G'day Chris here, and welcome back to Clickspring. In the previous video of this series, I cut the wheels for the clock. In this video I cut the matching steel pinions. 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 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. After cutting to length, I cut a 60 degree taper on the end of the stock. This little custom made support sits in the drill chuck. It provides just enough support
to stop the work deflecting under the cut. 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. 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. 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. I don't have a coolant flow, for my setup,
but I find compressed air does the trick. So I use a shallow depth of cut, I feed in
very slowly, and set the cutter to turn slowly too, about 200 rpm. I'm also listening out for any uncomfortable sounds from the cutter. 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. OK, with the profile cut, the blank needs to be drilled out, so now I need a way to
hold it. And a temporary pot chuck does the trick nicely. They can be quickly turned up to suit the job, and then bored out to take the pinion.
I'm aiming here for an easy press fit with the pinion. The pinion can now be faced to length. This is my first chance to see whether the
cutter was correctly centered. 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. 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. 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 Before I temper the part, I need to polish
up a shiny surface so that I can see the color changes as the part heats up.
So a quick polish with some oilstone powder, and its ready for tempering. With the part tempered, I can now do the final polishing. Starting with the leaves, and then finishing with the pinion flanks. 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. 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. This was my first time turning tin, and I've got to tell you, this stuff just flies off the tool! 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. So with both pinions complete, in the next video I'm going to get started crossing out the wheels. Thanks for watching, I'll see you later. And if you're new to this video series, thanks for checking it out. I release regular video's as the build progresses, as well as separate tool video's for most
of the tools I need make, to build the clock. Make sure you subscribe to stay up with the project, and be sure to like, share and leave me a comment. Thanks again for watching, I'll see you on the next video.
