Blind Tap/Hole

[Desert Rat]

I'm getting ready to mount an underib on a rifle and am curious to what a Blind Tap/Hole is? Does it mean when the screw is in place it is not visible and the rib looks soldered on? How is that accomplished? The only thing I can see is possibly putting the thimbles over the holes and soldering them into place but it would miss a screw.

Or, I'm way off in my thinking, Any help would be apperciated.

 

[catskin]

A blind hole (tapped or not) refers to a hole which does not pass completely through the object. In other words, you DO NOT want to drill the hole so that it penetrates into the bore! Tapping a blind hole requires a special bottoming tap that will cut threads as close to the bottom of the hole as possable. Many times you will use two taps - one to get you started and rolling and a second bottoming tap to cut the last few threads to full deapth. Use care that the chips are completely cleaned out of the hole before trying to use the bottoming tap or you'll break it.

 

[TANSTAAFL]

If this is your first attempt at such, use great care, many have come to grief on this operation.

 

[catskin]

I should clarify that when using two taps, the first tap is a gun or plug tap, then the second is the bottoming tap.

 

[paulvallandigham]

If you have never worked with taps before, most common taps will have a taper on the front portion of the tap, to make it easier to start the thread in the hole you have drilled. You can get a handy plastic chart that give you the tap drill size for various sized taps. A bottoming tap has to taper on it. Often, you have to sacrifice a standard tap, by grinding it back to make your own bottoming tap. Its cheaper to do it this way, than to have to order, and wait for, and pay more for a bottoming tap, only. Check with Brownell's for the correct set of taps. Blind taps are a common problem for gun makers.

 

[Mr. Chester]

Be super careful, make sure you do not drill through the barrel. As otehrs have said - two taps with a bottom tap as last - do not over tighten the tap or you will break it and it is a bear to get it out!

 

[xbowman]

I agree with the others. You do need a bottom tap to finish it. Use a drill press that you can set the depth you need and practice on a piece of other metal.

 

[Zonie]

I think when "Use a drill press that you can set the depth" was written, it was talking about drilling the hole, not tapping the hole.

Although a lot of us use a drill press to hold the tap perpendicular to the work to start it into the hole, most folks have learned that tapping with a power tool like a drill press is asking for problems.
IMO, it is best to hand tap the hole so you can "feel" the resistance and back off before you break the tap.

As for bottom taps, most of the general hardware stores don't have them.
To create one, buy a regular tapered tap and s..l..o..w..l..y grind off the tapered area. Cool the tap often in water to prevent overheating which will distroy the taps hardness.
When all traces of the tapered threads are gone, you have a "bottom tap".

 

[Bountyhunter]

Dont want to kick up dust here, but, if you are going to drill with a drill press, make sure that you have the barrel in a drill press vise that is securely bolted to the drill table, and the part being drilled is clamped securely. Drill slow and careful to the proper depth and the proper speed for the drill bit.

Now, if you have the hole drilled, and dont touch that barrel or vise, the hole you drilled should still be lined up under the drill quill. If you put the plug tap in the quill and run it down with the depth wheel and turn the quill with your hand real easy like, it will start the threads perfectly straight. You are only going to be going in maybe six threads. Just feed the depth wheel as it wants to go, dont force it, and turn the quill by hand. Whatever you do, dont turn the drill motor on. You can feel when you hit the bottom. Then you can put the bottoming tap in a hand wrench and carefully and with lots of drill oil, fresh that hole out to the bottom, as the start of the threads will be cut true and straight.

That's the way I do it.

Bill

 

[guncobbler]

quote: "most folks have learned that tapping with a power tool like a drill press is asking for problems"

I keep the tap in the drill press but take the belt off and turn the chuck by hand to finish the job. I like how it keeps me from gettin off line. GC

 

[TANSTAAFL]

Tap descriptions.
[url] http://www.jjjtrain.com/vms/cutting_tools_hand_tap.html#6[/url]

Good tapping information. Including drill press tapping video. (scrolll down past the white blank portion of page)[url] http://www.jjjtrain.com/vms/cutting_tools_hand_tap.html[/url]

 

[DrTimboone]

Me too. Sofar I never needed anything more than hand power to turn any tap. The press just keeps the alignment.

 

[Desert Rat]

Wow, Thanks for all of the input, I got the answer to my question and then some. I guess I should have been a little more clear in my question. I am re-ribbing a barrell that is already drilled and tapped. The only drilling I'm planning to do is in the rib itself. I was wondering if there was something to hide the screws afterwards so it looks soldered like what I assume the originals were.

 

[paulvallandigham]

YOu can get a product called " liquid steel" in a tube at most hardware stores, or auto supply shops. That and " Bondo" can be used to fill in the screw holes, and after they set, they can be smoothed to make it look like the rib. I don't know that you can brown the stuff, or blue it, but it will fill the drill holes.

 

[TANSTAAFL]

YOu can get a product called " liquid steel" in a tube at most hardware stores, or auto supply shops. That and " Bondo" can be used to fill in the screw holes, and after they set, they can be smoothed to make it look like the rib. I don't know that you can brown the stuff, or blue it, but it will fill the drill holes.

I would avoid both those products, IMHO there is only one epoxy to use for such, regular J.B. Weld

 

[Zonie]

I don't know of any epoxy type compound that will blue or brown. What you see is what you get.

I only speak for me, but I would much rather see a good "correct" screw than a blob of filler/epoxy of any color.
What is correct? A slotted screw head.
Phillips, Hex wrench, Star point, or any other screw head just wouldn't look right to me.

 

[TANSTAAFL]

Made no reference to blue or brown, if using epoxy for strength, the liquid steel and body putty are junk for strength or heat. J.B. Weld is the only one I would put any trust in that regard.

I have used the J.B. Weld for scope mounts and many other gun related items. Once prepared properly and cleaned, J.B. Weld applied, clamped in place and all excess wiped off, there is none showing.

Many use Loctite for keeping screws in place, big difference betwixt using Loctite or J.B. Weld,? Out of sight, out of mind.