Vac table evolution

[jTr]

Originally used a 5 zone vac plenum and placed individual "pods" of ultralite mdf on each zone, as learned by many examples on the forum. Separated them all with 8020 Aluminum rails for hold down as illustrated here as well. Misunderstood attachment method, and had placed individually sized pieces of bleeder down and pegged with dowels to index. Taped edges to create a sort of bellows/ edge seal that also helped firm up the seating of the pods over the plenum zones. Read here recently, I should have glued them. :o

So... A year later, I find I'm not using the aluminum rails, and tired of the gaps creating dust pockets, tear out spots on ply edges and catches as I'm sliding ply, etc.
Filled in the alu rail channels with fresh mdf strips and decided to glue down a full sheet of 60x96 Trupan. Rolled glue on entire plenum surface, keeping out of vacuum channels. Used glue to seal edges of perimeter of the full sheet as the vacuum was running to assist in clamping it down. I planned on routing some grooves in the new layer of bleeder in order to insert/glue in hardwood strips to act as vacuum zone dividers after this.

I'm elated to report that I've got a 75% increase in vac pull, since all is sealed nicely now. The catch is, I haven't dissected and inserted the zone separator strips, but the vac pull seems to remain well isolated. Based on commentary here, I understood the bleeder would readily leak sideways and weaken the hold down, but am surprised at how well focused it is, and now hesitant to manipulate any further... Seems the vac flows through one face to the other quite well, but is shunted very tightly in the lateral direction.

Anyone else have any thoughts or experience in running it this way?

jeff

[jerry_stanek]

I thought I had good vacuum when I had a whole sheet down But since I separated the zones with a piece of sintra I get better vacuum

[twelchPTM]

no seperators on my zones, the most I need to do is through some scraps of lexan around smaller pieces just to cover the zone being used.

[jerry_stanek]

I found that there was a lot of loss through the zones that I didn't use. It was more of an accident but I only had one zone open and was doing something on the zone farthest away and noticed I couldn't slide the piece.

[twelchPTM]

i suppose the particular vaccum being used makes a difference, don't know the specs off hand but i have the big monster unit from shopbot purchased along with my machine, I have held pieces as small as 6"x6" and all I do is cover the extra space on the open zone. Brady did our install and had a very elegant way of describing the force we get but I don't think I can repeat it on the forum...

[jTr]

I'll go ahead and dissect accordingly. I'm using the black box with 4 lighthouse motors, so every fraction of efficiency is important.

Thanks for the input everyone!
jeff