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Old Sep 28, 2012, 12:09 PM
dougmontgomery's Avatar
Glendale,Az.
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Machining right angles and greater

Is this a normal way of machining an angle so it does not have a radius? How does this get programmed when it is machining to go from outside of part to the off cut to back to part, does it just do it without stalling?

Using a .063 end mill?

doug
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Old Sep 28, 2012, 12:32 PM
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Not sure I fully understand the question. Are you looking to get rid of the radius highlighted in red in my screen scrape with the end result as highlighted in blue?
If so most CAM packages have a feature to do this. The ones I use call it Dog Bone (Phlatscript for Sketchup) or Concave (DevCAM)
But with a 1/16" bit, I usually don't worry about it unless the material has no give. Heck even in foam, the radius from a 1/8" bit is no problem.
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Old Sep 28, 2012, 12:39 PM
dougmontgomery's Avatar
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I retitled it, I was more speaking of the ends, I originally designed the part so it had 1/16 radius everywhere, but where it meets another surface I dont really want a radius there.

doug
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Old Sep 28, 2012, 03:32 PM
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For manual Gcode, if not using tool radius compensation you can just program the corner of the tool path parallel to the part. Another option is to use a radius equal to the tool radius to give the tool path rounded external corners resulting in smoother machine motion.

If using tool radius compensation just program the part outline and the machine control will take care of the rest. You should be familiar with the machine control because they don't all act the same.

If using CAM it should take care of this itself. If your CAM software is causing the curlycue tool path, you want to check settings.

What software is involved?

Greg
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Old Sep 28, 2012, 06:03 PM
dougmontgomery's Avatar
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I guess i am not explaining myself very well. The curly thing was so i did not have a radius on that corner. This way the router can maintain the depth an come in from a different angle rather then just making the radius of the .063 bit. Does that make sense.
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Old Sep 28, 2012, 06:12 PM
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Hi Doug. My CAM software (MADCAM) generates a toolpath that makes acute angle exterior corners like that come out perfectly sharp (or with whatever radius you've modeled in your CAD program). I thought they would be difficult, but they're not - as long as you have reasonably good CAM and your controllers and machine are working properly, you don't have to do anything funny to get sharp corners besides just compensating for the cutter radius (which your CAM software, if you're using it, does for you). If you're creating G-Code by hand it's going to be a bit trickier but you just essentially cut along one of the two lines that intersect to the corner/edge you want and go past the corner point (outside the piece you're cutting) until the cutter is clear of the corner location, and then start cutting the second surface. Hope that makes sense, it's possible I'm misunderstanding. Good luck.

-John
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Old Sep 29, 2012, 12:26 AM
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There is no need for the curlycue. Just program a radius equal to the tool radius. This will result in a square corner on the part, but a smooth tool path.

Straight paths
G1 X0.0Y0.031
G1 X10.031Y0.031
G1 X10.031Y-10.031

Same part geometry with radiused tool path

G1 X0.0Y0.031
G1 X10.0Y0.031
G17 G2 X10.031Y0.00I-0.031
G1 X10.031Y-10.0

In both cases because you are not using tool radius compensation (G41, G42) you must calculate the toolpath offset from the part geometry.

If you use tool radius compensation you just program the entry move and the actual geometry dimensions.

Post the code for that part. Are you hand coding?

Greg
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Old Sep 29, 2012, 04:48 AM
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On the external corner you should not have the radius, even without cutter compensation. I suspect the gcode has an arc, instead of a sharp corner. This could be from not regenerating the gcode after switching corner types. Or could be a box you checked in the cam software, on corner types.
Another cause could be the machine is starting to turn before it hits the end of the part. This can happen when your running rather fast, and don't have the acceleration/deceleration maps fast enough.
There are a few other causes I can think of. But I would start eliminating. First you need to look at the tool path. If you have Mach3 its is shown on the screen. Look to see if it has sharp corners. If it does have sharp corners then run the code at a slower feed rate. If that doesn't help then I can suggest something else.
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Old Sep 29, 2012, 09:47 AM
dougmontgomery's Avatar
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thanks for your help, I am designing some parts and thought I had a go around figured out for my friend that has the router. He uses mach 3 I believe.

Doug
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Old Sep 29, 2012, 10:25 AM
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I'm still at a loss as to the problem. The machine only does what you tell it. I'm unsure if the above image is of the tool path or the geometry you're feeding the CAM software, or if it's a backplot of hand written or CAM generated Gcode.

Either way, unless you are programming sharp corner and the machine can't reproduce them as Rob eluded to, it's all in the program or CAD file sent to the CAM. If your friend is doing the CAM or hand coding, just give him exactly the shape you want made, sharp outside corners are a non-issue.

Greg
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Old Sep 29, 2012, 01:38 PM
dougmontgomery's Avatar
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Well, with my ignorance to Mach3/machining, I was under the impression that Routers and machining put radius on everything, So I thought that I had to draw in my cad work the outside curlys to tell the machine what to do.(go around) I did not know it was in the software already.

I have an 80 watt laser so it is a non issue. I draw .dxf, it cuts.

Thanks for the clarification guys-

doug
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Old Sep 29, 2012, 01:48 PM
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I saw your laser and the current Frog project. Cool stuff!

Greg
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Old Sep 29, 2012, 03:42 PM
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The router works much like the laser. The CAM software decides how corners are handled. The more expensive software has more options on corners. So send him the file in the shape you want the part. I figure he is doing the tool path (g-code).
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