I am planning to build a couple of speakers (a bookshelf set, and then a floorstanding set) using 3/4" baltic birch ply and a hardwood front baffle. I have some 1" thick dense hardwood (ash? White oak? Cant tell which) in my garage, cut about a year ago on a bandsaw sawmill.
I was planning to just glue the hardwood baffle to a backer ply board using Titebond.
However, I found this thread on another forum when I googled. https://techtalk.parts-express.com/...1444871-solid-wood-baffles-with-mdf-ply-boxes
Is it bad to use the glue route? And I should instead float the hardwood front baffle on top of the birch ply with a thin gasket in between?
I was planning to just glue the hardwood baffle to a backer ply board using Titebond.
However, I found this thread on another forum when I googled. https://techtalk.parts-express.com/...1444871-solid-wood-baffles-with-mdf-ply-boxes
Is it bad to use the glue route? And I should instead float the hardwood front baffle on top of the birch ply with a thin gasket in between?
Not bad per se, just hardwoods dry out over time and can shrink/twist in the process, so if gluing, ideally need to 'pin' the two panels together out near the edges on the backside with screws/washers and depending on the baffle size, driver cutout size may need some stiffeners added to the plywood as the driver shouldn't be relied on as a brace/tensioner.
Good point! I was trained with 'old school' horse glue, etc., though once Titebond came along, rarely used anything else for furniture grade, i.e. no need for type 2, 3 except for some heavy duty apps and never with epoxy and my limited experience with Gorilla epoxy was bad enough to never use it again.
Just prime each side with epoxy and let it tack out for more than 3hrs but less than 12hrs. Then mix up some more epoxy and add wood flour until you have a nice goo that just resists flowing. Use this between the hardwood and ply face and space out with strands of fishing line. This yields a chemical bond that stabilises the hardwood. A veil of the finest woven glass cloth with epoxy will stabilise the face of the hardwood too. You can sand the epoxy back to the glass and stain and clear coat for an heirloom quality finish
I think i will try this.
I like this idea. My epoxy skills are poor, but I could see how the aggregate (wood flour) and fiberglass adds strength but reduces the rigidity of the epoxy bond. I can also see how the epoxy would seal the backside, allowing the whole hardwood piece to be nicely sealed.
Much to think about.
First, I will try tiger-striping the ash https://www.woodworkerssource.com/b...easy-fantastic-ash-wood-finishing-techniques/
If the wood comes out with wonderful graining after that, I will think long and hard about both methods above, especially the epoxy one.
I am really hoping to make this little bookshelf something special.
I can't wait to get back to that bandsaw and play with more wood. He has some nice large walnut trunks just lying around.
And I also now need to buy a planer. I love a good excuse for new tools. Looking at a Wen 15 amp 13 in bench planer.
I can appreciate that
Can I suggest something along the lines of taking out a quarter sawn block and then butterflying that for a mirrored grain effect. Another nice touch is adding a pigment to the goo so you can have something like a line effect between the plank and ply face or between your strips. Black or red works really well. Gold colour powder mixed into the goo can also give a nice effect that can match up with badges and fittings. If you choose to go the transom assembly route with epoxy, you are welcome to get in touch for detailed steps on setting up, assembly/epoxy process and final finishing. This process lends perfectly towards a finish that looks like deep molten glass but is super silky to feel and not grabby or plasticky like the usual poly or epoxy speaker finishes
Epoxy is not well understood and can certainly be tricky, but once you click on to it, it's much easier than usual furniture techniques. It's all in the setup. After that, epoxy basically applies itself! I am still very proud of the recognition that I received in another industry when I got named as one of the best if not the best finishers in a magazine article. The tech is something that I have always shared openly from day one when I approached it with the aspirations to master it back in 2006 after initially trying and finding it tricky in 1992
Exactly what I am looking for. I will be in touch when I get to that stage.
Personally, I would like to avoid the mirrored grain look. I have mirrored rosewood veneer on my current main speakers. I do love them, but hoping for that unique tigestriping look for the front baffle. Sides and back bitch ply will likely end up with either a gel stain or a whitish-grey enamel paint.
I have built six cabinets now entirely out of 1" solid white oak boards and yes, they will move a little and crack with seasonal humidity swings.
My concern with your situation would be the initial moisture content of wood itself.
What did you cut the boards from, green trees or already dried lumber?
Might want to get a moisture meter to check they are below 10% and uniform before you start.
Then I would suggest selecting a final finish that is very moisture resistant. I used Danish oil and later wax, which looks nice but didn't seal the wood enough. Live and learn.
I'm in the NE USA where the RH range is 10% - 70% and I don't have HVAC humidity control, so even after just one year I started to notice some small cracks forming.
Boards were cut from a felled tree trunk that had been resting outside for a year, and the cut boards have dried in my garage for another year. No idea the moisture content. I too am worried about cupping/splitting. I am also in the NE and experience those humidity swings. But we run a humidifier in the winter and AC during the summer to keep it fairly stable. My son has a $15k double bass, so we need to control humidity to preserve that from developing a split...
The wood flour and glass process that I described is to specifically address the issues that you bring up. The separating of grain on the face of a plank or ply is called checking, and the glass veil fixes that. The awesome shear strength of epoxy together with the cross-linking fibres from wood flour fixes the blank to the ply to address warping via a full structural contact and chemical bond, The whole structure basically becomes one and can be seen as such if a section is cut out for examination. The epoxy and glass also stabilises whatever reasonable amount of moisture is present in the wood. This is what I describe as heirloom level finish and place way above a showroom finish
At the end of the day one also needs to weigh in on the amount of effort vs if it's worth it and personal ambitions
Do some mock-ups and see if your baffle is going to be wide enough to display enough stripes to create a good effect. Also, Feast Watson wood finish tint in a lil bottle is awesome with methylated spirits to deepen the stripes. Start very dilute and build up in layers. But test as some woods it can effect the lighter parts more but that can also be exploited to create an ebony effect with mixing the Japanese black with walnut
You going to glue a stable substrate to a thick seasonal moving material, you need flexibility at the glue joint because eventually one of them will give away and crack or bow... epoxy will not hold this unless its sufficiently thick and reinforced enough to resist, you will get grain separation at the glue joint.(ask a seasoned boat builder)
Use a highly flexible glue or cut your hardwood into veneer.
Use a highly flexible glue or cut your hardwood into veneer.
Harry, a plank in a composite sandwich with epoxy encapsulation is environmentally stable through seasonal changes. My transom is dakua on damanu ply and the boat is fished commercially since 2015 and moored. With just 200gsm skins and still no issues in the tropics even with a category 5 thrown in. Do you really think a speaker baffle will fail where a 1.6m width transom with 25hp in the middle doesn’t?
I dont think he's going to fully encapsulate it with 200gsm matting drenched in epoxy its a speaker baffle not a transom.
Plus Agathis Macrophylla is well known its nautical uses due to it being stable, very straight grain and high resinous content also being reasonably light weight.