No-measure, no-fuss perfect Dado's

[Matt in NM]

As I do a lot of dado's in the various things I build for the school district, I've come up with a way of making perfect dado's with very little measurement. I'm going to rely on pictures to show what I'm doing as it is a lot easier to show it than explain it.

As each post can only have 4 pics, this will be a 5-part post, so don't post before I'm done with part 5.

PART 1 OF 5

Here's a pic of a set of Teacher's mailboxes. Each shelf is inserted into a 1/4" deep dado and each Divider is inserted into a 3/8" deep dado of the top and bottom. The important measurement to do this is the interior of each box. In this example they are all 5" high and 9 1/2" wide.


First step, is to cut your stock to width and approximate length. I'll be showing how I do the dado's for the shelves. Make sure you have both sides ready.


Now butt them together and butt the bottom edges against a stop.


This is a pic of the stop we use at work. What type of stop you use is up to you as long as the stop is at least 1/2" higher than your stock.

[Matt in NM]

PART 2 OF 5

To make this work properly, you need 2 Tru-clamps. The length of each doesn't have to match but they must be able to clamp twice the width of your stock.


Next step is to measure your clamps width. Mine are exactly 2 1/8" wide. As I said previously, I need 5" of interior space, so I will make a spacer out of scrap that is 5" minus the 2 1/8". Also I make another space that is 3/8" wider to compensate for the dado that the bottom and top of each divider is going into.


Keeping my stock butted together and against the stop, I place the 5 3/8" spacer on top against the stop. Then I take one clamp and butt it against the spacer and clamp both of my stock together. From here on out, the stock must remain clamped at all times by at least one clamp. For longer stock, I add extra clamps and move them as needed.


Now take a length of scrap stock that you will make your shelves from. Butt it against the clamp and then take your second clamp and butt it tightly against your spacer and clamp the stock.

[Matt in NM]

PART 3 OF 5

Now chuck up a 1/2" dado bit like this in your router.


Remove the stock spacer and set your depth of your router bit when it rests on top of the Tru-clamps.


Now with the bearing riding along one of the clamps, rout one side.


Then shift the bearing to rout along the other clamp and rout the other side.


Be careful not to go too far and hit the plastic on your tru-clamp. It won't hurt anything, but it gives your clamps a beat up look.

[Matt in NM]

PART 4 OF 5

Here's the trick of the whole thing in this post.

First slip your scrap stock into the dado you just made. It should fit perfectly.


Unclamp the LEFT clamp only and put your 5" spacer (that is really 2 7/8") next to your scrap stock. Then place your clamp against the spacer and clamp.


Then move your scrap stock next the clamp you just put down and move your other clamp to the left of the scrap stock and clamp.


Now continue on with routing as many dado's as you need. One more post to wrap this up.

[Matt in NM]

PART 5 OF 5

After you rout the last dado, place your scrap stock into the dado and unclamp your left clamp. Now butt the wider spacer against the scrap stock and then clamp your tru-clamp next to the spacer.


As you can see, I have a little bit extra on the left of the clamp. This part needs to be cut off. Draw a line, mark a line or whatever. Then unclamp everything and take your stock to TS, RAS, CMS or whatever you have and cut the excess off.  You will be left with 2 pieces of stock that have perfect dado's that also match each other. Make sure you mark each piece of stock so you know these are matching pairs.


Here's a closeup with a marking tape showing that the spacing is exactly 5". Notice also as a side benefit, there is zero tearout in the plywood.


Using this technique, I did 70 dado's in about an hour.

Thanks for looking and hope it helps someone!

[Steve in MI]

That's amazing coincidence, I was making cubbies almost like yours except there were only two rows.   Using the two clamp-n-guides is a great idea and is the missing link for my process.   We were using only a single guide and shimming in a narrow piece of steel and making a 2nd pass to widen the track.

I like your technique a lot.    One thing I do differently is I have found if you start in the center (cut the center dado first) and work outward in both directions it reduces the incremental variance you get from cutting each dado repetition based on the previous one.

[Matt in NM]

[quote author=Steve in MI link=topic=8122.msg89236#msg89236 date=1202004685
I like your technique a lot.    One thing I do differently is I have found if you start in the center (cut the center dado first) and work outward in both directions it reduces the incremental variance you get from cutting each dado repetition based on the previous one.
[/quote]

I had thought  of that  before  and  tried  it. Problem  I  had  was  getting  a  good  center. With plywood, it doesn't measure  3/4" exactly. My method makes  it  so  you  don't have  to  figure in the thickness  exactly.

Also  I  did  a run  of  dado's  on a  93" long piece and didn't  have any varience at  all  when I finished.  Trick is  to make  sure  you always  butt  the spacer, clamps up  tight each time.

[Jace Weber]

VERY nicely done Matt!  Thanks for taking the time to do this for TWW!

Jace

[Stu in Edmonton]

Thanks Matt. It's always a good thing to pick up a few new tricks. The idea of making the dado with 2 passes will assure the width of the dado is right for the stock you are using. There's always a new way to skin the cat.