dado sets - 6" vs. 8"

[Steven Triggs]

What is the benefit to 8" dado sets over 6". I assume people don't actually cut dados deep enough to need the extra depth? Is there some other benefit?

[Jim Becker]

Unless you are cutting deep, such as for half-laps on timbers with a RAS, there is fundamentally no extra benefit of the 8" over the 6". But of course, being human...most of us opt for the larger set anyway!! :D :D :D

[Bill Huber]

Unless you are cutting deep, such as for half-laps on timbers with a RAS, there is fundamentally no extra benefit of the 8" over the 6". But of course, being human...most of us opt for the larger set anyway!! :D :D :D


More of a question then a statement.

Would not the 8 inch make a better cut?
Would it not be moving faster in relation to the wood then the 6 inch at the same feed rate?

[Eddie Darby]

Angle of attack is different between the two.
Mass is different.
Load on your saws bearings is different.

[Jim Becker]

More of a question then a statement.

Would not the 8 inch make a better cut?
Would it not be moving faster in relation to the wood then the 6 inch at the same feed rate?

True, the rim speed of the 8" diameter cutters is faster and potentially can give you a better cut. But aside from how well the design of the dado set machines the very edges of the cut (how the outer teeth are ground), this is going to have less impact in most cases as the majority of the cut will be hidden within the project...and you don't need perfectly smooth for a good glue joint at least at the bottom of the dado, groove or rebate. The sides, however, should be smooth.

The better quality sets will give you that razor sharp, non-splintering edge.

The bottom line is that there could be a slight difference in cut quality between a 6" and 8" dado set, but if you are buying a good one (Freud SD50x, Forrest Dado King, etc) you may not really notice it. Do also note that some contractors' style saws and almost all bench top saws cannot use an 8" dado set due to internal clearance...be sure to check the saw manual before buying if you are using this type of saw.

[Cliff Rohrabacher]

What is the benefit to 8" dado sets over 6". I assume people don't actually cut dados deep enough to need the extra depth? Is there some other benefit?

Cuts both ways.

Rim speed is a factor but then ya gotta have the HP to drive a larger diameter cutter.

I am unsure how many HP you'd need to drive a 10" or 12" Dado through maple taking a deep cut like 3/4" or so but I have never seen or read about one that big.

Whereas a smaller cutter will allow more of the HP to be applied at the cut because the moment arm is shorter.

[Marty Rose]

Why is the arbor on ALL TS JUST long enough to just give the nut which holds the blades in place a couple of threads when using it as a 3/4" dado?:confused: I would think that for safty reasons you would need at least 4 or 5 threads showing after the Arbor Nut is in place?

[Greg Funk]

I am unsure how many HP you'd need to drive a 10" or 12" Dado through maple taking a deep cut like 3/4" or so but I have never seen or read about one that big.
The same amount of power it would take to drive a 6" blade. The larger blade will be going faster but if the feed rate is constant it will be taking a lighter cut (less wood) with each rotation and will require less force at the teeth to push through the cut.

Greg

[Byron Trantham]

My first dado blade was an 8" wobble dado on a Craftsman contractor's saw. I hated that blade! I bought a Forrest Dado King for the same saw and boy what a difference. I was told that my saw might not have enough poop to drive the 8" blade set to 3/4" width. I didn't have any problems with it. Since then I have replaced my Craftsman with a Unisaw. Obviously it cut easier but that was because of the additional horse power.

As Jim pointed out, most of us buy the "bigger blade", "just because". I'm in that category.:p

As far as the length of the arbor, relative to the amount of threads left over when you mount a dado blade set to 3/4" width, both of my saws exhibited that - not much left over. I don't install the belville washer. This adds a couple threads and because of the smaller diameter (8" vs 10") and stiffness, I haven't found that a problem either.

[Cliff Rohrabacher]

The same amount of power it would take to drive a 6" blade. The larger blade will be going faster but if the feed rate is constant it will be taking a lighter cut (less wood) with each rotation and will require less force at the teeth to push through the cut.Greg

I can't quite get my head around that concept. Seems to me that the moment arm is substantially important.

[Greg Funk]

I can't quite get my head around that concept. Seems to me that the moment arm is substantially important.
Torque = Force x radius. Assuming the Torque is fixed a larger blade will apply a proportionately smaller amount of force. But since the teeth are moving faster on the larger blade they don't need to take as big a bite on each pass through the wood hence don't require as much force to do their job. This assumes the wood is fed at a constant rate.

Greg

[Cliff Rohrabacher]

Torque = Force x radius. Assuming the Torque is fixed a larger blade will apply a proportionately smaller amount of force.

So far we are singing off the same sheet.


But since the teeth are moving faster on the larger blade
Well not really. They would be moving faster except for the energy required to spin 'em up as fast as the motor wants top go and the fact that the constant load from cutting - any cutting however slight - will slow the blade which won't be spinning fast at all after a rather small bit of feed.


