2.250 x 14 TPI tap

[mksj]

How deep are the hole/threads? I think it would be easier to just cut a 14 TPI piece of 2.25" tool steel stock and make some something like 6 - 3/8" groove reliefs in it with a ball end mill. Cut a slight taper at the nose before you start threading it. Threading in cast iron and chasing threads I would not heat treat tool steel. If you can't make it work let me know and I can see if I can make something for cost of materials and shipping.

This is a 2 1/4-12 tap.

 

[OTmachine]

rwm, Sounds like a plan.

 

[JimDawson]

I guess I would grab a chunk of steel, thread it for 2 1/4-14, then mill some slots axially through the threads, like a thread chaser, and give it a try. All you are doing is trying to clean up the existing thread. You don't really have to cut much, if any, material.

For a one shot use, wouldn't need to be hard.

 

[Cadillac]

I have a tool like what OTmachine shows but a larger one. I will look tomorrow and see if it goes to that size which I think it does. I’ll let you know tomorrow. Happy Easter guys and gals

 

[rwm]

Thanks for the ideas guys. I have a piece of mild steel that is large enough. I may try to make a primitive tap.
MSKJ-that is a generous offer. Let me see what I can do.
Robert

 

[Chipper5783]

With such a large open bore, can you hand work the thread using a boring bar fitted with a threading tool (after all, just chasing threads in cast iron)? You may be over thinking this.

 

[rwm]

The threads are actually worse than I thought! I am going to try scraping with a 7/8-14 TPI tap and see how that goes. Maybe follow that with a homemade tap if needed.
Robert

 

[OTmachine]

You will probably have a hard time getting enough pressure on the flute of the tap to chase the threads. We used to have / use a tool we called a thread rake which did not work too good on ferrous material.

 

[rwm]

The tap is pretty long and the threads short. I was planning on putting some kind of handle on both ends of the tap, laying the threaded hole horizontally and using both hands and my weight to force the tap against the threads. To make a handle I may tap a blind hole in the end of a piece of aluminum and bottom out the tap.
Robert

 

[OTmachine]

The good thing about having multiple threads to engage the existing threads is that it will follow the lead of the thread, whereas a single tool point has nothing to guide it.