Wood screw threads

oughtsix

oughtsix

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Am thinking about making butt plate screws for an old rifle. Do you make wood screws the same way as metal screws? The one I'm looking at is ~ 6 tpi, but there is a lot of root between the teeth. Is there some trick or is it just basic thread cutting?

Thanks,

-06
 
The 6 TPI is the easy part. It's cutting them at the taper that throws the monkey wrench in the gears, I hope someone comes forward on this one as I think everyone would like to know ho it's done.

"Billy G"
 
Yes you just cut the threads with a tool with a wide root. The threads on the main body are the easy part, getting the threads to come out right on the gimlet point is the hard part. 6 TPI seem very coarse, how big are these screws?

gimlet-point.jpg
 
I got distracted looking for a image of a gimlet point while I was writing my response and see Bill responded with almost the same answer.

Commercial screws are either cut on a tracer type machine or roll threaded.

Thomas J Sloan patented a machine in the mid 1800's to form and thread wood screws.
 
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I had just grabbed an old screw out that measured 6 tpi, an actual screw I hope to copy is about 12. Although I suppose the actual tpi may not be as important as the height of the thread is big enough to bite the wood. I was hoping someone would have a home shop answer to the gimlet point and taper.
Looks like playtime in the shop.
 
Make the point using a file or your compound. Grind a cutter with the right profile. Mount the cutter upside down in the tool holder. Lathe in reverse, cutter on the front side. Start cutting left to right. When you get to the start of the taper turn the compound in to follow the taper. A little tough but doable. Follow up with a file to clean up the tip.
Dave
 
I have seen a video of someone making wood screws but for the life of me I cant find it.
In the meantime, if you turned a taper on your stock that matched the TPI you should end up with a tapered thread form that had equally spaced, but also sharp vee crests for the length of the screw. Not sure if the taper would be too fast or slow for "technically correct" woodscrews.

Cheers Phil
 
Nothing good to report yet, first two I turned, the taper diameter was too small, and as the threads were cutting the screw shaft bent. You would think I wouldn't do it twice, but I tend to be a slow learner. Back to the drawing board.
 
I have seen gun screws that do not have a gimlet point; if the pilot hole for the screw is drilled to the root diameter of the screw, there is no need for the gimlet point. In screwing into hard wood, such as is used in gunstocks, the pilot hole is necessary to avoid splitting. For a grist mill restoration, we needed big long lag screws; they were screwed into big timbers, with pilot holes drilled; I cut the threads with a form tool with a wide nose and steep included angle, and it worked fine. I suspect that wood screws for gun work are, or were, mostly cut with an automatic die head, and I have seen a set of chasers for the purpose.
 
I made a wood screw on my 109 for the watchmakers lathe project, forget the pitch but it was a standard straight thread, worked fine. Just with straight threads it might be a good idea to drill a pilot hole first.
 
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