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One Inch Dado Cut

2K views 21 replies 14 participants last post by  SMP 
#1 · (Edited by Moderator)
All,,

Surprisingly, in all my years of woodworking, I have never had a dado set.
Now an upcoming project requires me to get one, which I did.
I got the Oshlun 6"set for my Ridgid R4513 portable table saw.

My question is I need to make a 1" wide dado (1.5" deep). This set only
goes to a width of 9/32". Would I make a 0.75" cut then and additional
0.25" cut? My only concern with doing it this way is I could run the risk of
making the dado too wide if my cut is not right on.

Does anyone have a better way to do this?
 
#3 ·
I'd do something similar to SMP, but with two spacers and a stopblock. Set the stopblock and put a 1" spacer (an offcut of the piece you're putting in the dado works best) against it. Put your piece against the 1" spacer and stopblock. Make an initial cut, which will be .6" wide. Take away the 1" spacer, and add another spacer the same width as your dado set (.6") against the stop block and make the second cut. Now you've cut a 1" wide dado.

This works best with a crosscut sled.
 
#4 ·
No real way around making two passes, but you can do some things to make sure you don't go over.

Are there a lot of dados in the same spot in relation to the end? If so a stop-block on the fence, to establish one side, and then a spacer to establish the other side is an easy way to do it.

You can do roughly the same thing with a spacer on your miter-jig or sled, same set-up as a a finger joint jig, if that makes sense. You'd just have to make all the first cuts, then all the second passes, so it may screw up your workflow.

If that's too much set-up, you can take a 3/4" pass, and then another that gets you just shy of the finished dimension, then use a router jig to complete the cut to the exact width required.

Lastly, just be really careful, and shoot for a butt-hair undersize, then massage the part to be fit into the miter with sandpaper or a handplane.

Which method to use kinda depends on what exactly the project is.
 
#5 ·
Don't know why I did think to flip the piece around, makes sense!
And I do appreciate the suggestions, will give them all a try.

I should have mentioned that I am making an iPhone stand and the portion
that requires the 1" dado is the foot portion that slides over a 1" wide tenon that at the bottom
of the stand. It's hard to describe without a photo, think of it as an angled "L" with the horizontal portion of the "L"
facing backwards and there are two 0.75" parts that protrude in the front to hold the phone and it rests against the vertical portion. Make sense??
 
#8 · (Edited by Moderator)
I am a little confused. Your dado set only goes to 9/32" wide? Most are closer to about 7/8". Yours sounds more like a finger joint blade, though those are usually exactly 1/4" unless it is a metric one and is actually 7mm? It is going to take at least 3 passes to get to 1" with such a narrow dado blade. Also, when you say a depth of 1.5" do you mean 1.5" long ? If you truly mean 1.5" deep, that is way too deep to make in a single pass so you will need to make at least 3 cuts for each pass going 1/2" deeper in each cut to prevent bogging down almost any table saw.

Here is the method I came up with to cut a dado to fit an exact width, even if the dado blade is smaller than the dado or groove you need to cut:
  1. Get a spacer that matches the width you want the dado to be-a cutoff from the piece that will be in the dado is ideal.
  2. Get or make another thinner spacer that is over half the width of the dado you want to cut and setup your dado blade to match that thickness exactly. I usually use a piece of 1/2" plywood and shim the dado blade to match.
  3. Place the thick piece between the fence and the piece of wood you are cutting and set the fence so that the side of the dado stack nearest to the fence (generally right side of the stack) will cut the edge of the dado you have marked out on the board that is nearest to the fence. Cut the dado by sliding the board with wide strip along the fence
  4. Remove the wide strip strip and replace it with the thinner strip that matches the thickness of the dado stack. Repeat the cut sliding the board and narrower strip along the fence to cut the edge of the dado away from the fence.

As long as the dado stack is exactly the same width as the thinner strip, the result is a dado or groove that exactly matches the thickness of the wider strip. Now if your dado stack is really only 9/32" wide, you will need to make 2 passes with the thin strips. First one using only one strip to cut the far side of the dado and the second with 2 strips to remove the center.

EDIT: I misstated the setup in step 3. It is now corrected.
 
#12 ·
I'd go the spacer block route if the dado isn't in the center of your board. If it's centered, flip the board like SMP suggested. Another option is to use a dial indicator or micro-adjuster to make sure you move the fence the precise amount for the second pass.
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#14 · (Edited by Moderator)
If that's the case, I would just make 2 cuts on the table saw and cut the rest out with the band saw.
Does your 6" dado blade even go up to 1 1/2"?
If it does, and your going to use the dado blade, I would just mark the lines and use my miter gauge.
(You may need to add a fence to your miter gauge)
You should be able to eyeball and cut on your lines. Set the width of your blade to 9/16 and make 2 cuts.

If your making more than 1 then maybe I would set up some stops.
I doubt you will be able to use a sled with the added height.

Also, if you are going to stand these up to run them through, make sure you have a good fence to clamp the piece to, and keep your hands clear when your cutting. Dado blades can be mean to you.
 
#15 ·
With that design, LRM's, approach is the way to go assuming your dado can be raised 1-1/2". If not, cut the sides on the table saw and clean out the waste with band saw, coping saw or jig saw followed by a chisel. If you use the dado blade, definitely add a fence to the miter gauge to make it easy and safe. It will also help prevent chip out. You could use a sled if the fence is tall enough.

Note that many dado blades have beveled teeth on the outside blades that leave batman ears which may detract from the final appearance. If don't want that, cut a little shy of the line and finish with a chisel.
 
#16 ·
Thanks all for the suggestions, very much appreciated and sorry for the typo, the Oshlun goes to 29/32 NOT 9/32.

I've got some experimenting to do to see if I can get this process down. I'll give these a go tomorrow and let you guys know the results. Another option I was thinking of is, would it possible to lay the piece flat and cut the 1.5" notch or would that be a no no with a dado?
 
#17 ·
If you lay it flat to cut the notch, you'll have to cut well shy and finish it with a chisel. You'd probably be better off cutting with a bandsaw and finishing the bottom with a chisel.
 
#18 ·
I would use LRM's approach with the dado blade and fence on the miter gauge. Very easy. I have done this before with a much more complex build (multiple angled cuts) and it works very well. Trying to do it flat, you will wind up with a scoop where you stop the cut that has to be cleaned out and it is hard to know exactly where to stop so you don't go too far.

BTW, my 6" Freud dado set will cut almost 2" high on my saw.
 
#19 ·
You used to be able to buy extra chippers from the manufacturer for Dado blade sets.
Of course your table saw arbor would have to be able to support it, but it might be one solution if you REALLY want to cut the slots in one pass.
 
#21 ·
I do this sort of cut all the time. Sure, if the cut is centered you can flip the board and cut from both sides.

Usually my dados aren't centered, so I mark a reference line, and cut to the line. On the second cut, stay inside the line, and creep up on it in several passes. Use the actual mating workpiece as the final gauge. Once the parts fit as they should, you're done.
 
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