A new thread about a new threader making a new thread

[IanW]

Hi CK. Bother!! Were the screws tassie oak? I was planning on trying some soon......

MA, I'm pretty sure the small (1/2" screw size) clamp is 'desert ash' (Fraxinus angustifolia), a very common street tree down your way & I collected a bit of it when I lived in Benalla in the early 90s. Although it turns & threads nicely, it's more brittle than European ash (F. excelsior), and it doesn't grow in the same direction for more than a foot or so at a time so the grain is liable to be pretty wavy, leading to sections of oblique grain in the turning (as demonstrated!).

I'm not sure what the larger (3/4") screw is; from the pic I think it might be wattle (out of my back yard), but I'll have to see it in the flesh before I attempt any firm id. When I can get sound, straight pieces large enough, these wattles make excellent screws but they are attacked by several small & large wood-munching insects creating defects that aren't always visible, which is what I suspect has happened. Sound wattle is tough & usually splinters rather than snapping cleanly like the piece above. Then again, I may not be able to id it because I have tried out so many woods over the years. Some I knew (or at least thought I knew) at the time but have forgotten since, others I was never really sure what they were to begin with.

My conclusions from all the mucking about over many years is that a very wide range of wood works for wood threading, particularly if you use a high-speed cutter to cut the threads. If it turns very easily (i.e. it peels freely off the skew), it will generally thread nicely either with threadbox or router. A popular choice in the northern hemisphere is birch (Betula spp.), which by our standards is a relatively soft wood, but it turns & threads super-easily & makes adequately tough screws. The last little while I've been favouring Chinese elm (Celtis sinensis) which is medium soft, but seems to be plenty tough enough and threads very cleanly. It's a very common, declared weed tree round here & I removed a couple of good-sized specimens from our yard years ago & kept a good pile of it out of curiosity. Various sources say the wood is garbage because it distorts too much when drying, but the boards (of varying thickness) I free-hand sawed from the trunks dried with very little distortion or splitting. I did discover borers absolutely LOVE the sapwood!

If you give your freshly-minted screws a good dose of Danish oil, it soaks right through the threads, which seems to toughen them up nicely. When the oil is thoroughly dry, get an old toothbrush & give them a good scrub with paste wax. This not only lubricates them, it will prevent any drops of glue that happen to fall on them from creating a very strong & permanent joint (damhik!).

Judging by the very old handscrews & bench screws I saw when living in Canada, you can expect a few generations of use out of sound threads. They do wear eventually, but the screw in my tail vise is >30 years on and still fine - it gets a little firmer in the wet season and creaks a bit in the dry (which I suspect is caused by the nut shrinking a little). I have no hesitation in leaning on it very hard when necessary. So far have never stripped any of my sound wooden threads though I have had sections of thread flake off because there was some defect creating a weak spot, but you can be pretty confident that sound threads will stand up to heavy use. A few chips along the threads, even quite large ones are unsightly but they don't affect the function very much.

When it comes to "nuts" just about anything from balsa to lignum will work, threads tapped across the grain are far stronger than screw threads in the same wood. I prefer softer woods for clamp jaws to minimise marking the job & just for fun I tried some Australian red cedar (Toona) for a set of small clamps. They work perfectly well & certainly don't mark anything I clamp with them (other than cedar ). Even pine will work for jaws, though taps tend to wander a bit in radiata because of the large earlywood/latewood difference in hardness.

Cheers,
Ian

[AJOE123]

I have thought about trying to grind some HSS cutters for thread cutting in the small router but longevity might be an issue in the ideal timbers.
Has anybody bought carbide cutters in say a 60 degree profile or maybe had some made?
Any thoughts?
Cheers
Tony

[Mountain Ash]

Carbitool sell a 60° cutting bit. I ordered mine through my local Total Tools. 1/2" shank

[AJOE123]

Great! How about internal?

