Shapers: Single-Phase Versus Three-Phase

      A discussion of what makes a three-phase shaper different from one with a single-phase motor, and whether the difference matters. January 23, 2012

I want to set up a dedicated shaper for making shaker style glass cabinet doors. I have two machines available to me. Shaper 1 is a used 5HP 3-phase Powermatic with a 1 inch spindle. Shaper 2 is a brand new single phase 5HP with a 1 1/4 inch spindle. I favor the 1 1/4 inch arbor because this would allow me to possibly stack cutterheads on the spindle. I favor the 3 phase machine because I think it probably has more torque.

Can anyone look at the amount of stock I intend to remove with this machine and opine as to whether or not a single phase machine would be up to the task or if I should stay with 3 phase? I have power for both, so this is not an issue. I am not interested in using this shaper for other purposes other than the door. The material will likely be poplar, but could also be white oak or soft maple.

Forum Responses
(Cabinetmaking Forum)
From contributor B:
Either machine will work. I like a 1" spindle because I set my bits up in a stack with T-bushings all shimmed so there are no setup changes. I can make several cope and stick patterns as well as glass rebate by changing the bits, but no machine changes are required.

The 1 1/4" spindle is a heavier machine and might be a better choice. Without seeing the two machines, I wouldn't know. For cope and stick the 1" is all that is needed. A single phase motor produces more torque than a three phase motor during startup because of the extra windings the single phase motor has. The three phase motor is cheaper to make. No switching windings and no start windings. I went with three phase everything.

From the original questioner:
I think I understand what you mean about torque at start up. What about when the machines are running? Would a similar horsepower single phase machine handle stock removal as well as a three phase machine? I remember a 1/2 horsepower 3 phase Davis Wells jointer I used to have. You could not slow the cutterhead down. I always thought it was so powerful because in 3 phase machines, one leg of power is always in phase. Would three phase cut better than single phase?

From contributor B:
I'd pick the best quality machine, as the motor can be easily changed. I think either would handle the stock removal. I use a 5hp 3 phase shaper for stick cuts and a 3hp 3 phase for cope cuts, both have a 1" spindle. So get both machines...

From contributor H:
Three phase motors are no more powerful than single phase motors. The starting torque is a new one on me, so I couldn't comment on that without further study. However on a shaper, starting torque isn't an issue.

There are several advantages of 3-phase motors. First, as already mentioned, is cost, as they are typically much less expensive to make. Second - and the more important issue in industry - is current draw. Basically it comes down to the same amount of current being drawn through 3 legs on a 3-phase motor versus 2 legs on a single phase motor. This means you can use a smaller gauge wire to the motor. There is no electrical cost savings as the net result of drawing 5 hp worth of current is always the same. You can just use larger motors with smaller wires and breakers.

You state that you have both power options available. If you have 3-phase direct to your building, then the single phase motor will probably be running on 208 volts instead of 220 (or 230 or 240). That is done all the time but I believe there will be a slight increase in current draw to the motor.

If you are running a rotary converter on a single phase service, then you will have full power to the 3-phase motor as long as it is a properly built converter. If you are running 3-phase off single phase with a static converter then you will only have approximately 2/3 of the actual motor rating power.

Not knowing your actual building service situation, and so ignoring the power issues, I would go with the 1 1/4" spindle unit. If they are both equally well built machines, the one with the 1 1/4" spindle will be heavier duty since it has to support the larger spindle. And the larger spindle itself is significantly stronger. Also I think you'll find most shaper cutters either come as 3/4" or 1 1/4" bore, so why bother bushing it down if you don't have to?

From contributor L:
No recommendations, just my thoughts: 3 phase motors are simple and very reliable. Typical capacitor start single phase motors have centrifugal switches that are the cause of most motor failures. Starting torque doesn't matter at all for the application and I don't know that what you said about 1 VS 3 phase starting torque is true or not. I'd choose a 1 1/4" spindle, all other things being equal. There is something very nice about using a heavy industrial quality shaper compared to the typical Powermatic/Delta shapers that most small shops use. All that said, for the use you propose, either will work.

From contributor J:
I pretty much agree with the others. You would never be able to tell the difference between a single and 3 phase motor by running your parts through. You may, however, notice a difference between different quality machines. You don't say what the second machine is (also Powermatic?), but I'd generally go with the machine with the bigger spindle and quill. However, if they're both Powermatic 27's, the quill and bearings will be the same size regardless of spindle.

I'm also not a fan of using bushings if not needed. I couldn't see buying a smaller machine knowing I'd be using bushings for everything... Just doesn't make a lot of sense to me.

From contributor N:
Both machines should be up to the task of a cabinet door profile. I would go with the smoothest running machine with the least spindle run-out.

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