Handfiled stock and screw threads

[Elnathan]

I'm operating on the theory that the only dumb question is the one that you don't ask.

I was watching Mike Miller's video on handforging a flintlock awhile back, and noticed that he doesn't seem to have any problems just filing a forged piece round and then threading it using modern dies. Looking up the tolerance specs for modern screw threads suggests that the stock would have to be within .010" of round, which seems kind of difficult to achieve by eye the way he seems to. Now, I'm pretty confident that Mike is a very good hand with a file, and, moreover, he is using wrought iron which can be swaged as well as cut into threads. However, I can think of a score of projects, ranging from replacement thumbscrews for old tools to ramrod accessories to a spontoon head, that would be greatly facilitated by being able to turn and thread parts of forgings. Since I don't have a lathe I would have to do this by hand, but while my filing skills are getting better these days I'm a little skeptical about getting within .01 on a round surface, so I'm curious to know how close to perfectly round I'd have to get on mild steel.

At the moment I don't have a die wrench, so I can't just go and experiment a little.

(Welding piece of round stock onto the piece is of course another option, but has its own difficulties and might not be feasible with some some of the projects.)

[Bob Roller]

Filing something round is a skill that comes with practice and good quality files.
If you look at any lock I made or still do make,take a look at the little stud trhat
comes thru the plate from the mainspring.It is hand filed to the size of a #44 (.086)
drill.I use a medium cut square file with one side ground smooth to rest against
the mainspring and that's it.About 5 minutes or less later,the spring is ready for the
next step which is tapering the upper limb. I do this again with a milling machine and hand
file it flat to wherever it needs to be.One more adaptation of a power tool and an ancient
method in unison.

Bob roller 

[T*O*F]

To file round stock to size, mount the piece in your drill press and spin it.  Hold your file against the stock to reduce it.  Have a pair of calipers handy for diameter measurement.  Not much different than turning a piece of stock in a wood lathe.....you're just doing it vertically instead of horizontally.

[bgf]

It's not that hard with mild steel, though I doubt I can do it as well as Mike or Bob!  You just have to get close to round and the right size; in fact, you can thread a square section (not that useful for a gun, though).  As long as the largest section fits the die, it will make threads, with the caution that the closer to perfectly round and properly sized, the easier it is to get the threads straight and the stronger they will be.

Get a die and try it.

[okieboy]

 The needed tolerance for a screw blank varies with the pitch of the thread; 20TPI are much more forgiving than 80TPI because the height of the thread is so much greater. The more threads the shorter the thread height. That being said, I have hand filed stock for 6-64 threads with no problem. I just drilled a series of progressively smaller holes in a piece of steel to use as a gage and took my time, it was slow. It helps to have some layout dye to spot your high areas that need more filing.

[Bob Roller]

IF you have an old American made bench grinder,the right side probably has a 1/2x20
thread. If it does,a Jacobs type chuck with a 1/2x20 internal thread that will substitute
for the nut that holds the grinding wheel on the shaft.This can be used as a sorta/kinda
mini lathe for round filing and it's orientation is right for safer filing.I tried vertical filing
on a drill press just try it and didn't think it was a good idea and awkward at best.
I got my chuck at Sears and use it on a Delta/Rockwell bench grinder I bought new in
1975.I do no filing with it but it will hold small,expanding rubber wheels with abrasives
to polish a tight radius or some other use that adapts to this idea.
There are pictures on this forum Taylor posted showing my modification of the bench
grinder and I have two of them and they are a major help.

Bob Roller

[Elnathan]

Thank you, gentlemen. It looks like I will have to give it a try at some point. Probably best not to start with a breechplug, though.

[Acer Saccharum]

At Dixon's Mark Elliott did a screw making demo using 18th Century tools.

The forged screw blank Mark ran through a hollow mill that rounded the screw body in preparation for threading. The threading is done in a FORMING process, not cutting threads, but by forcing the screw blank into successively smaller threaded holes. This raises a thread on the screw body. 

[jerrywh]

 For the first longrifle I made I was like you and all the screws were made by turning a piece of stock in an electric drill held in the vise and filed while spinning them. It worked very well. I threaded them with a regular die. That gun is still around somewhere. I sold it to a cancer surgeon in Portland Or.

[David R. Pennington]

At Dixon's Mark Elliott did a screw making demo using 18th Century tools.

The forged screw blank Mark ran through a hollow mill that rounded the screw body in preparation for threading. The threading is done in a FORMING process, not cutting threads, but by forcing the screw blank into successively smaller threaded holes. This raises a thread on the screw body.

Aw man I missed that one!  I couldn’t get my head out of the blacksmith shop for very long.

[David R. Pennington]

I have hand filed forged breech plugs. I used holes bored in thin hardwood board to test by holding up to the window and look for daylight.

[Elnathan]

At Dixon's Mark Elliott did a screw making demo using 18th Century tools.

The forged screw blank Mark ran through a hollow mill that rounded the screw body in preparation for threading. The threading is done in a FORMING process, not cutting threads, but by forcing the screw blank into successively smaller threaded holes. This raises a thread on the screw body.

I'm familiar with that process, but always understood that it was for wrought iron and wouldn't work on mild steel. I also thought wrought iron actually required it, as cut threads had a tendency to disintegrate due to the grain in wrought.

[Mark Elliott]

I use 12L14 screw stock and it is swagged in a screw plate just fine.   Trick is getting it just the right diameter to start.    That I determined by trial and error; then I made the screw mill to reproduce it.

[Steve-In]

We use a lot of Form taps at work.  We do not form any OD threads though.  If you look at most commercial bolts and screws they have formed threads.  We form tap 8-32 in 316 stainless with little difficulty.
It requires more force to form threads than to cut them which is why screw plates have multiple steps I guess.
I most cases the threads are stronger than cut threads.