Which is stronger in building a carcass

[Alan Tolchinsky]

of 3/4" plywood: a biscuited but joint or rabbet joint? What is your preference in joints in making carcases? Thanks Alan in Md.

[George Summers]

How about a pocket screw joint? Second to that I would go with biscuits, then the rabbited joint..

George

[Jamie Buxton]

of 3/4" plywood: a biscuited but joint or rabbet joint? What is your preference in joints in making carcases? Thanks Alan in Md.

If you believe that glue works (I do), and if you have a way to ensure that the middle of the joint is clamped while the glue cures, the two approaches should be equivalent.

Clamping the middle of the joint can be an issue. For instance, you might be attaching a shelf which is four feet off the floor in a cabinet which is 2 feet deep and 8 feet tall. Pipe clamps alone will not do the job. That's one of the good things about the pocket screws which George mentioned. You can use them to "clamp" right in the middle of a big panel.

[Jim Becker]

Rabbets/dados/grooves give you more glue surface, but I think that in practical terms, as Jamie says, they all should be equivalent. The other components you add to your carcasses will also beef up the overall strength. Unless they will routinely be used as elephant chairs, of course...

[Curt Harms]

If you believe that glue works (I do), and if you have a way to ensure that the middle of the joint is clamped while the glue cures, the two approaches should be equivalent.

Clamping the middle of the joint can be an issue. For instance, you might be attaching a shelf which is four feet off the floor in a cabinet which is 2 feet deep and 8 feet tall. Pipe clamps alone will not do the job.

That's true, but clamps and cauls will work fine, and the joint is metal-free :cool:

Curt

[Jamie Buxton]

That's true, but clamps and cauls will work fine, and the joint is metal-free :cool:

Curt

Ummm... What's the matter with metal?

[Alan Tolchinsky]

For building a dresser carcas which joint would you be most comfortable with?
I notice in my own dressers there are glue blocks that are screwed between the sides and top. We have Lane furniture that's over 30 years old and ,although not the best stuff in the world, has some of the hallmarks of good construction. The drawers are dovetailed front and rear with center glides. All the web frames are pretty beefy and include a dust panel. All the drawer dividers are very solidly attached. No, there aren't any dovetails in the carcass but again this is mass produced furniture.

It's amazes me when I see the build quality of some of the stuff out there. It's only when you get to the pretty expensive brands that things are built the way a woodworker would like. Oh yeah, I know expensive doesn't necessarily mean quality.

[Doug Cowan]

For pywood casework I would typically rabbet the back and use dados or biscuits for the shelves or dustframes. For the top, I would use figure 8's if the top overhangs, and biscuits or rabbits if I were putting moulding around the top. Personnally, I'm a little gunshy with biscuits, the last couple of times I used them it seemed like they started swelling up as soon as glue was applied. Instead of what should have been a relaxed glueup, I found myself with a real battle on my hands. I haven't had that problem when using dado's.

Good luck and don't forget to post pictures of the fabulous finished product!

[Todd Burch]

Between a biscuited butt joint and a rabbetted joint, my money would be on the biscuit joint. It provides good flat-grain to flat-grain surface area, which is a stronger connection than end-grain to end-grain or end-grain to flat-grain. Plus, for the butt joint, your clamping pressure is only in 1 direction, while a rabbet requires clamping pressure in 2 directions.

I would never pocket screw plywood. I've tried it before and the screws simply split the veneers apart and the screw drove all the way through the pilot hole.

[Jamie Buxton]

I would never pocket screw plywood. I've tried it before and the screws simply split the veneers apart and the screw drove all the way through the pilot hole.

I've had that happen with drywall or deck screws. It doesn't happen to me using washer head screws. The deck screws have a conical surface where they meet the wood, and use it to split through veneers. The washer head screws have a flat surface against the wood, and that seems to fix the problem.

[Dave Wright #2]

There have been a number of strength tests for biscuits versus conventional joint types. The biscuits do quite well, but the tests I've seen are usually in solid stock that would otherwise be a very weak end-to-side grain joint. I built with biscuits for a while, but in the last year or two have been drifting to rabbets/dados for plywood cases. With plywood it's a side-to-side grain joint- plenty strong if properly fitted, glued, and clamped. Differential movement isn't an issue. Against shear forces, like the weight of a shelf on a side panel, dados are unquestionably stronger than biscuits. The biscuits may, however, be better on moment and withdrawl.

