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programming a perfect polygon


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we have a large shaft that needed a big 3 point polygon on the end of it.

its about 7 inches dia in the polygon area.

i attemted to  make a sample of the mating part in our wire edm.

there was a very close tolerance on the shape and i could not figure out how to program it.

usually i draw it in mc and bring the dxf to the wire.

because its not an arc at all it became tiny lines that the wire would not like.

it seems like it would need to be figured out by the machine much like an arc is done internally in the machine.

apparently there were only 2 companies in the us that could cut this.

when i looked it up it looks like it was done on a grinder which followed a cam much like before the age of cnc.

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I assuming you are talking about a P3 polygon that is similar to a Reuleaux triangle. It is a triangle of constant width (I assume one of the companies you are referring to is General Polygon?). Modeling a Reuleaux from scratch is well documented if you look it up, they are made up of large arcs in a "venn diagram" configuration so if modeled correctly it should create relatively good code out of MC, not tiny linear moves. I am not 100% sure that a P3 is modeled the same way, if it is splines you may need to filter the code slightly get less linear moves. We have milled tight tolerance profiles like this without to much issue, If it is the male profile, you can simple Mic across it along the high points as if it were a tight tolerance boss. If you are trying to cut a female P3 a mating part or gauge is helpful. Let me know if this helps.

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1 hour ago, LMcFadden said:

if it is splines you may need to filter the code slightly get less linear moves.

We do a lot of lathe profiles defined by points. Creating curves defined by these points yields splines

If we chain the splines the resulting code is thousands of tiny linear moves and an unacceptable finish

The solution is to use the command "Break Many"

We launch the command , chain the spline, select "Curves" for output and set Tolerance to .0002"

This will break the spline into small arcs which yields an excellent finish 

I do not know if this approach will work with a wire EDM toolpath

You will need to change one setting in your System Config for this to work

On the Tolerance page you will need to set "Curve choral deviation" to .0002


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