Inconsistent part sizes

[greg_russell]

I am currently cutting out parts for a stool with two steps, specifically the sides. I am cutting them from 3/4 Baltic birch. I am using a 1/4 bit. Half of my parts are the correct size, the other half are exactly 1/4 inch smaller all the way around (i.e. 1/2 inch shorter, 1/2 inch narrower). In looking at the parts after they were cut, the smaller parts were the ones that I had rotated 180 degrees in part wizard. As the parts are L shaped, I have them nested together. I designed one part, and then copied and pasted it to fill out the sheet. Every other one is flipped 180 degrees.

I can tell that the ones I rotated (using the transform function) are smaller, but my question is why? I checked each individual part in Part Wizard to make sure the size was correct there and it is. My tool path is supposed to machine on the outside of the vector (which it did for the correct sized parts). It seems like the parts that were flipped were cut on the inside of the vector. Is that possible? As I am very new to this I really don't know where to look to figure this out. I am using Version 3 control software, on a Windows XP Professional machine.
Any suggestions you might have would be greatly appreciated.

Kind Regards,

Greg

[artisan]

Greg, I don't use PW....so I cannot say for absolute sure, but I believe you have already guessed the correct answer. Cutting to the inside of your vector with a .25 bit would give you exactly the results you've stated....a half inch cumulative offset. You will have to edit your toolpath....there should be an option to select which side of the vector you machine on. It seems you have probably reversed this function when you "flipped" the vector. If PW is like most Artcam products, you can simply open the toolpath (edit), change the function, re-calculate and re-save....hope this helps....D

[greg_russell]

Darrell,

Thanks for your help. Given that I had positioned and rotated the parts prior to calculating and saving the tool path, doesn't it make sense that all parts within that specific tool path would be machined on the same side of the vector (the outside in this case)? Or is is possible that those parts that were rotated somehow got treated differently when the tool path was calculated and saved? If all the parts in the tool path were the wrong size, then it would be more understandable that I had chosen the wrong side of the vector to machine on. But since only half the parts are the wrong size, within the same tool path, it is harder for me to understand what is going on. I will recalcuate it and try again.

Thanks again for your help.

GReg

[robtown]

When you "flip" or "mirror" vectors (or lines) you also reverse the order of the vertexes and/or reverse the direction of the normals. The normals in 3d modeling are what defines the inside and outsides of a surface.

In simpler terms, when you flipped the lines, you made the outside, inside.

[greg_russell]

Rob,

Thanks. That makes sense to me. So then, what can I do about it? Do I need to use two separate tool paths? One for the originally oriented parts, and one for the flipped ones? If I do separate tool paths and machine on the inside of the flipped parts, will it actually machine on the outside and yield the correct size part?

Thanks again for you help!

Greg

[robtown]

If you switch the toolpath on the afflicted parts from outside to inside, this should (SHOULD) fix your particular problem.

One thing I do when flipping or mirroring is to explode the shape, then remake it into a polyline. Another thing I've done is to flip (mirror), then simply redraw a new shape using vertex snap. (both of these options I do in ACAD) But for your problem, why go to all that trouble when all you gotta do is make a quick change in your toolpath setup.

Sometimes you can make a solution more troublesome than the original problem... (I speak from experience Grasshopper...)

[greg_russell]

Rob,

Thanks again for your help. I will redo the tool path and cross my fingers.

Thanks,

GReg

[greg_russell]

Rob,

Per your suggestion I switched the wrong sized parts from outside to inside and it fixed the problem. Thanks again for your assistance.

Greg

[bob_lofthouse]

I've had the same problem as the above... Many thanks for the answer