woodworking help with a T-60

[Rich4349]

I've been building a T-60 for the last, say, 6 months. (Very inexperienced builder here. It's all learn as I fail.) 27 inches wide with a LAB 15. I finished the build, and ran it, and I THOUGHT it sounded pretty amazing. But after a day or two, once the gee whiz factor decreased, and more critical listening happened, I noticed a rattle. Initially I thought it was room resonance, as my house is small and the room it's in is about 9x11. Eventually, I found that applying pressure to certain spots on the side of the cab eliminated the rattle. Since I didn't think finding someone to lie on the cab every time during use was practical, I knew it had to be fixed. I thought maybe that the brace between panels 3 and 8 might not be glued into unison, so I drilled a pilot hole through panel 8 and fished a narrow wire through, and swing the bent over end around to feel what was going on in there. Sure enough, I had forgotten to re-install a portion of the bracing there that I had removed to bring the cab closer into square. (The kerf removed with the sonicrafter x2 was about enough to do that.) So now I have a missing brace. Now I got the pleasure of ripping apart a cab assembled with PE. I set the circular saw to a cutting depth of 1/2" and started plunge cutting. And cutting, and cutting, and cutting. This is tricky: if you don't start at the edges and work your way inward, you don't have anything of existing height to rest the saw on for proper depth. Eventually you get to about nothing left to rest it on, so I took left over chunks of 1/2" plywood and used those. Running the saw back and forth sideways acted as an ad hoc router, evening up the surface. BUT, it still doesn't leave you with a nice even surface to glue back to, once you prep YET ANOTHER end cap. (I'm sanding, staining, and sealing, not dura-texing.)

So here's where I am now: when I put the newly prepped cap on the side, the interior walls of the cab do NOT reach it. Even with 10 gallons (83 lbs) of water in a cooler, and 115 lbs of plate weights, the inner portion of the panel has a disconcerting gap. The gap is at the outer limits of the PE's expansion capabilities. I have already spread a layer of PE on the very lowest parts and let it dry, to shim it up some, but once I laid the cap on, it still looks to big to chance it. Here's what I've come up with so far:
1) Add more layers of PE to shim. (Due to staining and trying to keep this looking marginally professional, the extra layers of PE will probably make the inside view of the throat look like @$$.
2) ACTUALLY shim with a 1/4" or so layer of wood. Where do I get this? How do I make it myself? Will this ALSO look like @$$ ?
3) Lay the cab on its side, and use the circular saw to just take a kerf worth of wood off of the outer panels as needed, effectively raising the inner panels by comparison. (Most likely to be successful, also most likely to fill my house with MORE sawdust in my spare bedroom. Note to self and others: sawdust in the cold air return= furnace self shutting down. Make sure the shop vac's filter hasn't fallen off inside! ) And then continue on with gluing the last panel with PE?
Any other options I'm not coming up with?

[Rich4349]

Ok I have pics of the process but I am too stupid to figure out how to post them. I upload them, but then they aren't there. What am I missing?

[Radian]

Rich,

To upload pics directly onto the forum (as opposed to having them linked from a hosting site) they'll have to be sized to at least 700 pixels on their longest side.

After you re-size the picture, check to make sure it's file size is less than 1MB. If not, reduce the quality a bit before saving it, to bring it into limits.

Re-sizing it without further compression is usually enough to make the image small enough to upload.

There's a sticky here:

http://www.billfitzmaurice.info/forum/v ... f=7&t=7603

I gather you've probably had enough for tonight, as it is.

-Radian

[quaizywabbit]

do #3 outside.

assuming the inner panels are lined up flat and square at the edges take a straightedge across the inner panels and transfer to the outer panels. Or put a straigtedge across the taller outer panels and measure the distance to the inner panels.
make sure the distance at each panel is the same at each and every panel. if so, then cut off the appropriate amount on the outer panels. if not, then try transferring via the first method.

