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Pre bore the chamber results?

LVLAaron said:
I've gone too far, once. Now I just keep a couple of drills set with stop collars on them so they're always ready to go for the usual suspects I chamber.
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My next project is a is a adjustable drill/reamer stop.
If I was doing this for a living is have a drill with fixed stop for every reamer or appropriate cartridge size range.


I did get a small solid carbide boring bar just for chambers and gauges, that was a nice upgrade.
 
LVLAaron said:
The pre-drill isn't a big deal. We're all over here measuring 10 thousandths of an inch... drilling a hole a quarter inch short should be pretty easy work.
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Even a eighth of an inch short shouldn't be much of a chore. Drill and bore is what I was taught 31yrs ago in gunsmith school. It speeds up the process markedly, especially if using a muzzle flush. Is it 'more accurate' to drill and bore? I don't believe so. But it is not an inaccurate method, either. I bore to .03 to .035" less than shoulder diameter and 1/8 to 3/16 short of the shoulder. The only chambers I don't drill and bore are .22LR.
 
shortgrass said:
Even a eighth of an inch short shouldn't be much of a chore. Drill and bore is what I was taught 31yrs ago in gunsmith school. It speeds up the process markedly, especially if using a muzzle flush. Is it 'more accurate' to drill and bore? I don't believe so. But it is not an inaccurate method, either. I bore to .03 to .035" less than shoulder diameter and 1/8 to 3/16 short of the shoulder. The only chambers I don't drill and bore are .22LR.
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I'd not use a hand sharpened drill for the 'drilling' part! Only a new one, or a machine ground one.
 
I drill "some amount" short of final. Frankly, I drill and bore primarily to get the indicator body into the barrel so I can indicate the throat, more than anything. So if it's 1/8th or a half an inch, it doesn't make much difference to me.
 
shortgrass said:
I'd not use a hand sharpened drill for the 'drilling' part! Only a new one, or a machine ground one.
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Good point. A good d-bit grinder and drill sharpener are on my list of things to collect. I have a drill doctor.. it works but does not inspire confidence.
 
I've had a Leslie Drill Grinder for at least 25yrs. I think I paid $325 for it when J&L had um' on sale with free shipping. It's not made anymore. It takes a bit of 'know-how' to set-up for each size, and not as 'user friendly' as some grinders I've used in other shops, but if you've got 1/2 dozen or more of 1 size it's worth it. I've been using it for so long set-up isn't a problem. I can sharpen up to and including 1 1/4". It's not hard to come up with 6 (or more) twist drill bits that could use a sharpening in the machine shop (5/16-3/8 or up to 1/2"). I buy twist drills by the package, 12 or 6 depending on "package quantity". For bigger twist drills, we have a old Sterling that'll do up to 3". For roughing out a chamber, before boring, you need a 'trued' bit. Most (me included anymore) can't grind a bit by hand as good as machine ground can be. If you ever run your bits under power feed , they'd better be 'true', or else... We still have many of those larger twist bits in the machine shop, but most are inserted for the CNC. Haven't used a large twist bit in a CNC in a long time. Inserted bits can be changed by about anyone, and they require less hp than a twist bit of the same size does. Smaller bits (1/2" and under) we still do. For a 'hobby shop' a good drill grinder is a luxury, and hard to justify the cost of. I don't usually sharpen a bit under 5/16"-3/8" unless I'm in a bind for one. I can still hand grind well enough to "make a hole", but it's probably gonna' be oversized, and that bit won't make as many holes as a machine ground one will. Buy yourself a drill point gage and check those bits ground with Drill Dr. , you may be surprised. Just as hand grinding lathe turning and threading tools is almost a 'lost art', so is hand grinding a twist drill.
 
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Tucker65 said:
Same here, luckily there was enough shank to set it back for me.

I guess that's where the old saying "measure twice cut once" comes in.
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Even after checking measurement parameters several times ive still made cut errors, most all of those errors stemmed from "distractions". Best advice i offer apprentice machinists ? Stay 100% FOCUSED on your current machining task !
 
One day I'll find a grinder on a local page... Right now I just buy several of each size I order and save the dull ones for that day when I get a real grinder. I don't use a lof of large drills so they're cheap enough.

I do have some big MT3 drills I'd like to get sharpened by a pro. I seem to do more boring in aluminum than I care to admit.
 
LVLAaron said:
One day I'll find a grinder on a local page... Right now I just buy several of each size I order and save the dull ones for that day when I get a real grinder. I don't use a lof of large drills so they're cheap enough.

I do have some big MT3 drills I'd like to get sharpened by a pro. I seem to do more boring in aluminum than I care to admit.
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If you're trying to drill a hole that is not much undersize from the finished size bored or reamed hole I could see where a new machine sharpened drill might be very helpful. If you're just looking to get a hole in something, or remove a bunch of material it's probably not necessary. I've sharpened plenty of drill bits from 1/8" up to 2" on a belt or disc sander. Hell, out in the field I've had my partner hold the angle grinder while I sharpened up some to put back in use in the magbase drill.
 
Tucker65 said:
If you're trying to drill a hole that is not much undersize from the finished size bored or reamed hole I could see where a new machine sharpened drill might be very helpful. If you're just looking to get a hole in something, or remove a bunch of material it's probably not necessary. I've sharpened plenty of drill bits from 1/8" up to 2" on a belt or disc sander. Hell, out in the field I've had my partner hold the angle grinder while I sharpened up some to put back in use in the magbase drill.
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Our mechanics got a new mag drill (milwaukee cordless) and it uses end mills instead of drill bits. It punches holes very quickly
 
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