G'day Chris here, and welcome back to Clickspring.
In this video I use these pieces of sheet metal,
to make the basic support structure of the mechanism.
So what exactly is the structure of the mechanism?
Well if you strip everything away, it comes down to this.
A single main plate, with a single main bearing located at its center.
The front planetary display is speculated to have been positioned just above the main plate,
and the rear display is known to have been located on the other side.
Its a 3 tiered structure providing support and alignment for the entire mechanism,
and you can see that it has features spread across all 3 levels,
that are all somewhat related.
Now some of these features will be depthed from the main central bearing,
some from features on the rear dial,
and some will be located relative to specific components once their position
within the mechanism has been determined.
Many of the features need to be formed with 2 or 3 of the plates stacked together for reference,
like for example the main bearing position.
But interestingly, not one of the features is carried through all 4 plates simultaneously.
So its clear.
I need an accurate method to bring the plates into register with each other,
that gives me the flexibility to combine them as required.
The clockmaker way to approach this, is to align them in a top down stack,
using tapered brass register pins,
Each plate is registered with the one below it, to lock in the relative orientation.
Now its impossible to know for sure if the original maker used the same technique,
but certainly some sort of systematic approach would have been essential.
There's a lot happening on that front dial,
so dropping in the first set of alignment pins requires a bit of planning.
Ideally they'd be diagonally opposed, somewhere out on the perimeter.
But there are some constraining factors affecting the placement,
that become apparent when you look underneath that top plate.
The sub plate is shorter than the upper dial plate,
reducing the common area to less than what you can see from above.
The 4 pillar locations also occupy some of the space,
and of course the center of the upper plate is largely occupied by the main display rings.
So the available space comes down to quite a small,
sort of triangular shaped area, just inside from each of the corners.
The pins can go anywhere inside that space,
and to some extent its preferable that they be a little asymmetric
so that the plates will only match up one way.
But the area does need to be clearly identified before I start making holes.
OK, so this is the space I have to work with
and a quick punch marks out where I'll drill the holes in a moment.
The next plate down in the stack is the front dial sub plate,
and it needs to be accurately located adjacent to the top plate before I can drill the holes.
I used the known dimension from the edges, as well as the common straight edge to position it.
Each of the marked locations was then drilled out in preparation for taper broaching.
I used this 5 sided clockmakers broach to taper broach each of the holes.
Using one of the pins to gauge the progress of the taper.
The pins were then hammered firmly into place,
and the opposing holes on the other plate given a light countersink.
Now for the plates to all sit flush when stacked,
the pins must sit beneath the surface of each matching plate.
So I used a file to reduce the pin length,
and then rounded off the tops using a shop made chamfer tool.
The two plates are now well registered, and the pins sit comfortably inside the opposing holes.
The excess pin length on the other side was then trimmed off,
filed back and then blended in with the surrounding metal.
The registering process was then continued for the remaining plates in the stack,
progressively moving from the top down,
registering each plate with the one beneath it.
Again taking care to align the plates carefully before drilling,
and placing the pins in regions of the mechanism known to be available space.
I can now work with the plates aligned in a complete stack like this,
or in various combinations as required,
and be confident that the relative positioning of features will be accurate across all 4 plates.
In fact the next operation is a great example of what I mean.
I used a wiggler to pick up the center bearing position,
and then drilled out the main bearing hole with the just the top 3 plates registered together.
The upper 2 plates were then removed to permit a light countersinking
of the main bearing position, and also the marking out of a key arbor position.
The sub plate was then returned to the stack to pick up the correct position for the pillars,
and finally the front dial plate was returned to the stack to drill out the pilot holes for the pillars.
Now without register pins, this would have been quite a challenging task to manage.
But with them, Its a fast, convenient and accurate process,
and one I'll use several times throughout the course of the build.
OK so that takes care of the pilot holes for the pillar locations,
but of course they need to be turned into squares to accept the pillar ends.
So I took care of that operation next, using this shop made square broach.
The broach was inserted into each of the pilot holes,
and then aligned with the edge of the work using the common reference of the surface plate.
I used the tip of a fine cut file to undercut each of the pillar locations,
to ensure a clean seating for the pillars.
