BS Motor stuff

[art3427]

My Ridgid 14" BS started squealing like it had a bad bearing. I stopped a project and tore it down to replace them. What I found was the bearings were OK but when the saw was factory assembled the key was left out of the large pulley on the lower wheel. As long as I was doing straight cuts it did alright. When I started a radius, that's when it squealed like a stuck pig. The pulley was galled pretty fierce so I ordered a replacement.

I decided since the saw was down I'd go ahead and change out the motor like I've been wanting for sometime. I am replacing a 1/2 horse, 1725 rpm motor with a 2 horse, 3450 rpm motor. Of course none of the mounting holes line up and a couple of other irritations, but I can handle it. Right now I'm wondering about doubling the rpm on the motor. It came with a 2.5" motor pulley and a 6.0" saw pulley for a 1725 rpm motor. What I need to know is will it be OK to run the blade at double the rpm, or should I slow it down some by changing out pulleys? What would you guys recommend?

art

[TDHofstetter]

Boy, that's running pretty fast for a bandsaw... it'd be better to bring it back down. Otherwise the wheels'll be turning twice as fast, and you'll see twice as much likelihood of tossing a tire.

As I think about it, I get a gnawing sense of uneasy, too, about using that big a motor. What might now stall the blade is much more likely to break one...

[fredbelknap]

Sounds like Tim Allens lawn mower.

[sawduster]

I'm thinking I would not go bigger than a 1hp motor on that, and try to find one that matches the RPM of the original. One HP is plenty on a 14" BS.

[brburns]

I'd replace the BS. (I hate my Ridgid BS)

[Joe Lyddon]

Yep, I think that's too fast... I'd slow it down...

[art3427]

OK, the consensus is to slow it down. As I said, the original setup was a 1725 rpm motor with a 2.5"motor pulley and a 6" saw pulley. Now that I have a 3450 rpm motor what size pulleys do I need to approximate the original blade speed?

For the record, I got this motor out of my fathers shop after he passed away. It cost me nothing. I was more interested in the hp than the rpm. My problem was this saw was just plain lousy at resawing. No matter how slow I fed it, it would inevitably stall on me. I figured it was a hp problem. Now that I found & fixed the lower saw pulley situation I realize that could have been the problem all along. But, I've already unwired and removed the 1/2 hp motor and installed the 2 hp one. I'm in no mood to do the reversal. I think I'm gonna go ahead with the 2 hp motor and see how it performs. If it speeds up resawing I will keep it. But I would feel more comfortable with a slower blade speed.

art

[Joe Lyddon]

Tim will nail it down...

My guess would be change the 2.5" to 1.25"
... or change the 6" to 12".

[Beamer]

joe's got you on the right track ... what you want is a 1.25:6 pulley ratio (or 2.5:12 or 5:24) - so ... any combination of sizes that gets you there is good. I would probably avoid going any smaller than your 2.5.

Do note - that's a 4x reduction in speed, and a 4x INCREASE in horsepower, too. At the blade, you're liable to end up with TONS more HP than you need and like Tim said, that's power enough to snap, maybe shatter, blades. I'd be concerned about the other items in the chain - pulleys, wheels, tires, blades, etc. Those things were engineered to BARELY tolerate the motor they were given at birth ... much less 4x the motor, at 4x the gear ratio ... you're talkin a fair amount of power there.

I sure hope nothin' gets jammed, for the sake of your saw and your safety

[TDHofstetter]

If you run this motor, I'd like to see you do one of two things: Either put a 2" pulley on the motor & a 10" pulley on the wheel, or...

...keep the same pulleys, but stick a jackshaft between the motor & the wheel and give that jackshaft exactly a 2:1 ratio with 2"/4" pulleys, or 3"/6" pulleys. It doesn't matter a whole lot which pulleys go where, as long as the smaller pulleys drive the larger ones. The final ratio will still work out the same.

Mmmm... will the power switch handle four times as much current? You'll need to change the power cord, too, unless it's pretty heavy.

[imahic]

I can't remember the formula for this but I think Tim is right about the 2:1 ratio. When I was wanting to slow down my sharpening station that I built, I went from 2 in on the motor to 4 in on the shaft and that was supposed to cut the rpm to half according to the formula I used IIRC. I then cut the rpm more by putting a smaller (1.25 IIRC) on the motor. I think that brought the rpm down to approx. 900 rpm. It has been awhile since I did it so I am going on memory and that is dangerous sometimes....lol.

I also agree with him on the wiring for the motor. I would check the amperage on the motor plate to see if your current wiring will handle that amperage. This includes your wiring all the way to your breaker.

Jason and Tim also bring up some very good points on the safety side as well. Would this not dramatically increase the amount of power on all the components of the drive and blade?? I don't know because I am not an engineer by ANY stretch of the imagination. It sure does seem dangerous IMO. You might want to check with Ridgid Technical support. As Jason points out, that is a dramatic increase in HP to what the saw is designed for and would thus increase the potential for something coming apart I would think.

[beagles]

I do not own a BS, so take these comments for what they are worth... They also assume the motor speed is brought back down to 1750 rpm.

Grizzly will gladly sell you a BS with a 2 HP motor. So I'd expect the blades you could put on those guys would also be suitable for your souped up BS.

The torques and forces on the balance of the parts tends to arise during any sudden change in blade speed (start-up and any time you stall it ). That loads the bearings & bearing supports. I'd expect you would have fewer stalls... but more "aggressive" accelerations each time you hit "Start".

[TDHofstetter]

Those torques also come into play when you load the saw harder than you could with the half-horse motor... as for resawing wet hardwoods, for example. A person will tend to push ahead with the work if they're not stalling the saw (which would be nearly impossible with a 2HP motor unless a belt is left loose), which may stress everything far more than it could have been stressed with only a half-horse motor on it.

[deathwish]

I know this thread is a couple weeks old, but I thought I'd add a link to an RPM calculator. It would help out anyone in the same boat!

www.culvermotor.com/Engineering-Formulas/Pulley-and-RPM-Calculator.html

According to that calculator, you were at 718.75 RPM on the saw, and went to 1437.5.

Switching variables, you would indeed need a 12" machine pulley or a 2" on the motor and about a 9-1/2" on the saw.

As mentioned going much smaller than a 2" pulley is not a great idea, though if you can find one, a 1-1/4 inch would give the proper ratio. Fitting anything bigger than stock under the factory pulley shroud should be measured out carefully as well.

Oh, and you'll need a belt too . . .

www.calculatoredge.com/mech/vbelt%20length.htm