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Thread: Redrilling/tapping slightly cockeyed 6-48 holes to 8-40?

  1. #1
    Join Date
    Jun 2004
    Location
    Eureka, CA
    Posts
    158

    Default Redrilling/tapping slightly cockeyed 6-48 holes to 8-40?

    So I'm 90% done building a rifle on a Savage 10 action...
    Only to find, now that I AM 90% done with barreling, action work, restocking, etc.. .that the rear set of scope screw holes and the front set of holes don't quite share the same centerline. Oops. (the factories oops, not mine... not that I've never done that... but I digress).

    I haven't measured the precise distance that the holes are offset from each other, but it's no more than the thickness of a 6" steel rule.

    So I'm thinking...
    How to bore/drill NEW holes over the top of the old ones - from 6-48 to a larger 8-40. (this assumes that after I'm done measureing, that the diameter and location of the new holes does not leave part of the old holes peeking out).

    Plug screws in the old holes, stub drill #29 and tap?
    Or leave out the plug screws, and HOPE that the drill is rigid enough NOT to follow the old hole...
    Unfortunately, I don't have an end mill of .136", nor a carbide drill... so those are not presently options.

    Any input appreciated!
    Paul F.

  2. #2
    Join Date
    Jun 2006
    Location
    NE Corner of NC
    Posts
    1,041

    Default Point of View

    From my own point of view, I would go with plugging the hole with a soft steel 6-48 "plug" and re-drilling it in the correct location. To me, if you try to redrill the existing hole, there is large possibilities of the drill following the old hole and breaking off in the hole and then there is a REAL mess to clean up. Ideally the plug could be silver soldered in place but then do you really want to heat the receiver? I would suggest using Permanent Grade Lock-Tite on the plug when you plug the hole. That should hold it in place while the new hole is drilled and tapped.

    Just my $0.02.
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  3. #3
    Join Date
    Aug 2002
    Location
    Topeka, KS
    Posts
    467

    Default

    Plug them. A drill will always take the path of least resistance.
    Jon Bohlander
    My PM Blog

  4. #4
    Join Date
    Dec 2007
    Location
    Montezuma, IA
    Posts
    949

    Default

    Plug the holes using Loctite on the screws. When it's cured, instead of drilling the new holes for the 8-40, find a metric center cutting end mill in 3.5mm, and plunge mill the holes for the tap. You're only talking a .0018" size difference, after all. Or, use a 9/64" end mill if you can find one.

    David
    Montezuma, IA

  5. #5
    Join Date
    Nov 2001
    Posts
    384

    Default Two Options

    I shop for DHT Springfields in pawn shops. The DHT ones that have been D&Ted usually have the holes crooked. If the greater diameter of a #8 screw will clean up the hole, the easiest method to fix the problem is to plunge cut with a 9/64 endmill and tap for #8 screws.

    The other option is to make bases to match the rifle. I usually do both as bases for Springfields that take #8 screws are hard to come by.

    I'b be willing to bet a Savage receiver is not as hard as the bridge on a DHT Springfield. This should be an easy fix, and you will end up with the advantages of the larger screw size.

  6. #6

    Default

    DHT= double heat treat?

  7. #7
    Join Date
    Jun 2004
    Location
    Eureka, CA
    Posts
    158

    Default

    Thanks for the replies!

    I like the idea of boring the holes with an end mill..
    Unfortunately, I dont' have an R8 collet for a 3.5mm.
    I DID, however, find that 9/64" end mills are not difficult to find at MSC :-)

    I don't really have the option of moving the holes if I want to use the already purchased one-piece base... (ironically enough, the 9/64" end mill, and a counterbore to open the holes in the mount from 6-48 to 8-40 will probably cost what I have into the mount... but I LIKE this mount!).

    Next time I take this rifle to bits for more fitting (the safety still won't engage after a new trigger, and I have some more fitting on the detachable magazine to do..). Pesky tuning, but not as pesky as measuring the proper hole spacing and alignment, and boring new holes.

    THanks again for the replies!
    Paul F.

  8. #8
    Join Date
    May 2009
    Location
    Michigan
    Posts
    3

    Default

    Scope mount holes out of alignment is quite common on older firearms . It's probaly why they invented the standard mount. As for redrilling the existing holes I think there's a good chance your going to trash your reciver.

  9. #9
    Join Date
    Nov 2001
    Posts
    384

    Default Counterbore

    Dial in your existing mount hole and counter bore with a 1/4 endmill. DHT= Double Heat Treat. Fishbait, congrats on a nice, upbeat, positive first post.
    Last edited by mike thomas; 05-16-2009 at 09:58 AM. Reason: typo

  10. #10
    Join Date
    May 2005
    Location
    Milwaukee
    Posts
    695

    Default

    Quote Originally Posted by fishbait
    Scope mount holes out of alignment is quite common on older firearms . It's probaly why they invented the standard mount. As for redrilling the existing holes I think there's a good chance your going to trash your reciver.
    Yeah, if he were to use a drill. An endmill will clean up and straighten the holes because it does not use the existing hole as a guide.

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