Making a top jaw screw

[Rich Jakowski]

I’m about to make a top jaw screw for my 1803 HF lock. I have an exact-size  photocopy of an original and plan to make one from ½ inch diameter water hardening drill rod. Turning down the threaded portion is no problem since I have one of those Harbor Freight 7 X 10 minilathes which is great for this type of small work. My question is the best way of shaping the top portion of the screw. The simplest way would be to use files while turning the screw in a lathe, but that seems like an awful lot of metal to take off with files. So, I’m thinking I could use a tool bit to remove most of the metal and then finish up the final shape with files. What’s the best tool bit shape to accomplish this? Can it be done with one shape, or would it take a couple of different shapes to do the job?

Don’t forget guys, as mentioned in the past, I’m no machinist, just a basement duffer who’s been tinkerin’ with charcoal burners for a good part of his 69 years.

[karwelis]

unless you have a radius cutter for that lathe, you are stuck with the files. also you will find it a good idea to cut(file) the head before you thread it.

[D. Taylor Sapergia]

I would turn the threaded part down first and thread it.  Cut the filisters or molding/coves at the top of the threaded length along with the deep cove that forms the base of the ball.  Then cut off the jaw screw with enough metal to form the head.  Reverse the screw in the chuck, and you can protect the threads with some thin sheet brass or aluminum.  Now use whatever cutter you like to take away the bulk of the ball, and finish it with files.  The whole thing is going to use perhaps an hour.  When you draw the temper, take it to a beautiful peacock blue for a spring temper.

[doug]

   I think I would make the screw overly long initially so that I could support the threaded end with a center in the tail stock.  After threading I would rough out the head with a narrow cutter like the one you would use for cutting square threads then cut the screw off the stock I was working from and turn it around in the chuck and finish with files.  You can protect the threads by putting a female thread in a piece of scrap metal and screwing the screw into that rather than clamping directly on the threads with or without shielding.

cheers Doug

[J.D.]

   I think I would make the screw overly long initially so that I could support the threaded end with a center in the tail stock.  After threading I would rough out the head with a narrow cutter like the one you would use for cutting square threads then cut the screw off the stock I was working from and turn it around in the chuck and finish with files.  You can protect the threads by putting a female thread in a piece of scrap metal and screwing the screw into that rather than clamping directly on the threads with or without shielding.

cheers Doug

I'm no tool maker, but that would be the way I would do it, if you don't have the confidence to cut it to the various radii and mouldings.

That said, radius tools are easily ground to nearly any configuration.
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[44-henry]

You can also buy (or build) a ball turning tool for your lathe which will allow you to cut a very accurate radius.

[B Shipman]

I use Taylor's method.  cut your radiuses on the lathe, but you're going to do some filing. Obviously there are set ups to do these things quickly but these are quantity operations and the tools and set up will take way longer than the bit of file work.

[davec2]

If you are only making one screw, you can do it with files.  I always end up making more than one of almost anything I make, so, in this case, I would grind a form tool.  It doesn't take as long as you might think and about as much time as forming the part with files.  However, now you can easily make as many identical screws as you like. 

Machine and thread the shank and leave enough material to form the head.  Put a piece of 3/4 or 1 inch scrap steel, brass, or aluminum in the chuck, face the end and then drill and tap to receive the threaded shank of the top jaw screw.  Using whatever size lathe tool blank (available for a few dollars from most machine supply houses) layout and grind a form tool that looks like half of the top of the screw.  For very narrow moldings and tight radius details, you can use a Dremel tool to grind the form and relieve the cutting edge.

Screw the blank into the threaded hole in the scrap piece still in the lathe jaws.  Set up the form tool in the tool post and plunge it directly into the material left to form the head of the screw.  You should be able to form the screw head in one plunge.

[Rich Jakowski]

davec2 -

I like that form tool idea and think I'll give it a try - if  your making gun parts from scratch why not make several instead of just one. Grinding a blank tool bit  to look like half of the screw top seems pretty straight forward, but do I have to undercut a form tool to make it cut effectively? I assume this would be somewhere around 7 degrees, similiar to the angle used for a regular tool bit. Another issue is whether my minilathe has enough power to make this kind of cut, but I assume if I take it real slow I can "git er done".

[Dale Halterman]

Is this an original or a repro lock?

Dale H

[doug]

     I think the concern that I would have with a form tool is with tool chatter because of the broad cutting face.  That would be accentuated by any slop or looseness in the headstock.  I tend to make screws from drill rod which is not particularly free machining.

cheers Doug

[Rich Jakowski]

Is this an original or a repro lock?

Dale H

Dale -

This is a repro lock - actually a TRS parts set.

Rich

[D. Taylor Sapergia]

I make mine from mild steel mostly, and case harden them.  They are very tough and resist corrosion, and with the hard threads, they tighten more securely than unhardened steel.  But now that I have a great lathe, I'm going to grind a cutter and give it a whirl, just for the fun of it.

[Acer Saccharum]

For much of this kind of work, round head screws and such, I use a plain lathe bit, but move the carriage toward the headstock and crossfeed out at the same time to replicate a curve. An easier approach is to move the carriage in a little, move the cross slide out a little, step and repeat until you have a shape close to what works, then finish the shape with files. With a little practice, you will get quite good at turning a radius on the end of a rod.

A lathe bit ground with a small rounded nose will nicely between the ball of the screw where it necks down to the collar of the screw.

As in all metal and woodwork, knowing the job you need to do often requires that you shape a special tool just to do the job. Eventually you will end up with a drawer full of tool bits of different shapes and sizes, from thin blades, to vee tools for threading, to convex nose tools, to concave edged bits. The list is almost endless.

[davec2]

Rich,

Seven degrees as a relief angle would be fine.  Make sure the tool is on or just below the centerline of the part.  If your lathe is big enough and the part is held well enough ( that's why I recommended making a "holder" for the threaded shank of the screw), chatter should not be a problem.  You will have to experiment.  (Actually, the best way to hold parts like this is with a collet).  If chatter turns out to be an issue in your set up, you can also divide the profile of the head of the screw into two or more parts lengthwise.  That is, grind a tool for the neck and another for the rounded head.  Plunge cut the sections independently starting at the outer most end away from the chuck.  The use of multiple tools has the added advantage that you can mix and match - make a screw with this neck and that head and that base molding, etc.  You can also get different profiles by changing the mounting angle of a given tool in the tool post.  This changes the "aspect angle" of the tool as it enters the work and can drastically change the range of forms that can be cut with the same tool.

The following parts were all machine with ground form tools.  Although these are mostly brass, I make all the same parts in steel as well.

The swivel tops for these items:



These gunsmithing hammers (brass and steel)



Cannon linstock



Ram rod tools (steel and brass)



Depth gages





I use 12L14 for screws - machines beautifully - and then case harden the screws.  I will post some pictures of several form tools and the resulting parts when I get a chance.

Dave C

[Acer Saccharum]

Some people are easy to hate.

Acer Sack O' Rum

[davec2]

I know the feeling, Tom !

Keep up the outstanding work !!

DC

[Rich Jakowski]

...and to think, all I'm trying to do is make a top jaw screw. I feel like a complete clutz.