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Dado blade for table saw-box joints

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Forum topic by Camper posted 08-16-2010 03:09 PM 2608 views 0 times favorited 10 replies Add to Favorites Watch
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Camper

232 posts in 2320 days


08-16-2010 03:09 PM

Topic tags/keywords: tablesaw question

I have a 3HP rated 10” Craftsman stationary saw. Model 315.228310. It runs on 120 V. I wanted to get your input on a 6” or 8” stacked dado blade. I do use a sledge that has 1/2” base. What would be my cut depth with 6” vs 8”? I know this topic has been discussed for 1-2 HP table saws running on 120V but I have not seen a discussion on a 3 HP rated one. Would an 8” be too much to handle for the saw? I have looked at Mibro and the price is pretty much the same for either size. Is the cut quality for the Mibro significantly worse than an Oshlun? I am am a hobbyist and would not be using this blade on a daily basis. Thanks in advance

-- Tampa-FL


10 replies so far

View richgreer's profile

richgreer

4541 posts in 2539 days


#1 posted 08-16-2010 03:25 PM

Even if you have an 8” dado set, I would advise you to make multiple passes and not try to chew off too much in any one pass – even if you have the power.

The typical 6” dado will cut 1.5” deep and the typical 8” will cut 2.5” deep. In my personal experience, I see no need for an 8” dado set and 6” sets are cheaper.

Put your money into buying higher quality and not bigger diameters unless you really need to cut a dado more than 1.5” deep.

If you need an extra deep dado seldom but every once in a while, just use a regular table saw blade and make lots of passes.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View Gene Howe's profile

Gene Howe

8254 posts in 2893 days


#2 posted 08-17-2010 01:48 AM

I have an 8” by Tenryu. I love it. But I don’t need the extra two inches. A 6” would have done me just as well.
To answer the power question, my 1.5 motor has no trouble spinning that 8” through mesquite! Then I seldom cut more than 1/2” deep.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Camper's profile

Camper

232 posts in 2320 days


#3 posted 08-17-2010 04:08 AM

Thanks for the feedback. I have my doubts on the HP rating as well.

Since you bring up the router, my main reason for looking into a dado blade is that, I am planning to make a toy chest using 3/4 inch stock and box joints to connect the 4 sides. I did some test cuts and even at 1/2” i get too much tear out (I am not sure that I am using a good but either) so I am not sure that I can do 3/4” in one pass. I have also read that anything more than 1/2” I should use a table saw to be on the safe side. Normally, if I am going to make a dado, I just set up a straight line and cut it using a router…I just am not sure what to do with these 3/4” box joints…any thoughts or inputs on this? I am not really working off of a plan so it just may be a bad design to begin with…

-- Tampa-FL

View Gofor's profile

Gofor

470 posts in 3251 days


#4 posted 08-17-2010 05:27 AM

I have a 120v 10” saw that pulls about 13 amps (regardless of the rating, the amps are the tell-tale, so its about a 1 1/2 hp saw). I run an 8” Freud Dado at full width and have cut up to 2” deep dadoes with it. I step it up about 1/2” at a time, but have hogged out 1” on soft wood like pine.

However, to prevent tear out, your best bet is to make a zero-clearance insert for it, and to put a backing board on the miter gauge when doing box joint cuts. For box joints, the backing board is the key to preventing tear out. It supports the back of the joint as you cut it, not allowing the wood to tear. Scrap play wood or MDF makes a good backer board.

A backer board is just a straight flat piece of wood that goes behind what you are cutting. A piece of ply screwed to the miter gauge that goes far enough over to be cut initially by the dado blade is what I am talking about. Sometimes called a sacrificial fence. The initial cut will also serve as a reference to align your other cuts.

However, whatever you do, do not buy a wobble dado cutter (Craftsman calls them adjustable dial dados). The will give a curved bottom on the cut. Buy only a stacked dado set-up.

