Big Wooden Screws

[Trevor Walsh]

I've started making the tooling to make big wooden screws 2 1/4 diameter with 5/8" pitch. Here is the tap body, I ordered forstner bits to hog out the holes for the major and minor diameters in the nut blanks and fixture. Drilling soft maple with an expansion bit didn't prove to be doable.

The unevenness in the kerf in the tap isn't as bad as it looks, does anyone know how fussy the tolerences are in wooden threads? I have only experience with metal threads and I know this would bind in metal, are the tolerences for fit great enough to account for 1/16"+- in thread spacing?

I also attached photos of the early stages in design for a hand cranked screw cutting lathe, cutter will be a router. Essentially it works like one of those jigs you see box turners use to thread lids. Only it can do about 40" of threads and will have changegears to cut whatever pitch I have gearing for. I don't know if I'll make this machine but it's fun to do the design and research the bits.

[george wilson]

A sixteenth of an inch is rather quite a bit of out of tolerance. It will function,I suppose,if the screw fits the threaded nut loosely enough. If the thread in the nut isn't too long(which I'm sure it isn't),I guess it won't matter too much.

Those threads look mighty coarse. For a thread that diameter,I recommend about 3 threads per inch. If the threads get too large,they get so deep that the strength of the screw becomes weakened. The screw is only as strong as its minor diameter. It can be subject to twisting in half if too much pressure is applied to it when tightening the vise,or,when trying to loosen a jammed shut vise(even worse,because you have no control over how much force it might take to loosen a stuck vise screw). So,be careful.

[Trevor Walsh]

Good points, I was roughly working off or the notes in Underhill's book which has the pitch equal to 1/12th the circumference, plus the lands. We'll see how it goes, worst case it was a good practice screw.

[Zach Dillinger]

worst case it was a good practice screw.

HA!

Sorry, that's my sophomoric tendencies showing again....

[ian maybury]

Just guessing, and no doubt there's a whole body of well developed methods for this work - but a wooden screw is inevitably going to have to make allowance for the fact that the nut and the screw could end up with the grain at 90 deg. So that it would need clearance to allow for movement of the wood. Which might be a factor in the choice of species too. Increasing the diameter of the thread would make it stronger, but would also increase the amount of clearance needed for this reason.

Wonder if sealing the screw and nut with epoxy well thinned 50/50 with alcohol (which would penetrate well without building a skin) would help the situation?

Vice screws often have a truncated/flat top to the thread which reduces the possibility of inaccuracies causing binding - done by making the larger (major) diameter a bít smaller than a full thread would require.

:) As an engineer there's a part of me that's not too sure why anybody would want to use a wooden vise screw. There's another that (kind of) understands...

ian

[Andrae Covington]

Cool, so you're making the tap from Bergeron's Manuel du Tourneur ? I've read St. Roy's translation and saw it on his show a few years ago. I'll be interested to see how well it works. The screw-cutting lathe would be ambitious to say the least. It is fun to virtually tinker with ideas like that though.

[James Conrad]

I'm no expert on the matter and can only speak of my experience of using my century old work bench that once resided in a mill belonging to my great grandfather. Both vises on the bench work flawlessly and lock up tight for any woodworking task I have called on them. Only recently have I had a need to fix anything and that was the top of my tail vise, not the screw. Anyway, hopefully the following information will be helpful to you. Below are some pictures of a spare screw, came form the same mill and period of my bench. It is 3 TPI, 1/2" pitch, 2 13/32 major diameter, 1 31/32 minor diameter. You can also see the top of the thread is flat. There is less than a 1/16" difference in thread spacing, so I would shoot for as little as possible, but there is also some slop in the female block so I would say there is room for some small variance.
244611244612
Good luck,
James

[george wilson]

It is wise and correct to have a good flat top on wooden threads. A sharp top would be VERY fragile,and soon would be getting all kinds of chips falling off.

[Jim Ritter]

In the Fine Woodworking book Techniques One there is a chapter on making your own tap and screw box, in case anyone forgot about it. Page 74. The book is a compilation of the first seven issues. The title is Wood Threads by Richard Starr. It might help someone. If it can't be found anywhere, let me know.

