Put the countertop on the base, put the MDF on top of the countertop, and line up the marks you drew on each end of the MDF with the countertop below it. When you have it lined up, clamp things down, and route the edge of the MDF using a 1-1/2" or longer flush-trim bit, with the depth adjusted so the bearing rides on the countertop. I clamped a couple of scraps of doubled MDF at each end to give the router base something extra to ride on at the ends.
I’ve seen antique cabinetmakers’ benches that are sixteen and seventeen feet long, more than three feet wide, and supported by a dozen drawers and doors—and that weigh as much as a felled oak tree. In contrast, jewelers’ cabinets seem to be on a dollhouse scale, with tiny tools to match. For most of us, however, space limitations preclude the biggest, and the smallest are just not big enough.
@cahudson42 I bored the holes in my sandwich top with a 3/4" power auger bit with the drill in a portable drill guide that kept it vertical and in a way a bit like a plunge router. The guide screw of the auger was dead easy to centre over the laid out grid points. The holes are dead straight and clean sided. The auger bit was new which probably helped. As stated I have three rows from an end vise running the length of the front as well as from the front vise and holes in the front apron to support long pieces as well.
Even with all of those faults my only regret is that it is too ugly. I didn’t take the time to make it more visually attractive as I was eager to get right into making beautiful furniture instead. Twenty years later the furniture is still beautiful (or not) but I go out to the shop and look at a drab uninspiring workplace. Yeah, nothing wrong with having a visually inspiring workplace in my opinion. All that shop furniture I slapped together years ago with no concern about aesthetics is getting replaced bit by bit. Why should my shop be downright ugly when it is one of my favorite places in the world to spend my time? I see no reason for that, but that’s just my opinion and as we all know everyone has their own one of those… Sadly, no one pays nor reveres me when I offer mine. bummer, I could be a rich egotistical maniac if they did coz I sure offer it enough. 😉
Be careful. Single 24x60" sheets of 3/4" MDF are pretty easy to lift. A doubled sheet is manageable. The countertop - 24x72" panel of 1-1/2" oak - weighs something over 100 pounds. It takes real care to lift safely. The joined top - 3" thick of oak and MDF - is past the range that can be lifted safely by one person. Don't try. Get a friend to help, or rig a block-and-tackle.
While a strict figure for the bench’s weight capacity is not available, a quick browse through their other stand and bench products shows a general weight capacity well above most other brands. As such, while we cannot say for certain that this bench provides the best weight capacity, it is more than likely that it the capacity is similar to the other products in the catalog.