Wooden thread......thread

[Mountain Ash]

Hi all. Happy to report that I have finally got round to having a go at tapping and threading my 1st wooden nut (and soon, screw). Thanks to WoodPixel for posting PDF's of IanW's articles regarding the same.

Began with a piece of Messmate for my "medieval tap".

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Turned up as per IanW instructions.

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Again set out helix as per the article and sawed lines. Actually had to do this twice because the saw blade keeper was wider than the kerf originally cut.

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Spent longer than I thought cutting angled mortice for the cutter and wedge, made up the block and had a go at cutting my 1st thread ever.

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Pretty chuffed with results but I have a couple of questions

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1. I could only adjust the depth of my cutter when the tap was poking out past the nut. This meant that I was cutting the thread by pulling the cutter back into my block. This seemed to work but it meant the swarf was dragged back into the block. I cut a clearance channel on the tap to help but surely this is counter intuitive. I can't see another way to adjust the depth without unclamping and resetting everything back up after each depth adjustment. Am I doing something wrong?

2. My test piece was Oregon and the threads look a little messy. What can I do to improve them?

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[Mountain Ash]

Well, not so much success today. Took a bit to tap a thread in Messmate and had trouble with the cutter moving, but got there in the end. Lining up the "threadbox" with the cutter took a lot of faffing about. I was able to produce an even thread bit if chipped like mad. Found it hard to get the sizing right. Adjusting the router height was a pain and the router bit was either too deep and the thread was loose or too shallow and I couldn't turn the stock. Disappointing afternoon, especially when IanW's instructions looked easy enough. Maybe the pine is the problem.

1st try
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The rest
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Any ideas on what I can do to improve?

[IanW]

OK, MA, coupla comments:
First wrt the tap - unfortunately you do have to unclamp the tap from the nut piece after each pass to advance the cutter if you want to cut in the "forward" direction - there is no other way I can think of. It's not a big problem, I have about 20mm 'lead' ahead of the cutter on the tap, and use that to re-align it when re-clamping. I haven't had any problems with it getting out of alignment. At least the swarf is pushed out the open end this way. You will always have a bit of a problem with the swarf with this system unless you make a very large hollow in front of the cutter, but again, I've not had too much of a problem as long as I take it in fairly shallow increments. I've not tried tapping oregon, but I imagine it wouldn't be easy to get a nice thread in it, particularly if it's old recycled stuff. If you want a 'gold standard' try a bit of merbau, I've always found it taps very nicely indeed.

Now the screw. Chipping, in my experience, has three main causes. The first & most obvious is the wood itself - some wood will chip no matter what you do so that could be your problem. A blunt cutter can cause chipping, but it has to be really dull - I've used some pretty dodgy cutters in my time & most worked surprisingly well. So that brings me to what I've found is the main cause & that is a slightly mis-aligned cutter, and especially if your blank is a bit tight - make sure it has good clearance - it should be a loose (but not sloppy) fit in the nominal major diameter hole. Once everything is working properly, it should take no effort at all to screw the blank through, the cutter almost pulls it along. If you are having trouble turning the screw through the jig, or especially if you notice it goes alternately tighter & looser, a misaligned cutter is almost certainly the problem. It's hard to get a perfect 'start' when you first begin, so the first turn of thread is often a bit wonky & binds as you screw it through the rest of the thread in the jig, but once it emerges, it should run freely and you should be able to turn the screw through with your fingers easily.

It can sometimes take quite a bit of faffing about to get it right - I had a very embarrassing experience showing someone how easy it is a few years ago, & all I could produce was chipped, chewed up threads - I felt like a complete idiot! After he left, I calmed down, took a more careful look at the setup, made a minor adjustment & bingo! - perfect threads.

I keep a bit of "good" thread handy to help with initial setup, but that's not much help to you until you do get your jig cutting nicely.

To be honest, I reckon you've made terrific progress for your very first attempt. You are almost there - just double-check that cutter position, getting it as close to the start of the first bit of thread as possible (& remember it has to be a teeny bit in front to align with the ramp angle of the thread..

Hope that is some help,
Ian

Addendum: I took a better look at the pics & it strikes me that you are cutting the lands are very deep & with very thin tops. It looks like your cutter is set too high and is struggling to remove the amount of wood it's taking off & that may be the main cause of chipping. Heavily truncated threads are the go with wood, try to find a happy spot where the thread is sufficient to pass comfortably through the nut without being so sharp, something more like these: Bench screws red.jpg

[Simplicity]

MA,
Wow,is all I can say,cutting timber threads looks way complicated.
Keep at it.
Your already doing an awesome job.

