Making the MK2 dial

Part 2

Last week we left you at the point where the CAM files were uploaded to the mill, the cutting tools loaded, and we were ready for action.  However, before we hit the start button, we need to step back in time for a moment. Making a watch dial out of Grade 5 Titanium is a complex but well defined process. The end result is not a mystery.   However the guilloche 'scribing' in the centre of the dial is something that is rarely done in Titanium. Actually there are only two other watchmakers who have released Titanium guilloche dials in the past.  The challenges are numerous. Guilloche is a scribing process - the tool does not rotate, like a drill or an endmill might. Obtaining a perfect cut is difficult even in soft materials like brass or gold. At the beginning of our project, we really had no idea if making a Titanium guilloche dial was even possible on our mill. Also, not every guilloche pattern produces an eye pleasing dial. The depth of the scribed line, the 'modulation' of the waves, the surface finish of the cut, and especially 'generation of the chip' are just some of the known unknowns.  There was only way to figure it all out: to start doing test runs and test cuts, then to tune the process and learn as you go. The very first step: the making of our own scribing tool.

The tool 'holder' is made from tool steel and the cutting edge of our tool is a detachable tungsten carbide tip. What you are seeing is a bunch of tools, making a tool to hold a tool to make a dial. The tool is made on the same milling machine that makes all the dials (the Kern!), starting from a sketch, design drawings, CAD and CAM files. But there is a twist: while the tool itself is made on a CNC machine, the tungsten carbide cutting tip, the part that actually does all the work, is sharped by hand and lapped on ceramic disc with a diamond slurry. Guilloche tools are definitely not off the shelf items, and this is not something we could order from Switzerland. If you can't make your tool, hand profile the cutter, make your own slurry, and sharpen it, no one else will do it for you. As an even more technical aside: The surface finish and edge sharpness of the tool itself directly correlate, 1 to 1, to the final surface finish of the guilloche. If you can sharpen and polish your tungsten carbide cutting tip to a mirror, then your guilloche will also be a mirror. Lapping the tool on a ceramic disc is the only way to do this. This is actually an incredibly difficult process to automate, and the fine feel and constant visual checks of a talented (human!) operator are the only way to achieve perfection. For example, the slurry on the ceramic disc needs to be constantly monitored- too much slurry, and the hydrodynamic forces take over and you end up "skating" over the lap, too little slurry and you run the risk of chipping the ceramic, or the tungsten carbide! Our toolmaker James is an expert at this process now, and after lapping many many cutting edges it takes about 30 minutes for him to achieve a perfect mirror on the tool. Once we had made the cutting tool, the first step was to cut a simple, straight line in a Titanium blank. If this was possible, and if we could achieve a good surface finish in just a straight line, then it would be highly likely that the next steps would be feasible! Below, you can see the first ever cut, and chip, of Titanium grade 5 made through a scribing process in our workshop, and I think it would be safe to say in all of Australia! With the know how of Titanium scribing safely in our pocket, we could start experimenting with guilloche patterns- to save prematurely wearing out the tool we did many of these tests in brass. Not every guilloche pattern is beautiful, in fact it's quite easy to make rubbish! But once we saw what we are calling "Curl Curl waves", maybe 20 or 30 test coupons in, it became clear that we had found our pattern!

Scraping: ready to cut test patterns in brass

As said before, not every pattern is eye-pleasing. The good patterns are those which are mysterious; patterns where the tool path is 'hidden' and difficult to work out. A pattern which makes the viewer wonder how in the world such pattern is even possible to make!

We settled for a wave pattern, which we immediately named 'Curl Curl waves'. Curl Curl is the closest beach to our workshop; and the name is said to come from an Aboriginal word meaning "river of life".

The moment of truth

The next phase we were ready to move to Titanium. The preparation starts with creation of dial blanks. A round bar stock is sliced in discs 4mm thick and 50mm in diameter on our Makino EDM wire cutting machine. Makin is 'the cutting edge of cutting': each cut provides the higher levels of precision and surface finish. The blanks undergo a heat treatment cycle to relieve the stress in the material. The exact parameters are something we constantly tweak, but in essence that material sits at 600 deg C for the better part of a day, slowly being brought back to room temperature.

Here is the shot of the first scribed line under the microscope. And even more important than the line itself is the chip: it's length, shape and surface finish tell us if our scribing tool is shaped and lapped correctly and whether the speed and depth of the cut are optimized for Titanium. Yay!

Dial manufacturing

The machining of the watch dial starts from the back side. One very special feature of the MK2 dials is that we make integral, or monolithic dial feet. Traditionally, dials are made from thin sheet, and have dial feet that are soldered onto the back. Having integral dial feet is a far superior method of making a dial: the feet are stronger, more rigid, and more accurately located. The trade off is that it's far more difficult to make a dial like this without it warping like a potato chip, and it's quite time consuming since you have to mill off quite a large amount of material.  Broken dial feet are a common problem for watchmakers and there is no practical way to solder back on a broken dial foot. Not with the MK2! Our feet will stay on the dial forever! In this photo you can see the back sides of the dial blanks being processed. Lots of material gets removed! Oil in the machine serves three purposes: to lubricate the cutting tool, to keep the workpiece and tool cool and stable in temperature, and to flush away the removed chips.

We make six dials at the time. The plate which holds Titanium discs is called a 'jig'.  Yes, we design and make our own jigs, in our workshop, specifically for the MK2 dials. Note that this particular jig is called 'number 7'.  When the back side is completed, the dials are now transferred to another jig for top side machining. In this step, we work on one dial at a time by milling away all but the raised section for the guilloche and the recess for the nameplate. The 0.2mm holes that will accept the numerals and hour markers are drilled as well.

After glass bead blasting to get a super smooth, even surface, the dial is then brought to the Kern Micro HD to do the ultraprecise, CNC guilloche of Titanium.

Part 3: Topaz blue, Curl Curl waves. Manufactured in Australia. To be continued...