Z position confusion

[baldysm]

I cut my first part with Madcam today, and something doesn't make sense with the Z position.

My part is .03" thick, with Z0 at the bottom of the part. So other than clearance, all the Z positions should be between 0 and .03". If I look at the finish tool path curves, there isn't a single movement that would be cutting the part. The lowest Z movement is at about .036".

The green region box emcompasses the part, that looks right. I'm using a 1/8" ball end mill with 0 stock to leave. In the planar finishing options, stock to leave is greyed out and 0 anyway.

In the roughing pass, its looks like I'm taking 9 passes, each .01" deep on a part that's only .03" thick. There are 5 passes cutting air above the part, 1 pass kissing the top of the part, and 3 cutting the part.

All the finish curves generated by Madcam are above the part in Rhino (ie above .03"). Given that, why is some of the Z positions in the Gcode as low as -.0165".

All that being said, the part cut ok (but see below), but I had to experiment with Z to get it to come out right. If I had touched the top of the part, told the controller I was at .03", things would not have come out right. I only ran the first 4 passes of the roughing program. On the finishing program, I set my Z high, and kept stepping down in Z until my part started to clean up and then let the program go all the way through.

So my question is, why is my Z so funky, and what am I doing wrong. How do I determine where to set my Z?

The other problem I had was some strange output. There are several times where I get about 50 lines similar to the following:

Y0.17849
Y0.17960
Y0.17849
Y0.17960
Y0.17849

Just those 2 numbers alternating for about 50 lines, and then the program continues normally. Not sure how to fix it or investigate what's causing it.

Thanks!

Scott

[rodneydeeeee]

lol, just out of curiousity, what the heck is MadCAM and where did this progam come from?

[baldysm]

Madcam is a CAM program. http://www.madcamcnc.com/start.html

Seems to work pretty good. I think the problems I am having are being caused by me doing something wrong, not the program.

[rodneydeeeee]

I've heard of many programs out there and for some reason MadCAM just doesnt ring a bell. Do you do 2D work or 3D work? How much is the program retailing at?

[baldysm]

I do both 2D, 3D and 4D, but I cheat on the 4D. Most of my stuff is pretty small, less than 2" x 4".

Right now Madcam is free if you have another CAM program. It's a plug in to Rhino3d. The guy who makes it is trying to get people to buy his forthcoming version of Madcam by giving away the current one for free. The upgrade is $500 and the full version is $2000, but it's not released yet.

[rodneydeeeee]

www.cadcamconsultants.net

Little bit cheaper than the $2000.00 and upgrades are cheaper as well. Just got introduced into the American Market. Turned alot of heads.

[JOM]

Hello Scott,

The toolpath curve is measured from cutter centre in Rhino. If you use a ball end mill and create a toolpath on the top of your model, the toolpath curve will be placed half the cutter diameter above the top. If you use a flat end cutter, the cutter centre will be the same as the tip. When using corner radius cutters, the centre will be located the corner radius above the tip.

There is also an option in the postprocessor for cutter reference centre or tip. By default this is set to cutter tip. If you have your work piece placed in Rhino with z=0 at the top, then you set z=0 in your machine when the cutter tip is touching the top of your work piece.

There is a filter tolerance in the postprocessor that should be set to the same as the resolution of your controller. This could have caused the 50 strange lines.

If you need more help, please e-mail the model to us and I will have a look.

Thanks,
Joakim

[baldysm]

I gotcha on the toolpath curve vs the actual g-code. I think all the results I am getting make sense now.

I'm not understanding what you mean by the resolution of the controller. The strange lines I am getting are generated by the post processor. The filter tolerance is .001, which is the default. Where do I check the resolution of the controller?

The term controller to me means the box that controls the CNC machine. The strange lines are generated before it gets to that stage in the process of making a part.

Thanks for the quick response!

Scott

[JOM]

Scott,

I am sorry. Perhaps the resolution of controller isn’t the correct words in English but what I mean is that the filter tolerance should be set to the same as the smallest possible increment your machine can move. If using mm and the smallest possible increment on each axis is 0.001mm, I set the filter tolerance to 0.001.

I am not sure if this is causing the trouble, but if you e-mail the model with the toolpaths, I will have a look and let you know.

Joakim