Cheers Matt.

[Mountain Ash]

Thanks Ian and Matt. The pine I was using is probably very dry and was from an offcut of a laminated beam (so grain direction is potentially counter productive). Cutter was brand new. Looking closer at my tapped guide the "lands" are a bit uneven. I have plenty of merbau, I will give that a try. Hole in the non tapped guide was drilled at 54mm and I was aiming for a shaft diameter of 53mm. Minor diameter was 45mm and I tapped to the depth of the angle on my cutter. Oregon was only an experiment and maybe the messmate was too hard.

[IanW]

... hole in the non tapped guide was drilled at 54mm and I was aiming for a shaft diameter of 53mm. Minor diameter was 45mm and I tapped to the depth of the angle on my cutter. Oregon was only an experiment and maybe the messmate was too hard.

OK, I think we are getting somewhere MA. Allowing a mm clearance for a 54mm blank is ample, so I think you have that right. Tbh, I don't measure my blanks with such precision, I just turn to a diameter pre-set on my calipers which I set to about 0.5mm less than the major diameter. When the calipers slip easily along the blank, I know the diameter of the blank is a little less than that, so mine probably end up around .75mm under nominal diameter.

I think your cutter is set too deep - by your figures you are cutting a thread that's 4.5mm deep & my guess is you probably only need 3/4 of the calculated depth, there is no need to set the cutter to full minor diameter. However, if the cutter is not positioned accurately, the skimpy theads you are making are necessary to allow the slightly off-pitch screw through the nut of the jig. Both the internal & external threads should be truncated - up to 10% or so of the height of the land is fine (again, I don't measure it to any precise figure, just a good 'flat' is what I aim for). By fiddling with the cutter depth, you should be able to get a sharp-pointed cutter to cut sufficiently deeply to produce the desired profile. For large diameter threads, I prefer to use a cutter that has a slightly flattened point, and I certainly use a slightly rounded point on the cutter in the tap.

It has only just occurred to me that starting with large diameter screws means much more wasted material getting experience & setting it up. I think larger diameter is a bit easier to work with than very small, but you can chew up a few blanks in the beginning, so I understand your wanting to use less than ideal material. The good news is that if you get it right, you should cut quite good threads on even the junkiest wood, so if you get it working reasonably well you'll be able to move on with confidence to your more valuable material for the real thing . I started with 1/2" threads which are harder to set up, but the amount of material you waste sorting it out is far less. I was really lucky & my first attempt worked almost perfectly. The next time I set it up to do more screws I had a hell of a time - if I hadn't had that initial success I think I would've gone cold on the whole idea of wooden threads, which would have been a pity as they have served me exceedingly well ever since! By the time I started making bench screws I had a slightly better idea of what could go wrong & how to correct it, so I didn't have too much trouble getting some decent threads (I was also using hard Maple, which is a pretty forgiving wood to work with for this purpose). However, as I mentioned above, there have been a couple of times over the nearly 40 years I've been mucking about with wood threading that things didn't go to plan. Sometimes it's better to put it aside and do other jobs 'til your frustration levels subside. It has often amazed me how when I've come back to some problematic task after a night's sleeping on it, the problem is either obvious, or (magically), no longer exists!


Ian

[Mountain Ash]

Thanks Ian.

[Andy_B]

Venturing into wooden screws now, MA. Nice!!

Reminded me of a DIY wooden screw on YT:
Self-Made Tools to make Wooden Threads Part I: Dowel Maker - YouTube

Is the article from IanW's 2-part piece for the AWR by any chance?

[woodPixel]

OK, MA, coupla comments:
First wrt the tap - unfortunately you do have to unclamp the tap from the nut piece after each pass to advance the cutter if you want to cut in the "forward" direction - there is no other way I can think of. It's not a big problem, I have about 20mm 'lead' ahead of the cutter on the tap, and use that to re-align it when re-clamping. I haven't had any problems with it getting out of alignment. At least the swarf is pushed out the open end this way. You will always have a bit of a problem with the swarf with this system unless you make a very large hollow in front of the cutter, but again, I've not had too much of a problem as long as I take it in fairly shallow increments

(my terminology is all over the place here! - refer to diagram)

What about for clearing the NUT(3) and NUT GUIDE(4), rather than unclamping the 3/4 combo, that a keyway is cut along the inside edge of the nut guide (4)? (about 5 to 10mm wide along the entire path).

