My clock project progresses (very) slowly. While it’s too cold to spend much time in the workshop I have been thinking about how to make some of the bits.
This is the pinwheel for the escapement. It’s 32mm diameter. the 35 pins are 1mm diameter brass or phosphor bronze rod, 5mm long (plus the bit in the wheel) on a 29mm pitch circle. There is 2.09mm between the finished flat on one pin and the back of the next. The curved back is the acting surface, and the flat is needed to keep the drop small by allowing the pallets to be closer together.
The question is the best way to cut the flats on the pins. I have a small rotary table for the mill, so I am thinking of mounting the wheel (with round pins) on the table (horizontal), and milling the flats with a 1 or 1.5mm end mill.
I am not sure the 1mm Brass pins would mill without bending, so I think I will make a support block as shown (it needs more elaboration for clamping) and put it behind each pin before milling.
Thanks Michael, but once I had made the pins I would need to insert them into the wheel with the flats accurately aligned radially, and that feels even more complex!!
I did consider that as an idea – especially as it’s possible to buy ruby pins for a Brocot escapment pre made to shape – unfortunately 2mm seems to be the smallest.
May be easier to drill the hole pattern on a scrap disc of metal and slip over the assembled pinwheel and then just do a series of radial cuts rather than having the possibility of the wedge coming loose
Thank you Jason. Almost the inverse of what I planned, but way easier to make. Something like this – would be moved each time the table was indexed, but much easier to clamp
An MDF support plate may be enough for machining the brass pins as it is only going to be between 0 and 0.5mm coming off. An alternative to a milling cutter is a slitting saw. A 1mm or 2mm saw will do this and will leave a nice surface on brass. A lot less flimsy than a tiny milling cutter where having one snap after a few pins are machined would be very troublesome in my mind.
If you want a metal support plate you don’t need to make one to go over all the pins at once, one that only supports a few of the pins at once would be enough as long as it can be slipped off and repositioned without much struggle.
Mount the whole thing in the lathe and index the spindle so you can move from one pin to the next. Grind the flats with a diamond disc in a cross slide mounted dremel or similar. It will probably help to file the pins roughly to size before installing in the pinwheel and use the grinding operation as a finishing operation.
Perhaps a daft idea, but here goes. Pin wheel on an arbour in a chuck, filing rest set up with both wheels outside the pin wheel and the file overhanging. Keep file in contact with rear roller and keep filing till it touches the the front one
Treated as a beam fixed at one end the 1mm diameter semicircle is much stiffer than a 0.5mm diameter rod. Rough checks with an online calculator suggest 10 times less deflection for the same load using the same material.
Thank you all for the ideas most useful! As I don’t have a filing rest, and am pathologically allergic to repetitive manual work, the indexed rotary table and a cutting tool are much more appealing. Using a slitting saw is something I had not considered, and the idea of a disc shaped jig appeals.
Not sure grinding is as appealing. Z control on my little SX1 mill is less precise than I would like for 35 repetitions of the same amount ground off. Locking Z tight and cutting at the same height with the saw looks a better bet.
I’ve made something similar in the past. Pins were high speed steel and glued into the holes in the wheel. Wheel was mounted on a mandrel in the lathe, with headstock indexing attachment fitted. The flats on the pins were then ground with a thin disc type grinding wheel in a toolpost mounted spindle. Worked well.
Not sure grinding is as appealing. Z control on my little SX1 mill is less precise than I would like for 35 repetitions of the same amount ground off. Locking Z tight and cutting at the same height with the saw looks a better bet.
Thanks again for the ideas.
That’s why if you did grind the pins you should lock the cross slide and take a lick of all the pins at the same setting indexing round as you go. (Hence my suggestion that you reduce the amount to be taken off by filing prior to fitting the pins)
Whatever you do I hope it works for you.
regards Martin
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