@Tom,
Wouldn't you know it, my Shop Notes subscription started with issue 110, those plans are in issue 109. If you get the plans, PM me.
@Randy
Yes, looked at the Thien concept, and may have to go bigger with an full size dust collector. The drawback is $$ and space in the garage. I have zero room left.
****
After searching topics on dust separators, I landed on Lumberjocks tallking about cyclone systems. I spent all afternoon building one of these. After I finished it, tested it. Worked like a champ!
I read pros/cons about other cyclone (fit a lid type). Similar to the very first photo at the beginning of this thread. I could have easily built the other version, but comments from people who built the same version I did (vortex?) seemed happier.
Start with empty vacuum.
Here is my first test. I will change hose configurations later, and all I had to make the connection to a 4" hose that will be used for the table saw. Note blue pail half filled with sawdust.
After sucking up the blue pail. Voila! hardly anything in the vacuum. It looks like I cheated the vacuum is so clean. The darker spots must be the intake air cleaning the bottom. This is what it looked like when I opened the lid, honestly!
Now for the bad news. At the very end of sucking up debris from the pail, the hose hit the bottom with suction. This crushed my cone, and while diving with both hands to free the bucket my cyclone unit fell (I didn't have it secured to anything) and broke my epoxied intake from the cone. #$#$!
So IF I were to improve it, make a cart like Tom pointed out (I was going to do that after), and try and build it with a thicker gauge metal. I used the recommended HVAC duct. I don't think it will withstand my 5hp vac. if it should happen again. I was so proud of my DIY, but sad that it was broken after the first test.
Here is the link for the info I used to build it. If you have a smaller vacuum, it may work without crushing the cone, and definitely not with a a full sized dust collector. I would consider a heavier gauge, but then you will need to be good with drawing out the template to get the cone to fit easier while building it. I wrestled with it a bit, but got the job done.
http://lumberjocks.com/SimonSKL/blog/10097