Joints for MDF?

[Keefaz]

Hi, all!

Well, the woodwork is going quite well. It's been almost a week since my last awful accident! I think I might be falling in love with my try square: how can something so simple be so useful? Anyway, my question today is about joining MDF. Up until now I've been working in proper wood and have joined wood with mortise and tenons, dovetails, half-lap, but my friend tells me you can't join MDF boards using normal joints?

Do I have to resort to dowels? Biscuits? Butt joints?!

Any advice, much appreciated.

 

[Steve Maskery]

Keefaz

It depends on what sort of structure you are making. If you are using MDF for carcases, biscuits are excellent. Pocket joinery works well, too, especially if you can keep it all on hidden surfaces.

On the other hand, I wouldn't try to cut traditional M&T's or dovetails ar anything like that. Just not practical. Housings work fine though, just don't cut them any deeper than necessary and keep them tight but not overtight (or you will bend the receiving board).

What are you making?

 

[Anonymous]

I use MDF for painted doors, but i would recommend that you use Moisture resistant MDF as it machines better.
So in terms of joins theres no problem with a profile and scribe.

 

[Keefaz]

Keefaz

It depends on what sort of structure you are making. If you are using MDF for carcases, biscuits are excellent. Pocket joinery works well, too, especially if you can keep it all on hidden surfaces.

On the other hand, I wouldn't try to cut traditional M&T's or dovetails ar anything like that. Just not practical. Housings work fine though, just don't cut them any deeper than necessary and keep them tight but not overtight (or you will bend the receiving board).

What are you making?

I'm making some storage boxes for some of our little things that have nowhere to go. They don't really have to be pretty, but I wouldn't want them looking terrible.

 

[Niki]

Hi Keefaz

In my book it's written:
MDF corner joints; Dowel - good. Biscuit - excellent.
MDF edge to edge joints; loose tongue, dowel, biscuit - all excellent.

niki

 

[Paul Chapman]

If you plan on doing a lot of work over the years with man-made boards, then I would rate the biscuit jointer as the best tool. It is fast, accurate and the joints are very strong. I have used one for many years and rate it as one of the best power tools I have ever bought. However, if you can't afford one just yet, a dowelling jig would be a lot cheaper and would also do a good job on man-made boards (see also Niki's recent posts on dowelling jigs). Both these tools also have lots of uses with solid wood.

Hope this helps :wink:

Paul

 

[engineer one]

i agree with all the foregoing, but in principle mdf doe s not have
the capability to be fixed in the same way as "normal" wood. its
strength is in the wrong directions.

spax or reiser screws are good, but biscuits and dowels are also good too.
although steve is right about housings, i tend to use biscuits
or dowels to enhance the strength.

go for titebond as a glue, and make sure your corners are
straight.

later you will find that when it comes to taking these boxes apart,
the joints won't fail rather the mdf around them.

paul :wink:

 

[Argee]

Depends what you've got available to make the joints, I guess :

Ray.

 

[George_N]

I've been trying out loose tenons to make frame and panel doors. Very easy with a router table, and so far they seem pretty robust. I,ve also just bought a Freud biscuit jointer for kitchen cabinet work.

 

[engineer one]

ray, very interesting use of your "leigh" jig

but what are you using the items to hold up? my
only concern is weight and bending actions,
paul :wink:

 

[Steve Maskery]

I've been trying out loose tenons to make frame and panel doors. Very easy with a router table

Yes, loose tenons are an excellent joinery technique. I'm just now making a sheet materials storage rack, and using loose tenons for that. I'm using the new Festool Domino jointer and it is just the best thing on the planet. Quick, accurate, easy peasy.

Cheap, too. NOT!

 

[Keefaz]

Hi, guys, thanks for the replies.

I'm wondering. If I go down the dowel route, whats the best (i.e. cheapest but OK) way to start making dowel joints? My eyes tell me it's just a case of making some holes and gluing in some dowels, but my head tells me it can't be that simple...

 

[PowerTool]

Wolfcraft do a reasonable dowel kit for about £15 - available from Machine Mart and Screwfix to name but two.

Andrew

 

[Argee]

ray, very interesting use of your "leigh" jig

but what are you using the items to hold up? my
only concern is weight and bending actions,
paul :wink:

These are drawer boxes. As the OP talked about storage boxes, the inherent problem would be to keep them square and as that's the same issue with drawers, I just thought of it as an alternative solution. The bottom would be set into a proportionate groove, which - if positioned correctly relative to the joints, is invisible, although it needs to be a stopped groove on two sides.

Through dovetails would be a bit more tricky in MDF, but the Isoloc (TM) joints, as shown, cut beautifully and the amount of glue surface is obvious.

That said, a biscuit joint, especially one involving a rebate, would also work. If a size 20 slot was cut in one board, then a 4mm rebate milled, the remaining slot will take a size 0 biscuit. A 2mm rebate will then have a size 10 slot remaining. You cut the corresponding slot in the mating board once you decide the depth of the rebate. The rebate shoulder assists with keeping things square and adds a little to the glue surface. This technique also works with conventional housing joints, but does require accurate milling.

Ray.

 

[Paul Chapman]

One of the best and most versatile dowelling jigs was the Record 148 (I think the later ones were sold under the Marples or Record/Marples brand). These unfortunately are no longer made but seem to come up quite frequently on ebay, so it might be worth keeping an eye open for one :wink:

Paul