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How to Reduce crown outer diameter by 0.15mm?


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I have a tap 9 crown with a short pipe. I need to reduce the diameter by 0.15mm for it to fit the watch case. I only have  a flexi shaft dremel at my disposal. Can I manage anything with a dremel?

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Hold the Dremel in a vice, chuck your workpiece in the Dremel, and use a file or abrasive stick to reduce the diameter. 0.15 mm on the dia. is 0.075mm on the radius, so just ever so lightly taking the tops off the knurling. Why do you need to reduce the crown o.d.? 

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10 hours ago, Klassiker said:

Hold the Dremel in a vice, chuck your workpiece in the Dremel, and use a file or abrasive stick to reduce the diameter. 0.15 mm on the dia. is 0.075mm on the radius, so just ever so lightly taking the tops off the knurling. Why do you need to reduce the crown o.d.? 

Thanks, I can hold the dremel (and abrasive files which come with it) in a vice but I am not clear on what to use to reduce the diameter of the pipe on the crown which holds the stem. 

This is a replacement (used, genuine) crown with its pipe's outer diameter (red arrow in picture) just slightly smaller than the pipe on the case so its a very very snug fit.  The crowns pipe needs to go through the pipe on the case. Perhaps the crown and case generations are not the same hence the difference, not sure🤨.

Please see attached pictures. 

caseTube.JPG

6mm crown.JPG

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OK, it wasn't clear which o.d. you wanted to reduce. Now I understand it's the pipe. If they actually go together but are a tight fit, then I would seriously consider broaching the i.d. of the pipe in the case. Much much easier to work on than the crown. The pipe in the case should be removeable if the worst comes to the worst, so you would not be making irreversible changes to the case itself.

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2 hours ago, Klassiker said:

OK, it wasn't clear which o.d. you wanted to reduce. Now I understand it's the pipe. If they actually go together but are a tight fit, then I would seriously consider broaching the i.d. of the pipe in the case. Much much easier to work on than the crown. The pipe in the case should be removeable if the worst comes to the worst, so you would not be making irreversible changes to the case itself.

Broaching is a good idea. I will see what possibility there is. But the case pipe is fixed to the case. 

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2 hours ago, Klassiker said:

OK, it wasn't clear which o.d. you wanted to reduce. Now I understand it's the pipe. If they actually go together but are a tight fit, then I would seriously consider broaching the i.d. of the pipe in the case. Much much easier to work on than the crown. The pipe in the case should be removeable if the worst comes to the worst, so you would not be making irreversible changes to the case itself.

That is how it should be sorted. If you tried to reduce the pipe that the stem screws into you might split the pipe or it just might bulge. Sorry for my other comment I thought it was the out side of the button you needed to reduce.

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Are you sure it's the crown pipe that needs to be reduced? 

Usually, the reason for the crown not fitting the case is that the pendant tube is too thick to fit into the space between the pipe and the crown washer.

I'm restoring a West End watch at the moment where the pendant tube is rather fat and the new crown just can't fit. The seller used a non-waterproof crown which doesn't have a washer to interfere. But that makes the watch non-waterproof.

There are 3 ways to solve this problem:-

1. Get a new crown with a larger gap to fit the pendant tube.

2. Chuck the crown that you have in a lathe and use a micro boring bar to open up the hole in the washer. But the oring in the crown might still be too small to fit the pendant tube.

3. Change the pendant tube to fit the crown.

I went with the 3rd option as Cousins didn't have a long pipe crown that fits a fatter pendant tube and I wasn't sure if the oring would fit over the tube if I went with the 2nd option.

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2 hours ago, k3l3k said:

the case pipe is fixed to the case

As Hector points out, the  proper name for the case pipe is pendant tube. But we can stick to case pipe in this thread, if you wish.

In any case, proceed very carefully with the broaching. It might just be a machining burr or surface finish issue. A gentle pass with a smoothing broach may be all that you need. Also, check out the other dimensions indicated by Hector before you start cutting, i.e. the washer i.d. and pendant tube o.d.

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12 hours ago, Klassiker said:

As Hector points out, the  proper name for the case pipe is pendant tube. But we can stick to case pipe in this thread, if you wish.

In any case, proceed very carefully with the broaching. It might just be a machining burr or surface finish issue. A gentle pass with a smoothing broach may be all that you need. Also, check out the other dimensions indicated by Hector before you start cutting, i.e. the washer i.d. and pendant tube o.d.

Yes, pendant tube is the correct name. But as I started from the crown and Cousins calls the thingy which holds the stem as pipe, pipe continued🤕. In case I damag the pendant tube, what is the correct technique to take it out?

I agree, I think I just need a smoothing broach and I need to take the measurements again carefully before starting. I do not have a smoothing broach - will check cousins now. 

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