Old Unisaw Purchase - What will I miss

[Dwain Lambrigger]

I have been active recently shopping for a new table saw. I want a cabinet saw, within my budget of 600 to 800 dollars. I found a 1948 Unisaw. it looks in fair shape, and according to the seller, it runs really well. My question. It has the original motor, but it is only 3/4 or 1 hp. Being single phase, will I miss anything between this, and a more recent two or three horsepowered cab saw? I really like the idea of old iron, but don't want to buy, then refurbish, then find out it is still too weak to do what I need. Besides, I don't know what the market would be like for an old Unisaw refurbished out here in AZ.

Thanks,

[Julian Wong]

Dwain, A uni cabinet saw of that vintage probably 1 hp repulsion induction motor.

Although it is rated only 1hp, but because of its design and being R/I, it puts out the power of probably closer to a 2hp motor of today. It will suffice unless you plan on cutting 10/4 or 8/4 hard maple all day every day with a full kerf blade.

[Robert Conner]

Those are Great Saws. That motor should do every cut you need to do as Julian said. The motor is very searched for because they run so well. The cast Iron and steel in those older models are thicker then the newer ones. Does it have the Goose Egg Motor Cover? If so grab it, someone else will.
Robert

[Ray Newman]

Old Iron is really nice.

I would ask the seller to make a cross out on a piece of wood 'bout 10" or so in width that you bring. Make sure that the edges are true. After making a cross cut, check it w/ a square. If it is off from blade wobble, the arbor bearings could be worn & need replacing.

You can check the bearings by unplugging the saw, removing the blade & placing a 1" diameter dowel about 24 - 36" long on each bearing & then have someone else turn the arbor by moving the belts while holding the dowel to your ear. This poor man's stethoscope will magnify any noise & bad or worn bearings will make a grinding noise.

See below link for info on rebuilding a Unisaw & other ideas as to what to look for --
http://www.sawcenter.com/unisaw.htm

[Sean Kinn]

Just incase you needed another vote...don't get caught up in the power issue. These old motors are very strong despite their rating. I just cut a bunch of 8/4 red oak and hard maple no problem. I do use a thin kerf ripping blade, but that was just because I already had it from my old saw. Fact of the matter is I'd love a 3 or 5hp saw just like the next guy....but unless you are cutting 8/4 or 10/4 stock all day (and in a hurry to do it) you simply don't need a 3 or 5hp saw. Even running several hundred bf of oak in a shot my 60 year old R/I motor never even got more than slightly warm to the touch (note: I do have it wired for 220).

[William Addison]

I used one a lot and I don't think it cut differently than the 3hp I have now. They are fine old saws.

[Mike Henderson]

Dwain, A uni cabinet saw of that vintage probably 1 hp repulsion induction motor.

Although it is rated only 1hp, but because of its design and being R/I, it puts out the power of probably closer to a 2hp motor of today. It will suffice unless you plan on cutting 10/4 or 8/4 hard maple all day every day with a full kerf blade.
I'm afraid that's not true. The repulsion part of an RI motor is only used during start-up. Once the motor is up to speed, the repulsion part is disconnected and the motor operates as a standard induction motor.

You can tell more by looking at the power into the motor at full load (voltage and current). An electric motor is a power conversion device so the power out cannot exceed the power in, and the power out will actually be less because of conversion losses.

Unless that 1HP motor is grossly under-spec'ed or mis-labeled, it will only put out 1HP under full load. If the service factor is greater than one, it will be able to put out more power for a short period of time, while generating excess heat - but you can't get that power continuously.

RI motors have greater start-up torque than capacitor start motors, but for woodworking applications that's not an important factor because most tools start-up without any load.

Mike

[Wilbur Pan]

I always thought that the advantage of repulsion induction motors over was that for a given horsepower they developed more torque under load.

From "Electric Machines (http://books.google.com/books?id=qa47a3XcGLUC&pg=PA786&lpg=PA786&dq=repulsion+induction+motor&source=web&ots=NbDLLm2SWs&sig=1GyQXKcHhToAjp8u_UhSw3NR77U&hl=en#PPA786,M1)":


Repulsion-Induction Motor

The repulsion principle is often used merely to provide a high starting torque at a a relatively low starting current. When the machine has accelerated close to the operating speed, it may be converted to a single-phase induction motor to provide essentially constant speed running characteristics. This is achieved if, in addition to an outer commutator winding, the rotor carries an inner squirrel-cage winding. The torques developed are then additive. Such a motor is called a repulsion-induction motor. At starting, the cage current is limited by its relatively high reactance and the commutator winding develops a major part of the torque, but during running conditions the cage torque increases, compensating for the natural drop in the speed-torque characteristic of the commutator winding.

