Installing drum

[MI MAN]

I am getting ready to install a drum on the barrel of a kit gun. The instructions just say to drill a 3/32 pilot hole (done) and then follow up with a letter I drill bit. There are no other directions other than the plug threads are 5/16-24 and various taps are recommended. See attached. Can anyone help me understand why they list both a plug and bottom tap for the drum and nipple threads?

 

[ord sgt]

With the plug tap, you run the risk of hitting the far side of the barrel while running in the tap too far. Use the plug tap to get the threads started, then change to the bottoming tap to finish the threads. Safer for the barrel that way.

 

[Zonie]

For those who don't know, a "regular or, tapered tap" has the outside of its threads at the starting end of it removed so the tap can start easily into the drilled hole. This thread removal is done in a tapered way so that by the time the 4th or 6th thread is entering the hole it is cutting a full sized threads into hole.
This makes it easy to start the tap into a unthreaded hole and it works great if you are threading a "thru hole" with no bottom. With this type of hole, you can run the entire tap thru the hole to complete the job.

A "plug tap" also has the starting threads cut away to help it start into a untapped hole but with this style of tap, usually only the first couple of threads are tapered undersize.

The problem is, often the hole is not a thru hole that goes completely thru the part. When this happens, the threads that are being made by those tapered or plug tap starting threads are not complete at the bottom of the hole. They are only partially formed so it is impossible to screw a bolt or screw completely to the bottom.

That's where the "bottom tap" comes in handy. Unlike the other two taps, there is no "lead in" taper on the starting threads. They are full size threads that will remove any metal that gets in their way. This allows the bottom tap to cut full threads all the way to the bottom of the hole so a bolt can be screwed into it to the full depth. The problem with a bottom tap is they are just about impossible to "start" in a unthreaded drilled hole.
Because of this, if you want to have a threaded blind hole with threads going to the bottom of the hole you need to start the threading using a tapered or plug tap. Once that tap has been run most of the way to the bottom of the hole, remove it and screw the bottom tap in. Then, complete the threading of the hole.

 

[Sidney Smith]

I would think this would be more of an issue with small caliber barrels, than larger calibers. When I threaded my .62 cal smooth bore, I only used a standard tap. Since the wall of the barrel wasn't hugely thick, and the bore was large, no problems running the tap in far enough to get full thread cutting.

Now with my .32 caliber barrel, I can see myself getting a bottom tap for the touch hole liner.

 

[MI MAN]

For those who don't know, a "regular or, tapered tap" has the outside of its threads at the starting end of it removed so the tap can start easily into the drilled hole. This thread removal is done in a tapered way so that by the time the 4th or 6th thread is entering the hole it is cutting a full sized threads into hole.
This makes it easy to start the tap into a unthreaded hole and it works great if you are threading a "thru hole" with no bottom. With this type of hole, you can run the entire tap thru the hole to complete the job.

A "plug tap" also has the starting threads cut away to help it start into a untapped hole but with this style of tap, usually only the first couple of threads are tapered undersize.

The problem is, often the hole is not a thru hole that goes completely thru the part. When this happens, the threads that are being made by those tapered or plug tap starting threads are not complete at the bottom of the hole. They are only partially formed so it is impossible to screw a bolt or screw completely to the bottom.

That's where the "bottom tap" comes in handy. Unlike the other two taps, there is no "lead in" taper on the starting threads. They are full size threads that will remove any metal that gets in their way. This allows the bottom tap to cut full threads all the way to the bottom of the hole so a bolt can be screwed into it to the full depth. The problem with a bottom tap is they are just about impossible to "start" in a unthreaded drilled hole.
Because of this, if you want to have a threaded blind hole with threads going to the bottom of the hole you need to start the threading using a tapered or plug tap. Once that tap has been run most of the way to the bottom of the hole, remove it and screw the bottom tap in. Then, complete the threading of the hole.

Thanks for the information on various taps. However I am still wondering why I would need a bottom tap for a drum install. Since the holes are straight through it appears to me that the plug tap would be all that is needed. Thanks

 

[nhmoose]

The taps are to freaking long the start tap and plug tap. In many calibers they hit the other side of the bore Hence why a bottom tap is used. to get a through thread.

I cannot explain it better.

 

[mooman76]

The tip is tapered to help start the tap. If you can't get it in far enough to get past the taper, then when you install the drum, it won't go in all the way and there will be a hole there for crud to build up.

 

[MI MAN]

Thanks I understand now.

 

[M. De Land]

The main thing with any tap use is to get it started straight which is just about impossible without the use of a tap guide. I always use a tap guide if possible or a T handle tap guide to be used in a drill press. These work very well when having to tap a hole on a contoured surface. With lots of taping experience you can learn to feel a tap through pretty well centered but it will never be a true as when a tap guide is employed. The other thing is you will almost never break a tap off in a hole with the use of a tap guide.
On any drum installation you will also want a close "contact" fit to the lock plate at the bottom half of the drum diameter so the narrow neck threads don't have to absorb the continual pounding of the hammer fall and eventually snap off if unsupported.
This is a good place to use a bit of glass bedding to get a mold fit of drum to lock plate mortise.

