Replies

1. 
   mrbird90 | Nov 10, 2009 05:03am | #1

   When I make cabinets the joints for the shelves are a slip fit in the daddo. My daddo set comes with a couple of blades less than 1/8" so I can adjust the stack to match the plywood I am using. In my opinion .015" is too loose and will show a large gap. If you screw the joints and don't care about the gap showing I wouldn't worry about joint strength.

1. 
   Panzer | Nov 10, 2009 05:21am | #2

   My specific question is what is the gap that should be used for a glue joint?  The 0.015" is what systematic dado set provides for a 3/4" dado and actual 3/4" plywood.  I also can adjust the dado but to what gap?

    

   Al

1. 
   mikeddd | Nov 10, 2009 05:35am | #3

      Al :

     Adjust your dado set to get a fairly snug fit, even if you have to tap it lightly together with the palm of your hand, but not so tight you have to hit them hard or need a rubber mallet to put it together. When dry fitting the pieces they should stay together without glue and require a very little bit of force to pull apart. I've never measured the exact gap, but you will be able to tell by the feel. Good luck and have fun.

   Mike

   Edited 11/9/2009 9:39 pm ET by mikeddd

1. 
   forrestb | Nov 10, 2009 06:24am | #4

   panzer I agree with mikedd that you want a snug fit. Think about the glue surfaces with plywood and you won't find much long-grain to long-grain surfaces. So the snug fit and proper screws are your real structural support elements.

2. 
   mrbird90 | Nov 10, 2009 05:12pm | #7

   Basically no gap, the pieces should fit with a light tap or just barely slide togerther. To answer your question I measured a joint that I just made and the groove was .720 ( the average of 5 readings) and the plywood ranged from .718 to .720 ( measured at 5 places over a 12" width of a shelve). Hope this info is what you are looking for.

   Edited 11/10/2009 9:13 am ET by mrbird90

3. 
   tom77 | Nov 10, 2009 05:13pm | #8

   In my judgment, a gap of .002" to .005" is proper and will produce the feel described previously. It is difficult to achieve tolerances this tight with plywood unless you cut the joint tighter and hand tune.Good luck, Tom.

4. 
   Dave45 | Nov 10, 2009 05:25pm | #9

   Do you make your dado adjustments with shims, or does your Systematic have a dial type adjustment?I can't remember the last time I saw plywood that was a full 3/4" thick, and the cabinet grade stuff I use is usually ~11/16". When I use my Systematic stacked cutter, I use three of the full width chippers, the thin chipper, and .032" of shims. This gives me a nice slip fit with minimal "gap".I also have a dado bit for my plunge router that is sized for metric plywood. With it, I get a slightly tighter fit, but nothing I have to beat into submission. With either setup, and some screws, I get rock solid joints.Quite frankly, I would put that micrometer away. This is woodworking - not tool and die machining, and sweating over a couple of thousandths of an inch might send to you to an early grave. - lol

5. 
   Glaucon | Nov 11, 2009 08:36am | #12

   I think push in tight is OK, but I've never relied on a dado glue joint for strength, esp on plywood. I have built more than a few bookcases with oak veneer plywood, and because of the sag and rack issues that books can create, I originally used splines to improve the strength of the dado joint. Eventually I was making so many, that splines became a real layout pain, and I broke down and bought a plate joiner. The PC has a mini cutter that works well for this purpose and simplies layout.Glaucon

   If you don't think too good, then don't think too much...

2. 
   gofigure57 | Nov 10, 2009 02:12pm | #5

    this would work

   
   

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   Edited 11/10/2009 6:13 am ET by gofigure57

   
1. 
   mikeddd | Nov 10, 2009 04:40pm | #6

     I also do the same thing as you. With 3/4" Plywood I usually plow in a 5/8" dado then take the mating piece to the router table and cut a small rabbet in some scrap until I've found the correct depth of cut. Plywood is rarely the advertised thickness (usually thinner)so this way is the easiest to fine tune at least for me.

   Mike

3. 
   oldusty | Nov 10, 2009 06:26pm | #10

     Panzer,

        You can use shims of thin cardboard or thickish paper to dial the dado in to fit your plywood in a few tries usually with the few thousandths if you want to.

      I run a small cabinet shop and do kitchen cabinetry and I do use a dado , but in the case side where the deck or floor of the boxes meet the finished end having some room in that joint can give you the ability to make the deck come out flush to the face right there.

        On the tops of wall boxes it won't matter if the dado is big , I push it tight to the inside of the box always .

      Did you say glued and screwed ? will there be  face frames ? where do the screws go ?

           Instead of changing my setup for each plywood I run the joints at 3/4" every now and then we get a full thickness sheet and with a little swelling from the titebond sometimes it can be too tight .

       I make my shelves adjustable so no need for a piston fit dado there either.

             regards             dusty

1. 
   Dave45 | Nov 11, 2009 06:16pm | #13

   Dusty-I quit using DIY and/or metal shims a few years ago. I made up a stack one day and when I turned the saw on, I thought the cutter was going to launch itself into orbit.When I tore the stack apart, I discovered that one of the metal shims had slipped (slightly) into an arbor thread and left the stack "cocked" by a couple of thousandths - just enough to totally screw up the balance.I got a set of these magnetic shims and haven't had a problem since then. They're like refrigerator magnets, and will stick to the blades/chippers and stay put while you build the rest of the stack.A bit spendy IIRC, but well worth it IMHO.

   
1. 
   oldusty | Nov 11, 2009 06:28pm | #14

     Sweet  , thanks for the link.

2. 
   Eef | Nov 12, 2009 08:21pm | #15

   hey dave,"...a bit spendy."that exact set of frige magnets came with the forrest city dado set. just curious, how much did they run you?
   eef

1. 
   Dave45 | Nov 13, 2009 02:59am | #16

   I got those at a tool store that closed last year, but I'm sure that they're still available somewhere.I don't remember the cost, but they've been worth whatever I paid. - lol

4. 
   bldrbill | Nov 11, 2009 03:53am | #11

   Panzer--It's easy to get your dados for 3/4" material dead on if you cut them with a router using a 1/2" bit and make two passes.  Run your router against a clamped down straight edge and cut the first pass 1/2" wide, then put a homemade spacer of the right thickness against the straight edge and make another pass.  Perfect dados are easy this way.  Good luck.  Bill