Flat bottom hole

You should be able to do it that way, but I'd put the screw hole in first because end mills don't always like to remove metal at their centers.

They do make counterbore drills for things like socket head cap screws. Maybe one of these from MSC or similar would work better for you. See:

Jeff

-- Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to place the blame on."

You can buy counterbores which have interchangable pilots. For a one off hole you could make your own pilot.

Chuck Pilgrim

Jeff Wisnia snipped-for-privacy@conversent.net

You can also easily make a piloted counterbore from drill rod (would work for Ti ?). Frank McLean, who wrote for HMS, did a piece on this. Turn a pilot for the screw bore, say 1/4 long on the end of a piece of drill rod. Then diagonally file (w/ triangular file) maybe three grooves--don't have to be evenly spaced, or even look quite the same--around the circumference. The tip of the file will bite into the pilot some to show when you're done. Then stone a bit of relief at the back of each of the "teeth" you made, to make the front of each tooth stand proud--as close to equal in height as possible. Harden and temper.

Works, and this way you are using the screw hole to help rather than hinder the process.

Another variation is to make the pilot, then grind down each side of the rod, say a half inch in length, leaving two teeth between the grinds to relieve. Frank Morrison

I would prbably be a lot less exciting if you did it in a lathe. I think your drill press may not go slow enough to machine Ti , either. We routinely grind drills with a 180 degree point, to make flat bottom holes. Just grind a little clearance on the web and they work just fine. Piloted counter bores can be bought in many sizes, not just for use with SHCS's. You usually have to turn the pilot to your job specific size so again a lathe gets involved. Sorry! Leigh@MarMachine

Others have posted good answers. Just a thought: Endmills don't have flat bottoms. They are ground with relief in the center such that it doesn't rub when contouring (as opposed to plunging or ramping). This is easily noticeable when touching off a part to get a Z height. The periphery of the cutter will leave a mark but the center will be untouched.

So in fact, no, they won't create a *flat bottom*.

Endmills are kind of crapy when the work is unsupported. The chuck doesn't do a wonderful job of holding them and the cut is unstable (lots of chatter and hopping around if done incorrectly). Much better to buy two drills of the same size and grind one flat. Predrill with the pointy one and finish with the flat one. You can, of course, grind the point flat after making all your pilots if you like to practice grinding :-)

I like the idea of the counterbore though. Much better on the *PITA* factor.

Regards,

Robin

Ted,

You might call Gary at Cascade New Tech in Portland and have him fix you up with a stock subland or a custom ground step drill.

Well to note Ti is best cut with fairly high primary clearance and rake angles, ideal conditions are usually found when tools are ground to geometry suitable for high production machining of aluminum--for this reason I would suggest having the tool professionally ground if you will be expecting any production volume on your project.

Meanwhile, Im pretty sure many will find the following link interesting :