[Trevor Walsh]

I made a mistake on my tolerance in the first go around, I believe it to be around 1/16th total that is 1/32+- which would be a lot smaller than my first number.

Zach, Brilliant! I didn't catch that.

Ian, I get what you mean about the why wooden screw thing, for me it's reactionary to a tendency towards "higher tech" a wooden screw has a smaller footprint it terms of manufacturing shipping etc. It's a weird mix of old tech fetishism, ecology, and my preconceptions about what good is. For what it's worth, I daily think about Benchcrafted vises on a bench I'd like to build. I may wind up with a giant wooden face vise and a Benchcrafted tail vise, or the Veritas quick action tail vise.

Andre, I'm unfamiliar with Bergeron's Manual of the Turner but I've watched St. Roy's Screws and Screwboxes episode half a dozen times and read the passage in his book a few.

James, thank you for the pictures and for the measurements.

George, Yes I agree, there is a great YouTube series about this guy (looks like he's maybe 19) building a bench and doing all the work for screws. He's got the 90 degree threadform, but they come to points! Excellent work otherwise, that's the only criticism.

Jim, dug up the article, in the Spring '77 edition. I have to read through it a bit more, but it seems like the perfect pickup point given Roy's stuff to get the rest of the way there.

The minor diameter forstner bit came today and I might have the major at work in a set. So stay tuned for an update. Maybe we'll have a tap and screw making jig this weekend!

[Trevor Walsh]

So we're back, I finally got the cutter ground and the set screw made. I didn't even get to harden the cutter yet because I was too excited to try it out. It came out pretty good, but I still want to try another wood for the nut to see if I can get something that cuts better on the side grain. After that option, I'm going to figure out a way to machine them with a rotary cutter or make a CNC program to cut them.

[Andrae Covington]

Hey, not too bad considering you hadn't hardened the cutter. Surely that will help reduce the tearout, but I imagine that harder woods will end up cleaner.

[george wilson]

Even with the very advanced,2 stage German 2" tap we had in Williamsburg,the holes would not tap fully clean all around. The cutting edges on this 2" tap were very acute,and angled back to give the best shear cutting action. The screw box was cast iron,also with 2 cutters. One did half depth,then the other did the full depth. I saw a similar one in the Dick catalog(European),and it was nearly $2000.00. The German outfit we had there was there long before I arrived in 1970. It serviced all the wooden vise screws in the museum.

[Trevor Walsh]

Good, I think that means I'm getting as good of an output on this project as can be expected.

[Hilary Jones]

If you need more info see Matt Evans tutorial http://www.sawmillcreek.org/showthread.php?163920-How-to-Thread-and-Tap-Large-wooden-Vise-Screws-and-Nuts or this guys youtube collection http://www.youtube.com/user/MrCartersAccount?feature=watch. I have done a complation of their info with Roy's and can say that my leg vice works great.

[William Lohr]

Thanks so much for all the info. I wouldnt have tried this if I hadnt seen the youtube video where it looks so easy. Considering the cost of a set of these, I'd rather spend the time, and learn the technique than outsourse if I dont have to. Thanks again.

[Trevor Walsh]

The Mr. Carter one is pretty good, I didn't quite get Roy's passage in the book, but after seeing the stuff on youtube it made a lot more sense, he's got a few things that I'd change, flats at the sharp points of the threadform for one thing. The Nut blank is at work waiting for my project's on commission to finish up, then I'll be back to it.

[george wilson]

I think those large diameter wooden screws are pretty reasonably priced. I had a lot of trouble getting 4"X4" hard maple when I needed to replace some vise screws for trade shops in the museum. One company,which the museum dealt with quite a bit

sent me a 6' long maple 4x4 for $130.00. it had a HUGE long V shaped missing void of wood in it about 2' long. Above that was a crack 2' long,leaving about 2' of USABLE 4x4. I told them I didn't know how they got off sending me that piece of junk for $130.00,and refused to accept it. I'd have gotten 1 screw from it,IF the crack didn't go a lot farther than it appeared to go into the remaining solid area.

It seemed like maple 4x4 was just hard to find. I can't remember how I solved the screw problem. Might have made them from beech,which I did have,though it wasn't as hard as hard maple. Plenty of old time vise screws were made from beech,though.