Threads : Slight Mismatches ? Hints ?

[BillWood]

Hey,

I have cut a male 1.5" 8tpi thread to duplicate my lathe spindle nose. Call it Piece AA.

AA fits all of my chucks very nicely and I thought I could use it as a test gauge for future female threads.

I have cut 2 female 1.5" 8tpi threads and piece AA fits into them both very well

However my female threads will not screw onto my lathe nosepiece. They jam after approx 540 degrees

Keep shaving .001" at a time until they do fit ? This will be painful and awkward

Do I have to do the 3 wire gauging in order to carefully compare the two male threads and see where I have gone wrong ?

Bill

 

[tertiaryjim]

There is a metric thread that is very close to 8tpi and it can fool you unless you check your gauge very carefully. Its common on the china machines.
You might also have not given the theading tool enough nose radius so even though you use enough infeed the thread is shallow.

 

[Wreck™Wreck]

Measure the external thread over wires, the pitch diameter is the crucial dimension.
PD is Max 1.416 Min 1.409, use .072 wires and the Constant is .1077.

I did several 1 7/8-12 threads Friday morning, we didn't have a ring gauge that size so I had to resort to wires and it only took 25 minutes to fish the one that I dropped out of the soup )-: Even with a plastic tray under the part.

 

[mcostello]

As for usual practice I just threaded a 3/4" and 5/8" bar and used new nuts for a trial fit,threads came out perfect. Tapped the holes that would use the threaded shafts and had majorly tight threads. Drug out the thread micrometer and found out he threads were big by .008 on both shafts. New nuts must not have the precision that they had in the past.( Go figure.) Gotta check everything................

 

[BillWood]

Fixed.

Put the job back in the 4 jaw chuck.

Aligned the tool with the thread.

Made it deeper.

Awkward job but managed.

Results attached.

Looks like my test gauge male thread is a tad too small compared to the lathe nose and will enter a female thread before the lathe nose will.

 

[Paul in OKC]

A cheapie way to check male thread against male thread is with calipers. If you are wanting to make a gage to match the nose on a spindle, you can measure down in the thread with calipers and run the new thread to the same numbers. Will get you very close. Note this is not all the way down to the root, but I have done this many times with success. As for using nuts as a gage for I'd threads, rarely works when mating to another piece. Mass produced nuts are run towards the maximum in tolerance, I suspect.

 

[BillWood]

A cheapie way to check male thread against male thread is with calipers. QUOTE]

Thanks Paul,

That's clever and I will use it - all I need is a relative measurement - doesn't matter what the measurement is - all I want to do is make the things the same size.

Bill

 

[george wilson]

Your old South Bend is not going to have a metric thread.