Strange toolpaths from mirrored surfaces.

[Jim Estes]

I have a part I am making electrodes for that basically has a compound radius on the top surface. The edges are flat so the best way I could see to create the surface was using one quadrant of this surface and do a 4 edge surface. I did this and it worked great, then I did a <mirror<make copy< and then <mirror<makecopy again. This gives me all four quadrants of the surface. I stitch them all together and try to generate the toolpath. It will generate the toolpath, but it is basically garbage, it will gouge the surface in a strange random pattern that is mirrored in the opposite quadrant.

I tried doing boolean operations to join the surfaces instead of stitching, however I got pretty much the same results. After working on this for about 2 hours I figured out that it was from using the mirror function on the surfaces.

I then went back and created each quadrant of the surface from the original geometry and I got a surface that generated a nice smooth even toolpath with no gouges.

Has anyone else had problems like this? Are there rules for how I can manipulate surfaces and still get clean results?

I also found out that hard way not to try and mirror toolpaths, I get code with retracts after each line segment cut.

Jim

[Gandalf]

This is a common problem found in a lot of software. Workaround? There isen't any. Find out what works, record the procedure and use it that way in the future.

[The One]

SURFACE NORMALS! When you mirrored the part, you also mirrored the surface normals. This reversed them and could possibly have been the cause in your gouging toolpath.

Regards

[Jim Estes]

Exactly what are surface normals? Is there a way to fix them once they are mirrored?

There has got to be a solution, I really don't like unpredictability when it comes to CAD/CAM, I can lose a lot of money if I can't count on my program not to ruin my part.

Jim

[The One]

A surface normal is basically the indication of the positive direction of the surface. In BobCAD you will only be able to see these if you have rendered the surfaces and have the Normal option turned on. To see these normals render a solid/surface, then Click on Drawing Options, then Surfaces and then finally Surface Normals. This will display red lines that are perpendicular to the actual surface, these are the normals.

To reverse a normal: Start with nothing selected. Click on Solids in the CAD window, then Surface Modifcation and then Reverse surface. Then click on a Surface. When you render that surface with normals again you will see it reversed.

Ther fact that the surfaces are doing this is expected. When you mirror a surface you want to see the inverse of the shape. Well, unfortunately, you also have the normal that gets reversed as well.

Regards

[Jim Estes]

Thank you very much The ONE, that is exactly what I wanted to learn. I have been using BOBcad since version 17, and I am still learning new things about it. This is the kind of thing that I wish was covered in more detail in the literature.

Thanks,
Jim

[Jim Estes]

I went back thru some old files that I had been having trouble with and I discovered that the "NORMALS" have created other problems. One problem was surfaces that weren't rendered properly. I had used the mirror function on a complex surface and made the other side of the part. When I rendered the solids, that surface that had been mirrored didn't even show up in the rendering. I reversed the mirrored surface and it renders normally now.

Thanks again.
Jim

[erase42]

exctly Jim, unfortunatly they only show the RIGHT way to do stuff on those cds, there is very little to no troubleshooting or "what to do if" info on those quite expensive cds. Perhaps the next time they gear up to make videos for v22 or whatever is next, they could scan thru a couple dozen pages of the bobcad forum here and see what sort of questions are on the minds of the common man. If anyone has the ear of any of the bobcad people maybe this could be suggested. Actually im only about 20 min from their office in florida, maybe ill mess my hair up, put my overalls on inside out and stop by for a little chat.

[tjones]

Originally Posted by erase42 exctly Jim, unfortunatly they only show the RIGHT way to do stuff on those cds, there is very little to no troubleshooting or "what to do if" info on those quite expensive cds. Perhaps the next time they gear up to make videos for v22 or whatever is next, they could scan thru a couple dozen pages of the bobcad forum here and see what sort of questions are on the minds of the common man. If anyone has the ear of any of the bobcad people maybe this could be suggested. Actually im only about 20 min from their office in florida, maybe ill mess my hair up, put my overalls on inside out and stop by for a little chat.

There are some free sample tutorials that will walk you through the process of generating g-code. However you are correct that there is little info on troubleshooting issues.

Sorin (the one who does the training seminars) has some free videos. (these are training videos based on doing a job) Go to http://www.cadcamtrainer.com/forums/index.php sign up there and after you complete the registration you will have access to the free videos.

Ask Sorin for a specific video on certain things and he can make them.

[CNCdude]

Erase42,
We would be happy to have you stop by and chat with us. We will take your request into consideration on the next round of videos that we do. Thank you for the input.
CNC Dude

[tjones]

A video titled FAQ or this .

Really a FAQ web page would work very well for that type of information. This way it would be easy to find and update as needed.


1) Why can't I snap to a line middle point?

A1) Check the snap settings in File>Environement>Snap Points to make sure the 'Middle of Line or Arc' is checked.

[tjones]

As for Bobcad's videos...I would not say they are expensive for what they contain. There are 11 CDs containing a huge amount of infomation. These CDs are to learn the software and what all those buttons, icons, menus are for.

Those CD's must have taken months to prepair correctly and to be edited/verified for accuracy. I would have to say they are well worth the money for someone needing to learn all the ins and outs of bobcad.

The training seminars are also very good. Sorin does an great job of training on the functional use of BobCAD. They go together but are different than the Bobcad training CDs. I would review the CD's and then take the seminar (in that order) then review the CD's once again. Sorin gives his training videos to review to keep up with those functional uses. So in short Bobcad CDs are informational while Sorin's seminars/videos are functional.