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I am in the planning stage of a new FT bin. I am going to construct it out of wood and line the inside with fiberglass. I just read through alot of the FT's people have made but few tell of problems and failures in earlier designs.

Considerations:1. I want to use scrap wood I already have on hand, so the max length could not exceed 4 ft.
2. I have 15" X 15" collection tubs available and my future source for replacements (they are a little brittle) has no end in sight.
3. I plan to use PVC with embedded screws as harvesting rods. I am not sure if metal rods are easily available nor how difficult it will be to use ( work with) metal instead of PVC.

Based on the above I can construct a bin 45"L X 15" W X 24+" H. By my calculations this is a little over 9 cubic feet of bedding volume. Actual size may be a little different, there will be some empty space for collection bins etc.

My main concern is weight. The overall weight of moist bedding on on the harvesting rods making them difficult to turn. The weight of the bedding on the legs or support. (I do not want it directly on the ground/floor). Most importantly the OUTWARD pressure of the bedding against the sides and connections.

Some of this I can alleviate by wood strips around the outside of the bin, particularly under the harvesting rods. I'm not sure if I need bridges or supports across the middle of the bin inside.


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Comment by Pat James on November 12, 2010 at 5:07pm
Rock, Yeah I figured I would have to use my rods on the 15" width. I was considering trying to widen the whole bin. But that is contingent on finding collection bins that will fit. I checked out several stores yesterday and could not find any of the right size (nor for the right price). I had a heart today so I cold not get out, but I will hit the dollar stores tomorrow to see what size collection bins i can find. I use 1/2 inch PVC for my bucket's but that only covers a span of 10 inches. A few more inches means alot more torque needed.
Comment by Pat James on November 12, 2010 at 5:08pm
BTW, I knew I read something about NOT using conduit somewhere.. It was on your page.
Comment by Pat James on November 12, 2010 at 10:18pm
I knew compost can hold a form as a solid. but I figured under a heavy wight it would act more like a liquid pushing outwards.

I used to own a pet store. Big tanks, especially over 50 gallons have a bridge to keep the long sides from blowing out. The sealant inside is forced even more tightly into the seams but even then a pin sized hole becomes evident quickly. I was worried about spending time and energy to construct a big bin only to have it crack down the middle and spill out.
Comment by Peter Barnard on November 13, 2010 at 12:39am
Outward pressure is certainly something you need to consider.
A 65 gallon trash bin develops a distinct bulge in the middle. click
Comment by Pat James on November 13, 2010 at 8:44am
Under some instances a solid will act like a liquid. For example grain in a silo. Open the bottom and grain will pour out- at least until enough piles up outside to build up enough resistance to stop the flow.

I know I will need to reinforce the bottom. I think I can design a simple enough system using cheap materials. I'm not sure if I will have to stay with the 15 inch width or if I can find collection tubs a little bigger. Just going to 18 inches will increase my surface area another sq ft.

I'm looking at minimizing the floorspace to some degree. I was wondering just how important surface area really is if you continually move product through the system.

I was thinking of raising the system up a bit on legs and use the area underneath for storage, but that also brings in some weight consideration. Also I need to make it ergo-friendly. I don't want to stand on my head to harvest nor stand on a ladder to feed.
Comment by Pat James on November 13, 2010 at 1:46pm
I just got back from Home Depot with 2X2 furring strips. They were only 1.48 each while the 1/2 were $1.97 I should get a little more support from the 2X2 even though they are rougher.

Larry, I noticed you painted the unit, inside and out. I was thinking of applying the fiberglass resin to the inside as waterproofing. What did you mean by sleeving the bin in the picture?

I'd already planned on using PVC as a grid only mine will turn like my kitty litter FT's to make harvesting easier.
Comment by Pat James on November 13, 2010 at 8:28pm
What kind of hand crank are you thinking about? I thought about a simple jack know the kind that cranks. You cout cut a groove in one side and a hole in the other of the tube.. Problem is I do not think PVC alone is strong enough to take the torque with that arrangement without breaking.. That was one reason I though about using conduit or some other kind of metal pipe.

But knowing what Rock reported I do not think that is smart either. I may stick with just gluing t's onto the PVC and see if they will take the torque.
Comment by Pat James on November 13, 2010 at 8:35pm
Well, I have most of the bin I described built. I ran out of power in my electric screwdriver and drill. They are on the chargers now. In the morning I will go back to Home Depot or Lowes and buy some PVC and the fiberglass resin. I'm just hoping my arms are long enough to reach all the places to seal it up.

Funny how you can talk out a design a little, figure faults and weakness, and then build it without even putting a pencil to paper.
Comment by Susan B on November 13, 2010 at 11:32pm
"But a flowthru is a complicated beast!" They don't have to be! You've got yours almost done, but for anyone else reading this thread, FTs can be really simple.

I know plastic is a no-no, but I'm sure you can find an old garbage can or 55 gallon drum. Try Craig's list or Freecycle. Wheels are good for the big ones. Cut a window out at the bottom to harvest from, drill holes and thread rebar or PVC piping along the bottom and add VC. You'll be up and going a lot more quickly. I guess it's a different thing if you're in to carpentry, but KISS. Keep it super simple.

Get ideas from
Comment by Susan B on November 13, 2010 at 11:34pm


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