Thread Cutting Question

Hello Carl,

Metal cutting taps and dies can be used to cut threads in wood freehand. I can't think of any way that they could be used to make threads on a wooden box. Threads in wood are normally cut with hand held chasers as the lathe rotates or with threading jigs that feed the wood into a rotating cutter mounted on the headstock. As the wood is fed into the cutter, it is rotated at some special rate, such as 16 tpi.

You can grind away 1/2 of the diameter of a metal tap and useit to hand chase threads. One tool then serves both as an inside and outside chaser. For a one time project, you can use a standard bolt that is about eight or ten inches long. Grind away the threads about half way through. This can then be used as a chaser, but it dulls quite quickly.

I should recommend my book, "Making Screw Threads in Wood," which is available from Amazon.com. It was published in 2001 by GMC Publications in England.

Fred Holder

Carl McCarty wrote:

"Fred Holder" wrote:iclip) As the wood is fed into the cutter, it is rotated at some special rate, such as 16 tpi. ^^^^^^^^^^^^^^^^^^ Fred, you must have been looking out the window when you wrote that :-) 16 tpi refers to thread pitch, not rotational speed. Any-hoo--the wood needs to be turning slowly, and the cutter has to be moved at just the right speed to produce the thread. It takes a little practice, which I am sure you have had, since you are pretty good at it.

Carl, I don't know how large an opening you are talking about threading, but most boxes have too large an opening to do this way. A tap this large would probably cost $100. You would still have the problem of threading the cover.

carl - you can buy chasers for taping wood, and you can buy chasers for taping metal - the latter are used in things like a Geometric die head and are frequently available very inexpensively on ebay or from a machine supply place - you also find them as replacements for pipe threaders, etc - just get a couple and braze handles to them and you are ready to tap wood - yes, you can make them by grinding away on a regular tap as well, but that's a lot of work and you'll detemper the tap when you braze a handle to it. You need a really sharp edge, and if you try to just "tap" wood by rotating a tap, you will generally get a messy (though occasionally functional) thread -

This thread kind of got my gears turning...

I recall seeing a number of websites a while back that had plans for spiral cutting on the lathe using a router with a cable attached to it that would turn the headstock as the router was slid along a carriage.

Now, I wonder if that would work for threading... it might take a little math, but I'd imagine a guy could rig up something to cut threads when the lathe is not under power by running a cable from the tool handle or a carriage that slides on the tool rest to a wheel and axle rig that is able to turn the headstock. Could be a Dremel tool, or just a nice sharp (tiny) v-chisel. It's a big leap to think a guy could make finer machine bolt type threads with that, but it might not be completely out of the question for something on the order of 2-3 tpi.

what you suggest is approximately what the bonney klein threading jig does - a 60 degree cutter goes into the lahte, and the item to be threaded is held in a chuck that is both rotated and moved by a hand crank.

Hi Prometheus

O.K. stop those turning gears, ;-))) it's all been done before, here's a very nice setup if you are interested, only one "heads up" before you start, to make good threads in wood you need real hard dense wood, that's all.

Have fun and take care Leo Van Der Loo

Prometheus wrote:

Leo, Sweet! TomNie

Hello Leo,

No, I wasn't looking out the window when I wrote that, but I was a bit careless. What I should have said, "rotated at a rate of movement of 16 rotations to one inch of movement, which produces a 16 tpi thread on the wood."

Incidentally, Beall has a rig that uses a router to cut external threads, but they sell a tap to cut the internal threads. The system would not be satisfactory for making threaded boxes because the threads are too coarse, but it works great for making wooden bolts and nuts.

Beall did have a rig for cutting threads that was actually designed to cut spirals in spindles, but could be set to also cut threads in wooden boxes. It wasn't on the market for very long and the one that I have was for my Nova Comet lathe, which I no longer have.

There are several threading jigs on the market, including the Bonnie Klein jig. The least expensive and the most difficult to use is the one sold by Craft Supplies LTD. in the UK. When mounted in a cross feed vise as one fellow did with it, the difficulty of use goes away.

There are many ways to cut threads in wood, but the best threads will only be cut in the very hard woods like boxwood and African Blackwood. The rotary cutter methods will cut fairly satisfactory threads even in the softer hardwoods, such as maple.

One other thing that I should mention, is that threads can be cut in softer woods if the wood is mounted in bowl mode with the grain running

90 degrees to the axis of rotation. I've done this for years with oak to make wooden faceplates and hand chased 8 tpi theads in the oak. I have made a couple of wooden boxes with the grain running across the box and I receintly tried chasing 16 tpi threads in a piece of pine in cross grain that turned out quite well.

All of that is much more than the fellow wanted to know, but I sort of got wound up this morning.

Fred Holder

Leo Lichtman wrote:

Bill

Now that sounds even easier! :)

Never ran across that one, but I'll look it up.

Thanks for the link, Leo!

*Note to self*

Stay the heck away from blackwood and boxwood, since they make maple seem like one of the "softer" hardwoods! :)

How does a guy even turn something that hard? Dry rock maple feels like my hands are getting pelted with sandblasting grains or tiny needles when I turn it, and it's definately not a material that I can quickly hog out (but it looks so nice, I can never resist turning it anyway)