Thanks for the info Dave,
I  assume that the plate you show is the base. You may want to consider porting and sectioning the base such you can put some small items or large items on it. Additionaly, if the base is sectioned as shown by the grey lines and you can turn off a section so more of the vacuum pumps suction can be applied to section being used. Placing tape or dense hard rubber over open holes would seal unused holes. The attached shows a number of holes in the top plate and the sectioning of the bottom plate. Makes it more complicated but more usable. You may want to get some Corian scraps and try that for a base.

Keeping it real "rough & basic" from the design point of view for the top plate.
If a perfect vacuum was pulled then you would get a holdown equal to 15 # per square inch. With an 1/8" hole,
it's area would be .012 sq in and times 15 #/ sq in = .2# of holdown per hole. With leackage, assume you get only
.1 # of holdown. This gives you an idea on the number of holes and would change how the base was ported for a section. Just a few thoughts.
RICH

Hi Rich,

Thanks for the info as well but since the plate was not finished, I don't think you might be understanding what I'm doing as I wasn't descriptive enough, or I just don't understand your reply, lol!

The cross slots you see will be filled with an o ring material to "block-off" a certain area. Much like the picture of a vac grid I've seen before. The main hole for the fitting will be in the center on the side (long section) and a 1/4" hole will go down from the top surface to the main hole for the fitting to create a "channel" that will reach out to all slots until they're blocked off with the o ring material. As I mentioned, there a lot of ideas I have this such as hold down screws for blocking in parts so they don't shift on me.

Here's a larger scale plate that I've seen but made for a router table:

Got it Dave,
Please continue posting as it progresses. It will be of value on my end when building one for the engraving machine.
RICH

Will do, Rich, how big is your engraving machine?

Dave,
Small and sits on a movable bench. I have it posted under SHOW AND Tell. The link is below.
No speed demon, it was built for accuracy. Additionaly to do probing, just not ready to go thru another
learning experience on the probing.

http://www.machsupport.com/forum/index.php/topic,6904.0.html
RICH

what a very slick machine!!! 

Is this the machine you did the chopper mirros and grim reaper parts on?

Very nice-   

design update - 

The outer tapped holes are for side clamping to keep material from sliding laterally if needed.

The rest is pretty much self explanitory. 

Hey Budman,
    Mind to share the .tap file for that grid ?
Thanks,
Lazy (RC)

I haven't done the CAM work on it as of yet, but when I do, I'll be happy to!

Thanks Budman,
The mirrors and the reaper plate were done on an old / small Atlas knee mill which I converted to CNC. Should probably post on it. The inlayed plate was done on the engraving machine. The pain on the engraving machine is holding down a real thin piece, very flat and being able to remove it without distorting it. So ground vacuum plate would probably do the trick. Some of the anticipated engraving work will be very light say 2 or 3 thou. I'm just goofy on some of things we try to make, but it's fun.
RICH