First Ever Fusion-8 Alchemy MTM Build Thread, Piano Black Finish - Page 4 - AVS Forum
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post #91 of 130 Old 10-14-2013, 04:44 AM
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I'd love to see/hear them as well though finding the time may prove impossible these days!

 

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post #92 of 130 Old 10-14-2013, 09:10 PM - Thread Starter
 
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Yeah just haven't gotten around to taking a finished picture yet
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post #93 of 130 Old 03-28-2014, 09:37 AM
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Yeah just haven't gotten around to taking a finished picture yet

I'm about to start on a pair of fusion 8s and is love to see some final pictures. I'm considering the same finish but it looks labor intensive smile.gif

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post #94 of 130 Old 03-28-2014, 11:40 AM - Thread Starter
 
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yeah definitely very labor intensive. After this really dry winter the "cracks" where the wood joins each other seems to have made little ridges. So there's a few lines on the finish now, I'm going to try to fix it this summer. The nice thing about this black paint I used is that technically it never fully cures, so when you spray more on it it will basically melt into itself and form a new full layer. Here's some pictures I took with my phone. They came out a weird blue tinge. The second picture half the speaker is covered in dust. The last picture you can see the line that developed over the winter.



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post #95 of 130 Old 03-28-2014, 12:35 PM
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Nice grill, how did you attach it? Magnets or otherwise?

 

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post #96 of 130 Old 03-28-2014, 02:21 PM - Thread Starter
 
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Nice grill, how did you attach it? Magnets or otherwise?

post 85 has some pictures of the grill construction. I have 4 neodymium magnets embedded in the front of the speaker, and the frame has 4 metal L brackets on the corners that stick to the magnets
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post #97 of 130 Old 03-29-2014, 05:39 AM
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Did you simply use a thick drill bit to get a hole for the magnets in the baffle?

 

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post #98 of 130 Old 03-29-2014, 06:45 AM
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Ouch on that line. I've had MDF telegraph through veneer and have seen it even in duratex (someone else's speaker). How do you plan on getting rid of it? Just spray more on or sand it out first.
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post #99 of 130 Old 03-29-2014, 12:37 PM - Thread Starter
 
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Did you simply use a thick drill bit to get a hole for the magnets in the baffle?

yeah i used a drill bit the same size as the magnet and then i put some glue in and then hammered the magnet in.
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post #100 of 130 Old 03-29-2014, 12:38 PM - Thread Starter
 
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Ouch on that line. I've had MDF telegraph through veneer and have seen it even in duratex (someone else's speaker). How do you plan on getting rid of it? Just spray more on or sand it out first.

yeah probably just lightly sand it with some high grit to get rid of the line and the wax on it and then re-coat and then re-wax
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post #101 of 130 Old 04-29-2014, 10:55 AM - Thread Starter
 
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So does anyone have any ideas why a lot of the lines appeared through the finish after this winter? They are on almost every joining area where the sides join the top and front. I wonder if putting wax on only a few days after the lacquer did it? Or the primer didn't fully seal the MDF and after this dry winter it sunk in? I'm going to be fixing it soon, as well as doing a subwoofer in piano black, so I'd like to figure out what went wrong so I can fix it and also change the painting process for my subwoofer so this doesn't happen again. You can see the line that appeared in the last picture I posted a couple posts up. Lines like that are also on the sides and the back of the top.
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post #102 of 130 Old 04-29-2014, 11:09 AM
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There's a great thread that I will try to locate later for you on how all seams on my will eventually show. Likely due to the expansion/contraction of mdf. Either on parts express or diyaudio.

The poster attempted several methods to mitigate the seam bleed, can't recall which worked best. Think it was cutting a trough into the seams and refilling the trough with a specific filler.

