taps and dies the hard way

[MattBower]

I was looking at a set of wing dividers with a wing screw to lock the dividers in place. It was made by Elmer Roush, and his site says it's patterned after a set that belongs to Colonial Williamsburg. He identified them as "16th century style." It got me wondering how a smith back then would've made a tap for something like that. (Once you have a tap, you should be able to make a die. I'm mainly interested in how you'd cut the tap.) Of course it'd probably be possible to hand file something like that with a lot of skill and patience -- although it'd take a very fine file -- but I'm wondering if anyone here actually knows how it was done. (Thomas, I'm looking in your general direction. )

[pkrankow]

Make the tap first. You can hand file a tap, then cut the die. If you have a lathe then it is easy screw cutting lathes are not new.

You can use a burr on a rod as a pilot tap. this would be a single point tool that then makes a nut from annealed hardenable steel, then drill out for the cutting edges.

Phil

[Sam Thompson]

First file a spiral groove on a piece of steel, form a cutting edge and harden it. Use this tap to cut an internal thread, form cutting edges and harden it. This die can then be used to cut another, slightly more accurate tap. Repeat the process until the threads have evened out. Threads made by this technique were common and were unique to the shop where they were made, standardised threads were not available until the mid 19th century.

[used-iron]

Those dividers were a necessary tool when cutting threads on a plain lathe,one without a lead screw. A series of parallel lines would be laid out down the length of the job. then step off with the dividers the pitch of the thread on the first line,and on each line in sucession, advancing by the necessary amount the thread would have progressed in the space between the lines. The points laid out would then be marked with a center punch and chalked or soap stoned so they could be seen. Then this would be cut by hand with a tool much like a wood turning chisel ,using the punch marks for guides. The tool would be hand held over a rest,and fed fast or slow as needed. This was slow work,as many cuts were needed. As stated in a previous post each shop had their own threads, no standardization .
Lee from NYS land of taxes

[myloh67]

Iniatially did they not twist slightly tapered square stock to form the tap..

[Mainely,Bob]

Roy Underhill gives excellent instructions how to do this in a colonial context in one of his books.
You forge the tap blank and anneal then wrap a paper spiral pattern around the blank which defines the threads as it is wrapped.You take a 3 corner file and follow the line,filing through the paper pattern to mark out the valleys of the threads if the work is small or both the valleys and the peaks if the work is large.You then file to desired final size and finish and file the flat on the end to drive it,heat treat it and "Bob`s your uncle".
If you can`t find this info let me know and I`ll search for the book.

[fciron]

Iniatially did they not twist slightly tapered square stock to form the tap..

Myloh, you can twist a square taper to make a quasi-wood screw, but not a machine screw or tap. Even if you got a usable shape it would have a four start thread.

[MattBower]

Thanks for all of these replies, folks. This is more or less roughly what I expected; it's just daunting to think of doing it on a fine thread machine screw. I'd like to talk to teh Williamsburg gunsmith about this. I wonder if they made their own taps, or if they cheat and use commercial taps.

It occured to me that the filing job might be a lot easier if the tap weren't round, but were instead closer to flat (or maybe an equilateral triangle), with the cutting edges on the narrow flats (or the points of the triangle). But that might have some other drawbacks.

Bob, I'll look for the Underhill reference. Thanks.

Used-iron, I follow everything you said as far as layout. I'm not sure I follow the lathe discussion. How would you advance the chisel by hand along a helical path, with the lathe turning at any reasonable speed?

[evfreek]

Hi Matt. I just did this, and it was quite a chore. Phil's answer looks correct, but it may not be all that practical. In those days, there were lathes, but screws were more like chased than threaded with a single point tool. Kind of like what used-iron was saying. Bob's suggestion about the paper spiral sounds really clever. I wonder how it would work on a fine divider thread.

Here is how I made mine. I built a jig out of wood and angle iron. I clamped a spring steel file guide (mangled sawzall blade) at the thread angle. At the far end of the jig was a screw with the same pitch sunk in two nuts, one captured, and the other to control slop. I then turned the screw 1/4 turn to advance the blank, and cut against the file guide with a three cornered file on a squared cross-section to make a four cornered tap. Four or three cornered taps are easy to forge, but do not cut well because they do not have the right relief.

It does work, however. I could thread the finished nut on by hand. But, I probably will not do this again very soon :blink:

[MattBower]

Hi Matt. I just did this, and it was quite a chore. Phil's answer looks correct, but it may not be all that practical. In those days, there were lathes, but screws were more like chased than threaded with a single point tool. Kind of like what used-iron was saying. Bob's suggestion about the paper spiral sounds really clever. I wonder how it would work on a fine divider thread.

Here is how I made mine. I built a jig out of wood and angle iron. I clamped a spring steel file guide (mangled sawzall blade) at the thread angle. At the far end of the jig was a screw with the same pitch sunk in two nuts, one captured, and the other to control slop. I then turned the screw 1/4 turn to advance the blank, and cut against the file guide with a three cornered file on a squared cross-section to make a four cornered tap. Four or three cornered taps are easy to forge, but do not cut well because they do not have the right relief.

It does work, however. I could thread the finished nut on by hand. But, I probably will not do this again very soon

Yeah, I have to admit that this is mostly a theoretical discussion for me. It's an interesting subject, but maybe not so interesting that I feel I just have to try it for myself. :)

[ThomasPowers]

IIRC Moxon speaks about die plates in "Mechanics Exercises" pub 1703.

