large cabinet back - construction method?

[Ethan Melad]

I'm in the process of building a 5'x7' wide glass-fronted display case in cherry, and am trying to figure out exactly what to do about the back. there is a shelf @12" off the bottom, below which are drawers, so the largest visible area is about 4'x7'. The case will be rabbeted to accept the back, which i'm planning to be 1/2" ply. It will be vertically oriented quartered cherry.

So, the question is: do I get 2 sheets of veneered ply or do i get a custom-layed-up paper backed veneer and a sheet of BB to lay it up on?

I am leaning towards 2 sheets of ply, as i am a little wary of veneering a 4x8 (5x10?) sheet by myself (this would be my first time veneering on my own in my new shop, with no vacuum press or anything...).

However, i'm also concerned about the vertical seam that will be at the center of the cabinet where the 2 sheets meet. Aside from biscuiting and being super careful to keep the joint flush and flat is there anything i can do to make sure the joint is invisible? Gluing plywood edge grain is not something i really like the idea of doing...At least it'll be straight grain, so hopefully that would help hide the joint..

Any suggestions?

Thanks

[Brian Tymchak]

I would suggest covering the seam with a bit of cherry hardwood trim that looks like it was intended as part of the design. Maybe add some more trim around the top, bottom, sides, and make the back look like 2 joined panels. Something that wide, I might be tempted to split the back panel into thirds and use trim to make the back look like 3 framed panels. If your front is made of multiple panels, you could echo that into the back for a bit of symmetry in the piece. In fact, you could build your back from actual panels, and when joined together, you will get the rigidity that a typical back panel provides for a cabinet. And if you plan to have shelves, you could use the trim boards or panel stiles to mount shelving supports.

[Ethan Melad]

Thanks for the suggestion. However, I'm not really a fan of the frame and panel look- I like a modern, minimal look. The case is just solid stock, with glass bypass doors.

Also, and probably more importantly, the case is for swords, which will hang on the cabinet back - so the back has to be flat.

In the same vein, though, I had thought of setting the back in a slightly deeper rabbet and then adding a batten on the back side.

Thanks

[Ole Anderson]

Our local plywood dealer carries Cherry in a grain pattern that runs along the short dimension, so on a horizontally oriented sheet the grain would be vertical. Is that the problem you are string to solve, the joint if you use ply that has the normal grain orientation?

[Ethan Melad]

Yeah exactly. My supplier doesn't stock stuff like that, and a custom laid up sheet is outrageously expensive. Maybe I'll call around to see if anyone else has it in stock.

[Richard Coers]

First, make a fresh edge on the plywood, as straight as possible. Then I use a 1/8" slotting bit in the router and run a groove in both pieces. Cut a piece of spline stock that slips in nicely because the glue will swell it slightly. Glue it up and use a card scraper to clean the seam. If all that fails, run a router bit down the seam and inlay a piece of veneer or solid stock.

[johnny means]

I would just edge glue it with a spline or Dominoes. I wouldn't cut to width until after gluing it. That way, if I wasn't happy with the seam, I could rip it apart and try again.

[Ethan Melad]

thanks guys, i guess i just needed a little reassurance that its possible to make a joint like that work well and look good. maybe next time ill try the veneer.

[Jim Neeley]

Any suggestions?

Thanks

I'd use ship lapped pieces vertically, 4 - 6" wide apiece, with the end pieces glued along the face grain and the first few inches of end for rigidity. They add a nice discreet touch, IMO.

[Ole Anderson]

Yeah exactly. My supplier doesn't stock stuff like that, and a custom laid up sheet is outrageously expensive. Maybe I'll call around to see if anyone else has it in stock.

Check with your supplier, HIS supplier might stock it and be able to send him a sheet on the next weekly shipment.

[John A langley]

If you are using the 1/2" plywood for strength or think it is necessary to use it for strength then forget this post. I would get two sheets of 1/4" plywood, I'd either back bevel the edges or do a mirror cut with a router. Turn the plywood over and contact a piece of Formica to the back side. And if you do a good job making the seam it won't look any different than the veneer seams in the plywood. Put two coats of contact cement on the wood and one coat on the Formica. Make the Formica at least 6" on either side of the seam and put a lot of roller pressure on it and you should never have a problem.

[David Werkheiser]

If you can not find 8'x4' (cross grain) see if you can get a 5'x8' or a 5'x10'. If you want a seamless back I am not sure you will get that using 2 sheets of ply. With veneer so thin these days you run the risk of sanding thru to the backing
David

[Ethan Melad]

Check with your supplier, HIS supplier might stock it and be able to send him a sheet on the next weekly shipment.

yeah, i checked - i believe they can do the short grain with no problem, its the quartered short grain thats a custon layup..


