Drawer Bottom Dado Thickness

[Jim German]

I'm making some drawers for my office cabinet project (http://www.sawmillcreek.org/showthread.php?179480-Office-Cabinets) and was planning on make the bottoms out of 1/2" plywood that is 0.460" thick. To make the Dado's I can either use my dado set, which will do a min of 0.485" or the router bit that was supposed to be for undersized plywood that is 0.495". Which one would be better? Or should I go buy a better bit/dado set that would fit tighter?

Thanks!

[Kevin Womer]

I don't think the difference would be noticable if you used the router bit, and once set up you can run all the sides in no time at all once they are cut to size. If there is any twist in the ply then a little wiggle room might save a headache, I learned that the hard way. Even though you are using plywood, I don't think I would glue them in the dados. Just my 2 cents. Another option would be to run the sides through with a 1/4 inch bit then sneak up on it for a perfect fit. Just run a sample piece until you are happy.

[Bill Huber]

I guess my question is 1/2" plywood, are these drawers going to be really big and hold things really heavy. I have not made a lot of drawers but the one I have I used 1/4" plywood and have had no problem with them sagging.

Just asking, maybe I should be using something larger for my drawer bottoms.

[Phil Thien]

I'd do a test cut with each, I think you will find that the dado cut will provide a nicer fit. The router bit's cut will be over 1/32" wider than the plywood, which may begin to look a bit gappy.

Bill brings up a good point, though. If you aren't storing especially heavy things in your drawers, you may want to consider 1/4" plywood. Quality 1/4" plywood, like BB, is very strong when used on drawers your size. And they make 3/8" (or the metric equiv.) if you think you'd like something a bit thicker than 1/4", but thinner than 1/2".

[Rod Sheridan]

Hi Jim, a dado can be adjusted in infinitely small increments depending upon your shim assortment. You should be able to make exactly the width you need.....Rod.

[Myk Rian]

I'm also asking why a 1/2" bottom. Just ads extra weight. 1/4" is fine.

A fellow in our WW group is making a 4 drawer chest. He's using 3/4" oak faced ply for the drawer sides, and 1/4" bottoms.
I can't figure out the 3/4" part. WAY overkill.

[Sam Murdoch]

My take on this is that I always make my dado in the sides first - 3/16" to 1/4" in the case of a 1/2" bottom, +/-, whatever the dado on the TS (or router/shaper table, if you prefer) will produce - and then rabbet the plywood to fit, taking the cut of the bottom face.

[Jim German]

I've never liked 1/4" thick drawer bottoms. Always thought they felt flimsy, plus I don't care about the weight. I also didn't really want to shim the dado that much, would be a decent gap, and I'd have to custom make the shims.

[John Lanciani]

5/16" or 3/8" dado, rabbet ply to fit. I always use 1/2" nominal for drawer bottoms, they feel and sound better to me and there are no negatives to speak of.

[Bill Arnold]

I run a 1/4" dado in drawer sides regardless of whether I'm using 1/4" or 1/2" plywood. When I use 1/2" for larger drawers or those that might have heavy items in them, I rabbet the sides and front to match the dadoes. I use a cutoff back, so no rabbet is required there.

[glenn bradley]

I like a tight fit. You mention using pre-finished ply for the carcasses so you could fully glue the panels in place. Yellow glue is not good for filling gaps and a tight fit is critical to the strength. High solids glues are available with better gap filling properties but, that is more of a band aid. Since you haven't made the cuts yet I would lean toward trying to make them more correct.

If you are using 1/2" ply for bottoms, these drawers are made to hold a truck. Doesn't make sense to me to then weaken this requirement by having a poor glue joint or a loose fit(?). Folks are different. I use 1/4" panels in my drawers (including shop drawers that carry a load of weight) without issue up to 24" wide. Others use 1/2" and some simply staple 1/4" panels to the bottom of finished drawer boxes. A dado stack that won't go under .46" has me intrigued. What kind is it (just curious).

[Kent A Bathurst]

2 more cents.........Just FYI....

I smiled when I read that the ply is .460. .46 +/- a couple-three hundredths seems more like the appropriate tolerance to me. The point - nearly all plywood is notoriously inconsistent in thickness, when you get to that hundredths decimal - forget the thou entirely. The thickness varies within any given sheet and any piece from that sheet. I recall a study by FWW[??] where they took a variety of materials - not just BORG stuff, but good stuff too - and cut out IIRC 6" x 6" squares from multiple spots in the master sheets, and mic'd them all....I was surprised.

[Jim German]

What's the point of rabbiting down the plywood? I thought of doing this, but it seemed like an extra step, and an additional source of error.

My dado stack would go under 0.46, I it would just need a custom 1/8" spacer, that I would perfer to avoid making.

So what's the ideal dado size? Obviously you want it to be a bit bigger so that the panel would fit in, 0.010" Bigger? 0.020"?

(and yes obviously those measurements are +/- a few thou)

[Neil Brooks]

Take your pick.

It should just slide in rather easily. Ply isn't going to move/expand much.

I wouldn't over-think it. Just leave yourself a bit of a gap -- whatever "a bit" means to you :)

[Sam Murdoch]

What's the point of rabbiting down the plywood? I thought of doing this, but it seemed like an extra step, and an additional source of error.

My dado stack would go under 0.46, I it would just need a custom 1/8" spacer, that I would perfer to avoid making.

So what's the ideal dado size? Obviously you want it to be a bit bigger so that the panel would fit in, 0.010" Bigger? 0.020"?

(and yes obviously those measurements are +/- a few thou)

My reason for rabbiting the plywood in any application for setting into a mortise - drawer bottom to sides or shelves to cabinet sides etc. - is to insure a consistent plywood thickness to a consistent dado dimension, plus the shoulder helps to mitigate racking as the rabbet creates a 4 point rather than a 2 point end. Yes, it's an extra step but I think I get a better job of it. The only time I don't do the step is fitting 1/4" ply as a drawer bottom. As for the thousands of an inch discussion - I defer to others.

Just my 2¢, because you asked :)

Sam

[Jeff Duncan]

I use 3/8" maple faced mdf for drawer bottoms and run the sides through a dado stack as it's significantly quicker than using a router. I like 3/8" as I also feel 1/4" is flimsy, nothing wrong with it, just my personal preference. It also happens to be the largest size I can use in between the tails on my dovetailed drawer boxes...therefore not leaving any gap on the outside that would require filling. And I prefer mdf for this application since it's normally much more consistent in thickness than plywood as previously mentioned.

As for the fit I wouldn't worry too much about being tight. If you do get a perfect fit on one piece, its pretty likely another piece will be too tight and not fit....much bigger problem. Not to mention if your using dovetail joinery and your off by a tiny little bit your pieces will not align perfectly and again, you'll be stuck not being able to get your bottoms in. Leave the groove a bit big, say two thicknesses of copy paper or so, and you'll be better off IMHO.

good luck,
JeffD

[Dan Hahr]

You could just use the outer blades for close to 1/4". The set should come with a 1/8" chipper if you wanted to go 3/8".
Dan