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11-09-2013, 01:41 AM #1
Drill hard receivers with carbide bits
I am looking at drilling and tapping a Husqvarna M38 Mauser. I havn't done one before but everyone tells me that they are super hard.
I thought that I'd just order a couple of No20 solid carbide twist drill bits and then use a carbide tap and just proceed as normal.
Is it just that simple?
11-09-2013, 05:12 AM #2
What threads are you tapping? I have yet to see a 6-48 carbide tap but I have not inquired about a custom. The last #29 carbide screw machine drill I bought was $32.
11-09-2013, 11:41 AM #3
That may not work too well. The carbide twist drills are usually for abrasive materials like fiberglass or G10. The best drills for hard steel are the 2 straight flute solid carbide or solid carbide spade drills. Same with carbide taps. They will often just shatter on hard steel. What I do is drill the hole, then anneal it with a torch and tap with a quality high speed tap and tapping fluid. Drill the hole dry with no cutting oil, anneal and tap. If you drill before annealing, you can anneal the sides of the hole without doing a large area.
11-09-2013, 01:32 PM #4
I would spot the hole first. Then use a very dull drill (even rounded a bit) to heat the spot to red if you can get it (no cutting fluid) this should anneal the spot. Drill the hole with a good Cobalt drill, again with no cutting fluid, drill to red if necessary and back to let cool and anneal. After drilling, you can heat the hole with a torch, but often this isn't necessary. Tap with a 2 flute carbon tap and cutting oil. If you have been saving a old can of Tap-Magic, now might be the time to use some. If you break off a tap, break out the remainder (that's why we use carbon taps) with a punch and get another tap and go at it again. Sometimes, these are surface hardened pretty deep (relatively) but get much easier once you get past the hard part.
11-09-2013, 03:45 PM #5
11-09-2013, 04:27 PM #6
I would try HSS bits before moving on to carbide, since Mauser receivers are only case hardened (to the extent of my knowledge) so once you get through the tough layer with a center drill it's easy to drill through until you hit the harder layer on the inside of the action. Here's a diagram.
I drilled through a 10/22 bolt to pin it this way. just a HSS bit in my mill and it went through.
If you want to be sure you will not break your bit use carbide.
11-09-2013, 05:26 PM #7
I use Toolguy10s' method. Some of those Huskies are quit surface hard. I use the carbide to get thru the surface then a HS twist drill for the soft part, finishing with the carbide if need be. I use a OOO torch tip for annealing. Tap it with a new, quality made HS tap and lots of Tap Magic w/EP Extra (JGS has excellent prices on HS 6-48 and 8-40 taps). It's the same method I've used on those "rock hard" Springfields that used to be around . Been using the same carbide spade drill for a long time 'cause I use it only where it's needed.
11-09-2013, 06:16 PM #8
11-10-2013, 02:49 PM #9
Toolguy,I think your wording was a bit confusing. I thought you were referring to carbide TAPS shattering,which I'd never advise using on hard or soft steel.
11-10-2013, 04:13 PM #10
I know EXACTLY what Toolguy10 and ditchdigger are trying to get across. Some of those receivers have brutal hard shells and butter soft inside. I have a huge collection of "the latest to come along" carbide drills. They just are not designed to take the pressure of of crushing through 60 Rockwell glass into absolute mush. On top of that most gun plumbers don't have the equipment, rigidity and feed rate needed to drive a modern carbide drill that size. I think my mills top out at around 2000 RPM and the one has a feed rate of about 1.3 thousandths per revolution. I'm at home right now and I don't have a Machinerys Hand Book jammed up my ass but that sounds way to slow and way to fast off the top of my head.
The old style carbide spades are a lot more ridged and are a lot more forgiving than the new style carbide twist drills and are not so likely to break or chip at the width of their lands.
I always start a job with good cobalt drills and if they fail, I go for the carbide spades. If I put a carbide drill in the machine I also finish with that drill as I have found that you can hit hard spots even after breaking through the case. If I have to I can re-chase the holes with a 3mm carbide slot mill or end mill to clean up any misalignment. I run the carbide slot mills at max speed of the machine with no coolant and feed them by hand.
I have never had a receiver that I couldn't tap with a good cobalt tap and Ridged Cutting Fluid. I use a start tap and finish with a plug or bottom.
11-11-2013, 04:02 PM #11
A good drill for this is the M.A. Ford "Hi-Roc" drills. 2 flute, strait, 135 deg. point, carbide. Some other manufacturers make about the same thing. They are a little thinner webbed than a spade drill so they take a little less force to drill with. No coolant, just air blast until you're thru the case or it will just want to rub and not cut. 2000 rpms will work, 2500 is probably better.
Of coarse a good old carbide spade drill as described will work too. I just thought I'd mention one carbide drill that is designed for 65 HRC steel that does actually work with a manual machine and a drill chuck.
I would only use a carbide twist drill if I felt I needed work on my broken carbide removal skills, the same for a carbide tap.
11-11-2013, 09:39 PM #12
Brownells used to carry 2 flute drills like that Tank. I still have a half dozen and they cut like the dickens. They can be sharpened with a diamond wheel pretty easily too but I find I have to grind them under a magnifier to get them right.
I see Brownells now carries single flute drills instead of the two flutes. They should be tough but I have never tried them yet. I'm not to sure about sharpening a single flute drill either. Because the drill is turning and not the workpiece I'm sure its not as simple to do as a deep hole drill.
11-12-2013, 01:53 AM #13
Put a piece of wooden dowel in the drill chuck spin it fast and let it smoke on the spot you want to drill.
A straight 2 flute carbide bit is what you want much stronger then twist drills. only drilled thin stuff with one so can't say how they behave deep drilling.
11-12-2013, 03:19 AM #14
Thanks for the responses gents. I think I'll try to source either the 2 straight flute carbide bits, or the carbide spade bit. I don't think I'll manage anything local, so can you recommend a supplier that stock and ships this stuff.
11-12-2013, 01:41 PM #15
MSC has them usually cheaper then the usual gun tool suppliers.
Screw machine length probably will be the best selection.
11-12-2013, 02:04 PM #16
11-12-2013, 04:32 PM #17
Those single flute carbide drills will work fine on anything hard, and I mean file hard. But in anything less hard, they are not very good. Usually, I have experienced receivers that have the hard outer shell and a much softer more ductile inner core (like an '03 or a Krag). The single flute carbide will drill right through the shell, then you need to switch to a two or three flute drill to finish the job. Remember, if you are drilling through (especially under feed), the other side may be file hard on the way out, back to carbide if you need to go through. Many times, it is not necessary to drill and tap through, there is generally enough there to do the job without going through.