Finishing and Polishing Brass

[Peterpasha]

I make pens in a Taig lathe, usually brass either left bright or electroplated copper. My question is about finishing and polishing brass. This is after 4 hours of using progressively finer grits of sandpaper, starting at 320 and ending at 12,000, followed by polishing with dialux yellow and blue. And I still have these fine lines. I want a mirror finish but at some point I wonder, are these lines just in the grain of the brass itself, or can I get rid of them? Any advice would be greatly appreciated!

 

[DavidR8]

Welcome aboard!
Curious what it looks like before you start the polishing process.

 

[PeterT]

To my eye, because the scratches look like they have a somewhat common orientation, it looks like either you have not completely removed the coarser scratches from some prior rougher grit stage during the progression. Or, sometimes if your polish applicator (cloth, paper towel, whatever) itself is somewhat abrasive, it can introduce new scratches during polishing. Or maybe you used the same polishing applicator/wheel/buff of the coarser grit on the finer grit?

A finishing technique I use is change direction with introduction of every new grit. Example, if you sanded radially with 600#, then switch to longitudinal on 800#, then radially again or completely different offset angle at 1200#. You should only see uniform micro-striations of the finer grit with no underlying striations of the prior coarser grit. Vs. if you always do them in the same direction, then prior deeper scours which haven't been completely removed may be getting masked. This isn't always possible on all objects (especially round things where you are trying to keep dimensional conformance), but something to try & do if possible. Brass has nil porosity unless its a very weird alloy, so you should be able to get it to near mirror. Also some polishes have a wax or agent which is more like a thin gloss coating which enhances shine & tricks the eye a bit. As opposed to abrasive only polish. The wax/additive type makes the finish look better for sure, but the wax typically wears or evaporates over time. But that's a different issue.

I also know that photographing metal makes them look worse than in real life so you probably have a nice finish, just want it better.

I just finished a few pen kits & other Xmas objects myself for the first time. I was lurking on that IAP forum & got some good ideas. But I have discovered I do not like 'the brown stuff' on my metal lathe even with ways wrapped in Saran & vacuum on. So if I ever pursue this as a hobby I'd be on the lookout for something like a Taig or Sherline. A lot of guys use a wood lathes but typically not for mostly metal bodies. I don't really have the room or the desire for a separate lathe.

Lets see some more of your work, I'm interested!

 

[Tom O]

I would think that you would have to use a polishing compound like brown Tripoli or jewellers rouge to achieve a high polish.

 

[Tomc938]

I would agree with PeterT. If you go to the next finer paper too soon, any fine scratches left will not com out without TONS of work. Also, you need to carefully clean the part between changes in sandpaper. All it takes is one grain of coarser grit to mess up the finish.

Finally, store each paper separate from the rest. You can introduce grit for a coarser paper to a finer paper if you don't.

 

[PeterT]

I bought some of these buffing wheels from AliExpress. They are significantly softer than the typical felt pads that come with Dremel tools. So not sure if I was ever using the felt pads correctly or wrong polishing compound or wrong stage because they seemed to be doing more scuffing than blending & polishing. Metals I find to be more forgiving because they are harder. But when it comes to clear coats, which is significantly softer & responsible for the optical depth look, you also have to be conscious of pressure & heat. I have some 3M auto polish left over from another hobby I used with these soft buffers & it was pretty easy to work with. It will take me about 98 lifetimes to use it on small projects. Another thing I've noticed is that polishes can lose their solvent over time & act differently as they become more pasty vs a thinner slurry.

 

[Peterpasha]

Thanks for all the advice, I will try Peter T's method of different directions for different grits and see if I can get a better finish. When I started out, I was making pens out of copper which finishes and polishes beautifully but is a cast-iron bitch to machine. I would have to stop and resharpen bits often, especially when drilling out the interior. Then I started using brass which machines beautifully but is harder to finish, and electroplating it with copper. That is how I will continue, if I can get the fine scratches out. Electroplating doesn't cover up the fine scratches, they show right up in the copper and by then it's too late to get rid of them.

