on calibration very helpful and decided to pursue this angle.
I ended up using the MDI (new to me) to send G91 G0 X850 and G91 G0 X-850 commands over and over (10x+ times) and seeing that they consistently hit a spot only 844mm from the start point. I used this to recalibrate the $100 parameter (40 * 850/844 = 40.28) and set it to $100=40.28. After that X was consistently hitting the right spot.
Did the same thing with the Y-axis – it was only off a tad (798 vs 800mm).
Once those were set, I reran the panel shown above and everything is where it should be. Hopefully this solves it and I’m not just putting a Band-aid over a different issue. I don’t usually make big or wide things, so it is entirely possible I’ve been uncalibrated this entire time.
Thanks for the help and hopefully this helps someone else with a similar problem in the future.
Checking your stepper motor pulleys is easy…just watch the gear on the stepper motor shaft to see that it is actually rotating with the shaft. You can make an alignment mark with a sharpie on them and watch that the line stays as one line when the shaft rotates. You can also check the two set screws that hold the gear in place on the stepper motor shaft are tight
Here’s a post I did on the pulley set screw issue. I had what sounds like exactly the same problem you’re describing and it was very hard to diagnose by looking at it. “Upgraded” the set screws and haven’t had an issue since.
