Tom's Watchmaking Blog

My mill.. not quite perfect as it is 🙂

Due to popular demand, another blog post!!! (well ok, a couple of people asked me about this)

When I bought my milling machine, I was limited largely by the amount of money I had to spend, my understanding of what I wanted to do, and my limited (at the time) understanding of what different mills were capable of doing.

I will try and break this down in to a few basic criteria, though ideally a workshop would have multiple machines with each one appropriately tasked. The key to this is knowing what each machine is capable of, and what is needed for each operation required..

as an example, for making a mainplate, ideally you need something that is capable of accurately pointing/drilling the holes for all of the jewels, screws, pins etc, as well as a machine for milling all of the recesses for the wheels, levers etc.. for making wheels and pinions a rigid machine that has precise angles and indexing capability (the ability to rotate a precise angle to form the right number of teeth on each wheel and pinion) and also able to hold the correct cutters.

At the time I believed the Sherline could fill all these requirements and more!! I opted for a CNC version as I have a decent understanding of electronics, and liked the idea of programming it and letting it rip!!  With around 7 years of tinkering with the mill I have a much greater understanding of what the machine is capable of, and while with a large amount of work it could perform all the duties I want of it, it would probably not be worth it in the long run.

Given an unlimited (or at least very large) amount of money, I would purchase 3 separate machines (and somewhere to put them all)

Machine No 1 – For precise placement of holes – A Hauser M1 jig borer, with the ability to co-ordinate drill holes to within 1/1000 of a mm, can’t get much better than this, though largely used as decorations in workshops…

http://www.lathes.co.uk/hauser/page4.html

Machine No 2 – For general milling operations – A Haas CNC Mini Milling station, fast milling speed, 10 tool changer… whats not to like.. apart from the price tag…

http://www.haascnc.com/mt_spec1.asp?id=SMINIMILL&webID=MINI_MILL_VMC

Machine No 3 – For wheel and pinion cutting – An Aciera F1, super precise, rigid as anything, made for doing this.. or a Dixi, unfortunately the dixi hasn’t been made for over a decade, and the Aciera is still quite expensive.. but they would round out any workshop superbly…

http://www.lathes.co.uk/aciera/
Of course the mill is only part of the equation, ideally a number of lathes would also be desired for the ideal workshop, notably a Schaublin 70.. using this for all turning operations, items can be transferred between this and at least the Aciera, as they share the same tooling..

The ideal milling machine is incredibly rigid, so that even at the extremes of its travels there is no flexing of the mill axes, which would create inaccuracies in the process.

The other main quality required for a good mill is accurate leadscrews, these are the parts of the mill that provide the movement of the axes, these need to be smooth running so that they don’t bind which would create jerky cuts.. and there also needs to be no slop or play in the threads, as this would change the repeatability.. you need to be able to move an axis forward and back, and have it return to the same place each time, this is what will add the most value (and cost) to a machine. most machines use a standard V cut thread to accomplish this, but on high end CNC machines this is replaced with a “ballscrew”

My sherline has issues in both of these departments, it is largely made of aluminium, which has (for something made of metal) a larger amount of flexibility than cast iron or steel, as well as this the way the spindle is mounted has its own issues as well… There are now ballscrew kits available for my mill, though the cost is fairly prohibitive given the initial cost of the mill..

At the end of all this, the milling machine I have is the best I could get for the money I have spent on it, and the things I have learnt while using it will stand me in good stead for when I am able to afford my ideal trio..

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After a quick clean of all of the bits, the movement ticks along nicely, all I need to do is fit the dial and hands to the movement, then this group into the case and figure out how to hold it all tight..

To attach the dial to the movement with the least possible fuss, I line up the crown on the movement and case, and use rodico (watchmakers blu-tac) to get the dial as close to upright as possible.

Once I get it as close as I can, I drill 2 holes through the already existing holes in the dial through to the movement, and place 2 screws through to hold the dial in place, when I test the movement/dial into the case it is thicker than I can use, so the gold layer has to be removed, this lets the register ring sit flat against the movement.

For holding the whole assembly into the case, I enlarge the holes normally used for the casing screws, and fit 2 of the bolts that I use to hold the case together as casing screws… a little bigger than normal, but they seem to do the job 😉

A quick clean up of any debris that got where it shouldn’t, all the screws checked a few times, and the movement is secured in snugly. I fit the case back, loctite all of the case bolts, another quick look… Undo all the bolts, remove the case back and the hair that had slipped in, repeat the process a couple of times, and the watch is basically done!

I fit the band and try it on.. not too bad.. though a little larger than I’m used to for sure 😉

A1 Front

A1 Back

A1 Side

And on the wrist!!

So after a whirlwind 7 weeks of machining, filing, scattered with the flu, dentists appointments, as well as a full time day job, my watch is ready to fly off to foreign climes 😉

A1 ready to fly

Stay tuned for A2……

and here’s a quick shot of all of the brass that was machined in the process, as well as the prototype (as far as it got) sooo many brass filings to clean up…

All up about 2kg of brass

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Working backwards in the watch I now need to test that the barrel will play with the rest of the watch and provide the power to keep it going.

