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Howitzer build - Page 2

post #31 of 452
Thread Starter 
You are right about the short open glue time in the summer heat, Erich. You have to move fast.
Another thing working against you is the porosity of the wood, which absorbs moisture from the glue, making the glue dry faster.
The solution to the second issue is to apply two coats of glue. If there is any concern about the strength of glue on glue, use Tite Bond I for the first coat, because it remains water soluble after it is fully cured. This means that the moisture in the second coat of glue will re-flow the first.

I used a 4" foam roller to apply the glue quickly.
You can begin assembly pretty fast if you ready your straps in advance.

As for panel alignment, I did not use brads to secure the curved side panels to the cabinet frame, but this plywood was very flexible. A less flexible plywood will try to move as you bend it.

I made sure I had an extra 1/2" in every direction on the side panels, in case of movement. I set the frame on a piece of 1/2" plywood scrap, then positioned the panels and snugged the straps tight.
post #32 of 452
Thread Starter 
As mentioned previously, you only need some ratcheting straps to secure your side panels if your plywood is flexible.

Unfortunately, flexible or "bendable" plywood is a little harder to obtain in some areas and when it is available, it is usually a bit more costly than some of the non-flexible alternatives. For example, Wood World in the Dallas area had three 4 x 8 sheets when I checked a week ago. Two sheets were 3/8" thick and cost $46/each. The third sheet they had in stock was 1/4" and cost $41/each vs. the $9.99 (un-flexible) Luan underlayment sheets you can get from Home Depot.

Flexible plywood is the easy way to go and the cost is worth it to me.

However, I want to help the DIYers who either can't find, or can't afford the more costly bendable plywood. I'm sure there are many ways to do this. Here's one.

I got the idea to build a form to press the un-flexible plywood around the cabinet, using clamps.


After making a template with an arc to match your cabinet, secure it to your workpiece.




Remove some waste.




Route.




I tested both halves against the cabinet and it was a real nice fit.

post #33 of 452
Thread Starter 
Here is a dry-fit test of the Luan. It shows some promise, but it is not good enough. The clamps are not completely tightened and there is some bowing in the spaces between the supports, but there is no cracking. This is encouraging.

Edit: I forgot to mention that I trimmed the supports down in size, so more of my clamps would fit.




Preparing to glue some hardboard to the form.




I shot some brads along one edge to keep the panel aligned during clamping.




I can already see that this is not good enough, as there is some slight bowing between supports.




I need more supports. I glued together some small scrap pieces.



post #34 of 452
Thread Starter 
Pull the back off.




Scrape some glue.




Dry fit check. A straight edge clamped to the workbench makes for a quick alignment of the pieces.




Apply some glue and spread it with a foam roller for speed.




I didn't bother to dry-fit the Luan, that's how confident I was that the forms would work. Now for the test.






The Luan really resists bending, so allow for some panel movement with some extra over-hang.



I would not consider it worth the extra work to build the clamping forms if the bendable plywood is available and affordable. Personally, I would pay the extra cost for the bendable plywood if I were making only one or two cabinets, but I plan on making six. The forms cost me very little except some time and glue, since much of it was done with scraps.
post #35 of 452
Holy crap! Those are quite the forms...

Looking really good so far.
post #36 of 452
If you cut a few more braces from scraps, you could have just built your enclosure from the braces. But since you're building six enclosures, that would be a LOT of cutting.
post #37 of 452
Thread Starter 
I realize the forms are a little extreme, even for the Extreme DIYers who frequent this site.
Even Looneybomber isn't looney enough to go that route.
I plan on experimenting further and trying different--and hopefully--more practical methods for bending the "affordable" unflexible panels, but not until I start on my second pair of enclosures.
For now, I can get the job done quickly with the forms.
One last comment on the forms--they should prove useful for veneering these enclosures.
post #38 of 452
Did you ever consider kerf-cut bending or steam bending in addition to your forms?
post #39 of 452
This is the second time I have seen this method - very nice job passing interest...
Extremely impressive job there sir....

Looking at this picture, did you think about using the straps anyways inbetween the main pressing points of the forms...
post #40 of 452
How about laminating 1/4" MDF?
post #41 of 452
Thread Starter 
Danielson99--I did not consider kerf-cut bending, because it is difficult to get a smooth bend that way. I've never tried steam bending and I have no equipment for it, but that is something I'd like to try some time. Thanks for the suggestions.