[IanW]

I have thought about trying to grind some HSS cutters for thread cutting in the small router but longevity might be an issue in the ideal timbers.
Has anybody bought carbide cutters in say a 60 degree profile or maybe had some made?
Any thoughts?
Cheers
Tony

Tony, there are at least 3 options.

The Rolls Royce option (IMO) is the solid carbide, 3-cutter bit from Lee Valley. It's gone up a lot in price since I bought mine and postage will add further to that, but it does a very good job & would last the average wood threader a lifetime.

Option #2 is something like this. Not quite as flash as the LV bit, but does the job. The problem is the wider cutter meeds a bigger access hole & it can't be set as close to the first thread land in the jig (the closer you can sit it, the easier it is to get it accurately aligned), but in fact you need something wider than a 1/4" bit if you want to cut 3 tpi or coarser.

Option #3 is to grind your own from a 1/4" drill nit (or whatever size matches the collet of your router). Just grind a 60 deg included angle with a decent amount of relief and Bob's your aunty. They don't need to be deadly accurate, but will last longer & cut cleaner if you get both sides close. Of course they won't last anywhere near as long as a carbide bit, but they can easily cut a half-dozen handscrews before needing a touch-up. My router has 3/8" and 1/2" collets so I made a 3/8" cutter to do the coarse (3 tpi) threads like these:

2 inch 3tpi.jpg

Cheers,

[IanW]

Great! How about internal?

I assume you are leg-puling? If you know how to cut internal threads with a router, I will be very interested to learn the technique.....

Cheers,

PS - You can cut internal threads for box lids or reasonably large & not-too deep nuts with a small rotary tool driven by the screw-fed on a lathe, but it doesn't strike me as practical for clamp jaws etc. Tapping nuts is very straightforward & has little to gain from using high-speed cutters except when attempting to thread long grain, as you tend to do for box lids....

[AJOE123]

Thanks Ian
I have seen a picture of a two winged cutter for internal thread cutting ; probably related to box lid cutting.
I have not found a commercial source.
You got a nice result with the converted drill bit.
T

[DJ’s Timber]

Thanks Ian
I have seen a picture of a two winged cutter for internal thread cutting ; probably related to box lid cutting.
I have not found a commercial source.
You got a nice result with the converted drill bit.
T

Search for “Double Angle Cutter 60 Degree”

[IanW]

Thanks Ian
I have seen a picture of a two winged cutter for internal thread cutting ; probably related to box lid cutting.
I have not found a commercial source.
You got a nice result with the converted drill bit.
T

Tony, yes, the cutters I've seen are as you describe, little two-wing things. But as I said, you need some mechanism to rotate the "nut", whilst feeding the cutter forward at the desired pitch. I've seen setups using the lead-screw & carriage on a metal lathe to feed the cutter (attached to something like a Dremel), or some elaborate DIY gadgets. It's a fussy setup & really only worthwhile considering if you want to tap end-grain. Normal wood taps usually just rip the wood out producing no thread at all or a very mankey thread if driven into end-grain. (There are a very few woods that you can tap along the grain if you are very careful, but the threads are going too be very weak compared with threads made across the grain).

Tapping cross-grain is usually very straightforward, though it does need a good deal of effort to drive a one-pass metal tap through for a large size screw. This is where the more "primitive" method I wrote about in the AWR article shines. Because you cut the internal thread in several passes (usually about 5 or 6), you remove only small amounts of wood at a time, and the going is pretty easy.

It may seem a bit challenging at first, or it did to me, but once you get into it, things tend to fall into place pretty quickly. People have been making wooden screws for a very long time (reputedly since Archimedes), starting with very basic technology and using various methods. There was even an article in a very early FWW about a bloke who carved both the screws & the nuts for his bench vise with a veining tool. That's dedication!

Cheers,
Ian

[Mountain Ash]

Tony, I can only agree with Ian. Tapping the nut was easy, my troubles were solely related to getting the threads to match the nut.

[Mountain Ash]

20221030_120225.jpg

You can't have just one clamp