will biscuit joinery for ceiling hung cabinets be strong enough?

[Kenny King]

I am planning on building some custom cabinetry for my kitchen. One run of

wall cabinets will be hung from the ceiling. This will be composed of two 30"

with one 24" sandwiched between them. The height is around 48". The depth

will be 16", which is non-standard, but will work ok with base cabinet, since

counter top will be extended by 4".

These cabinets will have cabinet doors with windows on both sides. Picture

an 85 inch peninsula row of cabinets jutting out from the wall and haning from

the ceiling.

The ceiling joists are 4x10, so I'm not worried about their strength. However,

I'm considering butt joints joined with biscuit joinery where the biscuits will

be attached horizontally or perpendicular to the direction of the cabinet sides.

Will this type of joinery hold? I'm considering using a dado joint instead, but

that means adding another 1" to the cabinet sides to make room for the dado.

Will the dado be a better solution?

Thanks for listening,

- Keny King

[Steve Clardy]

Biscuits will be fine, though time consuming. Just use plenty of them, say 4 each joint #20

[Kenny King]

Steve

Good info. Thanks. I've never used biscuits for joinery. Jim Tolpin's book recommended them as being a fast way to do joinery over dado's. I don't have a biscuit joiner, so i planned on doing them with my 25,000 rpm single speed router, which is kinda fast for a bit that big. so i'm worried 'bout that also.

OK, so maybe the biscuit's is sounding like maybe not the best idea.

other options include
- dowels -> need to by a jig
- dados -> maybe the best option, could use saw or router, not sure which is best.

OH, forgot, this is for 3/4" oak plywood. So probably need a dado that's slightly undersized. The freud dado is about $200 if you want to get width's down to the 32nd of an inch. The other option is getting a slightly undersized router bit. This is cheaper, but I probably would upgrade to a 1/2" router.

So there's my dilema. What's the lease expensive route that doesn't sacrifice on quality. I either get the dado saw blade, or get the router and a dado bit.

Let me know what ya think. I was really surprised to hear that biscuit joinery would be slow. Even with a biscuit joiner?

- Ken

[Dan Forman]

Can't help on the design question, but don't count on a "plywood router bit" (slightly undersized) being the correct size for any given sheet of plywood. My understanding is that there is such variation in plywood, sometimes even within a single sheet, that there is no guarantee that it would fit properly in a "plywood dado". Best approach there would be using a smaller bit and a jig to control the width while making two passes with a smaller bit, or using the table saw to plow a dado of a given width, then making a rabbet of a complimentary width so that the resulting edge will fit snugly.

Hope that makes sense.

Dan

[Mike Vermeil]

I'm sure the buscuits if used & glued properly would be fine, but if it were my own stuff...well, what's the peace of mind of a good dado joint worth?

Also, while buscuits can be faster, it's not like dados are all that time consuming to cut.

Maybe a compromise would be a spline joint - plenty strong.

[Steve Clardy]

Steve

Good info. Thanks. I've never used biscuits for joinery. Jim Tolpin's book recommended them as being a fast way to do joinery over dado's. I don't have a biscuit joiner, so i planned on doing them with my 25,000 rpm single speed router, which is kinda fast for a bit that big. so i'm worried 'bout that also.

OK, so maybe the biscuit's is sounding like maybe not the best idea.

other options include
- dowels -> need to by a jig
- dados -> maybe the best option, could use saw or router, not sure which is best.

OH, forgot, this is for 3/4" oak plywood. So probably need a dado that's slightly undersized. The freud dado is about $200 if you want to get width's down to the 32nd of an inch. The other option is getting a slightly undersized router bit. This is cheaper, but I probably would upgrade to a 1/2" router.

So there's my dilema. What's the lease expensive route that doesn't sacrifice on quality. I either get the dado saw blade, or get the router and a dado bit.

Let me know what ya think. I was really surprised to hear that biscuit joinery would be slow. Even with a biscuit joiner?

- Ken

Sorry. Had to shut down due to the storm here. Lost to many modems over the years, so I shut er down.

Your case, either a router bit, or an adjustable dado head.
To me dados are faster and better. Once your parts are cut, then dado them.
You can get a less expensive wobble dado head. Sears actually has a good one. I have two of them and thats all I ever use.
As above, the undersized router bits for ply are the cheapest way to go, but ply does vary. I had some in here just a couple of weeks ago that was actually full 3/4. Very unusual anymore.
Dowels. Well. I never did like using dowels. A pain in the rear to me.

