Myford PR11 Planer Motor

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Hornet99

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You will recall my recent purchase of the above planer that didn't run. I have traced the problem to the 3hp motor which, is massively over powered and so I wan to replace it with a suitable alternative.

Looking at the instructions for the planer provided by a very kind soul on the forum, tells me I have two choices in the size of the motor to run the planer.

1. 1/4 or 1/3hp 2850 rpm with a pulley of 3.25"
2. 1/3 or 1/2hp 1425 rpm with a 6 5/8" pulley

Having zero experience in this field logic tells me to go for the higher speed from the first motor? Why the difference is is something to do with the pulley sizes?

Or would it be cheaper to repair the current motor? We think it might be the windings.
 

dickm

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Repairing the 3hp motor would probably cost more than a new motor. As you say, 3hp is a bit of overkill for that planer. As you can easily vary the pulley size, go for whatever motor you can find of about 1-1.5hp and good quality.
 

Hornet99

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Thanks Dick knowing nothing about motors, what are the good and the bad to avoid please?
 

dickm

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Well.... Myfordman is your expert here, I'm just a dabbler. Given the chance and the time, would look for a Brooks/Crompton/Hawker Siddley or other old UK made iron frame job, but presumably the Italian stuff that is currently sold by the likes of Machine Mart would do the job perfectly well.
 

Old.bodger

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I may be wrong, but doesn’t the differing pulley size give the same rotational speed (at the cutter) assuming that the cutter block pulley stays the same size (perhaps a different belt length though) ?
 

Hornet99

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I thought that might be the case, the 3hp motor I had on mine has a huge pulley wheel about 8-10" at a guess.

I vaguely remembered something from my GKN apprenticeship assessment to be a draughtsman when I was 16 that involved pulleys and that was also the last time I thought about them in anger....
 

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