Trouble with projecting curves

[rlrhett]

I'm having trouble with the projecting curves feature. As an example, I have a straight line drawn in Rhino "suspended" over a sphere. If I project the line onto the sphere and leave Multi-z pass unchecked and Stock to leave at 0, I get a nice, single pass score line on the surface of the sphere:

[rlrhett]

Now assume I need to carve a slot .5" into the 2" sphere. If I tell Madcam to leave "-0.5" material I get this weirdness:

[rlrhett]

Finally, assume my cutter should only be trying to cut a .0625 pass at a time. I check the Multi pass z box, tell it to offset z by .5" (I assume that is how it should work) and tell it I need .0625 passes. I get rapids through the sphere and air cutting:

[rlrhett]

So what would the right way to cut a slot into a curved surface a specific depth using small enough passes?

[dcd121]

What about this?

Z offset .5

Stepdown .0625

check multiple z cuts

[rlrhett]

Originally Posted by dcd121 What about this? Z offset .5 Stepdown .0625 check multiple z cuts

Then I have a bunch of air cuts, right? The idea is to cut half an inch into the surface.

[dcd121]

another try,
This is cut along curves making the assuption you would like a straight slot versus a curved slot .

[rlrhett]

That does work for a straight slot. There are two things about that I don't like: a lot of air cuts and I do actually need a slot that matches the surface radius.

I am dissapointed that Joakim has not responded (I believe that is the name of the guy who created MadCAM). Perhaps I will e-mail him and ask what is going on with the strange cuts. If he responds, I'll post his response here.

[rlrhett]

I think I have a work around to the odd cutting paths. Instead of using MadCAM to project curves, I used Rhino. I "suspended" a straight line over the sphere and used Rhino to project the line onto the sphere. I deleted the straight line and moved the curved line .5" into the center of the sphere. Then I used the carve along curve feature of madCAM, selected multiple z passes, raised z by .5" and gave it steps of 1/16" of an inch. I also made sure that the safe clearance distance was at least .25" to make sure there were no rapids through the model. It seems to have worked. My only concern is that it know to start with the top arch and work its way down to the line. Watching the simulator seems to confirm this, but the only way to really know is to put a cheap bit in and hope I don't break it!!

[robinsoncr]

rlrhett,

You beat me to the punch! I had read your post during lunch and when I came back for a break, I worked out how to do this. Go to type up a reply and see you have already figured it out!

What material will the substrate be? Good luck and let us know if it worked. I think Joakim has been real busy lately. (I'm betting he's getting MadCam4 ready for release.)

Later,
Chris

[xlr8tr@mac.c]

I use this technique all the time to cut purfling channels into the curved surfaces of my guitars - works great.

[JOM]

Hello rlrhett,
I am sorry for the delay. I have been very busy finishing madCAM 4.0 for release. It is available for download from my web www.madcamcnc.com.


I think you already have figured out how to do it but I hope this will give you some help.

madCAM is designed for cutting out 3D models and not cut in surfaces on the model. The stock to leave is a 3D offset used for leaving material after Roughing or if setting to minus amount, used when cutting EDM graphite electrodes. The negative amount of stock to leave should never be more than half of cutter diameter. The only way to force madCAM cutting into material on the model is when using 2,5D functions or with the Along Curve command. The Along Curve feature will create toolpaths that follow curves exactly as you draw them in Rhino and the rapid traverses will be calculated from the 3D model.

It is also possible to use Project Curves and Along Curves in combination. You can use the project curve for getting a toolpath curve in Rhino. This curve can be modified as any curve in Rhino and you can modify it and use Along Curve for making a new toolpath of it.

If I would cut a slot on a curved surface, I would make the model in Rhino with the slot included and then cut it.

Joakim