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Question: how to attach crown to stem


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I've modded my SKX031 to house a NH36 movement with aftermarket stem and crown (Namoki). After having cut and filed (Dremel cylindrical sanding bit) the stem to the right lenght, I've cleaned it (using 'wasbenzine', a type of white spirit that the watchmaking school uses in the Netherlands), and used Bison lock bond (similar product to loctite) per instruction of a modding video on Youtube. However, this soon broke, and I tried GS hypo cement as an alternative. This broke too, however, and I tried again with the lock bond, but this broke a couple of days back. I tried cleaning and lock bond again, but again, it lost its bonding function and now the crown again screws loose. :-( 

So, what do you use to attach a crown to a stem? Is it a different product that I used, or can I clean in a different way to let the lock bond adhere better?

Thanks!

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42 minutes ago, iloveoxytocin said:

 I've cleaned it (using 'wasbenzine', a type of white spirit that the watchmaking school uses in the Netherlands)

That is refined benzine (NOT BENZENE). In English speaking countries it may be sold under the names Petroleoum ether, naphta, shellite, and some more.

42 minutes ago, iloveoxytocin said:

So, what do you use to attach a crown to a stem?

If the stem screws correctly into the crown, and is correctly tightened, it should hold even without a locking agent, which is most of a precaution than an absolute need. Normally medium strength Loctite is used, but other products should work too.

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Hey dutchy 😉, what broke exactly, the stem or did the stem get loose again?...I would get a new stem,  fit the stem & crown, press in against the spring pressure, and measure the space between the base of the crown and the case. Best is to cut the stem for the correct size, just sand the end a little to get rid of the sharp edges and screw the crown on. A bit of loctite or clear nail polish

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1 minute ago, Watchtime said:

 fit the stem & crown, press in against the spring pressure, and measure the space between the base of the crown and the case.

My understanding is that OP's SKX031 does not have a screw-down crown, not being a "true diver's". Which makes easier cutting a stem to length.

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2 minutes ago, jdm said:

My understanding is that OP's SKX031 does not have a screw-down crown, not being a "true diver's". Which makes easier cutting a stem to length.

As far as I know this does have a screw down crown

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2 minutes ago, Watchtime said:

As far as I know this does have a screw down crown

Thanks, you are correct. I don't understand however what exact problems the OP have, should post pictures of the parts in question not the entire watch.

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Just now, jdm said:

Thanks, you are correct. I don't understand however what exact problems the OP have, should post pictures of the parts in question not the entire watch.

agree...I think the OP means the "loctite" gave way...or he broke 2 stems...?

 

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9 minutes ago, Watchtime said:

agree...I think the OP means the "loctite" gave way...or he broke 2 stems...?

 

Indeed, the loctite gave way - the stem is still intact 🙂 It's indeed a screw-down crown. 

19 minutes ago, Watchtime said:

Hey dutchy 😉, what broke exactly, the stem or did the stem get loose again?...I would get a new stem,  fit the stem & crown, press in against the spring pressure, and measure the space between the base of the crown and the case. Best is to cut the stem for the correct size, just sand the end a little to get rid of the sharp edges and screw the crown on. A bit of loctite or clear nail polish

This is exactly how I made it! The length is the correct one; I filed it using the aforementioned Dremel tool to the exact length. But then, the loctite did not work. 

21 minutes ago, jdm said:

That is refined benzine (NOT BENZENE). In English speaking countries it may be sold under the names Petroleoum ether, naphta, shellite, and some more.

If the stem screws correctly into the crown, and is correctly tightened, it should hold even without a locking agent, which is most of a precaution than an absolute need. Normally medium strength Loctite is used, but other products should work too.

What does 'correctly tightened' mean, you mean to a certain amount of torque? I've cut the stem to the length that the crown bottom will touch te case side when screwed down entirely, when the stem is completely inserted into the crown. 

I will post pictures in a following post, gimme a sec..

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I would clean the stem first with isopropanol to get rid of any oil from the wasbenzine, then put the stem in a pin vice and screw the crown on a bit tight

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Please see the photos attached, two of the stem and crown and one where you can see the crown having been tightened all the way (to check for stem length). The slightly darker colour on the thread of the stem that is 'inside' the crown should be due to the loctite / lock bond having been used; it was not this colour before. I hope this pictures paint the picture.

4 minutes ago, Watchtime said:

I would clean the stem first with isopropanol to get rid of any oil from the wasbenzine, then put the stem in a pin vice and screw the crown on a bit tight

I'll try this! Can I soak the crown in isopropanol, or will that be harmful to the gaskets of the crown?

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8 minutes ago, Watchtime said:

I would clean the stem first with isopropanol to get rid of any oil from the wasbenzine

There is no oil in refined benzine. 

15 minutes ago, iloveoxytocin said:

What does 'correctly tightened' mean, you mean to a certain amount of torque? 

Yes you need to tighten it so that is does not come lose again. 

