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Thread: How to "really" hand cut a wooden screw?

  1. #1
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    How to "really" hand cut a wooden screw?

    About 8 or 9 years ago, I made my first work bench with a leg vise. At the time I use a length of 3/4-10 all thread for the screw. As expected, it has failed, and I need to replace it. I am thinking of using a wooden screw, but I don't have a thread box or tap.

    For a one off job, I was wondering how difficult it is to just layout and cut the threads by hand using a saw and chisel? I'm not concerned with the time it takes (this is a hobby after all), but more with what my chances of making something that will work are vs. the chances that I will end up with a useless, large dowel with ugly little rings around it.

    I guess the same question goes for the nut which I'm guessing I would split in half and cut the threads on the inside half then glue back together. I imagine cutting the inside threads are more difficult, but since the length is not so long, it might go quicker than the screw.

    I'm also interested in the ideal profile for the threads. I imagine that when they are cut with a threading box, the profile is something of a compromise between what the cutter can effectively do and the ideal for the screw itself, but if they are cut by hand, maybe this isn't so much the case?

    I could just buy a screw or a threading kit, but honestly I'm just as interested in trying to make one by hand as I am in fixing my leg vise .

    Anyone have much experience doing it this way that could share your experience or pain?

    Thanks,
    Jeff

  2. #2
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    I saw some second semester students at the North Bennett Street school cutting a screw by hand.

    They laid out the helix with what looked like a tailor's tape measure,
    leaving a "flat" at the apex of the helix.

    They were cutting away the wedge between flats, along the curve when I visited.

    When I inquired how long they had been at it, they replied -
    "Don't ask."

    If those with a more extensive machine tool vocabulary will please excuse my misuse of terms:

    The saw was a basic fine tooth backsaw, turned on and angle to remove the waste in the "valley"
    between the high points of the screw.

    The billet was roughed to a round(ish) shape to begin with, but not a perfect cylinder.
    This was merely held in a vise, and rotated, to allow access to the next section of the thread.

    When the waste was removed along the length of the screw, it was trued with a sharp chisel.

    Depth was checked regularly, to assure that the thread was concentric.
    The finished "screw" was carefully sanded, and burnished.

    The mating female portion was cut with what looked like a metal tap on steroids,
    after the waste had been removed with an auger.

    I was given to believe that this was an exercise, so that ornate turned legs could
    be made, without a lathe. It seemed an exercise in tedium, and it was not
    clear if to me if the student had been instructed to do it this way,
    or was testing out what was possible.

    It seems to me that the challenge of maintaining a consistent depth,
    so that the screw ran in without wobble was daunting.

    ******

    If you start with a straight grained dowel, that is either straight or can be trued on a lathe
    you should be able to manage with a fine saw. Mark the saw for a fixed depth and
    work your way along.

    This, I fear, is one of those exercises that cannot be mastered the first time out.
    It may be one of those projects that are best solved with a credit card.

    http://lakeerietoolworks.com/

  3. #3
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    Cutting the screw will be a piece of cake compared to cutting the nut (IMO). I recommend pursuing a purchase option.

  4. #4
    Quote Originally Posted by Jeff Wittrock View Post
    I'm not concerned with the time it takes (this is a hobby after all),
    Jeff
    I generally think that if this is a person's attitude, they should go for it. Having seen some of the awesome tools you've made, I've no doubt you will succeed.


    I guess the same question goes for the nut which I'm guessing I would split in half and cut the threads on the inside half then glue back together. I imagine cutting the inside threads are more difficult, but since the length is not so long, it might go quicker than the screw.
    You should look in Roy's books. I can't remember which, sorry, but he describes the tap for a large screw. Basically, you have a dowel that's turned to the minor diameter of your threads (or a tiny bit less). You make a hole, stick a cutter through, and wedge or screw it in place. You cut a saw kerf in the shaft that has the same pitch as your threads (might be good practice for cutting the screw). Then you bolt a piece of sheet metal outside the nut block; the sheet metal fits into the saw kerf and guides the tap. There's more to it than that, but this is the basic idea.


