vcarve toolpath issues

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cbbo
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Re: vcarve toolpath issues

Post by cbbo »

scottp55 wrote:Try some more conservative pass depth tests maybe?
Bit angle test looks like angle is correct.....kinda thinking machine flex from pass depth?
scott
Yeah I'm going to set up a test piece with different pass depth settings. I was reading more about clearance pass depth (apparently the depth used for when a v-bit has to make multiple cuts down to flatdepth) but it puzzles me that this could be the issue, since I see problems even at very shallow depths (like with a .05" flat depth!).
TReischl wrote:Well, it looked to me like there was a slight curve in those sides, but that could be an optical illusion caused by the overcuts in the corners.

Running tests at 55, 60 and 65 is WAY too big of a difference. That should be more like 55-65 in one degree increments and then look at them with a magnifier and a straight edge. I would also NOT cut them in particle board for testing. MDF would show things a lot better. Well, maybe that is MDF, but it is a lot lighter colored than the stuff I get. It looks a lot grainier to me too. But hey, pics can be deceiving.
I was satisfied with the test I did and I'm still skeptical that my bit angle is at fault.. but who knows. If other tests don't pan out, I may re-run an angle test at the single degree interval just to be sure.

It is MDF from the local big box store, the photo is a little zoomed so I think it looks grainier than normal.


And thanks for the feedback everyone! Slowly chipping away at this problem, hopefully can solve my mystery soon. I've stared at my test cut pieces for a long time trying to work this out, lol!

cbbo
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Re: vcarve toolpath issues

Post by cbbo »

So, forgot to take a picture - and now I'm at work so can't get one... but I did a test yesterday, more identical triangles in a matrix.. no flat depth.. the vectors were sized so the toolpath had a max depth of about .48 inches, as I wanted something deeper than my v-bit to ensure multiple passes would be made, and that the problem would show up on the walls (the material left when the corners are finished).

I had been using a Pass Depth of .2", with a clearance pass stepover of .12" and about 60 inches per minute.

To test if the speed/flex/deflection is part of the issue, I ran a 4x4 matrix of toolpaths. Across, they used a pass depth of .25", .2", .15", .1". Going down, they used clearance pass stepover values of .15", .12", .08", and .04". Feedrate was 60 ipm, plunge 30 ipm.. I thought for sure there would be SOME difference in these cuts, but they all came out nearly identical. The same little nub of material is left in each wall - just like my previous tests (where I'm not using a flat depth). I'll post a picture later.

I also found that Whiteside has downloads of .tool db files for Vectric apps, so I found the one for the 1550 - and woo boy, as a starting point, it's set to a pass depth of .433" and a clearance pass stepover of .1", and a feedrate of 140 ipm! So, I'm thinking I'm well within the boundaries of this tool, especially when dealing with just MDF.

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Adrian
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Re: vcarve toolpath issues

Post by Adrian »

It's not the boundaries of the tool so much as the boundaries of your CNC machine.

cbbo
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Re: vcarve toolpath issues

Post by cbbo »

I get that the machine plays a part as well.. maybe it was a poor choice of words. However, if it was really a limitation of my machine and/or the tool with regards to deflection or flex - don't you think there would have been some difference in the results with varying pass depths and clearance pass stepovers?

Do you think I should try even lower feedrates? If that doesn't show any difference, I'm not sure what else to try to help narrow this down.

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Adrian
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Re: vcarve toolpath issues

Post by Adrian »

Have you tried other shapes other than triangles? I can't see what else it could be other than an issue with the machine or setup. It's not going to be a VCarve issue or there would be loads of people reporting the same issue.

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mtylerfl
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Re: vcarve toolpath issues

Post by mtylerfl »

As a test, try setting your Feed and Plunge at 0.3” per second (aka, 18” per minute). Post your results when you have a chance, please. Hopefully, you’ll see an accurate result when “going slow” like this.
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cbbo
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Re: vcarve toolpath issues

Post by cbbo »

Alright.. here's a new photo album: https://imgur.com/a/90gXI0p

I showed a pic of the triangle tests using various pass depths and clearance pass stepovers that I mentioned in my previous post. I used pencil lead rub on the edges to hopefully help highlight the deviations.

I added a few more triangle cuts to that piece, using the slower feedrate of 18 IPM and then half that at 9 IPM just for fun!

I also carved some additional tests - a circle, square, and star - using the same 60 degree bit as the others, as well as a .50" 90 degree bit. The circle and square are .75 inch.

Still seeing the same issue here. I'm pulling my hair out!

I thought about recreating this in other software, just to see how it compared, but it doesn't automatically cut a profile out when using a V-Carve toolpath (for example, on a square, it just does the corner plunges) nor does it have a flat depth option - so not able to do a good comparison.

Any suggestions on more tests to help narrow down the culprit? I have other software with a startup license, so I can attempt to recreate this there as well, not sure how the vcarve toolpaths would compare.

cbbo
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Location: Huntsville, AL

Re: vcarve toolpath issues

Post by cbbo »

As a follow-up, the square shape allowed me to get some easy accuracy measurements in. The width and height across the center, where the nubs are left, are exactly .75" which matches the vector, but where the bit clears the corners, it's exactly .05" larger at .80".

Tomsav
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Re: vcarve toolpath issues

Post by Tomsav »

I see this is a pretty old article, did you ever find a solution? I am having the same exact problem....I’ve tried to trouble shoot everything I could like changing angles and other setting, this happens on all my v bits. 60 and 90....

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