“V” belt anomolies

[houstonceng]

In the process of trying to sort out my milling machine drive belt problem, (subject of another thread) I measured all the belts that I had bought, had been supplied with the machine and all that I have tried. According to information, B size belts are specified by the inside circumference and should be measured on the outside circumference then specified by minus 3 inches. On this basis, my belts measure (after the 3” deduction:-

Old B34 is 33.375
New B34.5 is 33.875
Old B35 is 33.375
New B35 is 35
Old B38 is 37.875
Old B39 is 37.625
New B39.5 is 39.5
New B40 is 40.375

This accounts for the larger than expected difference between the old B39 and New B39.5 when fitted to the machine. The former being tight, the latter too loose.

Are these sort of tolerances expected on the belts, or is it bad manufacture of belts from non-UK makers ? Also, since a B size belt is 13/32 inches thick, the reduction in circumference between outside and inside is not 3”. It’s only 2.55 inches. So how do I get the correct size ?

[racinjason]

When we buy belts for work where there are 6 belts on one drive we always get them together I.E same batch to make sure they are close in length.
Cheers Jason.

[jackrae]

Jun 29, 2020 10:02:52 GMT racinjason said:

When we buy belts for work where there are 6 belts on one drive we always get them together I.E same batch to make sure they are close in length.
Cheers Jason.

If buying belts for a multi-grooved pulley you must specify a "matched set", then all belts supplied should be the same size.


Andy, have you tried using Brammer type link belts. They really are the dog's b8888cks alternative where your system requires shaft removal to fit an endless belt

[houstonceng]

I don’t need twin belts and I don’t need to dismantle anything to get the belts off.

Basically, there is a belt from the motor to an intermediate pulley and then one from that pulley to the milling machine quill pulley. As supplied, there was a 38 and a 35 combination and that was a PITA to move from one shelve to another as the adjustment couldn’t be slackened far enough. When those belts wore out, I tried various combinations and settled on 39 & 34 inch belts. My local “belts and bearings” supplier didn’t have a great stock of B sizes. I thought that changing to a 39.5 or a 34.5 would give that little extra length without running out of adjustment.

Unfortunately, the.new 39.5 appears to be nearly 2” more in circumference than the old 39 instead of 0.5”