SB13 Flat Belt Slips Off Under Heavy Load

DanMc77 · Feb 22, 2018

On my 13" machine if I put a heavy load on the spindle, the belt will shift over to the left and flop off the step. The belt seems snug enough, but I can hear it slip a little bit as it flops off. This is one of the green belts that's glued.

What to do?

It could be as simple as adding a little more tension to the adjuster, or maybe putting some belt dressing on the underside of the belt, or is there something else that you would do?

fusker · Feb 22, 2018

I believe this is an inherent weakness with flat belts. Its often a problem when starting, We had to install an electronic soft starter.
I suppose you can't use vee-belts and sheaves at your SB? (yes, I know this is probly a silly suggestion, I'm not familiar with SB, but still - just my .02 euros).
Try your other suggestions first, they may well work.
fusker

toolnut · Feb 22, 2018

I have a 14.5" South Bend with the green belt and have never experienced any belt problems and I have cut 0.250 of the diameter on hot rolled steel.
I suspect you might have a pulley alignment problem or a damaged belt. It is worth investigating before making any drastic changes.
Bruce

Blob · Feb 22, 2018

I had a similar problem with the green belt on my 10K, which was caused by oil getting on the belt and pulleys. I couldn't figure out where the oil was coming from so changed over to a serpentine belt which fixed the problem. You might want to check and see if your belt has oil on it - I found that when the belt got oily it was near impossible to completely remove it, and believe me I tried everything other than a blowtorch. As stated previously it could be misalignment, but I'd suspect oil.

johansen · Feb 22, 2018

Tilt the counter shaft so the belt tends to rub the other way.. it might not slip off in the future.. at the cost of rubbing continuously.

The crown of the pulleys on my sb9 is not symmetrical, which may help it slip off, I'm not sure but its not worth my time to re-cut the pulleys because it only slips off when I stall the spindle. come to think of it this might actually be an intentional design feature.. the belt will slip off the pulley when stalling rather than slipping off in the other direction towards the next larger pulley.. which could theoretically cause the belt to jump to the next larger pulley which could break the belt or worse.

If it is slipping off under load very slowly then I would suggest increasing the tension. presumably the slip should be less than the natural tendency of the belt to ride the largest diameter of the pulley. if the slip is more, then it will fall off.. (far as i know) :leaving:

DanMc77 · Feb 22, 2018

There’s no oil on the belt. It’s totally dry.

iwananew10K · Feb 22, 2018

Try LESS tension.

Tony Quiring · Feb 22, 2018

The pulleys should be crowned and belts naturally climbing to top or center.

If shafts not parallel it could cause this.

Our 14.5 does same with heavy cuts and just have not taken time to fix it.

Real heavy work goes in the L&S 16

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

moonlight machine · Feb 23, 2018

DanMc77 said:
On my 13" machine if I put a heavy load on the spindle, the belt will shift over to the left and flop off the step. The belt seems snug enough, but I can hear it slip a little bit as it flops off. This is one of the green belts that's glued.

What to do?

It could be as simple as adding a little more tension to the adjuster, or maybe putting some belt dressing on the underside of the belt, or is there something else that you would do?

It's a light weight lathe made for light work, Monarch, L&S and LeBlond are a few brand names that will do 10x the work of a SB. I thought my 16" SB was pretty awesome till I used a real lathe.

ja762 · Feb 23, 2018

moonlight machine said:
It's a light weight lathe made for light work, Monarch, L&S and LeBlond are a few brand names that will do 10x the work of a SB. I thought my 16" SB was pretty awesome till I used a real lathe.

No offense, but was there a point to your post besides criticizing Dan's machine (and the rest of ours for that matter)?
This is a section where SB owners can share tips and info to make the most of what they have. We understand our machines aren't capable of what a Monarch 10EE is. Many of us don't have the space, and can't justify the cost, of buying a "real" lathe, so I guess we'll just have to make the most out of our toys.
If you have any useful tips they're certainly welcome and appreciated, though.
Peace, out.

Dobermann · Feb 23, 2018

Or.....perhaps a lighter cut or reduced spindle speed. A South Bend lathe is never going to win a "rate of metal removal" race. Trying to force it to do something it was never intended to do is just going to end up with frustration.

GenePoole · Feb 23, 2018

Is you belt joint straight? I avoided the green (Al Bino) belts as I'd seen a few that wandered a lot on the cone pulley due to the joint not being straight. When I finally broke down and bought a new green belt, I made a jig from aluminum to ensure proper alignment.

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DanMc77 · Feb 23, 2018

Moonlight: Actually, I was asking about how to address this belt issue, not what other lathe is better. Maybe in a few years I’ll be looking to upgrade again, but for now I don’t want the belt flopping off on a heavy cut.

spitfire_er · Feb 23, 2018

I had the same issue until I TIGHTENED the belt a little bit. There are instructions out there on setting the proper belt tension on just about every SB lathe. I have the original paperwork somewhere, but I would need to find it.

Servicar rider · Feb 23, 2018

I had this problem on my heavy ten. Got really frustrated with it, even knurled the spindle pulleys which didn't help. The local machinery dealer (long gone) sold me a plastic belt with a leather face and that cured all the slippage issues! That was 30 years ago and the belt is still on the lathe. Today I would do the serpentine belt conversion that others are using. MAybe the leather faced belts are still available? Mine came with a special glue for the joint

steve-l · Feb 23, 2018

I suspect you have a countershaft problem. parallelism is essential with flat belt drives. If the driven and driving pully shafts are exactly parallel, the crown on the sheaves will automatically center the belt. If you have lost parallelism because of say a bad shaft end bearing, bad mount or a distorted/worn belt, the belt will slide off. The symmetry of the pulley crown is not significant. Any crown will do nicely.

Servicar rider · Feb 24, 2018

The original pulleys are crowned and its unlikely the alignment is off the way the drive is made. The problem is the belt stretches under load and you get slack opposite the load and the belt slides off. Thats why the belt I mentioned above was a huge improvement over a standard unreinforced leather belt and why the guys who went the surpentine belt route love them. South Bend built a good machine other than the lousy stretchy belt.

Servicar rider · Feb 25, 2018

I did a little research this morning. It turns out that the belt I bought years ago is whats called a polyamide belt and still available from several sources with a variety of uses. Hope this helps?

GenePoole · Feb 25, 2018

Servicar rider said:
I did a little research this morning. It turns out that the belt I bought years ago is whats called a polyamide belt and still available from several sources with a variety of uses. Hope this helps?

Polyamide is the fancy name for Nylon FWIW.

steve-l · Feb 25, 2018

Servicar rider said:
The original pulleys are crowned and its unlikely the alignment is off the way the drive is made. The problem is the belt stretches under load and you get slack opposite the load and the belt slides off. Thats why the belt I mentioned above was a huge improvement over a standard unreinforced leather belt and why the guys who went the surpentine belt route love them. South Bend built a good machine other than the lousy stretchy belt.

How do you know the shafts are not out of parallel? It's an old lathe, wear occurs, things loosen. Flat belt drives have been in successful use for hundreds of years regardless of belt material. I find it amazing people think new is always better or a substitute for good maintenance.....it isn't. Yes, new belt materials can add durability for sure, but his drive is malfunctioning. Checking the parallelism of his countershaft is absolutely the first thing to check......it's quick to do and free.

SB13 Flat Belt Slips Off Under Heavy Load

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