I need a 6" LH 3/8-16 tap.

[marrt]

Here's an odd ball question. As the title says, I need a long LH thread 3/8-16 tap. I can't find one. I tried modifying an existing tap by welding an extension (TIG, MIG, various cooling techniques), but it didn't work as the weld site was always too brittle. I don't have the capacity to anneal and harden (properly) and I can't chuck the item in a lathe. Any ideas to solve this problem?

 

[boosted]

Any reason these won't work?

Tap Extension For ANSI, Metric & NPT, Pipe | Tap Extensions | USA

Self-Locking Tap Extension (No Set Screws) has Smallest OD For Straight Through Reach Up To 12”. USA Steel Made In Nevada. See For Yourself!

tapextension.com

 

[jim rozen]

Don't weld. Silver solder the extension on. I've done this.

 

[gbent]

I make extensions a snug slip fit on the shank. Then drill a hole through one side at the bottom of the bore. Insert tap with a flat aligned with the hole. A dab of mig weld will secure the tap in the extension, and can be easily removed with a zip wheel.

To tig weld HSS, use Inconel 625 as a filler. Hastelloy W is even better, but about the most expensive filler available.

 

[Nmbmxer]

I make extensions the same way except I use a dab of silver solder in the hole. Lately I got some flux with silver solder paste and can stick the end of the drill in that then put the extension on and heat it with a MAPP torch and it flows easily.

 

[marrt]

Boosted...thankyou. I didn't run across that company in my search. Seems like a larger counter bore is required for the extension's clearance but these would be helpful in many cases.

Thanks for the silver solder recommendation. I have silver solder of course, but rarely use it for some reason. Silver solder paste sounds really interesting.

I appreciate everyone's comments. Some good ideas to try.

 

[SteveEx30]

Tap extensions are one of those projects you make when the shop is slow. Very very handy and you will have them for life.

EDM the square in the one end to be able to swap taps out.

 

[Don Davis 87]

Here's an odd ball question. As the title says, I need a long LH thread 3/8-16 tap. I can't find one. I tried modifying an existing tap by welding an extension (TIG, MIG, various cooling techniques), but it didn't work as the weld site was always too brittle. I don't have the capacity to anneal and harden (properly) and I can't chuck the item in a lathe. Any ideas to solve this problem?

You can buy what is called a "Pulley Tap" I'm not sure if they come in a Left Hand thread. but the length is no problem.

 

[technocrat]

+1 on the silver solder. Sit the tap threads in a tin of water.

 

[mnl]

Just remember, when you silver solder, both parts should be scrupulously clean, and it is not a gap filler.

 

[rogertoolmaker]

I make extensions a snug slip fit on the shank. Then drill a hole through one side at the bottom of the bore. Insert tap with a flat aligned with the hole. A dab of mig weld will secure the tap in the extension, and can be easily removed with a zip wheel.

To tig weld HSS, use Inconel 625 as a filler. Hastelloy W is even better, but about the most expensive filler available.

 

[rogertoolmaker]

Actually, with this method of extending the tap, 60-40 melts at 360 degrees and will work without disturbing the metallurgy in the tap. I used this many times over the years.
Roger

 

[Bill D]

I would drill a hole to fit the tap in steel. Then crimp/pound the pipe to fit the square. Soft solder when done.
Have you thought about making your own tap from a length of unhardened tool steel? Heat treat after cutting the threads and gashing for flutes. You can even make set of three or cut the threads in three steps to reduce cutting forces on a homemade tap. Each step long enough to cut the full through thread depth
Bill D

 

[EmGo]

You can buy what is called a "Pulley Tap" I'm not sure if they come in a Left Hand thread. but the length is no problem.

Just took a look, for fun. Maybe someone has them but I couldn't find any left hand pulley taps.

 

[Limy Sami]

FWIW you can Loctiite the extensions on, I've ''got away with it'' up to 1/2'' UNF in mild steel