Go

-- Go http://ncwoodworker.net/pp/showgallery.php?cat=500&ppuser=730

View knotscott's profile

knotscott

7214 posts in 2840 days


#5 posted 08-17-2010 02:40 PM

The fact that your saw runs on a standard 120v circuit says it’s not really 3hp or it’d require 220v. The motor plate likely says 14 amp, placing it closer to 1-1/2hp. Either way, your saw should be able to handle an 8” set if you don’t push it too hard. A 6” will be a little easier to spin but will have 1” less depth. There are more 8” choices available, which should offer more bargain choices.

The Oshlun set uses C4 carbide….not sure about the Mibro but it’s doubtful, meaning it’ll dull faster. I’m not a big fan of the cheap dado sets, but if that’s the price range you’re obligated to and can’t spring for the Oshlun, DeWalt, CMT, or Freud set, I’d consider grabbing the better HF set on sale over the Mibro.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Camper's profile

Camper

232 posts in 2320 days


#6 posted 08-17-2010 04:51 PM

Gofor and BoiseJoe,

I always use a backing board but it seems like somehow the fingers always use a piece of board on their side as if the bit rips a piece out rather then cutting them. I am starting to suspect the bit (its clean but not a real high quality bit) or maybe my jig is just not very stable. It seems you do not seem to think that cutting that size box joints should not be a problem. I am using a Hitachi M12VC on a router table. Any thoughts?

Knotscott, thanks for the suggestion.

-- Tampa-FL

View Gofor's profile

Gofor

470 posts in 3251 days


#7 posted 08-18-2010 03:14 AM

Try clamping the work piece against the backer board. If the bit is dull, it may be vibrating out away enough to cause that little rip in the side. If it is clamped snug, there should be no way for it to tear out, as it should act like it is all one piece of wood.

It also may be a bit of a sloppy jig. If there is any space between the edge of the cut on the work board, and the slot in the backer, that is where the tear-out will occur.

I am assuming here that your jig is the backer board, and you are sliding the last cut over a finger on the jig. IF so, and the finger on the jig is a little loose in the slot, the play is what has given you too big of a slot where the cut goes through. Hate to say it, but you may need to repair the jig (i.e. tighten the cut hole with a couple of shims glued into it on the sides). After that, make sure you always press the work the same way against the jig (left or right). You may also want to glue a little shim to the finger guide and then shave it until it is tight.. Make sure you get the shim on the correct side of the finger so your slots line up evenly spaced to match the fingers on the next board.

Hope this helps

GO

PS, Tongue depressors, match books, cardboard, or even note-book paper, etc and super glue can easily build up a sloppy jig in a hurry to tighten it up. Trim off the rough edges with a sharp knife or chisel. Just don’t glue your fingers to it!!.

-- Go http://ncwoodworker.net/pp/showgallery.php?cat=500&ppuser=730

View smitty22's profile

smitty22

694 posts in 2411 days


#8 posted 08-18-2010 03:28 AM

My Craftsman TS (Model 21833, not like yours) with the 1.75hp 120v motor worked just fine with an 8” stacked dado blade. I used the Freud SD508 Super Dado (8”) and had excellent results, cutting 3/4” wide x 1/2” deep.

As I remember, looked like a 2” depth would be possible (not all at once!) .

Best of Luck!

-- Smitty

View Camper's profile

Camper

232 posts in 2320 days


#9 posted 08-18-2010 12:02 PM

Gofor, thanks for the tips on the jig, I think my jig need some work. I will post back after I build another one. I changed the title of the thread also to reflect all this good info on cutting box joints.

Smitty, thank you, it seems the saw will be fine, I just have to look for a decent deal on a blade (6” or 8”), the Mibro does not seem to be a popular blade around here :)

-- Tampa-FL

View Camper's profile

Camper

232 posts in 2320 days


#10 posted 08-18-2010 12:29 PM

Quick question, I have seen in several post recommending the grizzly dado set, is this the one?

-- Tampa-FL

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