How to machine a square hole

[jeremyinnys]

what do you think might be the best way to machine a square hole?(pocket)

i have a square i have to machine in titanium. i have a tight .001" tolerance from finished side to side, .503"-.504". the depth is .650". i can only have a corner radius of .05" +,- .01" (maybe i can get away with .062" max,not sure yet).

i planned on drilling a .5" hole on my cnc lathe on a prevoius operation, then milling the rest out on my vmc. so i would need a small enough cutter for corner radius, but a flute length of prolly .75".

then i thought of not drilling .5" hole first, and drilling 4 corner holes on vmc and then drilling center out, and finish pocket with an endmill, maybe .25" depending on how the corners look after drilling them.

what do you guys think? i'm just looking at all options and not final on anything yet. thanks.

[DareBee]

Edm

[jeremyinnys]

Originally Posted by DareBee Edm

what?

[pp-TG]

A wire EDM machine(cuts with a wire a electricity)! That or a broach and a press... I think trying to machine that on a lathe and mill would be a big headach... how many pcs.

[jeremyinnys]

well maybe 2000. but edm can cause fire with titanium, maching will be alot faster and easier.

[fpworks]

I think Darebee meant sink EDM.

This is a blind hole, correct? (with a flat bottom)

[DareBee]

Correct Sink

[cdlenterprises]

An EDM wouldn't be practical for these quantites(too slow) You'll defintely want to drill the 4 corners out. .05 max CR...I'd probably go in with a 3/32 or #41 drill. I would also drill in the center if possible(drilling is the fastest way to remove material). I'd stay less than 1/2 diameter 'cause if the drill walks or cuts O.S. the part is toast. Lay it out on a CAD or CAM screen and see what size drill you can squeeze in there without breaking into the corner holes. I'd shoot to rough the pocket out with a 3/8 or 5/16 EM, clean out the corners with a 1/4 or 3/16 and finish the profile a 3/32 em. That's one suggestion....I'm sure there's other ways to do it

[jeremyinnys]

Originally Posted by fpworks I think Darebee meant sink EDM. This is a blind hole, correct? (with a flat bottom)

no it's a thru hole. part is actually 2" tall, and square is .65"deep. the other end is already bored out to .97" to where square will be. and thanks so far.

[fpworks]

broach

[jeremyinnys]

well as far as i know, we will do that eventually, but now i have to machine them. it sux.

[fpworks]

Okay,
So you're only doing a few parts now for pilots? (or prototypes?)

If that is the case, I would have these first few parts wired for sure. Material cost of titanium, tight tolerances, and relatively low process security of trying to machine that feature with drill and endmills would definately push me to have them wired out.

Tough job...good luck!