Now I am struggling to create a perfectly flat table. I am screwing a 3/4" MDF board onto a sligtly smaller already existing table. Looks like this table is not very flat, as my MDF is now sagging about a millimeter in the middle of the 1600mm long table. I have built a steel frame on top of the table and will be working with shims to reduce it even further. Also, it will get additional 3/4" boards on the side for the rails/rollers to ride on.
But it got me thinking…how important is table flatness, given that I will be surfacing the spoil board? My assumption is that the side with the metal conduit should be no problem, as this is going to be straight/flat. But the side where the rollers ride on the table would be problematic, even with a surfaced spoil board, as basically I will be “bending” the stock to fit the non-flat table.
Hello there, and welcome to the forums and the v1e rabbit hole!
I never built a full sheet Lowrider, but I think you will manage well when flattening the spoil board. Many try to make tables as flat as possible, but Ryan (and others) general approach seems to be that we should worry less about the tables.
Don’t overthink it. I first tried making a dead flat table for my full sheet lowrider, took me a lot of work. It worked well, but it got soaked during a storm. So I built a new table. Took a used pingpong table, put a few strips of mdf on it as a spoilboard and surfaced it. Works just as well, maybe even better. Any simple table will do. want it flat? Surface it.
If you are only planning to do 2d through cuts, flatness does not matter that much. Just cut half a mm deeper.
"Your table needs only be as fancy as a sheet of wood on a relatively flat, smooth surface. A CNC can self correct many of its own imperfections if needed. "
There was also bit of discussion on tables recently here:
This was addressed too, but I can’t find it. Just relatively flat is fine.
If you are doing sheet goods and through-cuts, 100% not a problem.
If you are doing fancy carves in thick material, you are likely to need to surface the material before cutting anyway, and you shouldn’t have a problem.
“Relatively flat” and “smooth” are the only thing you absolutely need to shoot for.
Don’t stress over it.
If you want a quick sanity check, you can get a 6’ level or long straight edge and lay it across and shim the MDF from underneath.
I did this for under my rollers, but 1mm is not a big deal.
One of my attempts at a torsion box came out pretty deformed. (It was the largest torsion box I had built so I didn’t have a good reference surface for assembly. Should have shimmed more.)
The actual problem was that the origin was high compared to the majority of the table. I was always guessing how deep I needed to cut to compensate.
So I surfaced the table top itself. I figure flattening it and putting an MDF spoil board over it was good enough for most of my projects.
I live in a pretty dry climate so I don’t see anything detectable. I figure I can always surface the spoilboard immediately before a project that requires it.
Side note, I’d probably throw a dedicated spoilboard on before I surface because I generally like some of my spoilboard features for jigs and fixtures. (Unless it was so chewed up it needed to be dressed anyway.). These features trump flatness for me.
Flatness has some benefits, especially if carving, although as mentioned above, for through cuts you can just add a mm or two to ensure that you go all the way through over the entire cut. I ended up having to surface my table, as there was almost 4mm difference in places, so even adding 3mm extra on the DOC wasn’t completely cutting through the material.
Level, on the other hand, is completely irrelevant. Your table could have a 10 or 15 degree slope from one end to the other, and as long as it is flat or surfaced to be the same shape as the gantry (every point on the table surface is the same Z distance from the router bit), the cuts should be good
I was going down the rabbit hole over complicating my table build too. I was ready to pick up steel and weld/bolt up basically a steel torsion box. But after reading the info linked by mike etc and remembering I have two kids under 5, a job, and a million other projects I want to finish I went to craigslist and found a dining table that was about the dimensions I need for $50 and I think it’ll work just fine.
