Cutting dadoes on table saw

[Beechwood Chip]

I was cutting a 3/4"x3/8" dado in a 10"x4"x3/4" piece of oak.  I wanted it to be centered on the 10" side, so I was cutting a groove and then cut the same groove with the board flipped.  I set up a 3/8" dado stack and started off with the stack centered on the board.  After each pair of cuts I'd check the fit, and then move the fence a hair inwards.  I know that each move gets doubled using this method, so I was careful to make tiny adjustments. 

Finally, it was close to fitting, so I carefully made the last tiny adjustment.  But, the joint ended up being loose.  I figured I must have been too impatient at the end and made the last adjustment too big.

The piece I was making got rejected for other reasons, so I had a chance to re-do it.  This time I was super careful to move the fence less than the smallest tick on the tape each time.  And for the last adjustment I was super careful to make it as small as possible, definitely less than one tick.

Still, the joint ended up being loose.

Is there a trick to it?  Should I stop with the dado a hair too small and then use sandpaper or some other method to get the final fit?  Or maybe make the last cut on only one side (without flipping the board)?

 

 

 

[Von]

One trick I've seen, and have been meaning to try, is once you get close instead of moving the fence, add pieces of blue tape to it. The idea being adding thicknesses of blue tape lets you predictably dial in the dado width more than nudging the fence.

[Mark J]

Just to clarify, you are using a tablesaw.   Are you using a dado stack, or a regular blade?

[wtnhighlander]

I find it easier (usually) to make the final adjustment with a handplane on the mating piece, rather than dial the dado in perfectly. Failing that, I'd take the last pass from just one side, to avoid the doubling issue. Just take care to follow the same process if there is an opposing dado, as in a book case.

[Beechwood Chip]

On 5/4/2025 at 6:08 PM, Mark J said:

Just to clarify, you are using a tablesaw.   Are you using a dado stack, or a regular blade?

I'm using a 3/8" dado stack on a table saw.  The dado will be approximately 3/4" wide, so the stack is about half that.

[curlyoak]

The easiest sometimes can be the most elegant. I make the dado around an eight smaller. I like a rabbit on the corresponding material. I make the dado first. Then with scraps of the shelves I dial in the fit I'm looking for. Slight friction and the rabbit fitting all around. Once you have the set up it becomes repeatable. Dressing the lumber and trying to make a dado to fit with shims is not the method I like.

On the table saw.

[Ron Swanson Jr.]

Remember that the margin between too tight and too loose is at best a thou or two. Which makes it really easy to blow right past that perfect fit. 

Next time you get close to your fit, instead of moving the fence, you might want to consider adding a thin shim to your stack for a very small adjustment. 

[Mark J]

2 hours ago, Ron Swanson Jr. said:

Remember that the margin between too tight and too loose is at best a thou or two. Which makes it really easy to blow right past that perfect fit. 

Next time you get close to your fit, instead of moving the fence, you might want to consider adding a thin shim to your stack for a very small adjustment. 

+1.  Or very thin shim on the fence as Von suggested.  Definitely don't flip the board and double the fence movement. 

I don't know what others would say, but (depending on what you're making) if the fit at the joint is only a "titch" too loose, glue may still hold.  

[Beechwood Chip]

On 5/5/2025 at 11:57 AM, Mark J said:

I don't know what others would say, but (depending on what you're making) if the fit at the joint is only a "titch" too loose, glue may still hold.  

The pieces hold together fine with glue, and I wouldn't be remaking them if there weren't other problems.  I'm just working to improve my skills.

[gee-dub]

An alternate method.  If the dado is a little loose, it does not show as long s you have some front trim or use a stopped dado.

[Beechwood Chip]

On 5/8/2025 at 11:49 AM, gee-dub said:

An alternate method.  If the dado is a little loose, it does not show as long s you have some front trim or use a stopped dado.

Good suggestion, but in this case I'm more concerned with the appearance from the side/edge.  Mostly I'm just trying to level up my joinery skills.

