Thread: A wooden thread thread
6th Mar 2018, 04:58 PM #1
A wooden thread thread
The topic of wood threading pops up on a fairly regular basis, and there have been a number of threads (pardon the pun), about wooden screws, or where they have entered the discussion. Over the years, a lot of information has passed to & fro, but unfortunately, much of it is difficult to impossible to find on a search unless you know exactly what you are looking for, and many of the accompanying pictures are lost. Wood threading has come up in unrelated threads again a couple of times recently, so I thought it might help anyone interested in the techniques if I did a bit of a review and put some of the information together in the one thread. If others can add their own experience & opinions, perhaps we can make a useful resource for the future that will be much easier to locate.
I don’t need to extol the virtues of wooden screws, they either appeal to you or they don’t. While definitely ‘old technology’ they still have a myriad of uses. They are the bees’ knees for items such as ‘traditional’ vises & hand-screws (clamps), book & wine-presses & such unlikely devices as nut-crackers. This bench uses 3 vises made entirely from wood: T1.jpg
Well, ok, there are a few coach-screws in the mix, but you get the drift. Threading wood often requires nothing more than scraps for raw material, and can be a fun challenge with very useful outcomes. While the process is not all that difficult, there are a few pitfalls for the novice, but with a bit of care & preparedness, you can avoid most.
The first time I put up a post on the topic was back in 2004. It has lost most of the pics in the accidental ‘big picture purge’, unfortunately, but the discussions are still there. A later post on tapping wooden nuts has fared a little better, and so has another on making hand-screws. If you prefer paper to screens, I wrote about using a very simple method for making large, screws & nuts suitable for benches, presses, etc., in Australian Wood Review #s 92 & 93. There are also a couple of videos demonstrating the tap & router jig in action, here, & here .
For another perspective, there is a well-illustrated thread on tapping with a similar setup to the one described in AWR for the tap, but another way of organising the thread cutter here. There are other videos on YouTube of varying qualities.
There are several ways to go about making both screws and nuts. If you are cashed-up, but time-poor & just want to make a batch of handscrews, the simplest & probably most reliable way to get started is to get yourself a Beall kit. I have no affiliation with them, & in fact I’ve never used any of their gear other than the carbide router bit, but have seen it in operation. It does the job perfectly well, but cheap it isn’t. Their taps, while quite adequate in the smaller sizes (up to 25mm) are not what I would call best practice in the larger sizes, the 1 ½” tap has too fine a pitch, imo, but that’s just an opinion. If you want to start in a small way, & make a few handscrews, perhaps the most useful size is ¾” – with this size you can make reasonably rugged clamps with around 200 mm jaws that open to around 250mm (bottom facing row in this pic). T2.jpg
The 3/4" screw size is the one I use most, but I also find smaller & larger sets very handy. And in case someone asks, yes, there have been a few times when I have had just about every clamp you can see on the wall in use at one time!
All you really need to get started is a tap, with which you can make wooden nuts, which in turn can be used to make a threading jig for cutting the screws with your router. You can use metal taps in wood, they work quite well (cross-grain), which is very useful when making jigs etc., where you are using metal bolts that you want to screw directly into the wood. However, while fine-pitch nuts may be ok, the matching fine pitch does not make good screws in wood, you need much coarser threads to be practical. For example, 8tpi is about as fine as you can comfortably go for 9-13mm diameter screws, 6-4 up to 25mm diameter, and 2-3 for larger 50-60mm diameter bench screws. I’ve made some weird & wonderful taps in my time, including a 5/8” example from the guts of a water tap, and a 1 ½” 4tpi wooden job that I chased a 4tpi thread on, & used 14G screws for the cutters (it actually works!). T3.jpg
The tap from the tap is a good example of too fine a pitch – compare the pitches of the ½” and ¾” screws made using ‘proper’ wood taps with the 5/8” screw between them. T4.jpg
The clamps I made with these 5/8" screws work well enough, though slow to open & close, & cutting those threads cleanly was not at all easy!
Unfortunately, taps on their own are difficult to come by, but thread-boxes & taps as a kit are readily available. In general, these work well enough, but a traditional threadbox struggles with most of our hard woods – you’ll rip your screw blank to a useless corn-cob-like shred if the cutter is dull or you apply it to something like Bull oak! Several blokes I know have tried to sharpen the cutters in their threadboxes and never managed to get them to work satisfactorily again – if you have ever sharpened a vee-tool, you know how tricky these things are to sharpen properly . Also, the taps that are provided with these kits are really ‘bottoming’ taps which can be difficult to start straight & hard to keep straight when tapping a deep hole. In any situation where you are tapping deep or through holes, it’s helpful to have a reasonably long ‘pilot’, turned to the minor diameter of the nut (i.e., the diameter you drill for tapping), like this: T5.jpg
This tap runs nice & straight in any wood.
