Design Critique Aug 2012

Scott Keith shared some designs for a bench he is working up and asked for your feedback. For those of you new to the Design Matters Blog, this is an opportunity for builders and designers to get constructive feedback and generate ideas about a design. If you have a comment whether positive or negative, be prepared to explain what you are seeing and why. The process of explaining your own thoughts can be as valuable to you as to the builder looking for input.  The following are his comments and questions:

I have been reading your blog for a while now and really enjoy it.  As a mechanical design engineer I spend much of my time designing from a purely functional stand point, but as a woodworker I have been trying to develop more of an eye for “form” in my work.  To that end, I would like to get your thoughts on a design for a simple sitting bench that I have been working on.  

 It’s an Asian inspired piece with a rather heavy (currently about 1.25 thick) slab seating surface and substructure that gives it a floating appearance.  The overall dimensions are 40L x 18H x 15D.  As can be seen in the pictures, the outer two surfaces of each leg flair out as they go up, and the edge of the bench seat is shaped to match the line of that flair if it were to extend upward.  In order to soften the corners of the seat I created a “clipped” surface that again extends downward for a portion of the leg.  I noticed afterwards that when viewed from certain angles this feature give the appearance a strait leg or even a reverse taper depending on how large the corner clip is and how far down the leg it extends.

 I would like feedback on the basic design and proportions, especially of the front rail and legs, and if the exposed tenons of the under-rails make the design too “busy”.  Of course, any other thoughts would be welcome.

Updated addition to this post – Scott followed up with the following plus some new sketches based on feedback from this on-line community.

 The comments have been very helpful and encouraging.  Several of the folks asked for updated sketches of the piece after incorporating some of the suggestion.  Attached are two shots of the updated design, one with the corner clip and one without it, as suggested by “ejcampbell”. “

Revised Design without corner clip.

Original design front veiw

Revised design with corner clip

 

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21 Comments

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21 responses to “Design Critique Aug 2012

  1. I really this design, my only concern would be the strength of the joints where the tenons join the rails. I would also consider how the top is to be fastened down, after 20 years of professional woodworking I can say with certainty that all timber moves, regardless of how dry.

  2. Jim B

    I too really like the overall design of the piece. I’d lighten up on the base a bit though. The legs and aprons seem a bit chunky for the top. Oops, just noticed this is a bench, not a table. in that case, try adding a bit of thickness to the top and see how that looks. Adjusting these proportions would add the the “floating” effect of the top as well in my opinion. I’m no pro but think that slightly oversized screw holes in the underrails to secure the top would be fine.

  3. Carlos Dominguez

    Even though it is a bench and not a table I feel the legs and aprons are a bit chunky. I think I would also lighten up on the “exposed” part of the tenon. Asian inspired pieces are my favorite to build and feel you have a good concept with the floating top and a flared legs.

  4. I also like the Asian inifluence. The exposed tenons, floating seat, flaired legs, and matching flair on the seat play well together to suggest this. I would like to see a version without the clipping on the legs. I think the clipping fights the other elements. I would also like to see a version with a slightly larger seat to enhance the Asisan feel. These 2 changes should reduce the clunkiness.

  5. Scott,

    I like the general design of your piece. The chamfers on the corners of the legs and top are an interesting and effective way to relieve the edges. I think I would bevel the underside of the top, too. I might experiment making the top slightly (1/4″ or so) larger so there is a little more overhang over the base.

    The piece does feel heavy. Is that something you want? To make it more delicate, you could slim down the legs and possibly make the legs smaller at the bottom.

    Thanks for sharing your work with us and affording us the opportunity to critique your design.

    Chris

  6. I also really, really like this but on first glance thought the legs looked a little thick.

    Since the apron is only jointed to one side of the legs, it could be possible to remove some of the “depth” of the legs on the unjointed face. Then the corners could be chamfered around 60 degrees, instead of 45.

  7. I like this design and really like the legs.
    In keeping with the “brutalist” theme of the overall design, I think that the top is too thin and looks too lite for the rest of the design. If you make the top approximately 50% thicker, you will also be able to incorporate a little more bevel on the corners to follow the line of the legs.
    I drew a picture, but I don’t know how to post.

  8. Scott Keith

    Thank you all for your comments and suggestions so far. I have already begun to make some modification to the design and will hopefully post an update soon. One of the main areas of concern seems to be the overall weight of the base in comparison to the top or seat. In reading the comments and then looking back at the design, I can easily see that now and have made some adjustments to both the seat and the base. I increased the seat thickness to 1.5″ and decreased the proportions of the legs and the rails a bit and can see a positive affect in the overall feel of the piece. Maybe I can thin the seat just a bit so that I can get away with using 6/4 material…. I am also experimenting with increasing the overhang of the top and increasing the bevel.

    As Jim B pointed out in his post, it’s hard to tell from the pictures if this piece is a table or a bench. One of the inherent disadvantages of designing in
    CAD is that true scale of a part or piece goes out the window. But it brings up an interesting point; what design attributes make a bench a bench or table a table other than the obvious scale of a piece? Same for other pieces of furniture for that matter… Interesting.

