3 out of 4 fillets have a different radius?! I can't understand why. Does anyone know?

Hi there Avid community,

As of recently inner corners come out very odd on my avid cnc. I am not sure where to problem lies. This goes for pockets as well for outer profiles. For instance when I have drawn a cad file, a lot of corners randomly get a radius way larger than needs to be. This happens in pockets as well, where 3 out of 4 pockets get a different radius than I have drawn in Cad.
I can’t wrap my head around why this is.

I have tried reinstalling mach4 twice(thought it might be corrupted)but to no avail
I have tried making the cad file in rhino and in VcarvePro. Both with same results.
I have tried test pieces with different bit sizes; if I am using a bit way smaller than needs to be I can get it to make a correct corner but any bit closer to the actual size the fillet needs to be and the corner becomes way large. I have added a picture of the Vcarve file; what the test piece should look like and a photo how it comes out. Does anyone per chance have seen this type of issue before or know what direction I should be looking? Any help is greatly appreciated.

Cheers from Amsterdam,

Tijn

I have to add; dogbones and T-bones come out ok, just the normal fillets that form a problem. Also in this test piece the outside profile came out ok, but that is not always the case

That looks like you have path blending mode turned on, with way too high a value. This is G64 but I don’t know how mach3 supports that (I use linuxcnc, where G64 takes a parameter).

If the one corner that is tight is the one that it started the pocket on, then I would guess your CV mode settings are messed up. I am able to create that with VERY slow acceleration settings and really loose tolerance settings for CV in mach4. You would have had to run one of the CV wizards to change those though since the default values that come with the AVID build are good.

I can’t think of a setting in Vcarve that woudld do that, and even if there was, it should simulate it anyway.

On the other hand, if it were CV problems, then it really should show up in those two side pockets as well.

Have you tried someone else’s proven file?

Thanks for the replies guys, I am going to deep dive into each of your answers and get back to you

Hey Jim,

You guys are correct in that the problem lies in the CV modes. I did a the test lowering the ipm from 350 in steps of 50 all the to 150 ipm. This helped and the radiuses got smaller with each lowering of ipm.
Second thing now perhaps is adjusting the ´´McCVTuning´´ wizard on mach4. Avid has set this to a 0.005 standard, though mach4 default is 0.001. I have tried setting it to 0.001 but with minimal results so far. Have you yourself altered these CV settings?
I ran an older(way older) version of mach4 before and didn’t face any of these issues then. Perhaps Avid changed these settings a bit with the newer version.

I was wondering, since I saw your video about adjusting motors acceleration, if this would be a smart one to adjust in hopes of getting better results with these corners? For me it is very important that the cutting result is exactly the same as the cad drawing. I care less about the time it takes to accomplish it. Interested to hear your thoughts on this. Thanks in advance

Greetings, Tijn

Thanks yes you are correct. I wasn’t aware of this mode before, I guess you learn something new as soon as problems arise. I am going to do some tests now changing the settings in the ‘‘McCVtuning’’ wizard on mach4 in hopes of better results.

The weird thing is that I used to be able to make these corners without any issues running the machine way faster than it does now. I updated mach4 a few weeks ago the solve a different problem I had with my cnc. That problem got solved but then this one arised. I think some changes were made regarding this CV in that update.

The thing is if I run my cnc any lower in ipm to solve these CV radius problems I am not getting the correct chipload. The bit would get too warm. Sure I can use a smaller bit for the smaller cuttings, but that feels like a lot of hassle and I think I should be able to do some simple small pockets within a cad file with the same 6mm bit I use to cut the outer profiles. Running the bit on a lower RPM, lets say 14000 instead of the 18000 doesn’t do that much for the chipload and since the spindle is aircooled i’d rather keep everything at a higher RPM.
Sorry about the info overload, I am fairly new at all this and just figuring out how to get right balance between all the different parameters. Any advice is already deeply appreciated.

Greetings, Tijn

I tried playing with the CV tuning, and I basically could make it worse than the default tables that come with the AVID software releases. I found that I could get smooth results with pure circles and lines, but oval shapes were very jittery if I made changes. In the end I just went back to the default AVID numbers beause they worked best overall.