Posted By Chris Jerman Brain, sorry that there has been a distinct lack of replies on this one. I would suggest contacting a principal manufacturer on this - someone like Universal Abrasives or Flex-o-Vit. My background (some while ago) actually was with abrasive wheels and we used blotters not to spread the clamping pressure as you put it but to even out the rough texture of wheels and discs to prevent slipping and subsequent damage to the flange face - I guess that they amount to the same thing in practice. I don't recall ever having seen that they were an absolute requirement in any particular application. Perhaps you be so good as to give us the benefit of your findings once you find an answer. Good luck. C

Posted By Chris Jerman Well there you go, nice one. C