Tiling/Surfacing bow out of warped slab?

[scottp55]

I had a 17X34X1.84" quilted slab that had a 1/2" bow I had to get rid of, while leaving the cup on the top(so pencils/bits/etc will roll towards center of shelf---also had a 1/4" lengthwise warp I wanted to keep for same reason).
I got the good 1/4" out of it with the Bosch 4X24 at 80G, but one of the wheelchairs brakes is broke-so had to hold my left wheel to keep from taking a ride:) My right hand and arm gave out and it looked like it would fit with my shortest 3/4" straight in the spindle.
In the first pic(even after using a low angle Jack plane to get the worst out-when you see grain, you'll see why I didn't try to get into the flat-even my low angle Skew block was having problems-and you could shave with them), slab was resting firmly on 3 points, so I wedged floating corner.
No thickness sander and wouldn't trust it with a planer. Not enough Z to put it on 3/4" 0r 1/2"ply bed, and didn't have any 1/4" big enough.
I Thought zeroing to spoilboard would give the best results. Had to mess with safe Z's as .25" in VCP as it kept hitting topZ prox.
Wound up taking .22" off first section(boundary box was 12.5X 18.2).
I slid it forward, and rewedged same gap that showed(Mistake it turns out), and first cut(.05") on the left side was .03" DEEPER than than the previous .22"!
Went around back rewedged opposite corner and then took it down in stages until my 4' level showed me I was close.
I THINK I should have used Shopbot and shim gauge/paper to level slab with shims before starting second cut?
It's only my second attempt at feeding stock through Y-axis, but I have a lot more of same thickness material I would like to use(None as twisted as this-which is why I used it).
Z-ing to top of material would have been Very tight, but would that have been better?
Just wondering what I should have done different for more consistent results?
Will look for a different bit less CEL and overall length.
Long winded as usual.

[Burkhardt]

I had a 17X34X1.84" quilted slab.....

I think your best bet would be shimming and hot gluing to a flat sled board of same or bigger size. If you move and re-shim the likelihood of getting it in the proper position is very small. But if you only can fit 1/4" board that may be difficult since these are rarely flat themselves. Maybe 1/4" MDF?

Or you can do the insulation foam trick that I used for my juniper log (need to let it harden overnight) That makes the sled board and the slab one piece that does not wiggle. But that only makes sense if you machine the other side later anyway which will also remove the hardened foam. Or maybe wrap your slab in cling film so that it is supported and located but not glued to the foam (have not tried that yet).

[Brady Watson]

Move the workpiece in the Y direction a couple of inches. Then use the AL table bed extrusions and t-nuts as a foundation for your 'toe clamps'. That will resist the forces of clamping way better than the actual spoilboard or clamps on the edge - which appear to be bowing in your pics. Use shims etc as required to do what you need.

Vacuum would also work if it is High Hg".

-B

[scottp55]

Thanks G., Yeah, 1/4" sled predrilled to my inserts and then wedging and hot glue might work best. Thought about your foam trick, but didn't have anything but BB and hardwood ply.
The cling wrap idea might have worked to protect the top and that might work well.
I wonder what's out there in 1/4" that foam might be able to be cleaned off of and be reusable. Too bad everything is S2S max thickness in this case.

[scottp55]

Don't have any extrusion available anywhere showing, but do have threaded inserts every inch and a half.
I did get carried away tightening the .3" teak and 3/8" BB didn't I? :)

[Burkhardt]

Here is another wild idea. Wanted to try it sometimes but never got around to do that. So, for that matter it may not work at all:

You can buy "kinetic sand" (http://www.youtube.com/watch?v=50_-zqsgDA4) from Brookstone (http://www.brookstone.com/kinetic-sand-by-brookstone) and other suppliers (http://www.shopbecker.com/sand-water-and-sensory-play/sensory-materials/_/kinetic-sand?gclid=CIyxifCgxb8CFSbKtAodIUoAXg) which is actual sand with a very small amount of viscous binder that sticks only to itself. Intended as a toy because it can be shaped but does not scatter or stick to hands or clothes.

I wanted to use this as a bedding for warped boards on a sled, sealed around the edge with masking tape and held in place by its own weight or with some shopvac vacuum support (it is porous).

If you are in an experimental mood maybe you can try that and tell me if it actually works :rolleyes:

[scottp55]

I'll leave the esoteric stuff to you G. :) I'll be happy to get back to "teeny" stuff!
You let ME know how it works:)