So I guess you are down to how much moola you want to spend on tooling, and how much time you want to spend.
Biscuits and the sloting bit are still a good way to go. Just be careful feeding the stock into the bit. I have a couple of biscuit cutters, and pitched my slot cutter some time ago.

Steve

[Andrew Ault]

The cheapest way to cut the (nominally) 3/4" dados is probably with a 1/2" straight router bit.

You can do this a number of ways to do this. Here are two. 1. With some straight scraps and a gauge block. 2. With a dado jig.

For either method you will need some C-clamps and scrap wood.

With Scraps and a Gauge Block

1. Make two straight guides from scrap at least as long as the width of the dado you want to cut. These might be 4" wide and 1/2" to 1" thick. MDF is good for this or use what you have.

2. Make a gauge block from some scrap. The width of the gauge will be exactly the distance from the 1/2" straight bit mounted in your router to the edge of the base of the router.

3. With a sharp pencil and a square, mark the position for a dado on a piece of stock.

4. Use the gauge block to position a guide on each side of the marked dado layout lines. Clamp the guides in position with C-clamps.

5. Cut the dado with the router first with one guide and then then other. It is best to do each side in multiple passes until the correct depth is achieved.

With a Router Dado Jig

This is pretty similar, but first you construct a dado jig from scrap. See illustration. This can be handy when cutting multiple dados of the same size. You can still make a gauge block to help set the jig up and get it in the right position.

[Andrew Ault]

This can be a very strong, easy and inexpensive way to make the joints.

Look at the Mini Kreg Jig Kit.

http://www.rockler.com/ecom7/product_details.cfm?&offerings_id=5985&SearchHandle=DADBDADJDADADDDGDCDGGEGCGBGGGDDGCNGCD ADFDICNDEGGGEDFCNGCDAGDDJCNGEDHDGGFDEDJGGDEDBGDDDD HDADADADBDADADADBDAHAGPGDGLGFHECAGKGJGHDADADADEDAD ADADADADADADBDFDADADADBDADADADADADADADADADADADADBD ADADADBDAHAGPGDGLGFHECAGKGJGHDADADADBDB&filter=pocket%20jig

This allows you to quickly make glued butt joints with no clamps, no dados and no biscuits.

- Andy

[Scott Coffelt]

I would lean towards dado's if it was me, I'd hate to have a joint fail and land on someone or something. You could also use screws and plugs, but I would still lean towards dados. Will you have face frames? If so, this will add to the strength. That many biscuits would be seriously time consuming.

[frank shic]

kenny, have you considered confirmat screws? i just built an entire set of kitchen cabinets (11 altogether) using mostly confirmat screws for the base cabinets and the hidden edges of the upper cabinets - i used biscuits and pocket hole screws for the rest. you can get the confirmat starter set from mcfeely's but make sure that you order PLENTY (at least 200) so that you don't run out of them like i did over the weekend and have to resort to the hex head (allen wrench, anyone? ouch!!!) confirmat screws that rockler sells!

you DO NOT need to buy the expensive zentrix drill attachment to predrill the holes for these screws. i managed got FANTASTIC results with a simple cheapy hand drill jig (you know the one that you buy before buying a drill press?) which i modified by screwing on a small sqaure of 3/8" mdf which had another smaller piece of plywood screwed into the bottom to serve as a stop so that i didn't have to draw ANY layout lines to center the screws.

you can either remove the stop when you do the shelves (if they're fixed) but you'll have to draw layout lines or you can just biscuit them like i did.

good luck and don't forget to make sure that you give yourself at least 1/2" stile overhang on the last cabinets in a run to allow you to fit them tightly to the walls. try screwing three cabinets together before lifting/installing so make the process go more quickly.

BTW you'll need the 7mm (the larger) confirmats if you're using 3/4" ply or melamine and the 5mm confirmats if you're using 5/8" melamine.

good luck!

[Steve Clardy]

Heres a good read on confirmats. Not made for plywood.

http://www.woodweb.com/knowledge_base/Confirmat_screw_assembly.html

[Rob Littleton]

Is Miller dowels an option?

