miter we have consensus on joining cases or am I to continue making a butt of myself?

[Bruce Seidner]

Ok, having joined forces we have achieved perfect consensus on the use of biscuits, pocket screws, dowels, dado's, rabbets, and festooned dominoes (these are the Chinese versions and can double as Mah-Jong tiles) I can move on to a less controversial topic like the most efficient way to cut long miters on plywood to avoid the laminates from showing.

There is the table saw and one can crank the blade to 45degrees or keep the blade at a sacrosanct 90degrees and build a jig that guides the case side through at 45degrees.

Then there is the router with and without table and a 45degree cutting bit.

Then glue and clamp, with or without the contrivances noted above.

I did read the recommended wood magazine nov 2006 torture test of wood joints and it is trey cool. There is now no question that i will pre-treat all edges with a diluted glue preparation, let dry and only then glue and camp the joint. They measured a magnitude of increased strength that was impressive for so very little extra effort

I have to build a heap-o-cases in cab qual birch ply. My aim is to be efficient and accurate and strong instead of fighting the time vampire, getting all cuts with tearout and dead space so I can do a Bondo smakdown and paint everything in an oil based green porch paint.

The input has been great, come "join" the discourse.

Bruce

[Ken Deckelman]

I have to build a heap-o-cases in cab qual birch ply. My aim is to be efficient and accurate and strong instead of fighting the time vampire, getting all cuts with tearout and dead space so I can do a Bondo smakdown and paint everything in an oil based green porch paint.

The input has been great, come "join" the discourse.


I have never had any luck using miter cuts on plywood...there is always some defect in the veneer after sawing and/or clamping because it's so thin and delicate. But I've got to ask, if you are Bondo'ing the cases, then why bother with the hassel of the miter cuts? Simple/strong butt joints are fine and the Bondo will fill the end grain. If time is not on your side, then I vote for pocket holes and accurate 90* cuts.

[Mike Cutler]

Bruce

I'd personally use a rabbetted miter bit, or a lock miter bit, in a router table, and tape the edges. The joints would then be self aligning. I'd then use an adhesive on the edges and shoot the joints with a nailer knowing I was going to Bondo and paint them. I'd do it differently if they weren't going to be painted.
I'm not sure that "sizing" a plywood edge is going to buy you much. That's up to you though.

[Bruce Seidner]

I have never had any luck using miter cuts on plywood...there is always some defect in the veneer after sawing and/or clamping because it's so thin and delicate. But I've got to ask, if you are Bondo'ing the cases, then why bother with the hassel of the miter cuts? Simple/strong butt joints are fine and the Bondo will fill the end grain. If time is not on your side, then I vote for pocket holes and accurate 90* cuts.

I am just joking about how I have solved bad joinery in the past. I am hoping to move beyond the need for Bondo and Battleship grade paint. I want gto make presentable joints in this project. These will be new bases for shop equipment and storage cabinets in a shop makeover. But your point is well made about long miter joints with plywood and I have never made more than a drawer size box this way. And, if I remember it wasn't that pretty.

[John Piwaron]

Ha! So many methods, so little time.

I once used plywood to make a carcase. I think I'd rather gouge my eyeballs out than repeat that experience and method. I used miter joints. For me, it was an excercise in frustration.

First, I am not a pro, I build for myself and my wife.

Since then, all my cabinet projects have been made of solid lumber joined with dovetails. None of that pocket hole stuff for me. M&T where appropriate.

[lowell holmes]

My old cabinet maker friend mitered plywood corners leaving the veneer a little proud. When the corners were glued, the veneer corners being "proud". were sanded and you couldn't see the joint. IIRC, inside glue blocks were used.

I've used the joint myself. You miter the edge and then lower the blade a bit, running the same edge through leaving the top veneer a bit long.

177751

[Jamie Buxton]

If I were going to paint the outside, I'd edgeband the top with solid lumber maybe 1/8" thick, and butt the sides to the top. Besides being difficult to make, mitered plywood corners -- particularly at the end-grain -- are touchy and fragile. The corner must be a knife edge, or else you go through the veneer, but knife edges are unfriendly to the touch. And the knife edge is easily dinged. A little bit of solid lumber at the edge solves both problems, and is easy to build too.

[Chris Padilla]

Mike mentioned the lock miter bit. I used that once to join some plywood edges together. First, it is a bear to set-up correctly. I'm an educated man but I had a devil of a time setting this bit up and once I finally got it right or as good as I could without tossing the (expensive) bit into the rubbish bin, it then tore out decently on my plywood that was supposedly cabinet grade A. I ended up gluing in a small strip on the corner to clean it up. My personal opinion on the lock miter bit is that while it does provide a nice mitered joint that more or less holds itself together, don't use it on plywood. I think it is only good for solid hardwood.

Lowell's idea is interesing and one I think I'll have a go at.

[Gene Howe]

My old cabinet maker friend mitered plywood corners leaving the veneer a little proud. When the corners were glued, the veneer corners being "proud". were sanded and you couldn't see the joint. IIRC, inside glue blocks were used.

I've used the joint myself. You miter the edge and then lower the blade a bit, running the same edge through leaving the top veneer a bit long.

177751

I like that. Great tip! Thanks.

[Jeff Duncan]

Mitering plywood is very simple an easy. Assuming you have a decent well tuned table saw, and a good sharp blade, and decent quality (generally not Borg stuff) plywood, getting a good clean miter cut shouldn't be a problem. I've never bothered will any of those funky aftermarket sales gimmicks for joinery in this situation. Just seems like something to make a simple thing complicated.
First cut the 2 miters, set them next to each other on the bench with the tips of the miters up and together. Use some packing tape and tape the 2 pieces together tip to tip. Now carefully flip the pieces over, add glue and fold together. Use additional tape to make sure the joint is square, or whatever angle your shooting for and let dry.
I learned this method years ago building some casework for a local Museum at a former employer. That work was actually angled and not 90 deg. and is still together
today.

good luck,
JeffD

[Aaron Berk]

Can I give a shout out to Mr. Sawdust's book?

