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  1. #1
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    Default Help with chair design and joinery selection

    Apart from a simple chair made for a three year old, I have never made a chair. Time to start.

    Decided to make a new dining suite. The table will likely be a pumped up version of a recently made coffee table, because I like the look.

    But then there are eight chairs to be made. Having discovered that cabriole legs are time consuming, but not really difficult, I decided they were the go. Have fiddled about with design, and at this stage a likely candidate appears below.

    IMAG0644[1].jpg

    Most chairs are about 900 mm high, but I think I'll keep mine to about 800 mm high, a bit like a Danish chair.

    The legs and frame I can do with my current skill level. I even reckon that without too much grief I can make the bent/shaped backs. The trouble I have right now is deciding how to attach the back to the frame. The intention is to join the bottom of the two side pieces with a piece of timber about 40 mm high, and mortice and tenon joints are the plan. That should give me a back that is reasonably strong.

    My question is, how might the back be attached to the base? I have thought of several approaches. It seems that mortice and tenon would be a strong joint, but I am unsure of how to do that. The base won't fit into my morticer, so the mortice would need to be cut into the frame before assembly of legs and frame. Then these mortices would need to be extended by hand into the tops of the legs. Then comes the issue of cutting the tenon so it is vertical to the floor, and at an angle to the back. I was thinking of making up a jig to hold the back flat, tilting the table saw a tad and then cutting the tenon on the table saw with a dado blade.

    So, I'm on the hunt for ideas and alternative solutions. The easiest solution is to rip off about 3 mm from the top of the 40 mm piece mentioned earlier, glue and screw the back to the base, insert a 10 mm dowel through the 40 mm section into the base every inch or so and then to glue the 3 mm section back on over the tops of the dowels.

    Easy, yes ... but is it strong enough? ... My thinking is that if the base of the back is about 30 mm thick, and if it has a dowel every inch (or even less, if required) that the 12 (or thereabouts) 70 mm long dowels should give a strength similar to a set of floating tenons ... but is this correct?

    EDIT: Just had another thought. I could cut the mortice in the frame before assembly, and at the same time cut another mortice the same size (say 12 mm) into the 40 mm section at the base of the chair. Then a floating tenon the full width of the frame is glued into place. Alternately, I could cut the tenon into the base of the back before assembly with a dodo blade. Any more ideas?
    Last edited by John Samuel; 28th May 2014 at 11:08 AM. Reason: Oops

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  3. #2
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    Hi John, couple of quick suggestions.
    1. Any chair will eventually have someone try to rock back on it if they can. This places an extreme load on the leg/seat rail joint. It's a good idea to rake the back legs back as far as possible, to discourage rocking back.
    2. Whatever you do, an ingenious idiot will find a way to break either the back or front leg/seat rail joint. If this joint is dowelled, it won't be difficult. If it is a tenon, it will be more difficult. Therefore, use a tenon.
    3. Even if you use a foolproof tenon joint, a bigger fool will come along. Therefore, use a floating tenon. It's easier to do, and when you have to repair it (and you will) it will be easier.
    4. Only two types of glue will stick to each other - epoxy and hide glue. Use one of these. Do not use PVA, contact adhesive or Perkins paste (I've seen them all used) or similar. I'm not sure about polyurethane, haven't tried it. Hide glue is not as strong, but it's easier to pull apart and reglue if you need to.
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  4. #3
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    Quote Originally Posted by AlexS View Post
    Hi John, couple of quick suggestions.
    1. Any chair will eventually have someone try to rock back on it if they can. This places an extreme load on the leg/seat rail joint. It's a good idea to rake the back legs back as far as possible, to discourage rocking back.
    2. Whatever you do, an ingenious idiot will find a way to break either the back or front leg/seat rail joint. If this joint is dowelled, it won't be difficult. If it is a tenon, it will be more difficult. Therefore, use a tenon.
    3. Even if you use a foolproof tenon joint, a bigger fool will come along. Therefore, use a floating tenon. It's easier to do, and when you have to repair it (and you will) it will be easier.
    4. Only two types of glue will stick to each other - epoxy and hide glue. Use one of these. Do not use PVA, contact adhesive or Perkins paste (I've seen them all used) or similar. I'm not sure about polyurethane, haven't tried it. Hide glue is not as strong, but it's easier to pull apart and reglue if you need to.
    Thanks Alex.

    Why is it that amongst adults (kids can be forgiven) that it is so often the 100 kg+ monsters who want to rock on their chairs? Beats me. The good news is that this dining setting is in the formal area, and only gets used when we have guests, so it does not get a daily bashing the way most kitchen chairs do.

    If four cabriole legs are used, this limits how far back the rear legs can go ... but the design is far from finished.

    I am not really worried about the joint between the leg and the rail/frame. It will be tenoned, and I'll block the corners very well. It is the joint between the back and the frame/rail that I am worried about, but it seems your comments apply equally well here.

    I normally use PU glue on joints such as these, and will use epoxy or PU on these chairs. Have not been able to find out if PU will stick to PU, but if a repair is required, I know epoxy will. PU is generally preferred because of its versatility. Tarzan's Grip PU sets in 30 minutes, but has a wickedly short open time. The Titebond PU has 20-30 minute open time followed by a 60 minute cure time, so both are much faster to cure than epoxy. In my shop I generally only make one cabinet at a time. I often want a quickish cure time so I can get on with the job, and so I reach for the PU.

    Perkin's paste ... surely you are not serious!

    Cheerio!