    I'm also interested in the ideal profile for the threads.
    90°. Machine threads for most screws bolts etc. are 60°, but wood is more fragile. (by 90°, I mean each side of the thread is 45° to the shaft. Perpendicular to the shaft is a square thread, the predecessor to the acme thread, which you do not want). When you cut the kerf, I'd recommend either using a stair saw, or clamping a stop block to the side of your saw, to control depth of cut.

    This might be expensive if you have to buy premade dowels, but if you can turn your own stock, it should cost very little, except time. Have fun! Let us know how it goes!

  5. #5
    Quote Originally Posted by Jeff Wittrock View Post
    About 8 or 9 years ago, I made my first work bench with a leg vise. At the time I use a length of 3/4-10 all thread for the screw. As expected, it has failed, and I need to replace it. I am thinking of using a wooden screw, but I don't have a thread box or tap.

    For a one off job, I was wondering how difficult it is to just layout and cut the threads by hand using a saw and chisel? I'm not concerned with the time it takes (this is a hobby after all), but more with what my chances of making something that will work are vs. the chances that I will end up with a useless, large dowel with ugly little rings around it.

    I guess the same question goes for the nut which I'm guessing I would split in half and cut the threads on the inside half then glue back together. I imagine cutting the inside threads are more difficult, but since the length is not so long, it might go quicker than the screw.

    I'm also interested in the ideal profile for the threads. I imagine that when they are cut with a threading box, the profile is something of a compromise between what the cutter can effectively do and the ideal for the screw itself, but if they are cut by hand, maybe this isn't so much the case?

    I could just buy a screw or a threading kit, but honestly I'm just as interested in trying to make one by hand as I am in fixing my leg vise .

    Anyone have much experience doing it this way that could share your experience or pain?

    Thanks,
    Jeff
    You might check out the "Barley Twist Table #2" video here. Obviously, it is not about threads, but I have often wondered if you could use the rope-twist carving technique to hand cut a thread.

    Roy shows how to make your own threading box (to put threads on a dowel) in the "Screw Box for Wooden Threads" video here.

    I don't want to derail your thread, but I also wonder if a double start thread would be practical in a woodworking vise. My hardware with ACME threads takes a lot of turns to run it in and out, but I was thinking a double start would allow a much quicker open/close. I suppose you would sacrifice holding power, and thing might work its way loose or something. Does anybody know about the feasibility of this?

  6. #6
    To follow up on Steve's post, I have some pictures to help illustrate and elucidate...

    Backstory: I picked up an inch and a half Henry Boker thread box sans tap at an antique store for a mere $10. I wanted to make a Moxon vise (actually, I still do, as the one I made was given away as an Xmas gift) so I needed to cut the internal threads somehow. I watched the appropriate WWS episode, and made this.

    I made the pitch of the sawn slot the same as the thread box.
    100_7352.JPG

    The sheet metal plates are actually a bit loose, not screwed down tightly.
    It works better this way, as my sawing is a bit off, so some slack in the works makes it turn easier.
    It seems that the various inaccuracies cancel each other out.
    100_7351.JPG

    Here is a shot of the cutter.
    The nut blank (drilled for the root diameter) is clamped onto the base and the cutter run through repeatedly, with a bit more exposure on each iteration.
    100_7350.JPG

    Here is a finished nut, just needs a wee bit of cleanup.
    Note that swabbing the inside of the nut blank with BLO helps immensely in attaining a smooth cut.
    Same goes for the external threads if you use a thread box, soak the screw blank in BLO first.
    100_7353.JPG

    If you hand cut the screw, then you just make a second one (but just the root diameter) with the same pitch for the inside threads.

    Hope this helps further your interest...
    Darrell
    Wood Hoarder, Blade Sharpener, and Occasional Tool User

  7. #7
    That's a nice tap Darrell! The inside threads look good!

  8. #8
    As mentioned, the screw is the easy part.

    The nut is actually easy to make as well. Two methods I'd recommend.

