Cure for uneven crossmembers?

[myxpykalix]

If you look at the pic you'll see at the end closest to camera looks as if the crossmember is lower than the others and it is uneven in a few places. My intuition tells me to get another piece of mdf and put on top and surface it to make it all level but i intend to have a vacumn table and im not sure the feins would pull enough thru 3 sheets of mdf. My thought was to take another sheet of plywood on top of what you see there, run the pvc thru the bottom ply and 1st mdf and attach collar for pvc to the 2nd plywood. That then acts like the bottom of the normal setup and you are only sucking thru plenum and top mdf. So it would be a sandwich (from bottom) of 3/4 ply, 3/4 mdf, 1/2 (or 3/4) ply, mdffor plenum, mdf for spoilboard. Will that solve my problem or do i need to go to the trouble of removing ply and mdf and shimming crossmembers instead? In case you're wondering the outside C rails seem to be level and flat so its the crossmembers. HELP!!! sufferin suckatash...this is frusteratin!

7256

[lto]

Just surface the MDF til flat, then cut your vacuum grooves. You'll only be sucking through the top sheet, and replacing it as it gets surfaced to thin.

[Towersonline]

Two sugestions. Why not shim under the ply to get it close then surface the MDF flat. Large flat washers might get you close.

If the cross members are bolted to the main rail you could shim there.

[dhunt]

Isn't that ply sheet at the btm of the pile de-laminating??

If it is...you might want to take everything off and replace it?

[myxpykalix]

no its new plywood it looks like it is from the pic but its not. So far what i've determined is that it is mainly in that corner close to camera where the problem is. I loosened bolt and it rose up to be almost parallel with rest of board but i have a about 1/4" gap that i was going to fill with a shim. But the washers are a good suggestion also (i'm glad i thought of it bill). I will try that and report my progress...THANKS!

[scottcox]

Jack, What I did was cut that first layer of ply into strips that bolted (recessed heads) onto the cross members. Then I surfaced all of those strips to the same Z. (I hand planed the 2 end pieces even with the middle ribs which were surfaced by the bot). Then I glued my first layer of MDF to the surfaced strips of ply. Then I surfaced the MDF.