Thread: Making wooden vise screws

Originally Posted by jonsey850

Yeah Ok I think maybe what Ian was saying is that the 60deg is easier to get working smoothly. I’m guessing it is just more tolerant of any inaccuracies so I will try be as accurate as I can.

Jonsey

It may have been that a 60° was used because you can easily buy a standard router bit. He has told me in the past but I have forgotten whether this is exactly the case..

Regards
Paul

You are correct Bushmiller

He mentions having a 60 degree router bit on hand in this old thread:
Wooden Thread Profiles


But just looking at the AWR article and to quote Ian:

“Conventional wisdom has it that a thread angle of 90 suits wooden threads best, but after many years of making and using both 90 and 60 threads, my preference is for something more like 60.”


So it would seem the issue goes beyond what router bits are readily available?

Sorry folks, been ignoring the "General" section of late, so only just saw this thread, but you seem to have sorted most of your problems without me.

The reasons I prefer 60 deg. thread angles are not entirely logical or explainable. I suspect it has much to do with that being what I started with. In fact, I had a bit of trouble getting a 60 degree bit at the time (it was the 1980s), but they are easily obtained now, and 90 deg. bits are too, so no problems either way. As I said before, 90 degree threads seem to be most common on old wooden screws I've come across, though they were by no means the only angle used. I think in future I'll just say that the thread angle doesn't seem to be especially critical, so go with what seems right to you, or what bit you happen to have. I will say use a carbide-tipped or solid carbide bit if threading any of our harder woods. You can get away with a HSS bit for one or two screws, but the quality of the threads will start to decrease pretty quickly on hard woods & you'll get ragged, chipped threads which actually work, but look pretty manky.

Finish the tap & make the nut for your screw-threading jig first. I think you've already figured out that the nut is tapped in several passes (it would likely take me 7 or 8 passes to cut a 2tpi thread for a 2" screw, I'd estimate, but it will depend on the wood you use). If you get too enthusiastic advancing the cutter, it will be very hard to turn, and you'll get a lot of splintering at the beginning & exit. Nuts can be made from just about any wood, you don't need bone-hard stuff because the grain is with you - nuts very rarely strip unless poorly made. Screws are a different matter, the grain is as wrong as it can be in the thread lands, & the threads can break away very easily in brittle woods, even though they may be "hard".

The best advice I can give you is to dive in & give it a go, the learning curve is short & not too steep. The tap is pretty straightforward, there is not much that can go wrong. The biggest problem for a beginner would be knowing when the thread is "done", you'll just have to judge it by eye that you've gone deep enough, 'cos it's pretty difficult to measure accurately. However, the good news is that you don't have to be rocket-engine precise, even sloppy threads can work well, but after making a couple f screws, you'll get he hang of it & your precission will improve. The worst that can happen is you chew up a bit of scrap getting it sorted.

If you have any other questions, just ask - I'm tuned in now....

Cheers,

Hi Ian

Thanks for tuning in! Your experience here will be invaluable.

I always have questions, in fact I have a few right now if I may.

For a the 2” screw at 2tpi what size hole would you recommend for the nut?

I have the following two options?



The 40mm hole would leave a small flat on the crest of the threads. I’m guessing it would be easier to tap as well, but would it affect performance?


Also should the cutter be set at 90 degrees to the helix angle (ie the angle the steel plate that engages the tap is set to)?

Cheers

Originally Posted by jonsey850

For a the 2” screw at 2tpi what size hole would you recommend for the nut?

The 40mm hole would leave a small flat on the crest of the threads. I’m guessing it would be easier to tap as well, but would it affect performance?

Also should the cutter be set at 90 degrees to the helix angle (ie the angle the steel plate that engages the tap is set to)? .....

Ok, I was debating discussing this above, but decided to skip it for fear of complicating things too much!

So let me address your questions by stepping through the process:

First, there are no problems with the major diameter of the screw, you just turn the screw blank to an easy sliding fit in a 2" hole.

But the tapping hole diameter is obviously a function of thread depth. Since you elected to go with a 90 deg. thread angle and 2 tpi, it makes it easy to calculate the thread depth, which will be 0.25" (somebody should check my geometry, but I think that's correct). Therefore, your tapping hole needs to be 0.25" or 6.35mm smaller than the nominal screw diameter, which is 43.5mm or 1.713 ", rounding it up. That's significantly more than your maximum option of 40mm.

I suspect you don't have a 43.5mm drill bit (I certainly don't) but I do have a 1 3/4" bit (one of the advantages of being in this game for so long is that I've built up both Imperial & Metric sets of all kinds of bits!) which is 44.5mm. That's a little larger than the calculated root diameter of the screw, but for practical purposes, it'll do just fine, you need generous clearance with wooden threads. Even if you had a bit of the calculated "ideal" diameter, you'd be advised to go up a teeny bit.

