Is there a Unisaw in my future?

[Ross Becker]

Mike- you're describing the characteristics of a repulsion start, induction run motor. The Delta rockwell motors were Repulsion-induction motors- which are different than you're describing. The source Phil linked above describes the difference between those. Also, while 1HP is 1HP, there are different ways to measure HP, some more conservative and some less conservative. Do you really think that manufactures haven't altered how they measured motor HP in order to make it look better on paper since the 40s?

[Mike Henderson]

Mike- you're describing the characteristics of a repulsion start, induction run motor. The Delta rockwell motors were Repulsion-induction motors- which are different than you're describing. The source Phil linked above describes the difference between those. Also, while 1HP is 1HP, there are different ways to measure HP, some more conservative and some less conservative. Do you really think that manufactures haven't altered how they measured motor HP in order to make it look better on paper since the 40s?

Well, the definition of a HP has not changed and the engineers of the '50's were well able to measure (and calculate) HP. We're not talking about a motor made in the 1800s.
But beyond that, you can look at the power input to a motor and and see if the rating is reasonable. Those old motors were less efficient than the induction motors we have today so take the voltage and current into the motor, multiply it together, multiply it by about .8 to .85 for efficiency and then divide by 748 watts per HP.

None of this stuff has changed. I really don't think those old motor were underrated. A HP is still a HP.

And it doesn't matter what you call it, there's no free lunch with any kind of repulsion-induction motor. If the motor starts to stall in the induction part of the envelope the repulsion portion is not magic. To restore the required HP requires power in the form of current and that current will overheat the motor. If those RI motors were so great we'd still be using them. But we aren't so that should tell you something.

Mike

[Those old motors may be even less efficient than .8 to .85. Smaller HP motors are less efficient than larger motors so the efficiency on those old motors could be .7 or so.]

[Phil Thien]

There's no free lunch. A 1 HP motor is not going to produce 2 HP, and HP is the measure of work, not torque. Pushing a motor beyond it's rating (which is actually what Service Factor is) will reduce the life of the motor.

Just pointing out an important difference. RI motors are capable of delivering significant HP at lower RPM, as compared to cap start/cap run motors.

I'm not saying they will do it forever or that it is wise to bog any motor down.

The RI motors are typically substantially overbuilt and a local lumber yard pushed their 1-1/2-HP Unisaw very hard for decades and it still worked great (on the original motor) until the day they closed shop.

Their saw may have even been a 1-HP. I can't remember, I just remember it was the same HP as my contractor saw motor but substantially outperformed my saw.

[Art Mann]

I used a right tilt Uni for 10 years, and never once wished it was left tilt. The same can probably be said for a few hundred thousand woodworkers, over the years.

Well, I have used both left and right tilt saws too. After using a left tilt for a while, I lost interest in owning a right tilt saw. My experience is it is more trouble to use and use safely than a left tilt, especially when cutting bevels. I know of some other people who feel just like I do. Grizzly Tools is one company that holds that opinion. They have dropped right tilt from their lineup. I just wanted to point this out to the original poster, because he might not realize there is a difference. His opinion is the one that matters.

[Phil Thien]

If those RI motors were so great we'd still be using them. But we aren't so that should tell you something.

Mike

Modern cap start/run induction motors are substantially less expensive to produce on a per-HP basis. So the clear solution was to outfit cabinet saws with 3-HP and 5-HP induction motors. Less expensive, and any advantage of the RI is essentially moot.

[Phil Thien]

Well, I have used both left and right tilt saws too. After using a left tilt for a while, I lost interest in owning a right tilt saw. My experience is it is more trouble to use and use safely than a left tilt, especially when cutting bevels. I know of some other people who feel just like I do. Grizzly Tools is one company that holds that opinion. They have dropped right tilt from their lineup. I just wanted to point this out to the original poster, because he might not realize there is a difference. His opinion is the one that matters.

I've used both LT and RT and my current saw is RT and I find that I prefer the RT because while using a sled to cut a bevel, I get to stand to the left of the blade and find that works a little better for me.

