Pulley construction query

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Subject Author Date
Pulley construction query N_Cook 05-31-2008
Posted by N_Cook on June 1, 2008, 10:48 am
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>
> >
> >>
> >>>A picture of a random collection of pulleys
> >>> http://home.graffiti.net/diverse:graffiti.net/pulleys.jpg
> >>> plastic brass and aluminium for use with rubber drive bands in tape
> >>> recorders, VCRs etc. They all have a small groove at the root of the V
> >>> section of the pulley. Anyone know the function or reason for this
> >>> groove?.
> >>> All I can think of is it may avoid an aquaplaning type possibility of
> >>> air
> >>> getting trapped under the rubber band snd so wow/flutter possibiliy.
> >>>
> >>>
> >>> --
> >>> General electronic repairs, most things repaired, other than TVs and
PCs
> >>> http://www.divdev.fsnet.co.uk/repairs.htm
> >>>
> >>> Diverse Devices, Southampton, England
> >>>
> >>>
> >>
> >> Often the drive belts are square cross section rather than round and
sit
> >> neatly in the root of the pulley slot. Maybe this has some bearing on
the
> >> design?
> > Like I said, except that these pulleys all seem to be for square belts.
> > For these to work, the root radius of the pulley has to be smaller than
> > the radius of the belt corners. With an undercut slot like this even
> > perfectly square section belts will be fine.
>
> Out of interest what is the advantage of square section belts - are they
> easier/cheaper to manufacture than O section belts????
>
>

I've always assumed that it gave the best surface area and so drive force
for a given width of pulley. The contact area would remain much the same on
stretching compared to a circular belt in a circular section of pulley rim
and progressively less contact area on stretching. A circular belt in a V
section pulley would not have much contact area.
Square section belts can be made by cutting after the cyluinder is extruded
but round would have to be 2-part moulded I would have thought, leaving a
mould line.


--
General electronic repairs, most things repaired, other than TVs and PCs
http://www.divdev.fsnet.co.uk/repairs.htm

Diverse Devices, Southampton, England



Posted by Stealth Pilot on May 31, 2008, 10:21 am
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 wrote:

>A picture of a random collection of pulleys
>http://home.graffiti.net/diverse:graffiti.net/pulleys.jpg
>plastic brass and aluminium for use with rubber drive bands in tape
>recorders, VCRs etc. They all have a small groove at the root of the V
>section of the pulley. Anyone know the function or reason for this groove?.
>All I can think of is it may avoid an aquaplaning type possibility of air
>getting trapped under the rubber band snd so wow/flutter possibiliy.

more likely a machining aid during manufacture.
a V point tool cutting on both sides of the V is pretty well a
machining nightmare.
far easier to make a slot then do a single face cut out from each side
to form the V.

Posted by Steve Lusardi on May 31, 2008, 11:08 am
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The way V belts work is that they must wedge between the angled sides to
grip. If the bottom of the belt touches the bottom of the pully groove, they
will slip. Please refer to the Machinists Handbook for explanation. Please
also note that the angles are not same for all V belts, not even for
different diameters within a belt series. The angles are optimized for grip
and ease of release. The big boys make these pulley with a single plunge
cut, but the machine that do these are massive 30 ton lathes. The big
machines can cut 6, 5/8 grooves on a single plunge in iron. The rest of us
should do this in 3 operations per groove. First a plunge cut to total depth
with a parting tool and the second and third operation is to use the
compound set at the correct angle first one way and second the other way. No
stress, no pain, no chatter. Piece of cake.
Steve

>A picture of a random collection of pulleys
> http://home.graffiti.net/diverse:graffiti.net/pulleys.jpg
> plastic brass and aluminium for use with rubber drive bands in tape
> recorders, VCRs etc. They all have a small groove at the root of the V
> section of the pulley. Anyone know the function or reason for this
> groove?.
> All I can think of is it may avoid an aquaplaning type possibility of air
> getting trapped under the rubber band snd so wow/flutter possibiliy.
>
>
> --
> General electronic repairs, most things repaired, other than TVs and PCs
> http://www.divdev.fsnet.co.uk/repairs.htm
>
> Diverse Devices, Southampton, England
>
>



Posted by N_Cook on June 1, 2008, 3:34 am
Please log in for more thread options
> The way V belts work is that they must wedge between the angled sides to
> grip. If the bottom of the belt touches the bottom of the pully groove,
they
> will slip. Please refer to the Machinists Handbook for explanation. Please
> also note that the angles are not same for all V belts, not even for
> different diameters within a belt series. The angles are optimized for
grip
> and ease of release. The big boys make these pulley with a single plunge
> cut, but the machine that do these are massive 30 ton lathes. The big
> machines can cut 6, 5/8 grooves on a single plunge in iron. The rest of us
> should do this in 3 operations per groove. First a plunge cut to total
depth
> with a parting tool and the second and third operation is to use the
> compound set at the correct angle first one way and second the other way.
No
> stress, no pain, no chatter. Piece of cake.
> Steve
>
> >A picture of a random collection of pulleys
> > http://home.graffiti.net/diverse:graffiti.net/pulleys.jpg
> > plastic brass and aluminium for use with rubber drive bands in tape
> > recorders, VCRs etc. They all have a small groove at the root of the V
> > section of the pulley. Anyone know the function or reason for this
> > groove?.
> > All I can think of is it may avoid an aquaplaning type possibility of
air
> > getting trapped under the rubber band snd so wow/flutter possibiliy.
> >
> >
> > --
> > General electronic repairs, most things repaired, other than TVs and PCs
> > http://www.divdev.fsnet.co.uk/repairs.htm
> >
> > Diverse Devices, Southampton, England
> >
> >
>
>

The band used for these small pulleys are usually square cut rather than V
section but I think you have the reason for the groove.
If the square section deforms slightly to a diamond shape and a less than 90
degree corner sits in the pulley rim then you would have the same
bottoming-out effect.


--
General electronic repairs, most things repaired, other than TVs and PCs
http://www.divdev.fsnet.co.uk/repairs.htm

Diverse Devices, Southampton, England



Posted by Meat Plow on May 31, 2008, 12:49 pm
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On Sat, 31 May 2008 13:05:52 +0100, N_Cook wrote:

> A picture of a random collection of pulleys
> http://home.graffiti.net/diverse:graffiti.net/pulleys.jpg
> plastic brass and aluminium for use with rubber drive bands in tape
> recorders, VCRs etc. They all have a small groove at the root of the V
> section of the pulley. Anyone know the function or reason for this groove?.
> All I can think of is it may avoid an aquaplaning type possibility of air
> getting trapped under the rubber band snd so wow/flutter possibiliy.

I can't see any real reason for it especially in your applications.




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