Basic woodworking question...

[Shrug53]

If I join two pieces of plywood usings biscuits, do the just glue together? Do I use finishing nails or something? Just biscuits and glue does not seem like it would be enough.

Also If I want recessed screws, so that I can use plugs to cover them. Is there a special drillbit for that?

Many thanks!

[norm perkiss]

Shrug,
I'm not a woodworking expert, but here's my 2¢.
I've used the biscuit method a couple of times. Most of the glues available today create a bond that is stronger than the wood. The biscuits add strength and provide alignment of the joining surfaces. For cabinets and such, the biscuit method is plenty strong.
I use a "forsner bit" (may have spelled it wrong) for plugging. I start using the forsner bit, drilling deep enough the accept the screw head and the plug. Then switch to a regular bit and continue drilling to complete the pilot hole. There may be other methods, but it's worked for me.
Norm

[toypusher]

Shrug,

Try looking at this link: http://www.rockler.com/ecom7/product_details.cfm?offerings_id=10607

You can get these at most home improvement or woodworking stores.

I have used biscuits for my projects for years. The typical joint is very strong and can withstand quite a bit, however, I would need to know where the joint is being put in your aplication to give you a better feel for the strength. If is is used to extend your sidewall on a teardrop and is supported with vertical bracing and and interior wall, I belive that is should be fine. You may want to use polyurethene glue (i.e., Gorilla Glue).

Just my opinion, but hope it helps.

Kerry

[Shrug53]

Thanks for the info. Yeah the join will be for sidewalls. 4x8 is just not big enough. I would like my sidewalls to be 5x10 but that seems an almost impossible size to find. When you do, it costs a heck of a lot more.

[BrianB]

For countersinking screws, I've always just used a small bit for the pilot hole and then following that up with a drill bit the size of the screw head that only goes a little ways into the wood.

A little more work, but that's a good way to do it if you don't want to go out and buy more tools.

[Shrug53]

If I don't want to buy more tools? I don't understand. I know the words are english, but they make no sense in that configuration

[TWO-CANS]

Biscuits are meant to align your pieces of wood and when used properly, glueing the edge and into the biscuit cut, the biscuits expand and strengthen/secure the joint. Use the right size biscuit to fit your cut, I would, should I glue ply in this manner, not depend on the glue and biscuits alone but have a backer/ support built into the frame at this joint. Glueing with biscuits or scarving can not give the needed strength alone when used on plywood a multi layed edge. Biscuts and glued edges work fine on solid wood in the proper application.
There is a combination drill countersink in any decent tool section of Lowe's Home Depot etc. One hole one for the screw as a pilot and the second wider hole for the plug. Buy a plug cutter also and your plugs cut from scrap amtch the wood your plugging.

[BrianB]

If I don't want to buy more tools? I don't understand. I know the words are english, but they make no sense in that configuration

You're not the only one. I started to twitch while writing that.

[An Ol Timer]

Glueing with biscuits or scarving can not give the needed strength alone when used on plywood a multi layed edge

I have made many scarfed joints, and when made properly, and the right adhesive is used and cured out properly, you can't beat the joint for strength or looks. Just a boatbuilder's opinion

[doug hodder]

I agree with Ol timer's opinion. A scarf joint is going to give you excellent strength. I'm a boat builder too. I think that for the average woodworker, it might be a little bit of a challenge for a joint that may be 4 feet long. I look at it this way. If it isn't going to be seen and is going to be covered with either aluminum or a laminate, I go with using a 3 wing cutter in the router. It cuts a groove 1/2 inch deep into each of the pieces. I then cut a spline in a good hardwood, and glue it up using epoxy. (butt joint with a spline).. It's like adding 10 times the biscuits depending on how you space them. It works for me as I overlayed the plywood with 6mil mohogany on the exterior and birch on the interior. I stretched my 4x8's into 4x10's and they are plenty strong. For me, I always have a tough time scarfing veneered plywood so that the grain matches up really well without sanding into the core. I'm still learning though. Doug Hodder

[Boodro]

Hey Shrug, I extended my wall to 12 ft . Where the 8 ft met the 4ft section I installd a 1x2 poplar on the seam , glued & screwed all the way down the seam ,stagering the screws from side to side . After the glue was cured I filled in any voids with Elmers wood paste along with the counter sunk screws then sanded . You can only tell there was a seam there because of the filler. Other wise it seems to very strong. Have fun!

[len19070]

I had to build some 5X12' plywood for a project and I didn't think just a bisket & glue was strong enough either (though many experts said it was). So what I did was Rout a 1/8" slot in 1/2" Laun plywood, glue in an 1/8" spline to join the 2 pieces. Then laminate 1/8" Laun to each side, staggering all joints. 5X12X3/4 Laun...The Hard Way.

Happy Trails,

Len

[shil]

My trailer's about 10' long, so a 4 x 8 wouldn't cut it. I built the sides from solid 3/4" ply, butt jointed together with wood glue and dowels. I already had a doweling jig and didn't want to buy more tools. Shrug, you're right: those words make no sense.

Anyhow, once the glue set the joint was strong enough that we could easily pick the piece up and move it around, no worries. I positioned the joint right at the galley wall and backed it up with a butt block, with a dado for that wall ploughed into the block. If I hadn't used a dado I would not have bothered backing up the joint.

Scarf joints are swell for boats, where you may be bending the plywood into a boat like shape, there's no 'hard spot' caused by the butt block. IMHO it's overkill for a straight, flat wall. Like Norm said, glues today are stronger than wood.

What a great long post. Bored at work today...