Need a tool or method for creating a long miter joint without splines, but still quite strong

[Dolmetscher007]

I am using 3/4" hardwood plywood. I need to create a box that would require a 22-24 inch long mitered joint so as to not show the plys from the wood. 

• There is THIS thing...  from Rockler, but it is $350 and not at all worth it for this application. 
• Then there is THIS thing... from Infinity tools. It is a good bit cheaper. 

Does anyone have any experience with any of these kinds of tools?

Project Constraints:

• The plys cannot show
• It must be strong enough so that a 300 lb person can sit on the box 22 x 22" cube
• Can't use visible splines etc. 

[wdwerker]

Lock miter bits will do that in a router table. Just be aware that the set up can be fussy. The bits that have a set up block available is well worth the investment.  Featherboards are also a very good idea.

[curlyoak]

2 hours ago, wdwerker said:

Lock miter bits will do that in a router table. Just be aware that the set up can be fussy. The bits that have a set up block available is well worth the investment.  Featherboards are also a very good idea.

I would add consider spending a little more and get 1/2" shank bits along with a router with decent power. 2hp. or more.

[Unknown craftsman]

I thinkThat's going to be tough to cut that joint and come out square. Even a box that size with miters would drive me nuts, but then again I'm not really setup for sheet goods so maybe you are. 

For me I would find it easier to make the box with butt joints and veneer it. Or glue on some laminate you can find it with a wood grain texture.

[wdwerker]

1/2 shank bits are the only way to cut lock miters on 3/4" plywood. I would use a 2 1/2 hp minimum router. 3 hp preferred. This works but it's not easy or cheap.

If you don't have a big router and a decent router table veneer is a safer route. Take a look at Joe Woodworker's website and Veneer Supplies.  Paperbacked veneer & contact cement or Heat Lock glue that can be applied then ironed to fix it in place.

[Marmotjr]

The key to lock miter's, I have found, is proper clamping.   Clamp the one side to your bench.  I've used I-beams made from LSL in the past, but a work bench that is flat will work.  Tape the area where the miter will be, so squeeze out won't stick to the bench top.    Apply vertical clamps as you can to pull the miter together, and then tape or clamps at an angle to adjust the miter.  Use a square to confirm. 

[wtnhighlander]

I feel like doing locked miters on all 6 sodes of a cube is going to be extra finicky. If square joins and veneer are not a option, I'd probably lean toward simple miters and a bunch of biscuits.

 

Mmmmmmm.....biscuits.

[RichardA]

Sausage.  Uh huh!

[Woodenskye]

Domino. 

[wdwerker]

Biscuits, sausage, Dominos.....I've got the beer, who's ordering the pizza ?

[Coop]

I would cut mitered edges with an internal support such as a 2” square strip glued and screwed to the inside corners. 

[curlyoak]

Why is it imperative to use plywood? Why not use solid? The thickness of veneer is so slight. Solid you can have a better chance of success.

[shaneymack]

Why don't you use a long spline in the interior of the miter? It meets all your criteria and you don't have to buy anything. 

[Chestnut]

I'd do Shane's method.

Is edge banding an option? I cut my own from similar material and with a  bit of a rounder over you can usually one see it from one face. Then you can just cut rabbets and not have to deal with it.

[RichardA]

51 minutes ago, shaneymack said:

Why don't you use a long spline in the interior of the miter? It meets all your criteria and you don't have to buy anything. 

Aw, Shane.  I like doing it that way, but go back and reread the title. " A long miter joint without splines".    

[Wimayo]

22 minutes ago, RichardA said:

Aw, Shane.  I like doing it that way, but go back and reread the title. " A long miter joint without splines".    

No. He says: "long mitered joint so as to not show the plys". Then he says: "Can't use visible splines etc.". The long spline would not be visible except at the ends. If that is a problem then the spline can be stopped before it gets to the end. A similar option would be a series of close together biscuits that would probably not be as strong, but would be easy to do. Along with this, I think I would be inclined to use epoxy.

[wtnhighlander]

If the box is actually a fully closed cube as suggested, those splines would be completly hidden. They would have to stop just short of the corners, though.

[Isaac]

1 hour ago, RichardA said:

Aw, Shane.  I like doing it that way, but go back and reread the title. " A long miter joint without splines".    

Is it no splines, or no visible splines? It would take longer and be trickier, but you produce something similar at the router table that was covered, say 80" of the length of the joint and would still be quite strong and assist in the glue up.

[Tpt life]

Good Lord this smartphone big brother is getting nosy. 

[Immortan D]

You can set a single row of dowels to reinforce the join. But you'll need to buy or make a jig to drill the holes with the required accuracy.

[wdwerker]

If you go forward with the mitered ply construction I would search for the thickest face veneer possible. That mitered corner is going to be quite fragile. You could build it 5 sided and not worry about the bottom.

[jplemons]

It will probably be fine without anything additional. Just cut the miters on the table saw and glue it up. 

[Marmotjr]

1 hour ago, jplemons said:

It will probably be fine without anything additional. Just cut the miters on the table saw and glue it up. 

21 hours ago, Dolmetscher007 said:

It must be strong enough so that a 300 lb person can sit on the box 22 x 22" cube

Considering I have broken long miters by hand, intentionally and by accident, with very little force, I would hesitate to go this way.  Especially not if it's intended to be a chair. 

 

 

 

[Ronn W]

Get the 4 sides together with good fitting miters is hard enough but ( I would use hidden spines)  but are you going to miter the top to all 4 sides as well????  Sounds like a nightmare.

Here's and Idea.......miter all the corners that you want and then cut a 1/4" x 1/4" dado along each edge of the cube and glue in a 1/4" x 1/4" strip (could be a contrasting wood) along edge.  Make strip slightly oversized and then sand flush.  These could be mitered at the corners, or not. your choice.  This is a little more work but it eliminates the need for 100% perfect miters on all edges.

[wtnhighlander]

4 hours ago, C Shaffer said:

Good Lord this smartphone big brother is getting nosy. 

Yep. Sometimes picks up on conversations even when the mic is "off".