How about replacing the motor with Single Phase

DFWKen

DFWKen

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I started a thread about a new lathe I've purchased. It hasn't arrived yet. (Grizzly G0740 Heavy Duty 3-phase 14 x 40). My dilemma is whether to buy/build a RPC or simply change the 3-phase motor(s) with new single-phase.

The lathe comes with a very-wide speed range of 50 to 2,500 RPM. I can't imagine ever needing 2,500 RPM. So maybe a 1,750 RPM single-phase 5-HP motor would provide all the power and speed that I'd ever need. The 2-speed switch would then not be needed, but could stay in one position. The wire size within the lathe should suffice. I'd need to rewire the motor circuit, but that should be simple . . . even including rotation reversal via the apron control. The lathe would be changeable back to 3-phase, should a future buyer desire 3 instead of single phase power input. Reversible 5HP motors appear to be common and fairly inexpensive. A drive pulley change would probably be in order.

Any comments or ideas? Lathe is coming in less than 10 days.
 
Cutting 1/2" diameter aluminum with a carbide insert, at about the recommended 400 SFPM would want 3200 rpm, per the charts... My 13x40 goes to 2000 rpm, and I use it a lot, sometimes wish for more. Also wish for less than the 70 rpm minimum fairly often... I would go with the RPC and get all the speeds you are supposed to, and with no mods to the lathe.
 
In my experience 3 phase motors run on a good phase converter produce a better surface finish on the work than a similar machine with single phase motor. There are other factors in play regarding surface finish, but having a 3 phase motor is a better set up and gives you more options. If running a rotary converter its nice to put it in a separate room to cut down on the noise. For a 5 hp motor you will likely want an 8 or 10 hp motor for your converter.
 
Keep the 3-phase motor on your lathe. For the price of that single phase motor you can get a RPC and then have 3-phase available in your shop for any other machines that may come your way. You could get by with a 5hp RPC but I'd go larger just in case you want that big honken American Iron that you can get for a steal because no one knows how to power it up.
Used 5 to 10 hp, 3-phase motors can be gotten for cheap. Hunt up the motor then buy the RPC electronics box. If you are like me and don't have a bunch of electrical parts laying around you can buy a ready made box for less than sourcing the needed parts and building one. I run my RPC off of a dryer/range outlet in my garage. This means that the machine tools are not direct wired into the house power. I don't know how true it is but I've heard that some insurance companies don't like it when "Industrial" machines are direct wired. A dedicated circuit breaker to the outlet and the RPC is connected with a plug. As a bonus I can plug a generator into the outlet and back feed power into the house during power outages.

This may be more info that you asked...
http://phaseconverterusa.com/Standard-Series_c_27.html
 
Alrighty, thank you all for your opinions. The overwhelming majority advised against buying a single-phase motor; but instead going the Rotary Phase Converter with good explanations. (Actually, it was unanimous!)
So I found one on eBay for $750 or make offer. I made a $500 offer and the seller accepted. Shipping is a hicky at $75; but I'll get over it.
Ten HP, 1750 RPM rotary phase converter is on the way. I plan to remote it outside on a concrete slab and in a weatherproof enclosure. Won't be hard to penetrate the concrete block wall for the conduit.

Thank you all.

Ken
 
DFWKen said:
Alrighty, thank you all for your opinions. The overwhelming majority advised against buying a single-phase motor; but instead going the Rotary Phase Converter with good explanations. (Actually, it was unanimous!)
So I found one on eBay for $750 or make offer. I made a $500 offer and the seller accepted. Shipping is a hicky at $75; but I'll get over it.
Ten HP, 1750 RPM rotary phase converter is on the way. I plan to remote it outside on a concrete slab and in a weatherproof enclosure. Won't be hard to penetrate the concrete block wall for the conduit.

Thank you all.

Ken
Click to expand...

Smart move Ken, you won't regret having 3phase on tap and it opens up a wide range of options for industrial machinery on the second hand market.

Paul.
 
Something was said above about insurance companies not recognizing industrial machines being wired up direct in your home? If your are using the machinery for business, yes. In a home shop environment, I can't see where they can deny coverage as long as the wiring meets or exceeds NFPA-NEC requirements for rotary phase converters, static converters, and VFD's. A 1440 Lathe, I think everyone should have one in their shop! Yes, I think it is a good idea to have a means of quick disconnect from electrical supply in a home shop environment. That's how I have my shop wired up. L1430 plugs are cheap and easy to wire into your house, backed by a 30 amp breaker. Just my 2 cents worth!
 
Well, I have one of the two 3-phase converters hooked up in the workshop. Had to add a sub-panel with a 60-amp breaker, a 3-phase disconnect switch, a 3-phase 30-amp twist-lock plug and box,and EMT conduit and #8 wiring to get power to the converter and then 3-phase to the lathe.

TWO PHASE CONVERTERS? Yes. I bought the one on eBay by making an offer that I didn't think the seller would accept. I'd also made a low offer on Craigslist for one that's only about 60 miles from here. Then, both sellers surprised me and accepted. They're both here; I hooked up the one from Craigslist because it arrived first. I'll definitely remote it outside (after I decide which converter to keep and which to sell).

I've been running the lathe in all speeds. Last night, I ran it at the highest speed of 2,500 RPM. HOLY COW! It winds up like a jet engine for about 5 seconds. The chuck jaws disappear in a blur. Someone tell me again why such a high speed is needed.o_O

I'm getting to know the lathe. In another thread, I posted my experience with metric threading and how I broke 4 threading inserts by stopping the lathe or reversing it to make the next cut. One must draw the tool out of the thread before stopping the spindle or broken tips will result. I'm also getting used to the gearbox. There are up to five levers to throw to change speeds. Easy to get one in the wrong position. A scratch threading cut revealed my boo-boos before ruining the round stock.

It may be interesting reading to others about my decision to purchase this lathe and my experiences and review of the lathe so far and as I use it.
 
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