Tang bolt

[bob hertrich]

Is it politically correct to counterbore the tang bolt? I always seem to get the screw incorrectly countersunk.

[Jim Kibler]

I prefer to counterbore rather than countersink.  I have seen counterbores used on a number of original guns, though admittedly mostly English or European.  Makes for a a neat job.  Helps if the tang bolt isn't perfectly perpendicular to the tang as well.  I use a 5/16" diameter multi-flute countersink for the job.  Works well.

[Eric Krewson]

I counter sunk my first tang hole so poorly my barrel moved up abut .10 when I tightened the bolt.

I countersunk the hole after the fact so to speak,  I removed the rifle from my drill press table after drilling the hole for the bolt and countersunk the hole with a hand drill while holding the rifle in my vise.

Like I said, the countersink was really off and cockeyed, I kept trying to correct my goof-up and ended up wit such a mess I had to have the tang hole welded up so could start over.

On my next attempt I drilled the hole and countersunk it while my rifle was still clamped to my drill press table at the angle I drilled the hole, piece of cake and no barrel movement when I tightened the bolt .

My only problem was getting the counter sink depth a little deep, easy to correct with a little filing.

This time I am going to cut a tang bolt leaving about half it's length. I will countersink on my drill press table after drilling the hole, drop the bolt in the hole to check my depth and continue going down until I have it perfect.

Being a rookie I do weird stuff like the above to keep my goof-ups to a minimum.

[smart dog]

Hi Bob,
Listen to Jim.  He is bang on.

dave

[smallpatch]

Jim,

I'm a little confused.  This is something I've always struggled with as well.

A counter bore makes a flat bottomed hole.  How do you use them with a flat or domed headed screw??  Also, you say you use a counter bore  rather than a counter sink, then say you use a 5/16 multi flute counter sink.

Help me out,..... I'm even more confused than ever!!!

HELP!!!

[Dave Dolliver]

It helps if the counterbore is piloted to keep it concentric with the bolt hole.

Some years ago I got some piloted COUNTERSINKS from MSR but haven't seen any lately.  That sure helped with the countersink for the tang bolts.

Either way the operation should be completed while the assembly is still in the drill press vise and not allowed to move.

Dave Dolliver

[Jim Kibler]

Jim,

I'm a little confused.  This is something I've always struggled with as well.

A counter bore makes a flat bottomed hole.  How do you use them with a flat or domed headed screw??  Also, you say you use a counter bore  rather than a counter sink, then say you use a 5/16 multi flute counter sink.

Help me out,..... I'm even more confused than ever!!!

HELP!!!

Sorry for the confusion.  If you say a counterbore has a flat bottom, then picture one with the bottom angled to correspond with that of a countersink.  This is what I'm describing.  As I said, I use a countersink with a body diameter of 5/16" and sink it to below the break point of the angled tip.  Hope this makes sense.

Jim

[Dave Dolliver]

My piloted countersinks can work the same way you describe, Jim.  I have both 5/16 and 3/8 dia and both #18 and #8 pilots and have used them as you describe on occasion.  Have also used a 3/8 dia head tang bot\lt and turned the head to 5/16  so I could seat it in the deep countersink and then file the head flat with the tang surface.

Dave Dolliver

[Acer Saccharum]

This can be had from MSC or McMaster-Carr. Replace the drill with a solid pilot of your own making, if that suits your project. Different countersink OD's can be had, as well as different drill sizes, HSS or high carbon, 82 degree or 90.

[smallpatch]

Acer,

I actually have some of those, but I always thought they were just for wood, not steel??

[Acer Saccharum]

McMaster carries them in HSS, and says they can be used for steel. I haint tried one yet, so can't vouch for them.

[billd]

Regarding the picture Acer posted.....We use these at work for chamfering holes before tapping, drill and chamfer in one operation.  They work great on Aluminum, so so on steel.  The chamfer we do is a lot smaller than a countersunk hole for a tang bolt.  We use them in a high production capacity, power feed machine.  By hand, used carefully, Acer's idea may work.  It sure sounds good.

Bill

[Don Getz]

When I lay out the positions for the tang bolt, I first mark the trigger plate where I want it to come out, I then lay the
tang bolt on the side of the rifle and move it to the position on the tang where it will be at the proper angle, or a flat
fit.     I then set up my pointer on the drill press table so that I can get that proper angle.   I first drill the hole with a
tap drill (#29 for a No. 8 screw).   After that is done, I will drill down thru the tang  to the triggeer plate, stopping when I
touch it, with a #13 drill.     I then countersink the tang while positioning it on the pointer, this gives you that good countersink position.   I then leave everything in place and run my tap down thru the hole and tap the trigger plate in
place.    If the tang bolt head does not fit well after doing all of this, you have done a poor job of aligning it in the first
place..................Don

[Acer Saccharum]

The pilot is a huge advantage in keeping the countersink centered on a hole. A MUST if you're doing this by hand.

I can't tell you how many times my countersink has wandered. Fewer stayed on center than those which were off.



A single flute countersink can be used in a brace, and with partial rotation of the cutting edge, you can move a countersink over.

[B.Habermehl]

When I do my tang bolt layout, I us a large headed domed head bolt to figure the best compromise on the angle. The large flat head will show a equal amount of gap fore and aft when you have it laying properly on the side of the lock panels. Then drill a small pilot hole in the tang, 3/32 or so, measure for center, if a smidge off now is the time to fudge with the next larger dia drill. Get it centered within .005 or less, the eye can detect anyting more. Use your origional layout to determine where the bolt will come out of the trigger plate. The trigger plate usually allows a bit more leeway for the bolt. Now, pilot drill on the approximate angle tward the tang with a 3/32 dia drill. Set up the point to point fixture in the drill press. I usually countersink the tang first to just a bit shy of the finished dia. Double check for center. Now drill the clearence hole for the bolt body to the trigger plate. Flip the gun and drill the pilot hole out to the tap drill dia. I usually dissasemble and check if a bit of fudging needs done where the hole in the triggerplate meets the clearence hole in the stock. If OK then reassemble and tap the hole using the tang and clearence hole as a tapping guide.  Try your tang bolt and finish the countersink. BJH