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Baltic Birch Expansion
Baltic Birch Expansion
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Old 19th December 2017, 11:34 PM   #51
bunkie is offline bunkie
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I really wonder if the issue is the panels expanding. Plywood and, especially, Baltic Birch is exceptionally stable along its face because of the alternating grain. Wood expands laterally more than it expands longitudinally. If the plywood was expanding this much, I would expect it to begin delaminating.

Here's my off-the-wall theory: The front and read panels were always oversized and the veneer covered the gap, supported by the glue underneath which has dried and contracted causing the difference to become visible.

To prevent this, do what auto body folks do. Apply a guide coat of primer and use a large sanding block to expose the low spots then fill them using autobody filler sanding it absolutely flat using a large sanding block.
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Last edited by bunkie; 19th December 2017 at 11:35 PM. Reason: Typo correction
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Old 20th December 2017, 01:23 AM   #52
Richidoo is offline Richidoo  United States
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Quote:
Originally Posted by robert1111 View Post
Hello

I built speakers few months ago. I made the cabinets out of moisture-proof 18 mm baltic birch plywood

Did you use real baltic birch?

I ask because there is a 4x8 sheet of 13 ply sold locally that is from China. They call it baltic birch. Cheaper version for cabinet makers. Probably more warp resistant than 5 ply and that's what they care most about. It has overlapping plys and voids, splintery, doesn't smell right, glue is not moisture proof and it is whiter than real BB.

Real BB is 5 foot square, and has the purple stamp in cyrillic.
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Old 20th December 2017, 07:42 AM   #53
robert1111 is offline robert1111
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It is real baltic birch. I bought it from a good place, that is only selling baltic birch. I'm not sure what the moisture proof means, I thought it makes it more stable.
They do have big warehouses, so there must be quite big moisture difference, but I bought the material in the end of summer, so it was dry. Anyway the speakers were fine, and it took me long time to veneer it. After veneering they were fine for 2 months sitting at my desk. And the horrible Autumn has been wery humid for about 2 months. For me the strange part is, why did the panels move suddenly standing on my desk. That is a long time sitting in the same climate, and a very fast sudden expansion.

And yes it is panels expanding. Like I said, I did not veneer the bottom, and there can see how the panels are not flush any more. No cracking.

Next time I will use 45 degree joints, add a few screws and front, back panels will go inside the other panels. That would force them to move together. Probably will let them be unfinished for a long time, to see how they react.

Current speakers, I have decided not to fix them right now. I will probably wait for spring to see if it shrinks back. And there is a strange voice in my head that wants to build 2.5 out of these. Maybe I'll try to sell them for a break even price. So someone could enjoy great speakers for more than reasonable price. And the most satisfying thing about those speakers is, that I wanted smaller speakers, that would be as good as the Yamahas, that can be seen on the pictures ns-515f. And they came out sounding a lot better, costing 1/3 the price.

Last edited by robert1111; 20th December 2017 at 07:57 AM.
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Old 20th December 2017, 12:19 PM   #54
kevinahcc20 is offline kevinahcc20  United States
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Letting material stabilize before machining and assembly helps to avoid differential movement once the structure is complete, but there is also the need to design to avoid or accomodate relative movement between parts of the finished assembly. Your thought to use 45 degree miters at the corners is a good one so that the mating pieces are aligned along the axis of movement, and they will move together.

Wood structures including plywood (across its thickness) never rest and no pratical finish will stop the movement of moisture into and out of the wood. The biggest changes as you observed come at the seasonal boundaries, in the summer in your area I assume you are air conditioned and so fairly isolated from outside humidity changes. In cooler fall weather when air conditioning is not needed but humidity spikes the impacts indoors are larger. Here in the north during winter when temperatures are below zero there is a limit imposed on humidification to avoid condensation and freezing on cold surfaces. So the experienced builder develops instinctive insight into avoiding problem areas.
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Old 20th December 2017, 04:53 PM   #55
straight8s is offline straight8s  Canada
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This is what I do now, to compensate for any slight differences during assembly. Even if there are permanent differences however slight. By leaving myself a 16th of an inch overlap at each of the end cuts. Square everything up best I can then I flush later with a bench belt sander with 90 degree fence. I'm close as I can get to guaranteeing myself perfect butt joints ready to be veneered.

It wouldnt hurt to leave cabs unfinished, to settle. Then proceed with this step later, weeks months, whenever you feel comfortable. You can still enjoy functioning speakers until then. Providing it won't have you in the doghouse with your better half.
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Old 21st December 2017, 01:52 AM   #56
chrisb is offline chrisb
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Some of what I see in the photos is telegraphing of end grain plies through the veneer. If the material hasn’t already been sitting in the shop for a few day before cutting, I generally fill will bondo then random orbit sand flush before proceeding to veneering. It also doesn’t hurt to apply two thin layers of glue to the box with at least a full hour of drying time before the second.
Just make sure both have only a light “eggshell” texture. The first could be considering a glue-sizing.
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Old 21st December 2017, 04:57 AM   #57
simon7000 is offline simon7000  United States
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I gave one of my apprentices a wood moisture meter. Good reviews but checking its' calibration is nigh near impossible. He just got in a pallet of maple. Having been around too long I can pick up a piece and by feel tell him what the moisture content is, more accurately than the meter.

He did plane some pieces too soon and now they will be only suitable for barrel staves!

Interesting enough is that having a full shop allows us to resaw and plane inexpensive hardwood. Paying 47 cents per board foot for the maple randoms. Of course some of it is spalted. Will plane, size, sand and then resell as a table top unfinished for a reasonable price.

But the OP I think has done a fine job and made a good decision to wait and see how things cycle through the year.

When he wants to build new boxes my suggestion is to find a quality table saw he can borrow or rent time on. I would not try a miter cut with a hand saw even with a jig.
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Old 21st December 2017, 05:18 AM   #58
straight8s is offline straight8s  Canada
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Quote:
Originally Posted by simon7000 View Post
I would not try a miter cut with a hand saw even with a jig.
I made the most fire wood attempting angle cuts without a good power saw. And mitre jigs. I think they were invented not to cut properly with but to test a guys patients threshold. Either a table or sliding radial arm saw with a GOOD finishing blade is best.
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Old 24th December 2017, 10:15 PM   #59
phase is offline phase  United States
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All good practice to allow the material to stabilize to the environment and all, which he did, but the moisture in the glue sometimes takes a while to soak in when trapped under the veneer with a water based glue. End grain is going to suck up more.


If you can swing it, the 3m PUR system is pretty good, used by some commercial cabinet makers. Still not a solution for applying veneer though, I use a spray on contact adhesive for that, and a roller.
https://multimedia.3m.com/mws/media/...em-pckt-gd.pdf

Not exactly a practical purchase for a set of speakers however.
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Old 3rd January 2018, 03:00 AM   #60
jmkeuning is offline jmkeuning  United States
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When you mention using miters and screws I assume you are talking about screws from
The inside, with corner blocks. Any screws from the outside are going to telegraph through just like your end grain is telegraphing. I like the bondo idea. Hell, even if you have nice miters you can use bondo any defects if you are veneering over the top. The other idea of 1x4” veneers might work, but will be more susceptible to shrinkage. Also can be tough to get full contact with the adhesives unless you have a vacuum press. Any bubbles/voids might (probably will) rattle and make wierd noises.

I would cut 45s on an accurate table saw with a sled. Glue only. If you really need to screw, apply from inside - full length glued corner blocks.

But all that to say - your speakers look great and if they sound great I bet you’re the only person who notices the flaws. And flaws are good because only god is perfect. At least what the guys who hand-knot the $25k rugs say.
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