This way the GUIDE(2) can be lifted a tad, the TAP(5) can be withdrawn, the CUTTER(1) booped down another millimeter .... then reinserted all without disassembling anything. The cutter(1) won't foul on anything as it is withdrawn along the keyway....

Obviously the keyway would need to be as deep as the thread (maximum extension of the cutter depth).

It would also let one put a vacuum on the far end of the nut (3) and suck out any swarf as part of the process.


Could one not use a drill to make the equivalent of an engines oil pathways INSIDE the TAP(5)? drill down from the cutter towards the centre, then a FAT hole right up the middle of the shaft to intersect it? A vacuum could suck out any crud as its generated?


(apologies for my terrible diagram. It WAS drawn with one of my lovely hand made pens though! AND drawn on one of my kitchen cutting boards of BLUE GUM...so that makes up for the terrible art )

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[Mountain Ash]

Thanks AB and WP. Yes Andy, WP put the PDF's up in an earlier thread. Started by Jonesy.... I wonder if a keyway on the bottom of the opening could also allow for swarf collection.

IanW , you also mentioned having a sonewhat rounded tip to the cutter. My 60° router bit comes to quite a sharp point so would a rounded cutter in the tap work? I thunk I might start again with smaller components, finding timbers roughly 3" square is difficult

[IanW]

WP, that is such a simple potential fix, it just takes genius to think of it!

It has never occurred to me, but now you've suggested it, it's so obvious & I reckon it would work well. I can't see it would affect the guide in any significant way. Brilliant! I'll modify the jig next time I use it & see how it goes. You might have to suck some swarf out of the cavity because the cutter does sweep some back into it when you back the tap out, but it's not much & you could probably ignore it. Swarf build-up with these taps is a bit of a nuisance, but not a major issue. I find it best to work "dry" and take light cuts so the swarf is pretty fine & most of it just bypasses the cutter for the first few passes, then gets pushed ahead of the cutter as the groove deepens. I tried using some linseed oil to ease the cut (works very well with my all-metal taps), but it was a failure with the 'primitive' version, ithe swarf formed into a solid paste that built up around the cutter & didn't clear at all.

It will speed up the process a little if you don't have to disassemble the tap after each run, but to be honest, I don't find it all that much of a chore - I've only ever needed to tap one or two nuts at any one time (I may have done 4 or 5 demonstrating it at the wood show, but that was over 3 days ), so it's neither here nor there if it takes me 10 minutes or 15 minutes to tap a thread. It typically takes me 5-8 passes to cut the thread completely, and you need to test the fit as you home in on the final passes (for your first nut it's more a matter of judging it by eye unless you have a pre-made screw you wish to match). You could quite easily do this by screwing a test screw in from the back, of course, so there would be no need to dismantle the jig at all with your little modification.

If you decide to go into production making workbenches or something and need speed, I would suggest you get a metal tap that cuts the thread in a single pass - that's much speedier & very good for building upper-body strength!

MA: The solid carbide cutter (60*) I use for 4-6tpi screws is pointed, & quite a sharp point, too. It works fine for smaller threads (=>4tpi), it's all a matter of getting the depth right, but it does mean you have to accept a sharp-bottomed groove. That doesn't matter as long as the pitch is spot-on. The side profile of the land has to match the groove in the nut & but doesn't have to go all the way to the bottom of the groove (i.e., it can be heavily truncated compared with metal threads). Given the inevitable small discrepancies in your tooling & the nature of wood, about the best we can hope for is about 1/2-2/3rds of each land making contact with the sides of the groove in the nut. I think it's actually counter-productive to get too accurate a fit, given that wood moves with humidity changes. The Lake Erie people discovered they were making their screws to too tight tolerances & quite a few customers had problems with them jamming in humid climates. The screw in my tail vise was about the second one I made, and at that stage, my equipment was very crude & my experience zero & I ended up with it being a little looser than it should be. At least I've never had it bind in the middle of the wet season, but it rattles a bit when spun up quickly in dry weather. I put a lot of force on the thing at times, far more than I used to think a wooden screw would tolerate, and have fully expected it to give up at some point, which I why I made a couple of more accurate replacements quite a while back. But so far it has not succumbed to my heavy-handedness & it looks like they won't be needed in my lifetime...

