1725 or 3450 rpm?

[Ron Hampe]

I have a 12" Craftsman (Parks) planer model 112.23490 that I have decided to keep. It came with a very large vintage 1.5 hp 1725rpm craftsman motor that may be original equipment. The particle board base was cracked below the motor opening and I reinforced the area to prevent that from recurring. The motor was literally a shoe horn fit beforehand and with the repairs it won't fit now. Instead of trying to make it work I've decided to replace it with either a 2 or 3hp motor and this change will require new pulleys. My question is should I stay with a 1725 rpm motor or would it be better to go with a 3450 rpm motor?

Thanks

[Jim Matthews]

Bearings and knives are rated at the original speed.

If you can "step down" the pulleys to achieve the same speeds, it should be safe.

Turning these vintage machines at higher rates of speed is a recipe for failure. (And potential shrapnel)

https://www.blocklayer.com/pulley-belteng.aspx

[Ronald Blue]

If this is like yours it appears the original motor was 3450 rpm. Link attached with a motor view.
http://vintagemachinery.org/photoindex/detail.aspx?id=16238

[Bill Dufour]

I am pretty sure mine is 3450 and the two pulleys are about equal diameter.

[Matt Day]

And I’d doubt that the bearings will notice a difference between 1725 or 3450 rpm. Between 10k and 15k yes.

[David Kumm]

Generally keeping the pulleys closer in size and using the 2 pole motor is preferable in this application. Dave

[Ian Lerew]

The motor rpm doesn’t matter it’s the cutter head rpm that matters. I believe the proper rpm for the cutter head is around 4000 rpm. You could change your motor to any rpm you like but you would need to change your pulleys accordingly. If you need to change your motor it will be cheaper to find a new motor with the same rpm and shaft sizes so you can reuse the pulleys you have.

I should also add that the 1.5hp Craftsman motor may very well may more powerful than a modern 2hp motor. It may be more cost effective to make that work and it’s also cooler in some people’s opinion. I restored and eventually sold a craftsman badged parks to upgrade to a powermatic model 100. It had a 2hp craftsman motor that was a beast. Very bulky. I regret selling it but I did a really nice restoration and made a nice base for it and it needed a belt guard and dust hood. I didn’t want to scab something onto that looked stupid and a nice powermatic came along so I sold it.

[Mike Henderson]

I should also add that the 1.5hp Craftsman motor may very well may more powerful than a modern 2hp motor. It may be more cost effective to make that work and it’s also cooler in some people’s opinion. I restored and eventually sold a craftsman badged parks to upgrade to a powermatic model 100. It had a 2hp craftsman motor that was a beast. Very bulky. I regret selling it but I did a really nice restoration and made a nice base for it and it needed a belt guard and dust hood. I didn’t want to scab something onto that looked stupid and a nice powermatic came along so I sold it.

I'm afraid that those old wives tales of older induction motors being more powerful than a modern equivalently rated induction motor are just that - old wives tales. The old motors were generally physically larger because of improvements to modern motors but the engineers who designed and built those old motors knew how to measure horsepower and if the motor was more powerful, they would have rated it as a larger HP. People just seem to think that older things were better, when the opposite is usually true. [You can check this by looking at the voltage and amperage of the motor. A HP is about 750 watts but small motors are only maybe 80% efficient. Look at the nameplate and you can calculate the approximate HP. Older motors were generally less efficient than modern motors.]

But to answer the original question - horsepower is torque times RPM times a constant factor. So a 1725 RPM motor has to generate twice the torque to produce the same HP as a 3450 RPM motor of the same HP. This causes the 1725 RPM motor to be physically larger. So I'd choose a 3450 RPM motor since you have a size constraint.

Mike

[That's why those screaming universal motors that turn 20,000RPM (or more) can be fairly small. The torque may be small but the RPMs make up for it.]

[Ron Hampe]

Thanks everyone and I wasn't planning on changing the rpms just the motor and pulleys.