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RCDesign

Lapping a Speedmaster MkII case

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I have over the years refinished a few Speedmaster MkII cases for friends.

They are fun to work on as they are,usually quite beat up och the surfaces have been polished a few times to many.

Last week a friend of mine told me that there was a 1970 MkII for sale on a Swedish auction site. I was born 1970 so this watch I just had to have!

On Sunday when the auction was about to close the website where the auction was held started to act up and I could not log on.........
About thirty seconds before it closed the webpage loaded and I was able to submit my offer....then it was down again......did I win or not!!??,
I waited for the usual confirmation mail when you have won an object and five minutes later I had mail, -Yesssssss.....

The watch arrived On Tuesday and looked like this:

 

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Not to bad, but the sunburst was gone and the top surface had......"straight graining" .....I guess the previous owner used a abrasive rotating mop or something!

The case was practically free of deeper scratches and dings so a good prospect for a lapping session!

The case was stripped and I started with the sides:

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I do this part in my small Boley lathe with 90mm discs that I have made and a small tiltable table to set the angle.

Depending on the geometry of the case you can either slide the case directly on the table or use a adaptor to get the right angle - in this case no adaptor was used.

First run on one side done:

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First disc is 400P so you have to be careful, especially with the start/edge where the case can grip the disc - and you do NOT want this as you will have a case with scratches in places they where not intended to be!

After 400P I move up to 1000P and finally a last run with 2000P. This usually gets the surface almost up to mirror finish but,a quick final touch with a mop gives it,that final shine.

When the surfaces are flat and when needed polished, it is time to grain the sides and lapp the sunburstpattern on the top.

This is done in a small mill I have with a tiltable spindle using a 305mm rotating disc and another home made tiltable table.

For this case I use a 120P paper so you really have to take it slow and be sure all the angles are set up correct or the disc will chew material in places you do nor want it to!

The result

 

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I was not 100% pleased! There where some spots there the graining did not go al the way up to the grained edge around the glass. This was obvious in the pictures and reflections in some angles on the wrist - I relapped to top surface....

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Some grease from my fingers on the chamfer in the pictures but the graining is better now!

I am waiting for a NOS dial and crown - when they get here I will strip and clean the movement as well.

 

 

 

 

 

Edited by RCDesign

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27 minutes ago, vinn3 said:

is that a milling attachment to a lathe?   vinn

That's a stand-alone milling machine. Easily recognized by "mechanics".

Edited by jdm

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I have seen these lapping machines before, but I can not quite figure out how it works so that it forms this beautiful  sunburst pattern? Can you please show the principle of image , sketch, video , etc.

 

Very fine result by the way!!
Edited by maclerche

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the key to lapping is the diamond plate ( the disk in the photo).  granules are pressed into a metal disk.   mainly to be used on a lathe where you can control the speed. it is FM  [friggin magic].  used mainly by the Germans in WW11.

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On 2016-08-19 at 10:12 PM, maclerche said:

"I have seen these lapping machines before, but I can not quite figure out how it works so that it forms this beautiful  sunburst pattern? Can you please show the principle of image , sketch, video , etc."

Here is a simple picture of how it's done:

slipskiva-jpg.90909

The case is presented to disc at 270deg as close to the edge as possible and at the horizontal center using a tiltable table shown above. The case is rotated in this location using a specialy made holder/chuck and "viola" you have a sunburst pattern!


As the length of the case in contact with the disc is so short the brushing will be almost straight, but it will NOT be perfectly straight - that is the reason I want as big a disc as possible! 

 

For now I have settled for 305mm as this is the largest dimension I can get pappers for - easy!

I'm using standard paper right now but have a set of old cast iron discs that have been used by my grandfather to lapp using glue and a special absrasive mixture he had when lapping diamonds.

 

To use them I firs have to renovate the matching headstock of the lathe he used - but I think it will be woth while as that lathe will be a good base for a more advanced lappingmachine! :)

 

Here is a video of the principle for getting the pattern:

 

Sunburst lapping a Omega

 

I like to use a much lower rpm setting and use a fixture for the watch case - but thats just me!

 

Here is another machine

 

Edited by RCDesign

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Another example to show it's the ingenuity and skills that make  the results, not the tool.

In theory the large disc could be replace by a drum with abrasive on the side, but I've never seen anybody doing that.

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Thank you very much for posting this, great work!

in the future I would love to be able to setup a lapping machine, as most of the watches I like have a sunburst finish, and it is really the only way to achieve clean edges.

are you the same person who posted on the TZ forum a while ago! I think I recognise the milling machine from somewhere! 

Do you think one could achieve a good setup with a lathe (provided it can take a 305mm grinding disc of course)? I have been thinking along those lines...

 

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thanks for the very good  lapping  web sites,   they are both using lapping machines.  this could be done on a lathe (compound lathe) IF you can  buy or build a fixture to hold and turn the watch case.

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My lapping attempts have been posted on other sites as well so it's probably my mill you have seen before!

Lapping can be done in many different ways but with a disc seams to be the easiest way!

I actually built a small machine from a belt sander where I can index my existing chuck to the right angle. This will produce 100% straight graining IF I can get hold of good sanding belts that have no overlap (where they are glued together to a circle) => same thickness all around!

A lathe is a good starting point for setting up a lapping rig but my mill actually has one big advantage - I can set x, y AND z (the height) This makes setting pup the tiltable table and chuck so much easier!

" Do you think one could achieve a good setup with a lathe (provided it can take a 305mm grinding disc of course)? I have been thinking along those lines... "

Do not get stuck with my 305mm discs - the commercial lappingmachines I have seen all have 240mm discs! A titable table on you cross slide and a suitable chuck or holder for the case and you are good to go! ;)

 

Simple chuck I used when I started testing different lapping setups:

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Edited by RCDesign

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Thank you very much. Love the idea of the belt sander to obtain the straight lines, it would be quite a machine if you can make this work (better than the pros'!)

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The difference the proper finishing made is night and day, I love the look of this piece and I'm thinking the watch is lucky to have you for an owner. I still can't quite work out how you created the sunburst, despite the explanation, but then I've never used machinery like that. 

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On 2016-08-25 at 8:13 PM, Ishima said:

The difference the proper finishing made is night and day, I love the look of this piece and I'm thinking the watch is lucky to have you for an owner. I still can't quite work out how you created the sunburst, despite the explanation, but then I've never used machinery like that. 

If you look at this clip )abt. 40s in) you se how the sunbust lapp an Omega case! ;)

 

Nothing magical - you just have to have a sturdy setup and a good fixture to get the angle/s right!

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