If you have a metal lathe, or a friend who does, making your own taps is the best solution. No need for costly materials, a tap for wood doesn’t have to be hardened like a tap for metal – milder steels will give you years of good service, even in hard woods. Just remember to allow plenty of chip clearance and put negative rake on the cutting edges – they are really scrapers, not ‘cutters’.
When it comes to large, bench-screw sized monsters, it actually gets easier. Anyone can make this simple gadget, known from mediaeval times, which makes very acceptable nuts in any wood I’ve tried so far. It consists of nothing more than a piece of wood which is bored for the minor thread diameter and has a slot to hold a piece of metal (saw plate or old card scraper does nicely) which engages a kerf in the shaft of the tap to drive it at the required pitch. T6.jpg
It is described in full in the AWR articles & shown in action in the first of the two videos I referred to above. You could possibly get this tap to work in smaller sizes, down to say, 25mm diameter, but it is really at its best from around 40mm up. This is mainly because of the practicality of fitting & wedging the cutter in the shaft. Cutter fitted1.jpg (Both cutter & wedge still need to be trimmed, obviously).
While it may look a bit cumbersome, and not as quick as a more typical modern tap, it doesn’t take very long to make a nut – 7 or 8 passes, with incremental advances of the cutter is typical. The results are quite gratifying, there’s a bit of raggedness at the start & exit of this sectioned nut, but the majority of the thread is very clean. T7.jpg
So once you’ve mastered that bit of ancient technology, you are almost there. If you select a piece of wood around 200 x 75 mm for your very first nut, you can use that to make the threading jig for the router, as set out in the various articles referred to.
Now to a few of the ‘tricks’ I’ve picked up during the years I’ve been mucking about with wood threading. The first & very important thing to remember is that wood moves with the seasons, so wood threads need to have much more clearance than metal equivalents. The tapped nuts change very little, it’s the screws that expand & contract significantly. A loose, but not sloppy fit is the go. When the wood I’m threading is likely to be at its lowest EMC (after a long, dry spell), I try to make the screws a bit looser than when the wood is likely to have a higher MC. It’s an experience thing, but you soon get the hang of it.
A problem I’ve run into after years of using my home-made threading jigs is that the thread in the jig becomes a bit worn, and it’s possible to cut threads that are too tight to fit freshly-made nuts. If you only make a few screws in your router jig, you may not encounter this problem, but if you do, don’t just advance the cutter a little & run it back through. This will alter the pitch slightly and you’ll likely wreck the latter half of the thread. The trick is to screw the thing all the way back into the jig (it pays to have a plunge-router for this operation), advance the cutter a teeny bit, then fire up the router & cut while backing out. The bit cuts just as well in ‘reverse’ and the pitch of the thread will be preserved. An obvious thing, but it took me a while to figure it out!
A few words on suitable threading woods:
Nuts can be tapped successfully (cross-grain) in just about anything from Balsa to Lignum vitae – don’t try tapping into end-grain, it will end in tears with 99% of woods. Yes, I know turners make threads on long-grain for box lids etc., but they don’t use taps, they chase the threads in. Some woods cut more crisply than others & make very clean nuts (Merbau is a good example), but I haven’t yet struck any wood that doesn’t make a tolerable nut. I like to use softer woods for clamp jaws because they are less likely to mark my work pieces – here you see silky oak, Camphor laurel, and Australian cedar. T8.jpg
I made the cedar pair out of curiosity, and so far they are travelling well.
For screws, you need to be a bit more selective, but any strong, fine-ish-grained hardwood is worth trying. While you can thread virtually any wood with your router jig (& a sharp bit), there are lots you needn’t bother with. Crumbly, hard stuff full of insect tracks & gum veins is obviously of no use in this context, however much you may like 'natural features'. Curly woods or any with grain that ducks & dives should be avoided; the grain should be straight & run continuously through the shaft of the screw. I’ve had a few screws break, mostly because of hidden flaws in the wood, but I’ve never had a jaw strip or break in use. My current favourite threading wood is Crows Ash – it’s dense & strong, easy to turn, takes a beautiful clean thread and is greasy – what’s not to like about that list?! Crows Ash would thread well with a threadbox, I suspect, but can’t be sure as I have only used it with my router jig. She-oak is also usually very good for router threading, but I doubt it would behave well for a threadbox. T9.jpg
(Top to bottom the woods are: River oak (Allocasuarina cunninhamii), Celtis (C. sinensis), She-oak (A. torulosa) and Crows Ask (Flindersia australis). Lots of other woods are suitable for router threading, River Red gum, Penda, Bull Oak, Black wattle are some I’ve found to be very good for the purpose.
