cut2d tool compensation is incorrect?!

[mykrowyre]

I just started using cut2d, and when I cut holes (inside radius for the tool path) they are always smaller than specified. For example, I have a hole which is .07" wide, and a tool (physical) width of .0375. If I use that tool width in cut2d, my hole ends up .065 instead of .07.

So... I have to enter a tool diameter of .0275. When I do this, my hole comes out at .07".

Question is why did I have to tell it my tool is .01" smaller, to get the correct size hole?? It doesn't even make sense, because since the offset happens on both sides of the hole changing the tool diameter by .01" should also change the hole diameter by .01", but it doesn't, it changes it by .005!!

It seems like it is not correctly compensating for tool width, or it is trying to add an additional offset.

This has been driving me crazy all night, lots of wasted material before I figured out what was going on.

I am using EMC, but there is no EMC post processor, so I have been using G-Code Arcs (inches).

Any ideas? I'm stumped. No compensation is enabled in EMC either, I see G40 as the only compensation related g-code active (which is compensation disabled)

Thanks!

[ger21]

It's probably your machine cutting too small. Check the code to see if it's correct.

[mykrowyre]

It's probably your machine cutting too small. Check the code to see if it's correct.

Hmmm looked at the G-Code for a simple square and it seems correct. Unfortunately the part I am cutting is so complex reading the G-code would take forever, so that is out.

The only thing I can think of is that there was a slight change in dimensions when I imported the DXF.

How can I scale the DXF based on one dimension? I've only seen the measure tool which seems fairly difficult to do accurately (depending on whether you click on the line or over one pixel).

[mykrowyre]

Hmm dimensions look correct. I noticed two unusual things:

1) My tool diameter is .0375 at the flutes, but I can somehow cut slots .036. That's right, SMALLER than the tool diameter!!?!? I'm cutting G10 so I am wondering if it's just due to the material? I thought my micrometer was wrong until I pushed the tool into the slot and it didn't actually fit very well. Bizarre. While the tool measures .0375, I had to drop the size to .029 in cut2d to get correct sized slots.

I am using a diamond cutter (flute shape not material).

2) If the above oddity with the cutter isn't isn't due to the material, then I am assuming I have some backlash I need to take care of, which is why my tool size needs to be adjusted. Will check for this too.

Never had a problem until I started using these new bits... which I find strange.

[MrWild]

If you are cutting plastic, plastic is elastic and will not cut to size. Also what kind of machine are you using? it's possible the problem is machine/lash related.

[mykrowyre]

Hmm I cut the same slots vertically (instead of horizontally) and got the same measurements. Since my X and Y axis are completely different (one is acme screw on a rail and the other is rack and pinion) I think I can rule out backlash as the problem.

Would G10 spring back after being cut? I don't remember having this issue last time I cut G10, but I was using a different brand of cutter.

[ger21]

You could be getting tool deflection. Try cutting at slower speeds, or in the opposite direction.

[mykrowyre]

Ahhh I just noticed that the default cut direction is "climb" rather than conventional (seems odd that conventional is not the default), and that is the direction it's been cutting. This could have something to do with my problem, as it would remove less material.

Will fix that and try again

[mykrowyre]

Ok, well I have concluded that the problem is not cut2d. Sorry Vectric!!

I think it's a tool issue... moving this to another forum.

[mykrowyre]

Actually after further testing, the conclusion is that since cut2d doesn't do finishing cuts, my cuts of multiple passes are not uniform in width in the Z axis...

The slots are wider at the top where the tool passes twice as it steps down, and narrower at the bottom where the tool has passed once, with no finishing cut. This only seems to be an issue with something like G10 which isn't really cut but is torn.

The only way around this I guess is to do a larger cut in a single pass.

That stinks... it almost makes the software useless for what I am doing, which is ALL 2D CUTS.

[ger21]

Sounds like machine or tool flex. All the passes should be coded exactly the same. If the cut's are different, it's not Cut2D's fault.

[lsces]

Sounds very much as if you simply need to add your own 'finish' cut? Just drop in an extra full depth profile cut after creating the basic hole just to tidy up the edges.