Simple vacuum jig(s)....

[jrconca@innernet.net]

Have just finished making my vacuum table based upon design concepts I have gleamed over the years as well as on these forums. It works extremely well. Although since I've been racking my brain as well as precious time working out the problems I've been having with my steppers over-stepping that I haven't had the time to experiment. Anyway, my setup consists of running a file that drilled/routed 45 1/2" hole through my first 1-1/8" particle board subtop. Then we ran the same file using a 3/8" bit cutting 45 holes through my second 1-1/8" subtop. From the under side of the table we pressed 3/8" poly tubing (the kind used for refridgerator water line)into the 3/8" holes previously routed, we then trimmed the excess protrusion with a chisel and coated top with a sealant (lac sealer). Clear silicone helps seal the tubing in place although just like the second subtop, I don't think the silicone was really so necessary as the tubing was a bugger to push through. These tubes were to be tied into a copper manifolds via barbed poly "T" fittings. That was until I realized we needed somehting like 45 "T's" at $1.49 ea, not to mention that 45 was more that both local Lowes and one Home Depot had in stock. So instead, I bought 1 piece of 3/4" x 6" x 6" plexiglas, cut it into 4 pcs 3" X 3". In three pieces we drilled two sides with 10 3/8" holes and connected them with one 3/8" hole. The fourth piece of plexiglas has a total of 16 3/8" holes in it (5 holes in 3 sides plus one connector hole)! To put that many holes into such a small space took some figuring but, it worked. So, next we tied all 45 3/8" poly tubes into the (4) plexiglas manifolds and those manifolds were in turn tied into four copper nipples on the main 1/2" copper manifold. On the copper manifold I sweated four shutoff valves (this is so I can have any combination of hold-downs working. We connected the end of the copper manifold to a rotary vien vacuum pump via a 3/8" poly tube. I've been TRYING to make 45-55 4" melamine disks that will have closed cell tape around the preimeters of both sides, but the aformentioned Bot problems are causing me such grief. Anyway, the few disks I do have completed work quite well. With the pumps on you absolutely cannot pick up one up however you can slightly slide it, hmmm, me thinks its the foam sliding.
At only 7sq. inches and pulling 15 in of mercury thats what, only 70lbs holding force? But a rectangle measuring 6" X 14" is both impossible to lift or slide. I too, plan on experimenting with various other forms of sealants.
I personally like Gerald's great idea of soft surgical tubing, am definitly gonna try that. However if my experience with using fom tape is any indication, then just overlapping the surgical tubing should work, and yes possibly bubble gum or tape.
The neatest part of my concept is that I am going to make a file that has the exact placement of all 45 of my 4" disks, i'll svae it as a .sbp file and by running it in preview mode, it will appear on my computer screen then I'll simply run the file I'm gonna cut also in preview mode and Volia, the former file of the "disks" will still be there and I will know which disks to place where...half disks will go where there are close calls. BTW I have pics of my system. E-mail me at jrconca@innernet.net}
JRC

[benchmark@tesco.net]

After many hours of R & D for a vacuum table that works, I have come up with the following design.

It is easy to build and use, has automatic vacuum bed table sizing, minimum amount of parts and low in cost apart from the vacuum pump.

The base is a sheet (8 x 4) of 3/4” MDF screwed to the shopbot base frame, a suitable hole is cut in this for your vacuum attachment. Then screw a perimeter frame of 1” x 11/2” PAR softwood and cross bearers on 12” centres, these are 2” short of the outside frame.

Seal all the inside of the sheet and framework and the back of a sheet (8 x 4) of 3/4” MDF and let dry.

These wood spacers are then machined with our shopbot file (skim ) which will level and flatten the table.

We then attach the sheet of 3/4” MDF sealed side down to the softwood with a few screws , turn on your vacuum pump or shopvac to hold the sheet onto the softwood frame, and then run Shopbot file (Fix1) which will machine a series of holes with a 1/2” cutter 1/2” deep, through the bottom of these holes you screw the top sheet to the framework , then remove the few screws you fixed the sheet with. These 1/2” holes can be later used as holes for short pieces of 1/2” dowel as location pegs.

Then run Shopbot file (Pod32) this will machine a series of 32 pods into the top sheet, the run Shopbot file (VLV32) which will machine a series of 32 stepped recesses to take the valves we have made

Insert the 32 valves and your vacuum pump and away you go

The principle is that you can operate any number of valves from 1 to 32 just by placing your material over the valves which then operate the vacuum automatically for each pod.

