Tid-Bit 1 - Got Stones?
The restoration work I have done on years-duration weight driven Vienna Regulators has taught me how extremely important it is that the pivots and the holes in which they rotate are in perfect condition. In the case of pivots, this means that they must be stoned to give a flat surface that can then be burnished to perfection.
The first topic I want to present is focused on the restoration of clock and watch pivots, and one that is very near and dear to my heart: The kind of abrasives used to prepare a pivot for burnishing. Hence the rather catchy title of this particular Tid Bit: Got stones?
I’ve been asked this more times than I want to remember. And yes, I do have stones: I hit the MART tables for years. So yes, I have Arkansas and India stones, most of them 1/4 to 1/2 inch wide by 3 or 4 inches long. And this means that when I want to work a pivot all I have to do is reach into my stone drawer, pull out a couple of slips, and away I go.
So, YES, I HAVE STONES.
When I am introducing a new student to pivot restoration, I start them with a 1/8 x 1/8 x 2.5 inch hard Arkansas stone. This is what I teach my students to use when preparing pivots for burnishing. But these stones, as purchased, are too aggressive to do fine pivots and also a quite a bit too coarse for using just before burnishing.
When working on really fine pivots, my students also discover the joy of ruby slips (available in 0.04 and 0.08 inch widths), these are perfect for preparing the finest pivots found in a Vienna Regulator, or French mechanism for burnishing. While these are also fairly course, they can be refined as discussed below.
One of my students, K.C. Morrissey, spent some time a couple of months ago, modifying an Arkansas slip to make it extremely useful in stoning pivots. Not only did his work result in he and I having pretty nifty stones to use, but it also justified this Tech Tid Bit on stones.
Thank you KC!
See, KC is new to the concept of using slips to finish pivots. He has been introduced to the sand paper on a Popsicle stick approach. But, he had also heard me say before that you didn’t want to ruin a fine mechanism using sandpaper and Popsicle sticks. None the less, KC needed a stone. And, all I had are the 1/8 x 1/8 x 2.5 inch ones that can be gotten from Jules Borel (see sources listed at the end of this Tid Bit) - which come with a pretty aggressive cutting surface.
I had been thinking for some time that it would be neat if my students had access to stones that would cover the range of “grits” needed for Vienna regulator pivot work. Everything from a fairly aggressive stone (like the 1/8 inch ones), to a fine, and even a finest stone. Problem is, I just don’t know where they can buy the fine or finest stones. So, KC spent 2 hours sanding away the skin on the tip of his fingers, and in the process made what I think is a fantastic tool for those of you who want to work on clock mechanisms. He took a 1/8 inch stone and sanded the edges until he had one stone with three different “grits”.
WOW!!!
So, how does one “sand” a stone? First you get a piece of glass that you can use as backing for sand paper and sheets of wet or dry sandpaper – I recommend 80, 220 and 600 grit.
The first step is to flatten all four sides of the stone with 80 grit paper. I put dots on the faces with a Sharpie to make sure all 4 sides get sufficiently sanded. I sand until the dots are gone, then continue to sand until I have sharp edges between each face (The 1/8 inch slips come with edges that are rounded: This keeps one from working the surface of a pivot right into the shoulder between the pivot and the arbor.)
Laying the sand paper on the piece of glass gives a very flat surface for sanding the slip (another name for the small stones we are discussing), while lubricating the paper/stone with mineral spirits improves the cutting action and helps wash away the cuttings.
It is important to keep the stones flat against the paper and to not let them roll – which would round the face. 80 grit is nice because it very quickly flattens the faces and gives sharp edges between faces.
When done you will then have 4 sides that could be used for initial pivot work on a rough pivot.
Put a dot with a Sharpie on one end of one 80-grit face – this is now your coarsest face. Then make three dots with a sharpie on the other three sides – one toward each end, and one toward the middle. Sand these three faces with 220 grit wet or dry sand paper until the dots are sanded away. If you now put two dots on the end of the opposite faces that you have surfaced with 220 grit paper - you have two thirds of the stone prepared. Lastly you need to once again put three dots on the remaining face, one toward each end, and one on the middle. Sand the last face with 600 grit until the dots are gone, then put three dots on this last face and your stone is ready to use.
Figure 1 – Sanding a Stone
When KC was done we put a single dot with a Sharpie on one face of the slip, the face that was sanded with 80 grit paper. The two side faces got two dots, and the last face, the finely sanded face, got 3 dots.
Even though his fingers had no fingerprints left (and one or two were leaking red stuff; I warned him about how to hold the stone when sanding, but hey, you don’t even notice the 600 grit sanding away your skin until, well, the skin gets a bit thin), KC was still able to test out his stone on the winding arbors of his 3 weight Viennese mechanism. And, wow, it worked GREAT!
I cheated and did some pivot work with the second one he made (the one I get to keep) and have to admit, this is one experiment that worked better than I ever, ever imagined. The 2 dot faces are great, fairly fine surfaces that, with very light pressure, can give a very nice finish to a pivot. And, the three dot side truly gives a perfect finish, one that is so very easy to burnish!
Best thing is, as a face gets worn, or plugged with cuttings (I do use light oil, like automatic transmission fluid, to lube the stone when working a pivot), it is so easy to resurface the stone. Just go through the procedure above, first marking the face to be resurfaced with a sharpie so you can tell when you have sanded enough.
Take care when flattening with the 80 grit paper to not sand the stone such that the scratches in the face of the stone are parallel to the length of the stone: I canted it about 30 degrees on the paper such that the scratches go across the 1/8 inch face. This way, when using it to work a pivot, the scratches do not leave grooves in the pivot.
I decided to see if I could manage to document the differences between the various surface preparations – using the bellows I recently got for my camera – you can see the apparatus I used to shoot in Figure 2
