Ahhh, the New Year approaches and my thoughts turn to making new accessories for my boats.
Last year I made a prototype of a “hammock seat” for my Bell Magic. This seat was an alternative to a slider, and was 24" long, allowing me to slide fore and aft to adjust the boat’s trim. I made the frame (24" long x 22" wide) from 1/4" x 1-1/2" red oak slats, laminated up to 4/4 and the corners joined with…I guess one would call them finger joints (doubled half-laps?).
This seat was a winner in the comfort category, but I overlooked one important aspect: With the long fore/aft dimension I would hit my head on the front cross-member when the portage yoke was clamped on.
So this winter I plan on a Mark II model, this time with a curved front cross-member for clearance and made of ash. I will be using 4/4 ash I plan on ordering from Eds Canoe (good people) so I must use a different technique to join the four corners. My choices are:
Half-Lap - Easy for me to do on my table saw. Not the strongest joint, but the seat hanger bolts will pass through the joint to help strengthen it.
Mortise & Tenon: More challenging, but the tenon is easily done on the table saw, and I have a drill press for starting the mortise, finishing up with chisels. I would probably opt for a through-tenon, and once again the hanger bolts will strengthen the joint.
Finger joint: More involved, but probably doable with the table saw. Tolerances might be the bugaboo here. Not sure if it is actually stronger than the half-lap, but there is more surface for glueing.
Domino Joint (loose tenon): Easy to do, jigs are available, but I worry about strength.
Dowel Butt Joint: Easy, and I have dowel centers, but tolerances are critical and I worry about strength in this joint too. But I can obtain maple dowels. Because of the nature of this joint the hanger bolts will NOT strengthen the joint.
I am leaning toward the mortise & through-tenon despite the work involved. Any comments on the other joints?
Jim
Make your mortise first.
It’s lots easier to make the tenon fit than the other way around. If you don’t have a mortise cutter, you can buy a mortise cutting drill bit for your drill press. Rig up a fence on the press with wood scraps and you’re good to go. You might cross pin the joint with a small dowel when complete. That would sure make a strong joint. Email me with any questions.
Paul
Mortise and tenon
no questions. Doweled butt joints are notoriously weak. Second would be finger aka box joint.
Just practice a bit before you make the mortises, and make sure your chisels are sharp and the backs very flat.
quick search found these
http://www.woodworkforums.ubeaut.com.au/showthread.php?t=49488
http://festoolownersgroup.com/index.php?topic=845.0
Interesting threads
At first I was like “whaaa” when I saw they rated a dowel that high, then I read on and saw the outcry (which I agree with).
Interesting results
I am still leaning to the M&T because of the strength - I am a Big Guy and the front seat member will receive the greatest stress. And I am loathe to invest in a mortising attachment or dedicated jigs as I only have four joints to complete.
BTW, the seat is of a laced variety using 3/16" Dacron cord. A Royal PITA to do, but very cool and comfortable.
Jim
Chinese mitered mortise and tennon
More harmonious, and strong.
http://web.hypersurf.com/~charlie2/Joinery/ChineseJoinery/ChineseJoinery1.html
Ahh, yes Grasshopper
Harmonious and Strong.
And beyond my skill level. I’m gonna be parking my butt on this thing!
Jim
Challenge yourself
They’re not really that hard to do. Well suited for hand tools, or a combination of table saw and hand work.
You can cheat and do it with a floating tenon.
Me like simple
Chinese, Chinese Checkers, Chinese Algebra, and Chinese joints are daunting to me. Right now my biggest challenge is a drill press table that is not perfectly perpendicular to the spindle. That will challenge me sufficiently.
Jim
Bridle joint
Twice the glue surface of the half-lap, not as finicky as a m&t or finger joint (of which, I guess, it really is a variation).
There is a good article in the latest FWW magazine assessing comparative strength of a wide variety of right-angle joints with surprising test results. Interesting read that addresses your question directly.
Edit: The surprise result of the tests in the FWW article is that the simple half-lap won out when racking force was applied to the point of failure. Bridle was close second and, I think, splined miter was third with m&t (with three different tenon thicknesses) after those. All loose-tenon joints (including biscuits, Domino, and dowels) fared poorly. The methodology seems good and hard to argue with.
FWIW Jim, Ed’s doesn’t bend the curve
in their contoured seat’s front rail. I’d cut my joints on a straight piece first, then bandsaw the curve and radius the edges before final assembly.
I’ve got some nice ash scraps in my shop big enough for your project that I can send to you for naught, if you’d like. Not trying to take biz away from Ed’s, I like them too, just thought I’d offer.
The finger joint is stronger than
the wood.
