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3rd Jun 2020, 09:42 PM #1Golden Member
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- Apr 2009
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Harrison M250 Motor Belt Problems
When first acquired, the motor pulley had problems and a new pulley made.
Several years have passed with great performance from a VFD.
Recently, I occasionally get 'bump' noises.
Investigation reveals the 'bump' is associated with the belt.
I can initiate the bump by leaning on the motor to increase the belt tension.
The tension adjustment is one-way only using a pivot shaft and jacking screw, so easy to lean on it to increase then tension.
It seems to be associated with the belt passing around the motor pulley, always the same part of the belt.
The belt appears to be constant in section and appearance throughout its length.
Do belts have localized stiff areas that flex differently to the general belt performance ?
Tomorrow, I will increase the belt tension, check belt details and order a spare.
This post is just a general inquiry for any suggestions of specific inspection, test or investigation aspect that might be followed.
Keep well,
John.
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4th Jun 2020, 06:08 AM #2
Hi John, Guys,
When I did the bandsaw refurbishment, because I made a new motor mounting plate, I needed a new slightly longer belt. I got one that was intended for a car water pump. From new it had a lump in it. I later bought a Fenner belt and that runs perfectly smoothly.
I cut the water pump belt up and found that they used a round cloth like dowel to make a join, this bit of the belt is fatter than the rest of it and caused a bump and also caused the motor to kick each time it hit the pulleys.Best Regards:
Baron J.
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4th Jun 2020, 08:33 AM #3
Hi electroseam,
Could it be from the lathe sitting inactive in the cold weather for a time?
The belts, like the tires of a car that has sat around for a while, take on a shape and its noticeable when the car is driven.
Is a similar thing happening with the lathe belt ?
Perhaps not flat spot like the car, but basically,the belt taking on a a semi permanent new shape .
Time will tell perhaps when you obtain a new belt and fit it.
Grahame
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4th Jun 2020, 08:50 AM #4Mechanical Butcher
- Join Date
- Oct 2004
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- Southern Highlands NSW
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When the replacement pulley was made, did it take into account its diameter?
As I understand it, there are different V angles suggested, according to how much the V-belt is to bend around the pulleys.
The cross section shape of the belt does not remain constant, but changes as it bends, the more so the greater the bend.
You might get better performance with a different belt, such as one of those that have notches, which I think help maintain their shape.
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4th Jun 2020, 09:01 AM #5Most Valued Member
- Join Date
- Nov 2017
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- Geelong, Australia
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Thanks Nadroj - one of those snippets that's only obvious once you know about it.
Its going to be a good day - only 8am and I've already learned something.
Steve
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4th Jun 2020, 10:53 AM #6Golden Member
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- Sep 2008
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- Riddells Creek, Vic.
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4th Jun 2020, 02:46 PM #7Most Valued Member
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- Nov 2017
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- Geelong, Australia
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Sounds like you're thinking the degree of wrap is involved, but its only the diameter that controls the angle.
I'd always thought they were just a tolerance, but a bit of research online turns up consistent info that smaller diameter pulleys need to be at the smallest angle (34deg for an 1.5" A section) and then increasing up to 38deg for 7" diameter and over.
Steve
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5th Jun 2020, 10:03 AM #8Golden Member
- Join Date
- Apr 2009
- Location
- Kingswood
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- 930
The belt taking a set overnight in cold weather will be checked.
Pulley size and shape was carefully considered before manufacture and, as mentioned in the first post, the belt has performed faultlessly for a few years.
The belt does have notches at the bottom.
Inspection does not reveal visually any variations in the belt but, a DTI picks up a sideways bulge as the belt tracks past the DTI (slowly !).
A chalk mark at the 'bulge' coincides with the 'bump' as it passes around the motor pulley.
One can also see the belt track higher up the V groove as the 'bulge' goes round.
A new belt will be purchased but, progress will be slow as are other projects are keeping me busy, and the lathe is usable.
John
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