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Old 19th February 2010, 03:33 AM   #11
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Quote:
Originally Posted by wakibaki View Post
No, it is when you abandon using a flat rigid support that you start to get problems. Do not attempt to sand with the paper unsupported in your fingers.
Well I wasn't suggesting the use of "unsupported fingers", but more so expressing concern with having a rigid flat backer when sanding curved enclosures. The hard backer will only allow a very thin area of contact at any given point during the sanding. This, I believe, will increase the likelyhood of over working your finish.

Quote:
MDF as manufactured has a fine-textured finish on the faces of the boards. It is preferable not to scratch this finish if at all possible.
Unfortunately in my example it's very unlikely to have a "virgin" face to work with. The large bulk of curved enclosures using MDF are of a translam construction. So the majority of the finish process will be done on worked edges.
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Old 19th February 2010, 10:14 AM   #12
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I'll post my experience going through this process:

I did a little research and talked with a good HVLP painter and found out about a cheaper and faster solution. M.L Campbell makes a really nice primer called Clawlock which is designed specifically for use with MDF. They also make a great varnish called Resistant. Both are super thick (45-55% solids formula) and require a catalyst to use. Also you don't require a clear top coat using this method. The advantages of going this route are: a fraction of the coat needed to achieve a good result, the paint is much more durable and because it's pretty solid it's harder to make a critical mistake when sanding or polishing and it's much more water resistant then just about anything on the market. You don't have to worry about jerks leaving cups on the speakers, lol.

One of the speakers before the paint and the stain:
Click the image to open in full size.

I prep sanded with 400p, and I did every surface. I would suggest using 3 layers of primer and 3 of varnish, sanding every 2 layers. So 2 of primer, wet sand with 600p, 1 primer and 1 varnish, wet sand with 1000p and finally 2 layers of varnish and leave the paint to cure. They suggest not using more then 2 layers of primer and 2 layers of varnish but I talked with them and if you sand down as suggested above you'll be ok. You just don't want to have the paint be so thick it'll crack once it cures. They are oil based, so you'll need a good mask and a well ventilated area. They suggest waiting a month for the paint to cure but I decided on 2 just to be safe.

First couple of layers of primer:
Click the image to open in full size.

Sanding after the first 2 layers:
Click the image to open in full size.

My camera died on me at that point, so I don't have any of the second sanding stage. Here's the final layer of paint tho:
Click the image to open in full size.
Click the image to open in full size.

Post paint job results:
Click the image to open in full size.
Click the image to open in full size.

I waited 2 months before I started the final polish. I wet sanded with 2000p, but I'd suggest getting some 1600p to start out with, it'll save you a lot of time. This paint isn't like sanding a clear coat. I was able to get pretty aggressive with the sanding, but I was doing it by hand with a rubber block. You just want to sand until the surface looks like metal while dry. There were little dimples in the paint, you couldn't really feel them but when dry they were visible. I just sanded till they were all gone. Once you've sanded all the sides it's no different then what ShinOBIWAN suggests in the 'how to' thread. Just polish with the G3, I did 5 layers, and finish with the car polish.

Applying the G3:
Click the image to open in full size.

I'd never done this before and I'm not tool savvy but it wasn't too bad. It takes a lot of time and energy, but you can't argue with the results:

Click the image to open in full size.
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Old 19th February 2010, 12:51 PM   #13
Mark Kravchenko
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What I can do is say beautiful job. And I can't believe you sprayed inside! Oh what a smell.

My only comment that is more of a question is do you think that the choice of solid wood baffle is wise? MDF has near uniform expansion across the face in every direction. The wood baffle has about 2.5% expansion vertically and about 8 to 12% across the width if it is oak. It maw work it may crack itself off eventually. I personally only use veneer on cabinets for loudspeakers. It behaves itself guaranteed.

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Old 20th February 2010, 02:55 AM   #14
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Quote:
Originally Posted by mwmkravchenko View Post
What I can do is say beautiful job. And I can't believe you sprayed inside! Oh what a smell.

My only comment that is more of a question is do you think that the choice of solid wood baffle is wise? MDF has near uniform expansion across the face in every direction. The wood baffle has about 2.5% expansion vertically and about 8 to 12% across the width if it is oak. It maw work it may crack itself off eventually. I personally only use veneer on cabinets for loudspeakers. It behaves itself guaranteed.

Mark
I had some oversight from my friend who's built a lot more of them then I have and his wood working friend and they gave me the thumbs up. They work with MDF and oak a lot more then I do so I'll defer to their experience. I think they should be alright.

