Struggling to heaps to get a good specular polish

[gkmaia]

I got a zinc block from https://martyranodes.com/about-us/ and the bergeon fine diamond powder and oil.

When polishing a screw head I am getting a specular polish that I am happy with. 

But when polishing plates I am getting lots of scratches.

I suspected the zinc block was filled with impurities so I removed around 2mm of it's top with a file. Did not use a sand paper cause I did not want to leave any carbide incrusted on the zinc. Gave it a good clean then wiped with alcohol.

And before polishing the plate I gave it a good scrub with proper degreaser. Then an ultrasonic bath, distilled water rinse, then alcohol rinse. 

Very carefully polished with gloves to avoid any contamination. 

One thing I notices on the screw head. If I put little pressure I get some fine scratches, but if I put greater pressure the specular looks great. The same technique does not work with the plate. 

Also tried using most of the plate, of just a small part of it. No difference. 

Is it possible that the zinc plate I am using has some microscopic impurities in it?

I also tried to replace the zinc plate for silicone, paper, vegetal paper. Other surfaces that were soft and hard enough to allow the diamonds to sink on them.

I need help... I am out of ideas.

 

[HectorLooi]

I don't think it is necessary to use diamond paste to polish metal. Keep your diamond paste for hard substances like glass and rubies.

A metal polish like Autosol is good enough for most polishing jobs. I normally just put a dab of Autosol on a piece of peg wood and rub in a circular pattern. Or use a larger piece of wood and rub the object on it.

BTW, are you repolishing these surfaces or did you machine them from scratch?

[HectorLooi]

Oh yes. Be careful when polishing the plates, it's very easy to polish away the plating and expose the underlying metal.

[gkmaia]

Thanks, that was spot on.

Before reading your answer I had another go with a wood block. First I had a go with one of those wood cuts you get from a hardware store. Quite soft and I got way less scratches, but still not as good a silicone sheet I tried before. Then went to try on a piece of a tree I did cut a couple years ago. Really hard wood and I got only 3 small scratches!!!!

Was such a massive improvement. Exactly as you wrote Hector.

I think if I had an extremely pure zinc block with no internal blisters or sludge it would maybe do... but not sure where I could find one.... would be keen to try as everyone talks about a zinc block as the way they did back in the day.

On the zinc plate would firing a torch to melt the surface may close the blisters and some how improve surface?

 

Edited January 31, 2021 by gkmaia

[nickelsilver]

I imagine your zinc isn't the issue. What grit is the diamond powder? What type of oil are you using? The mixture should be thick, like twice as thick as peanut butter. Natural plant oil is better than mineral oil. The plate should have a textured surface, like from a very coarse file. It does have to be clean of course, and it's good to keep a file that is only used to dress the plate.

 

When polishing you want the paste to dry out. If it's wet the grains can ball up and give you scratches. It will get to a sort of "magic" state where it's just dry enough but not too dry. Some guys will use one part of the plate with wetter paste and have a dry patch for the final bit.

 

Generally you'll flatten the part on self adhesive precision graded abrasive paper stuck to glass, 12 microns is a good general grit, and you can go straight to polishing. Clean the part extremely well to not transfer grit to the plate. Something like your set bridge you'd want to glue or shellac to a subplate and hold that in your tripod.

 

I use round plates about 80-10mm diameter. When I dress them I make a line down the middle of the plate and keep the feet of the tripod on one side, part on the other. If the polishing is going well but it get just a bit too dry and you don't want to mess things up reapplying paste, just breathing on the plate can help.

 

Most folks I know use tin rather than zinc, but both work. I prefer tin. Swedish and Finnish watchmakers like to add about 0.5% of silver; but when I asked several how they add the silver they said they just add a little piece to the melted tin- which is nowhere near the melting point of silver and just proves how much superstition surrounds polishing.

 

As for abrasives, as Hector said diamond isn't necessary. I used to use aluminum oxide from Linde, 0.3micron, which was great. Around here everyone uses Biodiamant, which is a prepared diamond paste in like a giant chapstick tube, so I use that now. Both work fine.

[JohnR725]

19 hours ago, gkmaia said:

bergeon fine diamond powder

 

17 hours ago, HectorLooi said:

diamond paste

The real question is is it really diamond powder? It will be nice to have the catalog numbers so we can look up what it is. This is because traditionally watchmaking there is a another polishing powder that has a name kinda like diamond. This other Powder is white and it's basically aluminum oxide.

Than one of the things that would've been nice to see is what they both look like before you tried the final polishing? The reason I ask is Polish out scratches. If both parts had been finished previously differently then you results are going to be different. Usually you have to go through several steps of finer and finer grit whatever you're using to slowly reduce all the scratches down to almost if not nothing then you can polish. Otherwise you're wasting your time. The link below might be helpful.

 

 

https://watchesbysjx.com/2015/01/explained-the-fine-art-of-black-polishing-aka-speculaire.html

 

[gkmaia]

I start with 3000 grit till all deep scratches are removed. Then on a 90 degree angle I move to 5000 grit. Then 90 degree angle move to 7000 grit.

Always straight movements and good cleaning between grits. Also checking in the microscope if any 90 degree scratches are left from previous grit. 

Then a good clean on ultrasonic, distilled water and alcohol before the polishing.

My paste is made of Bergeon fine diamond powder and the same basic machine oil I use on my old lorch lathe. But the consistency is more wetter than fry.

I find easier to use just Pith Wood instead of 

"When polishing you want the paste to dry out. If it's wet the grains can ball up and give you scratches. It will get to a sort of "magic" state where it's just dry enough but not too dry. Some guys will use one part of the plate with wetter paste and have a dry patch for the final bit."

I will try today to give the zinc plate a **BLEEP** and or a 2nd file cut and go about a much dryer paste. See how that goes.

 

[JohnR725]

It's interesting is if you go to the bergeon and search for polishing powder you get something and I snipped out the image. But if you do a search for diamantine the classic watchmaking polishing compound which is not diamond but aluminum oxide it also comes up as a separate product. I snipped out both images.

Then a really good book to have is watchmaking by George Daniels. It covers all kinds of interesting things related to making a watch. Although action the book does cover how to make a watch but it covers all the components used to make a watch. Then aspects like polishing so I'm quoting a section but it's too big to quote so I just scanned it.