Fab time and assembly are also issues. I have found it faster to rip a few dados and rabbets than carefully place biscuit cuts. I like find rabbet/dado assembly more pleasant too.

[Todd Burch]

Dave Write #2 - what's your final answer? Given the situation, what's your vote?

I have the same philosophy on building carcasses - I use rabbets and dados - it's faster.

Alan back to the question of yours: "Which is stronger?". I don't ask this question. The question I ask is "What joint can I make fast, that is strong enough for the job at hand?" For most stationary cabinetry, believe it or not, butt joints with screws and glue are good enough.

When I was doing all those built-ins, ("built-in", in this regard, means you only see the face frame when done), seeing as they were anchored to a larger structure, (a house), I got to where I was making the tops and bottoms of a carcass the exact size of the width and depth of the box, and then making the sides 1 1/2" shorter than the height of the box, and simply screwing through the tops and bottoms into the edges of the sides. Most of the weight on the cabinet was downward, and this type of construction can take a LOT of weight. During assembly, I shot a could nails to hold it in place until I drove my 2" screws into place ("screws" in this regard are my "threaded disposable clamps").

Lower cabinets I did this way... Uppers used rabbets and dados if I need pretty sides. However, if the sides of the uppers would not be seen, I would reverse my logic and makes the sides full length, and shorten the length of the tops and bottoms by 1 1/2" and screw through the sides into the edges of the tops and bottoms.

Something I could brag on from a joinery standpoint? No.
Perfectly functional from a strength standpoint? I had to make that decision on a case-by-application-case.
Fast? You betchya chet!

[Jim Becker]

Interesting thing is that my cabinet-maker neighbor who does high-end work in mult-million dollar homes uses butt joints with glue and countersunk screws for the carcasses. These boxes are used to construct the units and any exposed ends get panels...the plywood used for the basic carcasses is never exposed to the room. (Insides, obviously are, and are sprayed with lacquer). He claims that this is more than enough strength for the job and VERY fast since he doesn't have to take the time for the dados, etc. Even his 1/2" ply cabinet backs are installed flush on the boxes since the edges will never be seen.

[Dave Wright #2]

Todd, I'm with you...joinery that is strong enough for the situation but not overdone. M&T/DT for loose furniture that has minimal joint area. Rabbets/dados for casework that will be moved occasionally, like bookcases and drawer units. The drawers in the casework would, of course, be dovetailed or otherwise more strongly built. I sometimes use butt joints for built-ins, but like the ease of alignment at assembly time provided by rabbets/dados.

Most of my joints are cut at the table saw instead of with the router. I find it easier to tweak the dado blade width to get just the right thickness than make multiple router passes. Stopped joints are also cut at the saw, then quickly completed with a chisel.

[Byron Trantham]

I use what makes sense for the project. I am currently making a wine rack that will be suspended from a ceiling and I originally designed a rabbit joint for the bottom panel. I thought about it and because of the heavy downward pressure I figured that a dato would be a much better choice in this situation. I have become a strong proponent of pocket screws. They are fast and they are strong!

[Alan Tolchinsky]

Interesting thing is that my cabinet-maker neighbor who does high-end work in mult-million dollar homes uses butt joints with glue and countersunk screws for the carcasses. These boxes are used to construct the units and any exposed ends get panels...the plywood used for the basic carcasses is never exposed to the room. (Insides, obviously are, and are sprayed with lacquer). He claims that this is more than enough strength for the job and VERY fast since he doesn't have to take the time for the dados, etc. Even his 1/2" ply cabinet backs are installed flush on the boxes since the edges will never be seen.

It's always good to hear how things are done by professionals. Sometimes I get too caught up in the details such as joinery and this bogs me down. Thanks for all the great ideas.

[Alan Tolchinsky]

of 3/4" plywood: a biscuited but joint or rabbet joint? What is your preference in joints in making carcases? Thanks Alan in Md.

I've really enjoyed this thread. Thanks for all the insights. It makes me realize that I can think too much about the details. Not that you should gloss over planning but I can see now that a lot of different methods can work in a situation.