Now, because the pitch is fixed by both the threading & tapping jigs, you can actually control thread depth on both the screw and the nut to quite an extent without altering the pitch and thus finesse the fit by these means. So that's why I say to make the nut for your threading jig first. If you tap it to what "looks right" it should be very close, and this will now be your "standard nut". Tap another nut to use as a test, and then set up the router jig and try cutting a screw on a scrap piece. If the screw fails to feed easily, the most likely causes are the cutter is slightly out of alignment, or not set deep enough. If the screw feeds easily through the jig, all is well, & it should screw easily into your test nut as easily. You'll now have a test screw as well as a test nut, so you can check all future productions and maintain a standard product.

As to the placing of the cutter in the tap, ideally, the cutter should face the helix angle of the thread, the same way you set a cutter on a metal lathe. However, that's pretty hard to do accurately. I tried to do it for a couple of wooden taps, but gave up on the last few, particularly small diameter taps (I've made wooden taps as small as 7/8" major diameter, which is about as small as you can go with his method), and just placed the cutter in the centre, with the face parallel to the axis of the tap. These seem to work just as well as the ones where I tried to match the helix angle.

I have to say that much of what I now know about wooden threads has come slowly over a lot of years (>30!) and a good deal has been worked out in retrospect rather than at the time. In the beginning, I just fiddled about 'til things worked, which was sometimes very frustrating & I had my share of failures, but when it all goes well, you'll be surprised at how easy it can be to make very good wooden screws...

Cheers,

I hadn't thought to match the helix angle, but it makes so much sense now that's its mentioned.

Looking at how Jonsey850 made their cutter out of a drill bit, this makes it so much easier. One could rotate it to match the proposed thread before locking it in place. In fact, a few flattened surfaces along the shaft to act as a grub screw surface (to lock it in place) would make this easy indeed.

It would also ensure that the presentation angle is matched as the cutter is extended as the thread is repeatedly cut.

A few screws, with a slot (or Philips end cut into it), embedded into the Tap Screw would aide in both extending the cutter nicely AND locking it in place! The screws would use these to make the holes, but one could use ordinary screws (blunted) or bolts....
How interesting!



Let me do a diagram with what I was thinking.

Whoa boy, whoa!
You are over-thinking this waaay too much, my lad. The beauty of this tap is its simplicity. As I said, facing the cutter to the helix angle seems to be unnecessary, in practice. The original tap I saw in FWW half a lifetime ago set the cutter square to the centre line, & I followed that at first. It was only because I got into cutting threads on my metal lathe that I learnt about catering for the helix angle & thought I'd try it. I think it is necessary with metal threads, where tolerances are much tighter, but with wooden threads? Nah, it just isn't needed.

I'm not sure grub screws would hold the cutter as securely as a wedge anyway. They might, but the wedge works so well - you just back out after each run through the nut, tap the cutter in a bit more, & go at it again. No faffing around with screwdrivers and risking losing your place if you loosen the grub screw too much & the cutter slips out of position.

It takes about 10 minutes to tap a nut, go to whoa, and let's face it, only wood-thread nutters like me are likely to want to tap more than half a dozen nuts in a lifetime, so don't waste time on the tap - it's going to spend the vast majority of its life sitting in a drawer or cupboard, unused....

Cheers,

Originally Posted by IanW

But the tapping hole diameter is obviously a function of thread depth. Since you elected to go with a 90 deg. thread angle and 2 tpi, it makes it easy to calculate the thread depth, which will be 0.25" (somebody should check my geometry, but I think that's correct). Therefore, your tapping hole needs to be 0.25" or 6.35mm smaller than the nominal screw diameter, which is 43.5mm or 1.713 ", rounding it up. That's significantly more than your maximum option of 40mm.,

Hi Ian just to clarify I think your geometry is correct but are you only accounting for one side of the thread? I think the root diameter would be .5” or 12.7mm smaller which is 38.1mm?

Cheers

Originally Posted by jonsey850

Hi Ian just to clarify I think your geometry is correct but are you only accounting for one side of the thread? I think the root diameter would be .5” or 12.7mm smaller which is 38.1mm?....

Yep - senior moment! Hopefully, I would've discovered my blunder before I'd got too far making the tap!

But what I said about plenty of clearance holds, so go with 40mm for your hole size. The tap shaft needs to fit the pilot hole, but make it a loose fit. If you make it too tight it can jam with shavings. As I've said elsewhere the one flaw with this 'primitive' tap is how to deal with the swarf from the cutter. Make as generous a 'scoop' in front of the cutter as you can, this is where most of the swarf sits until it exits (another reason for taking light cuts each pass). I make as large a recess for the shavings as I think is safe, but they will still build up if tapping a long nut, and you sometimes have to back out & clear the cutter. This happens more with oily woods. You can extend the recess to the tip of the tap, and it sometimes helps, but there is no significant force pushing the swarf out in that direction, so it still tends to just compact itself in front of the cutter. It isn't that big a deal most of the time, I've only had a couple of instances where I was tapping very oily wood & had to back out repeatedly halfway through each pass to clear the cutter.

