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RyMoeller

Navitimer Restoration- Turning a Replacement Bezel

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Well this isn't really a walkthrough because I'm learning on the fly but I felt it was worthy of sharing as the story will probably return some good advice.

A bit over a year ago I picked up a Breitling Navitimer movement complete with crown, dial and slide rule.  There were a few parts missing and a couple of broken pieces but I corrected those issues in short order and stored the movement away for that day when a case would come available.  

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A few months later just such a case came up on eBay and I picked it up for a fair price even though the bezel was missing.  The case has some issues- for example the threads for one of the chronograph pushers were stripped out (note the pusher held in with glue below) and it looks like the bezel was removed with a forklift.

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I widened the stripped out pusher hole and pushed in a stainless steel sleeve which will be tapped to accept the proper pusher (2.5mm tap, pitch 0.20mm).

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This work was completed some time ago then the project stalled out as replacement bezels are about as common as unicorns.  Frustrated by this I decided to roll up my sleeves and turn a replacement.

The correct bezel is approximately 3.25mm tall with a 41.0mm outside diameter, so I started with a 304 stainless steel ring which is 6.00mm tall and has an outside diameter of 41.0mm.  I've not turned stainless steel on the lathe before and was hoping to start with a softer grade (say 400) but was limited by what would fit in my three jawed chuck.  Now for anyone who is thinking, "you can't turn stainless like that on an 8mm lathe" you are of course correct (for the most part) but try I did and with a carbide graver I was able to make pretty quick work of the piece- chips were flying nicely but OH BOY DOES IT GET HOT!

About twenty seconds of turning was all I could do before cooling the graver; this is of course why you always see stainless steel milled or cut under a stream of coolant.  Since my workspace is limited and I don't want to make a big mess I moved on to Plan B (which was actually Plan A because I never figured I'd successfully turn a replacement stainless steel bezel on the lathe).

Plan B was using brass, which meant I could put the carbide gravers away as they aggressively dig into brass like it's chocolate.

This time I started with a thick brass washer and my usual HSS graver.  Pretty soon I was knee deep in shavings (which are useful for bluing screws).

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I turned the washer to a ring with an inside diameter of 37.5mm.  A recess was then cut 1.0mm deep to accept the crystal on one side and the inner bezel ring on the other.  The inner bezel ring (on which the bezel is mounted) is about 1.8mm tall so the recess needed to be about 2.00 mm tall to accommodate the inner bezel ring and the slide rule.  Getting the dimensions just right was achieved by using a black sharpie and a scribe (needle in a pin vice) to mark out the cuts then constantly checking and rechecking the fit.

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Once a proper fit to the case and crystal were achieved I proceeded to cut the exterior of the bezel.  The cuts were done by eye then checked and rechecked for proper fit and finish.  The outside diameter of the bezel where it meets the case tapers to 40.0mm and if I cut too much there's no way to add the material back.

The current status is promising- below are the pictures as it stands today without notches.  I'll be cutting the notches this weekend using a fine round escapement file.  To ensure the notches are evenly spaced the plan is to remove a stainless steel bezel from another Navitimer I own and glue it to this one.  The notches in the stainless bezel with then serve as pilot holes to guide my file.

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Once completed the plan is to have the bezel plated and the case professionally refinished (laser welded, etc.).  Even though it's not correct for this watch, I'm thinking I'll probably have the bezel yellow gold plated as it will be easier to sell when and if a proper stainless steel bezel ever comes to replace it.

A few things I've learned along the way that might be helpful-

  1. Don't get discouraged- I was 95% done two days ago when the bezel slipped off the chuck at speed and deformed- I had to start the whole thing over again.  I did get to test my notch making skills on the bent piece though and that's worth something.
  2. A three jaw chuck isn't really the right tool for this job.  There is a five or six jawed chuck for holding bezels, if you can find one, I'll bet it's a lot grippier.
  3. Turning large brass rounds on a lathe is great for your confidence.  You'll think you're a master until it comes time for clean-up when you realize you really do need a proper machine shop (separate from your service workbench).

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Well here's a quick update on the Navitimer project.

I tried to freehand cut the symmetrical notches in a piece of scrap brass and did not achieve stellar results.  Going back to the drawing board I tried several different methods to get evenly spaced notches in a round piece of stock and each new method was found wanting.  I returned to the original plan with some minor modifications and am now happy with the result.

