Drill larger holes in ti?

bruleront

bruleront

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Having trouble drilling the counterbore of a hole in .156" ti. The width of the bore is .375" and the depth is around 3/32". I'm using a table top VS drill press running at 500rpm, the lowest speed, with cobalt stub length bits and endmill. I've tried several different approaches and all I'm getting is chatter and a rough hole.

Would a counterbore work better for a hole this size? I'd rather invest in these than a new machine right now, if at all possible.
 
Try a regular 3/8" cobalt drill bit to get the hole started and go down with that. Then once you have some depth started where you can begin to see the walls of the hole you can use the end mill to flat bottom that hole and the walls created by the drill will hold the end mill in place so it stays put better. Anytime I'm drilling titanium with holes 7/32 or larger I always drill smaller holes first to ease up some on the heat produced by the larger diameter drill sizes unless your center hole does not go clear through. It seems to help a lot to me using drills in larger sizes. Also, it is much easier to use those end mills in an actual mill with infinite variable speed control and precise depth control with a good table vise. Drill presses just move a bit quick even in the slower speed ranges so thats probably why you are getting so much chatter trying to start the hole. Generally speaking you can speed that up a bit once the hole gets started and it has a distinct path to follow. I do anyway.

STR
 
Don Hanson III said:
I run the same bits and at at least twice that speed, no trouble here?
Click to expand...

Then you're turning too fast. :eek::D

The rules of thumb for machining titanium is high feed rate (diameter divided by 125 = feed per tooth), low depth of cut (1/10 dia) and low SFM (40-80).

It can be very strong, it is half as stiff as steel, and has very low heat conduction. These qualities can make it difficult to machine. Fortunately it doesn't really work harden much, so you can peck with impunity to let the bit cool.

500 RPM for .375" and cobalt HSS tooling is probably a good bet, so you're doing that right. Two or three flute will bore easier than four. The only thing I can tell you is you're going to have to lean into it harder, but your press may not be good for it.

Once chatter starts it is hard to get rid of. You can try a sharp new cutter and put a piece of oil soaked cloth in the bottom of the hole to iron out the chatter. Don't ask me why this helps, but it does. Then finish as usual.
 
Terrific information here. I'm going to apply whatever newfound knowledge I can--along with small amounts of cash, if necessary--and keep at it.

In the meantime, I'm happy to hear more comments on the topic. Will be moving up to .5" counterbores if I can ever nail the .375" ones with my current press.
 
Sometimes the problem it’s that you are feeding two slow (Z axis)
Also, how you locating the hole without a pilot
wen its only one piece:
Locate the hole using a pin , clamp, and a quick feed.
This is what I do went I use and endmill for counter bore
I clamp a piece of aluminum, and then drill a hole the size of my work piece hole
Put a pin on the aluminum hole only sticking out a little bit
It work as a pilot you can use a piece if the drill bit for pin
And counter bore whit out clamping.
---------------------------
Whit pilot: not need to clamp
Whit out pilot: locate hole and clamp
Quick feed
You can do a few quick peeks
 
Last edited:
Great info! Thanks. I'll be trying it out.

I do want to make the endmills work, but I did a test with a smaller, changeable pilot counterbore bit and it worked fine. Still waiting for the larger counterbores and pilots to arrive, but I'm getting the sense that it's going to work in the larger sizes. Will know soon whether I can move on to the next folder-building challenge or have to go back to the drawing board.
 
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