Indicating pre-drilled hole at 12 O'clock in mill vise.

cdhthethird · Nov 26, 2020

Hello,

I have a gunsmithing project we are working on right now and I can't figure something out. I have a round part (barrel) with no flat on it and it has a single drilled and tapped screw hole at lets say 12 o'clock. I need to drill another hole inline with it six inches away. How would I go about setting that up in a mill vise so that the original already existing drilled and tapped hole is at 12 o'clock in the vise? I need both holes to be aligned as close as possible in a linear fashion to one another.

Thanks,
Chuck.

gary s moore · Nov 26, 2020

put a long screw in existing hole and indicate it vertical

dgfoster · Nov 26, 2020

Put a machinist’s button in the hole. Put the barrel in the trammed vise on a wide parallel. Using your edge finder, find the center of the barrel. Now adjust rotation of the barrel so that the button is centered.

Screw and screw threads are not very reliable. Long screws, less so.

Denis

MilGunsmith · Nov 26, 2020

Make a tight fitting screw for the existing hole. Screw it into the hole and then grab it in a drill chuck, or collet, with the barrel held loosely in the vise. Adjust the table till the vise is able to be tightened without moving the barrel. Doing it this way keeps the hole in the 12'oclock position and there is only one axis on the table to be adjusted for alignment.

cdhthethird · Nov 26, 2020

Thank you everyone! I really appreciate the help!

tdmidget · Nov 27, 2020

Well , I'm going to be the asshole and ask why these weren't done in one set up. I will assume it is not your fault and you are cleaning up someone else's mess. This requires a premium charge and an understanding that not all will survive.
You charge a premium because:
You usually don't want this kind of clean up work,
You know that there will be complaints, re: quality, price, time, you name it, They will rarely be pleased
You should have had the job from day one to do it correctly
You could have been making money while asking this question.

kendog · Nov 30, 2020

tdmidget said:
Well , I'm going to be the asshole and ask why these weren't done in one set up. I will assume it is not your fault and you are cleaning up someone else's mess. This requires a premium charge and an understanding that not all will survive.
You charge a premium because:
You usually don't want this kind of clean up work,
You know that there will be complaints, re: quality, price, time, you name it, They will rarely be pleased
You should have had the job from day one to do it correctly
You could have been making money while asking this question.

Man after my own heart.

Jobs like this almost always start with "all ya gotta do is..."

OP one way is to put a gauge pin in the hole and another in the collet/chuck/whatever. Align them for vertical by eye (be surprised how close one can get this way), shim barrel as needed for taper/features, etc., and lock the barrel in the vise. Then locate a pin to the existing hole with your table.

kootne · Nov 30, 2020

How much taper is in your barrel? Will your vise compensate for it? If not, that may be another consideration. And on that same thought, make sure you take your centering touch off at the location of the new hole because unless you have your vise jaw indicated to 1/2 the taper of the barrel you cannot just run back and forth in the X axis and stay over the center of the barrel. Hope that makes sense.
Dennis

michiganbuck · Nov 30, 2020

Might make a bushing plate that is a hole (or two) in a bar that can bump the existing first screw and locate the second.

just a scrap source bar, perhaps with a v on the backside, having two holes 6" apart.

The V on the backside would keep holes dead straight.

Might make the hole the size of a center drill.

Might make it longer so you can use it for other jobs that need spaced holes.

A slip of masking tape would keep it from making the barrel finish.

Might use the part for a template.

Good to have a center punch the same diameter as your center drill so punching is also possible,.

a flat bushing jig like this can jo-block off and existing location to make next hole .002 or so close.

mhajicek · Nov 30, 2020

tdmidget said:
Well , I'm going to be the asshole and ask why these weren't done in one set up.

Hazarding a guess, the first hole was probably made years ago, perhaps by the original manufacturer, while the need for the new hole is based on a change in requirements.

SilveradoHauler · Nov 30, 2020

Best way to drill and tap a barrel is with the barrel installed in the receiver. Then use the receiver flats as a reference.

Example: A barreled action in my vertical milling machine with a 54 inch long table. Note this is a M700 Rem and I am using the bottom of the recoil lug as the reference. Caution: The barrel and lug must be installed correctly!! This is an aftermarket lug, I throw the stock Rem lugs in the trash. There is a parallel under the recoil lug.

I made this jig for aligning sights. To the bottom of the receiver of course. Bottom of the jig is machined flat so I can clamp it to the milling machine table.

All mating surfaces are machined. The bottom flat on the receiver clamps to the block, built in alignment.

cdhthethird · Nov 30, 2020

kendog said:
Man after my own heart.

Jobs like this almost always start with "all ya gotta do is..."

OP one way is to put a gauge pin in the hole and another in the collet/chuck/whatever. Align them for vertical by eye (be surprised how close one can get this way), shim barrel as needed for taper/features, etc., and lock the barrel in the vise. Then locate a pin to the existing hole with your table.

Well I am not a gunsmith, I'm not doing this for money, and it's on my gun. If I was doing this for money, I wouldn't have taken the job without knowing how to complete it.

kendog · Dec 1, 2020

cdhthethird said:
Well I am not a gunsmith, I'm not doing this for money, and it's on my gun. If I was doing this for money, I wouldn't have taken the job without knowing how to complete it.

Not taking a shot at you, just agreeing with midget, kinda off topic.

There are a bunch of different ways to skin this cat, and there are a lot of good suggestions here.

kendog · Dec 1, 2020

Another way would be to take a weaver style or picatinny base and screw it to your existing hole and sweep the top of it with an indicator. Grand Slam steel bases are flat on top. If you dont have the base with the exact radius on hand you could order one off the chart below, or use one with a lesser radius so the sides of the base form a kind of V block. Still have to shim the barrel for taper, and account for the base not being in alignment with the longitudinal axis of a tapered part, but it will get you good on the Y axis. I use paper shims on 3 sides 1/2 the difference of the taper over the width of vise jaws. In my case 6". Not flashy, but this will get you well within industry tolerance for scope mounting, etc.

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