1920s model A Drive belt question

[thessler]

Hi
I have an old I think a 1926 model A but not positive.
The drive belt is old and shredding, it is a rubber cog belt with a lower cog style pulley. Not sure but I suspect this is not the original set up. The top speed for this lathe is supposed to 311 rpm. Mine is running at 525 rpm. So I’m guessing the lower pulley is to big . I will try to load a picture.
could anyone please let me know what size and style pulley belongs on this motor and size and style of belt belongs.

Thank you, Tom

 

[Cal Haines]

If you want to slow down the spindle, the motor pulley needs to increase in diameter.

 

[thessler]

Are you sure ?

 

[Cal Haines]

No, you're right. Sorry about that...

Nice pulley calculator here: https://www.blocklayer.com/pulley-belteng

 

[thessler]

Looked at a million pictures today and I now am pretty sure it’s an AA.

 

[thessler]

So I guessing no one knows what drives these lathes , no one has had to replace a belt or seen the pulley setup.

 

[michiganbuck]

Might you check to see that the motor rpm is correct to the original motor?

 

[Cal Haines]

Post a photo of the data plate on motor. Let's see what you have.

It the pulley on the spindle toothed or smooth? It seems unlikely that they would have been using a toothed belt in the 1920s.

 

[thessler]

Exactly Cal
its a toothed belt and pulley.
Im pretty sure it doesn’t belong here . I’m trying to find out what does belong on this machine. There are a million of these long belt driven machines out there but all the pictures of them have covers over the belts. I’m trying to find out what is under the cover.
Thanks, Tom

 

[Cal Haines]

Both pulleys are toothed, or just the motor pulley?

 

[thessler]

Just the motor pulley. If it was both I would just get a new belt.

 

[michiganbuck]

Still, the too-fast spindle RPM was the problem and with the toothed pulleys being rather special I would first consider the motor rpm. I would say that it will be about a 70% RPM reduction.
Another motor or a motor speed control. Router speed controllers are about $20 but I don't know if they work on a brushless motor, and a proper speed controller is about $100 to $500.
Might make a smaller lower pulley

 

[M.B. Naegle]

Given the age, I'd give it a 90% chance it was a flat belt drive before, and someone used that cog belt as a way of avoiding slipage, as the teeth will grip the smooth surface of the headstock pulley. IMO its isn't really necessary though. You can get smaller diameter flat belt pullies on McMaster-Carr for not much money, or make one out of some steel, then get a length of rubberized flat belt (if maintaining the old school leather doesn't suit your fancy) and you're back in business.

I'd bet they replaced the motor at some point and the new one is slightly faster than the old one, and the "new" cogged pulley on the motor end could also be slightly bigger than originally making it run faster. IMO, you wouldn't lose power going back to a smooth flat belt drive, provided it's set up right and you used the machine correctly. Same issue happens on small tool room lathes where they take a little too heavy of a cut, or have a dull cutter that isn't at the right height, the belt starts to slip, and their fix is to get a more aggressive belt system instead of fixing their operation. Flat belts can transfer plenty of power if you keep them clean of oil and properly tensioned.

Another thing to consider if going back to the flat belt, a larger pulley on your motor will give more surface area, better traction, etc. I'm not talking much, like just up it 1" or so on the diameter, and to correct the RPM issue, you could use a VFD on the motor to calibrate the motors RPM's. That way you can set it at factory RPM so your headstock data plate actually matches what it's putting out, but you'll have the option to give it a bump higher if a job demands. A couple hundred RPM over factory shouldn't hurt your head stock and bearings (just keep the oil can on it and monitor the temperature). You get into trouble if you're running an old lathe that used to tap out around 600RPM at the chuck and now have it up to 2500RPM.

 

[thessler]

Very good info, thank you.
Tom