Know how on screw plates - Mark Elliott or Uncle Jim or Eric VonA?

[rich pierce]

I’m trying to learn what diameter stock to use to thread up in a screw plate. And I’m wondering if it’s trial and error until one knows, or if perhaps the key is in the screw plate holes themselves.
For example, would a rod that just passes hole #1 be there right size for threading in holes 4 and 3?
Similarly, can one use the holes to know the right drill size to use to tap holes? I need to make some taps.

[Bob Roller]

Do you intend to use this to thread screws or as a gauge to see what thread is on a bolt or screw?
A tap/drill chart will tell you all that's needed for drills and threads both fine and coarse as well as metrics.
Bob Roller

[Daryl]

Is it possible theses screw plates were meant to thread iron screws and won't work with steel?
I bought one at an antique store on Vancouver Island for $10.00 & gave it to Taylor. I don't  know
if he has attempted to use it, yet.

[rich pierce]

They work very well for me. The steel must be annealed and a slight taper made at the end to start it. Then a touch of cutting oil and away you go.

Bob, these screw plates thread entirety differently from cutting dies. There is no cutting at all. The threads are swaged and do not match the standard thread sizes we’re familiar with. The pitch is 32 on my screw plate for a good many of the holes.

[bluenoser]

This is right off of the top of my head so I may be way off in left field.
A 32 TPI thread will have a fixed thread depth dependent on the thread angle regardless of the diameter of the screw.  Let's assume it is a 60 degree thread angle. I BELIEVE the full depth of a 32 TPI unified (60 degree) thread is in the area of 0.019".  For a 75% thread, the diameter of the stock would be the diameter of the hole in the plate plus ((2 x .019") x .75).
How's that for a convoluted answer?
Surely, someone else will come up with a more down to earth answer.

[rich pierce]

This is right off of the top of my head so I may be way off in left field.
A 32 TPI thread will have a fixed thread depth dependent on the thread angle regardless of the diameter of the screw.  Let's assume it is a 60 degree thread angle. I BELIEVE the full depth of a 32 TPI unified (60 degree) thread is in the area of 0.019".  For a 75% thread, the diameter of the stock would be the diameter of the hole in the plate plus ((2 x .019") x .75).
How's that for a convoluted answer?
Surely, someone else will come up with a more down to earth answer.

I like it! I will try that for sure.

[James Wilson Everett]

Guys,

Check out the topic "18th C Screw Plate Use".

https://americanlongrifles.org/forum/index.php?topic=19172.0

Jim

[rich pierce]

Thanks, Jim. I’d forgotten I’d asked the same questions before, and gotten the straight scoop from you.

[Bob Roller]

They work very well for me. The steel must be annealed and a slight taper made at the end to start it. Then a touch of cutting oil and away you go.

Bob, these screw plates thread entirety differently from cutting dies. There is no cutting at all. The threads are swaged and do not match the standard thread sizes we’re familiar with. The pitch is 32 on my screw plate for a good many of the holes.

I see no advantage in such a device,a 6x32 is an abomination because it's a too small shank for that thread, a 10x32 makes a bit more sense and an 8x32 is acceptable but just barely.
Bob Roller

[rich pierce]

The advantage is doing it the way it was done. It’s a preference thing if done de novo, and a practical thing when restoring original lock screws.

[davec2]

In the aerospace world I have often used fasteners that had a "rolled thread" rather than a cut thread.  Much stronger.  The old timers were ahead of their century !

[runastav]

Hi all! Here is how I use the plate, no no dont start the macine but use hand on chuck
Runar

[rich pierce]

Runar, that will keep it square!
I still wonder if they had a trick to know the required sizes of the portions to be threaded. Because micrometers may have been scarce in the 1700s and earlier.

[Clark Badgett]

Runar, that will keep it square!
I still wonder if they had a trick to know the required sizes of the portions to be threaded. Because micrometers may have been scarce in the 1700s and earlier.

As far as I can tell, Micrometers were not invented until the late 1800s. The Vernier scale dates to the 1630s, it is conceivable that it could have been applied to calipers by the time we are interested in. My Vernier calipers and depth gauges are extremely accurate.

[Mark Elliott]

The answer as best I could determine is the next hole up(larger) on the plate.