I size the hole in the bridge and mainplate, drop the barrel in, and place the bridge on top. The teeth of the barrel are way to tight against the centre wheel, as this is about 2 weeks before heading to Switzerland, I decide that while I need to adjust the model to decrease the engagement of the wheels, in this case I will adjust the barrel, in the hopes that I will be able to have a running movement.

Barrel Bridge in Position

Barrel Bridge in Position 2

I have also noted that the barrel bridge is still not thick enough, so that if the movement is turned upside down, the lower pivot will fall out completely, to temporarily solve this, I will fit a bush to the bridge, that will stick out far enough to stop this happening.

To adjust the barrel I use an antique device called a “topping tool” or “rounding up tool” originally used when wheels were not always perfect, or if they had been stretched during a repair. What this tool does, is to re-shape the teeth to the correct profile, and in my case reduce the diameter of the overall wheel while doing so. This does not work perfectly, especially with modern watches, but for the sake of 20 or so minutes work, is worth trying.

Topping Tool and other bits and pieces

With the teeth reduced sufficiently, the barrel drives the centre wheel, not as smooth as it should be, but it turns!

Back to Pallets

I test fit the pallet bridge on the mainplate, and after adjusting holes in the bridge to try and get it located correctly, realise it will be much easier to just make a new bridge, the basic design is 5 holes with the banking sections (this limits the movement of the pallet fork, on older watches there are 2 pins that fulfil this function).

Off to the computer, and an hour or so later I have 2 bridges cut out (a spare is always handy) I size all of the holes, fit the jewel and steady pins into the bridge and place it onto the mainplate.. Everything lines up, with some minor adjustment to the profile, I am able to work the escapement with some pressure on the barrel. Everything is looking good!

Wind me up

With things looking like I might meet my deadline, I move to a couple of (seemingly) minor components, The ratchet wheel and click, these 2 parts prevent the watch from unwinding all at once. First the ratchet wheel is test fitted on the barrel, with a couple of small modifications due to machining artefacts (leftovers) the ratchet wheel is able to turn freely. The click is similar, and a small hole is drilled by hand into the barrel bridge to accommodate the click spring in the correct place. Turning the ratchet wheel by hand, the click works happily. With some more adjustments, the train bridge is put back in place (I hadn’t noticed that the click would try and occupy the same space as the train bridge, but a file soon sorted that out). Using a screwdriver, the ratchet wheel is wound without the pallet fork in, and the train turns relatively freely, some minor tweaks to wheel locations, and the wheels would be as happy as they were in the original movement.  With the pallet fork placed in, and wiggled back and forth, the train unlocks just like a real watch!!

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While having a movement is great, it really needs somewhere to live, so I started down the path of designing a home for my little brass machine.

My main criteria for the case is that it adequately protects and allows good viewing of the movement, and wears comfortably.. ideally some water resistance would be nice. I have taken some cues from an industrial context, and made the case quite solid, especially on the case horns (where the band attaches) as this is quite often where cases are damaged and need re-finishing.  I also have designed the case with rapid prototyping in mind, this way I can have the case made in a variety of materials, and even do combinations, for my renders I used a gold case with an ABS plastic case back, but silver or bronze is also quite a possibility.

Render of case side

Render of Case in Gold & ABS plastic

Side note on Rapid Prototyping:

This process, also called “3D printing” is where a model is built layer by layer using a combination of a material and also a “filler” that is placed anywhere there would be a void. Once the model is finished, the filler material is quite often just blown away with compressed air, leaving the finished piece.

Over recent years, the materials able to be used in this process have become quite varied, from a brittle yet very detailed wax, which is able to be used for casting in precious metals, to a stainless steel based powder that can be sintered into a solid steel object, though the minimum thickness of the steel is about 1-2mm vs .1mm for the wax. A variety of plastics can also be “printed” including ABS plastics which are quite strong and durable.

To secure the case main and case back I plan on using 4 bolts or screws, inserted from the sides, top and bottom of the case.

The front crystal is going to plexiglass (plastic) to begin with, as this will show how many times I hit the case on the front, as plexi marks easily,  yet doesn’t shatter, I will look into fitting a domed sapphire crystal when I find a supplier at a reasonable cost.

The rear crystal will be a mineral crystal to begin with to be replaced with sapphire at some point.

While getting quotes to have the case made in either wax or ABS plastic, I decided to mill a prototype of the front of the case, just to see if it looked at least partly ok, the only issue I still have is that the watch is fairly large.

Milling the Prototype case

Milling the Prototype case 2

The case measures 60mm long, and 44mm wide (definitely not a small watch by any means)

Height comparison with Breitling B-1

While getting quotes for the rapid prototyping I came across a company that could machine my case instead from solid metal, so I also obtained a quote for this service.

When the quotes came in, there was not a lot of difference in price between getting the case machined in steel, or made in a plastic or wax, plus the lead time required was not too long. The go-ahead was given and the process started.

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