Just how flat does the mounting table need to be?

I have done several searches on just how flat the table you mount the OneFinity machine and wast board has to be with no answers to my question. Everyone says to make a “dead flat” table surface but I am curious as to just how flat that needs to be. I am the type of person to try for" NASA accurate" when “handyman accurate” will do. I am starting to drive myself a little nuts over some unevenness in my table surface that can be seen by turning off the lights and shining a light from behind a long aluminum straight edge. Basically the top is slightly low (dished) in the center despite my best efforts of shimming & correcting. I am almost afraid to admit the measurement I am even sweating at this point. I know I am going to have to potentially shim the feet to true up the Y-axis then tram the Z-axis. And of course there will be the flattening of the waste board.

Just to save on people warning me on materials. The table legs & framework are all plywood and the top is MDF for maximum stability vs moisture movement without going to metal. Appreciate your input!!

I would say stable (doesn’t change with humidity or temperature changes) is more important than dead flat because once you surface the waste board, it will be flat to the machine and will stay that way if the structure is stable. If the 4 corners are not coplanar you will need to shim them to get them coplanar before you would surface the waste board, this can be measured using string lines from corner to corner and measuring any gap between them where they cross, there are a few good posts about it on here.

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Hey Glenn,

if you mean the unevenness, this is eliminated by flattening the spoilboard.

However if your machine bed is not coplanar (twisted), this cannot be eliminated by surfacing the wasteboard and your machine can only produce twisted workpieces as a result.

Useful for adjusting coplanarity is if you have the QCW Frame which now includes the Any Surface Leveling System, or height-adjustable feet or casters on your table. If the latter is the case, please be aware that rarely a table that is not welded of thick steel profiles and annealed for stress relief is stiff enough not to twist if moved around because of ground unevenness, and that you need to re-check for coplanarity everytime you moved the machine around.

Further reading

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Hey Glenn,

Do you have some braces under the table top? MDF is not stiff, it will hang if not supported. Most people here make a plywood torsion box (which should be called anti-torsion box if named correctly :slight_smile:)

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Thanks for the advice. I have leveling feet on all 4 legs and have the table as level as I can with no decirnable twist. There are several cross braces for support of the middle of the MDF. I was planning to use the fishing line method to ensure that the Y-axis was coplanar. My bit of OCD just has me fretting over the slight variation in the surface. I am thinking I am good to go at this point but I had to ask…

Appreciate the input! I do have leveling feet on all 4 legs and the table is level without any notable twist. I also have cross members supporting the MDF and in a test run for strength & stability I was able to walk on the surface with just a 1/2" test sheet of plywood and couldn’t feel any notable flex. And I am in the same weight class of many NFL linemen…

I was planning on using the fishing line method to ensure the Y-axis is coplanar and use the leveling feet first if it isn’t, or shim under the feet if for some odd reason it is WAY out of whack. And of course this will have to happen anytime I change position of the setup in my shop. My little bit of OCD when it comes to setting things up is getting the better of me on this and I had to put this out there. To be perfectly honest the amount of dishing of the surface is around 1/32" at worst…

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Coming together and the fishing line says I am good to go regardless which line is on top!