    Shelldon, you hit on one of my concerns as well; the structrual integrity of the under-rail to front/rear rail joint, which takes the entire load from the seat. Currently the through tenons are .75″H x 1.25″ T, so they are pretty beefy, but I have also been thinking if setting the end of the under-rail into a stopped dado in the rail for added support. Also, I have always planned on wedging the through-tenon (perpendicular to the grain of the rail of course) since there is very little long grain – long grain glue surface in this joint.

    Thanks again for your time and keep it comin’.

    • If you are doing alternate designs, i would really like to see one without the clipping on the legs. The outside corners of the legs have a graceful curve that would carry up into the bevels on the edge of the seat that the clipping interrupts. Allowing this to flow through wouold lighten up the piece, i think. That was the rationale for my original comment. I may be totally off base, but a sketch will show one way or the other.

      • Scott Keith

        Will do. That feature is easy enough to hide in the model to see it with and without. Thanks for the suggestion.

  9. I like the design too but thought it was a little too chunky for a table until I read it was a bench. You’ve got lots of good tips and whether you try thinner or thicker elements consider dishing or saddling the seat a little perhaps?

  10. Kurt

    Please forgive my ignorance, how does one account for the wood movement of floating the top when the stretchers’ grain is the opposite direction?

    • Scott Keith

      Kurt,
      There are a couple of ways to do it. One is to use sliding dovetails, but that can be a bit complicated and the dovetail socket would have to go through the edge of the seat at least on one side. For this application, I will attach the seat with screws coming up through the under-rails. I will use 2 or 3 screws per rail with one of the screw in each set (usually the center one) going through a standard clearance hole. The clearance hole for the other screws would be elongated perpendicular to the seat so that those screws have room to flex slightly with any movement of the seat. For a piece of this width (~15″) I would expect seasonal movement to be less that 1/16″.

  11. dan

    I like this a lot but to my eye I think it would look cool if the length and width of the top were extended a bit so as to follow the curve of the legs. Even cooler would be an section of an ellipse with the shorter axis beginning with the top and going down the leg. So from the top down the curve would reduce quickly at first then diminishing ever gradually down to the foot. this would lighten up the piece a bit as well. Or not ;-)
    Really neat design though.

  12. William Duffield

    I like both tables. But it appears you have “changed horses in mid-stream” without resolving all the decorative inconsistencies that remained. The floating top with chamfered corners and hidden end aprons looks good with the general lines of the legs and arches of all four aprons. However, unless you are designing something as “pure art” or wanting your viewers to ask “Why’d he do that?” it is important that form follow function. To that end, structure and joinery must come first, and afterwards, decoration may be applied to the non-structural surfaces. The problem is that the legs are designed for mortises in each of two perpendicular faces. I know this because I can see the axis of symmetry at 45°, and not parallel to the mortises of the side aprons. Therefore, the lack of joinery to the end aprons leaves two faces “unfulfilled”. TIn either table, the floating top is OK, in one case because it is answered by the ends of the through tenons. However, if you moved the aprons back to attachment with the legs, you would need to devise another support mechanism for the floating top. With the hidden tenons, I don’t know if cutting faux mortises on the inside of the legs and capping them with details similar to the ends of the end aprons would work, but it might stand out just enough if all of them were proud, with chamfered corners, and at least some viewers would appreciate the wry humor. The resolution of your 3D models is just a little too low for me to tell if you intended proud tenon ends, or even wedged tenons. I don’t think the table, as you originally designed it, is too heavy, if the piece of wood you have chosen for the top has strong enough figure to support the mass.

    • Scott Keith

      “The problem is that the legs are designed for mortises in each of two perpendicular faces. I know this because I can see the axis of symmetry at 45°, and not parallel to the mortises of the side aprons. Therefore, the lack of joinery to the end aprons leaves two faces “unfulfilled”.”

      I am not sure I completely understand your comment above. The joinery for this piece has been a concern of mine as well, and I commented on it above, but I wanted to make sure I understand your thoughts. Are you concerned that the assembly will not be structurally sound, since the end aprons (or under rails as I called them above) are moved inboard and attached to the front and rear aprons and not directly to the legs, or is it that there are surfaced on the legs that visually appear to be missing a structural part? Or both? It’s true that the entire load from the top runs through this joint as well as any twisting load on the legs. For this reason I beefed up the thickness of and left the through tenons as large as I can, I also plan to wedge them for additional strength.

      Let me know I am following you or if I missed your point all together. Also, to answer on of your other questions, I am leaning toward leaving the through tenons proud of the aprons surfaces but will probably save that decision for later.

      • William Duffield

        The second issue you mention is my only concern. Structurally, I see no problem with the location of the under rails. It is only a visual problem with the non-structural surface features.

        Something else I said may also have been misinterpreted by yourself or by others reading this thread. When I mentioned “two tables”, I did not mean the first table you illustrated and the subsequent table that you modified based on other comments. What I meant was that I could imagine a previous design of your table, with all four aprons attached to the legs. In that hypothetical table, all the non-structural surfaces follow the design of the joinery.

  13. Turnus

    I like this one – wouldn’t change a thing. I like the heft versus the lightness aspect. The curves are good. Ship it!

  14. Scott Keith

    William,
    That makes sense. There is no real reason to have those particular surfaces of the legs straight and plum since there isn’t any joiner there. I may experiment with changing those surfaces in some way to enhance the overall design. Thanks for the good suggestion.