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Hello people! I am cutting some tricone tops for a customer. I have drawn the files in Rhino and post processed in MADcam. I am having some issues with smooth lines, mostly on the shorter runs. I am using a 1/16" upcut spiral at 80 ipm and .050 doc. I thought the issue may have been speed related but in the 8 polygons inside the tricone I have the wavy cut pattern in each piece that is cut out at the same spot, so this is not a random event as one would expect with bit chatter, etc. I think I don't have some custom tolerance parameter set properly somewhere in Rhino. Anyway here are a few pictures that hopefully will help in advising on the issue.



Here it is in a plywood test run



You can see the unevenness of the cuts



And again



And here is the Rhino screen shot.

Thanks

Shane

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Canada

A couple of thoughts here--first, you should be able to look at the G code where it is cutting those polygons to see whether or not madCAM told the machine to cut one line or many. If it is programmed at one line when it's cutting the scallops, it's probably a machine issue of some kind. If you run through a simulation in Mach 3 and single step through the G code when it gets to the polygons, it should be easy to spot. It looks like you might be using a radius lead in rather than a ramp on your profile cuts--that can give you all kinds of weird little unwanted, but consistent, scallops.

Good luck!

Dave

Several things come to mine....

Engage/Retract (Entry/exit ....lead-in/out) of the tool
Precision of following the line with-in the cam program (Intol/Outol in Rhinocam)
Machine post processor is set to broad of a tolerance in following a line/curve....

One of the 3 is probably the culprit.

God Bless

Kevin

In madCAM, there aren't a whole lot of settings to deal with--you probably know this but if you hit the question mark on the madCAM toolbar and bring up the help page, you can go to the settings chapter and it covers everything.

madCAM has a setting for absolute tolerance--if it is set any finer than Rhino's absolute tolerance, it will default back to Rhino's in use if I understand it correctly. I leave both set at .001" and it seems to be a good setting. Too much finer than that and it takes forever to generate a toolpath and the toolpath it generates doesn't do any better job on the final work. There's also a setting for maximum distance from surface.

There's a good write up on tweeking madCAM at:/http://betterlivingthroughcnc.com/2011/10/14/maximizing-toolpath-quality-with-madcam/.

Other than that, there are the settings that you set at toolpath generation time--ramp lead in vs. radius lead in etc., including distance for these to go.

Dave

Thanks Guys. And thanks for that article Bill. I am thinking exactly along the same lines that this is an issue solved in Rhino. Here is a picture of four of the Parallelograms that were machined out of the tricone:



You can see that the 'bumps' all line up. So that has to be a toolpath issue rather than a random issue with machine rigidity or tool stability (my machine is Precix 49" x 49" table with timing belts and servos with Perske 3.3 kw spindle and is very rigid (about $25K to replace). So the issue is not the equipment but the operator! I have adjusted the mesh controls, surface to edge which I do as routine anways, and will try a couple of the tolerances expressed in the article.

Thanks again guys!

Shane

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Canada

Hi Shane, have you tried cutting this at a slower feed rate? I have seen some machines that lose precision as the speed increases.

Just something to check out...Good Luck!

Trev

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