Minimum size for a loading bench? Well, one friend used to have an 18" x 24" piece of 3/4 ply with his press mounted on it. He clamped it in a Black and Decker "WORKMATE" and it worked too. But I prefer a lot more space than that,. I had to make three benches before I got it right for me. That was in 1970, still happily using it too!
First, the height: A bench top at 30 - 31 inches makes a good kitchen counter for smallish ladies but that's much too low for taller men. I built my last bench top right at belt buckle-height while standing, for me that's 39 inches. Even that wasn't quite high enough for proper mounting of my press for easy work. I had to block up the bases of my (4) press(es) about 2-3 more inches so I can fully depress the levers without having to bend over - at all - to save my poor, sore back! When I want to work seated I use a cheap (yard sale) bar stool, a comfortable high backed, padded and swiveling type that keeps my upper body in the same relationship to the bench.
For max utility, I’ll say build the top as long as you can. Mine is a full 8 feet and that's not quite enough at times. The top need not be more that 24 inches wide but, actually, I think 21" is plenty because that's about as far as I can easily reach across while loading. Wider tops tend to collect “stuff..”
I prefer a smooth, solid top. Doubled and glued (Liquid Nails construction adhesive) 3/4" ply, OSB or MDF is good but doubled 5/8" particle board is excellent. It's nice if the top overhangs the under framing a couple of inches at the front and ends so other things can be "C" clamped to the top later. (Like a fly tying vise!)
I put two full length shelves under my bench. The lower shelf is about 12 inches off the floor so I can rest me feet on it while seated! The upper shelf is about 16" wide, the lower shelf is as wide as the framing will allow. I store boxes of miscellaneous stuff ( tumbler media, shotgun wads, etc.) under the bottom shelf. Painting those lower shelves with a couple of coats of white sure makes for better viability when looking for stuff down there.
Legs are important but need not be massive. Simple 2x4 boards in compression are plenty strong.
If possible, anchor the back of the bench to wall studs and lag screw the front legs to the floor. Or, just weigh it down with lots of stuff - misc. brass, tools, bullets, casting lead, etc, - on those lower shelves.
If you cannot anchor the back to a wall and MUST make a free-standing bench, add a back and ends to the frame for rigidity. A simple covering of 1/4" ply is plenty to make the frame into a strong box that will still rack enough to accommodate a moderately un-even floor.
Understand that you will need a LOT of storage shelves for powders, bullets, primers, dies, load books, moulds, etc., and a “book case” will do nicely for much of it. Use 1x8 boards, making the shelves wider than 8" (actually, 7 ½") will make it easy to lose small items on the back of the shelves. Make it long enough to cover the full length of your bench and tall enough to nearly reach the ceiling. It can sit on the back of your bench top if you anchor it to the wall with screws or, better yet, mount it hard to the wall and keep the bench top clear.
Make sure one of those shelves is just about nose high and plan to sit your powder scale and trickler on it. That way it will be easy to read and use your scale without bending over. I think there would be fewer of the very expensive digital scales sold if more people had better placement for their balance beam scales!
Plan to place all of your hard-mounted presses/lubrisizer, etc, on the right half of your bench if possible. Right handers should keep at least 14" on the left side of the presses clear for loading blocks, etc. Keep the full left end of the bench clear for working on cases & a gun cleaning space.
Do plan to add a sturdy 4", or so, machinist type swivel vise (from Lowes or H'Depot) on the left front corner. That vise will be handy of itself but it also makes a great base for holding a case trimmer and a "Sight-Vise" IF they are mounted on a small piece of 3/4" ply with a firmly glued/screwed 1x2 strip under it for the vise to grip. I have both of those and also a small Harbor Freight (3") variable speed dual wheel grinder/buffer that also mounts in my vise. The grinder, sight vise and trimmer are all great to have at times but I really don't need them set up permanently.
I could have also mounted my powder measure on a block for the vise but I really like to have the measure firmly mounted near the middle of my bench, behind and just to the left of my main press. It’s out of the way there but still easy to reach, and it's just to the right of my scale and trickler.
As much as possible, use bulk “wall board” type screws, plus glue and bolts for assembly,. Over a period of time, nails tend to work loose under the strains of reloading.
Enamel the whole bench assembly white (or a really light color) if possible but at least protect the top with a minimum of 3 coats of Min-Wax Marine Poly. That good stuff is easy to find and is very resistant to water, oil and gun solvent spills.
Install AC outlets or power strips at the ends of the bench for your radio, battery chargers, heat gun, Dremel tool, drill, tumbler, soldering iron, electric engraver. Mount a paper towel holder close by and an air line for a blow gun to clean things is nice if you have a compressor
Suggest installing at least one 48" dual tube florescent shop light directly above the front edge of your bench, twice that much light would be better. You will want a lot of light and you will not want it to cast your own shadow across the work area.
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