If you are not machining all the way through the material working directly on the table is OK , but not recommended as accidentally hitting a valve will damage it and the cutter, also damage to the top sheet will need to be repaired or replace the whole sheet (a long process).

This is the easy bit. Place a sacrificial sheet of 1/8” MDF the same size as your material or slightly larger (to the next sized area of pods) over the valves, place your material on this and turn on your vacuum the holding power even with a shopvac is immense and seems to work better than directly on the bed .

For larger parts I machine slightly into the sacrificial sheet and cut out completely, for smaller parts I use a tab function and a few blobs of hot melt

The cost of the 1/8” is minimal and is charged out the job, I always use one even when not machining through the material. I keep my sacrificial sheet for regular jobs and use it over and over again.


I am awaiting delivery of my side channel vacuum pump but the results with a 1100W vacuum are excellent

The number of pods is not fixed as they can be suited to your application, but I found that 32 covers each square foot of the sheet and will work in most situations.

If any one is interested in the valves let me know as the more I can sell the cheaper they will cost

What more can I say

It Sucks

Paul

[Gerald D]

Paul, are you telling us that the 1/8" MDF is porous enough to act as an air diffuser? If this is the case, then we have a whole new heap of possibilities.

For example, why have valves at all? Why not just have a big sacrificial sheet and cover the unused areas with Kling wrap?

[Gerald D]

Paul also see message from Mayo Pardo above on December 27th. I think your method is okay for relatively large parts. For small parts you will probably need something more "rubbery" with less air resistance.

[paul]

Gerald

Yes it is, I was amazed myself

The principle is to concentrate the vacuum to the area you are working on, to cover any area with Kling wrap or any other material is just another job to do and will create more leakages. The Idea is to keep it simple, slide the material and sacrificial sheet on the bed switch on the vacuum and away you go. Besides Kling wrap does not like dust.


Cutting small parts from small pieces of material will always be a problem even with a large vacuum pump on a universal vacuum bed.

Cutting small parts from large pieces of material is not a problem providing you use sensible cutting speeds or tabbing.

[alton]

Instead of kling wrap, I use two peices of shower
liner material that I purchased at Home Depot.
The material is about 1/16" thick and is like
rubber. Comes on a 36" roll cut to your length.
Handy for me, since my table is 36 x 48.
I'll overlap one peice over the other one.

Alton

[alton]

Sorry couldn't get the image to upload.

Alton

[danhamm@abccom.bc.ca]

I was at a glass shop on thursday and watched them
pack a large plate glass with handels attached to the plate glass, I new what they were using and
a light came on,I asked where I could get a couple
they said they had some that were not dependable
and they gave them to me..I have a little 1/25 hp.
vacuum pump,and have removed the over center
vacuum thingy and put tapped it for a fitting,
Now with a little metal work for a base..check out your glass shops fellas..

[jccwrks@aol.com]

All this talk about spoilboards and vacuum pumps is getting rather complicated. I build at least 50 acrylic and foam signs a week using a 1" thick sheet of gatorfoam as a spoilboard. I simply clamp acrylic sheets to the edge of the table with 5 or 6 spring clamps and cut. No vacuum, no problem. I'll use the same spoilboard for at least 50 different patterns, then flip it over and use the other side. It's clean, easy to handle, and provides absolutely no resistance to a bit that may protrude through the cutting material. A quick touch on a nearby 12" disk sander removes any trace of an entry/exit mark on the acrylic. I've learned that if I need to cut smaller, more articulate lettering, I can slow the cut speed enough to melt the gatorfoam spoilboard to the protective paper backer sheet on the acrylic. After cutting, I lift the letters off the table with a putty knife. Again, no vacuum, no problem. Of course the spoilboard needs to be replaced a little more often when you fuse acrylic backer to it, but it's still a reliable and simple way to hold down intricate acrylic components. And after listening to my router and dust collector humming all day, the last thing I need to hear is a screaming vacuum pump.

[danhamm@abccom.bc.ca]

If you are in to small box or jewel box or heart shaped item making, and want to round over and
pocket and cut out then round over the bottom
you can't use clamps, it has to be elevated,
and it has to be very secure.A good vacuum is sure nice in this situation...