It's not a good idea to make very long internal threads anyway. You are cutting them across the grain, so expansion & contraction with humidity changes will alter the pitch slightly. I've never had any problems with screws on benches etc., where the deepest nuts I've used are ~60mm (for tail vises). My own bench is hard Maple, made in Canada. About 4 years years after it was made, I brought it home to Oz., where it lived in Victoria (Benalla) for 4 years, & was then dragged up to Brisbane, about 28 years ago. Through all that time, in 3 very different climates, it has given no trouble whatever. That screw was about the 2nd or 3rd one I'd made, so it had the benefit of a very little bit of experience and a very large amount of luck!

From my own experience, nuts rarely cause you any problems. I have had a single 1 1/2" nut fail on a small tail vise. I blamed the wood at the time (Cherry) but in retrospect, I am 99% sure it was just a poor thread to begin with. It was made with a very Heath-Robinson tap which I made by chasing the thread on a blank, tapering the end, and driving in a series of 14G screws tat I filed into cutters. This is it, with the cobbled-up chasing tool:
wood tap.jpg

I made it before I tried making a "medieval" tap, thinking it would be quicker & easier. The 2" tap I made the same way worked ok, I used it to make the tail-vise nut on my main bench & it is still working well 30+ years later (though I have never been bold enough to try it on some Iron Bark or Spotted Gum!). But the 1 1/2" job was never up to scratch. Taps like the one you are making work far better, and as long as you take it slowly, should tap any wood you care to tackle.

The worst mistake you can make is making screws too tight. These will bind and even jam solidly in humid weather. There was a thread some time ago where someone in far Nth Qld got some Lake Erie screws and found they just jammed up on him - they were made too tight to cope with really high humidity. Maple is not a particularly stable wood anyway, and as a result of that experience & probably others, the company now make their screws with more generous tolerances. How loose to go is a matter of judgement, but be assured you have lots of leeway. I have made a few screws for clamps that I thought were far too loose, but I used them anyway, thinking I'd just replace them if they stripped. None of them have.

OTH, I've also made a few that were too tight. This happened mainly because the pilot thread in the jig I used was quite short & became worn after much use. The screw ran through the jig easily as I cut it, but was too tight in a freshly-tapped nut. I used them thinking they would soon "wear in", but they didn't. They'd work (reluctantly) by the end of the dry season, but were very difficult to open & close in the wet. You can deal with this problem if you realise it at the time. DON'T just advance the cutter a little & run the too-tight thread through again, the deeper cutter alters the pitch slightly so it feeds in out of phase with the existing thread & every couple of inches you cut away the existing thread. Damhik, as they say. It took a bit of head-scratching to figure out a remedy, but eventually the penny dropped. The "trick" is to wind the screw all the way back into the (loose) jig, THEN advance the cutter slightly and re-cut as you screw it out. This will maintain the pitch and deepen your thread a little. Then go & re-make the threading jig before doing any more.

The symptom of an out-of-alignment cutter is that the screw feeds in ok for a turn or two, then starts to bind. If you persist with a slightly misaligned cutter, the screw becomes a little tight fr a few turns, loosens up for a few turns, then gets tight again. The resulting thread will drive you nuts because it will run ok in some sections and bind in others - again, damhik.

I doubt you'll make any mistakes I haven't beaten you to already, but being fore-armed, you should keep them to a minimum & make workable screws & nuts without much drama.....

Cheers,

Wow thanks for the in-depth info Ian, I may need to read a few times. I think the main take away will be to make sure there is reasonable clearance in the nut and screw.

I had a 38 and 40mm Forstner bit arrive yesterday so hopefully I will be able to get at least the tap and nut made over the weekend.

Cheers

The tap is complete. I set the cutter at the helix angle which was too hard to do. Will move into the nut.

Looks like the goods, Jonesy. I would make the 'chip relief' at the front of the cutter a little larger, myself, it looks a bit skimpy as-is, but hard to tell from a pic. Once you start using it in earnest you'll soon see if that's necessary or not.

Cheers,

Yeah the relief is not real big I could take more out. I finished the block with the steel plate in it. I made the plate hinged, just lift the tab to disengage. I didn’t really have the right piece of timer to make this I would have liked it wider for easier clamping but will see how it goes.

Originally Posted by jonsey850

.... I made the plate hinged, just lift the tab to disengage.....

That's a neat refinement, saves hunting for the plate in the bench clutter after each adjustment.

Something to note, I find I need to press on the plate a bit with my left hand to keep it engaged whilst turning the tap with the other hand because it has a tendency to squirm out under pressure. With your setup, you could probably devise a simple latch to keep the drive-plate in position & use both hands for turning. I can see the makings of an "improved" model here - I'll pinch your hinged guide idea next time I make a tap. Hmmm, since I have now got taps for every conceivable size, it may be some time before I make anther....

Originally Posted by jonsey850

....I didn’t really have the right piece of timer to make this I would have liked it wider for easier clamping but will see how it goes.....

You should be ok, just use F clamps with the heads facing you, so you don't have much of the clamp getting in the way of the tap handle.

Looks like you're good to go - I'm expecting to see a couple of bench screws & nuts by this evening...

Cheers,