ply/mdf joint options

Biscuits Needs machine

Dowels Need jig at least

Domino dowels Needs overdraft

Depends on what strength you need, and what tools you have at your disposal.

Biscuits are quick and easy, give easy alignment etc, but don't add a huge amount of strength.

For big sections, a simple rabbet in the edge of one of the pieces:

########## _____########## ###############

Means that the perpendicular board now locates on two surfaces, the rabbet helps keep it square, and gives double the glue area. Also you can now drive pins into the joint from both sides of the corner through one panel and into the "end grain" of the other.

You can cut the rabbets very quickly on a table saw, or with a router.

I made up some filing cabinet style drawers like this - 1/2" ply sides, and 3/4" ply back with a 1/2" square rabbet out of the corners:

Another very handy technique for 3/4" board is a mitre lock bit on a router in a table. Like:

Glue - white PVA - and panel pins. TBH if you clamp/strap the thing, while the glue sets, you don't need the pins.

As long as you have a structure where the joint is notexposed to bending stresses, this is as good as it gets.

Used to build ply and chip loudspeaker cabs like this. In hundreds.

the joint has excellent tensile properties, but will still fail if you use the leverage of the thing to BEND the join.

Dovetailing and glue is rock solid, but the appearance is less good

plain glueing is stronger than flatpack stuff by a considerable margin.

Glue joints usually fail because of warping, but with ply and MDF there isn't much.

Oh on MDF which is loaded with resins, a resin glue may be better.,

Dependent on the finish you require and thickness of material (3/4" [18mm] minimum) , countersunk screws with wooden (ply) pellets glued into the countersing to hide them. If you wish to obtain a possible feature using pellets, you could use lighter or darker (real) wood for the pellets.

I use that system often when making garden furniture or internal shelving rather that using stopped housings and dovetails - when the use of hidden joints and fixings is not really that important.

Cash

Might be useful to know what kind of furniture you're thinking of

MRMDF - usually pale green is much nicer to use and delaminates less. The outer surfaces seem to have a better seal on them and take a paint finish much better. It does cost more but not a lot 25% say?

There are some special screws and matching drill bits for screwing into the edge of MDF - sorry can't remember the make. Whatever you do, don't screw into the edge with out drilling a pilot hole first. Watch out for turbo gold type screws too. The rifling in the threads tears MDF to dust and has very little strength - useless if you have to take a screw out and re-fit for any reason.

I suspect you might have meant confirmat screws.

I have used them myself to build a couple of melamine-faced board cupboards. Easy enough to use if you can ensure you drill holes nice and square - and the right diameter.

Yes those are the ones. Certainly drilling square and exactly in the right place is essential to decent results with any screws. Biscuits are useful to hold alignment in one axis but add no strength

Dowels. Depending on how thick the ply is. Or screws and glue depending on how strong it has to be. It will never look professional with ply unless you glue on edging strips.

You can use these things without a jig at a pinch.

glued in dowels, or rout a rabbit in one to take the other

I've got a dog that routs rabbits.

You can borrow him if you want.

Using mitred joints, bracing and inside edge/corner reinforcement? Don't see it being that strong otherwise.

Probably illegal to rout a rabbit in some parts .... and maybe mandatory in public schools

Biscuit cutters are very cheap these days. And they can be used for all kin ds of other jobs, e.g. cutting out floorboards, cutting slots, trimming the bottom off doors in place etc. For those who don't have one, a biscuit cut ter is like a tiny circular saw with guards around it.

inds of other jobs, e.g. cutting out floorboards, cutting slots, trimming t he bottom off doors in place etc. For those who don't have one, a biscuit c utter is like a tiny circular saw with guards around it.

mmm I've got router bit for these - used a few times bit awkward - is it ju stified to buy a dedicated machine?

Cheers Jim K

This is uk.d-i-y. It is always justified to buy a new machine :)

But seriously. I have both and use both. Much easier to do biscuits with a dedicated machine.

l kinds of other jobs, e.g. cutting out floorboards, cutting slots, trimmin g the bottom off doors in place etc. For those who don't have one, a biscui t cutter is like a tiny circular saw with guards around it.

t justified to buy a dedicated machine?

mmm Draper or Ferm for £45 odd eeny meeny miny mo....

or what else & why?

Cheers

Jim K

Well, out of those two the Ferm generally gets good recommendations in the Woodworking fora.