Accurate when testing, inaccurate when cutting

Hi All

I’ve got a strange issue where when doing calibration tests, I’m spot on, but when I go to cut a part I’m losing a millimeter over the 374 I’m looking for. That’s a lot for what I’m trying to do.

My concerns are that under load, something is flexing and throwing me off a bit.

I’m not overloading it, it’s just MDF and I have NEMA 23 motors all around. Very happy with the strength. I don’t seem to be skipping steps as everything is clean, just off. I hate to go in a fudge to compensate for this…that seems really cludgy…

Any thoughts? I’m all ears.

Custom made from Xcarve body parts, individual motor controls, and NEMA 23s all around… using easel for my cut

Thanks for any thoughts!

Most likely.
It will be a combination on mechanical give, tool deflection, backlash, runout. A 0.5mm deviation will accumulate to 1mm for a whole part. I assume a pocket will be 1mm undersized and a cutout 1mm oversized.

But there is a different possibility:
Do you make your design in Easel or other software like Fusion360 and similar?
There you have the option to set a “leave material for a finish pass”, incidentally default value is 0.5mm in Fusion360.

So it could be mechanical or software related, your initial post dont provide details on that matter :slight_smile:

Thanks for your thoughts Haldor-

I’m using Easel and some imported SVGs that check out size-wise. I remember that setting in Fusion 360 though.

Today I calibrated ‘under load’ and got a correct cut afterwards. I needed to bump my SPMM up to 180.5 from 180 on one axis, and up to 80.25 from 80 on another. I also manually put in the size of my bit.

Its sort of feels like a cheat, but it worked, so maybe that’s ok.

I would compensate by using bit diameter and/or compensation options is they are avaiable.

You dial in your machine with no load so the positional precision is intact, and use the above to fugde.
If you do a lot of holes for instance you want spacing to be correct, not say 0.5mm off incrementally

Say a 50mm grid, where row two is 50.2, row 3 is 50.4…row 10 is 51.6 or whatever :slight_smile:

In Addition to the above, have you put a calliper on the bit itself? I have .125" bits that measure .124 or .123.
and now that you post this, I recall having to test cut, measure, compensate, lather, rinse, repeat until I came up with a tool setting of .110 that gave me accurate cuts.
All that Haldor mentions about machine flex etc. probably comes into play that causes me to arrive at that number.

Thanks again, I see what you’re saying. This is all pretty frustrating
Does Easel have those kind of compensations? I don’t think I’ve ever seen them.

Blockquote I recall having to test cut, measure, compensate, lather, rinse, repeat until I came up with a tool setting of .110 that gave me accurate cuts.

Huh, so your tools measured .124 but you compensated by giving Easel an undersized tool? I “think” I get that concept…I “think” ha!

(I did measure the bits and they’re within .01mm, so that checks out)

I pull my gantry against precision-set stops on both sides to ensure squareness of the X-Y axis to each other.

Could you explain this more? Or was there a forum thread about this that I missed in my searches?

Easel do not, but you can cheat by entering a different bit diameter than actual.
Say you cut inside pocket, and result is 1mm less => 0,5mm deviation per side.
So you enter the bit diameter 0,5mm less than actual.