What's new
What's new
By:
Advanced search…

Southbend 9 A - zero torque except on back gears! Can hardly run a 19 thou cut

Savedbygrace77

Savedbygrace77

Aluminum
Joined
Jul 15, 2018
Hi all - so ive been familiarizing myself on the southbend since I picked it up 2 years ago.. ive learned alot but am still super green..

Embarrassingly ive noticed I am unable to make a cut without using the back gears - ive disabled the gearbox, everything is lubed and oiled- without back gears I cant even dream of even a 5 thou light cut unless I feed in pulses to give the chuck time to speed up- its beyond pitiful..

Ive tried the 2 slower speeds on the belt, ive cleaned the pulleys and currently using a ribbed v-belt I sewed to length.. I can hear the motor just laboring with the slightest of cuts / feed-

Is there a way to test the motor? Could I put new brushes in and check the armature? Weak magnets?

Option 2 is buy a late style servo motor and convert (with digital rpm and control knob) -

Thoughts?

Im sure this lathe is quite capable but Im pretty sure the motor is way under performing-

fwiw - im turning alu and steel anything from 2 inches thick to 8" wide spacers, I basically have to use back gears ALL the time to get anything out of it-
 
this is the current motor plate - I guess i should remove it and go through it? My friend rewinds motors and works on them-

southbend-9a-motor-plate.jpg
 
What horsepower motor are you currently using? I'd go with 3/4 to 1 myself. I put a 1-3/4HP motor on my unmentionable lathe about 30 years ago, according to posts on here that should have wrecked it, strangely its still working.

If you can get it rewound at friend pricing it might be worth it, but your still stuck with 1/2hp. Is there a run capacitor? If so maybe its time for a new one.
 
The question IS what motor is on there now ? Would be very unlikely your current motor has either brushes or magnets. 1hp motor is a bit big as SB's are limited by the flat belt for power transmission even with your ribbed belt.
 
Being that is a duel voltage motor it IS wired for the voltage you are using? I would think a 1/2 HP capacitor start and run motor would be the correct one for that lathe. As I said earlier SB's flat belt drive is somewhat self limiting as to the amount of power you can use. Get your friend to check the motor out -correct voltage -capacitors -etc.
 
There is no way that you should stall a 1/2 hp motor taking a reasonable cut with a correct tool bit/insert.
Taking a .100 at a fast feed rate with a negative or dull bit/insert might.
Belts slipping is common but likely you would see that.
Sounds like your motor is not putting out 1/2 hp
I dont see a problem going to a 3/4 hp
 
Cap start induction motor. No magnets, no commutator, no brushes. Just a start capacitor, start winding, centrifugal switch and two run windings. That's about it. 1/2 horsepower is suitable for that size lathe. Much more and the flat belt will slip.

Check for drag in the drivetrain by hand. Then inspect the motor. Verify correct connection for your system voltage. Check continuity of both run windings to ensure one hasn't failed open. Measure motor current in loaded and no-load states & compare to nameplate FLA to confirm. If you're pulling 1 amp no-load on a 7 FLA motor then it's surely connected wrong. Generally no-load current for small induction motors is between 40-110% of FLA.
 
Sparky hit it all.
My or any 9A will cut just fine with 1/2 hp until the belts slip.
Now if you're trying to cut on something 3-5 inch diameter yeah, you're going to need .020 deep cuts. Because the belts will slip, not because the motor is overloaded and being dragged down. *If you're losing a lot of rpm it will likely go back to the start winding which will burn up the motor.
 
Thanks sparky will pull motor and go through it-

Here is a pic of the cabinet (i did post the plate in my 2nd post).. Leaving on a trip wed so will probably only get round to it later this month. Is there a new motor equivalent I could buy off ebay with a dial speed control.. would be nice to not have to mess with belts.

southbend-lathe-motor.jpg
 
Grace, just something for your mental notes if for some reason you do replace the motor, be sure what you buy will fit in the cabinet while aligning the pulleys. There ain't much room in there. My 9" is also an undermount and uses a 56 frame 1/2 hp motor.

What comes standard on these is called an instant reversing motor. These will allow you to hit the switch to reverse while running and the motor will do just that. Otherwise the motor has to coast to a stop before it will reverse. Not 100% necessary but a nice feature such as if you're tapping and have to act quickly.
 
I think the belt is on backwards

Savedbygrace77 said:
Thanks sparky will pull motor and go through it-

Here is a pic of the cabinet (i did post the plate in my 2nd post).. Leaving on a trip wed so will probably only get round to it later this month. Is there a new motor equivalent I could buy off ebay with a dial speed control.. would be nice to not have to mess with belts.