These aren't in any particular order, just various ones that I've made .
This was the first pen I sold, probably should have gotten much better before I started selling them, but a friend overseas saw them on my Facebook and wanted to buy a few. She bought this one for herself and bought another one to give to J.K. Rowling as a birthday present (we all lived in Portugal at the same time), apparently buying presents for billionaires is a difficult thing!

Experimenting with different finishes, this was a thin layer of spray lacquer, but it didn't hold up to daily use. I want to get away from using Cyanoacrylate glue (superglue) which most pen makers use as a finish because a lot of makers develop sensitivities to the chemicals.

This is an electroplated pen, showing how the fine scratches from the brass show through into the copper.

Rejects get adapted into suncatchers and Christmas Tree ornaments.

A copper blank showing the difference between unfinished and on the way to being finished.

My first pen in copper for my wife. I hit it utterly out of the park on my first try and haven't come close to this again. This has a CA Finish which still holds up.

This is J.K. Rowling's pen.

 

[Bandit]

Welcome from south of Calgary. What happens if starting with a finer grit? Yes takes longer, but? Are the marks caused by metal build up on the paper? Try to see which grit is leaving the marks, likely well before the 12000 grit. How thick is the copper plating? Can it be plated over again? And, yes the marks appear to be around the diameter of the tube and the marks appear to be quite deep in the unfinished to getting finished picture. Are you turning down outside diameter of barrel?
Anyway some questions as I have not done pen turning.

 

[Peterpasha]

That's an interesting point, I'll try it with starting with a finer grit for initial sanding.

 

[PeterT]

You can try a finer grit at any stage if you are trying to get a spot check read on underlying scratches. Its kind of counter-logic to normal finishing where go progressively finer, but in that case you are trying to get a surface level or otherwise conformed before going to next stage. Otherwise you just end up making a smooth wood grain or polished potato or whatever the right expression is.

I order my wet/dry paper from this mail order place (Canada) because he carries a good line (Mirka) & price is decent enough. Autobody supply places are another source. And there is some real junk on the market to be avoided.

Mirka Waterproof Sanding Sheets - Wood Essence Canada

Mirka waterproof sanding sheets are flexible and tough for use on metals, finished wood, plastics & composites and are a great choice for tool sharpening.

www.woodessence.com

Particularly for contours, I really like the Mirka scuff pads which come in high grit#

Mirka Mirlon Total

www.woodessence.com

Wood Essence : Canadian Suppliers of Specialty Wood Finishing Products

Wood Essence : Canadian Suppliers of Specialty Wood Finishing Products

www.woodessence.com

 

[DPittman]

And there is some real junk on the market to be avoided.

I suspect the "real junk on the market" is the stuff I buy, but just in case I (or others) can avoid that stuff, I'd be happy to hear recommendations of brands/styles to avoid.

 

[PeterT]

My first two pens with CA finish. I've been using CA as an adhesive for models for +30 years but never considered as a coating system. But after seeing so many examples I just had to try out of morbid curiosity. I think there are better finishes but its the rapid buildup of glue + accelerator. Doing a regular clear coat would take much longer.

I went to polish on Green too soon. The picture looks better than real life. I can still see the rolling hilltops of the glue lines that were not blocked down to the base of valleys. But I kind of messed up the wood diameter which was already proud of the pen body diameter & was getting concerned my CA application was too thin in that area so I stopped. On brown burl I applied more coats & blocked with 600# between coats & that helped. More thickness to work with & a better surface to start sanding. The trouble with pens is if you want to sand in a different direction to the rotation axis (longitudinally), you risk making facets which is even worse. What I find works best is a foam rubber pad backing with the right amount of flex. And as mentioned above, fine grit scuff pads have a nice way of conforming to surfaces.

6061 aluminum model rocker covers with 600# scuff pads/wheel. I actually wanted more of a matte finish, just enough to blend out the prior hand filing/sanding. Some people use the scuff pads wet with water or WD-40 id loading is an issue. I know it works on copper but the issue is almost immediate oxide layer, so there may be some tricks to specific polishes.

