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Biscuit joining frames

Posted: Fri Jun 14, 2019 7:50 pm
by Bluesman
I'm thinking of using biscuits to join my frames, along with epoxy and the standard gussets as proscribed. Does anyone have any reasons why I wouldn't want to use biscuits here?

Your expert opinions are appreciated!

Re: Biscuit joining frames

Posted: Fri Jun 14, 2019 7:55 pm
by hoodman
I don't see any problem with it if you're using gussets as well. Might help you to keep things aligned.

Re: Biscuit joining frames

Posted: Sat Jun 15, 2019 2:46 am
by neel thompson
I think using biscuits to join frame members together is a good way to go. I used this method when assembling the frames on my PB 22 build. You can see the method I used if you look at my current build thread (Neel's Palm Beach 22 build).

Re: Biscuit joining frames

Posted: Sat Jun 15, 2019 4:48 am
by Bluesman
Thanks Neel! Skilled woodworking there...

Re: Biscuit joining frames

Posted: Sat Jun 15, 2019 6:17 am
by mrintense
I'll offer some counter advice. I am not an expert woodworker, so please take that into consideration, but from what I've heard, biscuits and or dowels only moderately add to the strength of the joint. The real strength is from the gussets. Biscuits and or dowels can add to alignment, and I used this approach when making my cabin walls last month. But even with the use of a doweling jig and careful bracing to keep everything flat, I still had very slight differences between panels. Very slight being less than 1/32". Definitely nothing to worry about and they sanded out quite nicely.

Anyway I digress, what I did with my frames was build them in sections using the garage floor(with a layer of plywood to nail the frames into position) and cinder blocks as weights over the joints. I didn't assemble the frames all in one go because I wanted to avoid any warpage from an uneven garage floor. But for the small area of the joint, this worked great. Of course I put wax paper between the floor plywood and the frame wood (as well as between the cinder blocks and the wood).

So I am not necessarily advocating this approach over the biscuit approach, just offering it up as another way.

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Re: Biscuit joining frames

Posted: Sat Jun 15, 2019 8:13 pm
by Bluesman
Good tips Carl! Always willing to listen to another idea. Thank you!

Re: Biscuit joining frames

Posted: Mon Sep 09, 2019 4:01 pm
by Idigplanes
Hello. I am just getting things together for a riviera build and first boat build as well. I was thinking biscuit joining frames would be a good idea. I also would like to ask thoughts on biscuits with today’s good quality wood glue as opposed to epoxy, then epoxy the gussets in place. In my experience, though slight, the wood itself fails before the glue joint. Thoughts please? Also, how about box store exterior grade plywood for the frames. I’m having trouble locating marine grade.

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 3:40 am
by DrBryanJ
I think several have used biscuit joiners for their construction. Some have used Titebond III or similar glues as well. Frames should be made from solid lumber. Difficult to screw into edge of ply. Exterior is acceptable, but might have voids in unwanted places and marine does not.

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 5:15 am
by gdcarpenter
Having been in carpentry/construction for that last quarter of a century, and having built a ZIP, I will add my 2 cents.

If you butt joint frames and they are 3/4" thick material, and the joint is 4" long, that gives you 3 square inches of surface area to bond together. Add biscuits and you help alignment and add significantly more surface area to glue up for extra strength.

In terms of full disclosure I used neither gussets nor biscuits on my frames. I joined my frame pieces with half lap joints.

When all is said and done, and the bottom, side, and top plywood is added, it seems to me that the stress on the actual frame joints themselves is significantly reduced by the totality of the structure.

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 5:42 am
by TomB
Biscuits are ok, big box ply not so much, glues not at all. I used half-laps too, I might use biscuits next time.

Titebond III has a very short open time, once it skins its done. Put it in a critical joint? Why? You're going to learn to use epoxy, ask questions about what works and use the good stuff, its tried and true. Use Titebond for convenience when a failure can be repaired, glue in bungs, glue a piece of trim inside the boat, etc.

Go to a construction site and find a scrap of exterior ply that's been laying in the weather for a month, curled, discolored, and delaminated. Marine ply is without voids and is of uniform thickness, the glue is tested for marine environment, exterior ply? On the other hand I've seen a lot of boats use the stuff. My concern goes back to figuring out how to fix it if it doesn't work.

Here are a couple of places for marine plywood. These guys ship to you and there prices are in line https://www.marine-plywood.us
KI's website says they carry marine plywood https://www.ki-lumber.com/lumber_panels.html. The big box stores will get marine plywood too.

Tom

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 6:11 am
by Idigplanes
Ok thanks for the tips. I see the plans are calling for solo wood on the frames. Everything says mahogany though. Is there a suitable replacement for that?

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 6:52 am
by DrBryanJ
Many have used white oak. I am using sapele. I think douglas fir is acceptable. I have to dig up my boat building with plywood book to be sure.

Re: Biscuit joining frames

Posted: Tue Sep 10, 2019 6:58 am
by Bill Edmundson