Hey guys, I need some help here. I'm getting my PP3 running very well and knocking out little annoyances one by one. I'm having an issue when milling out pockets. In Sketchup, I use the Pocket tool to generate the cutpaths inside each milled pocket, and then use the Sketchucam Centerline tool (at 50% depth) on those pocket paths to generate the G-code. That works fine... it zig-zags back and forth to mill out the pocket and then goes around the outside profile to clean up the pocket.

However, I think it's going the wrong way around the profile... it goes Counter-clockwise around, and from my experience hand-milling airplanes, it should be moving around clockwise to get the cleanest cut possible. Here's a picture of the resulting pocket... you can see how much trash it leaves around the edges.

Is there any easy way to reverse that direction, or am I wrong about what's causing the rough edges? I've tried multiple bits and feedrates and always get that ugly edge.

Thanks guys,

RJ Attached files

 

Are all of the other cuts fine? You might know this already, but make sure you select the "Overhead Gantry" checkbox in the Phlatboys Properties in Sketchup.

 

Yes sir, I do have that checked, and all the other cuts come out just fine. Come to think of it I don't know what direction it cuts them... I just feel like cutting the other direction would clean up this problem.

I read somewhere that reversing the faces in Sketchup might convince Sketchucam to cut them the other direction... any truth to that?

 

I've been playing with this... annoyingly, even turning off "Overhead Gantry" does not reverse the cut direction in the G-code. Reversing the faces doesn't change it either.

I'm trying to find a way to do it in the Ruby scripts, but, without any existing knowledge of how the SketchuCam/Phlatscript scripts are set up... I'm not going to get very far with that. I'm just chasing functions from one file to the next... not too optimistic.

This isn't really THAT big a deal of course, but it is annoying to know exactly what's causing the problem and not be able to fix it. My airplanes tend to get a lot of scrutiny at events, so I'd love to not have to explain that it isn't the PP3's fault, it's just some incorrect CAM work!

 

Thanks for the suggestion, but no such luck. That still cuts CCW.

The closest I've come so far is by using the inside cut tool with a bit diameter of zero and half the true material thickness. That makes the cuts go clockwise, but it still moves around the path segments CCW... so it plunges, cuts one line segment clockwise, pulls the bit out, then moves CCW to the next line segment, plunge, cut that CW, and so on. Not exactly what I'm hoping for.

 

Well, I have what seems to be a workaround for now.

First, set the parameters up for a bit diameter of .25" (my milling bit) and use the milling depth in place of the material thickness. Use the inside cut tool on the milling pocket face, then use the pocket tool on the resulting inner face, then the centerline tool (at 100% depth) on the resulting pocket lines. That way, the tool still cuts the pocket line backwards, but then goes around the additional outer path clockwise to clean it up.

Annoying... but it should work! Attached files

 

Naturally, you then have to have totally separate files for the milling paths and the cutting paths... but I've been splitting it up like this anyway. I find it's just easier to have separate CNC files than to manually group all the milling together in Sketchup, manually insert pauses for tool-changes, and then have to bookmark, re-zero, and start the cut back from that bookmark.

 

Actually, the inside cut path cuts CW... the outside cut path should cut CCW, right??

I realized that if I modify the pocket tool to skip adding the offset line, I can make this even simpler... just apply the pocket tool to create the zig-zag pattern, then apply the inside cut tool to create the perimeter cut. Then I don't have to deal with multiple sizes of perimeter cuts.

You still have to have all the milling in a separate file, though... but I've been doing this anyway. I always use 3 different bits (milling, hinge bevel cutting, and actual cutting), and it's easier to have separate files than to have to manually select all the milling features and add them to a group, to keep everything in order for tool changes.

Now, if only Sketchucam could default to 3 different bits, and keep track of what operations use what bit, and put them all in order, with appropriate tool-change stops... My life would be that much more complete. But I do a fair amount of coding myself... I know that's not exactly simple.

 

HI RJ, I have attached a test file for you and may have an easy work around to control direction. Try the file and see how I was able to get the one triangle to go clockwise and the other CCW on the outside line of the pocket! We may need to talk to explain better. BTW what bit are you using for your pockets I cant seem to get a perfectly smooth pocket, if you look at an angle you can see the ridge at each pass, I beleive it is just the type of bit I am using and that is a 1/4" end mill 4 flute.

John Attached files pocket direction test.cnc (10.9 KB)Â

 

RJ, read over this thread, you will find it very helpful, Kwok is amazing and helped me out with similar problems!
I had centerline cutting issues which in turn helped me through other problems I had when making pockets! viewtopic.php?f=102&t=2301
Hope this helps
John