Vent problems

[Kansas Boomer]

When I converted my 1" bore cannon to 209 primers, I thought my ignition problems were over. Only created a new set of problems. When the gun is fired, so much explosion comes back up the vent, it drove the hammer back so hard, it broke the welds on the sear. Rewelded the sear, put a stop plate on the hammer, first time I fired it, broke the welds on the stop plate. Rewelded the stop plate, this time when I fire it, it bent the screws holding the trigger to the barrel. Today, I thought I would just replace the screws with larger screws. The first one went great, drilled the second one out and proceded to break the tap off in the hole. Have the cannon torn down, set to go to the machine shop, as I have no way to get the tap out. I guess my question is, should I have a new vent liner made, with a smaller hole into the chamber? Possibly that would cut down on the explosion coming back up the vent.  boomer

[Cat Whisperer]

Two issues.  Getting the tap out and too large a vent hole.

First, note the nipples used on blackpowder shootin' irons - SMALL hole.  You might want to design something like a threaded insert (set screw) that could be replaceable that you could try several different sizes of holes in.

Second - removing the tap - there are special tools (work so-so), they can be milled out (usually sacrifice one or more carbide end-mills) or EDM'd out.  There are other techniques as well - chemicals, and shattering them.

Just some early am thoughts, good luck!

[Michael Az]

Broken taps can sometimes be a problem getting out. Like CW mentioned, the electronic discharge machine is usually the best but if you need to do it in your shop like I would have to do then a carbide end mill is about the easiest. It isn't any problem for the mill to cut the tap, but problem arise when pieces of the tap break free and with carbide being so brittle, a piece of the broken tap will get the mill in a bind and then break. To help with this direct a strong current of air down the hole while milling to try and blow the pieces out before they break the tap. Use lots of eye protection. If this doesn't succeed then you might have to make a hollow end mill that will cut material around the tap. This might be a way for you to go if you have to make a sleeve anyway to reduce the hole size.

Michael

[Double D]

Depending  on the size of the tap a dental burr on a Dremel tool will make a hole you can get your center punch into preferably in the web of a flute to shatter the tap. Larger taps, larger  burr and air grinder. Smaller hammer and sharp punch seems to give better shock and shatter effect.  Put the  punch tip toward the side of the hole and  break the side of the hole out.

Extremely sucessfull technique for 6-48 gun screws based on years of experience as a Gunsmith. Works on larger taps also.

I drastically reduce the incidents of taps breaking by using STP for tapping fliud, 1/4 turn and reverse to cut. Use a new dril bit and new tap or every job, and never ever using the cheap gray taps you get in hardware stores.

[Kansas Boomer]

The tap size is 8-32. Bought a new #29 drill bit and new tap yesterday, at the local hareware store. I think the tap was a Hanson. What taps do you recomend? May try the punch, and see if I can shatter it. Don't think it will make it any worse.   boomer

[GGaskill]

If the tap is carbon (versus High Speed) steel, you may be able to shatter it. #29 is the right size for 8-32, although what are you using an 8-32 for?  The tap probably broke because it was not perfectly aligned with the hole.

Read John Pike's thread "Drilling the Touchhole" and don't rush.  It would probably be worth the cost to find someone with an EDM and disintegrate the tap.

[Michael Az]

and never ever using the cheap gray taps you get in hardware stores.

Really good advise! Chinese drills, taps and dies are pathetic! Whenever I have a through hole, like a vent hole I always use a gun tap. They are made to shoot the chip ahead of the tap and you don't have to stop every half turn.
George is probably right about the tap breaking by not being straight. It is best to run a tap that small right after you drill the hole and use the chuck to hold it straight.
Michael

[GGaskill]

Chinese drills, taps and dies are pathetic!

Ordinary retail ones leave a lot to be desired.  I have even untwisted some "bargain" Chinese twist drills.  But I am also getting HSS taps from a Chinese supplier that are top drawer tools.  And their warehouse is just down the street from my house.

[Kansas Boomer]

Must be my lucky day!!!!!  Was able to drive the tap out. Started with a small pointed punch, three wacks got it started, used an 1/8" punch to drive it out. I guess I was real lucky, the piece of tap was only about 3/16" long. Didn't even mess the hole up to bad. Went back through the hole with the #29 bit. Think I can even see a few threads still in there. Michael Az, did you say to run the tap in the drill press chuck? How does that work?  boomer

[Double D]

The tap size is 8-32. Bought a new #29 drill bit and new tap yesterday, at the local hareware store. I think the tap was a Hanson. What taps do you recomend? May try the punch, and see if I can shatter it. Don't think it will make it any worse.   boomer

The ones not to buy are those gray Vermont American, made in USA. They come in a red bubble package and hang on pegs. They are soft and made for one time use. The taps don't even feel sharp.

There is another hardware store brand that are in yellow and  black bubble package that hangs on pegs. They are pretty good.

 I buy most of mine from from Machine Shop Supply or Tool Supply houses that sell in bulk either over the counter or on line.

When I was Virginia  I used Travers Supply www.travers.com  There are a bunch of others, Enco, Rutland, MSC.  I also used Brownells a lot www.brownells.com

[Michael Az]

Michael Az, did you say to run the tap in the drill press chuck? How does that work?  boomer

Glad you got it out. What I was referring to with the chuck is when you drill the tap hole, don't let anything move out of position like the spindle or vise. After the hole is drilled, put the tap in the drill chuck and put the spindle in neutral. Now you can carefully lower the spindle while turning the chuck by hand until the tap gets a start in the hole. After it gets started, then you can turn the feed handle loose and the tap will pull its self in. After maybe four revolutions you can be sure the tap is started  straight and then loosen the chuck from the tap and finish by hand. Another important thing you need is cutting oil. If you don't have any, bacon grease or Crisco will do a great job in steel.
Michael

[Rickk]

According to this story and poorly done picture ...

 http://web.mit.edu/course/other/machineshop/Drilling/threading.con.html

the hole in the back of tap handles actually has a use (in conjunction with a drill press).

I always saw that hole but never even wondered why anyone bothered to put it there.

[Kansas Boomer]

Thanks Guys, great info, I certainly never knew what the hole in back of the tap handle was for. I have an Enco account, that is where I get my 1" steel cannon balls. Think I will just order the most expensive HSS Sprial Point Tap they have. That should give me the best chance of not screwing it up again. boomer

[GGaskill]

What you need to use the hole in the tap wrench (or in the top of larger taps) is a spring center or micro tap guide.



It goes in the drill chuck with the point in the wrench hole and the spindle pushed down.  An internal spring pushes on the plunger which pushes the tap into the hole.  The plunger has a hole on its other end (left hand image) that can be used with small taps with the pointed back end instead of the center hole.  Very effective.

[Cannonmaker]

I just don't like to buy a tap without the centerhole.  I use the centerhole whenever I drill and tap on the lathe. 

It is allways good to have a broken tap come out with out distroying the work piece.

Rick

[Kansas Boomer]

The new HSS taps came in from Enco Monday afternoon. Almost to pretty to use. Very, very carefully and slowly started the new tap into the hole  I drove the old tap from. Used STP for  lube, very slow going, must be small pieces of the old tap still in there. Finally got what I think is enough threads to hold the spring loaded cannon lock securely. Did not get threads all the way through, felt like I was putting to much pressure on the tap. May go back to the #11 cap vent liner until I can get the 209 vent liner modified. boomer