No joint in the actual 90 …
...... keep it a solid as part of the front/rear memebers . If your front/rear members are to finish out at say 1-1/2" , then start with a 3" board . Radius the outside and inside of the 90 half the extension which is 1-1/2" (that means a 3/4" I.S. radius and a 2-1/4" O.S. radius) .
You don't have to make the O.S. radius 2-1/4" if you don't want to , any outside corner softening will be sufficient , just ease of the sharp piont to your liking if you want to , but the 3/4" I.S. radius is adding some beef to the wood in the 90 .
The resulting front/rear members will resemble a "D" .
Then determine your desired seat depth and fill in with the side pieces . If using 4/4 finish stock , personally I would use two 3/8" dowels set into the resulting butt 1-1/2" (that's 3" long dowels) . The dowels would be close to the edges (about an 1/8" if side members are 1-1/2" also) , leaving 1/2" of solid wood between then for the "stainless screw" !! ... or you could make the side pieces wider , say 2" which would give you 1/4" form the edges and 3/4" in the center to drill into ... in which case your 90 would be a change 90 , going from 1-1/2" to 2" .
This screw is installed inbetween the dowels , bored directly into the face of the ront and rear memebers .
Since you would have 3" of depth in the finish 90 , I would use a 1/2" "forstner bit" to bore a 1-1/2" deep hole ... then a pilot for the screw hole 3" (the pilot hole starts at the bottom of previously bored 1/2" "forstner hole (in the center) , goes the last 1-1/2" through the 90 , and another 1-1/2" into the side rail (in the center between the dowels) . Insert the screw with wax or dry soap on it to lubricate the threading ... "note" , the 1/2" forstner bore and the pilot hole are done last after the glued up joint is "set and dried"
"another note" , your pilot hole and screw should be matched size to each other . It "should be" so that you can hand set the 3" screw into hard wood ... if you can turn the (waxed) screw with hand pressure into a hardwood the full 3" depth , you have the correct size pilot hole (only the threads should bite , non of the shank as some do with power drivers forcing a screw into a "too small" pilot hole . Basically the bit for the pilot hole should be the same size or just wee tad smaller than the screws shank , the threads are wider than the shank , right .
The final step is to "plug" the end of the 1/2" forstner bore with a "1/2" plug" and sand out the plug to smooth with the face ... a piece of 1/2" dowel will surfice here , cut off a tad long after glued in (make sure the 1/2" plug (dowel) is bottom to the screw head in the bored forstner hole so you have solid wood to go through for your verticals (hangers). The resulting 1/2" round dot is a pretty thing , a trade mark .
If any of this suggestion is unclear , and you like the idea , just ask me about what seems to be unclear to you ... I think you'll understand what I have explained .
It's the strongest , it's easy , it leaves the least amount of end grain exposed , it's solid , it's a structural 90 .
it looks exactly like an old fashioned
… picture frame joinery .
M&T - the easy way
Jim - don’t you have a router table?
The way I learned to do M&T in the absence of a mortising tool (from Norm) is to use a spiral router bit for the mortise. Do the mortise cut in stages so you aren’t trying to remove too much wood at one pass, making sure the same side of each piece is always against the fence. Use stop blocks to keep the dimension of the cut.
Do the tenon on the table saw, as you said - but instead of finishing the mortise by hand (for square ends), make the tenons full-width of your mortise cut - then round the shoulders of your tenons by hand. It’s much easier to fit the tenons to the mortise than vice-versa.
My head is exploding!
Much good info.
tktoo: I am familiar with Ed's contoured seats (I initially replaced the stocj flat seat with one). My seat is now, and the Mk II will be a flat one - not contoured.
PW: Your description does make sense. My design (I have been refining it with a CAD program) makes use of a 1x4 front member, with the front edge radius to give head clearance. Minimum width is 2". My large seat hangs from a total of eight hangers: the four original holes, two more drilled fore of the original location, and two more utilizing the rear thwart hole locations.
Steve: No router table, but you should see the light bulb that is currently shining over my bald pate! The rounded M&T idea makes much sense.
I will try to locate my Photobucket album where I have pics of teh MK I seat installation.
Jim
Duh. That would be GroveStreet.
http://www.grovestreet.com/PicPage.do?id=1259590
Ah, when you described the new
front rail as curved, I mistakenly assumed in the verticle axis (a la “contoured”).
I remember being impressed by the pictures you posted of your(MKI?)seat. That’s a large area of woven lacing!
My reccommendation of the bridle joint and offer of free wood still stand.
Thanks for the offer
I still have to order from Ed’s as I need to replentish my stock of ash & walnut for my other planned projects.
Jim
it’s cool lookin seat …
… bet it’s comfy too !!
Did you make that one ??
Well , you got lots of ideas to consider for the 90 .
Show us a pic. when you get going with it OK .
I want one of those big ol comfy seats now , lol … given me ideas , hmmm !!