18th c Screw Plate Use

[James Wilson Everett]

Guys,

Just a note to bring this topic back to the top.

Jim

[James Wilson Everett]

Guys,

To bring this topic back to life.

Jim

[Bubblehead]

Looking at the taps, do they also swage female threads? I see some with a gouge parallel to the shaft filed in and some without.

[LynnC]

This has been a remarkable education in early screw threading.  I have run across a few screw plates over the years but all have been for the tiniest of screws. The largest perhaps a no. 4. Im will keep looking as I would like try what I’ve learned here.

[James Wilson Everett]

Guys,

Yes the 18th c. taps do not cut the threads, they swage them.  The little grooved capture the small amount of swag dust, tiny metal chips, that you get in the process.  For the female threads the I.D. of the hole is much smaller after the threads are swaged.

Jim

[Bubblehead]

I've just spent a few hours on the trial and error process of determining the proper rod size for the screws. It is not an easy task! Once that's done I'm starting on the various screw mills. Any tips on making them?

For your plate that uses modern threads, did you just drill and tap it as you normally would? And if so are you still swaging or does the modern version cut threads like a modern die?

Thank you again for once again sharing your wealth of knowledge here!

[heinz]

Jim, is the screw plate used to swage the tap?  I have thought about making a tp by swaging an annealed section of drill rod.

[James Wilson Everett]

Guys,

Great questions here, I will attempt to provide answers.

Heinz:  Yes the screwplate is used to swage the tap. With the paired holes, one is slightly larger but with the same pitch.  The larger hole is for the tap and the smaller hole is for the thread.  The tap must be very slightly larger than the thread to provide a bit of clearance, otherwise the male screw will be quite difficult to install in a tapped hole without this clearance.

Bubblehead:  Check out the posting in this topic for January 13, 2016.  This shows an easier way to determine the correct diameter for the blank shaft before swaging the threads.

Jim

[Pukka Bundook]

This has been a very enlightening thread, James!
I have a screw plate that has lived with the family forever, but was unaware of how the holes ran, for making the taps.

Thank you!

Richard.

[heinz]

Thanks James,  that simple pairing had never occurred to me.  I had thought it was two stages of swaging the screw, I get to laugh at myself on that one :-)