Soft Start for Lathe?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: Harold_V, GlennW

John Hasler
Posts: 1271
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Soft Start for Lathe?

Post by John Hasler » Sun Apr 28, 2019 8:33 am

David2011 wrote:
Sat Apr 27, 2019 10:29 pm
Ah, that makes sense. That's different from an air conditioning motor or other capacitor start motors that don't have starter windings. So much I have learned about other similar stuff is different with this motor. I didn't think about the switch discharging the cap. Thanks!
Capacitor start motors have two capacitors: a large nonpolar electrolytic that is switched out when the motor is up to speed and a smaller oil-filled run capacitor that is always connected. Both are discharged through the windings when the motor stops. Capacitor run motors have no centrifugal switch and have only the smaller always connected capacitor, but it still discharges through the windings when the motor stops. All single-phase induction motors have two windings though some rely on resistance rather than capacitance for the requisite phase shift.

Also, remember that this is AC. The capacitors don't charge up and stay charged while the motor is running. They charge, discharge, and charge to the opposite polarity 60 times a second.

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Mon Apr 29, 2019 1:46 pm

Thanks for the info. It's a little tight between the motor and the wall so I'll look for a second capacitor when I pull the lathe out.
Glenn Brooks wrote:
Sat Apr 27, 2019 1:53 pm
Sounds promising. Particularly the bearing caps. That suggests you might have split bearings- solid yellow metal spherical castings, split in half. If so, similar/identical to my 1919 circa Dalton lathe. These are easy to work with. First off, put a dial test indicator on the chuck and insert bar stock in the spindle and pull upwards. Proper tension on the spindle will result in .002” upwards movement. (.002 clearance allows for a film of lubricating oil between spindle and bearing surface.).

More clearance means the bearings are worn and/or loose. Less means the spindle is binding against the overly tightened bearing cap, causing the spindle to not turn and the motor to stall. This could be your problem. Try loosing the bearing cap screws and measuring the spindle play. Then set it properly with shims undermthe bearings and try your motor again. If it trips the breaker, try going to the 30amp breaker.

FWIW,my experience is the bearing caps come looser over time, not tighter. So all of the above might not mean anything...

Still, it’s always good to check spindle play every once in awhile, to assure precision matching if nothing else.

Glenn
Glenn, I think you may get the brass ring here. I checked for spindle movement using a test indicator and there is no measurable vertical or horizontal (front to back) movement of the spindle. I have Starrett and Verdict test indicators and the needles just didn't move on either. That would certainly explain the spindle being difficult to turn.

Since the bearings are retained by end caps (not split) is shimming of the end cap the correct way to make adjustments? It seems like a very thin shim on the order of .0005"-.001" would make a difference.

David

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Mon Apr 29, 2019 1:57 pm

John Hasler wrote:
Sun Apr 28, 2019 8:33 am
Also, remember that this is AC. The capacitors don't charge up and stay charged while the motor is running. They charge, discharge, and charge to the opposite polarity 60 times a second.
I'm more familiar with DC capacitors, particularly in electronic flash units as I was a professional photographer for many years. Those caps hold a nasty charge for a long time. The more I'm learning here the more I learn how little I know about AC motors and capacitors.

Not directly related to the lathe issue, I realized working with brushless motors for radio controlled airplanes that those motors are wound exactly like the 220V 3Ph motor in my milling machine. The 3Ph (DC) electricity is synthesized by the electronic speed control that varies the speed by changing the peak width of a square wave pulse. The 3 phase motor is easier for me to comprehend than the single phase AC system because of the RC exposure.

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Mon Apr 29, 2019 3:32 pm

Glenn and all,

Couldn't help myself and had to poke around a little more.

After removing the bearing cap behind the chuck I found a hard shoulder on the chuck end of the tapered bearing so clearly shimming would not reduce the preload. Clean oil ran out so the bearing has been running well lubed. Some studying indicated that a pair of nuts at the outboard (left) end of the spindle were likely responsible for the preload. I loosened them and the spindle spun much more freely with the drive belt disengaged. I snugged the preload nuts back up until I could feel drag and then backed off just a hair, about 10° and then locked it there with the lock nut. I put a bar in the chuck and checked for play. It still shows no play but the drag is greatly reduced. Made some chips with cut depths up to .030" at 510 rpm on 1" 4140. That would have popped the breaker in the past if I managed to get the lathe running at a medium speed. That's the highest speed of the low range. The lathe is noticeably quieter. I'll still replace the capacitors before long just to make sure they weren't contributing to the problem.

John Hasler
Posts: 1271
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Soft Start for Lathe?

Post by John Hasler » Mon Apr 29, 2019 3:49 pm

With tapered roller bearings there should be no play.

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Mon Apr 29, 2019 6:10 pm

It feels right. Better than at any time since I bought it. I'll just have to use it for a while and see how it goes. I hope to be moving the heavy equipment in about a month.

I'm very grateful for the contributions from all the participants. They all helped me narrow down the areas to evaluate.

David

User avatar
Bill Shields
Posts: 5510
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Soft Start for Lathe?

Post by Bill Shields » Mon Apr 29, 2019 6:55 pm

soft starts can be very handy on a flat belt lathe with a big heavy part / chuck....assuming you have a 3 phase motor.