Sometimes a bit of linseed to lubricate the tap works well, sometimes it doesn’t – testing with a scrap of the wood you want to use is the best way to decide. With the ‘primitive’ tap, over-enthusiastic use of oil can cause the swarf to bind together and block the chip-carrying area. T10.jpg
When using thread-boxes, it is usually recommended that you soak the shaft to be threaded in linseed oil. This softens the fibres & makes them easier to cut. I don’t recommend this when using a router, the swarf will stick & build up & cause you grief. At the most, rub some wax on the shaft & polish it off, but it usually isn’t necessary to do anything to the bare wood when the bit is sharp & everything is setup properly.
If you are having trouble screwing the blank through (you should be able to turn it very easily with fingers alone) it’s most likely because you don’t have the bit in the right spot relative to the first thread of the jig, or the screw blank is a bit too fat. I keep a piece of scrap drilled to the major diameters of the various screw sizes I make, & test each as it comes off the lathe for a good, but loose fit all the way along.
There are probably all sorts of aspects I haven’t addressed, so fire away with any questions or comments. Even more than 30 years after I cut my first threads, I’m still discovering things & I’m sure there’s plenty to learn yet…..
6th Mar 2018, 08:34 PM #2GOLD MEMBER
- Join Date
- Dec 2010
- Mornington Peninsula
I think it is time you did a video on this topic Ian.
7th Mar 2018, 08:48 AM #3Junior Senior Member
- Join Date
- Dec 2008
- Adelaide, SA
A great write up. Every time I read about wood screws it inspires me to make my 1st. Thanks.
7th Mar 2018, 09:14 AM #4
cava, there's a video of me demonstrating the old-style tap and another showing how to set up the router jig, both linked to in the post above. The router jig demo was filmed by my neighbor, a professional film-maker, with all sorts of fancy gear, & I think what he stitched together is far better than anything I could do! There are quite a few other videos on 'Youtoo(be)', of varying quality, so really, I think there's enough action material available. I'm happy to do demos for anyone within range of my shed. Like any other process, it's mostly a matter of giving it a go & you will pretty soon figure it out, & if you run into a problem you can't solve, the Forum is always here to help.
What I was hoping when I started this thread was that someone with a bit of experience in using thread-boxes (& I know there are some out there), will chip in & add some info on their use with Australian woods so we can build up a good resource in the one thread for anyone wanting to give wood threading a try. I have very little experience with the old-style thread-box - I used someone else's once, and made one for myself which didn't work very well. In fact what it did best was make 3/4 inch dowel thinner & rougher, and almost ended my wood-threading career there & then! I've often thought about making another, just for the challenge, & I will get around to it for sure, if I live another 50 years.
For many of us, I think the two most valuable applications for wood screws are clamps (both hand-screws and bar clamps are pretty easy to make) and large screws for traditional tail-vises, etc. The large bench-screws are in some ways an easier proposition for a beginner because you can make the simple gear from bits & pieces that you could find in the average shed. The only part I've bought specially for wood threading is the solid-carbide bit I use, but as I said in the AWR article, you can make a perfectly functional bit by grinding the required angle on an old HSS drill bit. They work well enough to cut at least a couple of bench-screws worth of thread before they need re-sharpening. So there's little or no cost in having a go - at worst, you'll end up with some odd-shaped firewood....
7th Mar 2018, 10:29 PM #5
I have used the thread-boxes sold by Carbatec but only in a limited way. The two mallets pictured below have threaded handles. Both handles are spotted gum. They were easy to do particularly with the addition of little oil.
What I don't know is how long they will perform well.
"Power tends to corrupt. Absolute power corrupts, absolutely!"
8th Mar 2018, 10:08 AM #6
Good info, Paul. I'm a little surprised that you were able to cut the S.G. well, even with oil, but then again, your S.G. is far nicer than the stuff I'm used to! I think you are right in suspecting the cutter may not produce too many miles of thread in that sort of wood - in my limited experience, the cutter only needs to dull a little and things start crumbling (literally).