Also, I did spray inside but it was right next to the exit to the garage with a fan sucking out the fumes. My biggest concern was temperature. It was close as hell that week and I wasn't going to ruin the paint over that.

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Old 29th May 2014, 06:28 PM   #15
V12 is offline V12  United States
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Default Sanding

Sanding should be done by hand or sander?
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Old 30th May 2014, 03:05 PM   #16
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I've made a few piano black speakers... I've learned a few things.

Bondo the seams. Spread it wide on the seams so you can feather the edges so it is flat. If you just put a small line of the seams it will just round over or sand right off. Make them perfectly flat and smooth by block sanding 80 grit. If you sand with higher than 80 grit initially you effectively "polish" it and it rounds over.

If the seams aren't perfect, they will show through all your paint and it will be a wreck.

I did a center speaker and used wood filler on the seams and they have all shown through and it doesn't look that good any more. I also blame the zinsser bin primer for contributing to the seams showing through, as well as using lacquer from a spray can as the finish. HVLP is so much better as it paints better and you can use high quality paint.

Use a high build primer. A lot of people recommend zinsser bin as a primer but I would advise not to use it if you are trying to get a gloss finish. I have used 2 part urethane high build automotive primer recently and it is very, very good.

If you have it perfectly bondo'd, then paint it properly, it is fairly easy to get it to be piano black as all you have to do is polish it either with high grit wetsand or automotive rubbing compound/polishing compound.
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Old 30th May 2014, 10:26 PM   #17
ArtG is offline ArtG  United States
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Here’s couple tips if you are looking for a “show quality” gloss black finish. It really doesn’t matter if it’s furniture or a show car. The base surface must be as close to perfect as possible. This involves a lot of block sanding and filler of the appropriate type, whether it is body putty and high build primer, or a wood filler and urethane primer.

Block sand and fill, block sand and fill, block sand and fill---until it’s perfect.
A tip to determine if the surface is perfect: wet the surface (don’t use water on bare wood) and place a common 2 bulb fluorescent light fixture horizontally above and to the side to the surface, and move your head back and forth (or side to side) and look at the reflection of the lamps. Every imperfection will be visible, as a distortion of the straight lamp tubes. Anything you see now will look worse when you are done!

Two stage polyurethane or catalyzed lacquer is “light years” ahead of any other material you can use. Have a professional spray the item(s), as use of these “paints” requires experience and proper ventilation. This doesn’t have to be expensive. I recently had two medium sized speaker cabinets sprayed with catalyzed lacquer at a local cabinet shop for $30 total, including materials.

Wet sand with “wet and dry” sandpaper wrapped around a putty block, which is a flat 2X4” piece of flat rubber with square edges. Rinse out the sandpaper often in a water bucket. Start with 600 or 800 grit. Next, do the same with 1200 grit. Finish up with 1600 or 2000 grit paper. Never sand with your fingers or bare palm—always use the putty block, even on curved areas. To check the surface, wet it with a sponge, and lightly drag the square edge of putty block over the surface. This will reveal areas that were missed or need additional sanding. The fluorescent lamp trick helps here also.
Power buff with medium to light compound. Power buff or hand buff (lot of work) with automotive polish to remove the swirl marks.
Clean up and you are done! The finish will probably out-live you!
DO NOT apply any kind of wax to this finish. Properly done, you cannot improve upon it.
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Old 30th May 2014, 10:38 PM   #18
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Years ago we used to use a poly-paint call SemPrime, it seals the wood and gives you a very hard finish to sand and finish, hide seams too, after sanding. Painting is show car like when done.
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Old 30th May 2014, 10:39 PM   #19
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Quote:
Originally Posted by ArtG View Post

T. I recently had two medium sized speaker cabinets sprayed with catalyzed lacquer at a local cabinet shop for $30 total, including materials.

.
30.00, where in rural China .... ?
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Old 30th May 2014, 10:49 PM   #20
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Products I like to use for the rare times I paint speakers are from the M L Campbell product line - Clawlock catalyzed primer and either Resistant tinted Conversion varnish or Magnamax lacquer, and for extra durability, a couple of topcoats of Krystal post catalyzed conversion varnish. All of these products are specifically formulated for the cabinet / millwork finishing trade.

As ArtG notes above, there's no substitute for scrupulous preparation, the right products and experienced skill with the application equipment.

I've said this before - the final tally on and materials to achieve a "show grade" paint finish can make the cost of all but the most exotic veneers and simple clear top coats pale by comparison, but certainly there are shapes and profiles that lend themselves to nothing else but solid colours.
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