And from "Electric Motor Repair (http://books.google.com/books?id=PpW71BbD8OYC&pg=RA2-PA84&lpg=RA2-PA84&dq=repulsion+induction+motor&source=web&ots=JD_ZndCwnx&sig=j3bIdkXhhYDMi2y9eH89tW6iz1U&hl=en#PRA2-PA84,M1)":


[Repulsion-induction] motors are also made with compensating coils to increase the power factor of the motor circuit.

If an RI motor can develop torque that would be equivalent to a higher horsepower induction motor, I can see how that might lead one to conclude that a RI motor has "different HP" than a modern day motor. The HP is exactly the same, but different 1 HP motors can generate different amounts of torque.

There's a parallel in looking at cars. HP ratings is what everyone focuses on, but more information on how a car's engine will perform can be gotten from looking at the torque band.

[Jim Andrew]

My experience with old tools is, old horses are bigger than new ones. Jim

[Jim Andrew]

Should also say, if they are in good shape. Sick horses don't pull. Jim

[Mike Henderson]

If an RI motor can develop torque that would be equivalent to a higher horsepower induction motor, I can see how that might lead one to conclude that a RI motor has "different HP" than a modern day motor. The HP is exactly the same, but different 1 HP motors can generate different amounts of torque.
The problem with that theory is that HP is force times velocity. In a motor, it's torque times angular velocity, essentially RPM. That's why universal motors generate such high HP in a small physical size - they rotate at a much higher speed than an induction motor even though they have less torque.

If an RI motor generated more torque than a capacitor start induction motor, at the same RPM, it would have a greater HP rating. So if you start with two motors with the same RPM, say 3450 RPM, they will have the same torque at rated load if they have the same HP rating.

Note that a four pole induction motor, which runs at 1725 RPM (in the US) has to generate twice the torque compared to a 3450 RPM motor to get the same HP rating, and thus is larger physically than a two pole induction motor of the same HP rating.

There's no magic.

Mike

[Also, you can't load an induction motor down to the point where the slip gets really high (and the RPM goes way down). If you did, the current into the motor would exceed the rated value and the motor would overheat fairly quickly. So induction motors run in a fairly narrow RPM band between no-load and full-load. This is different from an engine on a car which has a very wide RPM band.]

[David DeCristoforo]

FWIW, I would buy the '47 uni in a hot second assuming that it is in good working order and is complete (original base, motor cover, switch, etc). If any of the original parts are missing I would try and beat the price down a bit but don't get too carried away because some old iron buff will snap it up, esp if it had the "four legged" base.

[Seth Poorman]

I always thought that older motors ran better because motor windings were made from larger gage wire ,causing less resistance,,,,less resistance (under load) keeps the motor rotating..
Newer motors of today are still rated the same but since they use smaller gage wire,resistance is higher and once under load the power table drops........ I think...:D

[Wilbur Pan]

Also, you can't load an induction motor down to the point where the slip gets really high (and the RPM goes way down). If you did, the current into the motor would exceed the rated value and the motor would overheat fairly quickly. So induction motors run in a fairly narrow RPM band between no-load and full-load. This is different from an engine on a car which has a very wide RPM band.

I don't quite understand this statement. I think we've all seen a piece of woodworking machinery that was fed a piece of, say, 10/4 white oak and seen/heard the motor slow down, hopefully without burning out.

Your point about motors of equal HP generating equal amounts of torque at equal RPM is true, if the motors are operating at the same RPM. But that isn't always true.

The graph at the bottom of this page (http://books.google.com/books?id=T8FcWNgP2eQC&pg=PA520&lpg=PA520&dq=repulsion+induction+motor+advantages&source=web&ots=rH-z0tz2CN&sig=ZmP2THw_dMWQIPNq0pd3owxSv1c&hl=en) of "Electrical Machines" illustrates what I was saying poorly above. The lower curve on the left graph illustrates torque developed over the speed range of an induction motor. The diagram on the right shows torque developed over a range of speeds of a RI motor. Picture both motors powering identical table saws going at the same speed without a load, and toss some 10/4 white oak at them. Both motors will slow down. In the middle range of the graph, the RI motor will have more torque as the speed decreases than the induction motor, and will be able to recover faster. In fact, you can clearly see a region in the middle of the speed range where an induction motor continues to lose torque as it slows, while the RI motor actually gains torque as it slows. I think this is where the perception that an RI motor is "stronger" than a modern day induction motor of the same horsepower rating.