    1. Hand carve the nut. Sounds hard, but it really isn't that difficult.
    A.Take your nut block, drill bolt holes perpendicular to the face you'll put your hole for the threads.
    B. Mark the center of the block, or wherever you want the hole to be.
    C. Saw the nut block in half, bisecting the center mark.
    D. Bolt the nut block together and drill your hole. (drill the Minor diameter of the threads)
    E. Loosen the bolts, and brush some lamp black or similar onto the screw threads.
    F. Take your screw and lay it in the the hole. Tighten the bolts slightly, till the lamp black is marked on the interior of the holes' edges.
    G. take a flexible rule and connect the marks on the inside of the hole.
    H. start carving!
    I. Carve about half as deep as the screw threads height, then double check the progress against the screw. The lamp black will show any areas that you might have out of whack.
    J. continue carving, only carving half the remaining depth until you are a VERY close, double checking after each increment is carved.
    K. Once the Nut fits, make sure it fits all the way up and down the screw. Hand carved screws and nuts have irregularities, which are fine. It'll work well anyhow.

    Method 2: Make the nut first, by making one of those single point taps with a saw plate. Make two nuts. Use the first to make a Thread box.

    Its an addictive thing for the folks that like a challenge!
    Making furniture teaches us new ways to remove splinters.

  9. #9
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    Quote Originally Posted by Steve Voigt View Post
    90°. Machine threads for most screws bolts etc. are 60°, but wood is more fragile. (by 90°, I mean each side of the thread is 45° to the shaft. Perpendicular to the shaft is a square thread, the predecessor to the acme thread, which you do not want).
    That jives neatly with what I saw (if my brittle memory is accurate).

  10. #10
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    Yes,wooden screw threads are a 90º V thread.

  11. #11
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    It CAN be done, having done it a few years back. Not sure if it should since making a tap would take less effort, but I had a ton of fun doing it as a chance to show myself I could.

    IMG_7401.jpg

    Those who do things in normal, sane ways please recognize I did this knowing it was a silly way. I was curious, just gave the first step a try, found it worked easier than expected, tried the next...

    I didn't want to waste a nice piece of thick wood on it since I didn't have enough hope it would turn out. Instead I laminated three pieces of 3/4" hard maple from home depot. Lacking any sort of lathe other than a tiny unimat I turned it the following way:

    I did all the rounding of the long rectangular cross section by hand. I used a combination of spoke shave for coarse work, block plane for truing along the length, and a lot of use of a card scraper. This last I used mostly in the traditional way but also pushed it along flat against the surface so it was laying against the then near cylindrical piece of wood - that helped with truing small irregularities.

    I did keep it mounted between two larger brass screws that I had turned in the unimat so that the ends had a point and no threads, and I cut off the heads before turning so they'd fit in the lathe so I cut a slot for a screwdriver in the heads of the screws. That way I could tighten them as needed to hold the workpiece between two upright scraps clamped to the thing I used as a bench. I also clamped a scrap as a tool rest, though its only use was to stabilize a pencil that marked the high spots.

    In other words, I made it circular by removing the pencil marks and made it straight and true using the above tools to remove areas shown as high by straight edge and, significantly, by just letting the block plane do its work. This took a couple evenings when a lathe would knock it out in a short time.

    For threading I used a metal tape measure. I was so proud of myself for coming up with that idea, but as you see above it is not a new one. Perhaps I encountered it somewhere but I think not - I started trying to use a paper strip and quickly switched to the tape measure that was on the table. The trick was to really secure it with tape to itself and only unwind a few turns before sliding it all back further, lining it up, rewraping it and starting over. Otherwise it got ungainly really fast.

    For the initial cutting of the threads I mounted a bend Japanese dovetail saw blade in a frame - think of a squared off "U" shape trough that was turned upside down and put over the shaft. The end of the trough cut at the right angle for the threads (I recall I had to look up how to compute the tangent or something, it isn't exactly the angle I initially expected). The saw blade was mounted so it could pivot down against the shaft and cut at the correct angle. I simply hand-followed the pencil line (would use a marking knife or saw with the tape measure next time, if there were one). I twisted the shaft as I pushed down on the saw blade to make a light cut, repeated with the saw following the previous grooves easily enough.

