A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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

A V-belt won't work if it bottoms in the groove. This is just an undercut to
ensure there is no radius at the bottom of the contact faces.

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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.

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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?

"Den" wrote in message
...

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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.

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

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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 groove is just to make them harder to clean, of course.

The light-duty belts used in these small mechanisms typically aren't V-belts
of the common type used in larger appliances or machines.
The VCR and other belts are rarely ever cord reinforced, and belt tension is
low to barely adequate.

As Den mentioned, and I know Nigel already knows, the belts are often
square-cut in cross section (90 degree V).

The groove will allow the belt faces to completely contact the pulley drive
faces, allowing the most effective transfer of motion.
The square drive belts rarely shed (but commonly glaze), but can stay
completely seated in the pulley groove under varying conditions.

In addition to allowing full contact between the belts/pulleys,
manufacturers will do almost anything to save raw materials (the compound or
metal used for the pulleys), to save costs and to make the parts lighter.

It surprises me, the lengths that manufacturers will go to in mold making,
to save materials/resin, which in most cases jepordizes the strength or
mechanical integrity of a part (part weakness increases the chances of the
part being non-repairable or non-reuseable).

WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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

Steve Lusardi wrote in message
...
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

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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

"newshound" wrote in message
...

"Den" wrote in message
...

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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????

Den wrote in message
...

"newshound" wrote in message
...

"Den" wrote in message
...

"N_Cook" wrote in message
...
A picture of a random collection of pulleys
http://home.graffiti.net/diverse:gra...et/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

On Sat, 31 May 2008 13:05:52 +0100 "N_Cook" wrote:

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?.

It's there because it's impossible to make a pulley wiht ZERO radius
at that corner. The zero radius clearance is requuired because square
belts may come with arbitrarily sharp corners, which would keep the
belt from seating properly if there was any radius in the pulley.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
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