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faceting on a surface


cherokeechief79
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I recently ran a very large job on a heavy pc of steel.it required some surfacing but the majority of it was a round cylinder that ran about 20 inches down the length of it.i surfaced the radius from both sides and felt it would be best to just run it lengthwise and have it shift y and z and then just make a long x move down the length.it looked fine on the screen and the toolpath looked great from any angle I zoomed in on it but it came out slightly faceted on the part itself.it was well within tolerance but you could clearly see the faceting at about every 1/4 inch or so.i set the tol on the surfacing page to .001 and the stepover was only about .01.

what do you think caused this?

should I have set the tol even lower?

there was no sense moving the arc tol up higher because it was not doing arcs at all.

im sure if I had gone the other direction and generated arcs in y z that it would be smooth because it couldn't get faceted within just an arc move.

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Don't discount the machine as part of the issue as well.

 

 

 

set the tol on the surfacing page to .001 and the stepover was only about .01.

 

Without more info, this bit of information is useless....

 

What kind of finish are you looking to get?

 

Which toolpath did you use?

 

What is the tool size?

 

How many flutes?

 

What is the RPM?

 

Does the machine have a highspeed look ahead option?

 

What kind of holder?

 

How long is the tool sticking out?

 

Is the tool running out at all?

 

If I need a good quality surface on say a 1/4" ball......I will typically run about a .006" stepover with a .0002" tolerance filtered 2:1, speed & feed mostly determined by the material

 

But more info is needed

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sorry I cant share the file.

it was a 2 inch radius in 4340 heat treated steel abou 30-35 rockwell.i roughed it first with a different tool leaving .02.

I finished it with a 2 flute 1.25 inserted ball with fresh inserts.it was held very stubby and didn't run out at all.

the surface finish from the tool was great but you could see a faceting "pattern" at about every 1/4 inch all the way around.

I made surfaces from the solid on another level and drove the tool on the surface not the solid.maybe the surface itself was faceted .I didn't think of that.

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FOUND IF I TIGHTEN UP THE SURFACE TOLERANCE ON THE FLOW LINE SURFACE PERAMETERS PAGE IT MAKES THE FACETS SMALLER

 

There has been many discussions about Tolerances and Arc Filters on these forums, if you do some searching you can find some good recommended settings but as you have already found they DO make a HUGE difference in the finished products surface finish quality and different machines / applications may require different arc filters 

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There has been many discussions about Tolerances and Arc Filters on these forums, if you do some searching you can find some good recommended settings but as you have already found they DO make a HUGE difference in the finished products surface finish quality and different machines / applications may require different arc filters

although it is an arc surface, I chose to go in a long direction so the arc filter tol should have no effect.no arcs could be generated in that direction.

ill try to make a similar example on mon and post it.

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I played around with it tonite a bit.i found that the surface is very clean and created using just arcs.(not faceted in the model)

the stepover was .015 and the total tol was .005 with 100% in the cut tol field in the arc filter page.

as I dropped the cut tol I could see the facets get closer together in verify.if I dropped it all the way down to .00005 (the max)

it seemed to go awy and be very smooth.ill try it if I get the job again

thanks!

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  • 2 weeks later...

sorry to bring this up again but im still a little confused.

if I have a solid that has a good clean surface on it that was created using arcs(to make the solid),will I need to drop the cut tol way down to get rid of faceting?

the stepover is still very small so its not like it has to create facets because the stepover is too big.

and its not like dropping this cut tol way down is going to add to the program or calculation time because the stepover is still dictating it.

 

this happens now and then to me and I usually don't zoom into the verified part close enough to see the faceting until after I find it on the part.

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Stepovers have no real effect on faceting(unless of course you want really shiny facets!).

 

Think of stepover and tolerance as two perpendicular elements, working together.

 

The stepover determines the number of "slices" in the surface,

and tolerance says,"Hey guy, how close do you need me to stay on this slice?"

 

Like the image above illustrates, if you tell the system .005" tolerance, you're telling mastercam that "anywhere within .005" of actual, is fine by me."

 

Now, whether you do that 10 times(big stepover) or 10000 times(small stepover), you'll get the same facet along the part.

 

J

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