Gorton 8 1/2D arrived in the pouring rain last week

mwal689

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Sep 24, 2019
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It's now dried off, lubricated and leveled.

Looks to have been manufactured in 1940. No power feeds.

I only have single phase so first question is VFD or RPC. I don't have any other 3 phase machines so VFD seems like a good answer. But, I like the simplicity of an RPC. Cost isn't an issue, and I'm a computer/electrical engineer, so neither options seems particularly daunting. Any compelling reason(s) to go with one or the other?
 

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Bob Korves

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Being an electrical guy, you can make your own RPC for pretty cheap, or buy a VFD, cheap Chinese ones can be had for cheap. The trade offs are with whether you would like to have variable speed and some other useful bonuses that come with having a VFD, or the possibility of running multiple 3 phase machines off of a single RPC. The VFD can only really control one machine...
 

matthewsx

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If the contactors are anything like the ones in my former 1-22 Mastermill you will definitely want to convert it to VFD. When I looked into just replacing a few of them it became obvious that I'd spend way more money trying to keep it original than converting it. I still have the vacuum tube control for the table feed on it:big grin:

Cheers,

John
 

Winegrower

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A solid state phase converter is simple, quiet, will run multiple machines, and does not cost much.,
 

mksj

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A number of different things to consider. Assume the motor is 2 Hp based on what I have seen, but sure looks huge. Above 3 Hp the VFDs get expensive and there are very few native 5 Hp single phase VFD's. I am not going to get into the eBay specials, etc. that are rated at over 3.7kW, their longevity is questionable under hard use. They do not consistently work and you get no post sale support, fine if it is a throwaway. The other considerations specific to use of a VFD is the age and condition of the motor, the insulation is more prone to damage from the PWM VFD output. Still the insulation on these old motors were typically 1000/1200V which would should not be too much of an issue running the motor off of a VFD unless the insulation is marginal. On the flip side of the equation, I would probably want to replace the electrics in a 40+ year old mill if running it off of a RPC. So, as a single machine, a VFD gives you a bit more flexibility, would bypass the old electrics be the least expensive overall. You get some speed control on the fly and wiring up a control box/run switch is simple. Could do a nice VFD install in the current electrical cabinet.

If you go the VFD route keep the switching frequency lower, probably 6 kHz and would run the motor conservatively from a speed and overload parameter point of view. Might consider picking up a used VFD output sine wave filter which will mute the PWM spikes. An RPC as a turn key option would be 2-3X the cost unless you have a spare 5/7.5 Hp motor laying around, and this assumes all the machine wiring was good. Was it running when you purchased it?
 

mwal689

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Thank you all for the advice. My decision just got a lot simpler.

I found an unused 20hp, 3 phase motor for $200 on Craigslist. It was still on the pallet. Crazy.

Guess I'm building an RPC.
 

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