Why seal the edges?
By sealing the water chambers, we cover up the surface of the side edges of the plates. We are keeping the water off of them. Why do we do this? We do it because there are sharp edges, 90 degree turns, and in many cases there are surface imperfections caused from cutting and shaping the metal. If any edges stick out farther than the flat surface, electrons will crowd that area, causing a jam, and some will get pushed off the plate and cross the water; bypassing the other side of the plate. They will take the path of least resistance, and those sharp edges are a major source of the problem. Wherever the electrons mass together, there will be heat; excessive heat. Let me give you an example. Have you ever had a problem with starting your car, when the battery cable was a little loose. The starter turns but turns slow. You check your battery cables and find that the loose one is Hot. "Bingo". Electron flow was taking place across a small surface area; the small area that was making contact with the battery post.
Crosshatching the plates
Some famous HHO experts tell you to sand the surface area of your plates in a crosshatch pattern. They say it creates more surface area, and I will have to agree, it does. But it also creates peaks and valleys. It is these peaks that concern me. I realize the electrons take the path of least resistance, so, they will follow the surface, no matter how rugged the terrain. But this is going to create heat on those peaks. Electrons will accumulate on the peaks before they cross the water (at the paths of least resistance). I believe that the increase of gas production, that they claim, is associated with the surface area being harder for the gases to stick to, because of the rough surface. Remember, the gases are chemically formed on the plate surface. They form as bubbles on the surface. The bubbles lift off from the surface as they form. As they lift off, water fills their void. They rise to the surface. On the way they bump into other bubbles, forming larger bubbles, picking up speed as they travel. The chain reaction helps clear the plate surface of new bubbles that have formed - which in turn lets more water touch the plates.
Ok, that is a lot information to grasp, but it is the experts opinions that the crosshatching of the plates plays a roll in creating more gases, by keeping more water on the plate surface. I disagree. You see, a bubble is made up of gas that is surrounded by a membrane of water - and what ever is in the water. Water is always touching the plates surface, even as the gases are forming; the membrane around the bubble is proof. The plates are wet; they are always wet. The electrolyte we use is very slick and adheres to anything that touches the water. If you have ever touched your fingers together after sticking them into water containing small amounts of KOH, you would notice they are very slick. KOH is hard to wash off. Those electrical plates in the water are covered with that stuff and it is highly conductive. The bubbles we are making are tiny at the surface. They form in size like a balloon being blown up. As they grow, their skin (which is touching the pate surface) stretches to the point where it pulls away from the surface. I believe that part of the separation is due to other bubbles forming underneath them. Now that ---- is something to think about. But do not loose sight of those peaks the crosshatching created. Those peaks are jumping points for current; small as they are. At least, that is my theory. Personally, I do not crosshatch because it removes the protective oxide coating on the stainless steel. Sanding also reduces the metal surface; we are not in a rush to do that. We want the surface to last as long as possible; sanding is not going to help with that; at most, it will help clean the pores of the metal.