View Full Version : bad drill&tap

February 1, 2005, 12:37 AM
i drilled and tapped my mosin m44 for a base. front screw seemed like it was fine, rear scew never grabbed. OK methinks, acraglass the threads and bottom of base. That worked for about 40 rounds. i am assuming these are 6-40 screws. I bought one of the scope mount kits for the mosin that comes with base, drill bits and taps. could I retap to a slightly larger screw? What size? Thanks.

February 1, 2005, 12:55 PM
You should have a 6-48 screw. Brownells sells a tap and screws that is just slightly larger than the 6-48 that you use to fix stripped holes. If you don't want to spend that much money, try using red loctite. Clean the hole and screw with alcohol and then use the loctite. This should be allowed to dry for a few hours before you try it out. If you ever need to remove the screw, you will need to use a heat source like a propane torch directed at the screw for a few seconds to get the loctite to melt so the screw can come out. Good luck with it.

James K
February 1, 2005, 09:07 PM
Go up to 8x40 all around; that size is better for heavy recoil rifles anyway.


Harry Bonar
February 19, 2005, 07:42 PM
Dear Sir:
I ust got done installing one of the Advance Technologies kits, with bolt handle and mount and as you say, drills and taps on a Monsin.
The screws, drills and tap came with this also but the size was 10x32 - a rather odd size for guns!
The mount was solid as a rock; worked good.
Yes, if you had 6x48 screws, as you were told by Jim, go to 8x40!
Let me maybe help you with drilling and tapping; I ALWAYS drill with a drill about three sizes smaller than the "tap drill" specified. Then I use the tap drill to "ream" the final hole, the reason being that SOME tap drills will not have flutes correctly ground and will cut a larger than specified hole - reaming assures you will have a correct hole size. On some of these military rifles (such as the Monsin) I hate to admit it but I level off of a rear sight base, do my mount positioning with another level, scribe and center-punch a hole, recheck and use my cordless drill! (I know guys, it is better in the mill or drill press) but I get fantastic results.
If in reaming you get "chatter" put a folded piece of denim under the drill. Anytime you want to enlarge a hole with a larger drill, do this, it goes in like a reamer and makes a smoother hole. Old Dave Taylor, of Little Hocking Ohio taught me that and it works like a charm (particularly when you're using a twist drill in a center to cut excess metal away when chambering.)
Also, when drilling THROUGH a reciever (or other job) use a "gun-tap" it shoots its material out the bottom of hole and works great.
Harry B. :) :)

February 20, 2005, 11:23 AM
Drilled holes are always oversized. Not an issue for drilling and tapping coarse or deeper threads (deeper thread depth, not hole depth), a problem with fine threads that are shallower.
For a one off job you can use a drill about 0.002-0.004 undersize at some increased risk of tap breakage. For an exact hole size drill under and ream up to the exact size required. Numbered size chucking reamers are not very expensive, try MSC.
Fixturing is required to produce an exact hole diameter. Even clamping the gun to a drill press table, drilling the hole, then chucking a reamer and turning by hand without ever moving the gun will produce a much better hole (rounder and more exactly sized) than trying to free hand.

James K
February 23, 2005, 03:04 PM
I have seen quite a few guns that were drilled for scopes by "my brother-in-law down at the garage" or with "that thing I bought to hold a hand drill". I have also seen ones drilled by hand ("I got a good eye, and it worked great except I can't quite get this mount to fit, so I brought it to you").

Even seen a drunk's footprints in the snow? You get the picture.

Either buy the jig and drill press and do it right or take it to someone who can.


February 23, 2005, 03:11 PM
The guy using his handrill is a smith. He excused himself for using it saying he knows it is better to use a mill or drill press, but that he gets excellent results doing it his way. For the average joe, this wouldn't be a good idea. For a smith trained to do things right, and by the way he knows it has to be right, if he can save a step or two by doing it by hand and it still looks good, more power to the man. I think we can all learn something from Mr. Bonar. Afterall, he has been doing this longer than most of us have been around.

February 23, 2005, 05:06 PM
I've been a tool maker (plastic injection molds) for 30 years and a NYS licensed gunsmith for 25 years.. Drilling and tapping holes is second nature.
There is no-way in H*ll I'd drill a #31 hole for a 6-48 tap with a handdrill.
Not only would I NOT get it 90 degrees to the work surface, there would be "side" pressure involved that would result in a much too big hole.
Besides the 4 holes for the base would not be accurately enough placed.

One other reason is the depth of the holes...How could you control the depth??
Put tape on the drill bit?? hehehe..

February 23, 2005, 09:26 PM
I won't speak for Mr.Bonar, but I would think that the holes were through holes. I guess in all the years of your career that you never encountered a job that you couldn't take to the mill or drill press. I have many of times. Sometimes you have no choice but to hand drill and use a tapping jig to make sure the tap is ran in squarely. As far as gunsmithing goes, I would think that Harry made sure the job came out right. I don't think he would turn out a job that wasn't. If I had my rathers, I would always drill and tap using the drill press without moving the job. I did a lot of work on guns before I ever could afford to buy a drill press or belt sanders and other tools. I started out with a good collection of hand files and a couple of drill motors, a tapping set and some good chisels and gouges. I worked for a couple of years before I could afford to tool up my shop. Sure there were jobs that I turned down when it would have taken more time to farm out than the customer wanted to take, but I did alright. A skilled man with a hand drill isn't quite the same as a man that tries to do an occasional job.

Harry Bonar
February 24, 2005, 12:50 PM
:) Dear Smiths:
Yea, they were thru-holes; and I was too lazy to take all of the attatchments loose to disassemble the MONSIN. But it did turn out great.
I know the "cordless drill" isn't great but I don't push down on anything but the cylindrical part of the drill. It is true that you might not get a perfect 90 degree hold! One of the reasons I sometimes do this is that after I centerpunch the center of the scribed surface I can draw my drill easier than with a press or mill. The secret is to shank up your drill real short, touch down, look at it to be sure its centered in the circular scribed hole and then proceed.
If you do get a centerpunch or a drill off center take a sharp center-punch and punch opposide the side you want to go. It only moves a few thousandths but it helps.
Thanks for the defense but I should have put it in the mill! :)
I will add that when you level off of the sight base your scope does line up with "the sights" native to the gun.
I guess I just got lazy on this, but, I didn't think I could have gotten a better surface to level from on the bottom of the Monsin.
No problem guys, we're all human! :eek:

February 24, 2005, 03:08 PM
If you want to try the hand drill route, at least center punch the work and then chuck up a center drill. The 'drill' portion is only about 1/8 inch long with a larger shank. They are designed to start a hole exactly on a punch witout walking from drill bit flex. Even in a lath, milling machine, or drill press a center drill doess wonders to get the initial spot enlarged enouh to have a twist drill not wander.