HSE advice (see hsg17.pdf on their website) is that the inner flange on grinders over 560 W should be secured to the spindle to prevent rotation. I have seen an 8″ 900 W machine whose inner flanges were not secured other than by the friction of the securing nut and, noting that it carried a “CE” sticker, wondered whether the HSE requirement had been relaxed by Europe (the HSE document mentions the possibility of revision).
I have experience of two makes of 6″ grinder both of which had the inner flange secured against rotation by a pin and this arrangement is shown as “normal” in Ian Bradley’s book “The Grinding Machine” published by MAP in 1973, although the use of a pin is at least 100 years older.
We are all aware of the danger of wheels bursting. My impression is that the captive inner flange reduces the need to tighten the nut, over-tightening being one of the known causes of wheel failure. I have as yet been unable to verify whether the requirement has indeed been waived by Europe or what the reasoning for such a change might be. Any comments would be welcome.
All this might seem rather theoretical – we just want to sharpen the tool and get back to cutting metal – but it should certainly concern anyone thinking of buying a new machine. Grinders are sometimes designated as “offhand” but we probably should not be!