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Variable Speed Drive belts - acceptable dimension tolerance

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Adam Harris20/05/2019 16:50:16
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Although this is a general question, my specific situation regards a Hardinge HLV-H lathe. When the cost or difficulty in finding a replacement variable speed belt of an old machine is too great (in this case a US machine where the belt is still available in the US but expensive even before adding shipping cost) , similar belts can be found here in the UK and I am wondering what differences would be acceptable ie unnoticeable in use. The Hardinge belt is a 1" wide , 38" long , 26 degree sheave profile, variable speed belt . Available in the UK is a different variable speed belt 0.6 mm wider (2.3% wider), 3mm shorter (0.3%), but with a 27 degree sheave profile as opposed to 26 degree sheave profile of original. I was thinking the small extra width and shorter length would probably have limited combined impact on performance, but I was wondering if the angle profile difference of 1 degree would have a noticeable impact on smoothness of operation and of belt wear (and so subsequently smoothness of operation). Any thoughts on these dimension differences please?

Edited By Adam Harris on 20/05/2019 17:20:26

colin hawes20/05/2019 18:19:38
492 forum posts
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I would expect the belt to deform that one degree to seat in it's pullies after a running in period.

Adam Harris20/05/2019 19:34:44
388 forum posts
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Colin would the deformation process result in the outer top edge becoming hard and cracked/crusty or do you think it would deform remaining pliable ? The belt I am replacing has its outer top edge worn into a state where it is hard and cracked and I believe this is making the big noise from the variable pulley system. I'm not sure in the world of variable speed pulleys how significant a 1 degree difference is in profile of the sheave vs belt

Edited By Adam Harris on 20/05/2019 19:35:14

Ian P20/05/2019 21:42:04
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Posted by Adam Harris on 20/05/2019 19:34:44:

Colin would the deformation process result in the outer top edge becoming hard and cracked/crusty or do you think it would deform remaining pliable ? The belt I am replacing has its outer top edge worn into a state where it is hard and cracked and I believe this is making the big noise from the variable pulley system. I'm not sure in the world of variable speed pulleys how significant a 1 degree difference is in profile of the sheave vs belt

Edited By Adam Harris on 20/05/2019 19:35:14

I think that in the world of 'variable speed pulley' drives, none of the manufacturers did any significant research and testing on the effects of using the belts other than the ones they were recommending or specifying so really you are in unknown territory.

In practice 1 degree difference 'should' be accommodated by the flexibility of the rubber.

Is the noise coming from the belt contacting the pulley or is it caused by the sheave rattling on its splines or whatever. (I've never seen the Hardinge drive)

Ian P

Adam Harris20/05/2019 22:06:31
388 forum posts
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Ian it is difficult to know where the noise is coming from but it is from the area of the variable speed pulleys, and there should be no doubt that a belt that is hard and cracked (presumably from age and overheating) on the outer edge is at least a contributing factor. I think your feeling that only 1 degree should be accommodated by the flexibility of the rubber, and Colin's feeling that the belt will wear to fit the 26 degree sheave, is encouraging me to give it a go at least. My concern is that the wear process will cause overheating that results in the same hardening and cracking of the outer top edge of the pulley. The Hardinge HLV-H owner community is somewhat of a cult in my opinion and I don't think any of them could contemplate using a belt that is anything other than specified and branded by Hardinge.

Edited By Adam Harris on 20/05/2019 22:07:13

Adam Harris20/05/2019 23:52:11
388 forum posts
11 photos

EDIT: "of the outer top edge of the belt"not "pulley"

Edited By Adam Harris on 20/05/2019 23:52:30

Edited By Adam Harris on 20/05/2019 23:52:47

Hopper21/05/2019 02:36:38
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It's rubber. A one degree difference in belt profile translates to half a degree each side. The rubber will conform that little bit without issue, surely?

And your belt pulleys are ancient and worn -- and were wobbly variable pulleys to start with -- so probably not within half a degree of their original profile anyhows.

Rubber belt drives are very forgiving when it comes to issues of alignment and profile. I've run an A section belt on the Myford's Z section countershaft primary pulley with an A section pulley on the motor for several years without issue. It's rubber. It goes round and round. The motor pulley on my cheap Chinese drill press is at least a half inch out of line with the mating pulley but it has run like that since the 1990s, on the same belt.

I'd give your local belt a try. You can always splurge on the imported special later if this one absolutely will not work, which seems unlikely.

Adam Harris21/05/2019 13:09:36
388 forum posts
11 photos

Thanks Hopper - fair assumption of the existing condition of the pulley system.

colin hawes21/05/2019 18:14:32
492 forum posts
18 photos
Posted by Adam Harris on 20/05/2019 19:34:44:

Colin would the deformation process result in the outer top edge becoming hard and cracked/crusty or do you think it would deform remaining pliable ? The belt I am replacing has its outer top edge worn into a state where it is hard and cracked and I believe this is making the big noise from the variable pulley system. I'm not sure in the world of variable speed pulleys how significant a 1 degree difference is in profile of the sheave vs belt

Edited By Adam Harris on 20/05/2019 19:35:14

When I say deform I mean continually bend to wedge in its groove not wear; after all, the belt has to continually deform to go round the pullies. I have never seen the Hardinge drive but I guess it consists of interlocking pulley sides which must be hard on a belt anyway especially if the sector edges wear to be sharper. I don't claim to be any sort of expert on drive belts but just giving my thoughts as requested. Colin

Howard Lewis21/05/2019 21:32:24
1947 forum posts
2 photos

Hartridge Fuel Injection Pump setting machines, and those of other manufacturers, used expanding pulleys (with interlocking "fingers" at the smaller diameters ) to provide a variable speed drive. The early Majestic models were 5 hp, followed by the 10 hp version and probably even greater power in the later machines such as the 2500. They ran nearly all the time, with speeds being varied every few minutes, during the working day. I was never aware of belts being changed because of wear; and injection pumps cause some pretty big and sudden torque peaks each side of the actual injection point.

So, I would be surprised if a one degree difference in angle between the belt and the moving pulleys, on a drive with far lower torsional oscillations would give rise to many problems..

In contrast, my RF 25, with fixed speed ratio drive, shredded a primary belt within 6 months of hobby use, because the motor was out of line. Once aligned, the replacement belt is still going strong nearly 20 years later.

Suck it and see!.

Howard

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