Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Adam Phillips · **Posted:** Fri Mar 15, 2019 5:16 pm

If nobody has one, you could use a thread mill. To my knowledge, our Trak mills don't have the right package to do tapered threads with a thread mill. Our Moris frequently do tapered threads. I would find a friendly job shop with a capable mill and just thread mill it using the mating part as a plug gage, if available. Buying one of those taps new would be WAY more expensive than a couple of hours of machine time and a new thread mill. Good luck.

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

liallegheny · **Joined:** Mon Feb 26, 2018 12:47 pm **Posts:** 4

Have you seen this?

https://www.ebay.com/itm/steam-locomoti ... Swwo1XctSg

Nyle

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

NYCRRson · **Joined:** Fri Aug 20, 2010 8:25 pm **Posts:** 509

Maybe you can super cool the material to be tapped with nitrogen, then thread the ID as a 12 TPI thread, once it warms back up you will end up with a 11-1/2 TPI thread.....

Or heat up a 12 TPI tap until it is a 11-1/2 TPI tap....

Just kidding, if nobody has one of those taps, you might get by making one out of drill rod and skipping all the heat treating steps. For a few threaded holes a sacrificial "tap" might be cost effective. Maybe taper thread a chunk of drill rod, mill in three/five/seven flutes, sharpen it with a stone and cut your thread ?

Earl Knoob · **Posted:** Sat Mar 16, 2019 12:45 am

One has to wonder how many innocent washout plug holes were buggered by some guy chasing the threads with a 12 TPI tap.....

I know of at least a few.....

Adam Phillips · **Posted:** Sat Mar 16, 2019 3:14 am

"If we must, we can cut the rivets holding the part in question to the rest of the boiler, thread mill it and rivet it back on, but would really rather not."

I know what you mean. I don't have enough mass to handle a 90-gun. The price of a new tap seems justified and it can stay well preserved on the shelf for the next job.
Good Luck.

fairmontdave · **Posted:** Tue Mar 19, 2019 9:01 pm

You may want to try Melvin at ALMAC Machine in Johnstown, PA.....he has, I think, every known tap ever made and lot's of big ones. They have essentially the tool room of the old Beth Steel Plant repair machine shop. I am sure he would help out if he has one.

Ed Kapuscinski · **Posted:** Tue Mar 19, 2019 9:24 pm

Have you asked around on vintagemachinery.org?

crij · **Joined:** Sun Aug 22, 2004 12:15 am **Posts:** 585

Might be a stupid question, but the stupid ones tend to be the question not asked...

What about re-threading the hole to the common 3.5"-8 NPT (4.0" OD) and then have someone make an adapter to go between the old and new threads? Most people would not notice the added part, and you can use off the shelf tooling on the boiler. In addition, no riveting would be involved.

Regards,
Rich C.

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

Donald Cormack · **Joined:** Fri Dec 17, 2010 2:41 pm **Posts:** 166

Kelly,

Gonna suggest something really stupid here: Have you considered making the tap yourselves? Your shop is certainly outfitted with all the necessary machinery and talent to pull this off.

Best,
DC

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

Donald Cormack · **Joined:** Fri Dec 17, 2010 2:41 pm **Posts:** 166

Kelly Anderson wrote:

Donald Cormack wrote:

Gonna suggest something really stupid here: Have you considered making the tap yourselves? Your shop is certainly outfitted with all the necessary machinery and talent to pull this off.

Yep, that's probably the next step, but it doesn't hurt to ask.

That job/process would be a good candidate to share in your next iteration of "The Latest from the Strasburg shops..." Food for thought anyway.

Best,
DC

Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Who is online