 

[trevj]

I make pens in a Taig lathe, usually brass either left bright or electroplated copper. My question is about finishing and polishing brass. This is after 4 hours of using progressively finer grits of sandpaper, starting at 320 and ending at 12,000, followed by polishing with dialux yellow and blue. And I still have these fine lines. I want a mirror finish but at some point I wonder, are these lines just in the grain of the brass itself, or can I get rid of them? Any advice would be greatly appreciated!
View attachment 40927

I have a LOT of experience polishing brass and other metals to a mirror finish by hand.

4 hours is frikken insane time to bury in trying to get a decent polish! Something is very wrong in your set-up! It's either a wrong choice in methods, or materials. Maybe both.

I would suggest among other items worth pursuing, for your needs, is a MicroMesh Kit. https://www.aircraftspruce.ca/catalog/cspages/micromeshstd.php These are used for polishing aircraft wind screens and making them optically 'near' perfect. I have found that going much past 2000 grit is a waste, on most metals, unless you are trying to produce a truly flat, perfect, mirror finish! (hint, use a very flat, solid ( I used a lot of Acrylic sheet offcuts, because I had them), backing block as you sand that mirror face!) Past 1000 grit or so, you can get a great, near perfect finish, with a clean, soft cotton cloth or a lint-free towel and some metal polish (look for Solvol Autosol! my recommendation!) Clean carefully with soapy water between grits, and wipe off carefully! Use clean soapy water to lubricate the sandpaper (a couple drops of dish soap in a 500 ml squirt bottle is good!) when sanding.

But you should be able to get a lot closer than you have, using autobody grades of sandpaper (up to 2000-3000 grit usually available) used wet, with a little dish soap in the water, as well as some clean soft cotton cloth and metal polish. Same rules apply! Clean between grits!

Primary effort needs to be put in to removing ALL of the previous grit's marks before moving on, and paying close attention to keep from contaminating higher grit abrasives with lower grit particles! At first, you will likely have to step back in the process to restart it at a lower grit, but if you can pay enough attention to a project to work on it for four hours and still not be happy, I figure you have it in ya to spend 35 or so minutes and pay close attention, and get great results! It's a bit Art, and a Bit Science, but these are my experiences in doing what you are trying to!

FWIW, I would work in the same linear direction through all the grit ranges. I found that I had far fewer artifacts of previous work, showing up on the finished product. I did a LOT of this work, by hand, rather than under power and spinning, which would have been MUCH quicker!

Per your later posts, I would say that your problem is one of cross contamination, rather than of a problem with the metal. Consider whether your polishing papers are embedding particles into the work, that are ruining the later efforts! Suggest light pressures, and LOTS of cleaning between wet passes, of the various grits. I know that I never had any trouble getting to a near optically perfect surface, at far less a grit than you claim to be going to!

 

[Peterpasha]

Whoa! Thanks for the great reply.

 

[trevj]

Whoa! Thanks for the great reply.

Welcome!

I worked in a Military Machine Shop, on an Air Base, at a time when we were bleeding out people like arterial wounds! I made a LOT of retirement gifts as well as a fair few gifts for folks being posted out to new places. We developed a bit of a standardized 'set' of gifts, simple ones, like an acrylic cribbage board with a pre-planned inset that would take a brass plate, along up to a machined aluminum clock, with a five inch round brass dial set in to it. And lots of brass plaques for other people's presentation items also.

I started out, sanding the finish, to cover up the mess I made while machining the bits and bobs, mostly brass plates, that had the people's names and dates of service on them. Eventually got the process down well enough that I was actually using the machining marks to form part of the decoration on the items I was making.

I had access to a lot of residue left over from years before, when there were a LOT more folks around, and a LOT broader range of materials needed to cover the material specs for all the fleets supported, so we spent remarkably little of the actual budget on the stuff, mainly relying on surplus out of the 'not for aircraft use' store room we had in the back.

The actual machining time was often done by the Apprentice Tradesmen or Tradeswomen, to get them familiarized with running the various machines on something OTHER than the usual work, so they got a chance to 'play', and apply their own idea as well as gain a little familiarity with the CNC mill, and some of the various Graphics programs we used in the Trade.