Thread: Belt Tension

If my only experience with different pulley sizes of a 1:2 ratio is anything to go by then yes it does help, although the single A section pulleys were carefully fitted and aligned too. I see if I can get a photo today of a Waldown tool post grinder, I think it uses SPZ's like Eskimo suggested to reduce flap.

While I think of it, does a four pole motor run smoother than a two pole?, i.e. they both use the same stator stampings but the windings give half the speed in the four pole, so the distance between the poles are half and the motor would run smoother too. I suppose the acid test would be a flywheel on a 2 pole motor to ease the jerkiness.

Originally Posted by Anorak Bob

There is discussion regarding the above in Mark "Graziano"s triple spindle thread but I don't want to interfere with that. My tool and cutter grinder spindle is driven by a pair of M section vee belts. Richard "Eskimo" has said that these small belts need to be tight to minimise belt slap. Belt slap appears to be the major source of vibration on my grinder. To tension a pair of belts evenly may require some sort of screw adjustment on a sub plate fitted between the motor baseplate and grinder's mounting platform. I might be overcomplicating things.

Any thoughts on ways of achieving uniform belt tension when paired belts are utilized?

Also, Hercus literature indicates that a 2 pole 2850 rpm motor was fitted. Photographs of a couple of No.3s provided kindly by Mark, suggest that the motor fitted was a 4 pole, 1440rpm. The motor pulley on the latter is about 125mm in diameter, the former, 63mm. The driven pulley is roughly 50mm in diameter.

Do pulley size ratios have an influence on belt induced vibration?

BT

All I know from a related science but not machining is that the greater the rotational diameter is of an out of balance rotating body , the greater the vibration will be , for the same out of balance mass and velocity .
I have found that a bad small pulley will be better than a bad big pulley and lighter alloy pulleys have less potential to cause vibration because of less weight spinning .
I have contemplated going to a single belt alloy motor pulley on my lathe because of slight vibration at a certain spindle speed with the steel two belt large pulley setup .
I reckon one single bigger section belt can be better than two smaller belts when the bigger section can be accommodated in the centre distance and diameters.
With two belts , one can always be looser than the other creating vibration.

Hi Graziano,
But dont you have twice as many windings at half distance?

Stuart

Originally Posted by Stustoys

Hi Graziano,
But dont you have twice as many windings at half distance?

Stuart

yes....I should have been clearer, the stamping are identical, the coils cover twice as many of the steel "pole pieces" in a two pole compared to a four pole. Come to think if it, LP record player manufacturers used to make a big deal out of the high number of poles their AC motors had, i.e. the higher number of poles the smoother the motor torque.

But its spinning half as fast so takes the same time to get from one pole to the next.. You'd also need a bigger pulley wouldnt that amplify the problem?*it also has twice the torque(?)*

No idea really, just trying to get my head around it.

Maybe 3 phase is the way to go?(or is it already 3 phase?) Although the same question could still be asked.

Stuart

Hi Bob,
Do you really need 2 belts if they are running side by side for this machine? I am just wondering as you probably won't be using it like a commercial shop would.

Dave

It sounds like the 2 pole motor needs to go back on the shelf. The grinding spindle speed of 3600 rpm and the size of the motor pulley in these photos would suggest a 4 pole motor was factory fitted. The original motor was 1/2 a horse according to Hercus's literature but it was 3 phase. I want to use single phase which may be an obstacle to smooth running.

The twin belt thing is a puzzle.

BT

Bob some of the machines I work on have twin belt's and I always replace them with a matched pair if possible, two new belts are often not the same, a bee's dick difference in length can cause problems.
Has the grinder been used previously with only one belt and worn that side of the pulleys causing different belt tensions ?
Some cheap or old belts also can get a bit lumpy if left in tension.
Lastly, are the belts power rated or Leco or cheep ?

john

Originally Posted by Stustoys

But its spinning half as fast so takes the same time to get from one pole to the next.. Stuart

But the pole coil is now 1/2 the size so it travels only half the distance in the same time .

My current project did run with about half the belt flap when running with two grinding wheels instead of one that I originally started with. The second wheel would have more of a flywheel effect on the setup and the wheel balance would change the vibration too. Maybe a large flywheel mass can help smooth the motor pulsations.

Originally Posted by shedhappens

Bob some of the machines I work on have twin belt's and I always replace them with a matched pair if possible, two new belts are often not the same, a bee's dick difference in length can cause problems.
Has the grinder been used previously with only one belt and worn that side of the pulleys causing different belt tensions ?
Some cheap or old belts also can get a bit lumpy if left in tension.
Lastly, are the belts power rated or Leco or cheep ?

john

John,

The belts are Gates. Not real cheap. I have no idea about their power rating or the Leco thingo.

The spindle pulley is worn out and requires replacement. It's covered here -

https://www.woodworkforums.com/f65/he...ulleys-151896/

How tight are the twin belts on the machines you use?

Bob.

Have you got the option of using a tension gauge?
If not a field method is twisting the belt,grab the belt in the centre between the pullies,with one or two hands and rotate the belt from the horizontal to the vertical,if it is easy to move its too loose,adjust untill you need to struggle to get the belt to twist to vertical.

Thanks Peter,

I will give the field method a go. Sounds tight.

Bob.

Bob I just read the other thread that you linked to, if you haven't rung Gate's yet maybe you should, they might save you the headaches, there could be an unlisted odd bod belt they have to suit your needs, also I'm sure that they would also be interested, or at least offer advice for the vibration and belt flap.

The matched pair belts I mostly use are a kevlar belt made by gates for the manufacturer, these are A section, with a 4" engine pulley and a 5" driven pulley, they are supposed to transmit up to 27 hp, believe it or not they seem to do the job, haha, for a while.

john