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Dados in 4x4 timbers

DocOz's picture

My situation is this: I'm in Iraq as an Army Flight Surgeon.  My 3 year old daughter is wanting me to build her an elevated playhouse when I get back home.  I found a plan and have downloaded it from the net. 


The problem is I need to make dados in the 7.5 ft long 4x4 timbers 1.5" deep x 7.5" long.  There are a total of 12 dados that need to be done.  I'm thinking of buying a new Craftsman radial arm saw with a dado blade to acomplish this.  I'm aware of the safty concerns (I'm a doc in real life), but like the idea of pulling the dado blade through the wood.


Any thoughts from anyone experienced with the new version of the Craftsman radial arm saw?

MikeHennessy's picture

(post #93857, reply #1 of 16)

Can you clarify? Are the dados running with the grain? (I assume so, since they are longer than the width of the stock.) How wide? Do they start at an end, or are they blind? If they are not blind, and are with the grain, why do you think this would be better done on a RAS rather than a TS? (If they are blind, don't even think of using the RAS!) Any reason why you wouldn't consider using a router for these?


In my experience, the RAS is great for crosscutting, but for ripping, its a TS every time!


Mike Hennessy
Pittsburgh (which looks a whole lot better than your present location!), PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

DocOz's picture

(post #93857, reply #2 of 16)

The dados are 1.5" deep, 7.5" long and 3.5" wide (full width of timber).  I guess technically rabits on the ends and dados in the middle.  I had considered getting a router with a straight bit to cut them.  Since the dados are so large I didn't want to burn up a router doing it.  Maybe a large router would work? 

GLAUCON's picture

(post #93857, reply #4 of 16)

See my previous post.  Any > 2 hp router should be able to handle it, just make several passes. Cutting a dado 1.5" deep with a RAS is a bit gnarly- you'd probably have to make several passes and it would be difficult to end up with a consistent depth of cut each time.

Glaucon


If you don't think too good, then don't think too much...

Glaucon

If you don't think too good, then don't think too much...

GLAUCON's picture

(post #93857, reply #3 of 16)

I'd use a router. You can place the pieces to receive the dados edge to edge, clamp and cut the joint with a pattern bit- make a simple jig the exact width of the dado from some offcut ply or mdf and each dado will be exactly the same width and exactly lined up.


I've done dados with a TS, RAS and a router (as well as by hand with a chisel), and the router does the most precise work, is easier and safer.


Glaucon


If you don't think too good, then don't think too much...

Glaucon

If you don't think too good, then don't think too much...

JohnWW's picture

(post #93857, reply #5 of 16)

Doctor,


The easiest way to do this is with a hand held skil saw, using a safe technique that is standard procedure on construction sites. 


Lay out the dado, set the saw's blade to the depth you want, and using a guide like a speed square, make spaced cuts, around 3/8 inch apart, across the marked out area.  Now just use a chisel to clean out the wood remaining between the cuts, it will break away easily.  You'll be able to make a dozen dadoes in less time then it will take to just get a radial arm saw out of it's packing crate. 


Another advantage to this approach is it will work even if the 4x4's are a bit crooked, which they almost certainly will be.  Trying to get a long crooked post to sit wobble free on the table of the radial arm saw would be a time consuming hassle and, if the post shifted while being cut, you'll have some serious kickback and control problems.


Good luck while you're deployed, come home safe to your family.


John White, Shop Manager, Fine Woodworking Magazine 

John White Shop Manager for FWW Magazine, 1998 to 2007

forestgirl's picture

(post #93857, reply #6 of 16)

"if the post shifted while being cut, you'll have some serious kickback and control problems."  Kickback with a 4x4, holy smokes, there's an image.


Doc, in case you're not familiar with John's credentials, he's got 'em up the ying yang (sorry John<g>).  Please be safe!  We'd hate for you to get back from Iraq safe and sound and end up being a punching bag for a 4x4.


 


forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

JohnWW's picture

(post #93857, reply #9 of 16)

Thanks for the vote of confidence, though this wasn't an especially difficult question for someone who has done a lot of carpentry.


