Joining Three Pieces for a Mud Room Bench
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- This topic has 10 replies, 3 voices, and was last updated 5 years, 10 months ago by John Sherman.
7 August 2017 at 6:37 pm #314365
I am stuck in need of help. I have been building a mud room bench for well over a year (on & off). The project is my first serious piece to teach myself work working. The goal was to build a good piece of furniture without any screws/nails. Along the way coming to realize a strong preference for hand tools over machine (Thank You Paul Sellers). The actual parts of the project have been made on & off taking local a woodworking class (using both machine & hand tools) bringing me to this point: how to join the three main pieces (Back, Middle, Front). Attached is a PDF with pictures outlining the challenge.
Thank you, John
So if you can close the gaps with just modest hand pressure, then the gaps are probably acceptable. When you clamp the glue up, the clamps will close the gaps, and because you checked that you can close the gaps with modest hand pressure, you can be reasonably certain you aren’t clamping major stresses into your work.
To add mechanical support to the joints without screws or nails, just drill holes and glue in dowels. After they dry, trim them flush.
Or, you could design and build the components so they join mechanically instead of simply butting up against each other. Looking at your pieces, tapered sliding dovetails come immediately to mind, or the “B” rails could simply be mortise/tenoned into the other pieces. Probably a million other ways, too.
The only way to get this structurally sound is to use mortice and tenons throughout.
Think like a table apron joining the legs. Two tenons square to each other on two faces of the same leg.
It is possible to use loose tenons for this, but I’d make sure it is a nice snug fit. That way you’re not counting on your glue alone.
What you want to do is simply rely on a long grain Glue joints, hoping that this won’t work loose over time and still bear the load of someone sitting on it.
If a proper executed mortice and tenon joint on a chair works loose because of glue failure, it is still strong enough to hold the weight of the person provided there isn’t any torque along the long axis of that joint. If that’s understandable that is.
Come to think of it, you might use some strong lag bolts to strengthen it, but then you’re building furniture Ikea style….
Sorry if my answer didn’t make you happy but the pieces you have so far look very well done, so why possibly ruin the whole thing structurally as said above?
Diego8 August 2017 at 3:10 pm #314422
Thank you for your reply. The gaps appear even with modest clamping pressure. Interesting idea about the dowels. Haven’t thought of that approach and may add an interesting design feature. Would you assemble the three pieces first with glue and then drill the holes for the dowels? What spacing for dowels would you use? I was going to use dowels for the purpose of alignment of the pieces (4 corners)
With regard to design changes I am chalking this one up to lessons learned and would do it differently with more of the front to back better integrated than a butt joint. I like the idea of a sliding dove tail but that would be another day after getting my first dove tail box built. Dove tailing is actually my current skill building goal with material purchased special for this.
Again, thank you for the insights.
John8 August 2017 at 3:51 pm #314424
Thank you, very interesting idea. I do like your suggestions, even the lag bolt one. It’s actually one that I have thought about. The lag bolt is really my last option just because it goes against the original intent of no medal. This project has a design flaw for a glued up project. The original design assembled using screws. At this point I am looking to what can be a sound way to salvage this project. The suggestion about loose tenons is appealing but there are a few questions I have keeping in mind the “long grain” requirement:
1: how deep should the tenons be for the horizontal joints? and how thick? The box (part B) is 3/4 inch thick in the walls, seat, and bottom.
2: is there a suggested width of the tenons? How many would you suggest?
FYI: The material used is White Oak.
The gaps appear even with modest clamping pressure. Interesting idea about the dowels. Haven’t thought of that approach and may add an interesting design feature. Would you assemble the three pieces first with glue and then drill the holes for the dowels? What spacing for dowels would you use? I was going to use dowels for the purpose of alignment of the pieces (4 corners)
If the gaps can’t be closed with modest hand pressure, then I’d say you’re not done. You’ll need to better mate those surfaces…probably time to crack out the jointer or other plane.
After you joint the mating surfaces so the gaps will close under modest pressure, use your alignment dowels during the glue up, get the glue-up done right. The alignment dowels should prevent shifting as you drill the holes for the structural support dowels, but if you feel they might not, then just let the glue cure, and you’ll be sure nothing will move.
Remember, dowels in this sense are nothing but loose tenons which happen to be through tenons. Judging the spacing and size of tenons might have some science, but I’m unaware of it if it does exist…any mechanical engineers want to weigh in on this? In the absence of hard science on the size and spacing of tenons, do the best you can. You want the tenon to be as hefty as reasonably possible given the requirements (must support humans, so there are safety concerns) but you cannot leave the walls of the component that will be mortised too thin, either. White oak is good and strong, and assuming your components are of quality stock I’d want a quarter inch on each side of the mortise hole, and more if I could get it. As for the dowel/tenon, I’d want an inch in diameter if I could get it, but I’d settle for half that. If the components are too thin to permit sufficiently beefy mortise walls and tenon/dowel thickness, then you might have to resort to metal…i.e. screws / bolts. Can’t easily beat the strength of steel.
Looks as though your current design has 4 natural points for the dowel/tenons connecting A to B and B to C, so 8 dowel/tenons in total. The horizontal “B” rails would be my target, since that’s apparently the beefiest part of the middle component, and the vertical rails in the A and C components which abut the B rails appear to be the strongest parts of the A and C components, too.
Edmund and me are basically implying the same thing.
Ideally your floating tenons should be close to the corners. For the sake of strength to distribute the loading forces around the structure.
You would on a table have the tenons interfere with one another requiring a bevel on both inside the mortice.
Here you can offset the floating tenons so they end up right below the other ones you have in your front and back parts.
As for the width of the tenons you’ll have to account for the thickness of the narrowest part. So I guess that means 1/4″ tenons. You might stretch things and go to 3/8″.
I’d make them just 1/4″ under the depth of your front and back parts. And about the same in the center part.
Be sure to use a morticing guide and make sure your short walls are crisp, so you can really put your floating tenon in so it has no room to wobble.
I guess the trickiest part of the exercise will be to line the whole thing up. Fwiw I’d also put a few floating tenons near the middle of the seat.
Diego9 August 2017 at 11:58 am #314438
Hi Diego & Edmond,
Thank you both for the great ideas. Some of them I have floated in my head but not nearly as refined as you have described…or at least needed to hear it from others.
@Diego, the batten idea could be the trick to really bring all of these ideas together for me. If I am getting this right With the battens across the bottom joining the front and back providing the vertical support of the box and someone sitting on it. Tenons would then hold the front and back frames to the box for support against any lateral forces.
If I am missing something do let me know.
Just a great collaboration of ideas. Oh, my wife will thank you too when I get this bench completed.
Will post the finished product when done.
Cheers to you both,
John9 August 2017 at 5:46 pm #314440
LOL….your funny. This piece of furniture will cost me more than buying it out right. It has been fun all the way. No mistakes are a high priority of mine hence finally reaching out for help. I knew the spirit of Paul Sellers lives through his students. Thank you again.
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