[Rob Nayler]

Dear Forum Members,

I am considering jewelling the upper train of a year-going regulator I have made. Does anyone have any guidelines as to how much larger the diameter of the hole in the jewel ought to be compared with the diameter of the pivot? I am using 0.050" diameter pivots.

[David Walter]

As far as I know there there are no standards for this, in the past jewels were large regardless of the pivot size. Today's jewels are generally smaller and have a range of outer diameters.
The only guideline may be, the jewel needs larger than the shoulder of the pinion shaft.

[Rob Nayler]

Hi David,

thanks for your guidance. I had not considered the outer diameter of the jewel. My real interest is in the jewel hole inside diameter and the diameter of the pivot which fits into it. If the tolerance is too little the arbour may well bind in the hole. I have asked several of my UK colleagues and as yet there is no consensus. I think ultimately I will have to perform some tests myself. I will post the results on the forum.