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post #1 of 7 (permalink) Old 12-04-2011, 07:33 PM Thread Starter
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Default tablesaw blade speed

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This is my first post so bear with me. I realize that this is not about the router but it is about woodworking. I recently upgraded my Delta tablesaw. I went to a 2hp 220ah motor. My drive pully ( the one on the motor) is 4" and the one on the blade shaft is 2.5" the rpm is 3640, and as the best I can tell the surface ft per minute is 9524.6 I am used to a 1hp and the new motor turns a lot faster as can be expected. My question is how fast is to fast?. Do you guys think that the above numbers are safe. tks in advance
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post #2 of 7 (permalink) Old 12-04-2011, 08:22 PM
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Originally Posted by tmarvin View Post
Hi
This is my first post so bear with me. I realize that this is not about the router but it is about woodworking. I recently upgraded my Delta tablesaw. I went to a 2hp 220ah motor. My drive pully ( the one on the motor) is 4" and the one on the blade shaft is 2.5" the rpm is 3640, and as the best I can tell the surface ft per minute is 9524.6 I am used to a 1hp and the new motor turns a lot faster as can be expected. My question is how fast is to fast?. Do you guys think that the above numbers are safe. tks in advance
My calculation (4/2.5) * 3640 = 5824 RPM, no way of knowing the SFM from what you posted unless I knew it was a 8", 10" or 12" blade.

Next question what was the RPM of your 1HP motor? Are you using same pullies on the new set up or have you changed them? A quick look at blades in the 10" range came up with max speed 6000 RPM but I would look at the blade you are using just to be sure.

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post #3 of 7 (permalink) Old 12-04-2011, 10:59 PM
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Quote:
Originally Posted by tmarvin View Post
Hi
This is my first post so bear with me. I realize that this is not about the router but it is about woodworking. I recently upgraded my Delta tablesaw. I went to a 2hp 220ah motor. My drive pully ( the one on the motor) is 4" and the one on the blade shaft is 2.5" the rpm is 3640, and as the best I can tell the surface ft per minute is 9524.6 I am used to a 1hp and the new motor turns a lot faster as can be expected. My question is how fast is to fast?. Do you guys think that the above numbers are safe. tks in advance
The horse power of a motor has nothing to do with it's speed, this is determined by the number of poles and the mains frequency. Your new motor being run presumably on 60hz mains must have two poles.

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post #4 of 7 (permalink) Old 12-07-2011, 10:42 PM
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The RPM of the motor should be stamped on the motor tag. If this is a cabinet saw the motor probably turns around 3650 RPM, that said the blade arbor turns proportionally to the motor RPM. A 4" drive pulley and a 2.5" idler pulley would be 4"divided by 2.5" [ you end up with a ratio (motor 1 turn/ 4 divided by 2.5) ] multiplied by the RPM of the drive motor. Which according to my math the arbor of your saw turns 3650 divided by 1.6 equals 2281. The speed of your blade depends on the diameter of the blade.
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post #5 of 7 (permalink) Old 12-07-2011, 11:08 PM
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keven 4" on motor an 2.5 on saw arbor from the first post = 5824 RPM
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post #6 of 7 (permalink) Old 12-07-2011, 11:15 PM
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Originally Posted by tmarvin View Post
Hi
This is my first post so bear with me. I realize that this is not about the router but it is about woodworking. I recently upgraded my Delta tablesaw. I went to a 2hp 220ah motor. My drive pully ( the one on the motor) is 4" and the one on the blade shaft is 2.5" the rpm is 3640, and as the best I can tell the surface ft per minute is 9524.6 I am used to a 1hp and the new motor turns a lot faster as can be expected. My question is how fast is to fast?. Do you guys think that the above numbers are safe. tks in advance
Hi - Welcome to the forum
With a 4" drive pulley and 2.5" driven pulley you have a 1.6:1 step up in speed, which, with a motor speed of 3640 gives a blade speed of 5824 rpm. Not sure what you mean by "surface ft per min" nor how you arrived at it. Most mfg will give a max rpm and, while 5800 does sound a little fast for a table saw, I think most mfg have a rating of 6000 rpm on their blades. Being that close though, I would certainly verify that.
Kristin did ask a very pertinent question though, what was the rpm of the old motor?
Could be you want to change the driven pulley to a 3" which would bring you down to about 4800 rpm which is much closer to what I've seen most table saws run.

Edit - just had an afterthought. Is it possible when you changed the motor you could have gotten the pulleys reversed, ie. the driven pulley actually installed on the drive side. Switching the pulleys would bring you down to 2275 rpm. That sounds a bit slow to me but I haven't had much exposure to the higher powered saws except they do seem to run slower.

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post #7 of 7 (permalink) Old 12-08-2011, 07:07 PM
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Quote:
Originally Posted by tmarvin View Post
Hi
This is my first post so bear with me. I realize that this is not about the router but it is about woodworking. I recently upgraded my Delta tablesaw. I went to a 2hp 220ah motor. My drive pully ( the one on the motor) is 4" and the one on the blade shaft is 2.5" the rpm is 3640, and as the best I can tell the surface ft per minute is 9524.6 I am used to a 1hp and the new motor turns a lot faster as can be expected. My question is how fast is to fast?. Do you guys think that the above numbers are safe. tks in advance

As was already pointed out, you don not need to calculate SFM for your blade since all saw blades give max speed in RPM. That said, I'm guessing you bought the wrong motor. If the new 2HP motor is about the same size (or a little bigger) than the 1 HP, then you probably replaced a 1HP, 4 pole motor with a 2HP, 2 pole motor; doubling the motor speed in the process.

I'm don't know where the 3640 RPM figure is from. A 2 pole motor has a maximum sychronous speed of 3600 rpm on 60Hz power. True max speed is probably closer to 3450 rpm (5% slip). Anyway, using the 3600 number with your pulleys, this comes out to 5760 rpm (actual max will be closer to 5530 rpm), so, for a 6000 rpm max speed saw blade, this should be okay.

On the other hand, you've doubled the speed of your blade. I don't know how this will affect cutting wood but it will. I've read that you should not do this (TABLESAW TUNE). Also, you've doubled the HP but also the speed, so the torque at the blade will be about the same as with the 1 HP motor, so it may not perform that well anyway.

Solution: Buy a 2.0" diameter pulley for the motor (you probably have a 5/8" motor shaft). This will cut the blade speed in half. You'll need a different size v-belt too. You can try one of those adjustable link belts, or if you know (or can measure) the center distance between the shafts, you might be able to calculate the size of the belt you need.

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Robert
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Last edited by RJM60; 12-08-2011 at 07:09 PM.
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