Threading problem

R

Richrd

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I need to thread a hole appr 1.25 inch to 1/4 x 26.

My tap isn't long enough and I don't know how to cut threads on the lathe in such a small hole. Is it even possible?

Has anyone ground the shaank down on a tap to smaller o.d. than the threads to get more reach?

Thanks
Rich
 
Does the hole need to be threaded the entire length? Can you drill to depth and just tap the part that needs threads? You only need about 3/8" of thread to develop max strength for a 1/4" bolt.

Yes, you can screw cut that deep but you need a carbide internal threading bar. Micro 100 makes small solid carbide bars that will go that deep. I have a Circle Machine inserted carbide bar that will go that deep in that small a hole.
 
Richrd said:
I need to thread a hole appr 1.25 inch to 1/4 x 26.

My tap isn't long enough and I don't know how to cut threads on the lathe in such a small hole. Is it even possible?

Has anyone ground the shaank down on a tap to smaller o.d. than the threads to get more reach?

Thanks
Rich
Click to expand...
Yes, you can reduce the shank diameter. Some taps do have a smaller shank (generally 'el cheapo taps). I believe "nut taps" have a reduced shank so one can just keep threading the nuts on - right through (never have to reverse rotation). 1/4-26 is an odd ball tpi - what is the application?
 
Yes it has to go completely thru, I really wanted to make the part 1.5 inch. 26 is a common thread if you're working on older British motorcycles,

The final parts will be stainless but I,m just a beginner and practicing on alloy and cold roll.
 
If the tap isn't important and you don't need much further to go, I suggest grinding the tool shank diameter down to reach inside the hole without hitting...like Chipper has said. It will reduce rigidity, but it shouldn't be an issue if you go slow and break the chips properly. Is it a through hole or a blind hole?
 
I have reduced the shanks on many taps to just under the minor diameter through the years.
 
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