Wood Working Joint Question

Discussion in 'Other Skills' started by UAHiker, Feb 10, 2017.

  1. UAHiker

    UAHiker Supporter Supporter

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    so i'm fairly new to work working and am planning on building a buck saw in the near future. i've seen plenty of designs where the cross member ties into the uprights by a mortise and tenon joint which from what i know if done correctly is one of the strongest joints in wood working. i also know there a bunch of other joints for different applications like dado, rabbit, dovetail, finger ect... but i just ran across a webpage of a guy who built his bucksaw using a shallowish dado joint to join his cross members to his uprights....... i'll put a picture below...

    even though a dado joint is way easier to make then a mortise and tenon joint and most dado joints i see are on book shelves i wouldn't have thought to use one in this application. i would think there would be a potential of the cross member slipping out if there wasn't enough tension and when tension is applied by the string or what ever your using you might create a gap between the two pieces or cause over time a dent in the wood to occur. am i thinking correctly? any other disadvantages or potential advantages to a dado joint rather than mortise tenon joint in this application?

    also is there any special formula to determine the length of the uprights vs how far up the cross member should be? for instance if you want to be able to cut a 9" dia log you would need at least 9" between the bottom of the cross member and the blade but does it matter how tall above the cross member is as long as you have a few inches to create tension on the blade?


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  2. JIMBETHYNAME

    JIMBETHYNAME Tracker

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    Are you sure its not a hidden tenon? Any pics of it apart?
     
  3. JIMBETHYNAME

    JIMBETHYNAME Tracker

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    I dont see how just a dado would stop it from popping out
     
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  4. Broke

    Broke Back yard bushcrafter Supporter

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    I can see where a tight enough Dado would work. Having said that it will not last as long as a mortised tenon as the tenon gives you a much greater amount of wood to wood contact.
    Now the key question here is not which is better, as the tenon is obviously better, the question is will it really make a difference in the long term. And I can't answer that as I haven't tested it, at all...
    Adam G
     
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  5. Todd1hd

    Todd1hd Tracker

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    On the last bucksaw I built I do not have any "holding devices" between the cross and the upright. They just butt up to each other. I have yet to have an issue, the tension of the blade holds everything in alignment. I have used several methods in previous saws and found them more effort than reward. I will say an easy method is to assemble the saw and drill the cross piece and uprights together and use a dowel rod glued in either the cross piece or the upright and let the opposite end float.
     
    Last edited: Feb 10, 2017
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  6. UAHiker

    UAHiker Supporter Supporter

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    just this one.

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  7. UAHiker

    UAHiker Supporter Supporter

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    that's what i was wondering.... i might make one out of scrap 2x4's i have. granted won't be as strong but an interesting test
     
  8. Bob_Spr

    Bob_Spr Scout

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    The term I've heard applied to the uprights above the cross member piece is 'adequate'. They have to be long enough to provide 'adequate' tension to the blade and the cross member. If I am improving a saw, I get lazy sometimes and just add three inches to the above cross member pieces. In other words, if there is 9" between the blade and cross member, the uprights above the cross member, I make 12". It's not perfect and if I were building one at home, I would be more accurate. But it's improvised and I can remake one if it doesn't work the way I want.

    Bob
     
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  9. Backyard

    Backyard Supporter Supporter

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    Thinking out loud. I have made a few pieces of furniture and used most of the joints you mention above.

    I've used a mortice and tenon joint on a number of tables to keep the legs attached to the apron rails. This keeps the table base squared up. My thought is that the joints (2) are supporting force in multiple directions 90 degrees apart.

    The spreader in a take down bow saw is supporting forces that are pointed at each other, so when you add pressure while winding the cord, that force locks in the spreader. If you don't have enough pressure, the saw may twist and the spreader will pop out, but if you do have enough force, I have to believe the spreader will be locked in. Not as securely as if there was a mortice and tenon, but I believe it will function.

    My bow saw has a small mortice and tenon. I think the main benefit is that with the mortice and tenon, there is enough friction to make it easier to keep the spreader in place while tensioning the cord.

    Regarding the vertical arm length; if you are making a take down bow saw, the length of the arms are determined by the length of the blade. The location of the spreader will most likely effect how much you need to wind the cord in order to apply the correct force to the spreader. Maybe think about it as a lever and fulcrum.

    Just my thoughts.
     
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  10. Youcantreadinthedark

    Youcantreadinthedark Chaotic Neutral. Supporter Bushclass I

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    I'm not sure I would even call that a dado...In your example, for practical purposes, the dado is just a tenon with no shoulders, housed in an open mortise. I would not build something under tension with that method. Would it work? Sure; you probably can't put enough lateral pressure on the handles to dislodge the bar, but essentially you've sacrificed a whole lot of stability to save half an hour during the build. I've seen ad hoc bucksaws made with a V-notch in the braces and a flat point carved into the bar; even that seems like a stronger system.
    Mortise and tenons are strong joints for several reasons, namely because you're greatly increasing the long-grain gluing surface that you have to work with. The real beauty of the m&t (especially in an unglued application like this) is that you have structural insurance against lateral stress (ie it prevents your work from twisting) in two directions - along the y and z axes - because the shoulders and cheeks of the tenon check any movement in those directions. Go with the mortise and tenon. I've never made a bucksaw, but I would assume you want to cut your tenon shoulders on a slight bias, with the wider angle pointing towards your tensioning system, so that you're not fighting the shoulders when you tighten things up.

