Before doing anything with the 6498, I practiced with some brass discs to get a feel for how the perlage shows up. I also experimented with the Cratex. I sanded some of the tips down to a 3mm - 4mm diameter to produce smaller perlage.
On to the movement itself...I started on the outside edge and worked my way to the center. I overlapped each circle about 1/2 way into the previous circle. I like that the result isn't perfect. To me, I believe, it adds to the handmade quality of the watch. Perlage done by CNC machines are spaced perfectly, which is fine, but I much prefer the unique pattern of the perlage when applied by hand. This will make each movement I decorate even more unique.
I bought a bag of screws off of eBay to practice with…and that made a big difference. Just being able to see how different the shades of blue can be. With all the practice screws I turned blue, it gave me a good feel for what color I wanted and how long it took. Most of the time the screws were on the iron for between 5-8 seconds.
Now concerning prepping the screws. All the screws are nickel plated…which won’t turn blue unless the nickel is removed. So far I have simply polished the nickel off the top of the screw…so only the polished face of the screw head turns blue. I like how they turn out w/ the slot for the screwdriver staying silver…
Many of the screws I practiced with weren’t plated…so when they hit the iron, the entire screw turned blue…which is cool too, but the only way to get that w/ the 6498 screws would be to take them to a plating company and have the nickel removed (which I may try one day…but for this project, I just went w/ removing the nickel from the screw face).
I tried to level the movement as best I could from front to back…and we ended up with about a .0005” change from front to back. Side to side we had a .01” drop from right to left (mostly due to the .02” shim). But now that I think about it, we could have created that angle in the lathe chuck too. Anyhow, in the mill head we used a 1” dia. aluminum mandrel with a piece of 400 grit Trizact (a 3M product) super-glued to it. All the cutting is done dry – we tried lubricant, but it didn’t work…maybe it would if the lubricant was flowing over the material during the entire cutting process…but we just experimented w/ spraying a bit on our practice brass discs just to see how it worked.
With each pass, you are scratching about a ½” wide surface area of the movement…then, when you move over the 2.5mm and make a second pass, the stripe is created. Does that make sense? This is one thing we found out when we were doing our practice runs. I initially thought since the movement was angled, a perfect 2.5mm strip would be laid down w/ each pass…but that’s not the case…the “stripe” is easily ½” wide, then you simply put an edge one it w/ each pass. And there you go...
A couple of updates to the striping process. You need to make sure that you have as close to perfect of an edge on your mandrel. I'm currently working on a few more pieces and found that as I replaced the Trizact, the edge of the mandrel was getting a bit beat up. Also, I wasn't taking the time to perfectly trim the Trizact to the mandrel. And the result was...well, the result was nothing but crap. Take a look...this is how NOT to stripe a movement.
Once we straightened the edge of the mandrel and took care to match the edge of the Trizact with the mandrel, the stripes turned out perfectly.