Area Clearance and mirrored part problems.

[tomn1]

We mill down 1/2 polyetheyne material on one side, flip the sheet, mirrored in part wizard, and when it is finished milling and cutting out that side, the finished product is centered on the second side, but the first side is off center L-R 1/8" Up-down 1/4". Bot is square, updated, and otherwise is working fine. I've studied the toolpaths and they are exactly the same just mirrored. I am new to the shopbot but have experience on other machines. Any advice would be great. Scratching head for days. Thank you.

[tomn1]

Forgot to add. Material is squared on tablesaw, we just tried alignment holes on scrap, paths,etc are absolutely dead on, and yet when piece is flipped we still get 1/4" height. What am I doing wrong or not compensating for?

[tomn1]

1/4" difference in height between side a and b.

[fleinbach]

Thomas,

I have done this several times and it works great. I center 2 1/4" dowel pin holes on each end of the material. When drawing and positioning the holes in cad I place them on the first side then I mirror this side and lock them so they can't be moved. I do not place them on each side by measuring as this can possibly induce an error.

[tomn1]

I understand what you are saying we use that method on some processes. But I am really thinking something about the toolpath I am doing incorrectly and don't realize.

The table we use here has a "hard" X/Y Bed meaning that 2x3" Aluminuim strut runs their length on one side. We slide our material after squaring unto the table until it is butted up against the aluminum frame. That gives us repeatable, reliable square surface and a 0,0.

I am thinking for some reason the bit is cutting on the opposite side of the line on side A. Even though paths are exactly the same. We mirror several parts but it is only this one that is screwy! Even after redrawing the sheet, no luck. It is just strange.

[evan]

Be sure all lines in the CAD drawing for that cut are joined before mirroring the part. If it is a single line and you are using the profile toolpath and it is set for outside then on the mirrored part set it for an inside cut that will switch the side the tool will cut on. Hope this helps.

[fleinbach]

If I understand correctly you said "but the first side is off center L-R 1/8 " This can only be caused by the sheet not being positioned properly. If you are relying on the edge of the sheet instead of some form of indexing placed in the cad file you will have a problem if the mirrored image is off center even the slightest. Since you say you use the edge of the sheet if it were not exactly the size you are thinking it is or it is not really square you will have a problem. For repeatability when flipping any material the only thing I trust is index points I am sure are place accurately in both images.

One other thing that could cause the problem is if you lost steps and your zero zero are no longer acurate after the flip.

[tomn1]

Frank,

Yes you are correct about the L-R being off, that was our mistake. And as for the height issue, for some reason when I finished the drawing off again, it was just fine. I've never have a problem like this before and hope it is the last.
I've also drawn indexes also, but it meant loosing 2 parts, but it's worth the reassurance.

Thank you all.