He talks of case construction using a dado blade at a 45* just deep enough to whisper on the back side of the face veneer. Since the face is left uncut, you use it like a hinge and just fold the case closed using glue and tape/band clamp.

[johnny means]

I've done way to many mitered plywood cases in my shop and have tried every concievable technique. It took me about three years to settle on the V-fold technique. This involves cutting a v groove in the material, leaving a paper thin layer of uncut material, then folding the plywood along this line. This gives me a perfectly aligned joint and is nearly sanding free. Takes a little more set up time, along with a specialty bit, but assembly is a snap.

[Von Bickley]

O.K...... O.K......O.K.

I will share a secret with all of you. I know several professional trim carpenters that build cabinets and always have perfect 45's on the corners. One of these carpenters finally shared his secret with me for making perfect 45 corners. Never miter the corners at 45. Always set your TS for 44 - 44.5 degrees. You get perfect outside corners and the gap is on the inside of the cabinet where it is never seen.

Hope this helps......

[Phil Thien]

O.K...... O.K......O.K.

I will share a secret with all of you. I know several professional trim carpenters that build cabinets and always have perfect 45's on the corners. One of these carpenters finally shared his secret with me for making perfect 45 corners. Never miter the corners at 45. Always set your TS for 44 - 44.5 degrees. You get perfect outside corners and the gap is on the inside of the cabinet where it is never seen.

Hope this helps......

If you go less than 45 you'll have a gap at the outside. What you want is about 45.1 or .2 degrees. That ensures you'll have a closed joint but that there will be enough contact for a strong joint. Cut 'em, tape 'em, glue 'em, and fold 'em.

Then, before the glue sets, you want to burnish the joint with a hard roller (right through the tape). This will prevent glue squeezeout from preventing the veneer from closing when the glue hardens.

[Mark Salomon]

First, don't use mechanical devices like splines, biscuits, etc. because they only service to force a joint to 45*--it's perfectly ok for one to be 44* and the other to be 45*. Second, test your set up with some similar sized MDF panels and make sure that any error is slight and any gap in the miter is on the inside. Third, assemble the joint with tape. I find that clear strapping tape works best. After each joint is taped turn the assembly over, glue and then fold back up and tape the last joint. Finally, remove the tape after an hour, clean up any glue and lightly burnish the edge with a smooth shaft or burnisher. This will very slightly round over the edge but more importantly cause any slight gaps to close and be tight. If you follow this you will be amazed at how clean and tight your mitered carcass joints are.

[Von Bickley]

If you go less than 45 you'll have a gap at the outside. What you want is about 45.1 or .2 degrees. That ensures you'll have a closed joint but that there will be enough contact for a strong joint. Cut 'em, tape 'em, glue 'em, and fold 'em.

Then, before the glue sets, you want to burnish the joint with a hard roller (right through the tape). This will prevent glue squeezeout from preventing the veneer from closing when the glue hardens.

You're absolutely right Phil.... I should have said that the work piece should be about 44.5 degrees. We always run a test piece and check it with a tri-square to be sure we are less than 45 degrees.

[george wilson]

Violin makers,and most likely other users of end grain joints,were putting glue on open end grain before final gluing 200 years ago. Probably more. They'd also use a heated iron on the glue to drive it deeper into the end grain. Then,they let it dry,scrapped it if needed,and did their final gluing. This is standard procedure on gluing violin end blocks to tops and backs.

[Peter Quinn]

Honestly, I don't bother doing long miters on plywood utility boxes. Its not worth the fuss to me to make the grain turn the corner in an invisible manner because the grain isn't much to look at in your basic birch plywood in any event. So I'd suggest taking the assumption that the joint must be invisible and throwing it out the window. I prefer a basic finger joint in BB for really strong joints, like a step stool for an elephant or a stand for a drill press. Or honestly just butt joints and screws will do, maybe a little rabbit to give a shoulder for reference. I guess I don't see the shop cab as a place for me to use the highest level of aesthetics regarding joinery, though I suppose it can be a great place to practice for other things and some do seem to enjoy fine cabs in the shop. Me, I prefer a pinot noir, but thats another story.

Now to dress up fine cabinets with plywood carcasses I'll do finished end panels with FF construction that miter at the corners and glue these on to the case using a 1/4" packing for separation so the panel isn't bound. For long miters in FF's using solid wood I like a tape miter, which is quite strong if done well and doesn't need to be sized in solid wood, but can be if using plywood. You can burnish the edges while the glue is still moist with almost any round steel object like a screw driver handle or such for an invisible joint. You can clamp these joints too if you have lots and lots of of clamps. I find a $3 roll of clear packing tape much cheaper and a bit lighter to move around.

[Jeff Duncan]

Violin makers,and most likely other users of end grain joints,were putting glue on open end grain before final gluing 200 years ago. Probably more. They'd also use a heated iron on the glue to drive it deeper into the end grain. Then,they let it dry,scrapped it if needed,and did their final gluing. This is standard procedure on gluing violin end blocks to tops and backs.

Just for clarification they were not using PVA glues 200 years ago and you should not count on this method working with them today. In general you don't want to try to glue wood that already has dried pva on it. If your going through all the trouble to use hide glues, then that may be a different story.
good luck,
JeffD

[Mark Salomon]

I'll take the Krenov book. I also PM'd you earlier but wasn't able to post due to computer problems. Thanks