SB9 V pulley question

Roberti · Apr 12, 2021

Hello all,
First post here. I inherited a SB9a from my late father some years ago that he used it at his company. It was complete except for the countershaft motor assembly; headstock has the V belt pulley installed. I've acquired the motor mount assembly from ebay but I cannot locate just the V belt step pulley for the shaft as they seem to be only sold in pairs.

Where can I source just the V pulley for the countershaft?

If the pulley is difficult to find what are the drawbacks to just having a single pulley on the countershaft and run it by VFD for speed control?
If I go the single pulley route on the shaft what size diameter would be recommended?

Thanks for your advice.

tommy1010 · Apr 12, 2021

Since the countershaft pulley is the exact same size as the headstock pulley only reversed from each other I would have a pulley on the counter shaft for speeds that don't make you run the motor to slow for long periods of time. They tend to overheat on low rpms. The countershaft is usually 7/8" in diameter. You can try different size pulleys for optimum speeds and even make them movable since they are single pulleys and have a few options. Single pulleys are cheap and you don't have to match the original exactly because you will have the VFD. Maybe even a RPM gage on the headstock.

Roberti · Apr 12, 2021

Thank you. Good advice on the low rpms. Didn’t think about that. I do plan on putting a tachometer on the headstock. The 7/8 shaft proved difficult in finding a 4 step pulley from suppliers.

lucky7 · Apr 12, 2021

Would suggest finding or making the four step pulley as original had. I run a 1/2 hp motor on mine and find it far superior to the flat belt version. Broader speed range, deeper roughing cuts possible, can use positive carbide. Don’t understand why SB continued to make flat belt 9” lathes (and 10K) when the v belt was so superior.

Wouldn’t suggest a single pulley at back vfd set up.

Glad you were able to keep your Dad’s lathe.

L7

Roberti · Apr 12, 2021

lucky7 said:
Would suggest finding or making the four step pulley as original had. I run a 1/2 hp motor on mine and find it far superior to the flat belt version. Broader speed range, deeper roughing cuts possible, can use positive carbide. Don’t understand why SB continued to make flat belt 9” lathes (and 10K) when the v belt was so superior.

Wouldn’t suggest a single pulley at back vfd set up.

Glad you were able to keep your Dad’s lathe.

L7

Ideally I would like the step pulley to keep the lathe as original as it also has a lot of the sought after items from the factory. My problem is finding it as I've been looking for some time with no luck for just that one pulley. Plus I don't know enough to make one. *sigh*

bugman53 · Jan 2, 2022

A flat pulley with a serpentine car belt is hard to beat for smooth running. With a VFD no need to have 4 speeds on the counter shaft. You might find a set of flat pulleys cheaper and sell your v belt pulley to offset the cost.

If you want to get it up and running a couple cast iron pulleys from TB woods ect are not to expensive. and you could set up 4 on the counter shaft if you have room. Or just 2 with a VFD and a 1hp motor would give you plenty of speed range and torque.

dalmatiangirl61 · Jan 2, 2022

McMaster has 4 groove step pulleys with 3/4" bore, ream it out to 7/8"? No idea if diameters match the headstock pulley.

tobnpr · Jan 3, 2022

I don't see where you mentioned it, there's also a two-step pulley for the motor belt, which provides these with 8+8 (backgear) for 16 speeds.

comstockfriend · Jan 6, 2022

Two of those 16 speeds are not recommended by South Bend, they exceed the recommended back gear speed.

SB HTRAL Speed Chart, Edition 56, 1966.jpg

John

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