[gee-dub]

On 5/8/2025 at 9:11 AM, Beechwood Chip said:

Good suggestion, but in this case I'm more concerned with the appearance from the side/edge.  Mostly I'm just trying to level up my joinery skills.

Got it.  A nice tight dado or sliding dovetail at the front of a cabinet carcass is a beautiful thing.  There are certainly reasons for doing dados at the tablesaw; speed, repeatability, fence as a guide.  For me the move to a router for dados worked better.  This is not true for everyone.

For one thing, with routed dados you can use captured guides.  Something like this.  It measures off the insert piece that will go into the dado and prevents any dimensional variance.  It is however, slower than a tablesaw with a dado stack since the jig clamps to the work.  

Mine is a modified version.  Here is the original.

 

Dado Jig - Shop Notes.pdf

[drzaius]

There's a gotcha to using the table saw for dados. If the sheet stock is slightly cupped or warped, the depth of the dado can vary enough to give you a real bad glue up session. The easy fix is to run a router plane through the dado to even up the depth.

[Beechwood Chip]

Thanks!  I may switch to using a router for the dado.  Certainly saves me having to switch back and forth between a dado stack and my combo blade!

[gee-dub]

On 5/8/2025 at 11:24 AM, drzaius said:

There's a gotcha to using the table saw for dados. If the sheet stock is slightly cupped or warped, the depth of the dado can vary enough to give you a real bad glue up session. The easy fix is to run a router plane through the dado to even up the depth.

This is one of the things that had me switch over to the router.  I have a few dado stacks and do still use them but primarily for other types of joinery.  If your material isn't perfect you get the upper image when going across the tablesaw . . .

 

The small footprint of the router base can follow irregular material better.  This generally applies to sheet goods though.  Solid stock is assumed to have been well-milled and does not provide the problem.  The width and fit variance can still be a struggle for some of us (read me ).  Once we find a method that works for us to stick with it.  Neither is right or wrong but for a given operation sometimes one is more-better than the other for each of us.

[curlyoak]

I make dados with a router if the panel to be routed is on the long side.

[Beechwood Chip]

These pieces are very small, about 10" x 4".  I liked the table saw because I could get a perfectly centered dado by flipping the board.  But the router will be easier to set up and will get a perfectly sized dado in one pass.  I figure I'll position to board that will fit into the dado, use double stick tape to position two scrap wood guides alongside the board, and then use a straight bit with a bearing guide. Simple, quick, relatively fool-proof unless the tape slips, and the dado will be centered accurately enough.

[Beechwood Chip]

On 5/8/2025 at 5:26 PM, curlyoak said:

I make dados with a router if the panel to be routed is on the long side.

"If the piece is small, move it over a stationary tool.  If the piece is large, move a handheld tool over it."

[curlyoak]

Sometimes it matters that a dado is centered. Centering requires extra steps. But if the dado is off center by a tiny it doesn't matter in most cases. As long as the reference for the fence on the table saw is the same. Our eyeballs cant calculate a tiny fraction...

[Mark J]

Beechwood is using milled oak, but for others using plywood keep in mind that that the actual thickness of a sheet will be less than the stated thickness.  So 3/4" ply will be a tad thinner than 3/4".  But, more important, 3/4" plywood from two manufacturers may differ in thickness enough to play havoc with dado & tongue and groove joints.

[curlyoak]

On 5/9/2025 at 9:03 AM, Mark J said:

But, more important, 3/4" plywood from two manufacturers may differ in thickness enough to play havoc with dado & tongue and groove joints.

I would use the 5/8" dado for receiving 3/4" ply. I rabbit all my horizontal ends. If I had sheets from different mills at different thicknesses would not matter. All horizontal ends will be 5/8" matching my dado cut, not the ruler cut.

Milled lumber would work the same way.

[Mark J]

How do you cut the rabbit on the horizontal ends?

[curlyoak]

On 5/9/2025 at 7:16 PM, Mark J said:

How do you cut the rabbit on the horizontal ends?

On the table saw. I set the fence to the same dimension of the dado. Unless the shelf is too long to handle I turn them on end and run it through the saw. If it is too long then a router comes into play.