When I used my little No.O on a regular basis, the double lipped NAK oil seals fitted in the head produced, in my mind, excessive heat. The head would become uncomfortable to touch if run for an extended period even at its lowest normal speed. I never ran the mill at its highest speed of 1140 RPM for fear of causing irreparable damage to the head's Timken bearings.

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I had planned on replacing the seals with something along the line of Bruce "Abratool" 's nylon seals but never got around to it because I bought another mill. That mill has proper labyrinth seals and can be run for hours on end with the vertical head remaining cool. That head's seals -

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Hercus use a simplified version of a labyrinth seal on the roller bearing spindled 9 and 260 and to seal the grinding spindles fitted to the No.3A and No.1 tool and cutter grinders. So I thought I would have a go at making similar non contact seals for the vertical head. I made the upper seal to start with figuring I'd only be half as disappointed if it didn't work. It works but I think it probably can be improved.

The other mill's "proper" labyrinth seal has a bore 0.003" larger than the spindle end it seals. The Hercus 9 has a bore probably 0.012" larger than the spindle. A 5 thou feeler gauge readily slides into the gap.

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Because there was an element of uncertainty regarding the effectiveness of the seal I chose to use easy 1214. I also used a cheap internal grooving tool which worked well. I made the bore 0.004" larger than the spacer the seal seals upon. That bore may need to be enlarged.

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With the new seal installed and the lower lipped sealed end cap removed from the head I ran the mill for ten minutes at 1140 RPM. The initial cold temperature of the head, measured on the upper end cap, was 22C. After 5 minutes it was 34C and at ten minutes, 39C. Previously, with both lipped NAK seals in place, the temperature reached 47C in about four minutes running flat out.

My concern that the bore may not be large enough is that there may be some very slight contact between the ground spacer ( second photo at the top) and the seal because the residual oil was not perfectly clear when I dismantled the end cap. The spacer is not a precise fit on the spindle, rough measuring showed about one thou slop. Further investigation with some lamp black should determine whether there is contact.

If this all works it would be a pretty simple modification for those that own a mill with a hot head. Could be that Bruce and I are the only ones!!

Bob.
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