Grinder - burr runout?

[grchif]

'Lo,

Not sure if I be in the right forum, but here goes - anyone know what an acceptable level of axial and radial runout might be on the burrs of one's 63mm espresso grinder thing?

I've been concerned at the amount of wobble about my axes for some time when I peer down my throat, so to speak . The nut in the middle oscillates by a noticeable amount, so it does.

So, tonight I thought I'd dig out the dial gauge and measure it. I get around 0.03mm axial and radial, which is better by far than it looks (nut head seems to be machined off centre but the thread in the burr carrier is much better), but I don't really know what it should be...

Anyone have any ideas, or am I talking out of my doser shute?

Colin

[lukas]

The axis of Bruce's Cimbali Junior grinder that's still with me also wobbles a tiny bit when it is run 'dry', but the quality that came out of it was without doubt really good. If the coffee tastes good and the grounds look good, I wouldn't worry too much. After all, it's italian built

[P.B]

the nut in the middle seems to have no relationship to the axial position / runout of the burrs in either my Macap M4 or my Mazzer Mini-E. Both machines appeared to have that "wobble" (moreso the Macap) but the burrs worked fine.

[bruceb]

Since grinders can get quite warm when running a long time there must be a certain amount of play in the bearings. When they are under load (grinding beans) this plays no role whatsoever, beyond the fact that the grind may change slightly when hot. If enough wobble was present the burrs would touch on one side of the rotation. You would not like the noise they made if that were the case.

[grchif]

Thanks Lukas and P.B. Bruce. I agree with both of you, though being an engineer-type would still like to know the numbers if anyone has 'em.

Some searching of H-B seemed to imply that a Versalab M3 has 0.005" runout as a radial spec, (which given it's not a flat burr would probably translate into a similar axial runout for a flat burr), and some analysis if grounds they did showed particle sizes up to 200microns which is appreciably larger than the runout I have, and the coffee is good, so maybe I'll just pretend it isn't there and not worry about it

Colin