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Howitzer build

post #1 of 452
Thread Starter 
These cannons will be loaded with three 10" NHT 083s (no longer available). The work is progressing slowly, because I can only spend a little time on them here and there.

This is my first attempt at building a curved cabinet. I hope to know what the heck I am doing by the time I finish the last of six.


Tying up loose ends--I had previously built some test cabinets, but I was too new at testing to get any meaningful results.

Also, in WinISD, I eventually got around to looking at the driver excursion graphs and saw what some guys tried to warn me about, which is that these drivers appear to benefit from the excursion limiting properties that a smaller cabinet provides.

I intend to slip some graphs in at some point.

I expect this build to take a while, because I can't spare much time for it.
Knowing that, I have gotten off to a good start already, but delayed posting anything until now, so it won't seem quite so drawn out. I hope.

Many thanks to everyone who advised me previously on this build.


The best I am able to tell, it appears that a 1.25 cubic feet per driver cabinet will be a good choice for these drivers. I have no idea how to calculate volume in a curved cabinet, so I just over-sized a rectangular cabinet and hoped that I come reasonably close to a good internal volume after the curving reduces things internally. I'll give dimensions later.

Disclaimer: I am not an expert at anything--just a little bit of a DIYer.

Enjoy the show.
post #2 of 452
Thread Starter 
There are plenty of curved cabinet builds out there.
I offer nothing new to the seasoned veteran, but hopefully a new DIYer will find something useful in this build.

Let's begin.
Ignore the speaker cutout. This is just some scrap wood.
I knew I wanted a depth of 20", so I set a tape measure at the 20" line and used a ruler to check for a pleasing curve radius and offset. I found a 25" radius to be a good choice, with a 3" offset from the 10" center line. This meant that I can use a circle jig that I made in a previous speaker stand build.
Again, I held my fingers at different positions along the ruler and swung it in an arc and looked for a curve that I liked.




This would look a little less confusing if I had used a large sheet of scrap under the workpiece, but I just used small scrap pieces, so I'll try to explain how I lined things up.

I measured over from the table edge to center the long scrap plywood piece, since I knew that my pivot center is 10" - 3" or 7" from the edge.
Once I had the long plywood piece centered, I held a board along the two table edges to center my workpiece, using small scrap pieces under the workpiece for stability during arc-routing.

Once everything was centered, I shot some short brads into the workpiece to secure it to the long plywood backer. I also secured a small scrap piece with a small pivot hole at the 25" mark, to the same backer.

With everything aligned and secured with brads, I could now move the entire assembly toward the table edge, so I could get some clamps on it.

Again, it would be less confusing if I had used a larger backer.




Here I've secured the circle jig to the router.




Secure the pivot.

post #3 of 452
Thread Starter 
Route an arc.




Flip the workpiece. Align and secure it the same as before and slide it to the edge for clamping and route another arc.






I now have a template.

post #4 of 452
neat.
post #5 of 452
Very cool. I'd like to try this some time.
post #6 of 452
Knowing how thorough your previous build threads have been, I'll watch with interest since I want to rebuild my Dynamic 4T's with curved walls. I may have a CNC machine at my disposal, but coding is not my strong suit.

Side note: This is the first thread I have subscribed to.
post #7 of 452
Thread Starter 
I'd like to cut the front and rear pieces with a bevel to match the angle of the curved sides.

First, I need to determine the angle at the point where the curved side ends.

This is the front.




The rear.




The saw's bevel indicator reads "0" when the angle gauge reads "90."



Subtract 90 from 106 and set the bevel to 16 degrees for the front baffle.




Set the bevel to 30 for the rear (120 - 90 = 30).




The rear measures 9 3/8" across.
Set the fence for 9 3/8" with a 30 degree bevel.




Looks like a match. Do the same for the front.

post #8 of 452
Thread Starter 
Thanks for the encouragement, guys.

Make some blanks.

post #9 of 452
Quote:
Originally Posted by PassingInterest
Thanks for the encouragement, guys.

Make some blanks.
Thank you for the detailed instruction. I have been researching all the curved cabinet threads I could find in preparation for my build. I will be following yours closely. Good job, and good luck
post #10 of 452
very happy to see another one of your excellent build threads going up.
post #11 of 452
A PI build!!!

[grabs nachos]

JSS
post #12 of 452
inspiration for my next build.
post #13 of 452
I am ready! PI builds are more like artistic expression than a build thread. And you get to pick up some tips! As always with your builds...tuned in and willing to learn!
post #14 of 452
Now I know what's been bugging me lately, I have been jonesing for a PI build, now the world is back in balance

Thanks for sharing the knowledge PI, I always pick up so many tips, and new tools while following your threads.
post #15 of 452
Cool name for your subs by the way.

Are you going to wear full safety gear when you fire them


LL
post #16 of 452
Signing on to what will certainly be a great build. Grab the note pads, there's always something to learn in a build thread from Mr. PassingInterest!!!

Anyone want to wager that his Toyota T-100 gets thrown into one of the photos just to make me wish I still had mine?