[Mike Henderson]

Modern cap start/run induction motors are substantially less expensive to produce on a per-HP basis. So the clear solution was to outfit cabinet saws with 3-HP and 5-HP induction motors. Less expensive, and any advantage of the RI is essentially moot.

Absolutely. The only advantage of an RI motor is that it has greater staring torque than a capacitor start motor. And since our woodworking tools start essentially unloaded, the RI motor is useless in woodworking applications.

Mike

[Mike Henderson]

Just pointing out an important difference. RI motors are capable of delivering significant HP at lower RPM, as compared to cap start/cap run motors.

I'm not saying they will do it forever or that it is wise to bog any motor down.

The RI motors are typically substantially overbuilt and a local lumber yard pushed their 1-1/2-HP Unisaw very hard for decades and it still worked great (on the original motor) until the day they closed shop.

Their saw may have even been a 1-HP. I can't remember, I just remember it was the same HP as my contractor saw motor but substantially outperformed my saw.

A motor in a woodworking tool should not be bogged down to the point where it is running at .75 of the rated RPM. And even if you did that, you have not explained where the power comes from the maintain the rated HP at that RPM. Those old motors were pretty inefficient which means they were physically bigger than motors of today so they may tolerate short periods of excess current better than the more efficient, and smaller modern motors. But that has nothing to do with RI.

Mike

[Mike Henderson]

Mike -

you continue to amaze me, on any number of topics..on this one, I gotta ask: where from you get all this Gandalf-level knowledge?

I am an old man and I've lived an interesting life.

Mike

[Mike Henderson]

Just an added comment on motors. Ever notice that a 1725 RPM motor is bigger than a 3450 RPM motor for the same HP? The reason is that the 1725 RPM motor must produce twice the torque to produce the same HP as the 3450 RPM motor. And to produce that greater torque, everything has to be bigger.

If you could get a universal motor with a real HP rating, that motor would be smaller than the 3450 RPM motor for the same HP. The reason? Because the universal motor runs at 10,000 RPM to 12,000 RPM so it can produce less torque to generate the same HP.

Mike

[Phil Thien]

A motor in a woodworking tool should not be bogged down to the point where it is running at .75 of the rated RPM. And even if you did that, you have not explained where the power comes from the maintain the rated HP at that RPM. Those old motors were pretty inefficient which means they were physically bigger than motors of today so they may tolerate short periods of excess current better than the more efficient, and smaller modern motors. But that has nothing to do with RI.

Mike

When the RI motor slows significantly, the motor's starting mechanism is engaged and that starting torque comes back. It isn't unlimited but isn't insignificant, either.

I've stalled modern induction motors like the one on my 1.5-HP contractor saw. It seems that once the motor drops in RPM, you stand a pretty good chance of stalling it altogether. That is, it is often difficult to moderate your feed rate quickly enough to prevent stalling the motor altogether.

That doesn't happen so much on RI motors. You obviously can't feed stock like it is a 5-HP motor, but at the same time it is much easier to push the motor to its limits without risking seeing the blade come to a full stop. You have enough time to react to a drop in RPM's.

I've cut LVL's on a contractor's saw as well as a Unisaw equipped with a bullet motor with the same HP rating. The motors act quite a bit differently at the margins.

[Harold Weaver]

I got to go with Dave Cav on this one. The Unisaw will be a far superior machine than your contractor saw. The proof is inside the cabinet. The 1 horse RI motor will do anything you need to do, if you find that it does not, then you need a 12/14 saw and not a Unisaw. Just my 2 cents worth.

[Mike Henderson]

When the RI motor slows significantly, the motor's starting mechanism is engaged and that starting torque comes back. It isn't unlimited but isn't insignificant, either.

I've stalled modern induction motors like the one on my 1.5-HP contractor saw. It seems that once the motor drops in RPM, you stand a pretty good chance of stalling it altogether. That is, it is often difficult to moderate your feed rate quickly enough to prevent stalling the motor altogether.

