There are 3 main elements to the movement finishing that I do. First, Côtes de Genève. Second, perlage. Third, bluing the screws. I'll first describe the process I used to apply the Côtes de Genève.
Côtes de Genève
Here's the process in a nutshell:
The mill I used is a bit bigger than needed...eventually I want to get a bench top mill like a Sherline. But for now this one from Taiwan did the trick.
I used a lathe chuck to hold the Bergeon movement holder and had the bridges screwed into the base plate and the movement set in the Bergeon movement holder. This whole set up was mounted to the mill table w/ a small .02” shim under the right side.
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.
Mill RPM was set at 500…we experimented and found that slower was better…we started on the right hand side and did 14 stripes at approx 2.5mm per stripe. We dropped the mill head approx .0007” per stripe to compensate for the .01” drop from right to left.
Cutting direction of the mandrel was clockwise and we pushed the movement forward into the mandrel…then recorded the mill head height, raised the mill head, pulled the movement back, moved it to the right 2.5mm, lowered the mill head to the old height minus .0007” and did another stripe.
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.
The other update is a template that we built out of a scrap piece of copper. We set this up so we can screw two movements to the block, place it on the mill and go. We cut an angle in to the bottom side of the block, so the pieces sit at an angle...no more messy jig set up like in the pictures above. Now it's clean and simple to stripe the movements. It's drilled and tapped for the 6497 and I plan on adding holes for the 6498. The holes are drilled .90mm and the tap is 1.1mm. The holes for the locating pins are drilled 1mm. Thanks to my brother Mark for helping me with all the mill and lathe work.
And one last note, we found that we could feed the plates into the mill at a faster rate and get really clean stripes w/ good graining. Meaning from the time the Trizact hits the edge of the movement plates, it only takes about 4-6 seconds to make the pass. In some other practice attempts, we thought slower was better...but it's not. You want to have the plates pass rather quickly under the Trizact.