Shaft joining question...

[Engineeringtech]

Hi everyone. I am making a tap extension for my work. I have to braze the shaft to the tap holder, and don't have that much experience with brazing. I want the tool to hold up to the torque I am going to apply. I figured since this application might be similar to welding a flywheel to a crankshaft, people here might be able to answer my questions.

The tap holder is .406 dia. by 1.8" long W1 steel, and am joining it to a long shaft (3/8" dia. 12L14). I figure on reaming a .251" dia. x .5/16" hole in the top of the tap holder. I would then turn the end of the long shaft down to .250 dia. for a slip fit into the reamed hole. I know I can braze a filet at the joint where the shaft meets the tap holder, but would that hold up to the torque? Would any of the braze enter the 5/16" deep hole? I've seen some people put a small weep hole in the side of the shaft to get the braze to the joint, but I don't know if this is necessary. It might even weaken the tool.

Any thoughts on this?

 

[canadianhorsepower]

why don't you make thread instead and use red Loctite
much simpler and can be taken apart with little heat if needed

my 2cents

 

[Swifty]

Threading and loctite may not hold when withdrawing the tap if there is a fair bit of resistance, may tend to undo.
Brazing will not flow well, much better to silver solder.

Paul.

 

[Wizard69]

why don't you make thread instead and use red Loctite
much simpler and can be taken apart with little heat if needed

my 2cents

I can recommend this approach, I've done it several times to solve problems at work. Sometimes I use the bearing retainer Loctite if I have any, 690 I believe. In my case these are smaller taps but this doesn't appear to be a large tap so it shouldn't be a problem.

I dispense with the tap holder though and use drill rod or bar stock, drilled out to accept the taps shank. In most case we don't have clearance for a tap holder so you millage may vary.

An extended tap holder isn't a bad idea but I would braze or silver solder to it. The main reason not to is to avoid messing with the heat treatment. In any even there is an easy solution for larger taps, get a set of square drive tap holders. Here are some examples: http://www.irwin.com/tools/taps-dies-sets/two-in-one-tap-wrenches, with a price guess > http://www.grainger.com/Grainger/tap-wrenches/machine-cutting-tools/machining/ecatalog/N-c8uZ1z13jdh, here is a different approach > http://omegatec.com/tap-holding-sockets-female-square-drive-sae.aspx, here is a well respected set > http://www.lislecorp.com/divisions/products/?product=398

Getting the socket sets would be well worth the money, with 1/4" or 3/8" drives you basically have no limitation on length.

 

[Engineeringtech]

why don't you make thread instead and use red Loctite
much simpler and can be taken apart with little heat if needed

my 2cents

Interesting idea that I never thought of. But I'm still a little concerned that the loctite would give when I tried to unscrew the 5/16-20 tap. Red loctite is pretty tough stuff though....

 

[Engineeringtech]

I can recommend this approach, I've done it several times to solve problems at work. Sometimes I use the bearing retainer Loctite if I have any, 690 I believe. In my case these are smaller taps but this doesn't appear to be a large tap so it shouldn't be a problem.

I dispense with the tap holder though and use drill rod or bar stock, drilled out to accept the taps shank. In most case we don't have clearance for a tap holder so you millage may vary.

An extended tap holder isn't a bad idea but I would braze or silver solder to it. The main reason not to is to avoid messing with the heat treatment. In any even there is an easy solution for larger taps, get a set of square drive tap holders. ..........

Thanks. I have some Loctite Stud Lock. I believe it is just as strong as the bearing lock. I had already intended to peck out a semi-square hole in a piece of W1 steel using our manual Bridgeport. The socket sets sound interesting, but as this is a one time use, I can't justify the expense.

 

[Wizard69]

Thanks. I have some Loctite Stud Lock. I believe it is just as strong as the bearing lock. I had already intended to peck out a semi-square hole in a piece of W1 steel using our manual Bridgeport. The socket sets sound interesting, but as this is a one time use, I can't justify the expense.

The expense is an issue, bar stock is the cheap solution. If you have enough clearance you can always drill and tap the rod for set screws to grab the square at the end of the tap. That does weaken the rod though. I've never had an issue with Loctite up to 1/4-20, but do follow the instructions with respect to lean parts. Take your time and you should be able to go larger with little issue.

As to those socket sets, they have me thinking about a home made tapping stand. The nice thing here is that you can use those very same sockets elsewhere. So if a project comes up like you have, you just walk over to the tapping stand, grab the right tap and go to it. The only possible issue would be run out.

 

[pfb]

Hello,
If you want to braze a tap to a extention rod, it is clever to put a raw patato on the tread of the tap. It helps to hold the hardness of the tap.
And you can eat afterwards.
Peter

 

[Engineeringtech]

Neat idea! I would imagine that the moisture of the potato evaporates and keeps the tap from heating up, losing the temper. I'll have to try that. Thanks.

 

[Engineeringtech]

The expense is an issue, bar stock is the cheap solution. If you have enough clearance you can always drill and tap the rod for set screws to grab the square at the end of the tap. That does weaken the rod though. I've never had an issue with Loctite up to 1/4-20, but do follow the instructions with respect to lean parts. Take your time and you should be able to go larger with little issue.

As to those socket sets, they have me thinking about a home made tapping stand. The nice thing here is that you can use those very same sockets elsewhere. So if a project comes up like you have, you just walk over to the tapping stand, grab the right tap and go to it. The only possible issue would be run out.

Nice idea. Normally, I wouldn't use a whole set of tap extensions. But build them into a tapping stand, and I'd get more use out of them.

I guess there are a lot of ways for me to roll my own extension though. There's the male thread with Loctite. Brazing the joint, while using a potato to keep the tap from losing it's temper, using setscrews, and I think a 1/8" dowel pin might join my two pieces of steel just fine.