Z-height change problem

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MikeSibley
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Z-height change problem

Post by MikeSibley »

Hey folks, I first apologize if this has been discussed before, but I have a significant problem that is just beyond my skill level. Second, I apologize for the length of this post as without the proper description, it won't make true sense. I would appreciate any comments toward finding a solution.

Basic parameters. I'm running an AvidCNC 48x96 with an independent Lenovo PC. I work with Aspire v11 and use a separate computer for design and place the g-code file (with the proper post processor) to a thumb drive and load that onto the Lenovo with the Mach 4 to drive the CNC.

I downloaded the Vectric Buffalo Nickel Bank, made no modifications to the file (other than inserting the correct bit feeds and speeds) and cut it with the following toolpaths, 1) 3D roughing with a .25 endmill, then 1/8 inch tapered ball nose, then a 1/16 tapered ball nose for rest machining (handled by Aspire). Both heads and tails of the nickel are cut from one board in the same toolpath on a board that I have planed to the proper thickness, so I know that there are no discrepancies in material thickness.

The first cut of the tapered ball nose, using an offset toolpath. Into the tool-path, for whatever reason, the Z-height changed leaving a pronounced difference. Even though I knew it was incorrect, I used the touch-plate to zero the next smaller ball nose and it cut the depth properly but it looks horrible since the z height was off and it obviously kept the proper z-height as evidenced by the depth of cut into the model.

So, I thought that maybe this was associated with the offset toolpath and switched to a raster tool path
IMG_0400 2.jpg
and cut another model. Well, same issue occurred. I don't think that this is an issue with the actual model as hundreds of those have been cut and I don't know of any complaints about the model on this forum. Any suggestion or advice would be appreciated.

Would you folks think that this is a Mach4 issue or an Aspire issue or a machine issue?
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IMG_0403 2.jpg
IMG_0404 2.jpg

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TReischl
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Re: Z-height change problem

Post by TReischl »

Hey Mike, I would look first at it being a machine issue, then as a Mach 4 issue. Like you said, highly doubtful it is a software problem.

All the usual suspects, loose coupler, bad collet, something binding, something loose.
"If you see a good fight, get in it." Dr. Vernon Johns

MikeSibley
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Re: Z-height change problem

Post by MikeSibley »

Thanks Ted. It has baffled me as it is a regular occurance.

Mike

4DThinker
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Re: Z-height change problem

Post by 4DThinker »

With 3d surface cuts I've had the same things happen before. What I eventually traced it down to was wood movement. After slowly cutting part of the surface area the wood warped a little and as the cut moved over to another area that area was now just a little lower in the wood because the wood had raised up.

While this may not be what is happening to you your photos brought my memory back to what looked exactly like your stepped results.
4D

MikeSibley
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Re: Z-height change problem

Post by MikeSibley »

I've had the wood locked down pretty significantly, but I will check. Thanks for the advice!

Beltramidave
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Re: Z-height change problem

Post by Beltramidave »

Check to make sure your bit is not slipping in the collet. Honest John just had this same thing happen while running a file he has run many times and only happened when running an more aggressive toolpath.
Dave
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MikeSibley
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Re: Z-height change problem

Post by MikeSibley »

Will do, but I lock the bit down pretty well. Will double check, as it sounds like a potential solution.
Mike

neilgill
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Re: Z-height change problem

Post by neilgill »

If it was the tool path then I would think that it would be evident in the Preview in Aspire. I would suggest taking a simple circle or square, the using the modeling tab use the "create a shape from a vector outline" and create a limited height dome. Then cut it with roughing then finishing tool path. This should cause a problem if its the machine.

Neil

MikeSibley
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Re: Z-height change problem

Post by MikeSibley »

Okay, issue is identified. There was an update to Mach4 that corrected this problem. I reached out to Avid and there was an issue with the original Mach4, so I updated and cut and it is perfect. I really think it was an issue with a interface between Mach4 and Windows. Personally, I use a MACbook Pro and just in my opinion, Windows is the worst program ever stolen from IBM. It's pretty bad.

I want to thank everyone for trying to help me. It was a great outpouring of help and suggestions.

Mike

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