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making long taps

I am making forming taps for 3/4 and 1" Three and four feet long. I am drilling and taping into lead 13 inches deep. Then I screw althread stock into the taped hole and then set in epoxy. My question is what type of steel shank extentions should I use. The next question is how do I connect to the shank end of the tap. This is what I have been doing so far and every thing has worked ok so far but I might be just lucky. I take for lets say a 3/4 10 forming tap, a 5/8 drill rod and bore one end to .400 about 1.250 long. The other end of the drill rod I make the same as the end of the standard tap. I then grind down tap shank to .4006. I then heat up the drill rod to dull red and drive the tap in. I cool the drill rod with a rag soaked in water. I next have champhered drill rod tig welded up for a little extra force. Grind flush the weld and use it. Question #1 what should I do to the drill rod to make it stronger. #2 does the heating of the end of the drill rod make it weaker? #3 should I use drill rod or somthing like m2 tool steel. or 4130 post an answer or email me at snipped-for-privacy@netscape.net

Reply to
Don Huseman
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Be careful as some of the materials used to make taps will become brittle if tig welded, I've seen them snap near the weld if done that way.

As mentioned, silver soldering is a better approach.

Jim

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Reply to
jim rozen

Couldn't agree more. Silver solder is a wonderful thing.

michael

Reply to
michael

What kind of silver solder? How much silver should general purpose have in it?

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Reply to
RellikJM

Not silver bearing soft solder, which is used with an iron and has a ~700F melting point. You need a silver braze or silver solder that is used with an O/A torch, something like handy and harmon's ez-flow.

Jim

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Reply to
jim rozen

I can't afford to break a tap off. I am using what I think is the strongest way I know. I also have to have the end of the tap fit in a tap collet on my procunier tap machine. I am driving the tap with at least 1 hp of my 2 hp mag drill motor. But good idea mybe using 4130 heavy walled tubing would be better but the cost is about $50 to 100 verses 6 for drill rod

Reply to
Don Huseman

Yes it is very strong. It will be weaker if shrunk in place

*and* tig welded. The welding can ebrittle the tap under certain circumstances and if not annealed the tool steel can break ajacent to the weld.

Siver solder like that typically has about 20 to 30 ksi tensile depending on how the joint is made up - a proper joint will be as strong as the steel it is connecting.

Shink fits like that are tough to quantify because the surface finishes can vary greatly and change the amount of interference that is supposed to exist.

I would think a shink fit combined with the method of drilling a cross hole in a reduced diameter at the bottom of the hole in the extension would work well. This produces what amounts to a square sided hole which will drive the tap nicely.

This is how procunier fabricates their tap collets.

Jim

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Reply to
jim rozen

There are shrink-to-fit systems available for tooling used in machining centers. My knowledge of them is mostly limited to the fact that I can't afford one. They reportedly work quite well, so I've heard.

michael

Reply to
michael

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