I have been wanting try a mesh false bottom or something of the sort for a while. The bag can sit on top of it and when I get ready to chill it will keep the chiller off the heating element.
I happened to acquire some heavy 1/2" stainless mesh from work and I was considering making a mesh basket. After thinking it over I decided to make a mesh false bottom.
Knowing the mesh alone wouldn't be strong enough by itself I had a 1/2" wide flange cut from 1/16" thick stainless steel. The flange covers the ends of the mesh so the bag won't get snagged. The two flat areas on the flange are due to the steamer basket lip on the Bayou Classic pot.
I took a section of the mesh and laid it over the flange to mark my cutting points and began cutting the shape I wanted with my snips. A Marks a Lot works well here.
Mesh cut to shape.
A little bit of clean up trim to make sure there aren't any over hanging wires to snag the bag.
Used an old snare drum rim to give me a working fab frame and hold the hot metal off my wooden work bench. Vise grips to clamp the mesh to the flange. I used a die grinder with a scotch brite pad to smooth and prep the surface of the flange for soldering.
I used Stay Brite flux and Oatey lead-free solder to attach the mesh to the flange.
After rinsing the flux off with water here is the finished soldering job.
What it looks like from the top after hitting it with the scotch brite again.
I used 5/16" x 3" stainless carriage bolts as my standoffs. I used two 3/8" stainless washers to keep the 5/16" nut off the square on the carriage bolt head.
Four standoffs out near the flange to transfer strength. Two in the center opposite the heating element will keep the center from sagging if there is any.
The flats on the flange slip right past the steamer basket lip. Fits and sits perfectly in the kettle. By tipping the false bottom to one side I can easily grab and remove it.
I think this will work fine with the bag. I will find out for sure because I am brewing tomorrow.
I tried it out today but there was no noticeable improvement in circulation. I still had to use the valve to choke off the flow during recirculation.
Good news is I can still use the steamer basket and I don't have to build another basket. I am still going to use the false bottom because it worked great to rest the wort chiller on.
The holes in that mesh are far too big which is why you had no improvement. Notice that the holes on my false bottoms you can purchase for homebrewing are pretty small and numerous. They are only big enough to let liquid flow and hopefully keep grain out. In your bottom your grain bed will just go right through.
I think a lot of people are missing that this isn't a traditional false bottom in that it is not intended to come in to contact with the grain. It is in fact intended to be used in conjunction with a mesh bag that will be filtering the grain.
Now back on topic. I would guess that problems in flow are coming from your basket because i know that many people have posted before that modifying there baskets have helped salve this problem. Can you post some picture of the basket so that we have more info?