Miter joints - sell me on 'em!

[Paul Carmody]

I'm about to start cutting a lot of wood for a large-ish project (sorry, can't say much beyond that. Still highly classified ). I've always defaulted to butt joints, followed up by a pass through a flush trim bit on a router. Pretty reliable, especially with MDF.

This particular cabinet is rather large, though, so I was thinking of going with plywood instead of MDF to save a bit on weight. But butt joints with plywood has a very particular look, which is not really what I'm after this time. So... maybe miter joints all around would help keep the pretty face of the plywood veneer facing out all around (the sides at least).

A few years ago I played around with miter joints on little boxes--the results were kinda OK. Like, passable, I guess. So I ask you all, do you have some tried-and-true methods of making clean, secure miter joints, especially with larger cabinets?

[tomzarbo]

I usually cut my panels an inch or so large with the usual 90 degree cuts, then set the table saw for a 'nearly' 45 degree cut to the final dimension... then as long as the wood is flat, and the fence is square to the table, and the blade is square to the table... all that stuff. It should work okay.

Sometimes on a 'Miter Saw' it's possible to get a miter cut less than perfect -- say if you were cutting the short side of a longer board... say the top/side of a tower speaker... if the blade isn't perfectly square (perpendicular) to the back of the saw. But if you're doing basically everything on the table saw, it should be okay.

I always run some small test cut boards first on the 45's. It's easy that way to see with a square if you've gotten a good 90 degree angle once two pieces are pushed together... or something else.
Just a smidge under 45 is probably preferable to being over 45, but a perfect 45 is okay too.

I've only done smaller cabinets with miters, though. Like .3 to 2 cu. ft max, there may be tips for larger panels I don't know about.

You can use tape as a clamp to hold them together, so that's cool. I think John Hollander has done some larger glue-ups this way and his stuff always looks basically perfect.

TomZ

[Wolf]

I like to use miters with ply to wrap the grain around the cabinet; left side-top-right side. My Fenrir are a great example of this. It looks like it's continuous this way. I also like to use square stock just inside the joint so that it glues up true. Most clamps have the v-groove in the center to allow this kind of assembly by clamping on the outside and inside corners. I have been doing a lot of this on an in progress build too, and the inner square battens help a lot.

A bit of sanding will square up the outside edge, so don't worry about that too much. Yes, taping the corners and folding the glue up process helps a lot.

Lastly, plywood sounds different to me than MDF. I alternated 4" white marble masonry tiles with the layered Sonic Barrier down the length, and placed a rubber sport flooring layer and more SB in the bottom for the column and panel resonances. That took care of it on my EMP build.

Wolf

[Whitneyville1]

Paul, if I may make a suggestion. Go buy a THICK plate (at least .125") plywood tablesaw blade for cutting ACCURATE panel miters (Freud, Forrester, Makita blade $90-160 blade) to reduce wobble and "drift" when cutting as the blade heats up. Depending on the core material, plywood ( 11/32" veneer ) can be VERY HARD to cut accurately or very easy to cut. Freud sells a "veneer" blade in the upper price range that is outstanding IF YOU KEEP IT CLEAN! I'm proud that for breaking down sheet goods I use House Despots bargain "throw-away" thin-plate carbides and toss 'em when they dull. The glue in ply and MDF will ruin ANY blade, but cheap blades can't cut a panel miter for love or money, even with a sled.
Miters are a challenge and a skill I've not QUITE mastered, but very close. About 5% of mine still are DUHS!!! BUT now I almost always know what I did WRONG! The VERY BEST of luck to you!

Ricky-Pooh

[Paul Carmody]

I like to use miters with ply to wrap the grain around the cabinet; left side-top-right side. My Fenrir are a great example of this. It looks like it's continuous this way. I also like to use square stock just inside the joint so that it glues up true. Most clamps have the v-groove in the center to allow this kind of assembly by clamping on the outside and inside corners. I have been doing a lot of this on an in progress build too, and the inner square battens help a lot.

Yeah, Ben. That's what I'm talking about. Why didn't you miter the corners at the bottom of your Fenrir cabinets? Why not go all the way around? Just curious.

[9sheng]

Beveling the plywood, this is a headache, because the first time I tried beveling, I also used a 45° bevel cut, but eventually found that the plywood was too hard, and my blade didn't seem to be very sharp, which eventually led to There are some deviations at the head and tail of the incision, of course, a perfect splicing cannot be achieved in the end. Maybe my tools are not professional enough, I need a large machine (sorry, I can't pay his price, and I don't have a place to put it at home).
I am looking forward to Paul's large-scale project. I have built 4 pairs of your speakers, limited to the problem of woodworking tools (including woodworking skills of course), and have been unable to make the perfect cabinet in my mind.
I always give up 45° oblique spells, let's see what you can do

[davidroberts]

You can also cut the miters on a router if you have a table to accommodate the panel size. That opens the option for using a miterlock bit for increased strength and glue surface.

[Wolf]

Yeah, Ben. That's what I'm talking about. Why didn't you miter the corners at the bottom of your Fenrir cabinets? Why not go all the way around? Just curious.

I didnt have enough length of board to do it, it was really figured nicely, and the bottoms arent seen anyway.
Wolf

[Paul Carmody]

We'll see if I have the guts to pull off a true miter joint on these. They're pretty big panels, and I don't know if I could safely guide them through my table saw or router table.

Back up plan is to glue up a strip of hardwood at the edge of the plywood, and then butt join the other side to that.

Or... I just veneer over the whole smallest side and cover the end grain that way.

[JRT]

This might be of interest. Note that both vendors use different terminology for the same joint.




Infinity Cutting Tools

MCLS

[Steve Lee]

We'll see if I have the guts to pull off a true miter joint on these. They're pretty big panels, and I don't know if I could safely guide them through my table saw or router table.

Back up plan is to glue up a strip of hardwood at the edge of the plywood, and then butt join the other side to that.

This sorta where I wound up settling on finished plywood/MDF, Paul.
Only difference is that I apply a shallow rabbit to the the adjoining edges with a 3/4" straight flute router bit on the bench.
Makes for a stronger joint and is easier to glue up and clamp as it is self aligning.

Keep us posted of you adventure as able.

[jhollander]

Benefits, no joint that telegraphs through paint or veneer. You can pre-veneer panels then cut them to size. Fast assembly with tape. Cabinet dimension match the panel cut dimensions. Easier to finish without having to deal with butt joints.

Downside is they are harder joints to make. The 45's test your skills/ technique and your equipment. With a square you can gage your accuracy after each cut.

Large cabinets are tougher than small cabinets. For floor standers if you can cut a reasonably square 45 degree top piece you can do a 5-sided cabinet with 45's on the long sides. For the rip 45's the key is to make the last cut shallow or 1/8 inch. A riving knife and constant downward pressure is important to making a good cut. The blade on a 45 wants to lift and twist the board. A new blade helps. I use a panel jig with clamps to help make cross cut 45's and have also used a jig that goes over the fence that I can clamp pieces to for rip cuts. I also use a straight edge to align the panels and tape the joints. Be careful with clamps as they can push the joints out of square.

[Serenitynow]

Paul Carmody
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