Warpdrv--Thanks! That's a great idea about using the straps between the form's pressure points. I am sure that would have worked! Actually, that makes me wonder if straps alone could work on the un-bendable ply, if you space them closely. Edit: You've seen this approach used before? Dang, I thought I had an original idea here.

petew--I'm glad you suggested trying 1/4" MDF. I happen to have some on hand already. I know it is not very flexible, but neither is the Luan. It needs to be tried, just from what might be learned from it. I avoided it for this project, because the weight of MDF adds up pretty quickly. Still, it can be used in one layer, at least.
post #42 of 452
I'm curious how the 1/4" MDF will work for you, because that's what I planned to use on my build (3 layers). For the curved sides, I planned on doing straps and tossing on sand bags to get everything flat. A few hundred pounds oughta flatten it out.
post #43 of 452
Thread Starter 
Quote:
Originally Posted by Looneybomber View Post

I planned on doing straps and tossing on sand bags

You can get much more foot/pounds of pressure from clamps or ratcheting straps than you can with piling on weight.
post #44 of 452
Quote:
Originally Posted by PassingInterest View Post

Warpdrv--Thanks! That's a great idea about using the straps between the form's pressure points. I am sure that would have worked! Actually, that makes me wonder if straps alone could work on the un-bendable ply, if you space them closely. Edit: You've seen this approach used before? Dang, I thought I had an original idea here.


Nathan at Funky Waves used this technique when building my LMS box....
http://www.avsforum.com/avs-vb/showthread.php?t=1313021
Very similar looking Jig to what you have done...
I wonder if Nathan made multiple passes on adding sheets to the sides one at a time and glued along the way - or if he made a jig to glue all the sheets all at once (in a mass production thought process) and press then into a premade curved panel and then glued it to box / frame after the fact...

Keep up the great work my friend and thanks for posting all you progress along the way - awesome !!!

post #45 of 452
Thread Starter 
Oops! I had a little too much panel movement on one side.




Glue in some filler strips.




Tip: Place some scrap pieces under the panel before applying glue with the foam roller and you will keep glue from getting on your table. Glue on the table has a way of getting on the face of the panel if it moves just a little.




Clamp tightening comments--When using the clamping form, the clamps do more than just squeeze the pieces together. They also pull the panels toward themselves as you tighten them. A front clamp pulls the panels toward the front of the box. A rear clamp pulls toward the rear. An upper clamp pulls toward the top.

What seems to work best for me is to begin with a front/rear upper pair and a lower pair and to apply a small amount of pressure on the front pair, then the rear pair and go back and forth, applying a little more pressure each time, keeping everything in balance, pressure wise.

I used Quick-Grip clamps to pull everything in close, then switched to bar clamps to put some serious pressure on everything.




Hold the press! Folks, I just happened to find some bendable plywood at a local discount surplus store for $19.99/4x8 sheet. The price is too irresistible--especially since it is about twice as thick as the Luan. I used that on the one with the straps in this photo.




Glue cleanup is a breeze--just peel and toss after it dries. Tite Bond II does not stick to plastic.




I haven't been cleaning the foam roller at all and I keep reusing the same one over and over. Ziplock keeps it fresh.

post #46 of 452
Thread Starter 
Warpdrv--Nathan's clamping form looks good.
If someone is working with bendable plywood, you can easily glue and clamp a stack of panels all at once, because they don't move so much. But, you have to move fast, because the glue dries quickly in the summer heat.

The unflexible plywood moves too much for me to even think about doing a stack all at once, unless perhaps if I secure the panels to the cabinet frame--maybe right down the middle--with either brads or screws.

If I were making more than six of these cabinets and if I were using bendable plywood, I would do as you suggested and make two or three pairs of full-thickness curved panels at a time, which could later be attached to a cabinet frame. The bendable plywood makes this task that easy.
post #47 of 452
Thread Starter 
Quote:
Originally Posted by Looneybomber View Post

I'm curious how the 1/4" MDF will work for you, because that's what I planned to use on my build (3 layers).

I plan on trying the 1/4" MDF pretty soon in a dry clamping test. I'll let you know how that goes.
post #48 of 452
Thread Starter 
Three layers of the un-flexible, but affordable $9.99 (4x8 sheet) Luan from Home Depot. I think Lowe's carries it, too.




