Inquiry on original style machine screw threads.

[Artificer]

Folks, this is going to be a really jumbled inquiry as I've been told so many things over the years that I am rather confused.

I've been informed that machine screw threads in the 18th century were more "formed" threads than "cut" threads.  If this is true, was this because the iron barrels and locks were made of iron or low grade steel and would not cut cleanly?  Or was it that they didn't precisely match the diameter of the wire/rod so the screw theads did not come out sharp on the end?  Or was it something about the taps and dies they used? 

Over the years I've had a few 18th century and early 19th century original mainspring vices that seemed to have rounded threads or perhaps they had just worn over the years? 

I've also seen a few original pieces that had flat top threads.  Not sure what the correct nomenclature there is for this without pulling out my copy of the Machinist's Handbook.

Does anyone have some information, sources or links where I could find out more?

[rich pierce]

This is covered in the JHAT booklets- Journal of Historical Armsmaking Technology.  Gary Brumfield is your best source.  Wrought iron has some grain if it it not extensively refined and the threads we use today would cut and tear at the grain, if I understand it correctly.  I am just parroting what i have read and may not have it right.  I do have 2 antique screw plates that may be appropriate for making old-style threads on wrought iron screws/bolts.

[Acer Saccharum]

I think the old machine threads were more formed than cut. I don't know how the female threads were made; probably a tap of sorts.

Tom

http://www.sizes.com/tools/thread_maudsley.htm

[BillC]

Actually most modern threads ( as in bolts and screws ) are also formed. This is done with two threading blocks that have v shaped grooves in them running past each other in a threading machine and rolling the threads on the under size shank of a screw blank. When the blocks squeeze the roots of the threads the excess material fills out the top of the threads to full size. This method is cheaper, faster, leaves less scrap and is stronger than a cut thread. If the old time screw plates did form the thread I would imagine that the blank would need to be slightly under size as well. It would be interesting to hear from some of the current or former Williamsburg folks on this.
Bill

[Dphariss]

Interesting.
Would need to find some old screw plates and see. But then we would need dated screw plates, tought to find I am sure.
Thread forming taps and such are still available. MSC etc.
Dan

[J.D.]

I have a screw plate very similar to the ones illustrated in JHAT I. The threaded holes appear to be intended to be used in sequence of larger to smaller, to swage the threads into a screw blank, as described in the text.

The threads, from what I can tell, appear to be similar to Whitworth threads, with rounded tops an bottoms.

Metric threads were used, in gun making, at least as early as the War of Northern Aggression, as my dear old Grandmother used to refer to it, but I don't know when the transition was made to American Standard threads.

God bless

[flintriflesmith]

There are three original screw plates shown in my article on lock making in JHAT Volume 1 [Figure 36 page 42] and a late 18th century engraved plate from John Wyke's Catalogue of Tools shows both screw plates and taps [Figure 37, page 43].

One of the screw plates in Wyke has a built in slot that is used as a tap wrench.

Gary

[doug]

     Although the screw plates in the photo below were probably made in the late 1800s,  hopefully you can see that some have slots associated with the holes and some do not.  It seems reasonable to believe that the slots were a form of cutting edge for use when threading.  It also does not seem unreasonable (to me at least) that both types of screw plates were available in the 1700s and early 1800s.  Bottom line is that I would suspect that some threads could have been crushed into the metal and some at least partially cut into the metal depending on which type of screw plate was being used.
     Just my opinion anyhow
     I guess the question in my mind is whether or not forming or cutting dies were made in the 1700s and later for a single thread rather than the screw plates with multiple thread sizes on them

cheers Doug

[Dphariss]

This old plug has somewhat rounded threads. I suspect it dates to the 1830s but ??

Dan

[Artificer]

Thanks to everyone for your answers.

I have two original screwplates (maybe a third) that I think date from the early to mid 1800's.   One has no marks at all and the other what looks like Round English numbers.   With this information, I'm going to take a better look at them and run some brass rod through them to see what kind of screw they make. 

[Dphariss]

Seems I was temporarily photo posting challenged. Should have double checked. But I spent the day looking for a deer to shoot, without much luck.

[Artificer]

Neat photo, Dan, thanks.

[Acer Saccharum]

Doug, neat shots of the thread plates.

Those grooves on either side of the hole, they may be to allow lubricant to run down alongside the thread during forming. If the grooves were much bigger, they would be a place to relieve the chips, but they are so small, I doubt they are for that reason.