    As far as handle distance and acceptable length go, that is subject to what wood you use, and the characteristics of that wood. Choose your grain carefully (no run-out, good consistent rings, quarter-sawn if you want to get picky) and leave plenty of meat around your holes and notches, and you should be in good shape to create a handle to suit your needs.
     
    Last edited: Feb 10, 2017
  11. UAHiker

    UAHiker Supporter Supporter

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    thanks guys! just along the lines of what i was thinking :)
     
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  12. VtBlackDog

    VtBlackDog Guide

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    Todd1hd-brilliant, going to try that once the garage is above freezing
     
  13. 66drifter

    66drifter Scout

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    i have been pondering this issue for some time and IMHO there needs to be some sort of physical means of keeping the cross member/horizontal beam from slipping out sideways

    w/ the above pictured daddo it wouldn't/shouldn't take much to achieve this goal

    something like the mentioned dowel thru the vertical beam into the horizontal beam would be simple, inexpensive and if the dowel is cut so it doesn't stand proud of the horizontal beam's edges it would not snag or be snagged/broken while disassembled for carry

    something as simple as an allen head screw imbedded in the daddo of the vertical beam could fit into a hole in the horizontal beam

    doweling the ends of the horizontal beam would put the protruding dowels in jeopardy when disassembled for carry

    if i were to get really creative and make all 3 beams out of laminated material it would be quite easy to make a tongue n groove joint at that point

    in any case the joint needs a bit of slop to allow for the assembly/disassembly w/o binding

    sloppy butt snug if that makes any sense

    i guess the thing that'z holding me back is finding the piece of wood that calls me to make saw dust... to create a device that makes saw dust ;-)
     
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  14. lodge camper

    lodge camper Scout

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  15. Backyard

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    I respectably disagree regarding the bit of slop required for assembly disassembly. The tenon should fit snugly in the mortise. An application of bees wax is all the is needed to ensure ease of assembly and disassembly. Adding slop will wear down the mortise and make the joint weaker. With this type of joint, and the appropriate tensioning force created by the cord, there is no need to lock in the tenon with a dowel.

    Edit: I just reread your post. Putting a dowel into the spreader is essentially the same thing as creating a mortise and tenon joint. Question is if you want to run the risk of losing those dowels in the woods, or having the tenon on the spreader.
     
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  16. 66drifter

    66drifter Scout

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    me thinks i didn't explain my thoughts clearly enough

    in my feeble mind a MORTICE N TENON JOINT is a process where a squared(90ยบ cornered) tenon is inserted into a like sized/shaped hole and is frequently beyond the ability/desire of the casual wood worker/bushcrafter

    you are quite right in stating the M n T joint SHOULD be snug and have no slop

    my suggestion does not include the use of a doweled M n T joint, it only used a dowel that is glued in a hole drilled thru the vertical beam that just barely protrudes into the daddo groove

    this slight protrusion of the round hard wood dowel needs to have a very slight bit of slop to allow for ease of assembly/disassembly W/O added lubricant and still be snug when in use

    in my experience the addition of friction reducing agents, even natural ones like bee's wax, attracts/holds dirt particles which eventually generate issues

    maybe the term SLOP i used may not be the most correct one for my design feature since the amount of SLOP i am proposing is butt a chigger whisker's worth, just enough that the joint doesn't bind during dry assembly/disassembly(even in high humidity conditions)

    as i have seen these saws in action the vertical beams have to wobble ever so slightly for assembly/disassembly and my designed slop would allow for that w/o endangering the dowel pin's integrity

    once the 3 beams are assembled the flat ends of the horizontal beam fitting snuggly into the flat bottomed daddo and held in place by the spanish windless secure the joints quite well
     
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  17. Todd1hd

    Todd1hd Tracker

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    Above freezing makes life happier when woodworking. The dowel is a simple working solution unless you are interested in furniture quality projects, then it's probably frowned upon by true craftsmen.

    And if you are interested I can take a pic of my last saw and post dimensions tonight.
     
    Last edited: Feb 10, 2017
  18. clanmaki

    clanmaki Supporter Supporter

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    My mortis and tenon work is pretty horrible, so I have found using two oak dowels side by side for the tenon and two simple drill holes for the mortis work great.
     
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  19. Megalos

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    It seems that almost any joint works. My first bucksaw is built with a mortise and tenon joint and it works so far. I have groves in the uprights so they cover the blade when broken down. The tenon meets this groove and I worry about the strength of the wood there. I think you can get by with a very shallow tenon to keep things lined up.








    Other solutions...


    An Error Has Occurred!
    This shows a nice build with plenty of pics.

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    I have seen many designs that have the joint between the cross piece and uprights at an angle and some that are rounded. I believe this is to adjust to the pull from the cord.

    That's what I have anyhow.
     
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  20. MikeInBoston

    MikeInBoston Tracker

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    Why not mortise and tenon, did I miss something? 1/4" chisel, saw, hammer and square.
     
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