# Dual-Speed Table Saw?

• posted on October 2, 2003, 6:50 pm
Harbor Freight's on-sale \$20 dado set has 4500 max RPM. My single-belt, 1.5 HP TS's arbor spins at 4700 RPM per the spec sheet.
- Is the 200 RPM difference ignorable? - Any downsides to finding a slightly smaller (if my math is right) pulley for the motor and running the dado at about 4000 RPM? Does anyone run a "dual speed" TS this way?
Thanks.
-- Mark
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• posted on October 2, 2003, 7:18 pm
On Thu, 02 Oct 2003 18:50:40 GMT, "Mark Jerde"

I used to be a professional engineer, and the way I personally see these things is: 4700 is only 4.4% out of spec. I would never have designed anything that fails catastrophically if operated 4.4% out of spec. So I'd give it a go and see if it cuts well.

Yes - it's a pain in the neck, so why not try it at 4700 first?
Rob Bowman Amateur woodworker, professional sawdust maker.
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• posted on October 2, 2003, 8:10 pm
Rob Bowman wrote:

(Sorry if this is a duplicate post.)
Doesn't the energy required to hold the carbide teeth to the blade vary as the velocity squared? Ie, k.e. = 1/2mv^2 ? If so, (4.4)^2 is nearly 20% more energy. (I have no idea if this is an applicable calculation.)
-- Mark
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• posted on October 2, 2003, 8:25 pm
Mark Jerde wrote:

That should be 1.044^2 = 1.09 or a 9% increase in centrifugal force and k.e. at the tip.
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• posted on October 2, 2003, 10:50 pm
On Thu, 02 Oct 2003 20:10:52 GMT, "Mark Jerde"

You're right about there being a square law involved, but wrong to use an energy calculation. What you are alluding to is the FORCE required to break apart the brazing of the carbide tips. Force is proportional to w^2r where w (omega) is the angular velocity (commonly known as rpm) and r is the blade's radius. So, as Rico pointed out, increasing w by 4.4% increases the centrifugal force by 1.044^2, i.e. 9.1%, so we are still not in doomsday territory here. It's a personal choice: I wouldn't worry about it but if you are at all nervous then don't do it.
Rob Bowman Amateur woodworker, professional sawdust maker.
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• posted on October 2, 2003, 11:40 pm
Rob Bowman wrote:

Well, what if you rammed a hunk of steel into the blade? :):):)
Dick
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• posted on October 2, 2003, 11:47 pm
Did someone mention Sawstop (TM)? Whatever happened to them...
-Jack

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• posted on October 2, 2003, 7:30 pm
Feed the wood faster. The tablesaw will bog down to less than 4500RPM. Seriously, this shouldn't be a problem. However, when you first fit the blades and turn on the saw make sure you duck.
-Jack

1.5
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• posted on October 2, 2003, 8:26 pm
JackD wrote:

;-) I hope the scar on my left hand from a 100% preventable kickback accident a couple months back is permanent. It serves as a good safety reminder. Overreving a heavy dado set of known-to-be-not-Forrest-quality seems unsafe... Like somthing you'd read in the first paragraph of a safety article in a woodworking magazine. <g> "Though he knew the dado set was spinning faster than designed, Mark started the saw anyway. When the oak board he was grooving touched the blade, ... "
-- Mark
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• posted on October 2, 2003, 8:31 pm

Better:
"Though he knew the dado set would be spinning faster than designed, Mark finished his 3rd beer & started the saw anyway. When the oak board he was grooving touched the blade ... "
-- Mark ;-)
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• posted on October 3, 2003, 5:44 am
Mark Jerde wrote:

Appears you're answering your own question. Seem's like you know that HF is less than Forrest quality and you know how fast your saw spins and you ask if you should ..... Knock yourself out
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• posted on October 3, 2003, 5:54 pm
Henry St.Pierre wrote:

My question is whether or not anyone runs a dual-speed table saw to run blades such as these safely. I don't see any reason why it couldn't be done, but I don't know very much about the engineering aspects -- as evidenced by my misapplication of kenetic energy & binding of carbide to blade.
On a single-belt contractor saw like mine, it would be trivial to build in a multi-pulley setup similar to my drill press. I'm wondering if someone in the group knows that this a Bad Idea (TM).
-- Mark
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• posted on October 3, 2003, 2:39 am
This appears to have been said in jest but there is a good basis for it. When starting anything, it is a good idea not to stand in line with it until it has come up to speed.
However, when you first fit the

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• posted on October 3, 2003, 4:27 pm
You are right, this part was half serious. Stand to the side when machines start up.
-Jack

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• posted on October 3, 2003, 7:49 am

1.5
Risk analysis says that you are exceeding the design spec by 9%. Consequences of failure are a lump of sharp metal coming off the blade. Possibly limit the risk with effective guarding. Further risk of the shrapnel bouncing back into the blade and causing a grenade effect. Work out the tip speed to really worry yourself. You won't see it coming. Your risk.
John
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