    John

  5. #4
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    Quote Originally Posted by AlexS View Post
    Hi John, couple of quick suggestions.
    1. Any chair will eventually have someone try to rock back on it if they can. This places an extreme load on the leg/seat rail joint.
    I was thinking of putting solid wood seats on these chairs, rather than padded seats. Is it worth while gluing these seats to the legs and rails, for additional strength, or am I just making any possible repairs more difficult?

    Cheerio!

    John

  6. #5
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    A solid wooden seat is probably not necessary. The main load is vertical, so strong connections between the legs and seat rails are the most important. This requires rails of adequate depth. There's also the effect of someone twisting in their seat, but joints that are strong enough to handle the vertical racking load should be able to handle that.
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  7. #6
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    Default Rear legs of chairs - Cabriole legs?

    I really wanted to put four cabriole legs on the chairs. However, it seems to me that if (or is that when) someone rocks back on the rear legs, the legs are no longer holding in compression and there might be danger of the toe of the foot breaking off, or worse still, of the ankle breaking.

    Does anyone have any info on this? Did a web search last night and turned up nothing of use. Current design, with rear legs showing only the gentlest curve, is below. Planning on a padded/upholstered seat.
    Sketches Cropped.jpg

    Cheerio!

    John
    Last edited by John Samuel; 30th May 2014 at 04:22 PM. Reason: Update

  8. #7
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    hi John,
    I had to resolve some of these issues a few years ago but for a MUCH less stressed hall table. I looked at a lot of cabriole legged furniture and discovered to my surprise that, other than symmetrical tables, I could find no designs that had matching cabrioles on all 4 corners!
    Many chairs had 'full' cabrioles on the front and plain legs on the back or full on the front and side-splayed only on the back.
    To my eye, full cabriole on the front and plain legs on the back looked best on chairs AND had the added benefit of better mechanics to resist unruly sitters!
    The thread on the Cabriole leg hall table was......
    https://www.woodworkforums.com/showth...letty+cabriole

    fletty
    a rock is an obsolete tool ......... until you don’t have a hammer!

  9. #8
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    John, this video has a bit about the structure of chairs

    http://www.youtube.com/watch?v=qGuNIPHwHgE

    Taken form here

    http://www.youtube.com/results?searc...y=chair+making
    CHRIS

  10. #9
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    John, I like your chair design. It is both elegant and uncomplicated.

    As to four cabriole legs, I really don't think it has a place in the nomenclature of chair design.
    While four cabriole legs is fine for tables it would look decidedly odd on a chair.

    To me this seems to have something to do with symmetry. A table is symmetrical where as a chair
    is not and hence the better look with two different pairs of legs.

  11. #10
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    Quote Originally Posted by artme View Post
    John, I like your chair design. It is both elegant and uncomplicated.

    As to four cabriole legs, I really don't think it has a place in the nomenclature of chair design.
    While four cabriole legs is fine for tables it would look decidedly odd on a chair.

    To me this seems to have something to do with symmetry. A table is symmetrical where as a chair
    is not and hence the better look with two different pairs of legs.
    Did a web search and found no dining chairs with four cabriole legs ... and we likely know why.

    However, for bigger (arm) chairs, items with four cabriole legs are around, but such chairs are not as likely to be rocked back on the rear legs the way dining chairs so often are.

    So, The design of a couple of posts ago (with a few tiny modifications) looks like a likely starter. Next step is to do a test with steam bending to see if I can make it work for this design.

    The current design allows for the back to be fastened to the rear rail with a full length floating tenon. Both mortices can be cut with a dado blade before assembly, so I can use whatever thickness of tenon I want. The material will be about 25-30 mm thick, so a tenon about 10-12 mm thick seems to be the go. All will be revealed when the first test chair is built.

    Cheerio!

    John

  12. #11
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    Four cab legs were done, these ones were upholstered seats and backs and I'm pretty sure I have pictures of polished show wood backed ones as well

  13. #12
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    Here is some more , I was looking at some real nice ones a few days back but the book is at work
    Rob

  14. #13
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    Quote Originally Posted by John Samuel View Post

    Does anyone have any info on this? Did a web search last night and turned up nothing of use. Current design, with rear legs showing only the gentlest curve, is below. Planning on a padded/upholstered seat.
    Sketches Cropped.jpg

    Cheerio!

    John
    The thing about the web and all the different types of furniture that humans have made and the ways it was made is , the web has not covered 2% of the information that is in the books that have been published last century . And the other thing is the books that were published never covered it all either . It is so wonderfully vast . I would guess that books in the 19th[ edit 20th] century lightly covered 30 to 50 % of how things were done. not how they were made but just what they looked like from the Egyptians to now, roughly.

  15. #14
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    one thing I would recommend John, is to draw the chair you want to do full size , all true and square . I do them on a large board of the one straight edge at the bottom with a large square . One of the most important thing to draw is the plan view of the seat through the joints , specialy if the back of the chair is narrower than the front. Then the front and side elevation are transferred from that. All the templates and joint angles can then be taken off that to cut the wood . When I made these chairs, Going from the drawing to the real thing showed proportions that I didn't like, that I couldn't see in the drawing . If I did them a second time around they could have become 20% better than they came out, Proportionally . The third time around they may end up 95% right . And the last 5% you never get. In the old days they did cheap timber prototypes and that solved the 20% problem from the drawing. The chairs are standing on the full size plans that the client was happy for me to go ahead with.

    Rob
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  16. #15
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    Quote Originally Posted by auscab View Post
    Four cab legs were done, these ones were upholstered seats and backs and I'm pretty sure I have pictures of polished show wood backed ones as well
    Thanks auscab.

    Those chairs are very similar in basic design to mine, in as much as the back legs are splayed rearwards rather than vertical like the front legs. I think I am on the right track ... I hope so anyway.

    Cheerio!

    John

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