Isn't it like 140 degrees in Texas right now????
post #17 of 452
Always love your builds Passing Interest!

Max pass the nachos!

Erich H - How are the 10's treatin' you?


dbl
post #18 of 452
Quote:
Originally Posted by Erich H View Post

Anyone want to wager that his Toyota T-100 gets thrown into one of the photos just to make me wish I still had mine?



After reading that I immediately scrolled up to inspect each pic again, I thought we may have missed a reflection or a glance at a tire or something. Somehow it doesn't feel quiet right without the T-100 making a cameo.

Just the other day I read someone commenting on how ingenious some people can be and he recalled someone using a truck as a press. I immediately thought, oh yeah, that's Mr. Passinginterest
post #19 of 452
Thread Starter 
I bet Toyota doesn't even know they make a veneer press.

That's a great action shot of the "other" Howitzer model, MJAudio.

It is a little warm here in the Dallas area these days. I just drip sweat everywhere. But this build is long overdue.

Thanks again for the encouragement, guys.
post #20 of 452
Thread Starter 
Using screws, secure the template to two blanks and bore some holes.
Tip: Slightly oversize the blanks at the table saw and trim to size at the router.




Remove some waste.




Trim the outside.




Trim the inside.







Use the same template to trim the outside edges of the cabinet tops and bottoms. I chose to use some 1 3/4" particle board that I had on hand.
post #21 of 452
Thread Starter 
Roundover.




The particle board edges will absorb the glue very quickly and maybe the plywood edges will, too. I applied a coat of TiteBond I to the edges and let them dry before glue-up. I did this for 3 cabinet sets, then later decided to build 2 at a time.

You can apply the glue quickly if you treat all the edges as one large surface.




Then separate them and let the glue dry.

post #22 of 452
It's been a while since I've seen particle board used in a build other than mine.
post #23 of 452
Thread Starter 
Quote:
Originally Posted by tuxedocivic View Post

It's been a while since I've seen particle board used in a build other than mine.

I had some taking up space in my garage and couldn't think of a reason not to use it. As I understand it, particle board was once commonly used for speaker building.
post #24 of 452
Thread Starter 
Spread some glue.






I shot some brads into the pieces to keep things aligned.
Clamps are probably not necessary.




But, I have a thing for clamps.




The cauls will bow slightly in the middle from the clamping pressure on the ends.
You can curve them slightly to compensate for the bow. I just put 4 layers of masking tape in the middle.



post #25 of 452
Thread Starter 



Here you can see how nicely things lined up.




The next set of pictures is wrong.
First, I ran into a problem while attempting to curve some thin Luan underlament plywood ($9.99 per 4x8 sheet at Home Depot).
As I tightened the ratcheting tie-down straps, the edges of the Luan cracked and broke, because it is not very flexible at all.
So, I got the idea to fasten wood strips along the edges to distribute the pressure and avoid the cracking.

After I got the strips ready to attach, I remembered that I had a very flexible sheet of some plywood and decided to use that. The 5 x 5 sheet was actually a "pallet protector" on top of a new pallet of Baltic Birch. I asked the guy at the store (McCoy's in the Dallas area) what they did with the protector sheet. He said they threw them away. I asked if I could have it and he gave it to me.

That was months before and I was right about it being very flexible, so I did not need the wood strips. But the summer heat had cooked my brain, so I was not thinking very clearly and I attached the wood strips and they caused a problem, only I didn't realize it yet--not until after I had taken the following set of pictures.

The problem caused by the wood strips was an uneven application of clamping pressure from the straps. It wasn't until I was about to move the box back into the garage after taking pictures that I noticed gaps between the box top and the curved panels.

The solution was to remove the wood strips and re-tighten the straps--the flexible plywood did not need the wood strips. I apologize for the absurdly long-winded explanation.












Again, the wood strips are not needed if your plywood is flexible.
Nothing but some ratcheting straps are all you need to clamp your side panels to your cabinet frame--if the plywood is flexible.
post #26 of 452
This is now an official PI thread with the T100's appearance

Well done Mr. PassingInterest.
post #27 of 452
After seeing the pic's, I think a name change is in order! The should be called the Whodini subs! All those straps, nothing is gettin out of there. PI may be a great woodworker, but he is also a great photographer. He is also a closet Toyota worker. Using DIY subs as a way to try and sell Toyota trucks. Genius!!
post #28 of 452
Thread Starter 
Haha! I just like my truck.

Thanks, guys.
post #29 of 452
Okay, I have to know this. How did you have the time to wipe that glue on there and still get everything lined up and strapped down? And you did both sides at the same time! It seems like every time I try to do that the glue starts drying too quickly.

And if I smear the glue on, I also have issues with moving the panel after the 2 pieces come together for just a short amount of time. What's the secret Sir P.I.???
post #30 of 452
Erich H: Not sure how he did it, but I usually fire some brads along one side before clamping. This way, it doesn't creep one way or another once clamping/strapping.
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