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Phase converter or switch motors

BigB

Plastic
Joined
Nov 5, 2012
Location
Selah Washington U. S. of A.
I have a 1941 SB 14.5 x 6 lathe. It has a 3 phase 220 1 HP motor and a static phase converter.

I have a hard time taking what I consider to be normal cuts when turning. For example, turning aluminum I can barely take a .040 cut and it will drag the motor down.

At first, I thought the belt was slipping (it may be as it looks pretty junky) but at this point I think the static phase converter is causing some issues at least.

So...do I spring for a rotary phase converter or do I just get a 2 HP 220 single phase motor and eliminate the 3 phase all together??

Any help is appreciated.

BB
 
I have a 1941 SB 14.5 x 6 lathe. It has a 3 phase 220 1 HP motor and a static phase converter.

I have a hard time taking what I consider to be normal cuts when turning. For example, turning aluminum I can barely take a .040 cut and it will drag the motor down.

At first, I thought the belt was slipping (it may be as it looks pretty junky) but at this point I think the static phase converter is causing some issues at least.
Well. yes... not your fault, but a "static" converter doesn't actually "convert" anything.

It just "tricks" a 3-Phase motor into limping along on ONE phase, with but partial power off the capacitor's phase lag to keep the other two windings at only partial power, best case, and fall on yer nose at any significant load, worst-case.

QED . .right in front of you.

Nature of the beast.

Which can also damage the motor, long-term. DAMHIKT!

Presuming "not YET" damaged, just add an idler - as little as 1 or 2 HP will do yah.. use the static as its starter/controller ... and get roughly 91% of full-power out of the same dagone motor instead of 30-odd percent by changing nothing much else atall. Static makers publish how to use with an idler.

"Full" RPC, say 5 HP to 10 HP idler, ELSE a two-stage with selectable A, B, A+B idlers, and you've probably covered most other machine tool 3-P needs as well.

RPC are way to Hell and gone gentler on OLD motors than VFD are. Nice, clean, sine-waves, no hash, even if not as perfectly balanced as utility mains 3P.

I'm happier building a flexible-power RPC than scouting a whole tribe of replacements for motors of significant age and no longer common frame sizes, let alone "cheap".

Modifying mounts and shaft goods isn't even close to rocket science in a machine shop.

AVOIDING the need of messing with it is still a right welcome circumstance, even so. We all have other s**t to do with our time if not also our money.

YMMV
 
So...do I spring for a rotary phase converter or do I just get a 2 HP 220 single phase motor and eliminate the 3 phase all together??

Any help is appreciated.

BB

Most here prefer or would recommend 3 phase.

Another consideration is will you get other machines ? Might say no, till you drag a mill home. :D Catchier than covid, the disease usually leaves you upgrading to bigger and better, not going backwards.

Thermite had a good suggestion at 5 to 10hp rotary phase convertor. Besides that, you may want to upgrade your lathe motor to 1.5 or 2hp also.
 
Most here prefer or would recommend 3 phase.

"The usual reasons".

- A 1-P motor is "smooth enough"... until you get past about 60 or 70 percent load. That can still work OK for throwing green stuff off a trailer into a farm silo or pumping water out of a well, but ain't so smooth on a machine tool under heavy load.

- A 1-P motor isn't easy to reverse, let alone "at once" as 3-P can be.

- A 1-P needs a starter system to get it to move AT ALL. Those all wear-out if not fail unexpectedly now and then.

Whereas a 3-P motor is inherently self-starting, inherently "on the fly" reversible, delivers 100% power, still smoothly, can last indefinitely, yah just prevent the bearings from going too damned close to Hell before fitting new ones. Which are generally CHEAP as well as easy to change.

Grab an idler. Run what yah got.

Might have MORE than enough power, just as she sits, the motor gets proper rations instead of just death-camp sawdust soup.
 
I replaced the rotary phase converter that I used on my Bridgeport with a VFD that I bought on eBay for $75. The VFD works great, it’s nice having the variable speed, I added a remote start stop station on the the arm for the DRO, it’s got a potentiometer for speed, forward, reverse and jog controls.
I would suggest that you look into them.


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I replaced the rotary phase converter that I used on my Bridgeport with a VFD that I bought on eBay for $75. The VFD works great, it’s nice having the variable speed, I added a remote start stop station on the the arm for the DRO, it’s got a potentiometer for speed, forward, reverse and jog controls.
I would suggest that you look into them.

Thanks. I’m looking into the VFD, but from what I think I learned today, I can’t use one. The way I understand it, my motor is too old to use a VFD.

Plus, they look fairly complicated to program and I’m electronically retarded!!!


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I have a 1941 1 1/2 hp 3 phase motor in mine and I went with a 5hp RPC from American Rotary. The idler motor is a bit noisy for my tastes but at least you know it's on! I wanted to preserve my motor since it's an art deco beauty but if she goes I don't know what I would do. I kinda punted and took the expensive route to see how the machine would operate as designed and delivered. So I have instant reverse and she brakes nicely to a stop on "off". I heard you can make a VFD do all these things too but you are going to get deeper into the re-wiring of your machine.

