Drawing accuracy

[zaphod (Joe Stewart)]

How can I set my grid to 0.015625 or draw a line to 1.328125?

[Tod1d (Tod (with 1 'd'))]

You can’t. The best you’re going to get in CC is 4 decimal places in English (Inch) or 3 decimal places in Metric (mm). Your machine can’t machine to those tolerances anyways, so it’s redundant to store data to that precision.

[zaphod (Joe Stewart)]

So what do you do for pieces that have to fit in an opening like a tongue and groove?

[Tod1d (Tod (with 1 'd'))]

If you’re cutting pieces that have to fit together, until you’re more familiar with how your machine behaves you should do them in 2 steps. i.e. Cut one piece, measure it. Cut the other piece a bit shy & measure it. Now subtract the difference in the target dimension and the actual dimension, make an adjustment & cut again. Once you do a few, you will know how much you need to adjust.

This is all to make up for discrepancies in the machine & process. Cutter deflection, slop in the axis, etc…

I can’t think of an example on these machines where you’re shooting for 1.328125 and 1.328 won’t work. Although I do have one job with a +0.0 -0.001" tolerance. If you find an example where you need that kind of tolerance, let me know & I’ll show you how to do it.

[Chaotica (Joel McKenzie)]

In CCv7 you can type in a grid spacing as an expression “1/64, 1/32, etc”.

[WillAdams (William Adams (Carbide 3D))]

Or, draw one piece, then offset by the desired dimension and use the offset geometry to construct the other part.

That said, if your machine is calibrated, it should just work to draw and then cut the parts so that they just fit — though I will grant that the last such project I did required some effort at clamping to get together for a dry fit, and then couldn’t be disassembled for the glueup:

[thebeatlesin3d (Christopher Sileo)]

Your joints are flawless! Fantastic!

[WillAdams (William Adams (Carbide 3D))]

Thanks! (I think I put the file up for that somewhere here along w/ instructions)

I’ve been writing these up at:

Introduction

and am working on the next-to-last iteration (the final type, which I have a 3D model of) is perfect, but I’m not finding a CAM tool which will cut it as efficiently as I’d like, so am working on directly fashioning G-code for it.