aluminum or steel?

[Ken Fitzgerald]

From an engineering standpoint, I can't help but feel you're adding extra complexity, and thus increasing the odds of failure, for very little benefit with the rack and pinion system. But that's up to you.

As for aluminum vs. steel, I'd say it's an aesthetic choice. Either will work fine. I'd probably lean towards stainless steel if you go the steel route. Sometimes regular steel can darken some woods if left in contact, like oak or other high tannic woods.

Don't worry about aluminum galling. It's a real possibility in certain applications, but used with UHMW, it shouldn't cause any concerns. If the aluminum was sliding against something with a higher friction coefficient, it might be a problem. But UHMW is has as extremely low friction coefficient. And really, with the UHMW, you probably don't need any metal wear strips. My workbench's wagon vise has UHMW on maple, and it hasn't shown any wear at all. UHMW usually has a lower friction coefficient and better wear resistance than Teflon, so it doesn't usually even need a lubricant. That stuff is magic!

Jimmy, the reason for the wear strips is minimize any wear on the mechanism should there be any sag in the system. I might be making it overly complex. I can do that!

I won't tell you that I am mounting the tabletop sections (all 3) to their respective mechanisms using threaded inserts and stainless steel screws so the tabletop sections can be removed for transportation into our kitchen and the reassembled to reduce weight. I am still stronger than most men my age but I am fading. When I built a red oak entertainment center for our livingroom a few years ago, it took 3 of us to move from the shop into the house. On the hinged end of each of the butterfly sections, I am inlaying 1 1/2" x 1/8" steel bar using threaded inserts to minimize any warping in the butterfly sections.