Lapping firm vs micro finishing paper

[xyzzy]

When it comes to refinishing a case, does anyone know the difference between lapping film and micro finishing film?  The description of those two products seems to be nearly identical.  Even the price overlaps: with an adhesive back, lapping firm is cheaper than micro finishing film, but without adhesive the micro finishing is cheaper than lapping.

I think polishing with a film and backing might be more effective than a wheel when it comes to making a fair surface.

[JohnR725]

What kind of case refinishing are you thinking of doing?

Perhaps a picture of the case that you want to refinish would be helpful.

 

[Neverenoughwatches]

1 hour ago, xyzzy said:

When it comes to refinishing a case, does anyone know the difference between lapping film and micro finishing film?  The description of those two products seems to be nearly identical.  Even the price overlaps: with an adhesive back, lapping firm is cheaper than micro finishing film, but without adhesive the micro finishing is cheaper than lapping.

I think polishing with a film and backing might be more effective than a wheel when it comes to making a fair surface.

Better than a buffing wheel ?

[JohnR725]

41 minutes ago, Neverenoughwatches said:

Better than a buffing wheel ?

It depends upon what you're doing. I used various flapping films for polishing steel watch components. But those are flat components. Conceivably something on a watch case could be polished with a lapping of film where you want a straight edge otherwise I would go for buffing wheel of various sizes. Then of course if you're working in a Swiss service center with infinite deep pockets they do have special lapping machines for their street surfaces but none of us are ever going to get those and I doubt they use lapping film the probably using a diamond lapping wheel

[grsnovi]

In the machine shop, lapping would generally refer to a flat surface.

You would be able to apply a "micro" finish to any surface.

Note that the available size of the grit particles on the lapping film is significantly smaller in size than the grit on the micro finishing film.

[xyzzy]

14 minutes ago, grsnovi said:

Note that the available size of the grit particles on the lapping film is significantly smaller in size than the grit on the micro finishing film

But from 40 micron to 9 micron, they both overlap in grit.  One thinks 3M wouldn't make two different products that were exactly the same, but every published spec seems identical.

To sand a fair surface for paint, you don't use a random orbit sander or anything like a buffing wheel.  Instead blocks or longboards are used.  These are flexible yet stiff backers for sandpaper.  They bend to a curve but make a fair curve.  The high spots that are smaller than the curve get sanded down.  If you sand with something soft, like say sandpaper in your hand, it sands the high spots and the low spots.  So while the surface is smooth vs the grit you sanded at, i.e. at the micron scale, it's still lumpy at a much larger scale.

For sanding a flat surface, I use a glass plate as a backer.  Something like a zinc or brass plate with a paste is a more traditional method, but I don't have that.

But for the the sides of a watch case that should be curved lengthwise but flat across the short dimension I think there might be a better way.  I'd like to put some adhesive backed sandpaper on a plastic backer of the appropriate stiffness and try to longboard the sides.

 

[grsnovi]

Trying to figure out 3M's strategy isn't that helpful. Both films use aluminum oxide but the Cousin's spec doesn't say anything about the actual film material and it only mentions the thickness of one (unless you've checked the #M specs, I haven't).

Have you looked at any of the polishing/buff sticks that you charge with your own compound?

Also, have you watched any of Nekkid Watchmaker's videos? He does a LOT of case restoration and seems to be EXTREMELY good at it.

There likely isn't much difference in the films sold by Cousins. You'd likely approach a lapped finish using a glass backing. I don't think you can really hand-hold a truly vertical orientation by hand so unless you have a jig figured out you'll likely get curvature in both directions.

Watch a couple of Joe's videos (Joe is the Nekkid Watchmaker).

[xyzzy]

1 hour ago, grsnovi said:

Trying to figure out 3M's strategy isn't that helpful. Both films use aluminum oxide but the Cousin's spec doesn't say anything about the actual film material and it only mentions the thickness of one (unless you've checked the #M specs, I haven't).

 

Lapping film is "A high strength polyester backing" while micro-finishing film is "A high strength polyester film backing".  Sounds pretty much the same.  3M has thickness in what specs they provide, 3 mil for both.

[grsnovi]

Going to the 3M site you'll see they discuss both products in the same brochure. They have a range of film thicknesses running from 2 mils to 6 mils. They are optionally coated with aluminum oxide, silica carbide, diamond, cerium oxide and chromium oxide. 3M supplies them in sheets, disks and rolls with or without adhesive backing.

So, for all practical purposes I would think you could select either one or the other to suit your budget.

Depending how scratched your case is you might need to start with something with a heavier grit than micron grade.

Can you show us what you're polishing?

[nickelsilver]

I don't know the specific difference, but I've always used the lapping film in the finer grits, like 12 micron and down (1 micron is as fine as I use), and the micro finishing film in the larger grits, like 20, 30, 40 micron. The latter definitely seems more robust, but other than that both are great.