1911Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
405 Posts
Discussion Starter #1 (Edited)
So, I plunge-milled, threaded, and filled a misplaced feature with what appears to be a non-stainless set screw and Loc Tite 271. I milled it flush with the frame, center-drilled at relatively low speed with plenty of coolant, then attempted to start drilling with very small drills. It keeps work-hardening, or at least that's my guess, because very quickly, the drill just stops cutting. I'm able to grind through with a very small diamond-point or tungsten carbide dremel tool, but every time I go back to a drill, center drill, or even a mill, it clears a few chips, then stops. I've varied my speed, feed rate, etc., but still the same outcome. When I milled it flush, it didn't seem like particularly hard material, at least to start with. Any ideas on how to overcome this stalemate? I'm thinking carbide, either a straight-flute, or a carbide end mill?
 

·
Registered
Joined
·
405 Posts
Discussion Starter #3 (Edited)
This is going to sound stupid, and it probably is, but I'm desperate and willing to look stupid on the off chance that it would work: a carbide-tipped masonry bit? if not, would this work: http://www.amazon.com/Helical-Groov...40648852&sr=1-3&keywords=4mm+carbide+end+mill or do I need more like http://www.ebay.com/itm/IMCO-4-MM-1...TOOLING-CNC-/221855082473?hash=item33a797e7e9 ? By the way, I found a solid carbide 3/32, and it cut through it like butter. I then tried a drill that was slightly bigger, and got pretty much nowhere again.
 

·
Registered
Joined
·
1,494 Posts
Masonry bit????
 

·
Registered
Joined
·
405 Posts
Discussion Starter #6
Masonry bit????
Yeah, masonry bit and a hammer drill:dope:
I did almost try spot-annealing it, though. I think I'll just wait for the 4mm mill. It gets here tomorrow. This has got to finally be the end of this ordeal!
 

·
Registered
Joined
·
3,197 Posts
Joe5, if you are trying to fix a mistake, don't make another bigger mistake. Go to MSC or Travers or whoever and buy the right cutter once . A US made or German made drill bit in not expensive compaired to getting a professional to fit what could happen if you don't. I like using end mills in the case that you describe , but a straight flute drill will also work. Brownells sells numeric carbide drills if you know the size.
 

·
Registered
Joined
·
4,928 Posts
If you are filling in a hole and making a new hole, drill the holes smaller than you need and finish them with the appropriate sized reamer.

I remember you saying something about filling in and relocating the hammer pin in one of your threads. Is this what you are trying to do?
 

·
Premium Member
Joined
·
14,477 Posts
Using a set screw as the threaded filler was the next mistake in the chain. A Grade 5 bolt would have been a much better choice.

LOG
 

·
Registered
Joined
·
430 Posts
If I'm under standing your question is that your trying to drill through a SS set screw. And the drill bit dulls before you get very far. If this is the case make sure your using the right cutting oil. Can make a big difference on Drilling some materials. As for drill bits. You can use either a solid carbide or cobalt. With either one you feed must be constant pressure and the right rpm and feed speed. If you stop (back off pressure) you will harden the SS, like your doing now. Use one of the short length bits too, less likely to break.

If your just trying to get the SS set screw out. Apply heat to break the LocTite down.

Or just use a EDM and be though with it.
 

·
Registered
Joined
·
174 Posts
My mistake for posting an answer thinking he was dealing with S.S. It shall not happen again I'll only read, and ask questions I won't get wise remarks about.
 

·
Registered
Joined
·
1,287 Posts
How rigid is your setup? If you've got a tight machine, try carbide or cobalt. If it's one of the benchtop models with a bit of slop or backlash, stick with high speed steel drills. Not cheap hardware store drills, but actual HSS machine drills.

For carbide, run about 150 SFM. HSS and cobalt, about 50 SFM.
3.82 X SFM / drill diameter = RPM
For example, 1/8" carbide drill: 3.82 X 150 / .125 = 4584 RPM

Carbide and cobalt need constant feed, no pecking. You don't need to peck with HSS either, unless you get problems with chip clearance. If so, feed one drill diameter, clear chips, repeat.

If you've got power feed or a DRO, shoot for .001"-.002" per rev for carbide and cobalt, .002"-.003" per rev for HSS. This assuming, of course, small diameter drills. If the drill is .250" or larger, double the feed per rev.
Same 1/8" carbide drill for example: 4584 RPM X .002" = 9.168 inches per minute feed.

However, you've created another problem for yourself if the 3/32" drill is anywhere close to your finish size. Drills do not cut on the shank, only the drill point. If there's no material under the point, the shank will just grab and break. General rule, never pre-drill more than 1/2 of the finish diameter. IOW, unless the finish diameter is 3/16" or more, you risk breaking drills without removing any material. You may have limited yourself to endmills. If so, make sure you get a bottom cut, many small mills aren't.

In fact, I'd recommend a 5/32" two-flute endmill instead of your 4mm drill. Use the same feed and speed as the drill, depending on tool material.

As for coolant for small tools, high RPM and work hardened material, use kerosene. Keep a small container capable of supplying as steady a trickle as possible. A brush and cup would work, too, and be far preferrable to having a large container full of flammable liquid in proximity to a possible high heat source.
 
1 - 15 of 15 Posts
Top