Stupid milling question

[Joels]

When i try to mill a surface flat it always gets lines in it it is not flat. I get it flat with a fly cutter but not a endmill. I am milling Acetal plastic and i was using a 1/8 diameter 3 flute carbide endmill. I was running 5000rpm and a feedrate of 30 inches a minute. Is there a way to get a flat finish from a endmill?

[Chris Rizzo]

Lots of things:

 

-take a finish pass with a light stepdown (.005 ish)

-Slower feedrate

-Higher rpm

-less stepover (40-60%)

-Use a shorter tool.

-Use an em of larger dia, thus stiffer.

-Make sure your tool is sharp on the end.

-Use a bull nose tool, or put a small hone on the corners

 

 

-

[BernieT]

Is the head square (trammed in)?

 

+ 1 on finish pass, sharp tool, and bull nose.

[Saultspics]

All of the above. If the tool is flexing or the head is not square it will not cut the part flat.

 

Stephen

[Guest]

One more thing, keep some air on the part to keep the chip from getting dragged back under the cutter. That can rough up a finish pretty quick.

[chris m]

Never seen a 1/8 flycutter..

[El Scotthead]

Chris,

 

I think they market them the kids among us....isn't a 1/8 flycutter used to mill the wings off a fly? (Tricky setup though, flies aren't easy to squeeze in a vice)

[Mike Mattera - TFM]

Smaller the tool the more it will flex. 1/8" has got to be all over the place. Even in plastic. if you have to use the 1.8 for some reason, do a cross cut. one pass at 0° and another at 45°. Most lilelt still wont be flat, but better.

 

Check the head/table alignment (tram).

 

Mike Mattera

[Bill]

Is the 1/8 EM a flat bottom cutter?

 

I think cutting plastic with a small cutter will leave you something like a push of material where the previous pass was made as the cutter sweeps the material into a previous cut area. It is very slight.

 

the property values of plastic make that hard to accomplish with a small cutter or any cutter that makes multiple passes over an area.

 

If the part is coming out flat with a fly cutter passing over the entire width I would say the head is most likely trammed correctly. But I would still check it.

[Joels]

I use a 4 inch and a 6 inch diameter flycutter and the surface looks good. I was using a 1/8 dia 3 flute carbide endmill with 50% cutting on a Fadal 4020. The reasom i used a 1/8 is that is what the part required in one of its corners.

Thank you all for the input and i will see if i can get a fly and clamp it in the vice and let you know how it goes!

[Joels]

oh and i did use a 3/4 endmill and the finish was better but not as good as i wanted so i will try the .005 left for a finish pass.

[chris m]

quote:

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Fadal 4020

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NOW the problem is exposed....

[Rodney @ Roush Yates Engines]

Check the machine for level, if it isn’t level it will not cut a flat surface.

[Kelly Burns]

quote:

---

Is the head square (trammed in)?

---

Bingo. Plastic flexes, hold it lightly and tight.

[Hardmill]

Joel,

Try keeping tool down in your multi-pass box.

I have seen this problem before, its a fadal thing.

 

 

PEACE

[El Scotthead]

Joels,

 

I was just kidding about the fly thing. I wouldn't do such a thing!

 

Seriously,

Can you hit the part with a trickle of coolant? Not too much, just enough to keep the cutter cool. From my own experience, heat and plastic is not a good recipe for good parts.