Inconsistent tool path when cutting circle

[greg_russell]

I am trying to cut out a 5 foot circle from 3/4 material using a 1/4 inch bit in two passes. I imported a dxf file from my customer into part wizard. I created a tool path to profile outside, in two passes. In the simulation, the correct tool path is followed on the first pass. On the second pass, it deviates slightly, which will result in something that is not really round. It seems to be moving off of the original tool path by about 1/8 inch. It is not doing this all the way around the part, just about 1/3 of the circumference. There is individual detail inside the circle as well, but these are separate tool paths and they appear to be correct.

Does anyone have any suggestions of what I might look for to fix this? Thanks.

Greg

[beacon14]

It is probably a flaw in the customer's file. A quick workaround would be to delete all the code after the first pass from the toolpath file, then run the file using 2 repetitions to reach full depth.

[ckurak]

Greg,

What type of material? Is it a result of bit deflection due to wood grain?

[greg_russell]

Charles,

I am doing it in baltic birch, but I have not actually cut it yet. The deviation is showing up in the control software preview/simulation.

Dave, thanks for the suggestion, I will do that if I can't solve it some other way. I would like to understand why it is happening so that I can avoid it in the future.

Greg

[beacon14]

Greg,

Does the circle show up correctly before the toolpath is generated?

What happens if you play with the stepdown value to generate a toolpath with a single pass, or more than 3 passes?

If you want to e-mail me the .dxf file, I'll see if I can re-create the problem.

[greg_russell]

David,

The circle shows up with the problem in it. You can clearly see where the second pass deviates from the initial pass (the initial pass looks to be in the right place).

I have not played with the step down. I presume that I could cut it in one pass and be fine. I am just trying to use a 1/4 inch bit. I will play around with that and see what happens.

Thanks for the offer to look at the file. I will send it to you.

Thanks,

Greg

[ckurak]

Greg,

1) Obviously I didn't catch the part about the problem showing up in preview mode.

2) Is this simply a problem of perspective with the previewer? Try rotating the preview screen so you get a direct top-down view of the circles. Do they now line up with each other?

[greg_russell]

Charles,

Thanks for the help. I had emailed the file to David and he gave me the same suggestion about the orientation of the part within the preview screen. When you do this it lines up perfectly. So I have learned how to use the preview screen correctly!

Thanks again for your help.

Greg