Forrest Dado King size question

[Kent Adams]

I just purchased a PM 2000, 5hp, 1 phase TS. I'm thinking I can run Forrest's 10 inch dado stack rather than an 8 inch dado stack because the TS is 5hp. Any opinion on performance loss by running a 10 inch dado rather than 8 inch for my saw? Any application where the 8 inch might be a better choice?

Thanks in advance.

EDIT: Changed 1200 to 2000

[Jim Becker]

I can think of few reasons to run a 10" dado cutter outside of possibly doing tenons on big stock...and for that, I'd prefer the bandsaw. Unless you have a specific application that you really require the depth you can achieve with the 10" setup, sticking with the 8" will save you money and be more than adequate for most jobs that folks use a dado set for. IMHO, of course...

[David Kumm]

I'm not familiar with the 1200 but I would not run a 10 dado with a 5/8" arbor. Lots of weight spinning so you want a stout arbor assembly and good bearings. Tip speed will be higher and the exit angle will be less. I like 10-12" dados but on very heavy saws. Dave

[Mel Fulks]

No "performance loss" with the bigger set. It has more edge speed and does well. What I would look at the most is what widths you will be cutting since all pieces of a set need to be sharpened at once to keep the dados from being jackalantern toothy, so there is some waste in sharpening pieces that might not have been used. I would consider the WIDTHS more than diameter .

[Kent A Bathurst]

...... It has more edge speed.......

Hmmmm....interesting point. Curious:

Does this make a difference? On the Forrest, at least, both 8" & 10" sets have 24t. So, bigger dia = faster tip speed, but you get the same number of teeth cuts per second [or, rpm, or whatever].

Seems like if cuts per sec are equal, then the cut quality will be the same.

I'm with Jim B, btw - my 8" does virtually everything I've ever needed, and when it doesn't, I'll go neander.

[Bill Neely]

I have a 10" set by Popular Tools, the riving knife on my saw is difficult to setup so it's convenient to run a 10" main blade and dado.

[Mel Fulks]

Yep. Makes a difference,along with "exit angle". Read that recently in a dependable source.

[Kent Adams]

I'm not familiar with the 1200 but I would not run a 10 dado with a 5/8" arbor. Lots of weight spinning so you want a stout arbor assembly and good bearings. Tip speed will be higher and the exit angle will be less. I like 10-12" dados but on very heavy saws. Dave

Oops, meant the PM 2000

[Earl McLain]

I just purchased a PM 1200 5hp, 1 phase TS. I'm thinking I can run Forrest's 10 inch dado stack rather than an 8 inch dado stack because the TS is 5hp. Any opinion on performance loss by running a 10 inch dado rather than 8 inch for my saw? Any application where the 8 inch might be a better choice?

Thanks in advance.

Did you mean Powermatic 2000 instead of 1200? On many 10" saws, the reason for an 8" max on the dado stack is because of possible clearance issues as the stack gets wider. Don't know if that is why PM shows a maximum of 8" (in the specs of the manual for the PM 2000) on a dado blade or not--but it may be wise to ask them before making the investment in the blades. The 5 hp motor may spin the 10" stack just fine, but if the issue is interference the first cut could be expensive.

earl

[Rod Sheridan]

On my saw the dado cutter is limited to 170mm to avoid a collision with the table trunion.

regards, Rod.

[Steve Kinnaird]

Inches of blade per revolution.....
8" blade (4" x 3.14) 12.56"
10" blade ((5" x 3.14) 15.7"
Yet still only 24 teeth.
I think the 8" would be cleaner.

[David Kumm]

I run 6,8,10,and 12" dados and a well sharpened dado of any size will do a good job. The faster speed and greater mass of the outside chippers leave a little better cut on the shoulders with larger blades but the difference is negligible and likely more affected by how tight you hold the stock to the table. Larger sheets of ply will chip out if bowed up in the middle regardless of dado diameter. The larger diameter chippers in thin sizes, 1/16 and 3/32 won't be quite as stiff and vibration free as smaller but that only affects the bottom and really not an issue. I still believe the 10" saws made today fare better with the 8" max. A 10" dado is heavy and nothing good comes from stressing the arbor or bearings when you gain little benefit. Any runout will be multiplied when you spin more mass. Dave

[Kent Adams]

Did you mean Powermatic 2000 instead of 1200? On many 10" saws, the reason for an 8" max on the dado stack is because of possible clearance issues as the stack gets wider. Don't know if that is why PM shows a maximum of 8" (in the specs of the manual for the PM 2000) on a dado blade or not--but it may be wise to ask them before making the investment in the blades. The 5 hp motor may spin the 10" stack just fine, but if the issue is interference the first cut could be expensive.

earl

Thanks Earl, should have read the manual. I'm glad I asked the question though to get the benefit of everyone's opinion.

[Kent A Bathurst]

Yep. Makes a difference,along with "exit angle". Read that recently in a dependable source.

I can maybe see some benefit by having a wider gullet between teeth for waste removal. I can see that the angle of attack is shallower - digesting that thought, trying to figure out pro/con. I don't get that an increased tip speed, per se, adds a benefit........


You secret dependable source - they know the lotto number, or anything along those lines?

[Kent A Bathurst]

Inches of blade per revolution.....
8" blade (4" x 3.14) 12.56"
10" blade ((5" x 3.14) 15.7"
Yet still only 24 teeth.
I think the 8" would be cleaner.

Not to be picky, but isn't the circumference pi * D, not pi * R?

So then 25.132" v 31.415" per revolution. Which, at 2,000 RPM, adds about 11.9 MPH to the tip speed when you go from 8" to 10"...........

I think you might have tripped mid-calc on the area - pi * R sqrd.

Your point is correct of course, I just wanted to rescue you from the Picayune Police. And no - those are not double-prime inch marks, they are quotes.

[Steve Kinnaird]

Not to be picky, but isn't the circumference pi * D, not pi * R?

So then 25.132" v 31.415" per revolution. Which, at 2,000 RPM, adds about 11.9 MPH to the tip speed when you go from 8" to 10"...........

I think you might have tripped mid-calc on the area - pi * R sqrd.

Your point is correct of course, I just wanted to rescue you from the Picayune Police. And no - those are not double-prime inch marks, they are quotes.

You are correct :)
Diameter not Radius.
I just wanted the PIE back then
316971

[Peter Quinn]

I'm thinking all empirical evidence and geometric equations aside, there isn't much work I want to do with a 5hp machine spinning a 10" dado on a 5/8" arbor with the blade up at full reach. The 10" dado gets you an extra 1", but it's an inch I'd never consider using. I spin a 10" dado on a RAS with a 1" arbor, and that's because I need 10"'s to get around the motor housing and get the depth of cut I need on a saw that takes a 14" blade normally. I'm still not going in very deep. Point is an 8" dado goes as deep and reaches as far as I ever want to go on a powermatic. I might spin a deep cut with a 10" grooved on a big shaper, but the arbor size and bearings are worlds above that of a cabinet saw. Like Jim, if I need huge tenons I'm doing that on a BS. I run a 6" Forrest dado on a 5hp 66 at home and only a few times have I ever wished for the bigger set. The cuts are flawless.

[Kent Adams]

Thanks Peter, I never thought of the arbor as being an issue. Some others pointed that out as well. I'm glad I sought the advice of this forum before purchasing. I purchased the 8" set a couple of days ago and should get it on Friday and I'm looking forward to using it.