As you know, because we didnt have the original part to copy we had to try and work out what was there. The pipe of the cannon pinion was fairly easy, we pushed a smoothing broach up inside the hour pipe and marked the end, this gave us a rough measurement for the outside diameter of the pipe. The broach was then mounted in the lathe so the cross slide could be set-up to cut the correct taper. We used a dial gauge to set up so we could cut the taper as accurately as possible.
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When we chose the brass for the pipe we picked something of a diameter which was about 4mm larger than the base of the taper, this is so we could cut a shoulder and leave enough material behind the shoulder to rivett the wheel on. The taper in this case was starting at 5mm down to 4.8mm (this would give a tight fit inside the hour pipe), so we allowed 0.1 clearence and cut it 4.9mm down to 4.7mm. The internal hole went from 2.5mm down to 2.18mm(measured from the centre arbor) so we drilled it through at 2.1mm and then finished it to size by hand broaching.
When working out the length of the pipe we also had to remember to leave it long enough to file the square on the end for the minute hand to fit onto.
In this next photo you can see we started to cut the taper. The hole for the centre arbor was then drilled through just a fraction under-size so it could be finished by hand to get a good fit.
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Once the pipe was finished we then bored out the hole in the wheel for a good fit to the pipe ready for rivetting.
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The pipe was then held in split brass jaws in the vice and the wheel was hammered onto the pipe using a large flat punch to make sure it was seated correctly. We made sure when we cut the shoulder it was just slighly undercut to allow the wheel to sit dead flat against it.
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Once we were happy the wheel was dead square to the pipe a domed punch was used for the final rivetting.
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The cannon pinion was checked on the centre arbor for fit before filing the square for the hands.
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All was well so it was then mounted in the watchmakers lathe and the square was filed on the end to take the minute hand.
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Here it is with the minute hand in place.......
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and now my project clock now has a new cannon pinion thanks to Daryn
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