That doesn't happen so much on RI motors. You obviously can't feed stock like it is a 5-HP motor, but at the same time it is much easier to push the motor to its limits without risking seeing the blade come to a full stop. You have enough time to react to a drop in RPM's.

I've cut LVL's on a contractor's saw as well as a Unisaw equipped with a bullet motor with the same HP rating. The motors act quite a bit differently at the margins.

If you're going to make such claims, please tell me where the power comes from to generate that increased torque. Saying that the repulsion mechanism kicks in is not sufficient. That mechanism cannot produce power without increased current and that increased current will generate heat, which will affect the life of the motor. This stuff is basic electricity.

If the repulsion mechanism was some magic torque enhancer, the engineers would have designed the motor with it always engaged.

A 1 HP motor is still a just a 1 HP motor. A RI motor is no better than a regular induction motor when the motor is operated in its normal operating RPM range. And when you operate it such that the repulsion mechanism kicks in, you're in an area where the motor is drawing excess current.

Perhaps what we're seeing is that those old RI motors are very low HP motors and people actually do bog them down because the machine is so under-powered - and the motor can take it because it's so physically large that it takes a lot to get it hot. But that hardly makes RI motors a good choice for a table saw. It would be much better to have a motor that can do the work without bogging down in the first place. I think those old motors were small HP so that they could be run on 110 volts. And because motors were pretty inefficient - and physically large - they might not have been able to fit bigger HP motors into the units. Bigger motors may have also been very expensive back then.

Mike

[Gary R Katz]

The least I can say about this thread is that I learned a lot! I owned a bakery for 37 years and changed out a lot of single and 3 phase motors but I never had to delve into the details of which motor was best or adapting a motor to a different use.
I'm going to pass on this saw for now. I'm used to a left tilt and I'm an old dog who doesn't want to learn a new trick. The motor has no more power than my contractors saw and I'm not that interested in chasing after another motor or messing with the 3 phase motor and an adapter. I just want to saw wood!
I know I've got a slight alignment issue with my belt. I've got the pulley extended out almost to the end of the shaft and I've never looked beyond that easy fix. As I said, I just want to saw wood. I had 37 years of maintaining and fixing with old bakery equipment and that's enough!
Thanks for you help with this. I'll be much better informed when the next saw comes around.

[Phil Thien]

If you're going to make such claims, please tell me where the power comes from to generate that increased torque. Saying that the repulsion mechanism kicks in is not sufficient. That mechanism cannot produce power without increased current and that increased current will generate heat, which will affect the life of the motor. This stuff is basic electricity.

I have stated a bunch of times that the increased torque is coming from the starting circuit. I agree that it causes increased current and heat.

I hope you will agree that about the worst thing you can do to a motor is lock the rotor. I'd rather kick that starter in and have it give me a chance to back-off the feed to prevent locking the rotor.

If the repulsion mechanism was some magic torque enhancer, the engineers would have designed the motor with it always engaged.

I didn't call it a magic torque enhancer, but if it helps me prevent locking the rotor...

A 1 HP motor is still a just a 1 HP motor. A RI motor is no better than a regular induction motor when the motor is operated in its normal operating RPM range. And when you operate it such that the repulsion mechanism kicks in, you're in an area where the motor is drawing excess current.

I agree.

Perhaps what we're seeing is that those old RI motors are very low HP motors and people actually do bog them down because of that - and the motor can take it because it's so physically large that it takes a lot to get it hot. But that hardly makes RI motors a good choice for a table saw. It would be much better to have a motor that can do the work without bogging down in the first place.

Mike

I don't disagree with that at all. At the same time, it is what it is. Old Unisaws came with RI "bullet" motors. They work pretty well, certainly better than any modern 1.5-HP induction motor I've tried. While I'm not going to say a 1.5-HP bullet is the same as a 2+ HP modern induction, I also would go so far as to say it is the same as a 1.5-HP modern induction, either. The extra moving mass, the extra torque before a stall, the heavier construction all kind of help make them an okay compromise, IMHO.