[Richard McComas]

I've made a lot of plywood cabinet boxes with butt joints, glue and screws, never had a problem.

Do the lousy quality control with a lot of plywood theses days I’m building more and more boxes out of high quality melamine that do just fine with butt joints and confirmat screws and no glue.

[Scott Parks]

I'm with Byron... Use what makes sense for the project.

Food for thought.. Traditional joinery has been around for centuries.. I wonder why?

[Dale Thompson]

Alan,
If you use either a biscuit or a rabbeted joint, you are depending on the glue to hold the assembly together - forever! Glue dries out and cracks with time. I love both kinds of joints but I seldom use them anymore. Pocket screws will give you both the strength of the glue and the "snugness" of a screw connection. :D

Since plywood is such a spastic material in terms of thickness, I back my pocket hole bit setting off about 1/8". Use the proper "washered" screws and crank your driver torque down a couple of notches until you get the "feel" of the material. If you want to hide the elliptical holes, get a length of 3/8" (or other as required) dowel. Backcut the dowel at about 45 deg., apply glue and tap it into the hole. Cut off the excess with a flexible, no-rake blade and you're done. Those elliptical holes, when covered, REALLY make you look like a PRO. ;) :)

Dale T.

[Paul Prescott]

Wow. As a newbie I'me pretty much overwhelmed by the info on this thread.

But I have some questions.

If using rabbets and dados for carcas construction, in 3/4" plywood, besides glue I assume you also use screws. Does the 1 1/2 times the thickness apply? Pilot holes? Screw type? I love pocket screws - how far apart? Glue too? And Dale, you lost me completely.

Sorry if I sound simplistic, but my next project is a mobile base for my table saw. Help, please?

Thaks y'all!

[Jim Becker]

If using rabbets and dados for carcas construction, in 3/4" plywood, besides glue I assume you also use screws. Does the 1 1/2 times the thickness apply? Pilot holes? Screw type? I love pocket screws - how far apart? Glue too?

The glue gives you the majority of your strength, but most folks use screws. I happen to use 1 1/2" #8 square drive screws countersunk in most cases. While I haven't used pocket screws for major carcass construction...yet...I have used them for a lot of things related. When you do use them, yes, glue should be employed. Again, that's where most of the strength comes from. I would space them at about 6" or so for this job.

[JayStPeter]

I've been partial to pocket screws lately. They just make it so much easier to "clamp" up. No more cauls and struggling to make sure everything doesn't fall apart by the time you get the other side on.
On my last shop cabinet, I actually used a combination of shallow rabbet/dado and pocket screws. I did this because the plywood I used was bowed and I wanted to ensure it was flattened out. I think the depths were right around 1/16". I used the 1" screws.
After 4 or 5 shop cabinets using pocket holes with the cheapest HD ply, I've never had the problem Todd mentioned. But, I do pay attention to voids along the edge and avoid them. I have had problems where the pocket screw never really grabs because of a void. I've taken to doing my pocket holes in pairs and only using them as needed. I adjust my hole spacing based on how flat the ply is, but typically use around 8".
For solid wood projects, I use other joinery. It is far easier to clamp and ensure flatness than ply.

Jay

[Alan Tolchinsky]

For smaller projects I've used rabbets and then shot some finish nails after the glue was set. But for larger boxes I' d go with what's been said here: glue with countersunk screws.

Does anybody have any tips on assembly of larger boxes? How do you hold the parts together while you drill the pilot holes? It always seems like I need a third hand when I do these. Any special tricks that help with assembly much appreciated. I'm about to make some cabinets for the garage.

[Jim Becker]

Alan, I used some 15 guage finish nails to help hold things together while clamping so I could drill/countersink/screw. The nails were my "third hand"...

[Alan Tolchinsky]

Alan, I used some 15 guage finish nails to help hold things together while clamping so I could drill/countersink/screw. The nails were my "third hand"...

Jim, I don't have a 15 guage but I do own an 18 that can shoot 2.5" nails. That should do it.