Next I opened up the square hole in the main plate that will accept the main bearing.
And while its not essential, the sheet stock could do with a quick tidy up
to make it a bit more presentable for the rest of the video series.
So I gave it a light grained finish with some 800 grit abrasive paper.
Ok, next up is the main bearing.
And like a lot of this mechanism,
its tempting to apply 21st century thinking when visualising the part,
and assume that it was made as a single integral piece.
But a close inspection of the scans reveals something very interesting.
As the scan reaches what I'm calling the spacer section of the bearing,
the outline of a square hole appears in the center.
That square outline remains through the entire depth of the spacer
as the scan progresses through the part.
And this is significant, because the presence of a square hole in the spacer
leads to an unavoidable conclusion: That the part was in fact fabricated from 2 separate pieces.
A spacer with a square hole, and a main bearing body,
that were then pressed together to form the full bearing profile.
Now this fabricated approach may look like a bit of an odd way to construct the part.
But it does bring a particular advantage.
Because it permits the basic clearances in the device to be achieved
simply by using existing sheet stock of a known dimension.
Its what I've done for this part, and there are a few other parts in the mechanism
where exactly the same time saving trick will apply.
I also suspect that this approach delivered an even greater dividend
with the more complex sub assemblies.
All throughout the device, virtually every sub assembly
incorporates this idea of spacers and wheels,
Either riveted together as a sort of layered sandwich,
or threaded onto a shouldered arbor, or both.
Certainly the wheels and spacers could have been formed
from stock selected to achieve a specific clearance, much like this bearing.
But its easy to imagine the maker taking it a step further.
By starting with slightly oversize stock, and then reducing the thickness
of the wheels and spacers by rubbing them on an abrasive surface.
Using this simple method, whole assemblies could then be easily brought to very close
tolerances by simply abrading the components,
and then visually checking the fit until the perfect clearance was achieved.
With not much more than an flat abrasive surface and good eyesight,
the maker could have achieved exceptional dimension control
without any need for absolute measurement.
I think its an intriguing possibility, and its something I'll investigate further
throughout the rest of the build.
OK so back to the job at hand,
the basic profile of the main bearing body was formed on the lathe,
and I used the mill to form the squares.
The finish from the mill is quite acceptable for this part,
but the root of the shoulder still needs a light tidy up
to enable a clean seating for the spacer.
The spacer hole was then opened up until it was a firm fit on the end of the main body of the bearing
And you'll have noticed that a small section still needs to be removed
from the perimeter of the spacer.
It was a clever little dodge, used to keep the head on a nearby rotating hub as large as possible.
So with the bearing resting in position, I used a divider to mark out the clearance arc,
and then used a series of hand files to remove the metal.
A quick tidy up of corners with a slipstone,
and the 2 parts of the bearing were tapped together.
The bearing assembly was then tapped home into the main plate,
and then firmly riveted to hold it in place for the long term.
Ok, so now that I've got a few bits and pieces to work with,
let's have a look at how it all goes together.
As helpful as it is to be able to model something like this in CAD,
there's nothing quite like seeing the shape and scale of a new project,
in metal for the very first time.
In the next video, I'll begin work on the part that enables the user to drive
and control the mechanism.
The input crown wheel known as A1.
Thanks for watching, I'll see you later.
Now if geared mechanisms like this are your thing,
and you'd like to help me make these videos,
then I've got just the thing for you
A modern reproduction
of the 2nd oldest geared mechanism from antiquity.
The device known as The Byzantine Sundial Calendar,
and also known as the London Sundial Calendar.
I'm giving it the full reproduction treatment,
but more from the perspective of how an 18th century clockmaker
might have tackled the project.
So you'll see all of the techniques and materials that I've started to explore
with the skeleton clock project,
but developed further to work on this much more condensed scale.
Patrons get the same deal as for the first patron series project.
Exclusive access to the build videos,
free plans for the patron series projects,
and of course the added bonus that one lucky patron
will get to keep the finished project at the end of the build.
Visit Patreon.com/clickspring to find out more.
Thanks again for watching,
I'll catch you on the next video.