Inconsistencies in spiral finishing toolpath

[eisenmanguitars]

What might cause these inconsistencies?  Seems like sometimes the z axis changes for a few passes, or midway through a toolpath.  The background in this is supposed to be flat, the text and the symbol are supposed to be on the same plane .010 higher, the border another .010 taller than that.

[programming2C78B]

tool pullout or the wood raising as it gets thinner in the middle. upcut or downcut bit? 

[eisenmanguitars]

Tapered spiral down cut.  I will try running the program on a thicker piece of stock for troubleshooting purposes, but this happens at random times, and it seems like it just happens per pass. I could see if the wood was moving how it would be thinner/ deeper in the middle and gradually changes it goes out, but this seems like a sudden jump or dip.  I'm attaching pictures of another operation I did a couple weeks ago, the same thing happened.

[eisenmanguitars]

here's another project I recently did with the morphed spiral. The same thing happened.

[seth.madore]

What's the actual material (wood, duh, but what variety)?
It could be as simple as thermal growth of the machine/spindle in combination with the material itself.

[eisenmanguitars]

Thanks for asking. This is happened on birch plywood, spruce has shown in the original picture, and ebony as shown in the last picture.  The variation seems to me to be independent of growth rings/ wood grain. Is strictly follows a pass of the toolpath.

[seth.madore]

And what sort of tool are you using, and what is your machine and workholding methods?

[eisenmanguitars]

My machine is a mill right carve king 2, my work holding is a spoil board clamped, then masking tape on the stock super glued to the masking tape on the spoil board.  My tool is a .25 mm tapered ballnose end mill, the picture of the ebony I used a 0.75 mm tapered ball nose end mill.

[seth.madore]

Hmm, looking at their website, it appears to be a decent machine. I'd be curious as to where on the table you're clamping the part, and if there's any difference if you move to another location. Could it be vibration and machine harmonics? Possibly.

Would you be able to share your Fusion file here?
File > Export > Save to local folder, return to thread and attach the .f3d file in your reply.

It's possible that there's something going on with the model..