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Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?
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Author:  Kelly Anderson [ Fri Mar 15, 2019 1:48 pm ]
Post subject:  Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Checking out in the community:

Does anyone have a tap for tapered threads that is 3.75" major diameter on the small end, and 11-1/2 threads per inch? If so, may we borrow or rent it?

Thanks.

Author:  Adam Phillips [ Fri Mar 15, 2019 5:16 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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.

Author:  Kelly Anderson [ Fri Mar 15, 2019 7:02 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Adam Phillips wrote:
I would find a friendly job shop with a capable mill and just thread mill it
Good idea except the part in question is the boiler, not too portable.

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.

Author:  liallegheny [ Fri Mar 15, 2019 7:39 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Have you seen this?

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

Nyle

Author:  Kelly Anderson [ Fri Mar 15, 2019 8:14 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

That's very cool, and so close, but oh so far away. That tap has a 12 pitch thread, and we need 11-1/2 threads per inch. I know it doesn't sound like much, but it's enough to make a hash of the existing threads.

Thank you for the tip just the same.

Author:  NYCRRson [ Fri Mar 15, 2019 10:29 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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 ?

Author:  Earl Knoob [ Sat Mar 16, 2019 12:45 am ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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.....

Author:  Adam Phillips [ Sat Mar 16, 2019 3:14 am ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

"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.

Author:  fairmontdave [ Tue Mar 19, 2019 9:01 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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.

Author:  Ed Kapuscinski [ Tue Mar 19, 2019 9:24 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

Have you asked around on vintagemachinery.org?

Author:  crij [ Wed Mar 20, 2019 11:55 am ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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.

Author:  Kelly Anderson [ Wed Mar 20, 2019 1:09 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

crij wrote:
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.

Thanks for your interest. The issue with that idea is:
1. The housing in question wouldn't like to take the holes in question being that much larger.
2. We would need to set up a portable boring head (say a Bridgeport head) to make a true round hole of the proper size for tapping prior to attempting to use the tap. If we were headed that way, we would just tap it to 3-3/4"/12 TPI thread. We are set for 12 thread taps, just not 11.5 ones.

Thanks just the same. I'm happy to hear any ideas that are out there.

Author:  Donald Cormack [ Wed Mar 20, 2019 1:59 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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

Author:  Kelly Anderson [ Wed Mar 20, 2019 2:15 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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.

Author:  Donald Cormack [ Wed Mar 20, 2019 2:32 pm ]
Post subject:  Re: Anyone Have a 3-3/4" dia. x 11-1/2 TPI Taper Tap?

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

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