Author Topic: How to replace a jewel  (Read 507 times)


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How to replace a jewel
« on: October 04, 2016, 09:30:28 PM »
This tutorial gives you a quick demonstration how to replace a jewel on a going train.
Here I'm relacing a 4th upper jewel on an Omega cal. 1012. Beforehand I have checked with microscope that the jewel has too much side shake.

As I want to replace the jewel, I first need to drive it out of the bridge. It's good practice always to verify that pusher doesn't cover the jewel, otherwise the pusher will remove part of the bridge and that is a big fail. Here I'm checking the pusher. The pusher should be biggest possible but smaller than the OD of the jewel. 0.15 mm smaller diameter pusher is usually quite easy to choose.

Next step is to choose an anvil for the job. Omega is a good example that bridges have steps that make choosing the anvil a pain. Here I'm using special anvil specifically meant for Incablocs. Normally it's best to drive the jewel out from the top side. This is because we don't want to make any marks on the bridge. Marks are easily formed with small anvil and the contact pressure made by the jeweling tool.

When anvil and pusher are selected, it's time to drive out the jewel.

I never use jeweling tool without full control and this is the method how the jewel can be driven out with total control: First the pusher is set to same level with the jewel. The adjustment screw is screwed in so that the pusher can be very gently lowered to the surface of the jewel. Very small touch is all that is required. If too much force is applied, jewel moves unintentionally.
When the pusher is on the level of the jewel with very gentle power, the micrometric adjustment screw of the jeweling tool is unscrewed until it catches the pusher level. Now the pusher is at  the level of the jewel and force can be used at the jeweling tool lever and jewel is not moved.  I normally use other hand to hold the lever and with other hand I unscrew the micrometer adjustment.

Driving out the jewel is now simple. Again small force is at the lever. The micrometer adjustment is screwed in a bit. Then lever is pushed with moderate force.The movement of the jewel can be felt.
This is repeated until jewel pops out.

When the jewel comes out of the bridge, the OD of the jewel is measured and recorded.

Then the wheel pivot is placed on a jewel reference plate or measured with micrometer to get the jewel ID. This Seitz tool is handy because it's easy to verify the correct fit of the jewel. Pivot should nudge little bit in correct jewel. Tight fit is too small even if the pivot goes all the way in.

Now that ID and OD of the jewel is known, new jewel can be taken and placed on the back side of the bridge. Normally flat surface is all that is required as an anvil when replacing a bridge jewel.
Usually this phase is easy, as the OD of the jewel is known, 0.05 mm or 0.15 mm bigger pusher is selected. Pump pusher is good choice as it makes it easier to center the pusher. Normally it's adequate to drive the jewel to the surface of the bridge. Now the pusher acts as a limiter as the pusher OD is bigger than the jewel OD.

Last but not least step is to correct the end shake of the jewel. This is verified by mounting just that one wheel and fully screwing in the bridge. If end shake is correct, replacing the jewel is completed. Wrong end shake requires adjusting the depth of the jewel. As the jewel is left on the surface, wrong end shake is normally too tight, which means that jewel needs to be driven further down. This is achieved by selecting pusher smaller than the jewel OD and driving the jewel small steps down at a time and iterating this step until correct depth is found.

« Last Edit: October 05, 2016, 12:15:36 AM by kanikune »