Polishing Polyurethane

[fingwe]

I've mentioned before about the struggles I've had trying to get a good polish on polyurethane resin. I've tried numerous polishing compounds and nothing has ever brought it anywhere close to the shine that it is possible to get on a commercial acrylic blank.

I had previously been mostly using the Polishing Shop's 3 stage polishing kit for plastics, available here Plastic Polishing Kits I find that this gives an excellent finish on commercial acrylic blanks, but still only gave a dull shine to polyurethane. As usual, when it was time to place a new order, I stuck a couple of different compounds in my basket to try them out. One of them was Menzerna Glosswax 18, which I've swapped for the tripoli I had from the kit above.

By using this on a highish speed (around 1000-1500) and by pressing the resin pen really quite hard into the mop, I've found that I can get polyurethane up to a high shine, which now rivals commercial acrylic blanks. It doesn't look like it's working at first, but once you go through the other compounds, you really can see a difference. You do have to press really hard though....it seems to work best when the friction gets the resin warm.

I've taken a quick before and after photo. The front penholder was with the original kit compounds, and the back one is with the Glosswax 18. Both pens were sanded by hand using Rhynogrip grades 120-1200.

 

[Buckeye]

I use Tripoli, white lightning and P175 they come up to a mirror finish.

Peter

 

[fingwe]

That's interesting, I've used tripoli and P175, so the white lightning must be making the difference for you. Do they come up as well as an acrylic blank?

 

[woodhacker]

The gloss you've achieved looks pretty good to me.

 

[Buckeye]

That's interesting, I've used tripoli and P175, so the white lightning must be making the difference for you. Do they come up as well as an acrylic blank?

Yes, the gloss is immaculate.

Peter

 

[rayf6604]

My go to polishing method is Farecla Profile 200, 300 and 500 in that order, applied after sanding from 180 - 400. It's worked every time for me on all polyester and polyurethane and Corian.

 

[Penpal]

Melanie there is no doubt the finishing you produced is superior and absolutely sales friendly, congratulations and salutations for sharing with us. A picture says it all.

Peter.

 

[Neil Lawton]

Always used to use Vonax on the mops for plastic polishing, EEE for metal.

Canning Compound | Dialux | Vonax | Carbrax | AA Rouge | Steelcut | Radio Rouge | Hyfin

 

[21William]

Have you tried the Menzerna M5 Super Finishing Compound? It seems to have the highest gloss factor of any of the Menzerna compounds. Not tried it myself yet.

 

[fingwe]

I should say that I'm talking about water clear polyurethanes...the opaque ones haven't been a problem at all.

Ray, Interesting, I've tried Farecla, and that didn't give me the shine I wanted.

Neil, I've not tried Vonax, do you use it on water clear polyurethane? I haven't had any problem with any other plastics, just polyurethane.

Peter, thanks very much!

 

[fingwe]

Have you tried the Menzerna M5 Super Finishing Compound? It seems to have the highest gloss factor of any of the Menzerna compounds. Not tried it myself yet.

I'm not sure, without going through my box full of compounds! However, I don't believe it's a final finish issue, with polyurethane you seem to need to get a good gloss with the first stage polishes. The final gloss will only work if the gloss is already there. Hope that makes sense...

 

[Graham_C]

I don't use a polishing system, but I'd be happy with the result you show there Melanie

 

[rayf6604]

I should say that I'm talking about water clear polyurethanes...the opaque ones haven't been a problem at all.

Ray, Interesting, I've tried Farecla, and that didn't give me the shine I wanted.

Have you tried micro mesh? I used that before Farecla but stopped using it because I had to have containers of water and I found it a pain to keep changing the water. Having said that micro mesh was always successful. I would sand the material from 180 through to 800 grit dry then micro mesh from 1500 to 12000 wet and finish off with Hutt plastic polish. I've never tried to polish water clear plastics yet, apart from CA finish, but I've had good results with micro mesh and then Farecla to a high gloss on many translucent plastics. I expect that under certain light you may see some imperfections whatever product you use. In theory if you can remove all signs of abrasion it should be glossy

 

[fingwe]

Hi Ray, yes I used to use micro mesh before I started buffing them. I've tried all combinations. As I said, I can polish all other 'plastics' fine - acrylic blanks, CA, polyester, opaque polyurethane all come up beautifully. It's just the water clear polyurethanes which have been the problem. Given that I'm selling my pens, I really needed to have a consistent finish across all of my products, and not have to explain to customers that this one is a bit less shiny because it's made of a different type of plastic.

 

[Neil Lawton]

I should say that I'm talking about water clear polyurethanes...the opaque ones haven't been a problem at all.

Ray, Interesting, I've tried Farecla, and that didn't give me the shine I wanted.

Neil, I've not tried Vonax, do you use it on water clear polyurethane? I haven't had any problem with any other plastics, just polyurethane.

Peter, thanks very much!

We used to cast little bits and bobs in water clear PU when I ran a jewellery class, in the school I used to work in. Vonax worked okay for them. Is it possible you don't quite have enough hardener in your mix? it is more critical in the clear stuff. Too much makes it brittle but not enough can leave a softer surface that is easily marked, and that would buff with heat through pressure as you actually melt it a little.

 

[fingwe]

Hi Neil, I've probably done hundreds of casts, with several different brands/types of water clear polyurethane, and I've had the problem across the board, so I don't think it's a mixing/ratio issue.

I should say that I'm REALLY picky about the finish I want - I've sold lots of pens using the old polishing method, and not had anyone comment on it. However, it hasn't been at the level of finish that I was happy with. I've heard other people mention that they can't get as good a finish on polyurethane as other plastics, so I'm not the only one who has noticed it. I'll also say that the difference between the two methods of polishing hasn't been as noticeable on pens I've turned on the lathe, as pens I've hand carved and sanded.

I'm surprised that you used PU resin in school rather than epoxy....PU can be nasty stuff!

 

[Neil Lawton]

Hi Neil, I've probably done hundreds of casts, with several different brands/types of water clear polyurethane, and I've had the problem across the board, so I don't think it's a mixing/ratio issue.

I should say that I'm REALLY picky about the finish I want - I've sold lots of pens using the old polishing method, and not had anyone comment on it. However, it hasn't been at the level of finish that I was happy with. I've heard other people mention that they can't get as good a finish on polyurethane as other plastics, so I'm not the only one who has noticed it. I'll also say that the difference between the two methods of polishing hasn't been as noticeable on pens I've turned on the lathe, as pens I've hand carved and sanded.

I'm surprised that you used PU resin in school rather than epoxy....PU can be nasty stuff!

Schools tend to use whatever they can afford, or in a lot of cases given. Controls were always put in place for stuff like that though.

 

[21William]

It's only a guess but I would expect that the harder a plastic is the better the finish you'll get? I haven't cast Polyurethane for many years but it never struck me as being particularly hard as far as plastics go.

 

[21William]

https://www.redwoodplastics.com/brochures/plastic-hardness-comparison-chart.pdf

 

[fingwe]

Hi William, yes, you would think that, but water clear polyurethane is significantly harder than opaque polyurethane (shore hardness of around 85 for water clear, 72 for opaque), but is much harder to get a shine on. I thinks it has something to do with the fact that it is quite resistant to abrasion, so polishes with micro abrasives have a hard time working on it. I have also tried blending resins to create a softer resin, but that didn't work either!