I don't think the variable speed as a feature argument holds up on a good lathe with change gears but I am not super experienced. In my view if you are in the wrong speed then you need to change it! ...or your cutter is dull, or your material isnt supported well, or your feed is wrong, or something needs to be adjusted on your machine!

I have a mini lathe that I got many years ago and it spins to 3000 rpm spindle speed and has variable speed control. I really like that for polishing small work but our machines don't get up there so I'm kinda lost on the variable speed as a big selling point. Now the cost! That is a serious consideration and may be one that gets you to try the VFD. You'll need to do a bit of poking around the internet. There is a lot in here on your very question in the VFD section.
 
I have a 1941 1 1/2 hp 3 phase motor in mine and I went with a 5hp RPC from American Rotary. The idler motor is a bit noisy for my tastes but at least you know it's on! I wanted to preserve my motor since it's an art deco beauty but if she goes I don't know what I would do. I kinda punted and took the expensive route to see how the machine would operate as designed and delivered. So I have instant reverse and she brakes nicely to a stop on "off". I heard you can make a VFD do all these things too but you are going to get deeper into the re-wiring of your machine.

I don't think the variable speed as a feature argument holds up on a good lathe with change gears but I am not super experienced. In my view if you are in the wrong speed then you need to change it! ...or your cutter is dull, or your material isnt supported well, or your feed is wrong, or something needs to be adjusted on your machine!

I have a mini lathe that I got many years ago and it spins to 3000 rpm spindle speed and has variable speed control. I really like that for polishing small work but our machines don't get up there so I'm kinda lost on the variable speed as a big selling point. Now the cost! That is a serious consideration and may be one that gets you to try the VFD. You'll need to do a bit of poking around the internet. There is a lot in here on your very question in the VFD section.

So you have no trouble making cuts that are appropriate for the tooling and machine with that 1.5 HP motor and a RPC???

That’s one issue I’m having. I can’t take a cut I think the machine should take without dragging the thing to a stop.

I did figure out today that I think the drive belt is too long. I’m Maxed out on adjustment and the belt doesn’t seem tight enough to me.
 
So you have no trouble making cuts that are appropriate for the tooling and machine with that 1.5 HP motor and a RPC???

That’s one issue I’m having. I can’t take a cut I think the machine should take without dragging the thing to a stop.

I did figure out today that I think the drive belt is too long. I’m Maxed out on adjustment and the belt doesn’t seem tight enough to me.

I have no issues at all with cuts! I usually work with materials that are known to be easy to machine tho!

I had issues with belt tension for a while, then i discovered the adjustment on the back of the pedastal!

Do you have this bolt and locknut back there? If so maybe your belt is fine and you need to set the plate travel with this adjustment.

P10608492.jpg

P10608501.jpg
 
I have no issues at all with cuts! I usually work with materials that are known to be easy to machine tho!

I had issues with belt tension for a while, then i discovered the adjustment on the back of the pedastal!

Do you have this bolt and locknut back there? If so maybe your belt is fine and you need to set the plate travel with this adjustment.

View attachment 302338

View attachment 302339


Yes, I have that bolt, but I thought the belt adjustment was on the front side of the lathe, in the same area where you tension the motor drive belts. I thought that bolt you pictured is to center the motor under the lower cone. I could be wrong, as I usually am!!
 
Yes, I have that bolt, but I thought the belt adjustment was on the front side of the lathe, in the same area where you tension the motor drive belts. I thought that bolt you pictured is to center the motor under the lower cone. I could be wrong, as I usually am!!

The adjustment is for the V belts and shown in the "How to keep your lathe in trim" book. Yours may be fine but mine were not and the loss of power in cuts is what I was experiencing too.
 
I use a VFD with phase conversion and I have no problems with it. SB light 10 w/ 1 hp motor, using it for at least 12 years. They're very simple to install and program. They start around $150.
 
What VFD are you using??? I’d much rather have the VFD for all the things it can do, but it seems to me when I first bought this lathe in 2012, I bought a VFD (or maybe it came with it) and after working with it for about 15 hours I came to the conclusion (maybe I JUMPED to the conclusion and I could have been wrong) that the VFD wouldn’t work with the at that time 72 year old motor and wiring.

Either way, the static phase converter sucks.
 
I have an automation direct GS2. They also have the GS1 for a bit less. Looks like the GS2 are getting discontinued. They sell the WEG brand, but I haven't used them.

You can't use the VFD with the original contactors. You'd need to wire the switches into the terminal strip on the drive, or use the START/STOP on the face of the drive directly. The programming is pretty simple if you follow the book.

I've heard that really old motors are wound heavier and will stand up better to VFD's, others have said the insulation is old and will break down easier. I'm over 10 years on this motor, so far so good.

Drive is rated for 5A output, but i've never seen it pull more than 2.5A on my lathe with the heaviest of cuts. I can take a 0.080" cut on 1" steel with a good cutter and it doesn't bog down.
 
1) build a simple rotary converter with an idler motor. I suggest 5 hp as a good number for your 1 hp load machine.

2) a VFD will work fine with your older motor. You will probably have no troubles at all with it. I suggest a single phase 120 volt unit from Hitachi.
 
I built a simple rotary converter for my lathe, and it worked fine until it burned up my motor. I never bothered checking it, but the generated leg was around 165V and the others were 120V.
 








 
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