Shopsmith Forums

I thought forum members may be interested in hearing about an experience I had today where my Shopsmith in table saw mode put my Craftsman contractor saw to shame.

I am building some clamping cauls. I decided to rip the calls out of a kiln dried 2x6. Cross cut to length of 60". After jointing a face and edge flat, I took the 2x6 to my Craftsman table saw. This saw is a 1.5 HP contractor saw. It has a Forrest WW2 blade and an aftermarket rip fence by Vega. I am pretty religious about keeping this saw properly set up. I used saw PALS to ensure the blade and fence are perfectly parallel to the miter slots and I have always gotten very accurate results with this set up and I have never had problems with it. About 6 inches into the cut, I got a lot of binding. Could feel the saw stall. Shut of the saw and took a look. Fence was parallel. splitter was set up properly. Belt properly tensioned. Nothing I could see wrong with the saw. Checked the board. Flat, straight. Then I checked the end grain. Wow, practically a circular grain pattern in a 2x6! I think this board had lots of internal tension and it was pinching closed on the blade as soon as it was cut, not even getting to the splitter. Tried again using a slow feed rate. Same result. Stalled the Craftsman.

That's when I remembered reading on the forum about using the Shopsmith table saw at slower speeds to get more torque. Figured it was worth a try. Set up the Shopsmith in table saw mode, set the speed only at about F and ran the 2x6 through with the standard combo blade. The Shopsmith handled the job like a champ! Yes, I did have to use a slow feed rate, but this Shopsmith did not complain and just powered through this difficult cut. I have had my Shopsmith since January (used 520) and I am really becoming a believer in this tool

I often mention this feature to others who malign the Shopsmith as a "weak saw". When I purchased my 500 back in '83 the book "Power Tool Woodworking for Everyone" was part of the package. In this edition DeChristoforo brought forth the information that torque was increased as the speed is decreased. I've taken advantage of this fact of physics many times thru the years. This is a feature that truly separates the Shopsmith from other constant speed table saws that are designed to run on standard household 15 amp circuits.

The feed rate must be decreased proportionally because there is no increase in HP. Thus the only "handicap" is taking 30 seconds to make the cut instead of fifteen, which is hardly any disadvantage for those of us who are not engaged in production work.

Then the comeback is "Yes, but you have to tilt the table to cut bevels". Yada...yada...yada.....

8iowa wrote:I often mention this feature to others who malign the Shopsmith as a "weak saw". When I purchased my 500 back in '83 the book "Power Tool Woodworking for Everyone" was part of the package. In this edition DeChristoforo brought forth the information that torque was increased as the speed is decreased. I've taken advantage of this fact of physics many times thru the years. This is a feature that truly separates the Shopsmith from other constant speed table saws that are designed to run on standard household 15 amp circuits.

The feed rate must be decreased proportionally because there is no increase in HP. Thus the only "handicap" is taking 30 seconds to make the cut instead of fifteen, which is hardly any disadvantage for those of us who are not engaged in production work.

Then the comeback is "Yes, but you have to tilt the table to cut bevels". Yada...yada...yada.....

It may have been in one of your posts that I first read the tip about slowing the RPMs to get more torque.

I wonder what the max torque is of the Shopsmith Mark V and how it compares to other stand alone table saws with fixed speed motors of various hps. Would make a very interesting experiment, me thinks.

algale wrote:It may have been in one of your posts that I first read the tip about slowing the RPMs to get more torque.

I wonder what the max torque is of the Shopsmith Mark V and how it compares to other stand alone table saws with fixed speed motors of various hps. Would make a very interesting experiment, me thinks.

You can calculate HP required by first measuring voltage at the motor terminals and current draw. I don't know how to measure horse power on a machine like the Mark V. It is not very compatible to a dynamometer.

algale wrote:I wonder what the max torque is of the Shopsmith Mark V and how it compares to other stand alone table saws with fixed speed motors of various hps. Would make a very interesting experiment, me thinks.

