Machining Tap & Die for Woodworking

I'd like to make a tap & die to make screws and nuts from wood.

While one inch and smaller tools are commonly available, I have some ~1 3/8" hardwood curtain rods that I'd like to make into bench vise and/or clamp screws.

This fellow advises that regular steel and 6 TPI or so are fine.

http://www.woodworkforums.ubeaut.com.au/showthread.php?t=8513

While I have access to a lathe and Bridgeport, I've never made anything like this.

Would the threads be Acme, screw or something else altogether?

I'm not much of a machinist so any advice or experience you can share is appreciated.

I've done wood threading with dies. Acme is better since the sharp points tend to break off. Hard to buy but possible if you're making your own. However, there's a lot of chipping with dies and they don't generally look very nice or stay straight. What I'd recommend is threading with a router. It's a simple jig. Just a guide tube, a pin and a mount for the router. Once you start, it's self-spacing. Use a 60 degree V cutter. Same jig can make any thread. Just a different guide tube. I'm sure there are plans on the net. Then you just have to make a tap. Look at the commercial wood taps. Not hard to make. Much less trouble than a tap for metal. Cut a thread and taper it, counterbore the end, mill a slot all the way across. File some relief to the teeth. They usually have a T handle.

Beall made a router-based device for external threading of wood, and taps to match. The design could be adapted and enlarged for bigger screws. It came with a 1/4" shank router bit with a sharp 60 degree pointed end. Penn State Industries made a lathe-based device for cutting short male and female threads in wood boxes.

I knew a guy who used a metal lathe and tool post grinder to cut male threads in wood. He did not have one, but Dumore made a thread grinding attachment for their No. 5 tool post grinders. It allowed the wheel to tilt to the correct helix angle for the thread to be cut. For wood, I would use a sharp new 60 degree horizontal milling cutter instead of a grinding wheel. Or the 60 degree pointed router bit in a small router could be adapted to a metal lathe tool post.

Larry

Making taps and threading boxes (like a die, but single-point) for wooden threads is explained in one of the "Woodwright" books by Roy Underhill. I sppologize for not being able to remember which one, but it would be one of the original four books, not his most-recent fifth work.

Thanks all for your advice.

I don't own a router so I hadn't considered using one. I can now see the advantage over a die!

Thanks Bob and Larry for the 60 degree bit info and the router idea.

Interesting idea your friend had Larry using the post grinder.

Thanks for the concise description of tap making Bob. I believe I can handle that.

I haven't had any luck finding a plan for the jig and guide tube you described Bob.

I'll buy a router if I can figure out how to make it work for threadmaking.

The Beall threading equipment is not too expensive. Just looking at one will show you how to make one in a larger size. Note the bit is solid carbide and might be otherwise difficult to find. You can run a 1/4" shank bit in a small (inexpensive) router, like a laminate trimmer. The small router is easier to adapt to a lathe, too.
http://www.bealltool.com/products/threading/threader.php

Larry

Never make an acme thread for wood. The correct thread for wood is a 90 degree V form. The crests do not have to be sharp. In Colonial Williamsburg,I made wood screws up to 12" dia.,with threads 2" wide. We made the threads for many items,right down to thumbscrews for marking gauges,by using a metal lathe. we made a fixture for holding a wood router motor in the toolpost.the cutter was applied at a 45 degree angle,which worked out nicely for the 90 * thread that wood is supposed to have.

The trickier part is the tap. For clamps and other more usual size threads,I made taps. Wood threads are much more coarse than metal threads,so metal taps are not appropriate if you want decent looking wood threads. For 1" dia,the thread is like 6 threads per inch. The old taps were often made tapered,and ground square. They are diffucult to keep properly aligned in holes.

A more advanced type,which they had even in the early 19th.C.,which I always made,was a straight,threaded drill rod. At the cutting end,the thread is cut down to thread depth,leaving only a fine line of the original thread depth. On a 1" tap,this cut down cylindrical area should be about 5/8" long. Length is not too important.Just make it long enough to guide the tap into the wood. Then,turn a flat nosed tool sideways in the toolpost of the lathe,and run the carriage back and forth sideways,and plane away the first thread until it is planed so that you have a full width thread that is square on the end.In other words,a 90* thread that is flat on its end. Drill,or mill a hole right at the end of this thread,so that the hole leaves the formerly square ended thread with sharp,scalloped cutting edges. This hole can be about 3/16" in dia. This is what cuts the wood. Last,drill a hole into the very end of the tap so that on a 1" tap,the walls of the cylinder are almost 1/8" thick. The hole drilled through the square end of the tap exits on the inside of the hole in the end of the tap. This is where the shaving from cutting the thread into the wood goes.

You must harden the end of the tap,so that the cutter is hardened,and draw it to a dark brown color.

To use the tap,drill a hole into the wood to be threaded. Make the hole a little larger than the outside diameter of the cylinder on the end of the tap. The tap will easily cut into the wood with some downwards force while twisting,and the wood you are cutting away will come out of the end of the tap.

Wow

That is totally different!

I'm having a hard time picturing/understanding the tap making process but thanks for the totally new methods!