The solid-carbide bit is not so great for coarser threads like 2 or 3 tpi, partly because of the pointy-ness but mainly 'cos it's a 1/4" bit and even at full depth it won't cut a wide enough groove for really coarse threads. My router has a 3/8" collet insert so I just took an old 3/8 HSS drill bit, shortened it to a reasonable length & ground a 60* end on it. It worked very well (I included it & the results in that AWR article, I think). It cuts a slightly flat-bottomed groove because of the web in the centre, so when making cutters for the tap, I just eye-balled them to match the groove. I see no reason why a 1/2" bit couldn't be used the same way (it's the point angle that matters), but I didn't have an old worn-down 1/2" & wasn't about to sacrifice a new one..

A HSS bit won't cut miles of thread the way a carbide bit does, but it will cut 3 or 4 screws without trouble, probably many more, depending on the wood, but it would certainly dull after a couple of bull-oak screws. IIRC, the wood I used for my trial was much easier stuff like Crows ash or Celtis (both of which make very nice screws). However, it's a way to get the job done if you are only wanting to make a couple of screws for a bench.

Hmm, I'm downloading on you a bit, but I'm keen to see a few more folks master wood threads. It will be nice if there are a few other gurus I can hand the guernsey to.....

Cheers,
Ian

[Mountain Ash]

Thanks again Ian. Long posts make me feel more important so don't feel bad.

I actually got my hands on a 1/2" cutter and there is plenty of potential depth. I am thinking of starting again with some smaller threads (moxon vice and clamps) because 45mm thick timber makes up a lot of my offcuts collection. I am keen to work it out because the woodscrews will come in handy in many ways.

[IanW]

I reckon you'll get it sorted pretty soon, MA, you are almost there!

[johknee]

Hi MA

Have you had another go at threading?

I've been reading a lot on wooden threads lately (no shed time, unfortunately). I'd like to make a wooden tail vice screw and nut for a workbench I'm building.
I've read a number of WW threads and watched a few YouTube videos on this stuff, so hopefully some of it has sunk in! I found some interesting blogs on wooden threads by this bloke who makes bookbinding tools. Well worth a look through his site as he has some interesting contraptions and ideas on wood threading. Most are overkill for hobbyists, but interesting nonetheless. On that same site I was reading about thread geometry. I've noticed that most on this forum have suggested a 60 degree router bit for threads. Some others use 90 degree (Carter's Whittling on Youtube) and 80 degree cutters. Is there a reason to use one over the other?

The bookbinding fellow suggests 80 degrees, but he makes his own cutters (see here. Pretty cool!). Of course, he is making screws for commercial purposes, so I understand his motivation to increase efficiency and accuracy.

[IanW]

Interesting link, JK.

I think one reason for the 60* threadform is simply that it's the standard for US threads and people tend to blindly follow custom. There are theoretical aspects to thread angles, but for making wooden bench screws I'm not sure it matters very much what angle you choose. Chipping can be a problem for sure, but in my experience, it's more related to the wood you choose and the threading method you use than thread angles (dull cutters are a sure-fire recipe for chipping!).

A lot of older wood handscrews I've seen (from the UK) had 90* thread angle. About 30 years ago, a friend lent me his British 1" tap for 90* threads and I made a pair of bar clamps using it. At about 4 tpi, it's coarser than the 1" screws I've made since, using a 6tpi (60*) tap a friend turned up for me, but apart from being slightly quicker to run up or back, there is no other difference in functionality between them as far as I'm concerned, they all clamp up securely & I can't say I've ever noticed the difference in effort it takes to develop the same clamping pressure (there must be a difference).

I think what is probably far more important than thread angle for large bench screws is the tpi. That sets the "ramp angle" which is what gives mechanical advantage with a screw. The greater the tpi, the lower the ramp angle and the greater the mechanical advantage, i.e. the more force you can generate with the screw for the same amount of effort on your part. I cannot remember why I chose 4tpi for the 2" screw of my tail vise, but I was most likely blindly following something in FWW, which was my New Testament at the time. The screw I made has worked well & stood up to some pretty heavy use for almost 40 years and indications are it will see me out. My only complaint is that 4tpi is a little slow & can sometimes mean a good deal of winding back & forth if I'm working on several pieces of different lengths at one time, but it's not a major issue.

Nowadays I can make screws of any diameter & tpi I choose, and if I were making a new bench today (extremely unlikely!), I would give serious consideration to using a slightly coarser thread like 3 tpi on a 2" or even 2 tpi on a 2 1/2" screw for the tail vise (a larger diameter reduces ramp-angle for the same tipi). So I think it matters little what thread angle you choose, the diameter of the screw & what tpi you choose are going to have a far greater effect on usability, I think....

Cheers,
Ian