[Alan Tolchinsky]

Alan,
If you use either a biscuit or a rabbeted joint, you are depending on the glue to hold the assembly together - forever! Glue dries out and cracks with time. I love both kinds of joints but I seldom use them anymore. Pocket screws will give you both the strength of the glue and the "snugness" of a screw connection. :D

Since plywood is such a spastic material in terms of thickness, I back my pocket hole bit setting off about 1/8". Use the proper "washered" screws and crank your driver torque down a couple of notches until you get the "feel" of the material. If you want to hide the elliptical holes, get a length of 3/8" (or other as required) dowel. Backcut the dowel at about 45 deg., apply glue and tap it into the hole. Cut off the excess with a flexible, no-rake blade and you're done. Those elliptical holes, when covered, REALLY make you look like a PRO. ;) :)

Dale T.

Dale,

I'm with you on the pocket screws; you're preaching to the chior. :)

Now if I can just get over feeling guilty using them in finer furniture. How do you feel using them for projects you bring into the house? I can see manufactures use them all the time.

[Alan Tolchinsky]

The glue gives you the majority of your strength, but most folks use screws. I happen to use 1 1/2" #8 square drive screws countersunk in most cases. While I haven't used pocket screws for major carcass construction...yet...I have used them for a lot of things related. When you do use them, yes, glue should be employed. Again, that's where most of the strength comes from. I would space them at about 6" or so for this job.
Jim, I wonder how much extra strength glue gives when using pocket screws? Say in a butt joint in plywood you have end grain to side grain abutting. I wonder how much glue would improve this joint. I guess at least it would be a mechanical lock of some sorts as well as an adhesive. I probably would feel better using glue but it sure is neater without it when using pocket screws and no slipping around. I do love pocket screws.

[Dave Wright #2]

If using rabbets and dados for carcas construction, in 3/4" plywood, besides glue I assume you also use screws. Does the 1 1/2 times the thickness apply? Pilot holes? Screw type? I love pocket screws - how far apart? Glue too? And Dale, you lost me completely.

Sorry if I sound simplistic, but my next project is a mobile base for my table saw. Help, please?

Thaks y'all!

Hi Paul,

I use screws or nails on rabbets and dados that haven't been properly clamped. IME those reinforcements are not required if the joint fits well and was properly glued/clamped.

You mention a mobile base. There are lots of ways to put together a mobile base, but my most recent one did not involve rabbets or dados. If the saw's heavy you might want to consider somewhat thick solid stock and interlocking joinery.

Regards, Dave

http://www.woodcentral.com/vpix//pic204375.jpg

[Dale Thompson]

Dale,

Now if I can just get over feeling guilty using them in finer furniture. How do you feel using them for projects you bring into the house? I can see manufactures use them all the time.

Hi Alan,
Up until recently, I have been afraid to bring wood furniture into my cardboard abode. Wood is flammable and I was afraid that my open-fire furnace would deprive me of a shelter from the elements. :eek:

However, since I discovered oil the last time I changed the oil filter on my car, my fortunes have changed. My wife is no longer limited to $7 for a dining room outfit. :)

I have accompanied her in looking at some VERY expensive furniture. My observations are that the dovetailed drawers look like they have been chewed out by a beaver. Many are only dovetailed in the front. They are STAPLED in the back. :(

On the other hand, they almost ALWAYS use pocket screws to obtain a good joint where that is necessary. Rarely do they ever "plug" them. :confused:

Alan, in my humble opinion, pocket holes show supreme craftsmanship, especially when they are "plugged". I have no problem moving them into my house in any form of furniture. Check out a local store selling $8,000 bedroom outfits if you have any doubts. ;)

I also like the mortise and tenon doweled joints but I have not done much with them. They too are subject to drying glue and wood shrinkage. Besides, I'm not smart enough to MAKE them! :o

Dale T.

[Tom Jones III]

I've been making some fairly nice furniture for non-profits recently. In an effort to make construction fairly quick and keep the costs reasonable I've been using a lot of 3/4" walnut ply and solid walnut rails and stiles. I use through loose tenons on the rails and stiles and biscuits for the ply. Construction is very quick, and very error free due to the simple joinery. The resulting panel is very strong. I cannot imagine strength ever being an issue.

[Jim Becker]

Tom, if you want to dramatically decrease the time building those face frames...start using pocket screws. Even with today's machinery, it takes magnitudes longer to do M&T!! And you cut the rails and stiles to exact length, removing one more area that folks sometimes make measuring mistakes, too.