 

[Zonie]

Thanks for the information on various taps. However I am still wondering why I would need a bottom tap for a drum install. Since the holes are straight through it appears to me that the plug tap would be all that is needed. Thanks

Nhmoose pretty much covered the drum threads in his explanation above.

Since you are installing a drum that indicates the lock is a percussion style that will need a nipple in the drum.
Due to the small size of a drum and the length of the nipple threads a bottom tap is almost mandatory when your threading the hole for the nipple.

When I thread these holes I use a plug tap to start the threads and then run a bottom tap into the hole to finish the threads at the bottom of the hole.

 

[MI MAN]

The main thing with any tap use is to get it started straight which is just about impossible without the use of a tap guide. I always use a tap guide if possible or a T handle tap guide to be used in a drill press. These work very well when having to tap a hole on a contoured surface. With lots of taping experience you can learn to feel a tap through pretty well centered but it will never be a true as when a tap guide is employed. The other thing is you will almost never break a tap off in a hole with the use of a tap guide.
On any drum installation you will also want a close "contact" fit to the lock plate at the bottom half of the drum diameter so the narrow neck threads don't have to absorb the continual pounding of the hammer fall and eventually snap off if unsupported.
This is a good place to use a bit of glass bedding to get a mold fit of drum to lock plate mortise.

Thanks I will look into getting a tap guide. As hard as I tried I think I will have a tiny gap. Other posts suggested how to fix this issue.

 

[M. De Land]

You can easily make a tap guide from a piece of scrap steel. It needs to be flat and parallel on both sides, about and inch thick and the guide hole drilled perpendicular for a close slip fit of the tap body. For cylindrical surfaces a V notch in a flat plate with a perpendicular and centered guide hole works very well.
You don't need to buy anything other than a couple of taper taps then grind them to bottom taps when needed. I do this regularly.
Probably the most useful thing in hole taping is learning how to clear a broken tap out of a hole that is partially threaded when the tap snaps off.
The guide will go a long way in preventing this but even then after a tap gets stressed enough times you really have to pay attention on how much pressure you apply and how dull the cutting teeth are getting to lesson the chance of breakage. But sooner or later drill and tap breakage will happen no matter how careful and experienced you are. Take heart and press on as I've been doing a lot of drilling and tapping for over 40 years and have yet to not be able to retrieve a broken tap.

 

[Col. Batguano]

And with through-holes, the most resistance (meaning the time you're most likely to break one) seems to come just when you're breaking through the other side. Go slow then. I broke a tap off on a front lock bolt one time and never was able to get it out of there, and the steel was so hard I couldn't drill it out either. Probably worked on it for a day before I just gave up.

 

[M. De Land]

A few tips on tapping will also go a long way in preventing breakage. I always use a good grade of cutting oil to pre lube the hole to be tapped. Never take more than one full turn inward without backing up half a turn to break up the chips. After a couple of full turns and back up half turn for chip breakage , remove the tap and blow the chips out. With some experience you will be able to feel the tap binding and know it's time to clear the hole. You will be able to feel the tap shank twist and know when it is about to snap off. Most times though taping without a guide and not getting it started straight is the main cause of tap failure.

 

[Pete G]

When you do break a tap don't panic. There is a tool called a "Broken tap remover".

 

[Col. Batguano]

Thanks Pete. I wish they sold those at the home improvement stores, but they don't seem to. Maybe putting them right next to the taps would sour sales of the taps? Or, maybe it's the simple solution; sales of tap removers would be about 1/20 of taps. They put stuff on the shelves that will sell, rather than that which doesn't. The carry plenty of other things in the store that doesn't move already. Mostly because they HAVE to to be a "full service" home improvement store.

 

[M. De Land]

I get my broken tap removal tools from Brownell's Gun supply catalogue. Some times though they won't even work and the tap has to be broken up with a punch and or backed out also with a punch tapping on flute corners. I"ve broke many over the years and it still gives be anxiety when it happens but they have all been able to be removed so don't get to worked up when it happens and it will happen.

 

[M. De Land]

The trouble with tapping by hand without a guide as mentioned is getting the thread crooked and this keeps the shoulder on nipples from making even contact around their perimeter. It's not so important with a flint vent as they can be struck off flush with the barrel flat but still the hole axis is better postioned square and perpendicular to the pan, in my opinion.

 

[nhmoose]

Seems you need a cheap drill press and vise. No way would I start a tap for a drum without it being sure.

Hand drills are like Dremel tools. The work for pro's with experience but for armature beginners not so much.

The old smiths using hand powered drills WERE experts using them as in thousands of times.