Author Topic: FLAT BELT PULLY CONE ANGLE  (Read 439 times)

Offline Robert Hornby

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FLAT BELT PULLY CONE ANGLE
« on: July 08, 2019, 03:43:07 AM »
I have made a special belt sander for a specific job at our MEN'S SHED. The original belt size was just 12mm wide and I made the pulleys to suit (the photo shows the 12mm belt on). However there was too much flex in the narrow belt so we decided to upgrade it to a 30mm belt. The greater width allowed me to make the idler pulley crowned to keep it central. It works some of the time but not all the time. I made the crown angle 1 deg but I do not know if this is enough, my Machinery's Handbook is of no help at all. I made the main support column split so I can shim it if necessary. The 12mm belt ran very true.
So does any one know what angle the crown should be to see if that is the problem?



Robert
Age and treachery will always overcome youth and skill

Offline Ian S C

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Re: FLAT BELT PULLY CONE ANGLE
« Reply #1 on: July 08, 2019, 04:03:06 AM »
Robert, from what I can see your problem might not be down to the pulley and it's crown, but to flexing in the main collumn. I would extend at least the top shaft, and fit an outboard bearing. I would make the jocky pulley push / pull the belt in rather than out, this increases the belt wrap around, also make sure that the jocky wheel runs square, or it will throw the belt off. If all else fails, put a little rim around the edge of the pulleys/maybe just a large washer on each side, it just needs a lip a bit thicker than the belt.
Ian S C

Offline crueby

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Re: FLAT BELT PULLY CONE ANGLE
« Reply #2 on: July 08, 2019, 04:28:30 AM »
On my 1" belt sander, it also has crowned idler, but they made the idler with an adjusting screw to tip the idler in and out across the plane of the pulleys. Just a slight change on that screw makes the belt track to the side. That sort of adjutment is key. My bandsaw has a crowned top wheel, same tip arkustment for tracking.

Offline john mills

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Re: FLAT BELT PULLY CONE ANGLE
« Reply #3 on: July 08, 2019, 10:00:02 AM »
It all comes to alignment  i have worked making conveyer rollers alignment is every thing but they will crown rollers if the customer wants some people think they have to have a crown shape.I work with paper laminating machines and printing
and alignment of rollers is the most important to aviod creases and to track correctly.  the rollers must be stiff enough not to flex or bow .     

Offline Robert Hornby

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Re: FLAT BELT PULLY CONE ANGLE
« Reply #4 on: July 12, 2019, 05:01:54 AM »
Thank you gentlemen for the comments and suggestions. I brought it home from the men's shed and had a good think about it. Firstly I increased the cone angle to 2 deg each side and this improved the situation quite a lot, the belt stayed on the pulleys but not in the centre.I then removed the rubber lining on the drive pulley and reduced its diameter to give a greater lip flange. This worked very well and the belt is now running true.  :cartwheel: :cartwheel: :pinkelephant: :pinkelephant:
Robert
Age and treachery will always overcome youth and skill

Offline Ian S C

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  • Stirling Engine Maker Darfield Canterbury N Z
Re: FLAT BELT PULLY CONE ANGLE
« Reply #5 on: July 12, 2019, 01:49:07 PM »
Robert, that sounds good. My current job at the Menzshed(Kiwi version), is rebuilding the belt sander, the 2 pole shaded pole motor died, so its getting a 4 pole split phase motor(it was in the stores dept), just got to make a new belt guard to cover the larger pulley needed to keep the speed up, then wire in the motor through the switch, then see if the electrician will pass it as safe.
Ian S C