Creating Calibration Guide

I’m interested in creating a guide and video on how to calibrate the X-Carve with the 24V stock spindle, which can easily identify issues such as low potentiometer settings and such. I created a calibration pattern designed to test the X and Y steppers individually (2.000" squares), together in sync (2.000"wx2.000"h triangles), and together with varying settings (2.000" circles). I cut it this morning in 3/4" MDF using a 1/8" roundnose bit (0.1225" when measured).

I altered the following settings to really put a load on everything and encourage problems:
Depth per pass: 0.063 -> 0.075"
Feed rate: 40 -> 50 ipm

Here’s how it turned out, not too bad.

It sounded really rough, but I think it was a fair test of the machine. None of the dimensions are accurate and some are off by up to 0.100", but I don’t see any evidence of skipped steps, and the Z-axis looks to be square since there are no stair steps in the big rectangle (0.600" deep).

I figure a test like this can be useful for testing a lot of things at once. I also plan to incorporate how to adjust the step/mm distance once I receive a 600mm scale I just ordered, using the video that Rusty posted at Steps/mm Calibration. Once I get that adjusted, I want to run this test again and see if I can get this dead-on.

My questions for all you experienced folks are these:
-Are my increased settings for the MDF enough to bring issues to light, or should I increase the depth and feed rate even more?
-Should I use a different bit, maybe a 1/8" double straight flute bit instead? It would leave a flatter bottom, but I suspect the dust would load up a lot more in there and cause problems.
-I have my belts tensioned to where it takes about 6 pounds to lift the belt 1" in the middle with the gantry or X-carriage pushed against the static belt side, and I don’t see any indication of belt slippage. Does anyone know an ideal tension force? Does this sound high or low?
-Are there any other videos, references, or procedures you think I can incorporate into this calibration guide?

If anyone is interested in using this test pattern, it’s located at http://easel.inventables.com/projects/2DaOVRoLwaF8mAbPpbumFQ#.

Thanks,
Rob

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I would use a flat endmill for the test pattern. Most of my work is cut with a 1/8" two flute spiral upcut bit. The advantage of using a flat endmill is that for the pocketing test, you should be getting a really smooth result. If you’re not, then most likely your gantry isn’t correctly squared up.

The triangles make the pattern look cool, but is there anything to be learned by cutting them? Square/circle/pocket seems like a decent test, and takes up a little less space (which is handy if you’re going to be running this several times).

Six pounds @ 1" sounds about right for the belt tension.

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The only reason I included the triangles was because the response on the X and Y steppers should be linear, and problems may be more noticeable if they are moving at an angle to both. I’m not certain that’s a good hypothesis though.

I set up a calibration pattern to test my SO2 a few months ago. There were some minor errors that I corrected by adjusting the “steps/mm” for the axes. There are a couple of discussions about that on the forum.