Subject: Loose Motor Pulleys

From: David Carson <[email-masked]>
Date: Tue, 11 Feb 1997 03:31:12 -0500

I have experienced difficulty in being able to keep drive pulleys
mounted firmly on their motor shafts.  In both cases (Taiwan and Chinese
Machines) the pulley is held onto the squared-key shaft by an Allen
screw of sufficiently small size that it is difficult to get a real
tight purchase on the screw via a conventional Allen wrench.

In other words, I tighten 'em, and they come loose. I haven't tried
locktite yet, but will.

Any other suggestions?

Thanks in advance.

Kit

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From: [email-masked] (Stev)
Date: 12 Feb 1997 12:55:53 GMT

In article <[email-masked]>, [email-masked] says...
>In other words, I tighten 'em, and they come loose. I haven't tried

Run a helicoil in it and go up a size. Get a new screw, it may be rounded,
maybe your wrench is rounded too. And do use blue locktite. If theres
only 1 screw, drill and tap another one 90 degrees away.

stev

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From: [email-masked] (John Paquay)
Date: 12 Feb 1997 18:20:49 GMT

>In other words, I tighten 'em, and they come loose. I haven't tried

A common method of locking in a set screw is to add another screw on
top of the first, wedging the two together against the tapped threads.  It's
a good solution, and good insurance if you have enough thread available
to add a second screw.  Either way, Locktite will work.  Do go through
whatever trouble you need to to assure that the screw is as tight as possible.

-- 
John Paquay
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http://www.physics.purdue.edu/~jep/
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From: Dave Druckerman <[email-masked]>
Date: Wed, 12 Feb 1997 13:56:21 -0700

> In other words, I tighten 'em, and they come loose. I haven't tried

Fundamental questions - 

a)  how well does the pulley mate with the shaft?  Is there a lot of
play when the set screw is loose?  If so, this needs to be fixed first
or you'll be continually having this problem and may even damage the key
(okay, they're replaceable) or the shaft (big bummer - replace the motor
or tool depending on which end of the belt the problem is on)  If the
shaft measures okay to a standard diameter (1/2", 5/8", 3/4", etc.
probably +.000/-.001) but the fit is loose, get a good new cast iron,
machined pulley.  

If I'm remembering correctly, a company named Browning makes cast iron
pulleys that use a collet-like arrangement that grips the whole shaft
instead of the set screw.  I'm not sure if I have the manufacturers name
right.  Go to a local industrial supplier and tell them what you're
looking for.  These distributors typically get categorized in the Yellow
Pages as sellers of hydraulic hoses & pumps, belting, motors, chains,
gear reducers, and the likes.  When I was making a log splitter some
years back, I got a 10" double row cast iron pulley using this collet
like arrangement for gearing down the pump (had a 15 hp pump that I
wanted to drive with a 5 hp motor).  The collet arrangement gives a
couple of advantages - all of the torque isn't taken by the shear force
on the key, eliminating your loosening problem, and there are collets
for many different sized shafts so that the distributor can easily have
all sizes in stock (don't have to worry about having the right
combination of pulley and shaft size, you select each seperately). 
Seeing you're at RPI, you're in luck as there are a lot of good
industrial supply companies in the Albany-Troy area.  I got mine from an
industrial distributor in Poughkeepsie when I lived there.  Out here in
CA, they're fewer and farther between. 

b)  Is there a significant amount of vibration / imbalance that is
creating a pounding on the key and setscrew?  This will loosen the screw
for sure.  This may also be solved by replacing the pulley as described
above.  (As you may be able to tell, I was trained as a mechanical
engineer at RPI, and I hate designs that use a single set screw to
secure a pulley.)

c)  Are the pulleys coplaner?  If not, then the belt tension will have a
vector acting along the axis of the shaft, trying to pulley off of, or
further on to, the shaft.  Have to fix that or the problem will keep
coming back.  

Options I can think of if you are having none of the above mentioned
problems:

1)  Use allen screw that has the type of tip that digs into the key (if
it doesn't have one already)
2)  Drill and retap for larger allen screw (usually pretty easy, use the
machine shop in the basement of the Johnson Engineering Center if its
still there - I'm an alumnus, class of 1983)
3)  Use a locking style allen screw (nylon insert in the side).  I seem
to remember that these exist in one of my industrial supply catalogs.  
4)  Use allen screw with nylon tip which should lock better onto the
key  (not so sure how well this one would work).  
5)  Lastly, if the problem is just a matter of the screw loosening due
to loose threads, then the Loctite-type solution should work.  

Enough rambling, pontificating, etc.  

Dave Druckerman

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From: [email-masked] (Mark Popp)
Date: Thu, 13 Feb 1997 16:26:35 GMT

>>In other words, I tighten 'em, and they come loose. I haven't tried

Is what I would do is drill and tap for another setscrew 90
degrees on the shaft from the first one.  Heavy duty pulleys
often come this way, (setscrews at 12 and 3 o'clock, 
or 12 and 9).
Mark P.

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From: [email-masked] (John K. Warsaw)
Date: Fri, 14 Feb 1997 14:17:29 GMT

Sometimes simply replacing the set screw helps.  The tip is supposed
to be sharp enough to dig into the shaft and lock the screw, but if
the tip becomes dull, the screw won't lock.  If you compare a new set
screw with one that has a habit of working loose, you will see the
difference.

Yes, this does sound too easy.  That's what  I said when I first heard
it.  But it has worked for me more than once, and if it doesn't solve
the problem you're not out much!
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