Discussion on dado blades

[Pop Golden]

Since we are talking about dados here, I'm going off on a little tangent. I keep seeing folks writing about using dados on the RAS. What is if any the advantage? My idea is that with a cast iron table and a good throat plate your depth accuracy would be much better. I have used a RAS for many years and am well aware that the table flexes verticaly. Also the reason blade companys make negative hook angle blades is to lessen the self feeding tendency of RAS & sliding miter saws. Having used dados on my saw you bet they self feed. Hoging would be more like it. The RAS at best with self feed etc. is as the old joke goes "Makes a novice woodworker stop woodworking and take up stamp collection". Ripping with a RAS is a death wish. I'v had my saw in ripping mode take a good size piece of plywood away from me and leave me with a very small piece and counting my fingers.

Pop G

 

[ehpoole]

Another for the Freud 508 stacked set. Before you buy the dial-a width Freud, make sure your arbor shaft is long enough. If I am not mistaken, you need a longer arbor for it. My old Rigid TS3650 saw runs the 508 fine, even though its just a 1 1/2hp saw. The 608 is too wide so I cannot get the arbor nut on with it. With the 3/4" 508 stack, I can get two threads clear after the nut is tightened, but do have to leave off the shoulder washer (not unsafe, and is common practice).

IMHO, the 6" vs 8" debate is a little over-blown. With the 8" you have more mass moving, as well as faster cutting speed on the teeth. As long as you let the saw come up to speed, and don't feed too fast, the 8" cuts fine. With the lower powered saw, reducing the feed speed is a given, even when ripping thick lumber with a 10" blade, so is not going to be new obstacle. I am saying that as related to my experience with a belt driven saw. If the saw is a direct drive, the 6" probably would be a better choice

I went with the 8" to to get more depth when cutting deep dadoes in 2x lumber projects and am glad i did. No problem with cutting shallower ones in oak, etc.

JMTCW

Go

The added width of the Freud Dial-a-Dado (SD606 and SD608) was why I added the caveat "if your arbor is wide enough". The dial hub on the Dial-a-Dado set adds about 5/16" (or thereabouts) to the width of the dado stack. For many saws this limits the user to at most 1/2" to 5/8" for a maximum dado stack width unless they have a wider than typical arbor. The dial hub also limits the maximum depth of cut (still plenty of depth available on the SD608, but in principle the maximum depth is reduced from that of a standard stacked set (not that I can practically imagine needing/wanting a full-depth cut on an 8" dado set).

One can get away with running an 8" dado set on a 1.75-2.0HP tablesaw if it is powered by an induction motor (they are vastly more forgiving of overload conditions), has a very robust trunion and arbor assembly and is not amperage limited by any lengthy extension cords which will starve the motor under load (which can overheat the motor and/or stall the saw). If your saw has a universal motor, is not a cabinet or well designed hybrid type saw or is powered by way of an extension cord (e.g. a jobsite unit) then you really want to stick with a 6" dado set.

An 8" dado set also requires more torque (133% if my math is right?) to sustain rotation against an equivalent resisting force due to the added inch of leverage versus that of a 6" set and, thus, can be more easily stalled on underpowered saws than its smaller brethren (similar to the difference between a full kerf and a thin kerf blade).

Safety-wise, it is also important to keep in mind just how massive an 8" dado set is and how severe an imbalance can be created (in an instant) if an event should occur that damages the blade -- the kind of forces that can actually destroy a lesser tablesaw well before the user could find the off switch! It isn't just whether or not the saw can spin up the dado set or whether or not the user slows the feed rate, it is also about being able to survive an accident without a chance of the dado set being catapulted loose of the tablesaw.

All of which are just recommended guidelines, it is ultimately up to each woodworker how they choose to equip their shop and evaluate their needs, abilities and shop safety. I do run an 8" dado sets (both the Freud SD508 and SD608) on my 1.75HP Steel City hybrid saw, though if I knew then what I know now I'd estimate a 50/50 chance I would have gone with 6" dado set instead (though I am comfortable that my saw can handle 8" sets safely -- I'd feel very differently if it was a more lightly built tablesaw).

 

[Mr Woodie]

Just got the Christmas catalog from Grizzly, and the Dewalt 7670 Dado set is on sale for $99.
I have the same set, and it is great, cutting flat bottom dados.

An advantage of a ras for cutting dados, is, you can see the cut, and cutting dados on long stock (shelves) is a breeze. I needed to cut about 20 dados in 2, 2x4's and ganged them together, and cut all dados, in a few minutes.

 

[Mr Woodie]

The Dewalt is on sale at grizzly, for $99

 

[JackLeg]

I personally like doing dado's on my RAS. In fact, it's dedicated to dado almost entirely. I believe the safe way is to start shallow and increase the depth until you reach the desired depth of the dado. I too like being able to see what I'm doing, and, when removing large amounts of stock, (think WIDE dado's) you don't have to move the fence, just the material.

Just M2CW! :wsmile:

 

[Charlie Buchanan]

I have an 8 inch Freud D208 set (about $90) It makes very clean, flat bottom cuts between 1/4 and 7/8 in. It has chippers for making common width cuts but you have to use thin shims (included) for 23/32 and other plywood thicknesses. The shims are a nuisance but they can be very accurate if installed correctly. They are hard to slide over the arbor because the thin shims tend to catch in the threads of the arbor--they are bored so close to the exact size of the arbor. It is fine for me since I don't do much plywood. If I were doing plywood regularly I'd go for the more expensive sets that have specialized chippers for plywood thicknesses.