Finishing H frames

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rockdrummer

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Finishing H frames
« on: 17 Jul 2018, 11:44 pm »
Hi all, after selling my super v cabinets and tops, I'm getting H frames going. Plan to hopefully match them with wedgies in the next few months.

Anyway, I've read up a lot on this forum about epoxy for cabinets and hiding seams, etc. Never used it. Looks like I have a couple assumptions and I was hoping you could steer me right in case I'm wrong!

1. Applying the epoxy is fine on vertical as well as horizontal surfaces.

2. Rolling on with a foam roller is common, but what about the inside corners? Is a bristle or foam brush okay?

3. 127 resin and 350 non blush hardener works.

Things I don't know:
Do I need to use thinner and what do I use?

Is 1 and 1/2 quarts from Raka as a kit enough to do subs, stands for something like wedgies, and wedgies themselves?

I used bondo on my last project and had okay results but it was lots and lots of work.
Thanks for any advice everyone.
Have a good night.
Ben

mlundy57

Re: Finishing H frames
« Reply #1 on: 18 Jul 2018, 01:52 pm »
Ben,

I only use the epoxy on the outside of the cabinets.

I use West Systems epoxy. With that it takes about a pint of resin to do one coat for a two driver cabinet. I mix it up in two batches per coat. I roll on on, no brush needed. I put on two coats sanding back between coats.

Some folks thin the first coat 10% for better penetration. West doesn't recommend doing that so I haven't tried it.

I haven't used the Raka so I don't know how much it would take but I expect it would be similar.

Mike

lacro

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Re: Finishing H frames
« Reply #2 on: 18 Jul 2018, 01:56 pm »
Using epoxy to help hide seams and harden MDF has worked well for me.

Your questions:

1. Applying the epoxy is fine on vertical as well as horizontal surfaces.  YES

2. Rolling on with a foam roller is common, but what about the inside corners? Is a bristle or foam brush okay?
The thin foam epoxy roller covers are commonly used, however, I prefer the mohair type roller covers (adhesive rollers). Cheap chip brushes work good. Cut them shorter so they have stiffer bristles. After rolling on the epoxy, tip off with a foam brush.

3. 127 resin and 350 non blush hardener works.
There are lots of epoxies that will work fine. I have the most experience with Raka 127/350 building boats, so it is the one I recommend only because I have successfully used it on speaker cabinets.

Things I don't know:
Do I need to use thinner and what do I use?

You don't need to thin epoxy, actually it is not recommended as it will weaken the epoxy, but I did for the first coat so it would soak into the surface of the MDF. Not concerned about weakened epoxy on speaker cabinets. You can thin with alcohol, acetone, or lacquer thinner, but only thin about 5-10% max.

Is 1 and 1/2 quarts from Raka as a kit enough to do subs, stands for something like wedgies, and wedgies themselves?
That should be enough.

You will probably need 3 coats of epoxy including the first thinned one if you decide to thin. If you do the roll and tip method, the orange peel effect will be less making sanding easier. You should sand between coats (when hard) enough to knock down the high spots. If you sand through a spot, just reapply new epoxy at the spot. Raka 127/350 is a 2:1 mix by volume, but I like weighing it instead with a digital gram scale. the mix is 100:44 by weight. Don't mix more than 3 oz. at a time, and dump it into a roller tray. Cut your covers to 3" so you get 3 from a 9" cover. You should probably practice on some scrap MDF before committing to the speaker cabinets.

  • wear nitrile gloves
  • eye protection
  • dust mask when sanding
  • work outdoors if possible

Good luck....


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rockdrummer

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Re: Finishing H frames
« Reply #3 on: 18 Jul 2018, 02:25 pm »
Thanks for the advice! Much appreciated. I had to look up brush tipping, but now I think I'm as prepared as I'm gonna be.
I will post pics when I get going.
Thanks again.
Ben

Captainhemo

Re: Finishing H frames
« Reply #4 on: 18 Jul 2018, 03:09 pm »
Ben
As  mentioned, try and work  outside or at least with extremely good  ventalation.  Pretty  powerful  stuff.  .
Have the cabinet(s)  well prepped before starting with the epoxy,  I block them out  until any seams are  as close to unnoticable as possible.

If you  do go with a  thinned  coat, the mdf  really  sucks it up.  Like anything you apply,  the open cut MDF will  soak up the most.
You'll  have  very little  saning after the  first coat,  jus,   Just lightly  scuff it smooth. After  the  first  coat,  the subsequent coats will  start to build.   Alsways use a block when sanding  the  flat  surfaces

Don't  think you're going to find the epoxy any less work than  using bondo / other fillers but the  effort is well worth it.
Looking forward to  pics    :thumb:

jay

rockdrummer

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Re: Finishing H frames
« Reply #5 on: 18 Jul 2018, 11:47 pm »
Thanks Jay, I was really hoping to get to this soon so I would have the open garage and good weather. Waiting for a friend to cut the pieces and then I will try to design a top and base I'm happy with.

I think I made the bondo work harder than it should have been. Thanks for the hint that this does take work. That way I will not rush, which I tend to do :nono:

Ben

lacro

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Re: Finishing H frames
« Reply #6 on: 19 Jul 2018, 03:22 pm »
If you use Raka 127/350 you don't really have to tip off with the foam brush, it's just something I do. Raka is self leveling so you won't get much orange peel. Also you don't need the 350 hardener as it is designed for clear coating over wood. One of the other hardeners are cheaper, and will work just as good, but they might cause Amine blush which leaves a waxy surface that must be removed before you apply another coat. The 350 is non blush hardener. The other thing you need to be aware of is how slow epoxy cures. It is not like Bondo which is Polyester resin that cures very quickly. You can get faster hardeners for the 127 resin so decide how fast you want the job done, and how fast you can work. If using 350 hardener you will get 1-2 coats per day. I prefer slow hardeners so I can work at a relaxed pace. Always mix small batches (3-4oz) and spread it out in the roller tray to increase pot life. If you leave it in the mixing cup too long exothermic reaction will accelerate the cure, and the cup will get hot, ruining the batch. Apply many thin coats, not fewer thick coats that can run, which will be difficult to remove. Full hard cure takes a week or more so try to wait a week before painting.

rockdrummer

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Re: Finishing H frames
« Reply #7 on: 20 Jul 2018, 09:52 pm »
Thanks. I will definitely prefer a slower relaxed pace. Especially since I have never done this before.

Thanks again for the help everyone.
Ben

rockdrummer

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Re: Finishing H frames
« Reply #8 on: 7 Aug 2018, 05:08 am »
Hi everyone. Anxiously awaiting info about the exciting super seven projects. Meanwhile, I have started gluing up my H frames.






I used half inch glued together to make the baffle, rounded over the back side and attached the small driver dividers. I wanted both servo woofers facing the same direction.




Put that onto a side panel, marked it up, sanded to fit pretty flat, then drilled pilot holes, counter sunk them and glued it on.








I will end up with 1.25" sides (.75 + .5). Looking for design ideas for bases and tops. I was thinking something like an oval. But would like to carry the same theme to the stands i will use for whatever kit I end up with.
Thanks for looking.
Ben