Hi Dian:
You wrote
"0.01"? really? how much do you retract?"
Yep, that was not a mis print.
Remember this is drilling on a Bridgeport, not drilling on the CNC.
For those of you not familiar with how to do this on a manual machine with a quill, you set the quill stop, then lift the quill a bit, spin the quill stop a bit , slam down the quill, retract out of the hole, spin the stop a bit more, slam down into the hole etc etc.
The "slam" is not actually a wallop, but it is a fairly forceful push, and the peck increment is so shallow so you don't overfeed the drill, but you can still avoid rubbing it.
You also want to make very short chips that will not pack in the bottom of the hole, but can come out more easily.
There's a trick to gauging how hard to pull on the quill handle, and it varies a bit for different materials.
Those that are prone to work hardening like 304 SS or titanium typically get a smaller peck with a harder push than those that drill freely but need the control of a peck like drilling waterlines through a cross hole in an injection mold, or breaking through an angled exit surface.
I don't know how commonly it's still used among manual machinists, but it can be a bacon saver, especially when drilling small holes in challenging materials and I first learned it drilling tiny fluid holes in graphite electrodes for sinker EDM, 40 years ago.
With regard to retraction, it depends on how the drill feels through the quill handle, how deep the hole is, how much noise it's making...all that warm fuzzy "real machinist" shit you don't get to experience on the CNC.
In titanium if you don't run it sloppy wet and you don't clear the hole often enough you will have a misadventure sooner or later; also if you run the drill just a wee bit too fast, you'll drill for a bit, then get one horrible squeak when you burn off the corners of the flutes and then get a twisted off drill buried in the hole on the next peck.
So clear it often but not necessarily on every peck.
On a 1/8" diameter hole I try to get down about 0.100" before a full retract...sometimes I can, sometimes I have to clear every 0.040" to 0.050".
It just depends, and that's the beauty of drilling deep holes by hand...you can compensate on the fly in a way you can't easily do on the CNC, because you have more cues to follow and you can stop when you see hear or feel something wrong.
So I will sometimes spot and start deep holes on the CNC and finish them on the Bridgeport, just for that extra bit of security on a high value part.
You'd think I was nuts accepting the extra setup and squandering my time but there are times when it's a bacon saver.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
PS, BTW, I agree with Thermite and Milland about titanium being a poor bearing surface, but having said that, there are lots of bicycle nuts who accept this shortcoming to get the "feel good" about the weight saving.
They'd probably be better off accepting a pre-race enema to get the total package weight down...but that's another discussion for another time
