Proper fit for a dado joint?

[Dewayne Reding]

I just dodged a bullet last night. I was gluing up the carcas on my Norm's Super Deluxe Router Table. After a couple pieces, it started getting VERY difficult to assemble. With the help of my rubber mallet and pipe clamps I pulled it together. If I had hit it much harder I would have ruined it so I want to avoid that again. Didn't really need any glue. My panels were pretty accurate so I know it was the interference fit of the dados.

For simplicity, assume I have perfect 3/4 stock. The dado groove should be about how wide?

[Mike Cutler]

3/4", or .750 material should have a dado that is .750. There is enough crush in the wood fibers of both mating pieces to get the joint to together.
Many times material sits around for a few days, or weeks in my case, after it is cut and the exposed butt ends gather moisture and can "swell" ever so slightly. I know this because I have experienced it.

The accumulation of thousandths over all of the combined joints is where your trouble came from. You may not even be able to measure an error on any one particular joint.
In your post you make reference to a "rubber mallet". You may want to consider purchasing a nice quality "dead blow" mallet, with a non scarring face. I have found that they work very well.
If at the end you are still having slight fitup problems that are anoying you. Try to find a set of Stanley #98 &99 side rabbet planes. Lie- Nielsen makes a set. These are used to make a dado, or a rabbet wider.
If the router stand maintained it's shape on dry fitup. You must have done some very good work. We'll look forward to the completed pic's.

[Dennis Peacock]

Dewayne,

I like my dado's to be a nice "slip" fit. I don't like forcing a joint because it applies undue stress on the wood and can have undesirable effects over time...or immediately in some cases of mine. :o
I've found it much easier to sand the "tenon" part just a tad for a nice fit into the dado joint. And, Mike is correct on cutting the pieces and letting them sit around for a while. Joint swelling has caused me more "headaches" than I care to count. :)

[Gary Keedwell]

I agree with Dennis. A slip fit is what I strive for. As far as getting technical on the width of, say 3/4 dado. I would have to say that .752-.756 would be good. Seems to me I read where glue will fill a .002- .003 gap. ( on EACH side of plywood)

Gary K.:rolleyes:

[Dave Richards]

I like Pat Warner's method for cutting dados with a router. He uses a bearing guided straight bit. Clamps a straigh board as a fence along one edge of the dado to guide the router. Then he puts the piece that will go in the dado up against the fence. Then a piece of paper and finally another fence. He runs the router between the fences to cut the dado. The piece of paper gives just enough clearance for gluing. Pretty slick method with no measuring.

[Dewayne Reding]

Thanks for the dado schooling. Just spent 30 minutes with a file/rasp on the last couple dados so I don't have to force any more joints. This is my first wood project that didn't involve deck screws or 16D sinkers. I'm a Howitzer mechanic, we use a 20 ton arbor press for assembly. Not stretching the truth when I say it stayed together without glue. I had them tight. :) Something will likely crack some day. I'll get pictures up in a few days.

Dennis, do they still have Toad Suck Days near Conway? I ran a 5K down there a few years back.

[glenn bradley]

I do what Dennis does. Trying to machine and extra .002" of width in the dado is way more work than a quick rub with a sanding block. Also if the dado will be exposed, I want a tight fit (although maybe not as tight as you describe, eh?).

[Cliff Rohrabacher]

I like my dado's to be a nice "slip" fit.

Ditto on the slip fit.