Biscuits in 1/2 ply?

[merrill77]

Has anyone tried this?

I've read that biscuits cause problems in MDF because the expansion of the biscuits will distort the MDF. Will I have this problem in 1/2" ply?

TIA,
Chris

 

[DaveO]

The problems with biscuit "telegraphing" in the surface of the joint are more related to dry time and sanding than anything. Biscuit are compressed pieces of (generally) Beech. Once the water based PVA glues are placed on them they swell to fit the slot cut for them. If you sand the joint before the glue cures you can sand down the potential high spot caused by the swelling and result with a low spot once the glues has cured. That said I have never found that to be a problem, a 24 hour set time is enough to cure the glue to move to sanding....IME

Dave

 

[JimD]

I agree with Dave. Never been a problem for me and I have used them in 1/2 BB.

Jim

 

[Travis Porter]

Ditto for me. Never had a problem with them.

 

[lwhughes149]

Chris, May I ask a few question? I have made projects with 3/4" plywood but never used 1/2". My question concerns the dado's to assemble the project. I cut 1/4" or 3/8" dado's for my 3/4" plywood, what was your measurement for the 1/2". My reason for asking is that I have about six or seven full sheets of birch plywood in the storage building and I am not sure about using it.

 

[JimD]

I would not cut dados more than half the thickness of the wood. I often make them only 1/8 deep. My shallow dados are as much for convenience in assembly as added strength.

Jim

 

[lwhughes149]

So you think 1/8 " is strong enough?

 

[merrill77]

I've been debating dados vs biscuits for this particular project. I'm using 1/2" ply to keep the weight (and cost) down. This is my first time using primarily 1/2" construction - so I'm not sure how deep I would go if I chose dadoes - probably 3/16-1/4. Heck, I'm not even sure how close to 1/2" deep the biscuits will go :>

 

[McRabbet]

Chirs,

The key issue you will probably face using biscuits in 1/2" plywood will be their depth, particularly in 90º joints. Use the smallest biscuits you can and be sure that your biscuit jointer does not penetrate all the way through by testing on some scrap material. If you use dados, I would recommend 3/16" depth and be sure they are sized to the thickness of your material.

 

[JimD]

Relative to my 1/8 dado comment, yes, I think that shallow dados are strong enough for what I use them for. For instance, if I am putting dust frames into a cabinet, I would prefer to use shallow dados, like 1/8, and screws from the other side to hold them in place while the glue dries. It is hard to clamp this arrangement and the screws perform that function. If I use a deeper dado, it gives the screw less to grab into and I think it makes them less effective in clamping the joint.

My other observation is that wood is pretty strong in sheer. Even a shallow dado will resist vertical load well. There is a difference in glueing area but with modern glues I think the 3/4 or 13/16 on the end of the dust frame is enough. I get worried about glue on the outer surface and would probably not try and load up a deeper dado anyway.

As stated originally, the primary purpose of my shallow dados is not strength, however, I think glued and screwed butt joints are strong enough. My main reason for putting in the shallow dados is it makes it a lot easier to assemble the piece.

Jim