I did most of the work under a stereo microscope which allowed me to see the entire piece while I filed away.  On the original test piece I tried cutting notches while the part was held in a vise- well this didn't work very well because I wasn't able to turn the piece over in my hand while I worked to ensure each cut was correct from all angles.  It took about two days and I'm finished now but the muscles in my forearms are a bit sore as is my elbow.  I wonder, does anyone else suffer from tendonitis as a result of this hobby?

I'll send the bezel out tomorrow to be plated along with the case which needs some laser welding.  In the meantime I have to revisit the movement.  It runs fine but I've discovered the fourth wheel currently in there is from a Venus 175 movement.  The correct wheel has a longer extended pivot for the small second hand.  They are also hard to come by but I think I have secured a replacement.  Hopefully I'll have a finished piece to show soon.

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Well, that is some pretty amazing hand work there.

I would say, the most accurate way to do the slots, would be to set up the part in a "nest" (scrap piece, usually aluminum, turned to the ideal diameter/shape which is used to support the part and is itself subject to the chuck jaws) to more evenly distribute force and provide better support. We used these all the time diamond grinding thin wall parts. Even in a six-jaw chuck, you would end up with high and low spots (six of each!) around the part without a nest.

Once that is sorted, it would go into a dividing plate fixture. This is a chuck (or collet) on a bearing shaft with an attached wheel with a LOT of holes in it. Each ring of holes is a different number of stops around the diameter. So, pick the circle with the correct number of notches to cut.

That out of the way, set the dividing head under your mill, and install an endmill of appropriate diameter. On something small like this, you can probably do one pass for the full width (mill equal to groove width). On wider grooves, it is best to use a smaller mill, and cut each side of the slot separately. On stainless, I'd suggest no more than 0.003" depth per pass. Brass might be able to take a heavier cut. A square end mill will give square bottom cuts. But you can also get a chamfered mill (the sharp corners are cut at ~45 degrees) as well as a ball end mil to get a round bottom groove. With those, you have to get the right width mill and do the groove in one pass to have a smooth bottom radius. Solid carbide mills are rather cheap in small diameters, but regular uncoated tool steel mills are fine- just use oil when cutting.

Repeat "X" number of times around the ring. I'd leave 0.001" or so of "meat" for polishing away if a mirror finish is your goal.

Buff/finish as needed.

PS having something like this made at an Aero machine shop around here would be a couple hundred bucks. Sometimes it's easier to have stuff made by those already equipped to do it, although I'm right there with you regarding the whole "I did it myself" thing...

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Well I finally completed this project yesterday.  There were a few challenges even after solving the bezel issue which took a bit of time to put to bed.

First, I discovered the pipe on the running seconds hand was both too short and too wide (the extended pinion on the fourth wheel has a diameter of 0.18mm and the pipe on the hand was around 0.25mm). I had thought the fourth wheel was incorrect but that turned out to not be the case.  Now I have two extra fourth wheels (I'm not a quick learner apparently) but I'm sure they'll come in handy down the road!

To fix the pipe I used a bit of brass tubing I grabbed off eBay which had an ID of 0.18mm and OD of 0.50mm.

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A broach was run through the pipe on the hand to widen the inside diameter then the tubing I purchased was tapered and cut on the lathe to fit inside.  Originally I was going to remove the pipe from the hand but settled on pushing a sleeve inside when I realized the tubing I had was too narrow to rivet to the hand.

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Next I needed to address the watch crown which was damaged and lost its rubber o-ring.  The o-ring is secured place by a riveted cap but on my crown the cap was missing.  Naturally, I first searched for a replacement crown but when one was not readily available I opted to fix the one in hand.  A replacement o-ring was ordered and a new cap turned on the lathe.  With the o-ring set in the crown, the cap was secured via a hammer and stake.  It seems odd that these old Navitimers have rubber gaskets on the crown, pushers, and caseback but there's nothing to stop water from entering under the bezel. <_<

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Lastly I noted the new chronograph pushers I ordered were too short.  I turned a pair of boots on the lathe to increase the length of each pusher rod.  Neither boot is fitted too tightly so removal should not be an issue down the road.

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Then it was time to assemble...

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It was certainly worth all the time and effort but I must say, I'm looking forward to some really straightforward services in the future. :)

 

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14 hours ago, clockboy said:

Great workmanship to what is in my opinion the best looking Breitling ever produced. This also confirms if anyone want to take their repairs to a higher level then a lathe is a essential tool. 

Thanks @clockboy, you know, I didn't realize until you pointed it out that each of these repairs required the lathe.  It's an indispensable tool when doing big restoration projects.

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