My 16" south bend, on the higher speeds, often slips the flat drive belt off when powering up (did so for 40 years). It has a very big / heavy 12" chuck on it that I take off every decade or so....

With a soft start (all I use it for is that..not speed control - don't want to run the spindle any faster than it was designed to go), the belt stays on, saving a lot of headaches.
Too many things going on to bother listing them.

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Mon Apr 29, 2019 8:28 pm

Love those old South Bends. We had about 8 of the 14" model in the gunsmithing class but seldom spun anything heavier than a rifle barrel.

Glenn Brooks
Posts: 1766
Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: Soft Start for Lathe?

Post by Glenn Brooks » Tue Apr 30, 2019 2:07 am

Ok, great. Sounds like you are narrowing it down to the preload. Now, I am not familiar with SB lathes that require pre loading - only the older split bearing styles, pre 1934 models, that have bearing caps that lift off the top of end of the spindle at each end of the head stock. You should be able to find older threads that specifically address pre loading your vintage machine.

If not, just pose the question again, specifically asking about how to measure preload. You’ve already received one or two comments about preloading characteristics, so should be a lot of help from knowledgeable folk available.

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

User avatar
Bill Shields
Posts: 5510
Joined: Fri Dec 21, 2007 4:57 am
Location: Somewhere in the World
Contact:

Re: Soft Start for Lathe?

Post by Bill Shields » Tue Apr 30, 2019 6:52 am

all my SB lathes (3 of them) have split bearings and all are post WWII...

All of the SB rebuild books have instructions on setting the split bearings. My 16" even has instructions on a plate riveted to the headstock.
Too many things going on to bother listing them.

David2011
Posts: 26
Joined: Wed Apr 24, 2019 3:18 pm

Re: Soft Start for Lathe?

Post by David2011 » Tue Apr 30, 2019 1:15 pm

Bill Shields wrote:
Mon Apr 29, 2019 6:55 pm
soft starts can be very handy on a flat belt lathe with a big heavy part / chuck....assuming you have a 3 phase motor.

My 16" south bend, on the higher speeds, often slips the flat drive belt off when powering up (did so for 40 years). It has a very big / heavy 12" chuck on it that I take off every decade or so....

With a soft start (all I use it for is that..not speed control - don't want to run the spindle any faster than it was designed to go), the belt stays on, saving a lot of headaches.
Bill Shields wrote:
Tue Apr 30, 2019 6:52 am
all my SB lathes (3 of them) have split bearings and all are post WWII...

All of the SB rebuild books have instructions on setting the split bearings. My 16" even has instructions on a plate riveted to the headstock.
Thanks, Bill.

I don't have a three phase motor. I have used and taught people to use South Bend lathes but I don't own one. I was asking specifically about soft start devices and not VFDs in general since this is a 1970s Jet lathe with a 110V single phase motor.
Glenn Brooks wrote:
Tue Apr 30, 2019 2:07 am
Ok, great. Sounds like you are narrowing it down to the preload. Now, I am not familiar with SB lathes that require pre loading - only the older split bearing styles, pre 1934 models, that have bearing caps that lift off the top of end of the spindle at each end of the head stock. You should be able to find older threads that specifically address pre loading your vintage machine.

If not, just pose the question again, specifically asking about how to measure preload. You’ve already received one or two comments about preloading characteristics, so should be a lot of help from knowledgeable folk available.

Glenn
Glenn,

I'm afraid the conversation has become confused a few posts back that my lathe has split bearings like your Dalton. I don't have a vintage South Bend. My lathe is a 1970s Jet which has one piece end caps that go over the ends of the spindle and completely surround it. Russ/BadDog posted a photo of a Jet 1024 near the top of page 3. You can see a bearing cap in that photo. It's the silver ring behind the chuck.
The preload is adjustable via a pair of nuts on the spindle. I reduced the preloaad and ran the lathe some more last night and it's much better now. It's quieter and can be run at higher speeds without popping the circuit breaker.

Patio
Posts: 1195
Joined: Wed Oct 06, 2010 3:14 pm
Location: Centralia Wa

Re: Soft Start for Lathe?

Post by Patio » Tue Apr 30, 2019 10:48 pm

liveaboard wrote:
Thu Apr 25, 2019 5:10 pm
whateg0 wrote:
Thu Apr 25, 2019 12:45 pm
Is a GFCI breaker? I have a buddy who has GFCI on one wall and he can't start his mill without it tripping.

Dave
A friend of mine had a drill press; gfi would trip if you touched it while it was running.
So he put a thick rubber mat on the floor in front of it to stand on while using it.
Problem solved.
A bit of info:
"Kirchhoff's Current Law" states, in summary, that current in equals current out!

The simple version of how a GFCI device works is that they measures the current going out and coming back. If it all does not come back, it trips. Because if it is not coming back, it is leaking to somewhere it shouldn't and if you touch a leaking device, you may become the path to ground for the leak. GFCI devices that are used for personal protection trip at 5 milliamps. Some say it only takes 1 amp across the heart (hand to hand or hand to foot) to end you.

Liveaboard, you friend is very lucky. The leakage in the drill press, had a high enough resistance that your friend may have felt nothing. I would also have questioned whether the unit was grounded.
Live for the moment!
Prepare for tomorrow!
Forgive the past!

Post Reply