After having hand harvested my first batch of castings, I'm quite certain that a simple sifter may not be very useful.
Something that vibrates violently or one of the rolling screen units is probably what is required.

Challenge I see with a simple sifter is that the stuff is usually too moist not to stick and plug things up. And you don't want to dry it out or you kill the worms you are trying to separate. The cocoons and the castings are so similar in size that they will be very hard to separate in a moist condition. I don't see any mechanical way to separate out the baby worms since they tend to stick to anything.

Here is a link that might be useful: worm harvesters

I agree in part and indeed my idea is my best effort to accomplish my goal within my means. When I said large I didn't mean that large. I meant larger than a simple hand held sifter, about double or so the size of the wheel barrow it would be sitting on.
I am a simple home backyord vermicomp, Iv'e seen ads for the harvesters and while nice are WAY out of my price range and even if they were not, are too big to fit in my Florida "postage stamp" yard (well maybge somewhat bigger than most down here so maybe two postage stamps:)).

Where I agree is in both the vibration thus the need for rocker arms which allow you to pick up and bounce down the sifter onto the wheel barrow repeatedly. The fact that they will be attached on one end will allow the use of leveraged force thus producing quicker and more forcefull repetitive lift and drop and require less strenth and energy than a hand held sifter.
What I refered to as a "stirring arm" is what I have in mind to function as the "roller" you suggested. Also the idea I have to assist working the compost through the levels is that once it falls through the larger screens and the bigger undigested items are removed then I will use the "Stirring arm" along with my hands ( heavy rubber gloves help here) and finally at the last stage(s) instead of fighting the stickyness caused by wetness I will go with the flow and add a little additinal water to help rinse the smallest particles through the last screens untill I have the castings and coocoons separted from the "other". If they are indeed the exact same size and I can't use a screen size to separate them then I will simply have too hand separate the two.
Still hoping some aid in specing it will find it's way. thanks inadvance

I have made what you probably need. The rectangular frame is of wooden 2x4. It is about five feet long and about three feet wide. It is about a foot longer than the bed of my wheelbarrow and about six inches wider. The corners are held together by two 2.5 inch deck screws in each or you could buy metal corners from a harware stor. The screen is 1/4 inch hardware cloth which is folded up the sides and stapeled with a staple gun. I cut the hardware cloth so I wouldn't have any sharp wires sticking out. The wire mesh is on the bottom of the frame so it has a four inch high sides to keep the stuff from falling off the edge. The width of your hardware cloth may decide the width dimension of your rectangular frame. If the harware cloth is 48 inches wide and you want it to fold up on both side by three inches, then the outside dimensions of the frame should be 48 inches minus three inches for each side = 42 inches.
On one end I have 2x4 legs that are joined to the corner of the frame by a 1/4 inch diameter lag-screw through the leg,with a washer between the leg and the frame so that they can fold flat against the side of the frame for storage. This also makes the height a bit adjustable. I put the end with the legs at the higher, far end of the wheelbarrow and I stand at the end with the handles, between the handles. The wooden frame ( the end without the legs) rests on the handles of the wheelbarrow. I take a couple of shovel fulls of vermicompost and load it onto the mesh frame. I pick up the lower end of the frame and jerk it so that the compost jumps a couple of inches. The stuff smaller than 1/4 inch fals through the mesh into the barrow.The compost tend to slide down to my end of the frame as it is lower. With an extra-hard upward jerk I send the stuff flying back to the top end and shake it back down again. All the bits too big to go through the mesh slide down to my end and I throw into a pile to be further composted.
WhatI get is all the finest compost in the barrow, but unfortunately a fair few worms also. I leave the barrow out in the sun and when the top couple of inches has dried out I skim it off the top and put it in a bag. I gradually reduce the pile and all the worms will be in the last bit, hiding rom the sun and the dry conditions.

Good Luck.

thanks so much for your info, i will definitely be using many aspects to include the two end legs, metal corners, hardware cloth as my screen and more. thanks again.

anyone and everyone who has ideas and will share is welcomed and apreciated.!!
Merry Christmas to all!

Last night I posted on another thread about a screener that I just built for about $16. I used 1/8" hardware cloth. The sifter is about 28" wide and just under two feet tall.

I used PVC pipe, various joints, two bucket lids, the hardware cloth, and a few screws. I kept the cloth in a cylinder and fit it into the lips of the bucket lids. Then basically built the PVC frame. There's no arm for cranking it but that should be easy enough to do.

You might be able to do something similar with different size lids and hardware cloth.