It takes two layers of this bendable plywood to equal three layers of the Luan. Not that it is important, I'm just letting you know. Unfortunately, the discount surplus store where I got it doesn't have any more and the guys there didn't know what it is called, so that is not much help to anyone here who wants to get some.




Allow for some panel movement with some extra overhang, to be trimmed later. Some of the panel offset you see here was deliberate panel re-centering after the first glue-up. The rest was panel movement during clamping.




I think I mentioned earlier that for the first layer, I set the cabinet frame on some scrap 1/2" plywood, to create panel overhang for the lower end of the cabinet.



Edit: I decided to go for 1" panel thickness.
post #49 of 452
Quote:
Originally Posted by PassingInterest View Post

I realize the forms are a little extreme, even for the Extreme DIYers who frequent this site.
Even Looneybomber isn't looney enough to go that route.
I plan on experimenting further and trying different--and hopefully--more practical methods for bending the "affordable" unflexible panels, but not until I start on my second pair of enclosures.
For now, I can get the job done quickly with the forms.
One last comment on the forms--they should prove useful for veneering these enclosures.

Not extreme at all, IMO. I love your solution. Low cost and effective. Patience is a virtue, it always gets better results and, in these cases, it's all that's required.

This thread reminded me of a corner MBM I built using 20-6.5" in a push/pull sealed for 60 Hz and up.


I used 1/8" thick hardboard and glued 7 or 8 layers. It's very flexible, cheap and makes for a very solid box. Just passing the info along, FWIW.

Great stuff, PI. Lookin' very good.

Bosso
post #50 of 452
Thread Starter 
Thanks, Bosso!
Wow, that MBM of yours look great. How did you do the ribbed curves? Kerf cuts?

Thanks for the tip on the 1/8" hardboard. I almost used some on this build, but I was not sure about the strength. Good to know it is okay to use. And, the 1/8" hardboard is flexible enough that you could glue all 8 layers at once, as long as you move pretty fast, so the glue doesn't dry before you get the clamps or straps on.
post #51 of 452
Thread Starter 
Now we need a trimming jig.
Use your router's base plate to mark the mounting holes.




Drill and countersink.




Mount it to your router.




Plunge a through hole.




Drill/countersink a hole and mount a handle from closet rod stock.
Also, drill/countersink holes to mount some risers beneath the jig.




I mounted 3/4" plywood strips to the jig and 1/2" strips to the 3/4". This way, I can remove the extra 1/2" boost when it is not needed.




I made sure that the front-to-back measurement of the jig would allow the jig to fit on the narrow back of the cabinet. Here, I'm just checking for fit and function, power off.




If there's any wobble, shim it.

post #52 of 452
Thread Starter 
One more check before setting the cut height.




I can easily clear everything with the jig, so no problem.




The extra height is not needed for this cut.




Fold a piece of paper in half a couple of times and set your cut depth using that. After routing, sand the rest of the way.




It looks good for most of the cut.




But, I get a divot at the beginning and end of each cut. I need to replace the wood strips with a full piece of wood, because the router is unsupported at the two extremes with the wood strips.

post #53 of 452
Thread Starter 
It looks the same as before, but the wood strips have been replaced with a single piece of wood.








I'm getting a good, clean cut.




And sanding the rest of the way.






Make it stable before routing.




I intend to veneer, but if your final panel layer is an attractive plywood, you won't need to veneer.

post #54 of 452
Amazeing work! I can't wait to see these finished!
post #55 of 452
PI,

You are like watching an internet version of the New Yankee Workshop. You make it look so dang easy and the results always look fantastic.

James
post #56 of 452
Thread Starter 
Thanks, SlickWillie8 and James. I appreciate the encouragement.
post #57 of 452
This thread delivers! Thanks for sharing, PassingInterest.

-Max
post #58 of 452
That's some workmanship - looking great - and looking forward for further development and pics
post #59 of 452
Great workmanship. I should've made similar clamps to put my veneer on my curved top cabinets, was a pain getting it to stick.
post #60 of 452
Thread Starter 
Wow, thanks guys!
Honestly, anyone can do this. It's the tools that make the difference.
And yes, sometimes a jig or fixture can save us a lot of trouble later.
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