Started building my table today. I’m going for a full 4’ x 8’ usable cutting area so a 56" x 111" table it is. This thing is big!! Barely going to have enough room for it in my garage (until I move it to its new home). Anyway, I didn’t go full MDF and Torsion box - I don’t have a table saw big enough to cut down 4x8 MDF easily. I went with 2x4’s instead and just reinforced it. I got the base done today and will finish the rest of it tomorrow and then start testing.
Like others, I’m using Unistrut (SuperStrut from Lowes) for the rails that the LR2 will ride on. I really liked Jeb’s idea of how to attach the belts so I completely copied it - Thanks Jeb!!
I doubled up on all the 2x4’s running the perimeter and before doing the internal supports I squared the whole thing up. I was able to get it to 1/64th of an inch square, which I’m pretty happy with.
As Ryan says, pics or it didn’t happen, so the pics are here.
-Jeff
P.S. - I’m not sure why some of the photos are posting sideways…
Anyway, here are the pics from my (finally” completed table. It took a lot longer than I thought. I’m guessing the table took almost 20 hours to build. About 3-4 hours of that time was fixing a design flaw I had in the table. I made the base of the table flat with the Unistrut rails level with the base, not factoring in the 3/4” sheet of MDF that will be the work surface and the 1/2” sheet of MDF that will be the waste board, so my Unistrut rails were 1.25” too low.
Due to my design there was no easy way to fix this (I could have just added spacers to my Z Axis to compensate but I didn’t think of that until it was too late). So, what I did (and what actually helped in the long run) was to make a jig for my router and route out the middle 4’x8’ of the table where the 3/4” MDF is going to sit. I took out 35mm of material in that section which dropped the MDF that amount to make it more level with the sides. The added benefit is that the table is now perfectly level and parallel to itself. Using the jig and running it on the sides of the table let me basically plane the surface of the table smooth and level. Hopefully this will help with the alignment of the LR2.
Once the routing was done I then dropped in the MDF sheet and used that as a level guide to install the Unistrut. Hopefully everything is going to work. Now I just need to put on the LR 2 and start testing.
It wasn’t too bad. I put the jig together in about 20 mins. The routing (2 passes for depth of cut) took a couple hours.
I also thought of use the LR to do it again to the 3/4” MDF sub-Board so that it was perfectly level to the rails and the LR but then I realized that my workpiece would rise over any small valleys so it may not be worth the trouble.
I do want to take a dial indicator to the Unistrut rails and see how “Off” of parallel to the MDF they are - more for my own knowledge then anything. Most of what I will be doing will be through cuts so it being off by a handful of thousandths really won’t matter.
I did not surface my LR spoil board, but I did test it by drilling 4mm holes in a 3x4 pattern or so and measuring the depth with the calipers. I agree that a small error is negligible, and part of the gig. IIRC, it was ± 2mm, and my build is about 36x48", which I consider a big win. I built my table as a torsion box, with 3/4" plywood as spoil board.
It will make more of a difference if you’re V carving, but there are strategies for making that better too, like a smaller angle bit or doing smaller carves in local areas with their own Z offset.
It would be interesting to actually measure your “flatness” now, since presumably, it’s as flat as your router jig, but not perfectly parallel/offset/trammed with the LR gantry.
Drilling the hole pattern is a good idea. I’ll have to steal that one. lol.
The flatness/level to itself should be good (at least as good as the MDF sheet is). I used MDF as well to build the jig so that should be fairly flat. I’m thinking the only way to get everything flat/parallel to each other would be to use a “known” true flat surface to plane down one of the Unistruts until it is perfectly level/flat across its length, then (with that one mounted to the table) use it as a reference to plane down the other one so that they are both level/flat to each other. Once that is done, then use the LR to plane down the surface (or spoil board) of the table so that everything would now be level/flat together. I think that an operation that is beyond my machining skills. It would be easier to take the Unistruts to a machine shop and have them machined flat then it’s just a matter of installing them parallel to each other and then planing down the table with the LR. That should ensure everything is perfectly level with itself.
Considering this is a hobby I don’t think I’m willing to go to that extreme, yet… lol. At some point I might just to see how close I can get it.
If the low rider was consistent, which I think it is, then using it to surface the spoil board means that if it sags in the middle or has a high corner due to unistrut stuff, the spoil board will be flat to the cutter, which is more important than actually flat. Any sheet you put on the spoil board will deform enough to take the shape of the spoil board. But this is definitely splitting hairs.
I never considered gravity and the working sheet conforming to the spoil board. That makes planing the entire thing flat to itself a little more intriguing, but as you said, this is more splitting hairs or an intellectual exercise. Something to play with if/when time allows or the machine just isn’t cutting properly.
