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Old 17th January 2013, 06:33 PM   #41
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MDF can be powder coated and and infrared light is used.. This process is used alot for many applications and It's growing in popularity for office furniture and cabinet doors
The faciility I'm looking into is well experienced so I'll trust what they have to say about the swelling.. plasic Powder is used for metal so I think it would be the same for mdf..

I use brad nails all of time and haven't seen glue coated nails or if they are coated then I wasnt aware of it..

Thanks, Joel
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Old 17th January 2013, 06:35 PM   #42
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Quote:
Originally Posted by JMFahey View Post
Never had that problem.
The minute amount of water contained in a water based finishing "paint" is not enough to cause that, by a long way.
Or simply glueing or painting with latex or similar would have even worse effect ... yet nothing like that happens.

You'd need to leave them in the rain, then dry in the scorching Sun for something like that happening.
Yeh, I think your right so its probably related to the heat thats used on the mdf to cure the powder..
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Old 17th January 2013, 07:22 PM   #43
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Quote:
Originally Posted by JMFahey View Post
Never had that problem.
The minute amount of water contained in a water based finishing "paint" is not enough to cause that, by a long way.
Or simply glueing or painting with latex or similar would have even worse effect ... yet nothing like that happens.
Primer coat on mdf should never be latex paint because of the swelling. Use shellac, or oil based paint, first. After, you can slop on as much latex as you want ...
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Old 17th January 2013, 07:42 PM   #44
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A couple of thoughts here. First the nails with a coating on them are typically vinyl coatings and are put there to help a nail slide into wood as it melts from the friction of the nail entering the wood and then re-hardens as soon as the nail stops moving. I personally never would use a nail that stays in the cabinet after assembly as I have seen and heard them buzz in pro-audio enclosures, a real problem if that happens. It might only be a problem with plywood and not MDF but I just never wanted to find out later. I have used screws in cabinet builds that had other than 90 degree angles, such as a trapezoidal cabinet design. If the cabinet is square use bar clamps they are your best solution. A temporary method of clamping could be to use a strap and clamp system as used in packaging to hold something while transported. If you use screws in mdf do not use the screws that are typically used for drywall as they are fine thread and do not bite very deeply. I always use very coarse threaded screws with deep threads for mdf. Watch out for any water based adhesives or finishes with wood. I don't care how little water is in the formula it will swell the mdf and will certainly make life much harder on a veneer finish as it will swell the wood grain and then you will have to sand the first coat before adding any additional finish coats. If you are using screws make sure that they are far enough below the surface not to print through into the veneer or paint coating you use. I would use auto body filler to cover the screws myself if I was using that method. I only use two part polyurethane finishes on my wood veneer finishes. I have used lacquer in the past and the problem is cracking of the finish over time, seen it to many times. Shellac is going to add color to any finish you are using it on and sometimes will remain sticky if you do not thin the shellack with enough alcohol to keep that from happening. If you don't have access to a good table saw then the circular saw and a straight edge works great. I also have a panel saw, takes a lot less room than a table saw but you do need to make sure that the saw is set up square to begin with. The cheaper versions are often not of welded construction so they can be knocked down but they take much more care to get and keep square in use. Watch out if using mdf and you are after a piano black finish. The glue lines will often show and the only solution to that is to seal the inside of the enclosure with the same paint or a good sealer before painting as you will see every glue line otherwise. If not at first the lines will show up the first time the humidity changes and the cabinet absorbs water or dries out. It is a real problem to deal with but by sealing the internal surfaces of the enclosure and any cutouts you can avoid this problem.
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Old 17th January 2013, 07:55 PM   #45
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I use shaellac as seal coat or transistion coat between finishes or grain filler. so it goes shellac/epoxy or other grain fillers/shellac/finish coat( multiple choices)

On the brad nailing.. I wont do it again and was trying to have speed for some small cabs but not crazy about fasteners in cabinets.. next I try straps like Kindhornman suggests..

Cheers
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Old 17th January 2013, 08:16 PM   #46
JMFahey is offline JMFahey  Argentina
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Quote:
Primer coat on mdf should never be latex paint because of the swelling.
I never talked of "primers"
Nor had any swelling.
I have been painting my for_rental PA cabinets flat black with Sherwin Williams Loxon (or the earlier brand they used) for over 40 years now with excellent results.
Sherwin Williams
All other PA rental companies do the same on the low cost stuff.
Why?
Strong, waterproof, dries fast and without smell, very easy to touch up.
The cabinets "go to work", and if any come back scratched, dirty or whatever, 5 minutes with a brush leaves them as good as new.
Not showroom stuff but daily use workhorses.
Of course, to each his own
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Old 17th January 2013, 08:27 PM   #47
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JMFahey,
very true that flat black will hide most sins, but most people aren't going to use a flat black paint for their home systems, especially if they have a wife or girlfriend to deal with! For PA I am all with you, especially for rental equipment. But to say that the wood doesn't swell is just not going to be true, you just don't notice the effect with flat black. I also doubt very much that you are using any mdf in any rental equipment, first time someone drops a cabinet on a corner it would be a hot mess, so you must be using plywood for any PA cabinets. Ever had a nail buzz in a plywood enclosure such as a bass bin?

Ps. never saw a design for the tin can headphone amp. I am still interested in having my daughter do the project.

Steven
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Old 17th January 2013, 09:17 PM   #48
JMFahey is offline JMFahey  Argentina
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Agree that flat black hides lots of sins
Yes, I have lots of painted "good chipboard" and MDF cabinets for rental work.
Like everybody else here.
In USA, *many* homes are made out of wood, so plywood, 2"x4", drywall, etc. are real cheap, because of the huge production and competition.
Plywood costs little more than MDF .
Here, cost difference is 3:1 , plus chipboard/MDF are available in 6' by 12' or 15' sizes; plywood in smaller unefficient 5'x5' or 8' .
Why? Don't know, but it explains the preference.
And if a speaker cabinet crumbles , it gets replaced for peanuts.

As of the designs, I haven't set up yet to make the PCBs.
When the amp is actually mounted and working , I'll publish it.
Not a big fan of simulations, much prefer "real flesh" stuff.
Good luck.
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Old 17th January 2013, 09:38 PM   #49
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JM,
With all the rainforest in South America I guess we just assume that you have a thriving wood industry. Yes the plywood does come in off sizes, especially the European Baltic birch which so many people seem to prefer. I have seen the larger sizes of mdf sheets but typically here they are special order only and not standard sized which is 4'x8' in size. As far as price the cost difference between the mdf and the plywood is not even close to one to one. it is at least 2 to 1 here in favor of the mdf. I can't say when the last time I have seen any mdf here in pro-audio, it just isn't done because of the problems of breakage compared to plywood. But I will say that some of the plywood that some manufacturers use I wouldn't touch at all, pure junk that will peel between plies and would make for a crappy cabinet no matter who built them. Construction grade can be used fine to reinforce a house but not something to use in a speaker enclosure.
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Old 17th January 2013, 10:55 PM   #50
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Kinderhornman, if your shellac is remaining sticky, it is old. Best to buy shellac flakes to mix with alcohol. Just be sure to let it sit to de-wax before you use it. The wax will sink to the bottom of the jar as a thick, ivory-coloured, slime letting you pour the shellac off the top.
You're correct that it can change the colour of the wood, though usually in a positive way. However, there are different grades of the flakes available, ranging from very light to darker orange (Shellacs - Lee Valley Tools), which let you control, to a good degree, the colour cast you'll get.
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