Vacuum jig and spoilboard question.

[gundog]

I am designing a vacuum jig for my milling machine to cut some aluminum. I got the vacuum plenum drawn up and had planned to use some trupan for spoilboard. The plenum is going to be made from 3/4" UHMW plastic that I had laying around. The work envelop of this machine is 31" x 17" x 23".

I planned to cut with coolant and after drawing up the plenum it occured to me my spoilboard will not hold up to coolant use. Back to the drawing board I wonder if the spoilboard will work for one project and then change it or will it just fall apart when the liquid hits it anyone know?

I planned to tap into my existing vacuum hold down system that I use on the bot. The SB uses 2 house vac lighthouse type motors attached to a manifold. I planned to add a T and valve to supply vacuum to this new machine.

Mike

[billp]

Mike,
Could you do your cutting with a cold air gun instead? it would sure save you a LOT of swapping out the spoil board(s)...!

[CNYDWW]

Sounds like a job for a vacuum puck or a couple. The venturi versions are around along with the diy's. If i get a chance i'll see what files i have kicking around.

Regards
Randy

[steve_g]

Michael

In another life... we painted using a fluidized bed of powder coat. to Fluidize the bed of powder we used a plastic membrane about 1/2" thick and put compressed air on one side and powder on the other. I can't help but wonder if this material might be something that would work and be waterproof for your application. A quick Google search didn't get me a better specification than a "fluidized bed membrane". however I'm sure a good commercial plastic supply house would know what we're talking about.

Just an idea...

Steve

[gundog]

Check this out I found it researching vacuum jigs on youtube.

http://www.youtube.com/watch?v=X3yHh6N_fQQ

[michael_schwartz]

I wonder how expensive it is, since it is intended to be single use. Otherwise it looks useful.

[Brady Watson]

Just make your own vacuum mask that directs vacuum under your parts. You can use something as cheap as PVC dunnage (Sintra) that you machine a grid into, or AllStar gasketing spoilboard cover. You can use a BradyVac II or a whole host of other setups. (Read up on the ShopBot main site under Web columns)

My only caution would be to watch coolant getting into your vacuum pump. Buy a pressurized paint pot from Horrible Freight and use it between your plenum and vacuum pump as a 'catch can' to keep liquid from getting into your pump.

-B

[gundog]

Thanks Brady I was wanting this jig for occasional use for aluminum parts. For example I want to cut some parts for the SB to mount a drill to my machine. I bought a Milwaukee electric drill and I plan to cut some .250" aluminum for mounts.

I also am thinking of buying a Gast vacuum pump for another part that I need to make on a regular basis. Do you think this would work?

This is a separate jig than what I started this thread about using the Gast pump. I have a part made from 6061 T-6 that I am thinking of making a special vacuum jig to hold about 10-20 parts at a time each part is 2.25" x 5" x 1" the part will have 5 - 1/4" holes drilled in that surface. I plan to gasket the parts and use a jig machined from plate aluminum so that it is held with no leakage. I need to machine a 1" wide dovetail .370" deep length wise through each part.

What size pump would I use for a jig like this that seals the vacuum and does not leak like spoilboard? Do most of the Gast pumps allow you to run them at full vacuum without a problem?

I will machine through with a straight end mill to rough out the groove and the dovetail pass will be cut last. The part also has some other machining to do but the 1" wide dovetail groove will put the most pressure on the part. I plan to gasket around the holes with O rings I am just wondering if the remaining surface area will hold the part?

The other alternative is to build a jig that clamps the parts. I would prefer using vacuum because it will make changing parts much faster. These parts will be made on my CNC milling machine not the SB because I can take a heavier cut and use coolant.

The part with the detail in it is the part you can see the 5 1/4" holes in it.

Mike

[myxpykalix]

Thinking outloud here, and i'm not quite sure i understand what you are trying to do but understand that you want a jig and to use coolant but don't want to mess up your spoilboard.

Could you make a jig that was big enough to encompass the parts you want to cut, say out of metal or aluminum, and you could make it kind of like a pan and tap a hole in the side where you could use a liquid coolant, have a drain and have it recirculate but be contained within the pan so as not to ruin your spoilboard?:confused:

[gundog]

Jack,
I have 2 CNC machines this is for my milling machine not the Shopbot. My Shopbot has a vacuum table and it works great I use Trupan on the Shopbot and no coolant. I am just wanting to setup some vacuum jigs for the milling machine because the vacuum table on the SB works so good for me.

I am going to build the vacuum jig with the spoilboard for making parts on the mill and just plan to toss the spoilboard after each use if it destroys it. I am going to machine a recess in the UHMW plastic to hold the spoilboard in place and tape the edges with painters tape. I will make every effort to cover the spoilboard to protect it from the coolant and see how it works.

The second project is the one I am not sure about because I am not sure the part has enough surface area to hold the parts while milling.

I have lots of time to design and plan right now while I am healing up from my battle with the table saw that I lost.

Mike

[Brady Watson]

If you are doing these on a mill then no hold down is better or more efficient than a Kurt vise. Drop the part on the parallel bars, cinch it up and machine.

-B

[gundog]

Brady,
I have too many parts to do with too many tool changes to make that a viable option. This is a part I plan to make on a regular basis.

Mike

[Brady Watson]

Mike,
I don't think you have enough surface area to hold those parts down with vacuum. You'll have to do the math to figure it out, but it won't be easy because you have no way of determining how much force you will be applying to the workpiece with the bit.

You'll need to measure the surface area/footprint of the part you want to cut. Then calculate actual max vacuum that will be used to hold the part. Let's say your little Gast does something around 25 inches of mercury.

Constants--> 29.92 Hg" = 14.7 psi

25 Hg" / 29.92 = .835

.835 * 14.7 = 12.2 pounds per square inch.

If you have 4" square part, that equates to:

4 * 4 * 12.2 = 195.5 max pounds of downforce on the part @ 25 Hg"

Aside from flycutting or other light tasks...that just isn't enough holding power to deal with the forces against the material as well as the not readily apparent influence of harmonics and vibration that comes from cutting AL. This is why you don't see vacuum being used very often on milling machines.

-B

[gundog]

Thanks Brady
I think I will make a jig like this one and use clamping rather than vacuum making a vacuum jig will be a lot of work which would be worth it if it worked but chances are it won't.

http://www.youtube.com/watch?v=Dj3n9IOVqL4&feature=results_main&playnext=1&list=PLFE564BF1545E8B05

Mike

[Brady Watson]

Yep - good idea. You can also make your own cam clamps without much fuss.

-B

[meatbal80]

Could you make a block/jig that the pices could be bolted to on the back of the part. Then the entire block could be held with vacuum, the slots for the parts could even have small ports for the vacuum to help hold the pieces and cut some of the vibration.

[Regnar]

This was a pretty good read and might help you out

http://blog.cnccookbook.com/2012/02/18/fixturing-with-vacuum-tables-vacuum-chucks-and-vacuum-clamping-systems/