Torque (ft.lbs.) = (HP x 5252)/RPM

So, a standard Mark V has a 1.125 HP motor at 700 RPM = 8.44 ft.lbs.

The PowerPro is 1.75 HP at 250 RPM = 36.76 ft.lbs

1 hp = 550 ft pounds/second.

1 1/8 hp = 620 ft pounds/second

At 3600 rpm the distance a 10" blade travels(circumference) in one second is 1885 in = 157 ft.

620 ft pound /157 ft = 3.95 pound.

At a 5 " radius, the torque is 5/12 x 3.95 = 1.65 ft pounds torque

As an example of increasing torque by speed reduction with constant horse power input, consider reducing the speed to 1800 rpm(half as fast)

At 1800 rpm the distance a 10" blade travels in one second is ft

620 ft pound / 78.5 = 7.9 pound

At a 5" radius, the torque is 5/12 x 7.9 = 3.3 ft pounds torque


So it is quite linear, so decreasing the speed from "S"(3800 rpm) to "N"(2600 rpm) increases the torque available by a factor of 38/26 = almost a 50% increase or the same as a 1.7 hp motor.

Not as dramatic as we probably hoped, but quite useful!


I believe there is a 60:1 error due to miscounting rev/second. Correction DONE!

michaeltoc wrote:Torque (ft.lbs.) = (HP x 5252)/RPM

So, a standard Mark V has a 1.125 HP motor at 700 RPM = 8.44 ft.lbs.

The PowerPro is 1.75 HP at 250 RPM = 36.76 ft.lbs

Cool!

Now, according to the manual my Craftsman contractor saw is rated at 1.5 hp and 3600 rpm (no load), hypothetically giving torque of 2.19 ft.lbs. per your formula.

So now, what about those big honkin cabinet saws with 3 hp motors? I looked up the Unisaw, one version of which is rated at 3hp and 3450 rpm = 4.56 ft.lbs. torque.

So I guess all us Shopsmith owners should go on the other tool forums and mock out all those Unisaw owners with their "inadequate" torque ratings!:D

algale wrote: So now, what about those big honkin cabinet saws with 3 hp motors? I looked up the Unisaw, one version of which is rated at 3hp and 3450 rpm = 4.56 ft.lbs. torque.

Working the numbers, a standard Mark V can get as much torque as the Unisaw by simply cranking it down to 1295 RPM - or "F" on the speed dial.

A PowerPro will provide that torque at 2015 RPM.

Not bad!

A unisaw does not run at those reduced speeds. Granted we get higher torque, but at the cost of the rpm's. If they geared their blades down, their torque would also be higher(and higher than 'ours) We get higher torque, but must feed slower.

The torque is increased, but the horse power remains the same. Our is smaller!:p

At least we do have an option!:)

michaeltoc wrote:Working the numbers, a standard Mark V can get as much torque as the Unisaw by simply cranking it down to 1295 RPM - or "F" on the speed dial.

This is an interesting issue.

As you have ably pointed out there is a simple mathematical correlation between HP and torque and rpms. Presumably you need a combination of all three to spin a 10 inch diameter, 1/8th inch metal blade through a piece of wood of a given thickness and hardness. But is it six of one half a dozen of the other? Or does it matter which combination of hp/rpms and torque you use to cut a given piece of wood using a given blade?

The first and obvious thing that jumps out at me (and which 8iowa mentioned) is the lowering rpms to generate more torque reduces the speed at which you can make the cut. Not a big deal unless you are a production shop (or a hobbiest in a big hurry). I would guess secondarily, rpms/speed will correlate with the amount of heat generated during the cut. Are there other factors that have a real world impact on woodworking?

Or put another way, are there certain operations for which you need a 3HP table saw running at 3450 RPMs that simply can't be accomplished on a 1.125 HP Mark V running at 1295 RPMs?