View attachment 326273
Click to expand...

I believe the consensus is that the ribs should be against the pulley.
If you have enough tension on the belt so that it doesn't slip on the flat side you may be loading the bearings to the point where the oil film breaks down.

Agree with speculation that the motor may be wired for 240 and running at 120.

If you are cutting 2" or 8" diameter as your post suggest you will need to be in back gear. More information on the diameter you are cutting and the spindle speeds you are running would help us.

Best of luck.
CarlBoyd
 
I think John Evans was pointing you in a possible direction that needs to be confirmed. Over on OWWM it has been seen time and time again where someone improperly wired a 110v plug for 220v and vice verses. Your complaint is exactly what would happen if it was wired for 220 and you are trying to run it on 110v. You could have a 1 HP motor wired for 220 and plug it into 110v and could just about stop the shaft with your bare hand.Check this carefully and confirm beyond any doubt.
 
Take pictures of the wiring before you pull the motor. Use a Brady booklet to label the wires if they're not color-coded. Saves headaches later. Even if the connections are wrong you'll at least have some idea of what's going on in there instead of just four red wires (and possibly an equipment ground depending on it's age). Reversible cap-start motors are usually powered by two fixed polarity conductors for the run windings and two reversible polarity conductors for the start winding.
 
This is either the dumbest or the smartest question on the site. When you put the lathe into direct drive, are you engaging the drive pin on the bull gear? To make sure the pin is not sheared off, if the pin is in and the back gears are engaged, the spindle should lock up.
 
Thanks for the info guys - ill check the wiring once I get the motor out.. The old timer I bought it from had couple of lathes the size of my house and the ol southbend was tucked away in a corner - who knows what they used it for byt someone prob tried self wiring it as mentioned and messed sth up -

soon as I have it on the bench ill post pics and so forth!
 
Bob Leistner said:
I think John Evans was pointing you in a possible direction that needs to be confirmed. Over on OWWM it has been seen time and time again where someone improperly wired a 110v plug for 220v and vice verses. Your complaint is exactly what would happen if it was wired for 220 and you are trying to run it on 110v. You could have a 1 HP motor wired for 220 and plug it into 110v and could just about stop the shaft with your bare hand.Check this carefully and confirm beyond any doubt.
Click to expand...

Is it possible to correct this with the motor in the cabinet? ie without pulling the motor? I try see if I can get in there 2moro possibly and access the motor wiring- if not I guess ill have to pull that thing out of there-
 
Easiest test is checking motor current. Requires no removal of parts. Hell, I could probably tell you blindfolded if it's wired correctly just by listening to it start up if you upload a video.

As long as you can access the motor termination box effectively you don't need to pull the motor. SB was kind enough to include not one, but three access panels on their UMD lathes to facilitate maintenance like this. Your motor is too small to have a pickerhead, so pull the inboard side access panel and you'll see an integral wiring box built right into the rear end-bell of the motor.

Century motors of this vintage often have wiring diagrams nailed to the outside diameter of the frame - kind of a pain in the butt to read when installed in a lathe. But you might get lucky and have one stickered to the inside of the termination box cover instead.
 
You must log in or register to reply here.

Similar threads

M
AXA or 0XA for a South Bend 9" (Model C I think)
2
Replies
33
Views
2K
MrCreosote
M
N
Southbend and Hercus 9” DRO Install
2
Replies
31
Views
1K
M.B. Naegle
M.B. Naegle
R
Cutting gears on a shaper
2
Replies
23
Views
2K
rustyiron65
R
8
Mysterious wire break on Agie EDM main cut
Replies
2
Views
165
michael.guzzi
M
Savedbygrace77
Van norman boring bar - struggles around 20 thou cut?
2
Replies
21
Views
3K
JoeE.
J








 

ABOUT PRACTICAL MACHINIST

With more than 10.6 million unique visitors over the last year, Practical Machinist is the most visited site for metalworking professionals. Practical Machinist is the easiest way to learn new techniques, get answers quickly and discuss common challenges with your peers. Register for the world’s largest manufacturing technology forum for free today to stay in the know.

Learn more about us.

STAY CONNECTED

Facebook Instagram YouTube LinkedIn Pinterest Twitter Tiktok

Register Become a forum member. Register today.

Sign Up Sign up for our e-newsletter.

© 2024 Copyright Practicalmachinist.com. All Rights reserved.

Back
Top