Machining Small Fillet with Big Endmill

[randommachinist]

I have a question about machining a fillet with a tool that has a bigger radius than said fillet. For example, i'm working on a mold that has a couple fillets in some corners that are pretty tight (.125). The last toolpath i ran was with a 1/2'' ball endmill leaving ".015" stock to finish (optirest). My plan was to then run a finishing program (stock to leave "0.0") with the same endmill and clean up those fillets as much as possible. Here's my problem: I used the Surface/High Speed/ pencil toolpath and ran it in the machine. As soon as it came to the fillets, the endmill chattered like crazy. It looks as if there's a lot more than just ".015" stock to clean up. Why is that? Did mastercam ignore the fillets and not bring them down to the correct size because i'm using a tool with a larger radius than my fillets?

[jlw™]

Can you upload a file?

[Matthew Hajicek - Singularity]

If it's doing the corner first it'll have about 130º of engagement, which is a fair bit.  But yeah, I think we need more info in order to be able to help.

[randommachinist]

Sorry I was out of the shop all weekend. Anyways, unfortunately I'm not allowed to share the file with anyone outside of work, or I would! What do you mean it would have 130^o of engagement? 

[Matthew Hajicek - Singularity]

 

This assumes the fillet is in a 90° corner.

[randommachinist]

Thanks for the illustration. I see what you mean now.

[RaiderX]

remachining is your friend for this. pick the corners before finish

[Mic6]

^^YUP

or

 

Finish the wall to sayyy  R.3, then come back and remachine and blend.  Remachine rules.

[g huns]

 

This assumes the fillet is in a 90° corner.

 

Perfect illustration of "the tyranny of the corner".

 

You can only run as fast as the largest angle of engagement will allow. It took me a long time, and a lot of cutters being sucked out of holders, to get that beat that into my head.

[Guest]

Helix bore is your friend in corners.