The problem with kickback on a radial arm is that the saw head fires back at you and the wood stays in place (unless the fence breaks loose).  The movement can definitely leave your arm bruised and usually knocks the saw totally out of alignment.


John

John White Shop Manager for FWW Magazine, 1998 to 2007

forestgirl's picture

(post #93857, reply #12 of 16)

Ooops, I was thinking table saw.  Need to pay attention here, I guess.

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

DocOz's picture

(post #93857, reply #7 of 16)

I didn't tell it in the beginning but John's method of making the dados is the recommended method in the plans I'm using.  As usual, I'm trying to make a better mousetrap.  I will follow through with John's recommendations to the letter.  I appreciate everyones input.  Now to convince my 3 year old daughter her 6 month old brother does not want the playhouse to be pink!  ---DocOz, LSA Anaconda, Iraq

PeteBradley's picture

(post #93857, reply #8 of 16)

For rough carpentry such as a playhouse, you can knock most of the sliced material out with a hammer. It will just snap off on the short grain. Then clean up with a chisel.

One other thing to keep in mind is that this method has a tendency to send short grain chunks of wood flying when you make the cuts, so good eye protection is a must.

Notching and dadoing with this method is very satisfying and a skill you'll use over and over.

Be careful out there,

Pete


Edited 3/22/2006 1:25 pm ET by PeteBradley

JohnWW's picture

(post #93857, reply #10 of 16)

Pete,


If this weren't Fine Woodworking I would have recommended the hammer claw approach myself, but we have to keep a little things a bit classier.


John

John White Shop Manager for FWW Magazine, 1998 to 2007

PeteBradley's picture

(post #93857, reply #11 of 16)

:-)


Actually a carpenter friend taught me that one.  You don't actually use the claw, you hit the sliced part with the head.


 


Pete

cowtown's picture

(post #93857, reply #13 of 16)

I'm gonna concurr with John. Not only would it be likely safer and faster, but likely less wear and tear on the back. As for precision, yer talking about wet, checked , out of square, roughish stuff for the most part, so if yer joints is out by a 1/16th yer doin pretty good I figure.

Oh, ya, knocking the stuff out, wear yer safety glasses too.

Just get yerself and as many others home as intact as possible.

Eric


Edited 3/23/2006 11:18 pm ET by cowtown

Samuel's picture

(post #93857, reply #15 of 16)

your way of cutting the dados is the quickest and it can be done safely and accurately.  while building decks i've had to do this type of cut many times into 4 x 4 material.  there's  only two important cuts with this method, the start of the dado and the end of the dado.  the others don't have to be that accurate.

mudman's picture

(post #93857, reply #14 of 16)

I have built a few high end arbors, trelisis (sp) and the like using the same joinery and we always use the skill saw/ chisel technique. Don't use your good chisels. If you are using pressure treated lumber the stuff chisels very easily while it is still wet.


As far as using a RAS goes, I am a big fan. I have a 1955 14" monster RAS that out weighs my Unisaw. It is the second most used machine in the shop. It is as accurate as my miter saw and is a lot safer for crosscutting 8" to 16" boards than the table saw. I also do 80% of my dadoing on the RAS, and it is a lot easier. Tennons are also super fast. Unfortunately the newer consumer grade saws are not made so well. They do not reproduce angles consistantly (today 45 deg is dead on, next time it is off) even if the angle is 90 degrees. The arms are also not stiff enough to handle a full Dado set without "walking" off the cut. So unless you drop $1800 or more for a comercial duty saw or get an old Dewalt (pre 80's) for a good deal you will likely be dissapointed.


Mike

Pardon my spelling,

Mike

Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

tinkerer2's picture

(post #93857, reply #16 of 16)

     Have used a RA for over forty years.  Have built some nice furniture with it.  (For me anyway).  If used for cross cutting it is as safe as any tool in the shop.  In my opinion, it should not be used for any form of ripping operation.  Use a table saw or hand saw.