 

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post #103 of 130 Old 04-29-2014, 11:13 AM
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That's the expansion/contraction of the MDF due to temp and humidity changes, it's almost impossible to entirely prevent. You almost need to use a veneer over the MDF to prevent the joints from becoming visible or use a thick resin like coating to seal the MDF before painting.
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post #104 of 130 Old 04-29-2014, 11:25 AM
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Originally Posted by mtg90 View Post

That's the expansion/contraction of the MDF due to temp and humidity changes, it's almost impossible to entirely prevent. You almost need to use a veneer over the MDF to prevent the joints from becoming visible or use a thick resin like coating to seal the MDF before painting.

What about something like bondo in the joint ? or over the top ?

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post #105 of 130 Old 04-29-2014, 11:31 AM
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Originally Posted by mtg90 View Post

use a thick resin like coating to seal the MDF before painting.

I think this would be effective. Smother the whole thing in epoxy or some kind of MDF sealer. Sand it back, then start the finishing process. I'd be tempted to give the mdf edges a sip of yellow glue and water 1:1 mix before the epoxy. Get the edges to swell and harden, then sand them back. Then epoxy. That would make it pretty stable.

Plywood would have been more stable probably, but those edge never disappear. Doesn't matter how much sanding you do cool.gif

Sorry about your luck.
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post #106 of 130 Old 04-29-2014, 12:55 PM
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Bondo should work, same with the 1/1 mix of glue and water, both "should" seal MDF so this does not happen.

ive been lucky with my boxes i just coated in duratex as it did not show and I have some wicked humidity swings to the point where i use a humidifier in the winter that goes through 2 gallons a day and cant keep up, and a de-humidifier in the summer that just has a drain hose and runs 24/7


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post #107 of 130 Old 04-29-2014, 01:18 PM - Thread Starter
 
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I was under the impression that shellac primer I used sealed the MDF

So if I fix these lines do you think they will reappear after it gets more humid in the summer and then dry in the winter again?
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post #108 of 130 Old 04-29-2014, 01:27 PM
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The shellac would put a top coat on it, but wouldn't penetrate that edge I don't think.

I had some movement around my waveguides that I bondo smoothed into place. They showed a witness line around the corners of the waveguide. Even though I prepared and primed the joint thoroughly. And that wasn't an edge. MDF edges are worse yet.

You might be fine now if they acclimated, but piano black is very sensitive to imperfections.
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post #109 of 130 Old 04-29-2014, 03:20 PM
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I have used fiberglass resin all over the MDF including the edges. It seals and also fills and somewhat self levels in any small enough gaps. It smells nasty, but sands decent and have not had any problems. I have not used it in a while since most projects have not been highly visible.

If you have larger gaps in the seams use bondo and then use a couple of coats of BIN primer with light sanding in between coats. If you wanted a "guarantee" trench the seam which a v shape router bit or a Drexel tool and fill it with bondo.
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post #110 of 130 Old 04-29-2014, 04:54 PM
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Quote:
Originally Posted by mtg90 View Post

That's the expansion/contraction of the MDF due to temp and humidity changes, it's almost impossible to entirely prevent. You almost need to use a veneer over the MDF to prevent the joints from becoming visible or use a thick resin like coating to seal the MDF before painting.

I've read that the seams eventually show through even veneer which I found surprising.

Here is the thread BTW...

http://techtalk.parts-express.com/showthread.php?214399-Best-methods-for-finishing-MDF/page5

 

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post #111 of 130 Old 04-29-2014, 04:58 PM
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To late now, so this advice isn't all that useful for you, but maybe someone else. If doing a piano black finish, always good to mitre fold the mdf. Even then, don't want the corners to show a crack. Takes a ton of work to get it prepared.
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post #112 of 130 Old 04-29-2014, 05:37 PM
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Is it possible that the moisture gets in through the ports and effects the inside?
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post #113 of 130 Old 04-29-2014, 05:46 PM - Thread Starter
 
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Originally Posted by tuxedocivic View Post

To late now, so this advice isn't all that useful for you, but maybe someone else. If doing a piano black finish, always good to mitre fold the mdf. Even then, don't want the corners to show a crack. Takes a ton of work to get it prepared.