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2 minutes ago, jdm said:

There is no oil in refined benzine. 

Yes you need to tighten it so that is does not come lose again. 

I have tightened it pretty tight before - to the point that the stem started to rotate in my pinched left thumb/finger.

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11 minutes ago, iloveoxytocin said:

I have tightened it pretty tight before - to the point that the stem started to rotate in my pinched left thumb/finger.

To tighten the stem you need to hold it with a pin vice, or small serrated pliers. Personally I prefer the latter, holding on a non functional section and not exaggerating with force, exactly how is shown in this video by our Host Mark Lovick. 

 

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Hello there, 

I have just fitted a new stem in a watch which needed cutting down. I held the stem in a pin vice, cut it to length (did it in stages to make sure it wasn't too short!) and then held the stem in the pin vice while tightening the crown on. 

The idea is to use no threadlock or glue if you can help it - what you are looking for is a mechanical stretching (carefully) of the threads of the stem caused by it "bottoming" in the crown and slightly pulling the threads against each other. Pretty much like tightening any stud into a blind hole in engineering. It's about feel and not over doing it as the threads are only tiny and it doesn't take much to strip them. 

Getting the stem to the right length is crucial when using no threadlock or glue as you don't want it too short that it doesn't return to its seat, or too long that it sticks out a bit. Took me a while to get it right as I only had one chance for it to be at the correct length and not too short!

 

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Thanks guys!

I've used a small serrated plier and that did the trick. Indeed, there's much more force available then to fasten it than when I used my fingers or tweezers before. Also, I tried it without loctite first so that I could check the results, and indeed it is (now) not needed, it works fine now and does not unscrew when fitted to the watch. 

(I already let this loctite cure for 3 days so do not think that would influence it further, though I could be wrong there.)

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If you used  serrated pliers have a good look with a loupe where you held it; there's a good chance you raised some metal on the stem, which will now act like a surprisingly efficient file that will wear away the bearing surfaces for the stem on the plate and bridge.

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4 hours ago, nickelsilver said:

If you used  serrated pliers have a good look with a loupe where you held it; there's a good chance you raised some metal on the stem, which will now act like a surprisingly efficient file that will wear away the bearing surfaces for the stem on the plate and bridge.

That is why I wrote about holding to a non functional section, that is one which never contacts anything else.  The threaded section nearest to the crown is perfect for that.

As indicated above already loctite is just insurance to hold over time, with a good mechanical lock there is no need to wait for curing time. 

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3 hours ago, jdm said:

That is why I wrote about holding to a non functional section, that is one which never contacts anything else.  The threaded section nearest to the crown is perfect for that.

On many stems the thread is smaller than the bearing diameter.  So, watchmaker mode, normally I hold the stem in the lathe in a collet,  right next to the thread,  do adjustments, fit crown, out.

 

Without a lathe we'd hopefully grab the stem in pinvice on the diameter that bears in the plate and bridge* then do the work.

 

You don't want to grab anything other than just before the thread as you're into "after detent" territory there and the stem is very weak there, often 0.5m. or less, easy to break things tightening crowns

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Just now, nickelsilver said:

On many stems the thread is smaller than the bearing diameter.  So, watchmaker mode, normally I hold the stem in the lathe in a collet,  right next to the thread,  do adjustments, fit crown, out.

 

Without a lathe we'd hopefully grab the stem in pinvice on the diameter that bears in the plate and bridge* then do the work.

 

You don't want to grab anything other than just before the thread as you're into "after detent" territory there and the stem is very weak there, often 0.5m. or less, easy to break things tightening crowns

Wiith all the respect I disagree with the need or convenience of using a pin vice, and much less a lathe to tighten a stem into a crown, this could be one of the many things that can be done differently according to the individual preference. 

The argument that is safer to hold the stem at the other end because the threaded one is weaker is not convincing to me, because no matter where you grab it, the most twisting (shearing) force will always be at the stress point - that is where the stem enters the crown. Just use cautious but adeguate force according to the stem size.

More than seeing Mark doing with pliers in his video I am supported in my belief by not having ever damaged or broken a stem this way.

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I know where you're coming from JDM, but you have to tighten the crown let's just say "an order of magnitude" more than any unscrewing force it may meet, which often exceeds the coupling tenacity of the groove for the detent. 

I'll admit to grabbing "prior detent groove" and screwing on, but I'm always amazed when that happens and I didn't break the stem.

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On 1/21/2021 at 5:12 PM, iloveoxytocin said:

Thanks guys!

I've used a small serrated plier and that did the trick. Indeed, there's much more force available then to fasten it than when I used my fingers or tweezers before. Also, I tried it without loctite first so that I could check the results, and indeed it is (now) not needed, it works fine now and does not unscrew when fitted to the watch. 

(I already let this loctite cure for 3 days so do not think that would influence it further, though I could be wrong there.)

Good to hear mate, now on to your next repair....👍

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