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....


[/list]

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

rockdrummer

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Re: Finishing H frames
« Reply #9 on: 16 Sep 2018, 03:37 pm »
Hi everyone. Summer is over, moved my oldest into college for her freshman year  :cry: and have 2 weeks of school over with. Finally getting back to my subs.
I really like the roundover look, and my bases are decent. I learn something not to do during every build. I used a jigsaw to cut the bases, on a line drawn out, and I see I made some adjustments while cutting that you can really pick up if you look for them. Oh well, not a big deal.

Here are 2 pics of them, bases are drying, hoping to test an attempt at epoxy application on scrap mdf later today.





For some reason, the one photo won't display vertical.

Have a great Sunday everyone.
Ben

Tyson

Re: Finishing H frames
« Reply #10 on: 16 Sep 2018, 07:32 pm »
Looking good!  Have you heard servo OB subs before?  Or will you be hearing it for the first time once you get the build done?

rockdrummer

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Re: Finishing H frames
« Reply #11 on: 16 Sep 2018, 07:40 pm »
Thanks Tyson, yes I have. And can't believe how good they sound. I had a set of super v and sold the cabs and tops and kept the woofers and servo amps. I had a sunfire sub before that, and will NEVER go back. I love OB sound.

I am planning on getting wedges in the near future.

Ben

rockdrummer

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Re: Finishing H frames
« Reply #12 on: 20 Sep 2018, 12:04 am »
Hi, I tested some pieces, must have mixed well, they came out rock solid. So here is my first cabinet, first coat.
I see lots of little bumps, I'm assuming from the raw mdf. I think that will all come out after first sanding. I didn't thin the first coat.

I do have a question, do you guys re-use anything? Not the roller I know, but the pot you mix in and the pan you roll from? Just curious.
Thanks for looking.







mlundy57

Re: Finishing H frames
« Reply #13 on: 20 Sep 2018, 12:26 am »
 Ben,

I don’t reuse anything except the roller frame. Can’t get anything else clean.

The bumps could be from small particles on the cabinet that weren’t cleaned off before you applied the epoxy, they could have settled out of the air while the epoxy was drying, or ??. They should sand out with no trouble.

rockdrummer

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Re: Finishing H frames
« Reply #14 on: 6 Dec 2018, 10:49 pm »
Hey everyone. I'm getting to the final stages of finishing and wanted to post an update.
I started sanding my first coat with 150 paper. That was so, so slow going, that I bumped it up to 100. In hindsight, that would have been fine if I didn't do it on my final, 4th, coat. I did take lots and lots of time sanding with 150 afterwards especially on that last coat, but I still have swirl marks from sanding. I used a block and took my time, but didn't get through them all. Oh well.




I did fine using my garage, but as it cooled this fall in Minnesota, the cure time for the epoxy went from 6-8 hours to 4 days. Less that 70° or so and it really slowed. I wasn't in a hurry so that was fine.




I didn't notice I sanded through the epoxy in a couple spots, so painting didn't cover easily there. The areas felt very smooth, so I assumed the slight contrast in color was underneath.  In the picture above, you can see the spot in the very front top left corner. The side spot was underneath. I used a primer inside, sanded the rough spots, then got to spraying. I used Rustoleum painters touch paint plus primer, Satin Espresso.

This is where I'm so glad I used epoxy. It covered so easily over the sanded epoxy. I sanded the final coat to 320. In this picture, the color looks like copper. Really is a dark brown.



After finish spraying, I used a flat paint to finish the inside cavities.



This final picture doesn't have a great look due to the flash. From back at the listening position, I love the look. The roundover looks great, the seams are all gone, and despite the few swirls from up close, I'm really liking the results.


Any comments and critiques, especially advice for the epoxy and paint, I'm going to be building stands for the wedgies in the future, so I will be working with it again. Thanks for looking. Happy Holidays everyone.
Ben

fishboat

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Re: Finishing H frames
« Reply #15 on: 7 Dec 2018, 02:57 pm »
I'm a bit late to the discussion..just noticed it..but, for future reference.. has anyone tried fairing fillers (micro-balloons) added to the epoxy.  It makes sanding much easier.  I used them years ago when fairing a sailboat rudder..worked well.

Could be used via the following schedule:
>lay down unfilled epoxy base coat on an area to wet the surface
>follow immediately with micro-balloon filled epoxy
>cure and sand..

https://www.westsystem.com/filler-selection-guide/

(RD..very nice looking subs btw..)

Captainhemo

Re: Finishing H frames
« Reply #16 on: 7 Dec 2018, 05:25 pm »
They look   great  Ben  :thumb:

jay

mlundy57

Re: Finishing H frames
« Reply #17 on: 7 Dec 2018, 06:02 pm »
Ben,

Looks good.

I only use the epoxy to seal the MDF and stabilize the seams. To that end, I sand the epoxy back with 100 grit. I don't worry about swirl marks at this point since the purpose is to make sure there is enough tooth to bond whatever comes next. If I am going to paint I would use a primer, likely more than one coat. This is what I would get smooth before applying the color.

Enjoy,

Mike

lacro

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Re: Finishing H frames
« Reply #18 on: 7 Dec 2018, 06:18 pm »
Any comments and critiques, especially advice for the epoxy and paint, I'm going to be building stands for the wedgies in the future, so I will be working with it again. Thanks for looking. Happy Holidays everyone.
Ben

Ben, I think you made the same mistake most of us do when first working with epoxy, coats applied too heavy. Several thin coats are better than fewer thick coats. The rough surface is probably dust nibs from the surface or maybe the roller, and or air bubbles. Use a tack cloth for dust, and don't vigorously mix epoxy as it can induce air bubbles.

I still think a thinned first coat makes the whole job easier as it seals below the surface without building any thickness, allowing subsequent coats to be applied very thin without leaving the high spots that a thick coat will, which have to be sanded out. I use the mohair type roller covers because they have little bristles that help pop air bubbles. Also, I tip off the rolled on coat with a foam brush which helps smooth roller tracks, and further remove air bubbles. Sometimes I use a second fresh cover to move the epoxy around from wet (shiny) areas to dryer (dull) areas. Also it absorbs some of the excess epoxy on the surface. Remember, thin coats are best. If you build multiple thin coats, sanding will be much quicker/easier.

I like to sand big flat surfaces with a long board, not a sanding block. Then I go over with a ROS, hand sanding the radius. The long board held diagonally along the surface knocks down the high spots, exposes any low spots, and keeps the panel perfectly flat. If you have applied enough coats, all sanding can be completed in one session, but that rarely works for me. I usually lightly sand between coats, and even when I think all is done, I need one more very thin coat of epoxy. The key is to have a nice smooth, scratch free surface ready for paint after the epoxy cures for a week or more.

undertowogt1

Re: Finishing H frames
« Reply #19 on: 7 Dec 2018, 07:46 pm »
These look great. I may take the plug and try this myself when I build mine ( eventually). Is it difficult to do or just a little time consuming?