How To Make A Clock In The Home Machine Shop, Part 5, by Clickspring.
In this video I cut the pinions for the clock from drill rod, and then harden, temper and polish them.
Another milling operation carried out on the lathe, using a cross-slide mounted vertical slide, a light duty milling spindle, a Sherline motor/speed control, and the Divisionmaster CNC indexer.
I also make an improvement on my Sherline lathe tailstock polisher, by making a tin lap for polishing the pinion flanks.
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Other Videos to Watch:
Home Machine Shop Tool Making – Machining A Finger Plate Clamping Tool – Part 1
Machining a JANSJÖ LED Work Lamp Adapter Plate In The Home Machine Shop
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Transcript:
00:10 Clock trains and some instruments tend to be designed so that the larger wheels do the driving of the pinions, rather than the other way around. So traditionally the tooth profile for a clock is cycloidal. Quite different to the involute shape of most geared mechanisms. Today’s job is to cut that traditional tooth profile into these 2 steel pinions, and then harden, temper and polish them
00:40 So lets get started. I would have preferred to have made these pinions out of EN8 steel, which is a real pleasure to machine, and can also be quench hardened. Unfortunately I don’t have any. What I do have is plenty of drill rod, so drill rod it is.
00:52 After cutting to length, I cut a 60 degree taper on the end of the stock.
01:15 So I turned the outside to the correct diameter. And then set up the cutting gear on the lathe. It’s pretty much the same as for the wheel cutting. The spindle is indicated square, and the cutter is lined up on the center of the work.
01:38 Although its a bit more critical this time. If the cutter is even a little bit off center, the leaves will have an obvious lean, and the work’s ruined. It’s also worth mentioning that cutting pinions is a lot more problematic than cutting wheels.
01:51 Brass mills very easily – you can rip into it with the cutter, and providing its all lined up as it should be, its hard to get a bad result. But pinion cutting is something else altogether. For one thing, silver steel is much less forgiving, and really hard on the cutters. So chip control is really important to look after the them.
02:26 To be honest, I’m always a bit on edge cutting pinions, and kind of relieved when its over. It’s just so easy to wreck the cutter. I’m taking care of the 8 leaf pinion here, and the 6 leaf was cut in exactly the same way.
04:34 Thankfully it was, but I’ve had plenty that weren’t! The part is then flipped end for end, and given the same facing cut, followed by drilling and reaming. The reamer I’m using here is a piece of the same pivot steel to which this pinion will eventually be bonded. So a nice fit is guaranteed.
05:37 A piece of pegwood shaped to fit the gap, along with a coarse grit, was used to remove some of the tool marks before hardening. OK, ready to be hardened.
06:01 I used this wire basket to hold the part, and I also coated it in a mix of boric acid and denatured alcohol, to keep the scaling to a minimum. A light touch with a file to confirms that the hardening has been successful
08:13 The MDF lap brought up a nice scratch free polish, but you can see its rolling the edges of the leaves, which doesn’t look great. So its time to try something better. I put the job on hold for a few days, and ordered in a small round casting of pure tin.
08:31 Tin is well established as a polishing base. Its hard enough to keep edges crisp, yet soft enough to allow the polish to charge its surface. I machined the tin into a new lap for my tailstock polishing jig.
09:11 One shiny new tin lap; lets give it a run. And based on the result, that MDF lap is going in the bin! A tin polisher is definitely the way to go.
John Wilding workshop and clock construction books:
https://www.ritetimepublishing.com/
I purchased mine from Ian Cobb at: https://www.clockmaking-brass.co.uk/clock_construction_books.html
Lester Caine – Divisionmaster
https://medw.co.uk/wiki/DivisionMaster
How To Make A Clock In The Home Machine Shop, Part 5, by Clickspring.