[Jim Becker]

Construction of the cabinets is one issue...HOW you mount them to the ceiling is another! Preferably, you want to carry the weight down to the bottom of the cabinets. One method I've seen for that is to use threaded rod that ties into blocking between the ceiling joists. If you plan things out carefully, you can fully hide the rods between false panels, etc. Remember, it's not the weight of the cabinets that's the problem...it's what you stick in them! That can get quite heavy. And personally, I'd probably rabbit for the top and bottom of the carcases to help carry that weight, too.

[Kenny King]

Thanks folks. Everyone provided some very useful input. I had originally
planned on using 1/4" threaded rod to support that cabinets from the cieling, but forgot all about it when I got into the details of maximizing the space used by the cabinets.

Anyways, I'm convinced on using Dados for cabinet joinery & six 1/4" rods to suspend the cabinets from the ceiling joists (1 pair at end, and two more pair between cabs).

thanks,
Kenny King

[frank shic]

steve, although the confirmats are not MADE for plywood, they still work MARVELOUSLY! i'm very familiar with the woodweb link that you included - don't you just love hearing professional advice? i'm not sure what the original poster did wrong, but i had absolutely NO BLOWOUTS whatsoever and the screws are SO EASILY driven with an impact driver. i suspect that he probably didn't clamp the two pieces tight enough as evidenced to the fact that he used quikgrip clamps and not even on an ACTUAL carcase just a simple butt joint - i used bessey k body clamps prior to drilling the pilot holes. i think that confirmats are seriously underutilized which is a shame because they require such little effort and yet hold like a TITAN!

[Steve Clardy]

steve, although the confirmats are not MADE for plywood, they still work MARVELOUSLY! i'm very familiar with the woodweb link that you included - don't you just love hearing professional advice? i'm not sure what the original poster did wrong, but i had absolutely NO BLOWOUTS whatsoever and the screws are SO EASILY driven with an impact driver. i suspect that he probably didn't clamp the two pieces tight enough as evidenced to the fact that he used quikgrip clamps and not even on an ACTUAL carcase just a simple butt joint - i used bessey k body clamps prior to drilling the pilot holes. i think that confirmats are seriously underutilized which is a shame because they require such little effort and yet hold like a TITAN!

Hi Frank. I have considered those confirmats for quite some time for my cabinet shop, but haven't pulled the trigger yet.
I use all plywood in my cabinets, no PB or MDF. So I don't really want to make the jump, a bunch of screws and the bit, and then not be happy with them.
If I did this, looking back at my research, I would need a short bit for a 3/8" drill, not the long ones that are for the machines.
Any idea where to get the shorter bits?

[Marcus Hutchison]

Hello Steve,

I have a cabinet shop and I just started doing a lot of commercial work about a year age, which means either dowels or confirmats. I had been doing only residential cabinetry, up till that point, and dadoing my joints like a lot of others do. I was very leery of using the confirmats, but when I tried them I couldn't believe how strong they were. I don't use dadoes any more. The confirmats are much faster and are plenty strong enough. I even switched to melamine for my box construction, which is a whole new debate. If the confirmats hold as well as they do in melamine with no glue, you can imagine how strong they would be in a glued joint. Also, you don't even need to clamp your pieces together. I staple the boxes together with 1 1/2" staples and then drill and screw in the confirmats. The staples keep everything lined up. You can get the screws and drill bits from McFeeleys if your local supplier doesn't have them.

Hope that helps,

Marcus

[Steve Clardy]

Yes. Thanks. I'll check McFeeleys

[frank shic]

steve, you won't be disappointed! once you try confirmat screws out, you'll wonder why more hobbyists aren't using them! i would highly recommend an impact driver like the ridgid right angle impact driver (now on sale at home depot and bundled with a cordless 18 volt drill!) for driving the screws so that you don't strip the screws even though the pozi drivers are designed to minimize this phenomenon. don't forget to pick up or dig out that cheapy drill jig that most of us replace with drill presses - with two pieces of wood screwed to the bottom and adjusting the depth stop, you can EASILY center the drill bit and drive them just deep enough to get an AIRTIGHT fit. the only drawback on the confirmats is that the shiny heads aren't the prettiest but you can either cover them up with matching plastic covers or you can reserve them for the hidden sides/backs of your future cabinets. good luck!