Issue 4422

[Sub MandrelParticipant @submandrel]

Two thoughts on the latest ME-

 

Philip Hill questions whether or not a belt will stay on a convex pulley – well if they don’t we’ll have to write the indutrial revolution out of history! Most of the dark satanic mills used line shafting with hundreds of convex pulleys and never a flange in sight! Switching between fast and loose pulleys to engage a machine would be impossible with flanged pulleys too. Plenty of pictures of lathes with copnvex drive pulleys have appeared in ME over the years.

 

Second thought – what scale is David Bretten’s Fordson Model F tractor? My retirement project is a 1/4 scale Fordson F and I’ve made the gearbox internals and a gearstick together with some crude patterns. Now retirement is (hopefully) some 17 years away but I wonder if he can be contacted about getting some castings made from his patterns?

 

Neil

[Sub MandrelParticipant @submandrel]

Comments on this issue

[Alex gibsonParticipant @alexgibson50133]

Hi Neil,

I’m a field service engineer with Xerox, I work for the production services group repairing and maintaining large factory based printers. Most of the paper transports in these machines use belts running on convex pulleys. I can’t recall having any problems with the design of this kind of system other than worn belts and bearings as one would expect with machines handling circa one million prints per month.

 

 

regards

alex

 

[TerrydParticipant @terryd72465]

Posted by Stub Mandrel on 27/01/2012 20:53:02:

Two thoughts on the latest ME-

 

Philip Hill questions whether or not a belt will stay on a convex pulley – well if they don’t we’ll have to write the indutrial revolution out of history! Most of the dark satanic mills used line shafting with hundreds of convex pulleys and never a flange in sight! Switching between fast and loose pulleys to engage a machine would be impossible with flanged pulleys too. Plenty of pictures of lathes with copnvex drive pulleys have appeared in ME over the years……………………….

 

 

Neil

 

 

Hi Neil,

 

What memories you have stirred!

 

In a dark satanic corner of the factory where I served my time was an large old lathe which had originally been driven by line shafting. A large electric motor was substituted for the shafting but the cones of convex drive pulleys retained. The motor was mounted high on a hinged mounting to keep the tension on the flat belt, more or less where the original shafting would have been.

 

The old boy who ran it (as if it was his own property and wore a brown cow gown to distinguish himself from us mere mortals in blue boiler suits), used to change speed on the lathe while it was running by hitting the side of the belt with the side of his left fist – without looking or pausing. Low down to the left to increase speed. higher up to the right to reduce it. I thought it wonderful in my then innocent wisdom, but of course it was really the only way to change speed on a flat belt/convex pulley system, i.e. while it was running.

 

Thanks for the stirring of the grey cells, “Nostalgia ain’t what it used to be”

 

 

Best regards

 

Terry

Edited By Terryd on 28/01/2012 07:13:09

[JasonBModerator @jasonb]

Stub, the tractor is 1/4 scale and the engine actually runs, what the photo does not show is all the casting patterns that were also on display.

 

J

[TerrydParticipant @terryd72465]

Posted by Stub Mandrel on 27/01/2012 20:53:02:

Two thoughts on the latest ME-

 

Philip Hill questions whether or not a belt will stay on a convex pulley – well if they don’t we’ll have to write the indutrial revolution out of history………………………….

 

Neil

 

Hi Neil,

 

Don’t forget to write out all of the agricultural industry history too while your at it, all those threshers and balers, not to mention ‘portable’ sawmills etc with their plethora of belts and pulleys.

 

Regards

 

Terry

[maurice bennieParticipant @mauricebennie99556]

Hi there my band saw has a convex pulley drive system ,I wondered how it worked when I first saw it. ,and it is made of plastic of some sort.

Wonders will never cease! Maurice

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Neil, I used to maintain many large conveyors some of which were about a quarter of a mile long and had 30″ wide flat rubber belts, the head and tail drums which the belt ran on, were always convexed along with various snub drums associated with the drive drum, this convex was known as the crown. The drive drum was flat on some but convexed on others depending on the manufacturer. When any of the drums became worn and the crown became more of a concave, it was difficult to keep the belt tracked, as it would always climb to one or side or other. To overcome this in the short term untill a new drum could be ordered and its shaft fitted, a 150 mm or more wide band was rolled from some 10 or12 mm flat bar and welded in the centre of the drum, which gave the effect of a new crown, and thus the ability to restore proper tracking of the belt.

 

The point of the convex shape is for the forces of the belt trying to move sideways is to be balanced either side of the drum or flywheel, and thus keeping it central, as flat belts try to climb to the highest point.

 

Regards Nick.

Edited By Nicholas Farr on 28/01/2012 10:01:24

[Diane CarneyModerator @dianecarney30678]

Posted by Stub Mandrel on 27/01/2012 20:53:02:

Two thoughts on the latest ME-

 

 

Second thought – what scale is David Bretten’s Fordson Model F tractor?

 

Neil

 

Hi Neil

It does say in column 3. page 185 that it is quarter scale.

Posted by JasonB on 28/01/2012 07:27:20:

what the photo does not show is all the casting patterns that were also on display.

 

J

Hi Jason

Photo 8 on the next page does though.

 

Regards

Diane

 

[martin perman 1Participant @martinperman1]

Gentlemen,

 

I show Lister Stationary engines driving pumps and generators with flat pulleys and convex pulleys on uneven grass which means the engine and pump pulleys can be at odd angles to each other but as long as they are in line with each other the belts will not come off untill I pack up to come home.

 

Martin P

[Geoff TheasbyParticipant @geofftheasby]

Hi,

 

I have often wondered why a flat belt will stay on a convex pulley, and don’t remember ever seeing a reason why. I once was asked why by a visitor to a steam engine museum, who thought I looked knowledgeable!

 

Thinking about it, I wonder if it is because the linear speed (feet per minute) is slightly higher at the crown of the pulley, and this creates friction between belt and pulley in a direction towards the faster movement. As this happens on both sides of the belt towards the centre, it will tend to stay at the crown of the pulley.

This happens in fluids at the junction between two bodies of fluid, where a stream joins a river, for instance. The faster or more massive body drags the smaller along with it, creating turbulence. In a belt drive this will warm up the belt and pulley slightly, as well as will the overall friction between belt and pulley, as there isn’t 100% power transfer.

Alternatively, see film of the Great Red Spot on Jupiter and how it is affected by the adjacent bands of cloud.

 

Regards

Geoff

[colin hawesParticipant @colinhawes85982]

It seems to me that a flat belt stays on a convex pulley simply because it is forced to stretch to a longer length at the middle of its width than at the edges,a bit like wearing in a new pair of shoes ,so the edges of the belt being shorter than the crown means they don’t easily slide across the crowned pullies.

Colin

 

[JasonBModerator @jasonb]

It works in much the same way as a belt sander but instead of tilting the adjustable pully to one side to get the belt tracking the crown of the pully tilts both ways. So as the belt moves say to the left the change in the angle of the crown will move the belt back to the right, as it goes too far right the crown on the other side will make it move back to the left. so in the end it hovers around the middle of the pully.

 

J

Edited By JasonB on 28/01/2012 17:05:19

[Sub MandrelParticipant @submandrel]

I wonder if its something like self-sterring coned wheels on rails?

 

Neil

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