G'day Chris here, and welcome back to Clickspring.
In the previous video of this series, I completed the barrel.
So in this video, I take a length of this steel rod, and make the barrel arbor.
The barrel arbor carries the barrel and the mainspring of the clock, and It has 2 bearing surfaces,
called pivots, that run in the clock frame. It also has another 2 surfaces that run in the barrel caps,
that support the rotation of the barrel as the clock runs.
Now It looks like a fairly easy piece of turning, but it's surprisingly easy to mess up this part.
I've turned a quick demo from a piece of aluminium, to show you what I mean.
The arbor has a series of stepped shoulder features that have to dead on for it to work.
And some of the key dimensions for those features must be taken directly from the clock,
like for example the pivot shoulder distance.
For the clock to run freely, there must be a small amount of clearance between the arbor shoulders and the plates,
to give a little bit of end shake.
There's a similar issue regarding the dimension of the inside of the barrel.
The cap has to be in place to give the true dimension, but then how can the inside be measured?
The American clockmaker Bill Smith came up with a beautiful solution many years ago,
this barrel transfer gauge, which I'll use later in the video.
So that's the plan, lets get started.
The steel I'm using is silver steel, or drill rod; I don't intend to harden it,
but the arbor will last a lot longer, being made from this tougher steel.
And I'll be forming the features between centers, so the next step was to form center holes on each end of the stock.
Then I set up the lathe for turning between centers.
This first line marks out one end of the thickest part of the arbor,
and from here I can start turning the shoulders for that end.
The part was then reversed, to form the profile on the other end.
And this is where I get to use the barrel transfer gauge, to pick off the dimension on the inside of the barrel.
Its basically just a rod with 2 shoulders, one of which can move relative to the other.
Its passed through the holes in the barrel caps, and at this point can loosely contact each side of the barrel.
It's then expanded until the shoulders are in snug contact with the inside of the caps,
and then carefully pulled out so that the dimension is not disturbed.
It's then measured, and the dimension transferred to the work minus a small amount to allow
for a little bit of end shake inside the barrel.
I used the tool in a similar way, to pick off the inside plate dimension.
And at this point the shoulder dimensions are all in place, so I started on cleaning up the pivot surfaces,
using this combination pivot file/burnisher. First by using the fine cut file, to remove the tool marks.
Followed by a hard slip stone to remove the file marks, and to square up the surface.
and finally I prepared the burnisher with this coarse grit emery paper, and burnished the pivot surfaces.
I reversed the work, and did the same 3 step operation on the other end.
The next feature to be formed on the arbor is the winding square, which I took care of on the mill.
I'd like the square to have a slight taper, so that the winding key will slide on and off easily when it's in use.
A small shim under the collet block gives a taper of about 4 thou per inch, which will do nicely.
At this point the bulk of the metal is gone, but the surface finish needs to be much better,
so I took care of that by hand with some needle files, and emery paper.
Now the arbor also needs a hook for the mainspring,
and traditionally the hook could be made by turning a raised section like this, and then using files to shape it into a hook.
But I didn't like my chances of making that look good any time soon, so I went for a fabricated hook like this,
which can be screwed into the barrel.
So then it was off to the lathe to form that threaded insert.
The other bonus of fabricating the hook, is that it can be replaced over time as it gets damaged by the spring.
I then drilled and tapped the arbor to accept the threaded insert.
The main body of the arbor now serves as a great little handle to hold the screw,
while I use the belt sander to shape the hook profile.
So with the arbor almost complete, now is a good time to fit it into the barrel caps,
and I'm going to do it using this 5 sided clockmakers broach.
If you're accustomed to the usual engineering practices, then you're probably thinking this
is a pretty relaxed way to make a precision hole.
But in fact the taper broaching of holes is clockmaking best practice, and its a technique that's been used for centuries.
The 5 sided broach cuts the brass very easily, and opens up the hole until it's very close to letting in the arbor.
The slight taper on the broach means that the hole is tapered too.
Once the hole is big enough to just let in the arbor,
it's followed with this smoothing broach to work harden and smooth the surface.
This ensures that the bearing surface has a longer life, and it also opens up the hole
that last amount to let the arbor run freely.
Now by forming a tapered hole in the end caps, the bearing surface that's in contact with the arbor is made much shorter.
So the friction acting against the barrel rotation is greatly reduced.
The arbor has a nice amount of end play inside the barrel, so I'm calling that done.
All it needs is a decent chamfer on the edges to reduce the surface contact with the caps.
I'll do the same thing with the pivot shoulders that contact the plates, when I let the arbor into the clock frame.
Thanks for watching, I'll see you later.
And if you've just found your way into this video series, thanks for checking it out.
I release regular video's as the build progresses, as well as separate project video's for most of the tools I need to build the clock.
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Thanks again for watching, I'll catch you on the next video.