Attaching middle thwart with a mortise and tenon

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WMegl
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Attaching middle thwart with a mortise and tenon

Post by WMegl » Tue May 14, 2019 1:39 pm

On my Redbird, I intend to attach the middle thwart with a mortise and tenon joint. I entend to epoxy a short block under the inner gunwale to provide a little more meat for a thicker tenon.

What thickness tenon would you recommend? I go by the rule of thirds: a third of the thickness above and below, and a third for the tenon.

Right now, I am thinking of each third being 3/8 in. I want to minimize the thickness to prevent the outer ends of the thwart from looking "klunky" bbecause they are so thick to accomodate the mortise and tenon joint.

Thanks.

Wayne

I tried to attach pictures, but I received the message that my files were too large. I have attached pictures previously. Has the forum changed the size picture it will accept? If not, how do I attach .jpeg's around 2+ mg.
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WMegl
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Re: Attaching middle thwart with a mortise and tenon

Post by WMegl » Tue May 14, 2019 1:48 pm

I created a folder on Google Photos and here's the link. Please let me know if this doesn't work.

https://photos.app.goo.gl/wnRFGme6Vt2cvz319

Thanks.
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Jim Dodd
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Re: Attaching middle thwart with a mortise and tenon

Post by Jim Dodd » Wed May 15, 2019 8:59 am

Thwarts, usually receive more downward pressure, and so reinforcing on the bottom would be good !

I worry about the size of your mortise. Will it weaken the inwhale ?

I've been experiencing trouble with Photobucket, sharing my recent pics. Having the same sizing problems.

here is an old pic (I hope)
Image

Old pics work, just not the new ones. So who's fault is it ?
This needs to be fixed ! HELP !

Jim
Keep your paddle wet and your seat dry!

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WMegl
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Re: Attaching middle thwart with a mortise and tenon

Post by WMegl » Wed May 15, 2019 9:44 am

Jim: Thanks for your reply.

I don't think it will weaken the inwale because I will be adding to it's depth with the additional piece and as you know, epoxy is stronger than the wood.

I can't mortise the yoke to a 3/4 in. inner gunwale- that's too thin- 1/4 in. on top, a 1/4 in. tenon, and 1/4 in. on the bottom.

So, what is the correct thickness? I think my choces are a 7/16 in. tenon (toal thickness of 1-5/16 in.), a 3/8 in. tenon (total thickness of 1-1/8 in.), or maybe even a 5/16 in. tenon (total thickness of 15/16 in.)
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Jim Dodd
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Re: Attaching middle thwart with a mortise and tenon

Post by Jim Dodd » Thu May 16, 2019 10:43 am

Butt join two pieces of wood with epoxy. Wait a week and try to break ! It will break at the glue joint. That is the reason we Scarf the wood we use on gunnels ! At least an 8-1 ratio ! I usually do a 10-1 ratio.

I don't like mortising thwarts, as it makes it near impossible to remove, or repair if broken. It may look cool, just not structurally a good idea, in my opinion.

If you want the thwarts level with the gunnels, Just pin and glue a block to the thwart, that can be attached to the underside with glue and screws. This way if it breaks, you are not destroying the inwhale.

Just an idea, not a recommendation.

Good luck !

Jim
Keep your paddle wet and your seat dry!

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WMegl
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Re: Attaching middle thwart with a mortise and tenon

Post by WMegl » Fri May 17, 2019 3:27 am

Thanks, Jim.
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Patricks Dad
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Re: Attaching middle thwart with a mortise and tenon

Post by Patricks Dad » Sat May 18, 2019 4:16 pm

I have always attached my thwarts with just epoxy and level with the gunwales. Rather than a beefy mortise and tenon joint, I use biscuits (as in biscuit joiner). They are quite strong and don't take much space.
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Re: Attaching middle thwart with a mortise and tenon

Post by WMegl » Tue May 21, 2019 7:24 am

Randy: That's
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Re: Attaching middle thwart with a mortise and tenon

Post by WMegl » Tue May 21, 2019 7:29 am

Randy: That's a good idea. I didn't think of it because I was thinking I needed a stronger joint so a mortise and tenon was the only joint I considered.

Thanks for the reply.
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Jim Dodd
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Re: Attaching middle thwart with a mortise and tenon

Post by Jim Dodd » Tue May 21, 2019 9:29 am

Just a thought !
If broken a thwart that is bolted to the inwhale is easier to replace, than one that is glued .

Jim
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Patricks Dad
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Re: Attaching middle thwart with a mortise and tenon

Post by Patricks Dad » Tue May 21, 2019 10:09 am

Jim, I think a bolted on Thwart might indeed be easier to replace. But consider the case where a bolted-on thwart breaks and due to its firm attachment to the gunwale, causes the gunwale itself to be damaged in the process. I think I'd rather have a thwart break clean away from the gunwale than tear out a portion of the gunwale as it fails.

My only experiences with broken thwarts (actually yokes) was on kevlar canoes where they are indeed bolted on but the aluminum gunwale is flexible to not be permanently damaged when the yoke was broken. In that case, the repair was fairly easy.
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Re: Attaching middle thwart with a mortise and tenon

Post by Cruiser » Wed May 22, 2019 12:49 pm

I am a little late to this party, but I tend to favour removable thwarts just for ease of maintenance. If you want to replace or varnish, you just remove and replace/refinish.

I have also taken to top mounting the thwarts to maximize room beneath for pack loading ... when i mentioned this previously, some folks indicated it would/could interfere with loading and unloading, but I have never had that issue.

Have you considered just mounting with regular hardware or even helicoils? This is a pic of my mount for a removable yoke .. it is pretty simple and weight cost efficient, you can get locking ones for more permanent installations, or free running for easily removable ones.

Image

And a mount using regular hardware

Image

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Jim Dodd
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Re: Attaching middle thwart with a mortise and tenon

Post by Jim Dodd » Wed May 22, 2019 2:02 pm

Patricks Dad wrote:
Tue May 21, 2019 10:09 am
Jim, I think a bolted on Thwart might indeed be easier to replace. But consider the case where a bolted-on thwart breaks and due to its firm attachment to the gunwale, causes the gunwale itself to be damaged in the process. I think I'd rather have a thwart break clean away from the gunwale than tear out a portion of the gunwale as it fails.

My only experiences with broken thwarts (actually yokes) was on kevlar canoes where they are indeed bolted on but the aluminum gunwale is flexible to not be permanently damaged when the yoke was broken. In that case, the repair was fairly easy.
A good point Randy ! The size of the thwart would come into play ! A Heavy thwart, would tend to break the inwhale first.
Most thwarts I've seen over the years were bolted on. Not to say that is the best ! Just the most common.

Also how well it was fastened as far as gluing ! Biscuits ? Would they break before the inwhale ?

I guess we should have a Thwart braking contest ! Ha ! Count me out !

Cruiser
Giving a little thought to putting your thwarts on top would be OK, if you didn't slide your canoe on the rack, like I do.
I like the Heli coil idea !

Jim
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Patricks Dad
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Re: Attaching middle thwart with a mortise and tenon

Post by Patricks Dad » Wed May 22, 2019 2:30 pm

You could use Brian's Helicoil solution mounting the thwart on the bottom side of the inwale and still slide your canoe on the rack without issue.

I used these to mount my seats on a Freedom Solo a few years ago. Very clean.

And no, I'm not in on the thwart breaking contest either....
Randy Pfeifer
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