Thread: Best method for 2 metre MDF mitre joint

Mdf when it's glued, even edges, is very strong. It will rip apart the mdf long before the glue breaks.

I make a lot of things with MDF. I align with small edge-jigs that push the lip over the edge by a width of 3 sheets of paper. When it's glued and bradded, it leaves a tiny overhang. Sand this back with the ROS and you get a great gap free edge.

The brads used are just shot out of a micro-bradder and usually are the 3/4" or 1". The heads are all but invisible.

Glue is Titebond 2. I use 3 if my hand falls to it, but it doesn't do a better job.

Edges are painted with Gesso and sanded by hand with a strip of 180. Gives a perfect finish.

I'd probably use a lock mitre bit for something that long. Much easier to assemble, larger glue surface, stronger.

My 2c worth.

Cheers

titebond and pocket hole screws.

Firstly, DO NOT use pocket screws. For anything. At all. Ever. End rant.

If it's getting painted why mitre it? Butt join, PU glue and 50mm screws (pilot-drilled and counter-bored) then just fill over the screw heads with fine auto body filler.

Originally Posted by elanjacobs

If it's getting painted why mitre it? Butt join, PU glue and 50mm screws (pilot-drilled and counter-bored) then just fill over the screw heads with fine auto body filler.

Originally Posted by elanjacobs

Firstly, DO NOT use pocket screws. For anything. At all. Ever. End rant.

If it's getting painted why mitre it? Butt join, PU glue and 50mm screws (pilot-drilled and counter-bored) then just fill over the screw heads with fine auto body filler.

No pocket screws and yet it's alright to use body filler ? body filler is only good to one thing. You can stand on the can to reach for your pocket screws and your kreg jig on the top shelf

Originally Posted by justonething

No pocket screws and yet it's alright to use body filler ? body filler is only good to one thing. You can stand on the can to reach for your pocket screws and your kreg jig on the top shelf

When something is going to be painted it needs to be filled. What, exactly, do you propose to use instead?

Pocket screws are just an inferior method of joining. Aside from being inelegant and lazy, they're weaker as well. http://woodgears.ca/joint_strength/pockethole.html
Also, the way pocket screws are done would mean that in this application there would only be about 10mm of useful thread holding it together which simply isn't enough.

1. Pocket hole screws may be inelegant compared to a mortise and tenon joints but it can't be any less elegant than using screws anyway.
2. I watched that guy doing his experiment, he didn't even conceal his bias. Using only 2 tiny #6 20mm screws with pocket holes on the side with weights putting on the edge, of course it is weaker than two 10mm dowels probably at least 35mm long. I'll bet if the force was applied on the side, it will be a different story. It will be a different story too if the material is not 19mm but 32mm where you can put longer screws in.
3. Polyester fillers are carcinogenic, it doesn't stick very well to wood. Use a sand-able epoxy filler if you must, or cut some wood plugs.

Pretty much EVERYTHING is carcinogenic if you breathe enough of it, dust extraction and/or a mask will sort that out.
I've never had a problem with filler sticking to MDF; never cracked or fallen out.

I like the idea of routing a Mitre Lock, but Ive found even on smaller jobs setup is really tricky. Out a hair and it doesn't work. Long sheets might be a hassle to get right.

Initially there was the option to say "use your domino", but not everyone has the Mighty Spare Cash for such a beastie. If you have a friend with one, con them the borrow it. Its magic.

I've given some thought what everyone was saying. Kreg pocket screws are fantastic, so I disagree with what people say about "strength". I edge glue 16mm MDF to make bookends commercially. I table-route a mortice to 6mm deep and >16mm+0.5 wide on one end, using my little home made MDF align-o-matic (a-la 90° square) I swipe a little TB2 on the edge, get the other bit and rub join it and put in 3 brads. I like using 3/4" brads shot out of my cutsie little Freeman 1" Micropinner (which, BTW is AWESOME). When this assembly dries, it's a very quick blat with the ROS to tidy the overhang.

As a test, just because it was kids stuff and I felt destructive, I tried breaking these. Im a pretty big chappie and the force needed to break a 150mm wide joined board was very significant. In either case, the MDF underlying it gave out well before the glue.

This was good enough for me to say "damn strong". Pre-drilled 1" coarse pocket screws would be very strong indeed. (I'm not disagreeing at all with Mathias W or his methodology, I really enjoy his experiments)