Seeking Advice For Restoring Front To Back Tilt

[Aiph5u (Aiph5u (not affiliated with Onefinity))]

Hey John,

@jnordyke

a different amount tilt when at Y=0 inches than when at Y=32 inches

this remains to be found out why. How much is it?

And how shows it up? When measuring towards the front?

The swinging arm of 15 inch length, doesn’t it overhang the surface towards back at the end of Y? And towards the front at the beginning of Y?

And where does stand X then when you measure a deviation of tilt on different Y positions? Did you measure different deviations when X is at left, at middle and at right?

@jnordyke

The Support: Removing Twist From The Onefinity Rails procedure I did use 9 months ago when I first installed my machine and using the metric of how well feet sit flat on table surface there is now no twist in the rails.

For this of course there is a table with coplanarity necessary (no twist between the positions where the feet stood). I hope there was no error here.

@jnordyke

My table surface is a torsion box constructed of 3/4 inch MDF with 4 inchx1/2inch MDF webbing.

That sounds reasonable to prevent twisting. Important is that a twist is not already in the box when assembling it. The torsion box’s rectangularity lives from avoiding minimal displacements of the parts which cannot be assured if the surface part of torsion box is lying on a surface that already has twist, i.e. deficient coplanarity, when assembling it. Parts may have true right angles, but twisted surface would shift them in a minimal way if torsion box is forced into a twisted shape obtruded by twisted underground.

@jnordyke

Flatness and coplanarity were judged with a 48 inch bubble level and a 36 inch steel machinist’s rule.

With a bubble level, you can check coplanarity, which means the absence of twist in the surface, and 48 inch is very long, but bubble levels are not that precise. That’s why I didn’t mention them in my list of tools to check coplanarity of the surface (fishing line method which is simple and very accurate, winding sticks, water tube level and level (optical instrument)). A lack of coplanarity, which means a twist in the mounting surface, i.e. if one of the machine’s feet is higher than the others, cannot be removed by surfacing the surface. The spindle axle will deviate from a vertical position on a machine with a twisted surface and with a long enough measuring arm, error might become apparent because the existing surface deviates from the imaginary plane perpendicular to the axle. This would be one of possible reasons for why you measure different tilt on front and back of Y travel. Do you think you could use the fishing line method to ensure coplanarity again?