Continuous flow worm composter design

I have looked at several types of continuous flow composters using worms and have the following questions.  I compost around 2or 3 five gallon buckets of kitchen waste per week

If I am using a drawbar slider sitting between the castings and the grate, under the compost what size should the grate be ?  1/4” 1/2” 3/4” 1” The grate will be in direct contact with the castings.

I am planning on using a 24” x 96” expanded metal panel bottom with a 24” piece of 2x4  angle iron sliding against the grate and shaving the underside of the compost inside the bin.

It will be powered by a small 110v boat winch to drag it from one side to the other to cause the castings to fall and sift through the grate.  

The inside of the box, and lid will be insulated with 2” foam panels and then lined with PVC panels.  The grate under the box will be exposed in the warmer months and closed off and insulated with a slide in panel in the winter.  I also have incorporated (2) 100w waterproof seed heating Matt’s on both ends of the box down near the bottom to kick on if the soil temp gets to cold.  

The bin will be located inside an open woodshed and protected from direct sunlight.  

Thoughts and suggestions on design are welcome

Where in this system are the worms most likely to be?
You probably don't want to commit mass murder because you harvested castings.

The bin depth will be around 36” in deep and I will only be disturbing the bottom 2” of castings.  If I see worms in the collection tray I will know that they are not high enough in the compost and I’ll wait another week or so before sliding the draw bar across the grate

This sounds very similar to a CFT bin I built two years ago for my unheated garage. Mine is 24" x 24" x 24" with 1" conduit at 2" OC (leaving a 1" gap for castings to be scraped out). This seems to be pretty ideal — I get an extremely minimal amount of castings self-harvesting. I think going 36" deep is a good idea, I still find a decent amount of worms down at the bottom of mine when it's full. I might think a lot about the weight of it though. A bin that size will be extremely heavy. Make sure it's in it's forever home when you start filling it up and make sure it's on a floor that can handle the weight. To be honest, I'd probably think about splitting it into two 48" long bins at that size.

The seedling mats might work, but I ended up opting for soil heating cable instead. I was able to spread out the heat to all four sides of the bin and have better confidence that the product was designed to be immersed in wet conditions continuously. I'm also not sure that two mats will be able to effectively warm the soil in a bin that size. I can't remember how many watts mine draws, but it takes several days to bring the soil temp up a few degrees. With a larger bin and feed volume like yours, I might just opt to rely on thermophilic energy and mass to keep the bin from freezing. A more robust heating solution would be to look into a water pump/heating situation and circulate warm water through PVC pipes in the bin.

All in all, it sounds like a great plan. Let us know how it turns out!

Kyle;  Your CFT is very similar to what I had in mind.  How many castings were you able to harvest on a weekly basis.  You stated minimal harvest.  If I was to use conduit or heavy duty fence pipe with 1” spacing could I use push pull sliders on the top of the pipes to scrape the bottom of the pile for harvesting ?  I’ll look into wattage for ground heat loops as well.  The heating would only be used during extended cold snaps that we occasionally get here in central VA.  
I may start OT with a 48x24x36 bin at first and if I need to expand then I’ll bolt them together and I use a horizontal separator screen to migrate worms between bins as needed

How many castings were you able to harvest on a weekly basis.  You stated minimal harvest.

Sorry, I was referring to self-harvest, as in the amount that falls through without me scraping it out. So minimal is good! I'm not sure of the volume of harvest I get as I don't pay much attention. Enough for me to serve my indoor garden, indoor plants, and have enough leftover for compost tea for the larger outdoor gardens. I'm going to wildly guess 10gallons/year? I'm not too specific about throughput on my bin, I built it primarily to recycle all my food scraps since my city doesn't have a composting program.

If I was to use conduit or heavy duty fence pipe with 1” spacing could I use push pull sliders on the top of the pipes to scrape the bottom of the pile for harvesting?

I haven't personally tried this, so I can only speculate — but I suspect a setup like this should work. The key really is to just keep a 1" spacing for the castings to fall through.