G'day Chris here and welcome back to Clickspring.
In this 3 part video I make one of the "must have" tools for any clockmaker:
A pinion head depthing tool.
A few of years ago I met a retired clockmaker who sold me a lot of his tools,
and one of the things I picked up from him was this depthing tool.
If you need to depth wheels and pinions that are already fixed on their arbors,
or maybe made from a pinion wire, then this is the tool you'd need.
But today its common to build a clock as separate components,
and then bond them together later,so a simpler tool can do the job while the parts are still separate,
and in a lot of ways its easier to use. So that's what this 3 part series is all about;
building one of these simpler pinion head depthing tools.
I'm following Bill Smiths design, and its based around what I'm calling the tool bed
that holds these two moveable carriers. The carriers consist of a bolt with a central hole, and a matching nut.
And when in place, they accept runners, that with simple bushings, act as temporary arbors
on which wheels, pinions and even escapements can be mounted
to perform the task of depthing.
And there's also a threaded thumb screw, which fine tunes the meshing action.
So lets get started.
Some of the key dimensions are set by how the bed turns out, so I made that part first.
The tool faces need to be perfectly flat and true, so I made it out of precision ground tool steel.
The only drawback is that its obviously quite tough material, so a bit more difficult to machine.
Mostly it wasn't a problem, but I did have an issue tapping it, which you'll see later.
I cut off a piece of stock, and started the job by squaring it up on the mill.
And then I found the edge and using the DRO, located and drilled the end holes that will define the central slot.
I used an undersize slot drill to roughly open up the slot first,
and you can see I'm taking pretty shallow cuts, just nibbling away at it really.
My mill is quite light duty. I can get good results from it, but I do need to nurse it along when cutting slots.
That took care of the bulk of the metal that needed to be removed.
But the inside surface is really chewed out at this point,
so I took finishing cuts with an end mill down each side to bring the slot to final dimension,
and to get a good surface finish.
The adjustment screw is supposed to run right down the center of the slot, and it will really
stand out, if it's not right down the middle, so I took quite a bit of care positioning
and clamping the work for the next step.
The top end was then drilled and tapped for that screw.
And at this point I nearly got myself into a bit of trouble. I'm using a carbon steel
tap here, and it was a mistake; the tool steel is just too tough for it. I could feel the
tap was right on the edge of snapping off with every turn; not a nice feeling!
I took it really slow, used lots of cutting fluid, and I did get away with it, but only just.
Next time I'll buy a high speed steel tap for the job.
That extra bit of time spent on the setup was worth it; the thread came out right down the middle.
This is my version of Frank Fords rotary sub table.
I've put a link to it in the description box below.
It really makes this sort of job a lot easier. The whole thing can be indicated in very quickly.
and specially turned spigots in the center can be used to accurately locate parts on
the table axis. and best of all, there's plenty of room on the table for dowel pins and clamps
to hold everything down. It took a bit of time to make, but It's made the table so much more usable.
So once it was all locked down, I milled the curves on one end of the bed,
and then I did exactly the same thing for the other end.
A quick deburr and the depthing tool bed is complete.
The 2 carrier bolts were made next, and these are probably the most difficult parts to make in terms of accuracy.
The underside and top surfaces need to be perfectly true to each
other, and perpendicular to the bore for the tool to work correctly. So this part will need
to be finished between centers. But a lot of it can be roughed out first,
and some of the features machined before that happens.
So starting with bar stock I roughed out the basic shape of the part.
Then I cut the thread and then drilled and reamed the central bore.
And at this stage I've left all of the key surfaces a little bit oversized.
They'll be finished when I've got the part between centers later.
The next step was to drill and tap a hole to take a set screw.
When the tool is in use, the set screw will hold the runners in place.
But its going to come in very handy in a moment, to help finish off the part.
And here's why that set screw is so helpful: I can use it to mount the part onto this little arbor for the next operation.
With the part running on its bore between centers,
I finished off those oversized surfaces, and brought them to final dimension.
Its not a very rigid setup, so you can see I'm taking very light cuts to avoid any chatter
The result of all of this between centers operation, is that those two flat surfaces
that are critical to the tools accuracy, are now true with each other, and also perpendicular to the bore.
The corners were lightly broken with a file,
and all thats really required now is to give each of the holes a light deburr with a countersink
And thats the carrier bolts done. In the next video I'll make the knurled carrier nuts and the adjustment screw
Thanks for watching, I'll see you later.
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