It's useful advice as I'm doing an 18" sub this summer and I plan on doing it piano black again. Also going to do L/R some time in the future as well.
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post #114 of 130 Old 04-29-2014, 05:47 PM - Thread Starter
 
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Is it possible that the moisture gets in through the ports and effects the inside?

I guess it would be possible in certain situations, but I don't think so because in my case it was EXTREMELY dry this winter where I have my speaker.
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post #115 of 130 Old 04-29-2014, 05:50 PM - Thread Starter
 
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Originally Posted by btinindy View Post

I have used fiberglass resin all over the MDF including the edges. It seals and also fills and somewhat self levels in any small enough gaps. It smells nasty, but sands decent and have not had any problems. I have not used it in a while since most projects have not been highly visible.

If you have larger gaps in the seams use bondo and then use a couple of coats of BIN primer with light sanding in between coats. If you wanted a "guarantee" trench the seam which a v shape router bit or a Drexel tool and fill it with bondo.

so bondo for bigger gaps and fiberglass resin for small ones? Can they be used on the same surface? Which one is better overall?
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post #116 of 130 Old 04-29-2014, 05:50 PM
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Great thread so far, thanks for posting.

I came across another thread on another forum about how to paint mdf to a mirror finish... He used Vinyl Spackling on the edges of the MDF to prevent it from continuing to soak up like a sponge.

Here's the thread:
http://forums.shoryuken.com/discussion/67501/how-to-paint-mdf-to-a-mirror-finish-worklog
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post #117 of 130 Old 04-29-2014, 05:53 PM
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Extremely dry can be even worse. I found that out the hard way this winter when the bridge on my Martin D-35 cracked.mad.gif
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post #118 of 130 Old 04-29-2014, 07:46 PM - Thread Starter
 
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Great thread so far, thanks for posting.

I came across another thread on another forum about how to paint mdf to a mirror finish... He used Vinyl Spackling on the edges of the MDF to prevent it from continuing to soak up like a sponge.

Here's the thread:
http://forums.shoryuken.com/discussion/67501/how-to-paint-mdf-to-a-mirror-finish-worklog

Yeah I was actually just looking at that thread today. The thing about his though is he just did one side of a small piece of mdf, and if you look it has a lot of visible imperfections around the edge so there's no way to tell if that is any better than just using wood filler and shellac sealer. The problem with mine is on the joining edges, not the sides. I think I might try a high-lustre clear gloss lacquer on top of my black paint this time like he did, as his looks quite shiny - shinier than mine is.
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post #119 of 130 Old 04-29-2014, 07:53 PM
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so bondo for bigger gaps and fiberglass resin for small ones? Can they be used on the same surface? Which one is better overall?

Overall, I would say bondo. You have to work very quickly with it though and it can also be tougher to sand, but it holds up the best that I have seen and is relatively inexpensive compared to the high priced wood epoxy's on the market.

It really all depends on how you are planning on finishing them.
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post #120 of 130 Old 04-29-2014, 09:43 PM
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Some other thoughts:

1. Glue/adhesive and chemical compatibility of it and the paints - it's possible that it could lead to a witness mark like that.

2. It has something to do with the expansion and contraction of MDF - the two panels could be expanding/contracting opposite each other and causing a sheering motion, or some kind of moment is created where the panels pull apart from each other.
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Unlike solid wood which sees the greatest expansion and contraction parallel to the growth rings but changes very little in length (0.15%), the composite nature of MDF causes it to expand and contract equally in both width and length (0.3%). This means that in general you should expect less movement across the width of an item in MDF compared to solid wood, but you should expect much greater movement in length.
http://www.koetterwoodworking.com/controlling-wood-movement-part-ii-mdf-and-new-product-announcement-2/

I'm betting it has to do with humidity conditions more than anything else. If the outside of the box is properly treated sealing out any moisture, you might look to coating/treating the inside of the box to create the same moisture barrier.
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