I built a torsion table, but looking down the rails, they aren’t quite perfect. I was going to try making a small lip of tape, then pouring self leveling epoxy to get them perfect, maybe 1/8 inch thick. I’m thinking it would make the rails perfect before surfacing the spoil board.
The only issue I can think is that the epoxy may not be a hard enough surface for the Y axis rollers.
Is there a simpler way to do this? Am I missing something?
Any thoughts are welcome.
Youre going to find getting a consistent depth to be more difficult than you think.
I’m not sure what you mean, the depth should no be consistant, as the goal is to level the surface, the depth should vary based on where the epoxy needs to fill the valleys.
What I think Nathan may have been eluding to, is problems related to surface tension. In order for the epoxy to level itself properly, it must overcome its own surface tension and the thinner the layer, the more difficult that it will be for that to happen. And regardless of the depth, there will be some surface tension related artifacts around the perimeter. Think of the meniscus around the perimeter of a glass of water, the same sort of thing will happen with epoxy.
Tolerance is a funny thing. Having a perfectly level Y doesn’t really matter. Even having it very flat doesn’t matter. The material will bend a certain amount easily. If you had a 5mm bump in the middle of your table (so the Y axis was an arc) a 2.4m piece of sheet goods is going to match that arc perfectly. Same with some amount of twist or X axis arc. You just need to get close enough that the material will lay flat and there aren’t any small bumps. If you really care beyond that, then you can surface the spoil board. But most 2D or 2.5D cutting is very insensitive to the table arc and 3D or carving still don’t need a perfect table.
That’s me arguing that it isn’t necessary. But I didn’t answer if it was possible. AFAIK, resin/epoxy has a pretty high hardness scale. So I doubt it would be a problem. It would be hard to do. But if you did it, I don’t think it would hurt you.
Build a really rigid base first. The last thing you want is to make a super flat surface and then move the table and have an arc…
Right, right. So I’d have to pour a thicker layer to compensate for that? The perimeter is fine, I can just sand that down, so long as overall the pour has actually levelled.
Thanks for the in depth comment. I see your point about materials conforming to whatever surface they lay on. I will mostly be working with thinner materials, however I’d like to build kitchen cabinets at some point with 3/4" plywood. My thinking is the thicker material would be less likely to instantly conform to any imperfections in the table. My table is based of the design from Ryan, so it’s quite rigid, but I worry about processed materials used to make it(OSB, MDF) and the ability to sag over time.
Maybe I should just resurface, and deal with any issues as they arise.
I recently heard someone say “If you can make it perfect, make it perfect. If you can’t make it perfect, make it adjustable.” I’m sure this isn’t a new sentiment, but it makes a lot of sense to me. If you’re worried about parts sagging, have a plan for addressing the sag if/when it shows up, but don’t let that keep you from getting the machine up and running.
Go to home depot and put a pencil in the middle of a 3/4" sheet of plywood. It won’t break and it won’t be able to keep one end up. You can probably believe me without going to HD.
So that’s a starting place. If you can have a “smooth” table, but it isn’t perfectly “flat”, but it is within the width of a pencil, then you don’t have to worry about it. I bet the actual acceptable tolerance is much bigger.
Since the LR rides on the same surface, it will conform to the shape of the table as well. So the best thing you can do is to just make that surface the LR rides on the same as the surface the material is on.
For through cuts and kitchen cabinets, this matters even less. The spoil board is meant to be cut into. You just overcut by a few mm and the parts you take off are perfect. If you need a rabbet or dado, you just design in a few mm tolerance (you probably need them for wood movement anyway) and the extra depth of cut doesn’t hurt the final product at all.
Where it really matters is if you are doing a V-carve, where a change in depth translates to a change in the width of the design. Inlays, or 3D carves too. That’s why it’s pretty rare to see them span the width of an entire door. They are hard to nail the Z across long distances. Small designs (10" or less) are easy to do with some careful setup.
Are both the flat side, and the EMT rail side concerning you, or just the flat side?
If just flat side is a concern, have you already considered using ~1/8" thick strip of metal for the bearings to run along? I can’t imagine your torsion box being so bad that layers of paper shims are needed to achieve “true level” perfection, but that would be an adjustable option with this approach.
You could always add a metal strip later on, after first using your vanilla yellowbrick road Lowrider to make some neat epoxy enhanced projects. Then, decide later on, if you want a metal strip for the flat side for the bearings to roll over.
Both sides have small variation. But after reading Jeffs comments, I’m not going to try to epoxy it. The metal seems like a good idea!
Thanks Jeff, I agree completely!
Here’s how I made my y surfaces adjustable. I built a steel table for my lowrider. On each side there is a length of 2" angle iron welded to the frame as parallel as I could get it. Then I bolted 1"x3" steel tubing onto the angle iron. This gives me several points where I can shim the rails to get them parallel.
If you do decide to use metal, L angle could help provide extra rigidity and provide some dust/debris deflection, just make sure the L strip is as perfect as you need, and, that the upstand isn’t too high and interferring with motion of bottomed out gantry. The upstand deflector may make loading/unloading material from that side harder, especially for a full sheet build.
Pretty much. I’ve poured a lot of epoxy. Self leveling isn’t the same as level 
once the epoxy has cured out comd the tools to make it actually flat. I overpour intentionally so i can work it down without cutting into the workpiece. It takes more to get the epoxy finished than it would to just sand your rails. And thin layers are not s durable as you would like. They will bend and groove fairly easily.
Beyond that. Is it even worth it? If you’re making mdf cabinets your going to drive yourself insane trying to get brain surgery precision when what you need is just mdf flat.
Perfection is the enemy of good enough.