17-03-2013, 07:00 PM
Hi,
Many thanks Lawrence for your explanation; I hadn't grasped that a variable pulley could be made to idle thinking it only covered a certain speed range. It's taken me a while to think about such a pulley in depth and as you rightly say a pulley with cheeks separated enough should not provide any drive to the mandrel; these cheeks will require the lower sections to be straight as in my drawing? If I can design and make such a pulley it should be a very neat solution but so far I've not seen it done even on Practical Machinist Forum; I thought adding a lot of belt slack would cause the belt to slip but I was proven wrong so I wonder what lays ahead should I tackle trying to make such a pulley and will it actually work?
Sleepless nights are OK Gary because I tend to get my best ideas in the early hours but it's good to see you giving my problem some thought. I'm pretty well advanced on the special pulley idea and believe the belt will separate the pulley cheeks; it would at first appear the belt will try to drive whilst in contact with both cheeks but having played around for many hours using a fixed or standard pulley I've reached the conclusion that if one of the pulley cheeks is allowed to move in a linear manner the belt will actually force the cheeks apart and as Lawrence says will eventually drop onto the boss thereby affording no drive? Pulling a lever though to apply pressure to the thrust bearing will force the pulley cheeks together allowing the belt to ride up to its correct operating position? It would be possible to spring load the release bearing making default in pulley closed position? I can foresee a lot of experimentation ahead of me which will prove most interesting. So far in browsing the web I haven't found a simple solution other than to use two flat pulleys with a flat belt which will definitely slip if the belt tension is released. This project is shaping up like many of my projects and is biting me.
I've given this clutch project so much thought that I'm now seeing what I want to see and I refer to the video I added in post #16. I watched this video many times and even jogged it to freeze frames; I had seen the guy pull the lever thus slackening the drive belt and stopping the lathe? I was so convinced by this I thought a "V" belt could be made to slip so I then spent many hours trying to get my belt to slip but without success. Why can't I get me belt to slip because it looks so easy in the video; the guy simply releases belt tension and the lathe stops turning?
Eyes can deceive as mine have in this case; this afternoon I spent more time watching this video and sure enough it certainly would appear the guy is stopping the lathe by pulling the lever but he isn't doing this at all; put yourself in the guy's position at the lathe and very; very carefully watch what you do with your left hand; this is so quick it's very easy to miss; the left hand switches off the motor whilst the right hand pulls the lever so what is happening? The guy is simply changing pulley speeds and nothing else; pulling the lever is not stopping the lathe but even after watching this video many times I missed the action of his left hand time and time again?
I could not understand why my lathe would not stop even with lots of belt slack; I thought if the guy in the video could stop his lathe so easily by pulling the lever then surely I could rig my lathe to do the same; I seldom take things on face value but I got badly caught out in this instance. I still have plenty of ideas to play around with but I need some decent weather as I'm sick of playing around in the cold.
I've completely removed the hinged motor platform returning the motor mounting back to standard; I sure can weld though.
Kind regards, Col.
Many thanks Lawrence for your explanation; I hadn't grasped that a variable pulley could be made to idle thinking it only covered a certain speed range. It's taken me a while to think about such a pulley in depth and as you rightly say a pulley with cheeks separated enough should not provide any drive to the mandrel; these cheeks will require the lower sections to be straight as in my drawing? If I can design and make such a pulley it should be a very neat solution but so far I've not seen it done even on Practical Machinist Forum; I thought adding a lot of belt slack would cause the belt to slip but I was proven wrong so I wonder what lays ahead should I tackle trying to make such a pulley and will it actually work?
Sleepless nights are OK Gary because I tend to get my best ideas in the early hours but it's good to see you giving my problem some thought. I'm pretty well advanced on the special pulley idea and believe the belt will separate the pulley cheeks; it would at first appear the belt will try to drive whilst in contact with both cheeks but having played around for many hours using a fixed or standard pulley I've reached the conclusion that if one of the pulley cheeks is allowed to move in a linear manner the belt will actually force the cheeks apart and as Lawrence says will eventually drop onto the boss thereby affording no drive? Pulling a lever though to apply pressure to the thrust bearing will force the pulley cheeks together allowing the belt to ride up to its correct operating position? It would be possible to spring load the release bearing making default in pulley closed position? I can foresee a lot of experimentation ahead of me which will prove most interesting. So far in browsing the web I haven't found a simple solution other than to use two flat pulleys with a flat belt which will definitely slip if the belt tension is released. This project is shaping up like many of my projects and is biting me.
I've given this clutch project so much thought that I'm now seeing what I want to see and I refer to the video I added in post #16. I watched this video many times and even jogged it to freeze frames; I had seen the guy pull the lever thus slackening the drive belt and stopping the lathe? I was so convinced by this I thought a "V" belt could be made to slip so I then spent many hours trying to get my belt to slip but without success. Why can't I get me belt to slip because it looks so easy in the video; the guy simply releases belt tension and the lathe stops turning?
Eyes can deceive as mine have in this case; this afternoon I spent more time watching this video and sure enough it certainly would appear the guy is stopping the lathe by pulling the lever but he isn't doing this at all; put yourself in the guy's position at the lathe and very; very carefully watch what you do with your left hand; this is so quick it's very easy to miss; the left hand switches off the motor whilst the right hand pulls the lever so what is happening? The guy is simply changing pulley speeds and nothing else; pulling the lever is not stopping the lathe but even after watching this video many times I missed the action of his left hand time and time again?
I could not understand why my lathe would not stop even with lots of belt slack; I thought if the guy in the video could stop his lathe so easily by pulling the lever then surely I could rig my lathe to do the same; I seldom take things on face value but I got badly caught out in this instance. I still have plenty of ideas to play around with but I need some decent weather as I'm sick of playing around in the cold.
I've completely removed the hinged motor platform returning the motor mounting back to standard; I sure can weld though.
Kind regards, Col.
Happiness is a wreck of a cabinet to restore.
