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I've unboxed a new blade for my circular saw, (I've had the blade for a while so can't take it back but it's the first blade replacement I've come to do.) to find that the blade has reducer rings to step the 30mm bore down to the 16mm spindle.
The clamp/arbor? that sits over the blade is however only 31.75mm wide, so while the press fit reducer will hold the blade central the amount of arbor that clamps the actual blade is a ring of 0.852mm around the rim.
Is this normal, or pushing ones luck?
no good - blade could slip and may damage arbor and clamp
I am not an expert , but I do not see how the blade could slip. Yes you are only "trapping" it by 0.852 mm all round, but the reducer is a tight fit in the bore ( you have to tap that bad boy in with a hammer - should be a press fit.
What brand of saw do you have ?
Friction is proportional to clamping force, not contact area. So the key point is whether the reducer ring is thinner than the blade. If it's not, most of the clamping force will be stopping the reducer ring spinning, which isn't helpful. But if you want to be safe, I'd ask the blade manufacturer.
I use these https://www.axminster.co.uk/blade-reducing-bushes-ax23230
They are finely ground to a precision fit , I use the 15mm version - thats proper oddball arbor size
they work on my saw because the clamps are big enough to grab plenty of the saw blade plate , the size reduction is only for radial force , the clamping force is being challenged by the motor .
So you either need to buy a 20mm bore blade and reducer - not so easy - a 16mm blade - or have some
wider clamps made up - its a pain but you need to do it properly.
Do not use it.I had the same set up many years ago and the blade became loose while I was using it.Now I only buy blades with the correct dia. centre.