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Maximum Blade Speed (rpm at the arbor) - 4,000 vs 4,400

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Forum topic by MerylL posted 04-11-2017 01:02 AM 864 views 0 times favorited 4 replies Add to Favorites Watch
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MerylL

70 posts in 1204 days


04-11-2017 01:02 AM

All, I turn again to the fount of the faithful. :-)

I figured out yesterday why my new dado stack was making noise on wind-down after powering off. The darned drive pulley is loose on the shaft. It’s a new Baldor motor, but the original PM 66 3-groove sheave is wearing out in the bore. It shows a 3-thou difference between the end that is on the shaft vs the end that has never touched the shaft.

They do not make that anymore. You cannot buy one direct. In fact, you cannot even buy a “bushing” type sheave/pulley, 3 groove, as small as this pulley is at 3.45 OD. I COULD go to a 2-groove, but that means changing the arbor pulley as well. I’d rather avoid that if I can.

I CAN change to a 3.75 OD 3-groove driver (smallest available). I used an online formula, and this is what I come up with:

With the 3.45 original, I am just under 4K rpm (3967).

With a new 3.75, I am just over 4300 rpm.

I looked at my blades that still have writing on them, and so far I’ve seen warnings to not exceed 7,000 rpm.

Anyone have anything to add, admonish, warn, wave off or otherwise caution me on?


4 replies so far

View sawdustdad's profile

sawdustdad

333 posts in 718 days


#1 posted 04-11-2017 02:17 AM

Change to the two groove, and just use two belts, leave the arbor pulley alone, just use two of the grooves.

On the other hand, the additional 300 rpm will never be noticed if you go with the larger pulley…

Personally, I’d put the larger pulley on, and keep the three belts. Slight loss of torque at the blade but would not be noticeable.

-- Murphy's Carpentry Corollary #3: Half of all boards cut to a specific length will be too short.

View MerylL's profile

MerylL

70 posts in 1204 days


#2 posted 04-11-2017 02:38 AM

ha ha – I’m sure any loss of torque would not be noticeable. I’m no “woodworker” or pro or anything like that. I’m restoring an old house, learning it all as I go. My first project is window screens on this saw, hence the dado stack.

Thanks for the reply. I am definitely leaning to the larger sheave.

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MerylL

70 posts in 1204 days


#3 posted 04-12-2017 04:46 AM

Well, in case anyone reads this, I discovered something interesting. I talked to an “old equipment” shop in Vermont. Very adamant to get my old pulley bored, and a sized insert. I did some more research, and my original PM66 manual says to not exceed 11,000 SFM. Eh? More research, and the formula is blade diameter in feet (.8333) x pi (3.14) * RPM (4000 native). That is 10,466. By adding 6/10 of an inch to the diameter (the smallest 3-belt I can find), I add about 320 RPM (based on OD) and I pop it up to 11,300. So now I am over-speed. I can buy a new pulley, and replace the arbor pulley at the same time. I can bore out the old one ($90 vs $200). I could buy a new 2-belt, in a nearly-same-size. Small difference would not put me over.

I need:
3.4375 (3 7/16) OD
7/8 bore
3 groove
4L
Does not exist.

View knotscott's profile

knotscott

7782 posts in 3208 days


#4 posted 04-12-2017 09:32 AM

Speeding in your wood shop….shame, shame. ;-)

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

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