    EDIT: In reading the above replies in more detail I remembered one more thing: the saw that I used to cut the centerline of the thread groove was only able to saw to the correct depth because it was attached to a wood backing that kept it from flexing (it was a thin pull saw blade I'd stepped on) and acted as a depth stop.

    I hand cut the grooves for the threads as well but I found it MUCH easier to roughly saw them out at an angle by hand than try to gouge it out the whole way. I didn't have the right gouges, perhaps.

    I did use that same trough thing as a gauge to check the threads: I nailed it to a bottom board so it made a tunnel the shaft would fit snugly in, drilled holes along the sides and top at the correct spacing, and inserted dowels in the holes. The dowels had pointed ends and rode the threads - when I found it didn't turn smoothly I could easily tell where the problem was. That made tuning it very simple.

    For the nut I made a test piece that worked well too: I just used some soft lumber scraps and made a two-piece nut. I actually think it would work fine as it is since inside threads are much stronger. If it failed it would be simple to swap out - were I to ever use it on a vise.

    I'll post pictures in a few. Edit: added old photo. I forgot to mention that I also laminated up a thick portion for the head of the screw so I could use it in a vise. I decided I would hold off since I would like to make a solid one, though it would work just fine as is if I finished turning the top and cleaned up the last couple inches of threads.

    It was a fun project - I always was curious about bootstrapping precision in earlier times and this was just a toy version of a tiny piece of that.

    Don't laugh
    Last edited by Fitzhugh Freeman; 09-30-2014 at 5:21 PM.

  12. #12
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    Thank you all very much for the suggestions and details.

    Fitzhugh, thanks for the detailed description of what you have already accomplished. It is very encouraging, and it does look like something enjoyable to try.

    I have had people look at me a bit oddly when they see the hurddles I end up jumping to try and accomplish something. Sometimes it is hard to explain that I am just as interested in making something as I am in the final product. I think the Neanderthal types probably get that better than most.

    Thanks,
    Jeff

  13. #13
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    Cutting the nut from a solid piece of wood 18" deep was the big challenge when figuring out how to make the giant cider press.

  14. #14
    I know I get it. And I get the same looks.

  15. #15
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    Well, I finally finished one wooden screw / one wooden nut.

    Thanks to all for suggestions on how to proceed. Basically, what I did:

    To make the screw
    1. Laminated three pieces of 3/4" red oak to get a blank big enough for a 2" screw. I also laminated additional pieces for the larger head.
    2. Turned the the blank down to 2" on my lathe.
    3. Made a template using CAD that I could print and wrap around the circumference of the blank and tape in place.
    4. Sawed a spiral kerf 1/4" deep following the template above using a dovetail saw with a piece of tape on the side to help with the depth.
    5. Chiseled out the thread profile starting midway between kerf lines down to the kerf at 45 deg.
    6. Cleaned up the threads with a fine rasp

    To make the nut.
    1. Again laminated three pieces of 3/4" red oak for the nut blank.
    2. Drilled holes for bolts to hold the nut halves together, then sawed the nut blank in half.
    3. Bolted the nut blank together and drilled a 1-1/2" hole in the center.
    4. Made a template using CAD that I printed and affixed to the ID of the nut blank using spray adhesive.
    5. Cut the threads with 1/4" chisel and a paring knife.

    I made the garter plate from some 3/16" steel plate.

    Making the screw was enjoyable. Making the nut was not. I guess I'm just not much of a carver.
    Red Oak was probably one of the worst choices in wood, but it's what I had laying around and that generally determines my wood of choice.

    All in all, it was a fun project for a one-off screw, but I don't think I would get in the habit of making them this way if I had need for more. I think I remember reading someone (maybe even on this forum) saying that you should make something at least once manually before you attempt to make a jig to do that same job. I might make a jig now.

    The big bonus is that my leg vice is back in service! I have to say that my cobbled together bench gets a little more cobbled every time I decide to add or fix something.
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