If I'm off about my interpretation of these graphs, I'd be glad to be shown where I went wrong.

[John Cooper2]

Can't speak to the one your looking at, but I bought one of the same vintage for $500.00 and spent a few $$$ on link belts added a few hours of cleanup/tuneup. Now I have a wonderfull old saw that has plenty of power and it's something you don't see everyday.

[William OConnell]

I have a 1949 complete with users manuel and honeycomb motor. I use it all the time. I'm amazed at the amount of work Ive thrown through it the last 6 years without a single breakdown or even belt breakage. Buying, tuning , tweaking and using mine was and is almost a spiritual experience
You should haggle a little but what ever you do buy the saw. Mine now has an incra fence with a router tale built in. Your not a lumber yard or sawmill so the motor will be fine. I can't be for sure but I think most people who say the saw is underpowered for cutting ,whatever, haven't used or owned one of these older Unisaws. I think older Unisaurs are the best value in a cabinet saw purchase. Notice how the design has changed so very litlle in over half a century

[Richard M. Wolfe]

A few months ago while hunting a table saw for the new shop, my friend came across a 1939 unisaw. Saw was/is ugly, price was right - he got it. The bullet motor was wired for 110 which he changed to 220, cleaned it and put a new fence on it. I'm not going to get in a discussion about torque, etc but that sucker 'chops wood'. I can't say you should get the saw you're thinking of as I don't know everything about it, but if it has the R/I bullet motor underpowered is one thing it won't be, if it's like the one we got.

[josh bjork]

I always thought that older motors ran better because motor windings were made from larger gage wire ,causing less resistance,,,,less resistance (under load) keeps the motor rotating..
Newer motors of today are still rated the same but since they use smaller gage wire,resistance is higher and once under load the power table drops........ I think...:D

Yes and no to the OP. There is some extra mass so things won't stall quite as easily. Btw, I actually have a 90's sears saw and a 50's sears saw and there is a little difference but not a ton. The new saw will pop the breaker, my power isn't good in the garage. The old saw will bog down but not stall. It'll keep spinning so you can back off and keep going. 1 old hp cuts plywood fine. If I have to rip wood, I do use a rip blade or it'll bog down if I push too fast. Old saws are a project. If you don't enjoy that, do yourself a favor and don't buy one.

[Mike Henderson]

I don't quite understand this statement. I think we've all seen a piece of woodworking machinery that was fed a piece of, say, 10/4 white oak and seen/heard the motor slow down, hopefully without burning out.

Your point about motors of equal HP generating equal amounts of torque at equal RPM is true, if the motors are operating at the same RPM. But that isn't always true.

The graph at the bottom of this page (http://books.google.com/books?id=T8FcWNgP2eQC&pg=PA520&lpg=PA520&dq=repulsion+induction+motor+advantages&source=web&ots=rH-z0tz2CN&sig=ZmP2THw_dMWQIPNq0pd3owxSv1c&hl=en) of "Electrical Machines" illustrates what I was saying poorly above. The lower curve on the left graph illustrates torque developed over the speed range of an induction motor. The diagram on the right shows torque developed over a range of speeds of a RI motor. Picture both motors powering identical table saws going at the same speed without a load, and toss some 10/4 white oak at them. Both motors will slow down. In the middle range of the graph, the RI motor will have more torque as the speed decreases than the induction motor, and will be able to recover faster. In fact, you can clearly see a region in the middle of the speed range where an induction motor continues to lose torque as it slows, while the RI motor actually gains torque as it slows. I think this is where the perception that an RI motor is "stronger" than a modern day induction motor of the same horsepower rating.

If I'm off about my interpretation of these graphs, I'd be glad to be shown where I went wrong.
The first graph in your reference shows the torque curves for an induction motor and for the repulsion part of the RI motor. Note the torque peak on the induction curve. That peak is actually way outside the normal operating range of the motor and the motor is drawing a very high current when you're at that point in the curve.

Now look a the combined curves, in graph b. If you loaded the motor to the point where you exceed the torque peak of the induction motor and began to slide down the curve (lower RPM), you'd reach a point where the repulsion part would began to increase the torque allowing you to keep using the motor.

