I wanted the left edge of the jaw of the front vise to be flush with the left edge of the top, the right edge with the left edge of the left front leg. So the amount of overhang on the left depends upon the width of the front vise jaw. The width of the jaw is, at a minimum, the width of the plate that supports it, but it's normal to make the jaw extend a bit beyond the plate. How far? The more it extends, the deeper a bite you can take with the edge of the vise, when, for example, you are clamping the side of a board being held vertically. But the more it extends, the less support it has. I decided to extend by 1-12", which gives me a 2-1/2" bite, and which should still provide solid support, given that the jaw is 1-1/2" thick. This means the top needs a left overhang of 12-1/4".
So drill the benchdog holes through the MDF layer. Begin by laying out their positions. You'll want these to be precise, so that the distances between the holes are consistent. The vises you are using will constrain your benchdog spacing. My front vise worked most naturally with two rows of holes four inches apart, my end vise with two pairs of rows, with four inches between the rows and eight inches between the pairs. Because of this, I decided on a 4" by 4" pattern.
If you're using drywall screws, you'll want to countersink the holes. Drywall screws are flat-head, and need a countersink to seat solidly. If you're using Kreg pocket screws, the way I did, you won't want to counter-sink the holes. Kreg screws are pan-head, and seat just fine against a flat surface. Both drywall screws and Kreg pocket screws are self-threading, so you don't need pilot holes in the second sheet of MDF.
First, we need to drill out the holes for the screws that will hold them together. While the two layers of MDF are glued, the countertop and the MDF will only be screwed. The oak countertop, like any natural wood product, will expand and contract with humidity changes. If it were glued to the MDF, the difference in expansion of the two layers would cause the countertop to buckle and curl.
If you opt for a bench with drawers or cabinets built into its base, don’t forget the toe spaces: Leave a space roughly three inches deep and four inches wide at floor level for your toes, just like kitchen cabinets. The absence of a toe space means you’ll be forever kicking the face or sides of the cabinets which is irksome and, with tools in hand, potentially dangerous. And you’ll have to lean over farther to reach the back of the benchtop.
Then I flipped the top and the base, lied up the base in the proper location relative to the top, I then positioned the front vise and the support MDF for the end vise, and marked the locations of the bolt holes. Then I flipped the base right side up, drilled small pilot holes from the bottom side where I had marked the locations, and then drilled shallow countersink holes from each side, then a through hole that matched the bolts. Finally I tried out the bolts and washers, and deepened the countersinks until the heads of the bolts were just below flush.
There is a mandatory safety class you have to take where they walk you around the shop and make sure that you know how each major machine works and general shop safety. You also have to sign a waiver saying you are participating at your own risk. You DO NOT have to take that safety class if you are signing up for one of their classes. They will cover those basics during the class.
The book is well written and easy to read. The illustrations, I'm sure were excellent in 1914 and, are still adequite now. Most of the designs seemed repetitive, though. I wish more attention had been given to lashing materials. If you are looking for that you will find almost none here. The book was fun to read and provided enough inspiration to make my brother and me attempt a large hut.