I'm making an ultrasonic welding horn, and I need to drill (and then tap) a hole for the stud. It's a 1/2"-20 thread (thus, 15/32" hole) and the hole needs to be about 3/4" deep with a flat bottom.
The only machine I have available that could do the job is a Tormach CNC mill (there's also a lathe with 4-jaw chuck (the horn is rectangular) but I've never used it). I've done this horn in aluminum, but I'm told I really need titanium for the amplitudes I'm using.
I've read that Ti chips work-harden a lot. So I suspect that a deep-pocketing operation would be problematic as chips would get worked and re-worked. (There's no through-tool coolant option on the Tormach.)
I only need to make one of these, so I can take extra time - for example, drill or pocket 1/20", clear the hole manually, drill or pocket another 1/20" - if that's what it takes. Also, I can buy whatever tool I need for the job - it'll still be far cheaper than the $2000 price to get the horn made elsewhere.
I've read what I can find on machining Ti. Mainly it boils down to:
1) Keep the surface speed low, and the chip size large (depending what your tool will tolerate - I've been using GWizard)
2) Never dwell a running tool.
3) Use lots of coolant, and carbide tools, either uncoated or modern TiAlN coated.
So... what's the best recipe, and what do I need to know?
- HSS drill? (Harvey Tool doesn't seem to have any carbide drills.)
- Carbide end-mill for pocketing?
I'm inclined toward using maybe a 1/4" end-mill and pocketing bit-by-bit all the way down, because that'll leave at least a little space for chips, and if it breaks I've got a chance to get it out of the hole and save the part. But I don't know if a 1" stickout on a 1/4" tool will be stiff enough for Ti.
If you can't tell by now, I'm kind of self-taught on machining. I've made aluminum injection molds for 0.040" wall thickness parts that worked the first time, and my aluminum horn worked the first time. So I am capable of learning... but on titanium, I don't even know what questions to ask, and I don't really know what options are available or how to select the best one. Feel free to point me at a web page (or even a book! :-) that will help.
Thanks!