Such operation is significantly outside the normal operating range of the motor, causing the motor to draw excessive current and generate excessive heat.

Let me give you an example of using a standard induction motor this way. You have an underpowered table saw and you push the wood into the blade until the saw starts to stall. As the saw starts to stall, you back off on the feed rate until the motor gets back to the RPM represented by the torque peak. You keep doing this until the board is cut. Such operation would grossly overload the motor and generate excess heat. If you kept doing this, you'd burn the motor out or pop the thermal switch, if the motor has one.

With the RI motor, you push the wood into the saw until the motor reaches the RPM of the induction torque peak, but you don't back off - you keep pushing, slowing the motor down even more, until the motor reaches the upward slope of the repulsion torque curve (this transition would happen quickly). The motor is running quite slow but still turning, and drawing significant excess current, generating excess heat. If you kept doing this, you'd eventually burn the motor out or pop the thermal switch if the motor has one.

But when operating within the normal operating range, an RI motor and a capacitor start motor are both standard induction motors and follow the standard induction motor torque curve. And a 1HP RI motor will operate in that range essentially the same as a 1HP capacitor start induction motor. By the definition of HP, they will both have the same torque within the normal operating RPM range.

The big advantage of an RI motor is the higher starting torque - that's where people use that better low end torque - not in normal operation. But for woodworking it doesn't have much value because we start our tools off with no load. The big disadvantage of the capacitor start motor is the relatively low starting torque, much lower than the peak of the induction torque curve.

Mike

[Those RI motors are not that old. The engineers working back then were very well able to measure HP so the motors are not under-spec'ed to the point that you'd notice a difference. Being old, they generally have more thermal mass so they can tolerate excessive current a bit longer than a modern motor.]

[Dwain Lambrigger]

Well, I bought it. I went and looked, and it was in GREAT condition. No breaks or cracks. The table top has some "patina" but no rust. The thing started right up and ran like a champ. It doesn't have a motor cover ($130 for a fglass reproduction) and the actual switch in the switchbox isn't original and the lock know on the angle adjustment wheel is missing. Everything else is working and in great shape.

I will need to invest in a few missing parts, and new miter gauge and fence, and clean some things up. I bought it for $370.00

Excited to get started. I will get pictures when I get it home.

[Craig McCormick]

I traded out my 1 1/2 hp jet contractor saw for a vintage 1 hp Delta Unisaw. All I know is the vintage 1hp is much stronger than my Jet 1 1/2hp was. I love my vintage iron.

I'm in Chandler, AZ

AZCRAIG

[Richard M. Wolfe]

Congrats on the "new" saw, Dwain. As I mentioned in my original post we got a 1939 Unisaw for out shop. It too did not have a motor cover...but it never did. Look at where the cover will fit and see if there are mounting holes for one. Ours does not and I did some digging and found that not all saws came supplied with a cover. 'Course if you would like one for yours it wouldn't be any big deal to drill and tap for it. Kinda neat looking items.

A couple weeks after getting the 1939 saw my friend was in town looking for a window and came across a 1940 model, which he latched onto also. It did not have a cover on it but it was missing on this one as there are mounting holes for one.

[Pete Bradley]

Congratulations! I just finished up a restoration of a 1940 Uni. I saw your post over at OWWM, you'll get good advice there.

Pete

[Pete Bradley]

I would ask the seller to make a cross out on a piece of wood 'bout 10" or so in width that you bring. Make sure that the edges are true. After making a cross cut, check it w/ a square. If it is off from blade wobble, the arbor bearings could be worn & need replacing.

The bearings would be long dead before they showed up in this test. A much better test is to slip off the belts, remove the blade and turn the arbor by hand to see if it turns smoothly. Better still is to just replace them, not a difficult job on a Unisaw or you can have Sawcenter in MA do it for you.

Bearings in woodworking machines tend to get junk in them and start to catch and stiffen up. This can lead to them spinning instead of rolling, causing wear to the shaft or bore. This is often hard to detect over the noise of the machine and is difficult to repair if the wear is more than minor. Best to swap them before it happens.

Pete

[Ray Newman]

Pete B: agree, esp. about replacing the bearings & more so on a saw that old.

But a good thing about the cut test is that it will tell just how well the motor & the switch works. Some sellers have just no idea as to what they’re selling as the saw might have belonged to a family member & they are just repeating what they’ve been told about it.

Then there’s the case of someone deliberately misleading a potential buyer, which I’ve seen happen.