HELP! Converting bench grinder to wood lathe trouble... - Woodworking Talk - Woodworkers Forum

 
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post #1 of 8 Old 03-06-2012, 04:45 PM Thread Starter
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Question HELP! Converting bench grinder to wood lathe trouble...

Hello all. Im a newbie. Not even gonna try to hide it. Just gonna describe the problem as best i can and hope someone can help me out. So here is the issue.

I have a 3450 rpm bench grinder, which i am trying to use to power a tiny, old beat up wood lathe. I have a 2 inch pulley on the grinder, and a 6 inch pulley on the lathe, running a half inch belt, but still cant get it up to power WITH WOOD ON IT. Without wood, it works fine, and gets it going real fast. But as soon as i put even a small (1 inch diameter, 10 inches long) piece of wood on it, it bogs down and wont go anywhere. My lathe looks similar to the one in this link

http://vintagemachinery.org/photoindex/detail.aspx?id=5657
except mine is much smaller and does not have any motor or anything other than the bare necessities.

I have seen others online who have succeeded in this operation, but dont know how they did. Any ideas on how to get this to work please?? Im just getting into wood turning, and even though i have not once actually done it, i love it already and cant wait to get started. Thanks all. Dave
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post #2 of 8 Old 03-06-2012, 05:25 PM
where's my table saw?
 
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RPM's

2"/x = 6" / 3450
6x= 2 (3450)
x = 1150
Edit:
Yep I had the denominator and the numberator basakwards!

Problem is a lathe needs several speeds to work correctly.
You need to look at an existing lathe or pictures to get an idea of what I'm talking about. Step pulleys, jack shafts, variable speed drives, electronic speed reducers etc. 3 phase motors on a variable speed drive.... it ain't quite as simple as you might think. Spindles turn at faster speed than large bowls. Roughing cuts need slower speeds than finish cuts. etc.

The answer to your question will only be as detailed and specific as the question is detailed and specfic. Good questions also include a sketch or a photo

Last edited by woodnthings; 03-06-2012 at 07:00 PM.
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post #3 of 8 Old 03-06-2012, 05:49 PM
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The step size up from the smaller pulley to the larger pulley affects deliverable torque. I would try a stepped pulley on the grinder, and the same stepped pulley (reversed) on the lathe (if they will fit)...like it's done with a multispeed drill press. That way you can change speeds in order to get better torque.






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post #4 of 8 Old 03-06-2012, 06:04 PM
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By your description...2" pulley on the motor and 6" on the lathe your rpm should be at around 1150 rpm no load. Is your belt tension high enough or is it slipping? This speed is only good for small diameter spindle work.
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post #5 of 8 Old 03-06-2012, 06:10 PM
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Quote:
Originally Posted by pvechart
By your description...2" pulley on the motor and 6" on the lathe your rpm should be at around 1150 rpm no load. Is your belt tension high enough or is it slipping? This speed is only good for small diameter spindle work.
Yup, 1150 rpm should be the speed.

Bill, check your math :)
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post #6 of 8 Old 03-06-2012, 08:07 PM
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Make sure the belt is tight if it slips on the pulley it won't work
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post #7 of 8 Old 03-06-2012, 08:23 PM
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I suspect part of the problem is that the grinder is underpowered. Is it 1/2 horse or 3/4. I have owned a lathe similar to that one. Ideally you need a step pulley on the motor. There should also be one on the spindle of that lathe.
For small turnings you would want to be on the medium to big pulley on the motor and medium to small on the lathe.
For larger turnings like bowls the small pulley on the motor and big pulley on the lathe. This last set up should give you the slowest speed and most power. If your motor is stopping with this set up then it is probably the motor.
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post #8 of 8 Old 03-09-2012, 03:51 PM
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Also take a look at the amps of the motor (should be on the plate).
You do need the step pulleys but IF it doesn't pull enough amps it
won't help except to lighten your wallet. Imho very minimum 5+ amps and the closer to 10 the better.

They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety. Benjamin Franklin
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