Richard A Downing explained :
But now I need a new grinder. Is it worth buying another sub-20 GPB
grinder or should I get a 60-70 GPB industrial unit? If so which
model? I still have lots of 115mm/22mm Norton cutting disks left that
I'd like to use up.

If you intend regular use for the grinder (cutting up more tanks) then
pay the price for a good quality one, otherwise a sub £20 (sub £10)
will be quite good enough. I've had a couple over the last ten years,
the first got lost and the second is still working fine. 115mm was far
too small for that use anyway and even the best would suffer.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk