Someone posted a T39 assembly jig...

[dextermcneil]

OK, someone who was building a bunch of T39 (I THOUGHT it was Stan from SoundInMotionDJ, but not sure) built an assembly jig for holding the inside baffle plates in place while the glue dried without having to attach a second virtual side and work around that. Pictures were posted. I can't find that thread to save my soul. I'd like to take a look at it again before I build one for my self.


Thanks,
Dexter McNeil

[SoundInMotionDJ]

I assembled the entire horn section using the top and the internal brace for support. The assemble was done in three stages (so the glue from the last stage was dry and I had something to push or pull against)

The internal brace was a single piece of 1/4". I laid out the T39 on scrap ply, then cut "near" the lines. Then I screwed a straightedge to that blank and routed each edge with a straight pattern following bit. When I cut the internal brace I used a collar, so it was 1/8" oversized on each edge. That fit into a 1/8" dado I milled in each of the panels.

The internal brace pattern:



In order to make this work, I changed how a couple of the panels matted together. Here is a photo of the dry fit that shows how #4 and #6 were cut. Basically, I only cut an angle on one end, and left the other end cut @ 90deg. This reduced the length of both of those panels slightly.



Here is the assembly of the horn section for four T39's. I did one ahead of time to be sure that it would work, and the next three as an assembly line.

Stage 1:



Stage 2:



Stage 3:



Is this what you were looking for?

--Stan Graves

[dextermcneil]

Stan,
Thank you for the reply! Yes that was part of what I remembered. Someone else had made a jig that held the internal panels all in place while being assembled. Since I plan on building 14" wide T39s, the single brace down the middle won't be enough to support the panels and keep them square. Hence the desire for the jig info. I can make one, but if I don't have to reinvent the wheel....

I'm planning on doing the single piece brace installed in dados, and as Bill showed on the revised T39 plans, I'm going to use the flanges for the access panel as the mating surfaces for two of the driver chamber walls.

Thanks again for posting the pictures - they were very helpful.

Cheers,
Dexter

[Mark Coward]

I think the only jig was camryn's who did the same thing Stan did, except with dual braces in a T48. He just had a couple of scraps with slots to hold the two braces parallel while adding the panels. He used 1/2" I believe, which I think I would choose also for this purpose as the 1/4" BB has a lot of warp IME

[dextermcneil]

Thanks, Mark! I think you are right, it was camryn that I remember. I knew it was someone who built a large number of Titans.

I don't think I'll have too much trouble with the 1/4 BB bracing. It will be in 1/8" deep dados on both pieces which will take the warp out of it. If I can keep the assembly square and even, I think it will work with out problems. The key will be a good jig. I'll post details once I get it figured out and tested. I don't think I'd be worrying about this as much if I was building a wider cab with two braces. But that one brace down the middle? And yes, I could put two braces in a 14" wide cab, but that's a bit too much overkill.

[SoundInMotionDJ]

Since I plan on building 14" wide T39s, the single brace down the middle won't be enough to support the panels and keep them square. Hence the desire for the jig info. I can make one, but if I don't have to reinvent the wheel....

Those are T39 @ 14" wide. The single brace is enough... Those pics were taken right after I added the panels - that is how they sat to dry. Seriously.

Here is why this works:

The top (#1 with the access port) was already complete and fully dry. I made sure that the access hole flanges were straight and square. So I was able to use the access hole rim to keep the panels that connect to the top square to the edges. The brace set the distance between the panels. By aligning them with the edge of the top, and nailing them in place, everything was held square as it dried. When necessary, I used clamps to keep the brace set into the panel until the PL dried (look at the Stage 3 pic for an example).

On the next step, I was able to use the existing panels that were dry and *firmly* in place thanks to the PL to keep everything square and in line. I used a large framing square to double check everything before adding any brads to hold the panels in place while the PL dried.

So, in between each stage, I allowed the PL to cure "overday"...I did a build session in the morning, and another in the evening after work. There was 10-12 hours of dry time before beginning the next stage.

When it came time to mate the first side, I used cauls and *lots* of clamps to hold the brace in place on the side until I could get brads around the parameter, and a few in the middle.

For the second side, I traced the actual panel location and drilled 3-4 holes in the "middle" to let screws pull the side tight. Brads around the parameter did the rest.

The largest gap I had in assembling 8 T39's this way was about 1/16". A little sanding with 80 grit and a good bead of PL was more than enough to take care of that.

To be fair: I trimmed each panel to width on a table saw in one session. Every panel for every cabinet was *exactly* the correct width. Also, the ply I used (Arauco) was *flat*. I did not need to take any twist or warp out of the panels during assembly. If the panels were in need of "persuasion" to be square...then my method would not have worked.

--Stan Graves

[Mark Coward]

I'm sure that the 1/4" works fine, I still think 1/2" would make the assembly a little easier, as you can shoot brads through the panels into the brace.

Now that I think about it, I suppose that for a jig you could duplicate the brace pattern leaving off the 1/8" allowance for the dadoes. With a couple of these, one on each side of the single brace it should hold the whole assembly square. You could make them out of 3/4" for additional stiffness, and put a few cleats around it to help square the panels.

[dextermcneil]

I was thinking (smell the smoke yet?) about it, and what I think it's going to look like is a pair of end plates with cleats to hold the panels in place. I'll make the cleats high enough to square the panels up. I've got a bunch of 3/4 inch pipe type bar clamps, so I can drill a hole through each panel, run the pipe down it and have a way to clamp it all in place. It may need two clamps to distribute the pressure evenly, I won't know until I get it set up.

I expect to build everything on top of panel 1, then build the box around it installing the last two corner reflectors as I go. To me this seems to be the most logical way to build the things based on my experience building lots of other wood projects - including a full kitchen for SWMBO (that's how I got the wood shop, including the Unisaw!).

I'll post about the jig when I get it sorted. Wood arrives first thing Monday morning - I had to postpone it this week due to a snow storm and family time.

[SoundInMotionDJ]

Bump...how's the build going?

--Stan Graves