Well, I learned a valuable lesson with my LongMill work table this week. Three quarter inch plywood will not stay level in the center of a 4x4 sheet. No matter how strong you think it is it will sag without support. Somewhere between 1/16" and 1/8". Some will say just run a leveling routine. I’m somewhat of a perfectionist so that won’t fly in my book with that much deflection. So I am in the process of rebuilding my work table top. I have already removed the cnc and starting to build a torsion box. The box will be 2x4s sandwiched between 2 sheets of 3/4" plywood. Then topped off with 1 layer of 3/4" MDF for a good flat surface. Then another layer of 3/4" MDF with t-track for spoil board. This may be overkill but I am going to make sure the top is level and won’t sag. Word of advice to those soon to get their LongMills - spend the extra time and money to strengthen your table top. Don’t try to cut corners and save money. Think it through - measure twice/cut once works. You’ll be glad you did in the long run.
With that design, I’d be a bit concerned that the 2x4s might warp as they dry. Could you use hardwood instead?
I guess that is always a possibility but there will be 4 cross boards screwed and glued between the 2 sheets of plywood as well as along the edges. Also screwed to the rest of the table frame. I don’t think there will be too much, if any, warping. And the wood is kiln dried. Thanks for the concern though.
Thanks for the tip!
Going through my table design right now…
What do you think about two layers of ¾ MDF screwed together? Stable?
Considering the density of MDF that would definitely be a good start. I think I would still brace it somehow. At least with a couple or more cross members. I think some are using 1" MDF. Some of the guys and gals are just using multiple 1x4s or 2x4s spanning the opening in several places. Especially the center area. And some are using a honey comb or cubby hole type. See Keith Fenske’s layout on facebook.
That’s a good idea. I think I have some scrap 3/4" plywood laying around that I could use. I may have to see if I have enough. The 2x4s I have are kiln dried but I know there is still some moisture probably in there.
Clyde, how wide are the mdf boards between the t-tracks. That’s what I’m doing when I get the table top put back together. I have 6 36" t-tracks but haven’t figured out the spacing yet.
My table is 48" wide then I put a 8" piece on each side. 6 t tracks . 5 1/2 " for pieces in between the last piece you have to measure could be a little different.
I used a kreg jig bit to drill the holes on my drill press. Works great with the kreg screws.