Short story - my cuts don’t match my CAD. I’ll spell out what’s gotten me to this point.
I’ve had my X-Carve for a while and just love it. Done a bunch of signs. Everything came out great.
I upgraded to the new wide maker slide. Which is awesome. Made more signs with no problems.
Then I decided to get fancy and see how accurate my cuts were. I found that my CAD dimensions didn’t match my cuts. But I figured, no big deal. You just need to calibrate your X and Y axis.
I did this by inserting a V bit to act as a pointer into the spindle. Although I did the same for the Y axis, I’ll only describe the X-Axis here for time sake.
I positioned the bit over the 10 cm mark of my measuring tape. And then using UGS, moved the spindle 650 mm to the right. I don’t remember the result, but let’s say it was 660. I did the math, and reset my $100 to the appropriate step size. Ran this same process a couple of times until I got a consistent answer for my steps/mm. Then did the same for the Y.
$100 = 34.019 steps/mm
$101 = 37.229 steps/mm
Got very repeatable results.
So I cut a 1" diameter circle, and then a 1 x 2" rectangle. The media was placed in the lower left part of the table. I was off.
Circle was 0.885 in the X, and 0.931 in the Y. The rectangle was 1.733 in the X, and 0.937 in the Y.
Let me be clear. I’m not one of those guys who thinks he can buy a hobby machine and get 0.001" tolerances. But I’d like my cuts to be within 0.05" inches.
I figured I just needed to recalibrate. It had been a day or two since I had done the calibration. But my calibration came out dead on. Starting a 10 cm, issue a move X 650 mm, ended up at 660mm.
So I decided to move across the x-axis in 10 cm steps. Each 10 cm movement gave a different number of millimeters moved.
Moving 300 mm actually moved 350ish.
So here is my question. Is it possible to stretch segments of the belt so that your teeth pitch is not constant across the belt?
It’s pretty clear to me that since my steps per mm are 34.019 and 37.299 versus the 40 that an unstretched belt claims, I may have over-tightened my belts.
A few other points that folks may wonder about.
Yes, the machine is square.
V-Wheels are properly adjusted.
Yes, I have dialed in the POTs according to “the overload” method. Can’t remember where I read it. But it works.
Cut are repeatable. If I position my media in the exact spot every time, the parts I cut out are exactly the same size every time. If I position my media in another part of the table, then the cuts will be different from the other cuts. (If that makes sense.)
Easel, or Fusion 360 through UGS makes no difference. Results are the same.
Some folks have reported that they have issues where each progressive cut shifts a bit to the (pick a) direction. To me that indicates skipped steps. As far as I can tell, I’m not skipping any steps. Unless I’m skipping the same step whether the spindle is running around a path clockwise or counter-wise. Maybe I’m not saying that right either. Anyway, my vertical walls are perfectly smooth. No “ghosting.”
So what do you think? Am I missing something really simple here? Or have I pulled sections of my belts past their yield point? Z-axis - of course - is dead on. So I will be upgrading to ACME lead screws for the x and y in the future. But before I can do that, I’ll want to be able to accurately cut my new aluminum plates.
My next step is to remove the belts and compare that to a spare belt I have to see if I can spot areas that are excessively stretched. But I don’t want to do that until I hear some responses. That’s obviously a bit of disruptive work if there is an obliviously simple solution. That and I just can’t shake the idea that it would be impossible for me to stretch the same sections of the Y axis belts the exact same way. But maybe I did.
Looking forward to the response.