Positioning platform - accurate drilling

[SuffolkM]

Hi folks

I'm in the process of replacing a worn platform on a French clock. The main plates have holes tapped holes where the previous platform sat, and I'd like to drill the new platform to use the same holes. I prefer the holes not to be oversized, so that the platform locates precisely each time it is installed. However, to get the platform in the perfect place for the pinions to engage the contrate wheel, I need to position it over the existing holes for testing and confirming the final position.



I'm curious if anyone has any tips on a good approach for locating the centres on to the top of the platform while it's in situ? I'm thinking along the lines of scribing from two fixed datums, or using precise measurement with callipers from several locations which I can repeat with and without the platform in its test position. Any other ideas?

Michael

 

[Uhralt]

The depthing of the platform pinion to mesh correctly with the contrate wheel is rather critical. Therefore, a little oversized holes that allow adjustment are normally a good thing. You will notice that the holes in the original platform are also oversized for that purpose. I know only of modern clocks that lock the platform in an exact position.

Uhralt

 

[Christopher Lloyd Owen]

Out of curiosity, Michael, what is wrong with original platform do you think?

 

[SuffolkM]

Thanks Uhralt. If X is the width of the movement and Y is the depth of the movement: I think I will mark the X positions on the plate fronts and back, and then based on the fact the holes are central in the middle of the plate thickness I'll mark a crossing line to get the Y centres. I'll start with the holes small and see how it goes.

Christopher, the problem with this balance is that a pivot has broken off in the jewel (top of the pallet). Additionally, the bridge has been lifted with a shim, and there is a problem underlying that which I suspect was to try and lift the pallet above preexisting wear. These two issues combined are leading me to replacing it rather than having the clock come back.

Michael

 

[Christopher Lloyd Owen]

There's just a bit of me that would do my best not to replace an original (seemingly good quality) lever escapement. The fact that it is shimmed slightly wouldn't worry me unduly. A pivot can be repaired. Where are you? UK or US?

But if you have to replace, Uhralt is right, the holes in the platform are always a little oversize to get the depthing correct, having set the endshake of the contrate wheel first. I'm not sure how you'd set the platform otherwise!

 

[SuffolkM]

Hi Christopher - I definitely share those reservations! I am in the UK

 

[Christopher Lloyd Owen]

Michael - I'll PM you ... Chris

 

[Jerry Kieffer]

Hi folks

I'm in the process of replacing a worn platform on a French clock. The main plates have holes tapped holes where the previous platform sat, and I'd like to drill the new platform to use the same holes. I prefer the holes not to be oversized, so that the platform locates precisely each time it is installed. However, to get the platform in the perfect place for the pinions to engage the contrate wheel, I need to position it over the existing holes for testing and confirming the final position.

View attachment 677770 View attachment 677771

I'm curious if anyone has any tips on a good approach for locating the centres on to the top of the platform while it's in situ? I'm thinking along the lines of scribing from two fixed datums, or using precise measurement with callipers from several locations which I can repeat with and without the platform in its test position. Any other ideas?

Michael

Michael
I would agree with others that the existing platform can likely be repaired and that would be your best option.

However, assuming that a new platform is best option, new precise hole locations are easily marked with easy to construct blind hole center punches.

The attached sketch should be self explanatory.

After constructing the punches, the platform is set in position on top of the installed punch points. At this point, finger pressure downward on the platform will form tiny prick marks that can be enlarged after the fact, clearly and precisely marking the holes for drilling.

Jerry Kieffer

 

[SuffolkM]

Thanks a lot, Jerry - that's a good idea indeed. I'll make some punches on the lathe side that seat in the holes but will drop back out reasonably easily, and see how it goes.

This situation is now likely to be two projects - one to investigate repairing and resilvering the early part, and another to fit a new balance as requested. I will give the owner some input on this in the hope they will want to engage a watch repairer for the balance, which can then be returned to the clock. As no harm is being done to the clock or the original part it's not too stressful!

Thanks
Michael

 

[Leigh Extence]

Michael,

Whatever you do, make sure the original platform is put in a clear bag and labelled that it is the original to the clock. Then someone in the future can get the platform repaired and put the lost value back into the clock. So many valuable carriage clocks have been ruined by losing their original plaforms.

Leigh

 

[SuffolkM]

Leigh, I assuredly will. I tend to place replaced parts in small velvet bags. I find it encourages customers to consider the part to be valuable and keep it properly with the clock - even though these bags are themselves not expensive. I think we all know there is only so much that can be done so I will persist.