This assumes the wood is fed at a constant rate.

I'm thinking the word "microscopic" should be used in place of constant.

[Greg Funk]

Well not really. They would be moving faster except for the energy required to spin 'em up as fast as the motor wants top go and the fact that the constant load from cutting - any cutting however slight - will slow the blade which won't be spinning fast at all after a rather small bit of feed.

Maybe you need a stronger saw.:) I am assuming that you wouldn't start the cut until the blade had reached its normal operating speed.

I can comfortable cut through 3" of solid maple with a 1/8" thick 10" diameter blade. If I increased the blade width to 3/4" then I might have to reduce the cutting depth to 1/2" to remove the same amount of wood. Not a problem for most 3HP saws.

I've never heard of anyone having a problem moving from a 6" dado to an 8" dado so I have trouble imagining that going from a 3" radius to 4" radius is OK but as soon as you move to a 5" radius everything falls apart and the saw stops.

Greg

[Charles McCracken]

Greg,

An 8" dado requires 33% more torque to maintain the RPMs in the cut than a 6". This definitely makes a difference on saws that are 1-1/2 HP or less. A 10" dado would require 25% more torque than an 8". A 12" would take 20% more than a 10". This is also true of single saw blades. You can use smaller diameter blades on under-powered saws to reduce the load.

[Greg Funk]

Greg,

An 8" dado requires 33% more torque to maintain the RPMs in the cut than a 6". This definitely makes a difference on saws that are 1-1/2 HP or less. A 10" dado would require 25% more torque than an 8". A 12" would take 20% more than a 10". This is also true of single saw blades. You can use smaller diameter blades on under-powered saws to reduce the load.
Charles,

Is the 33% based on measurements or simply extrapolated based on the larger diameter? It doesn't sound like your measurement accounts for feed rate. Because an 8" blade is travelling faster each tooth can take a smaller cut which should take less force.

Greg

[Charles McCracken]

Greg,

That assumes correct chip load for the tips which should be constant so the feed rate would vary based on the diameter of the dado and the resulting velocity of the tips.

[David Dundas]

Before I bought a Domino, which has essentially made regular tenons redundant, I used to cut tenons using a tenoning jig and the outer blades of a dado set, with a spacer in between. By fine-tuning the thickness of the spacer with shims to match the thickness of a router-cut mortise, you can cut a perfect tenon in a single pass using this method. Of course, you still need to round or chamfer the ends of the tenon to fit the mortise. For this operation an 8" dado set is essential.

David

[Cliff Rohrabacher]

Maybe you need a stronger saw.:) I am assuming that you wouldn't start the cut until the blade had reached its normal operating speed.

Not I. I have a 4 HP with about 80% efficiency on my slider.


I can comfortable cut through 3" of solid maple with a 1/8" thick 10" diameter blade. If I increased the blade width to 3/4" then I might have to reduce the cutting depth to 1/2" to remove the same amount of wood. Not a problem for most 3HP saws.

Width would increase the loading. So too would increasing the moment arm ( bigger blade diameter) work exactly like a long handled wrench - only in reverse.


I've never heard of anyone having a problem moving from a 6" dado to an 8" dado so I have trouble imagining that going from a 3" radius to 4" radius is OK but as soon as you move to a 5" radius everything falls apart and the saw stops.


Me neither. For years I had a Grainger 1HP on my contractor saw and I used a Craftsman micro cut 8" dado. I just had to take it easy on tough materials and keep the cutters sharp. My Hammer with it's high efficiency 4HP is un-stoppable - I mean I've tried and can't.

However, most of what I was getting at earlier on was the notion that increasing the diameter of a dado will cause the efficiencies to drop off because the motor is trying to work against a larger moment arm. I wasn't saying that stepping up from 6 - 8 inches would be fatal.

[Cliff Rohrabacher]

Just the other day I was on Ridge Carbide's site and noticed that they have a 10" dado.

It looks intertesting.

[Ed Falis]

Just the other day I was on Ridge Carbide's site and noticed that they have a 10" dado.

It looks intertesting.

I've got their 8" set, and it's awesome - very clean cuts. Their TS2000 combo blade is great, too.

[Cliff Rohrabacher]

I've got their 8" set, and it's awesome - very clean cuts. Their TS2000 combo blade is great, too.

For a couple hundred it's a great deal.

I like Ridge. I just sent 'em my whole blade collection to re-grind and re-bore to fit my new saw.

They aren't too cheap when it comes to tooth replacement at $5.00 a tooth but the rest of their work is quite inexpensive.

[Curt Harms]

I can't quite get my head around that concept. Seems to me that the moment arm is substantially important.
but that never stopped me before:eek::D. Going from an 8" dado to a 6" dado seems like it'd be like shifting from 4th gear to 3rd in a motor vehicle. Constant RPM at smaller diameter=Slower rim speed=less "mph"=more torque available. With a slower feed rate the 'cuts per inch' would be similar. Make sense?