My Portable Wide Slab Flattening Jig

[SkinnyB]

Ill test your idea once my jig as accessible again. (Big slab on at the moment).

So far it seems to work.... When I first made it I did quite a bit of testing. I had flattened one side of a wide a slab, flipped and turned it checking it in both direction and the planed side sits flat on the trestles in both orientations.
If It didn't work I guess I would be planing the slab twisted... Then when I flip it over the twist would still be there and I would get a slab that only sits on the trestles in two spots.

Anyway is must work because Marius Hornberger did it
Time:9:30
https://www.youtube.com/watch?v=ssndGQxs8ZM&t=741s

 

[rafezetter]

I'm not convinced by the string method for levelling...

Consider that you set up the jig and check for level, finding the string touches in the middle - one of two corners needs raising to pass your level test, yet only one of those will make the jig closer to level, the other will make it worse.

I've seen the string trick before, and iirc moving the wrong one will also raise the string at the corner enough to notice, so as long as you are vigilant at the corners, you should be OK.

Obviously you have to make sure it's pretty tight so there's no possibility of any sag.

 

[John Brown]

I'm not convinced by the string method for levelling...

Consider that you set up the jig and check for level, finding the string touches in the middle - one of two corners needs raising to pass your level test, yet only one of those will make the jig closer to level, the other will make it worse.

I think level and coplanar are different things.