I'll have to dig it out---our home computer is dead right now and I'm getting ready for a demo/show this weekend so I may be slow...

[MattBower]

IIRC Moxon speaks about die plates in "Mechanics Exercises" pub 1703.

I'll have to dig it out---our home computer is dead right now and I'm getting ready for a demo/show this weekend so I may be slow...

Thanks for the lead. I downloaded a copy from Google Books. He mentions screw plates and taps very early on; I'll have to look around and see if he goes into more detail.

[fciron]

Thanks for the lead. I downloaded a copy from Google Books. He mentions screw plates and taps very early on; I'll have to look around and see if he goes into more detail.

I can Moxon from Google? I'll see you all in a month.

[MattBower]

http://books.google.com/books?id=t_IRCzjTf08C&dq=mechanick%20moxon&pg=PP7#v=onepage&q&f=false

[thingmaker3]

I wonder if they made their own taps, or if they cheat and use commercial taps.

"Cheating" requires "rules." The rules were (and are) to meet customer specs with maximum return on investment. They were no less profit-motivated in Ye Colonial Days than we are today.

There were screw cutting machines being made and sold at least as early as 1739. The question then is whether it was money ahead for the individual American Colonial shop to make their own or order out.

[MattBower]

"Cheating" requires "rules." The rules were (and are) to meet customer specs with maximum return on investment. They were no less profit-motivated in Ye Colonial Days than we are today.

Agreed, but at CW "customer specs" include a certain amount of authenticity in the manufacturing process. People aren't paying $20,000 per rifle for mass production techniques. You can get that for under $1000. I'm just wondering how far CW goes with the authenticity. :)

[used-iron]

Matt, you start the thread with just a scratch, leading or draging the tool as needed to follow your marks at slow speed. After the thread is deepened the speed is raised. Have read that it would take the best man in the shop approx 1 1/2 days to put a coarse thread on a 12 inch shaft for a steam engine. Not a word said about the nut or female thread to mate up .
Lee from NYS land of taxes

[Mainely,Bob]

Female thread`s the easy part.
Chasing a thread like this usually involves a lead in area to help you get your feet under you.As long as you are making a part/bolt then it`s easy to extend that lead in area to allow for starting mistakes,which can be cut back to remove them(this ideally leaves a tenon which fits the hole to be tapped and aids alignment),and extra length.The extra length becomes your tap after you cut in the flutes.Any discrepancies cut by the short tap section will be formed up later by the actual threaded section of the part you are going to use.
Once you have everything working right you cut the lead in and tapping sections off and trim the part/bolt to length.
Essentially the part or bolt taps the hole it goes in.

[Frank Turley]

In the video, "The Gunsmith of Williamsburg", Wallace Gusler is using a screw plate. It has a few dies lined up on a single plate so in use, the handles would sometimes be eccentric of the part that's being threaded. The overvoice says that Gusler and his helpers made all of their hand tools "except files and hacksaw blades." I have taken apart a number of old flintlocks, and each tapered wood screw had to be labeled and put in its own envelope. The screws were not interchangeable; they were individually filed to shape.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

[wolfshieldrx]

Roy Underhill gives excellent instructions how to do this in a colonial context in one of his books.
You forge the tap blank and anneal then wrap a paper spiral pattern around the blank which defines the threads as it is wrapped.You take a 3 corner file and follow the line,filing through the paper pattern to mark out the valleys of the threads if the work is small or both the valleys and the peaks if the work is large.You then file to desired final size and finish and file the flat on the end to drive it,heat treat it and "Bob`s your uncle".
If you can`t find this info let me know and I`ll search for the book.

Actually, Roy told how to make taps and dies for cutting threads in wood. However, I can see how some of his methods might be adapted to metal. bart

[MattBower]

This is wonderful info, guys. I don't have a lathe, but I may have to take a shot at this by hand just as a tribute to all those of you who stepped up with input. Of course at the rate I work, it might take a couple years.

evfreek, I'm having a little trouble picturing your jig. I get the general idea, but I don't suppose you could have or could get a picture?

[Mainely,Bob]

Actually, Roy told how to make taps and dies for cutting threads in wood. However, I can see how some of his methods might be adapted to metal. bart

I`m doing my part to restore balance to the Universe.
I use metalworking taps to make threads in wood whenever I can. B)

[evfreek]

...
evfreek, I'm having a little trouble picturing your jig. I get the general idea, but I don't suppose you could have or could get a picture?

Hi Matt. Here are some pictures. They should be self explanatory. Oddly enough, there is some inaccuracy at the end of the cuts. I don't know where it is coming from, but I think it is caused by tilting of the file or taking too big of a bite. By the way, the first cut should be done with a knife-edge needle file. A typical triangular thread file is much too coarse.

[MattBower]

Yep, totally self-explanatory. Thanks!

[Nick]

This is something I've been thinking a lot about. I've looked closely at several late medieval (15th century) bolts and nuts recently as part of my studies, and I've been wondering how the nut was threaded. Since the bolts could only be used on a particular nut or hole, I was wondering if perhaps they are in essence self-tapping? Since these are some of the earliest screws, were they using lathes to make the components?