[Zack Brock]

I'm willing to bet it is one or more, or even all three, of the horizontal crossbraces that have come unglued. Applying pressure (or even standing) on one of the sides would alleviate the problem if so.

I had a similar issue on the first T60 I built and tested; turns out that I didn't sufficiently glue the braces in and thus when the pressure wave of sound exited the mouth a rattle came with it. Removing them, sanding the spots and re-gluing solved the problem for me.

Check out those braces too, they might be rattling whereas your space that you need 'shim' could be another problem altogether.

[Tom Smit]

Don't give up yet! You're close!
One type of spacer that I used was a paint stir stick. If you put a straight edge across from one outer panel to the other outer panel, you can see how much of a gap there is between the brace and the straight edge. Then cut a spacer to fit the gap.

[Rich4349]

I could not believe how many places the PE didn't bridge the gap between panels.

Still haven't decided on how to go about buzzing down the sides: haul the thing to the front porch in the snow, or once again fill my spare bedroom with sawdust.

[DanielNY]

Did you stain the ply or is that lamination? either way, not good!

[SoundInMotionDJ]

2) ACTUALLY shim with a 1/4" or so layer of wood. Where do I get this? How do I make it myself? Will this ALSO look like @$$ ?

This is the right method. Do you have a table saw?

Use a good sharp chisel and remove all the PL from all the edges of the panels. Using a straight edge, find out how large the gap is between the panels and the sides. The size of the gap will play into the exact nature of the solution.

Here is one technique for cutting thin strips:

http://www.youtube.com/watch?v=lp4ZR5Ws ... 8&index=40

Alternatively, if you have a crosscut sled, you can use that to cut thin strips as well.

--Stan Graves

[Rich4349]

Did you stain the ply or is that lamination? either way, not good!

That is stained and polyurethanes auruco plywood. In the places where the panels came close, and the PE was sufficient, adherence was no problem, only where the gap exceeded the expansion capabilities of the PE. In those cases, I got nothin!

[bzb]

You do mean PL, right? PL is the name brand of the polyurethane construction adhesive we use.

Hopefully it's not some other weird stuff you found called PE that may not do the job... although it certainly looks like PL in the pics Although, mine certainly expands more than yours seems to.

Two things here:

1. This is why I won't use Arauco on the big cabs. Warpage = pain in the ass on the large panels.

2. PL nor Duratex should not be used when it drops below 45 degrees or so. The cabs I built in the summer are FAR different from the ones I built last year.

[Rich4349]

Yeah, I meant PL. I've read HUNDREDS of pages of these posts, especially the monster thread:

http://www.djforums.com/forums/showthre ... 107&page=1

The arauco definitely warped more than the BB I used on the auto tuba, though I drug out the project so long it's no wonder. I might even suggest not buying ALL of the plywood at the beginning, unless you're SURE you're going to be ready, willing, and able to complete it promptly.

And I glued the last panel on when it was still warm out, though not summer warm for sure. Will colder temps reduce its expansion properties?

[Chris_Allen]

My first T48's were built with warped ply and it was an absolute nightmare. The constant movement of the ply trying to get back to it's original position after bracing didn't allow the glue to set/expand properly.

[Rich4349]

Well I ended up removing the final side panel via death by circular saw. I set the depth to a hair under 1/2" and just plunged and plunged till I couldn't plunge any more. And then I did. It was a super pain in the a$$, but it had to be done. I got a fresh / unwarped piece of Auruco (when it's new it's not a bad plywood), sanded, stained, and PL-ed it in place. Didn't need anywhere near as much weight as I did with the warped piece. And I used a bit more PL to boot. Gave it 2 days to absolutely cure, and badda bing, I was in business. The sound is amazing, as well as house quaking. Now I just have to figure out what tops to build to match, without them being completely out-gunned by the T-60. I'd like to play to a big room sometime; the one I have in mind is about 60x80, with 25 foot ceilings. Any suggestions? I'm thinking 280s or 300s.

[Dan30]

I bet screws would have done a better job with the warped wood staying in place.