Getting the most from my 3/4 hp motor

[dicksterp]

Using the numbers that jpg used (3000 rpm) his calculations are correct up to and including ft/sec. At that point things go south. The std conversion of ft/sec to mph is 88 ft/sec = 60 mph. Using jpg's numbers you get 89.3 and 80.5 mph. This is for 3000 rpm. Ed's numbers are correct for 3400 rpm

[2manband]

As foxtrapper pointed out, there ARE two things to consider. [Exponential???]

1)The circumferential speed(Teeth/time if you will).

2)The distance from the center(Lever arm if you will).

Slowing down the rpm's WILL compensate for #1, but will not compensate for #2. The Power gain by adjusting speed will be far short of the 50% larger 1 1/8 HP motor.

Yes you can get the job done if you also slow down the feed. It just takes longer.

#1 - I think we're in agreement here.

#2 - because of the design of the Shopsmith's speed changer mechanisim, as I understand it, the full motor HP (be it 3/4 or 1 and 1/8) is available at any speed. Because HP = Torque (ft lb) * RPM / 5280 - if the HP is constant, and we reduce the RPM's, the torque must increase by a commensurate amount. Others have run some calcs showing that a tooth speed averages about 100 mph on a 10" blade, and about 90 mph on a 9" blade. By slowing the 10" blade down 10% to achieve the 90mph tooth speed, we'd get about 10% more torque. By switching from a 10" to a 9" blade (10% smaller diameter), while maintaining the same RPM, we'd also get about 10% more torque and 10% less tip speed.

Think of a car climbing a hill - you could stop and mount smaller wheels, but downshifting is a lot easier.

A lot of times a smaller blade will give better results on a less powerful saw - but I'm of the opinion that on the shopsmith, because of the unique design of the speed changer mechanism, one could achieve the same results just by slowing it down. The feed rate would also have to slow down, of course - just as the car would slow down in the hill climbing analogy.

The only caveat I can think of is that there would be more drag and frictional loss in the bearings etc. when operating at higher RPM, so there would be slightly less power available, but I'm thinking that would be pretty negligible.

[2manband]

Good Question, 2 man!! Very astute! BTW where are you living now days?

Not far from Lancaster PA, as a matter of fact.

[dusty]

Not far from Lancaster PA, as a matter of fact.

Maybe you'd consider putting some of that data in your personal profile.

Welcome to the forum.

[2manband]

Maybe you'd consider putting some of that data in your personal profile.

Welcome to the forum.

What, you guys don't want an international man of mystery?

[ralphtaff]

OK guys heres an other way toook at it .I had a chev pickup 4 speed had 650x16 inch tires it had a low torge rear end. it spun out on snow and ice on the parking lot. haf tread trouble and could not aford new tires. change to old tires on a fored that was not being used. the tires were 700x16 tires. no more spinning out in the parking lot evengoing off road i never got stuck and had to put chains on any more. i know some one is going to say different tread design. guess what next year dad got his 650 i got the 700 put on and the tires were the same brand and same tread design. its like using a bigger hammer all day a smaller hammer you are not as tired at the end of the day.just had to say that. course when you use sharp blades it does make a big difference also.

[JPG]

Let us not forget the source of this discussion. Alec commenting on the apparent problem with his 50 yr old 3/4HP goldie. Add to that the fact that SS has been selling Mark V as a 10" saw the last 35? yr. The Goldie was sold as a 9" saw even after they increased the motor to 1 1/8 HP. Newer blade designs(thin kerf etc.) have made a decrease in the power needed.
We got into this 9"/10" discussion to try to understand the difference in performance relative to a 9" blade/3/4HP motor vs a 10" blade/1 1/8HP motor.

Aside from my 190+ MPH screw-up, I think we have ascertained that reducing the rpm's on a 10" blade by 10% WILL produce an equivalent 'tooth speed' of a 9" blade. This 10% speed reduction will result in an available power increase of also about 10%. This 10% increase in power will be reduced back to the original since the saw diameter has increased to 10% over a 9" blade.

Therefore, the power from a 1 1/8HP motor IS 50% greater than a 3/4HP motor when driving EITHER size blade at an equivalent 'tooth speed'.

You can 'increase the torque available' by increasing the speed reducer ratio, but the increased torque required to cut with a 10" blade vs a 9" blade is also increased by the same percentage.

BTW the SS 'speed reducer' adjustment range includes the ability to 'increase speed'. Its range is about .2 to 1.5. At 'SAW' speeds (O to S) it is .8 to 1.1.

[2manband]

Fair enough JPG - maybe I've been getting a bit off the original topic, and into the realm of the theoretical. If the SS in question is designed for a 9" blade, I certainly don't recommend that anything larger be used.

[JPG]

Fair enough JPG - maybe I've been getting a bit off the original topic, and into the realm of the theoretical. If the SS in question is designed for a 9" blade, I certainly don't recommend that anything larger be used.

We all got a little 'off track'. We kept throwing in the two motor sizes when comparing the two blade sizes. The two motor sizes WERE relevant, but clouded the discussion about power/torque.speed etc.

We should have known the conclusion initially(you can't get anything for nothing). Conservation of energy! The point I kept trying to make was that reducing speed etc. will NOT make up for the smaller motor. It helps and slower feed rate can get you there. Ripping is when all this REALLY matters.