# Burr Adjustment Thread Size



## VernS (Aug 26, 2017)

Most hand grinders utilize a centre burr shaft thread to adjust grind size. Because the shaft diameter and thread size can vary between manufactures and models direct comparison of grind size or burr rubbing is difficult.

Somewhere I read that my Aergrind has a smaller diameter burr shaft than the Feldgrind and therefore a smaller adjustment per turn. Does anyone know how the shaft thread size and diameter compare?

It would also be interesting to have these dimensions for other high end manual grinders. If the grinders use different burr sets, I suppose it would be necessary to have the conical burr angle as well in order to calculate the gap between burrs.

Any help or corrections to my assumptions would be appreciated.


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## ajohn (Sep 23, 2017)

In terms of rate of adjustment all that matters is the pitch of the thread. Diameter doesn't matter in that respect.

I suspect you will find that any of European origin will probably use a pitch of 0.5mm, I think the Kinu does. If originated from the USA and maybe a few other places it might be 40 tpi. So in one case one turn moves the burrs by 0.5mm in the other 1/40 of an inch / 0.025". These pitches are usually the ones used on mechanical micrometers irrespective of their resolution. Some might have a vernier scale to increase that and some might just use a larger diameter for the scale allowing more markings to be included.

If you can find one that uses a finer or coarser pitch the movement for a turn would change accordingly. Personally I would also wonder about the diameter of the scale they use as larger allows finer graduations.








Maybe some use a differential thread arrangement but I doubt it. 2 threads one coarser than the other arranged so one turn moves something by the difference between the pitches. These are a wonderful theoretical idea but have complications in practice. They have been used for certain things in the dim and distant past though.

John

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## El carajillo (Mar 16, 2013)

I have a Hausgrind, the shaft is 8 mm and the thread pitch is 1 mm. This is the standard pitch for 8 mm X fine thread.

8 mm metric coarse thread is 1.25 mm pitch. 6 mm metric coarse thread pitch is 1 mm.


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## VernS (Aug 26, 2017)

Thank you John for that good information. That was very helpful.


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## coffee3253 (Jun 12, 2016)

Thanks for that


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