I now have halves. Scraps of 5/8” shelving work well for re-enforcement or joining. I also slapped together a small form (not shown) to do a test pour of the plaster of paris/rubber shreds mixture.
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Lessons from test pour:
The rubber doesn’t settle out a bit. These is no reason not to use all sizes of rubber shreds, or not to be generous with them in the mix. These will still be plenty heavy. Time to get this done.
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A minor concern has proven to be a real problem. The Menards (outer) forms are not waxy enough to fend off moisture from the PofP mix. A rigid makeshift cradle may have saved the day. Will reassess in 24 hours, but the forward portion of the cabs will need a Plan B.
? didn’t not understand - is the moisture making the carbord forms bulge? but doesn’t concrete have mositure - supposed to handle it.
If you fill the form with concrete the load is evenly distributed so there’s no place to bulge. You could argue that if I’d left one end open and filled bottom up it might have worked. I’m not so sure, and cutting in half lengthwise would have sucked.
I compared an old Home Depot form I had laying around. It’s thicker AND waxier, but only 8” long. I’ve already cut and glued attempt #2, as I don’t need to wait overnight to see that this first shot is trash. The next filler will not be PofP.
Live and learn. Sucks when a plan goes awry, but it’s definitely a part of experimentation. You’ll get it
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I’m at the point of the 2nd attempt where I believe I should line the outer wall with a 1/8” neoprene layer before pouring P-of-P to fill the remaining gap. Postmortem of the first try tells me that probably would work well. But I need to choose between what will bring a project to conclusion and what likely won’t. TBD as of this moment.
Examination of the first carcass tells me that the Menards tube not only failed to maintain it’s roundness, but it also started coming apart in layers. The inner ULINE tube was fine. However, no more 6” mailing tubes. But I do have just enough 6” plywood tubing with a 5/16’ thickness. Whatever I choose as a filler this time, at least the inner wall will have solid robustness and overall wall thickness will be slightly > 1”. I will lose a small amount of cabinet volume, but I can make that up with other dimensions.
6" plywood tubing? Some sorta drum shell stock?
I’m not sure what the expected usage would be, but I used them on the MT portion of my rebuilt Relayers, and glued narrow strips on the inside to bolster thickness/stiffness. It was not inexpensive.
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can you posts some pictures of the failed tubing before you trash them? will help to understand the issues you are describing
Here is where we are after 48 hours. Note that the gap on the left was filled to 1” from brim full. A spline between layers blocks the mix from going beyond the halfway mark. The one on the right had only about a third of that. The one on the left had a supporting cradle through the first 24 hours. The ULINE tube, which forms the inside wall, held up like a champ. The concrete form, not so much.
thanks for the pix. i guess the round shape of the full tube keeps it from deforming when used as a concrete form. is it only in the edges or the backside too? if only the edges, maybe a support on the outside would help till it dries. any fill will have moisture, unless you are going dry fill like Craig.
Those cardboard tube forms are designed to survive just long enough for the concrete to cure. Beyond that they’re engineered to be disposable. Might need to apply your own water proofing before pouring. Could be a simple as a piece of plastic cling wrap.
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The deformation only seems to affect the portion that was contacted by the Plaster of Paris. Not knowing how disastrous it could turn out to be, I didn’t even mix up enough to fill one entire “half”. I think I’m in stasis until I get confidence in a new plan. Nothing wrong with planting a few flowers this weekend. 
Maybe gobble down some brainstorm candy. 
I’m back to halvsies. Target store brand unscented cat litter is on hand. It’s dense and sugary in handling and texture.
I’m a bit sad that the insides could end up being the best looking part of these cabinets. 
And these concrete forms worry me in that they are awfully uneven in the seams for applying a covering or veneer. I think I may go purchase a Menards 1-1/8” stair tread for the remainder of the enclosure. The wall thickness of the round halves is 1-1/8”.
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The thin and uneven nature of the Menards concrete form finally got to me. This is what I should have addressed from step 1. I went to Staples for some poster board and wrapped the outer surface. Then I scuffed it up with 60 grit and applied two coats of wood hardener. That put the thickness at 1-7/32”. Add veneer, or whatever, and we’re at a very hefty 1-1/4”+. I am now ready to move forward with the rest of the cabinet and intend to have something more substantial to show after the long holiday weekend.
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How’d you adhere the poster board to the cement form tube?
I just roughed up each surface a bit with sandpaper and used my regular wood glue. I overdid the end a bit then sliced off the extra with an exacto blade. The poster board is NOT foamcore. It’s more like 1/16” stiff cardboard. It made the spiral seams vanish. Bonding is solid.
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While the PE Memorial Day discounts are live, anyone wanna chime in on the route to go with the MAC-06 on the tweeter choice?
- On hand - SB Acoustics SB26ADC-C000-4 Aluminum Dome
- Peerless DA32TX00-08 1-1/4" Corundum Dome
- GRS Planar (Mid) Tweeter (If so, which one?)
- Peerless Beast Mode (Could be snagged from another project)
- This idea is BEST! (Name it below.)
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voters
Keep in mind that I have no measurement capability and will have to beg, borrow or steal assistance to wrap this. I’d really hate to go to my back-up plan, but…
The beast mode kinda matches the vibe of a high-value build, a lot of people have used it, so there should be plenty of help on implementing it on this build.
All options listed look great.
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