Do you shim your dado stack?

Chris C

Chris
Senior User
I have relatively limited experience with a dado stack....Oshlun set if that matters. It cuts like a dream but I find my fit a little tight.

I test cut and shimmed with two . 005 shims for what I though was a perfect fit. I had all the parts cut to final dimension yesterday.

I find the fit now at initial fitting to be tight... like rubber mallet tight. Normal? Should I shim for a looser fit?

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Mike Davis

Mike
Corporate Member
It rained here yesterday, still raining. Maybe the wood swelled a little. I usually allow 1/64 or so for glue and other variables. Yes I use the shims in my dado set. You could recut or sand a little.
 

Bill Clemmons

Bill
Corporate Member
I occasionally use shims when the dado has to be exact. I usually like the fit to be a little tight. Then I sand the edges of the work piece at a very slight angle (bevel) and ease them in. 'Rubber Mallet' tight, as you described, is just about right for me.
 

Jeff

New User
Jeff
Is that 3/4" plywood which is actually 23/32"? Your Oshlun dado set with shims should have got you pretty close to 23/32" wide.

A rubber mallet "tap-in" fit is pretty good.
 

JimD

Jim
Senior User
It depends for me on how many parts have to fit together. If it is more than two, I definitely want 1/64, maybe even 1/32.

For example, I built the last couple drawers of a set of 10 for a utility cabinet last week. I used 5mm plywood for the bottoms and I cut the dado with multiple passes over my normal table saw blade. I checked the fit against the corner of the bottom plywood but not the full length. When I assembled the drawer, with glue on everything, I discovered I cut it too tight. A 2 lb dead blow and some plane work on the bottom of the drawer got it together but it was a tense few minutes. Drawer works fine but I took another cut of about 1/32 for the second drawer and it assembled much easier. In this instance any misalignment of the drawer sides turns into reduced dado size for the bottom. So a little looser fit tends to work significantly better.

If it is just a shallow dado to get the pieces in the right place when assembling a cabinet, a little tighter fit is desirable. Allowing 1/32 misalignment may affect fit of the drawers. But 1/64 should still be fine. So it depends some on what I am doing. I do not enjoy having to pound on things during glue up. If it takes more than light tapping I think the fit is too tight.
 

Oka

Casey
Corporate Member
JimD points out most of what I do as well. To me a tight fit is 8-12 lbs of force to seat it. That force ratio is about the same as pushing an easy opening door with 2 fingers as a comparison. Btw, that is the Ada requirement for coefficient of door opening resistance. More than that and fit is too tight for the glue.
 

Jeff

New User
Jeff
JimD points out most of what I do as well. To me a tight fit is 8-12 lbs of force to seat it. That force ratio is about the same as pushing an easy opening door with 2 fingers as a comparison. Btw, that is the Ada requirement for coefficient of door opening resistance. More than that and fit is too tight for the glue.
Are you satisfied with your fit of the shelves in the dado? If so, we don't need to discuss it to death.
 

Chris C

Chris
Senior User
No I'm not. I believe them to be too tight and I worry about adequate glue.

Any information is helpful and appreciated.
 

zapdafish

Steve
Senior User
I like it where it takes a minimal effort to slide it in and if I turn it upside down it stays put. If I have to presuade it with a mallet it needs to be light taps otherwise to me its too tight. If it takes shims to get it there, i shim
 

Charles Lent

Charley
Corporate Member
With a Freud Dial-A-Width dado set, I install the right number of chippers to get close, and then dial in additional width as needed. One click = .004". Just about perfect every time. I like a fit that is just a few thousandths loose so it it snug when glue is added. I also do my dados or dovetail joints on the same day that I'll be doing the glue-ups. I have had rainy days mess with my dimensions.

Charley
 

Rwe2156

DrBob
Senior User
I've had this happen, too. I think its because I left the wood out overnight and maybe it swelled a little.

I don't like messing with dados once they've been cut.

Often a little sanding on the underside is all it takes.

One way to handle is a Japanese technique some people call "killing the wood". Simply hammering along the edge compressing the wood a little.
 

Jeff

New User
Jeff
I find the fit now at initial fitting to be tight... like rubber mallet tight. Normal? Should I shim for a looser fit?
How did your test cut pieces fit? Light taps with the mallet?
Rubber mallet tight fit? Light taps with the mallet or brute force? If it's light taps you're probably fine and your glue will be fine too. I've sometimes used a block plane to chamfer the edges of both pieces to make it easier to start in the dado then a few light mallet taps or a hand press fit.
 

Chris C

Chris
Senior User
The test pieces fit perfectly... Firm hand pressure seated them. Nice wobble-free fit. The actually parts required force... Hard hammer blows.
 

BSevier

Bryan
User
I typically will aim for tight. My thinking is that I often find inconsistencies in the plywood or have to deal with the changing humidity. For the spots that are a little tight, I will sand the panel that gets inserted just a bit to get the fit I like shortly before assembly.

Once I have the dados cut, I typically wont go back to them. I would rather size the piece being inserted.
 

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