If you are using the 1/2" plywood for strength or think it is necessary to use it for strength...

good idea - unfortunately i do need the 1/2" (at least) to hang the items in the case.

[Jeff Duncan]

I'd go with the 8' x 4' for it and probably opt for 3/4" over the half. Prices for them are generally within a few bucks, 3/4" should be easier to find in the 8 x 4' , and the 3/4" will give you more strength. Places to try...Atlantic Ply, Robert Bury Panels, Boulter Ply, and Goodfellow all have pretty decent selections.

The problems with trying an edge joint are multiple. First off plywood these days is not flat, so you have to force the two pieces into a flat position as well as clamp them together. Veneers are pretty thin so if you have any issues with the glue line your not going to be able to sand all that much, and finally you have a weaker structural panel then if it's a solid panel all the way across. It can be done, just be wary of those pitfalls.

good luck,
JeffD

[John A langley]

Jeff. All of what you said is true if you are using plywood. I buy all my veneered materials on MDF. The only drawback is that it is heavy.

[John TenEyck]

If you can't get a wide enough piece of plywood, or MDF, I'd use two sheets joined by a rabbet joint. I'd make that joint at least about an inch wide. Cut it with a router as close as you can to perfect, and then sand or hand plane one side of the joint until the joint fits perfectly flush. Glue it together with a piece of 1/4" plywood maybe 4 - 6" wide on the back for reinforcement.

John

[Robert Chapman]

I sometimes use tongue and groove hardwood in about 2" wide by 1/4" strips that I buy at the local Menards store. It comes in many different hardwoods and is easy to work. Makes a nice back for some cabinets.

[Tom Ewell]

If you end up joining two sheets together, most times the tightest joints are accomplished by double cutting the joining edges with a router and a straight edge.

Lay the sheets down joint edges together or spaced slightly apart (book matching not stacking) and secure with clamps or some such, a straight bit of your choosing in the straight edge guided router cutting both sheets at the same time (on a sacrificial surface below).
The resulting joint should be flawless as can be for the material used, glue together using method of your choice.

[Ethan Melad]

Thanks all,

i may use 8/10x5 if i can find it, otherwise ill go with 2 sheets of 4x8. i realized today that unfortunately i'll need something wider than 4' to span the vertical area from bottom shelf to top, so that part of the problem solved itself.

i think if i use 2 sheets i'll either lap or spline them, and possibly use a batten on the back to reinforce the joint.

jeff, thanks for the suggestions - i usually order from Atlantic, but checked with Boulter today as well. no short grain quartered in stock, and custom layup on 8x4 (which now i cant actually use) would basically be the same cost as 2 4x8 sheets.

since there will be items hung on the back i'm avoiding MDF, as its screw-holding power is somewhat weak.

thanks again - ill get pictures up when the piece is done

ethan

[Mark Bolton]

Custom layup (if you can get the size you need) at the cost of two sheets and you haven't pulled the pin on that option? Seems a no brainer to me. You'll have way more than that in a splice and likely won't be happy with it. 3-4 times would still be reasonable if its a big deal and what you want.

[Jeff Duncan]

Jeff. All of what you said is true if you are using plywood. I buy all my veneered materials on MDF. The only drawback is that it is heavy.


John, I use a bit of mdf myself, though mostly for door panels....ie. non structural. However I wouldn't ever use it as a back to hang a extra large and heavy cabinet as is described here. MDF is by far the worst material for any type of screw or staple holding power. I just wouldn't ever trust it!

JeffD

[Jeff Duncan]

Ethan, just a note of caution.....be wary of Atlantic Ply, while they're good to go to for a sheet of this or that, they are very expensive for small outfits. I cringe everytime I need a sheet or two as I know I'm going to get stiffed on price there. I only included them as they have a good stock and sometime have products others don't. Now ironically their custom layups are usually pretty reasonable if your doing any type of quantity, say 10 or more. I had some custom 1-1/4" mdf made up several years back and it only cost an extra $20 per over the cost of the material.

good luck,
JeffD

[Ethan Melad]

Jeff, Atlantic's been ok for me so far. They don't seem particularly expensive (aside from having a $350 min. order); the quartered cherry 4x8s are running a little more than $4/sqf. I imagine thats more than if i were buying in larger quantities, but doesn't seem any different than prices elsewhere.

Unfortunately (my fault with the design...) i can't use an 8x4, and it doesnt look like they can do a custom layup on another size that will work - or at least not one that i could afford. and i'm over budget on this, so ill have to do my best to make the 2-sheet option work.


Custom layup (if you can get the size you need) at the cost of two sheets and you haven't pulled the pin on that option? Seems a no brainer to me. You'll have way more than that in a splice and likely won't be happy with it. 3-4 times would still be reasonable if its a big deal and what you want.

and you're right, Mark - i wasnt thinking. if i could use an 8x4 i would do the custom..
thanks again