mirrored parts problem

[MadPickinSkills]

I have a small router in my garage with nema stepper motors. Im using Mach3 to control it and Mastercam to program. I'm cutting a part that required machining on the back side. Do do this, I cut the perimeter and routes on the front, then I take the geometry and mirror it to cut the routes on the back. I also us the same mirrored geometry to created a "negative" of the part so that I can machine a reference fixture. When I try to flip the part over and place it in the reference geometry, I find the geometry doesn't match, even though I used the same geometry in mcam and just mirrored it. Is this possibly do the the stepper motors or the controller or mach 3?

thanks

[mx_masta]

This is my first post so everyone don't jump on me straight away!

I don't use mcam so it's a bit hard for me say but what I would do in ProE is create a new fixture part and insert copied geometry from the parent part to create the negative surface.

Also your tool paths would all need to be switched to the otherside of your edges, maybe this was your problem?

It's all a bit hard to say without seeing your part.
If the geometry is not symmetrical about the CL of one face as well as the CL of the part then you might need 2 fixtures.

[HuFlungDung]

I'm trying to rack my brain about when I would mirror and when I would rotate (180°), and as a general rule, I would not mirror to machine the back side of something, but I would mirror if I was making a left and right pocket where a parting line produced exact left-right symmetry.

Now it might be safe sometimes to mirror front to back, but if one flips the model over with rotation, for sure, nothing gets transposed.

[MadPickinSkills]

lol somehow I knew this would happen. I'm sure I have the geometry correct and I'm sure mirroring the part is the solution for creating the fixture. The issue is not in Mastercam or the method.

Think guitar body

[HuFlungDung]

Can you post any pictures of how it turned out (incorrect)? Some guitar bodies are not symmetric even though they look close

[MadPickinSkills]

Originally Posted by HuFlungDung Can you post any pictures of how it turned out (incorrect)? Some guitar bodies are not symmetric even though they look close

one second

[MadPickinSkills]

check these. sorry for the shadows. In the pics it doesn't look like its off by much, but .060" too far one way will make the routes on the front of the body not line up with the routes on the back that go through.

thanks

[HuFlungDung]

Did you actually mirror each half of the profile when you created the initial design? I'm just wondering if some subtle difference could have somehow crept in, that would make your model non-symmetric.

I guess the easy way to check that is to take a copy of your original geometry (topside) and rotate it 180 degrees in X or Y (depending on how you have it set up in your CAM) and make sure that this copy exactly matches the geometry that you mirrored when you cut the back side.

Apart from that, I suppose anything is possible with steppers losing steps unannounced and that is why I'd personally have nothing to do with stepper motors on a machine tool.

[MadPickinSkills]

[QUOTE=HuFlungDung;645966].....

I guess the easy way to check that is to take a copy of your original geometry (topside) and rotate it 180 degrees in X or Y (depending on how you have it set up in your CAM) and make sure that this copy exactly matches the geometry that you mirrored when you cut the back side.
....QUOTE]

I've done that twice just to be sure. I used the geometry in the program for the top side, mirrored the geometry, then programmed the back side. It should be identical.

[ger21]

Are you sure the machine is cutting accurately? Perhaps print the parts full size and see if they match? If you're using CV mode, it's possible that the path is deviating a little from the programmed path in the curves.

[HuFlungDung]

I'd take a look at your geometry, if you wish to post a DXF file. Different set of eyeballs, and all that, you know

[MadPickinSkills]

Originally Posted by ger21 Are you sure the machine is cutting accurately? Perhaps print the parts full size and see if they match? If you're using CV mode, it's possible that the path is deviating a little from the programmed path in the curves.

Gerry,
Thats kind of what I was thinking. It is in cv mode. The parts do match printed. I think it's also possible the slop in the machine was making it drift a but while cutting or causing the z-axis to become un-perpindicular with the matherial, or both. The machine has many unsupported linear rods that I need to upgrade to supported or thk style bearings.

thanks