I'm really keen to hear about any experience of re-sharpening & re-setting them, and what sorts of woods they found thread well with this system, and what didn't. The one and only time I used a commercially-made threadbox was when I was in Canada. This was a 3/4" box (of European manufacture as I recall) sold by Lee Valley. It cut very nice threads in the Birch and Apple wood we tried it on, throwing out a continuous ribbon from the cutter as it went. These are both woods which 'peel' beautifully on the lathe. The only two local woods I find similar are Crows Ash and Bush Cherry (Exocarpos cupressiformis), but I haven't tried threading them with a threadbox because I chucked the one I made away after some frustrated attempts at getting it to work on bone-hard woods like She-oak. I know it was largely due to my inexperience & impatience that I had so little success, so I'm really interested in hearing how people with a more sensible approach have gotten on with our local species - how nicely they thread & how durable the threads have been.
Frank Weissner wrote an article on making bench-screws in an early AWR; he used Mountain Ash and cut the threads with a threadbox. Auscab used River Red Gum for his bench screws and cut them with a (German-made) threadbox, so these things will work on some of our hard woods, at least. Mountain Ash strikes me as a reasonable choice, and E. camaldulensis is finer-grained and a bit more tractable than say, Ironbark! I have threaded R.R.G. with my router jig system and would class it as middling good, but I reckon it must've tested the limits of a threadbox. Auscab's bench attained its majority last year, by my calculations, 21 years of steady service in a busy workshop, so those screws have well & truly stood the test of time, showing that the R.R.G. is certainly durable if you can cut it. I was hoping Rob would've pitched-in by now, but he's probably busy earning his keep, not sitting at a keyboard nursing a dud shoulder like I am....
8th Mar 2018, 02:44 PM #7
Watched some off the video
What a handsome fellow we have with Ian.[emoji41]
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8th Mar 2018, 03:29 PM #8GOLD MEMBER
- Join Date
- Apr 2011
- McBride BC Canada
If this was a hard cover book with a DVD , I'd buy a dozen. Mostly, to donate to museums.
They never find these resources and their budgets never allow for purchase.
Simple little gift which could accelerate some indulgence.
My name is as good as my word.
Put me on the list.
Brilliant because I can see this technology evaporating before my very eyes.
One question which puzzles me.
Being so far into the iron age, how did the wooden thread persist?
Economic divide between the "haves" and the "have nots?"
8th Mar 2018, 04:00 PM #9
8th Mar 2018, 05:25 PM #10GOLD MEMBER
- Join Date
- Jun 2014
- Seattle, Washington, USA
Thanks for the post, Ian.
As someone who's seen you do this first hand, I can attest to how simple it is.
Let me rephrase that... I can attest to how simple you make it look.
It's good to have all of this info here in one spot.
Getting set up to do this is still something which is high on my list of things to do. I've been seriously considering "cheating" and buying the tap and the carbide bit from Beall, and then using the two to make my own die nut setup for cutting the male threads. It seems like a reasonable enough way to skip a lot of the guess work.
One thing which gives me pause about doing it that way, however, is that your screws have a more coarse pitch than theirs. I'm concerned that the lands cut on the screws made by the Beall kit may be a bit fragile, and I'm also concerned that, after using your screws, they may be slower and not to my liking.
At some point I know I have to make a move though... I often find myself thinking about how something or another could be improved through the addition of a wooden screw here or there...
8th Mar 2018, 05:35 PM #11SENIOR MEMBER
- Join Date
- Dec 2011
- Buderim qld
8th Mar 2018, 06:47 PM #12SENIOR MEMBER
- Join Date
- Dec 2011
- Buderim qld
8th Mar 2018, 06:57 PM #13
8th Mar 2018, 07:15 PM #14
Yairs, it is a different age - too voyeuristic!
When I started out, there wasn't much, Fine Woodworking didn't start until 1976, & that was a game-changer for me. When you saw something in a magazine or at a craft show that got you fired up you just went out to the shed & bumbled along til you either got it to work, or gave up in frustration. Router threading fell in the former category for me, threadbox-making in the latter. But there's a lot to be said for just giving things a go.
8th Mar 2018, 07:53 PM #15
Beall use a 'sensible' pitch on their smaller sized taps but why they went for 6 tpi for their 1 1/2" size, I'm at a loss to understand. Everything I've read, plus personal experience, says coarse is good with wood threads. I have a 1 1/2", 6tpi tap that a friend had made by a machinist friend of hers, as a thankyou present for some work I did. It was made on a lathe that couldn't cut anything coarser than 6tpi, & the tap looks just like a 1 1/2" Whitworth tap for metal. It's too short & has no pilot shank to speak of. I've never had the heart to tell my friend it's a dud - used it a couple of times, but it's just as you suggested, the thin thread lands are too fragile & too slow for a bench screw. The one 'flaw' with wooden screws is that the threads are all cross-grain, it's amazing they work at all, but work they do, and both of us have the living proof of that....
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