Chronometer seconds hand replacement on Landeron 51

[Jakub]

Hey guys!

I recently finished service on Chronographe Suisse with Landeron 51 movement, and it went very well except one cosmetic issue.

Alredy at purchase there was a problem with chronograph center seconds hand that is indeed very beautiful, but too heavy for this function. Every time resetting chronograph function it wouldn’t return to “0” but it slipped a bit when hammer hits heart on seconds wheel. Didn’t bother me too much, since I inspected mechanic function and that looked OK. My initial thought was to tighten it with pin vice and maybe use a drop of epoxy to keep it in place.

During disassembly I inspected this closer and find someone before already messed with it and tube was badly damaged and cracked. This lead me to decision to replace it. 

So measured the end of pinion and I see 0,29mm. Put down note and went to search for replacement. Found on Cousins they have these hands with maximum diameter of 0,27mm. 

Since I’ve never replaced hands my question is if that is ok to if hand diameter is this 0,02mm smaller and is possible to fit it without any adjustments?

Regards

Jakub

[nickelsilver]

0.02mm is a bit too much. But, where did you measure? The pivot there is tapered normally, so it will be smaller at the end and larger a mm or two back from the tip. When I make tubes I usually drill 0.01mm smaller than the smallest part of the pivot, then use a tapered broach to bring it to final size. When broaching check often, and when the hand fits about 1/3 of the way it needs to go with normal pressure (you can still pull it back off with tweezers), stop. That should be a good friction fit for a chronograph hand.

[clockboy]

I have not worked on this movement but I suspect it could be that when fitting the centre seconds hand the hammer has to be engaged as well when fitting. I found this issue to my cost working on a Brietling fitted with 7750. I therefore purchased a dedicated 7750 movement holder and it resolved the issue. Also worth noting the centre seconds has to be tight or it will drift.

[Jakub]

43 minutes ago, nickelsilver said:

0.02mm is a bit too much. But, where did you measure? The pivot there is tapered normally, so it will be smaller at the end and larger a mm or two back from the tip. When I make tubes I usually drill 0.01mm smaller than the smallest part of the pivot, then use a tapered broach to bring it to final size. When broaching check often, and when the hand fits about 1/3 of the way it needs to go with normal pressure (you can still pull it back off with tweezers), stop. That should be a good friction fit for a chronograph hand.

Thank you for taking time to help me with my small problem I really appreciate it  This help a lot! 

Gonna get down to cousins and order broaches right with hands (don’t expect to nail it on first attempt)

Regards 

Jakub

[Jakub]

56 minutes ago, clockboy said:

I have not worked on this movement but I suspect it could be that when fitting the centre seconds hand the hammer has to be engaged as well when fitting. I found this issue to my cost working on a Brietling fitted with 7750. I therefore purchased a dedicated 7750 movement holder and it resolved the issue. Also worth noting the centre seconds has to be tight or it will drift.

I my case it is engaged when fitting. Anyway I still find challenging to fit this center hands on chronos. All good and aligned until press down and there we go, one second off

[clockboy]

51 minutes ago, Jakub said:

I my case it is engaged when fitting. Anyway I still find challenging to fit this center hands on chronos. All good and aligned until press down and there we go, one second off 

51 minutes ago, Jakub said:

I my case it is engaged when fitting. Anyway I still find challenging to fit this center hands on chronos. All good and aligned until press down and there we go, one second off

I have not worked on this movement but I suspect it could be that when fitting the centre seconds hand the hammer has to be engaged as well when fitting. I found this issue to my cost working on a Brietling fitted with 7750. I therefore purchased a dedicated 7750 movement holder and it resolved the issue. Also worth noting the centre seconds has to be tight or it will drift.

[clockboy]

Fitting chrono hands can be tricky.I own an upright hand pusher tool such as below. Makes fitting so much easier

 

[Jakub]

3 hours ago, clockboy said:

Fitting chrono hands can be tricky.I own an upright hand pusher tool such as below. Makes fitting so much easier

 

That for sure must be nice. One day... Now I’m more about buying tools for first year of BHI course. There is plenty including lathe and jewelling set besides many others so

[Poljot]

5 hours ago, Jakub said:

I my case it is engaged when fitting. Anyway I still find challenging to fit this center hands on chronos. All good and aligned until press down and there we go, one second off

ETA7753 is another "good" example of how painful and frustrating it is to remove and install Central Second hand. I think i mentioned this before, that i had to use a fine sub-punch during removal process. Nothing else worked. To avoid any  issues with fitting that old hand, i ordered a new replacement Central Second hand. Fitting the new one was also not easy, even with the use of a special holder.

Edited December 17, 2020 by Poljot

[Jakub]

52 minutes ago, Poljot said:

ETA7753 is another "good" example of how painful and frustrating it is to remove and install Central Second hand. I think i mentioned this before, that i had to use a fine sub-punch during removal process. Nothing else worked. To avoid any  issues with fitting that old hand, i ordered a new replacement Central Second hand. Fitting the new one was also not easy, even with the use of a special holder.

Well if the picture shows result then well done!

So far I worked on 1 Seiko and it was 6139B from Pogue and, that was so easy. I’m sure you guys know this well but it was first time for me to see center pinion with specially shaped pinion on dial end to fit hand. I mean that solves so much trouble. Wish to see this more often since I like to work on chronos the best, but this hand is like “sweet end” before casing. Well I guess practice, practice, practice...

[rodabod]

That watch has a stunning dial and hands, and what appears to be a gold case, judging by the lugs. I'd be tempted to try to get an old blue steel hand which matches more closesly than a new part from Cousins. Although they may have something suitable. It's not too hard to tighten hand pipes very slightly if they are too large, but this can be problematic with chronographs due to the flyback operation (which I'm sure you know already). Don't be afraid to make your own broach from an old pinion if you have a suitably sized spare - you can make one with a single cutting side which is good enough for brass pipes.

[Jakub]

On 12/17/2020 at 11:35 AM, nickelsilver said:

0.02mm is a bit too much. But, where did you measure? The pivot there is tapered normally, so it will be smaller at the end and larger a mm or two back from the tip. When I make tubes I usually drill 0.01mm smaller than the smallest part of the pivot, then use a tapered broach to bring it to final size. When broaching check often, and when the hand fits about 1/3 of the way it needs to go with normal pressure (you can still pull it back off with tweezers), stop. That should be a good friction fit for a chronograph hand.

Hi! Just want to give you a update. Finally I received parts and tools for hand replacement. I didn’t do the drilling since I don’t have tools for that. Broach worked perfect and I successfully replaced right on first try. About 1/3 with tweezers and then push down. 0,3mm tapered broach was the one to take it home for 0,27 hand to fit 0,29 pinion.

BR

Jakub