Vacuum / Hold Down System

[CajunCNC]

A question that I have pertains to the vacuum hold down systems. I understand how the plenum distributes the vacuum, but then everyone appears to attach a "spoil board" right on top of the plenum. How will the vacuum hold down the material, it is now isolated from the plenum.

Does the vacuum pass thru the spoil board?

I assume the plenum is MDF as well as the spoil board.

Thanks in advance,
Steve

[robredick]

You simply need to take the skin off of both sides of the spoil board & the vacuum passes right through. The spoil board is just that. It keeps you from ruining the Plenum when your bit goes through the work.

Most people here like to use Trupan for their spoil boards. I have found Arreis from Sierra Pine to be fantastic. It is formaldehyde free, it cuts like a dream, and it holds up really well. It is also a fantastic alternative to mdf. Formaldehyde is a really bad thing.

[mrps]

Your spoil board will most likely be some kind of mdf. If you can find it you want low density mdf (trupan). The edges need to be sealed to keep the vacuum pulling down on your material. I do have some spoil board out of plywood that has holes and cut outs for special parts.

Your plenum should be out of PVC or other plastic if you can afford it. If you use wood, you need to seal it to stop vacuum leaks. My prototype is out of the ¾ in. plywood crating my buddy came in and then sealed it with silicone. When I think I've work out all the problems for what I intend to use it for I will make it out of PVC.

[CajunCNC]

1st of all, thank you . . .it now makes sense . . .


What is the "ultimate" material for a plenum?

What is the "ultimate" material for a spoil board?

When the spoil board is "worn out", do you then just mill it away and replace it?

Trupan, is that a brand name?

Thanks again . Steve

[angus_hines]

Well Steven,

The Ultimate would be the way Boeing sets there machines up

3/4" aluminum table bed. $1600.00

1" 4x8 Phenolic sheet (vac plenum) $1450.00

Then Trupan spoilboard....and Yes that is a brand name it's manufactured by DuPont....The "Better living through Chemistry" guys.

This is an expensive solution.

I have not seen this but this is what Im told by SB that they do.



I used 3/4 PVC for the table base. $350.00

Then did a glue up of Corian to make it 1" and cut my vac plenum out of that. $600.00

Then the Trupan.

[cabnet636]

steven, plenum in my booK

1) aluminum $$$$$$$
2) umhv $$$$
3) phenolic $$$$

i made mine out of mdf presealed the bottom and glued to base layer, presealead top prior to machining plenum, resealed after machining plenum.

works quite fine!!

spoilboards can be masonite pegboard, ldf (trupan)hard to find for many, i use mdf, we edgetape all outside edges then machine both sides, keep spoilboard toolpath on computer and remove 1/16 everyso often,

taking the time to make a great plenum can be a good investment

jim

[cabnet636]

the investment is in the vacuum pump or blower!

jim

[cabnet636]

i attach the spoilboard by countersinking screws to 1/4"

then chucking the sheet when i get close
jim
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[CajunCNC]

James, I assume the picture with all the squares routed in it is your plenum.

Do you glue your spoil board on, or simply lay it on top and seal the edges?

Steve

[john_hartman]

Steven, Look-up Brady Watson's thread. I recently set-up a kissass 4-zone vacuum using the 2 Fien III vac's and a 3/4"x4x8 piece of Ultralight wieght Trupan MDF. As per Brady I milled the plenum grid into the Trupan/spoilboard. I couldn't believe how it worked. Actually until this past Friday I was using just a single Fien and could hold down any sheet good and cut completely thought it. You can kidda see what I did, which is pretty common from these pictures: well the vacuum crane part isn't..
http://www.talkshopbot.com/forum/messages/28/38770.html?1234650233

[joe]

I made one of these vac systems several years ago. When I moved to our new building, most of it found it's way to the dumpster. I've read the threads on all those systems and they take take time and money.

Perhaps it might come in handy at times, but can't say I've really missed it. Were too busy to take the time and trouble.

Joe
www.normansignco.com (http://www.normansignco.com).

[cabnet636]

the spoil board is screwed down or pinned with aluminum nails, the vac will pull it flat

yes that is the plenum before spoil board.

there is also some more info in the modifications section of this forum
jim

[cabnet636]

to a great extent joe is right, unless you are processing panel most of the time (Cabinetmaking) then the vac is a bit of a nusience, i use clampsystems, screws and bricks (just kidding) for most all non panel work.

jim

[CajunCNC]

Without vacuum, wouldn't a piece move from the force of the bit after the majority of it's perimeter was cut away?

Let's say you were cutting 50 paper plate holders with logos for a company picnic out of a 4X8 sheet of MDF. What is to keep the "plate holder" you are cutting from moving once all but a .25" is left to cut. (TAB & hand cut later?)

Sorry for all the questions, I intend to attend a "CAMP" as soon as possible. . . Work is in the way right now, but "downsizing" is on the way at my office.... That's why I need a ShopBot . . :-)

[joe]

Steven,

There's gotta be dozens of examples of where a vacuum hold down would come in handy. Fortunately I've not been in a position to need it.

[CajunCNC]

Joe, thanks . . . .

But I did not mean to question you, only curious if my scenario is where you would HAVE TO HAVE a vacuum system . .

Thanks, "Still Learning, always will be . . ."
Steve :-)

[cabnet636]

you can create tabs in most software. vectric is easy to use, in a full sheet application i would tab then create on more cutout path and run it slow.

jim

[benchmench]

Steven,

This thread was very helpful to me when setting up my vac table: http://www.talkshopbot.com/forum/messages/7/28298.html?1205515838 And have been very happy with it.

The multiple zones of different sizes work well together for panels or individually for small projects, such as the 2'x2' zone. Machine small parts by placing small strips of 1/4" melamine face-down around any uncovered areas, directing the vacume to the project.

If you use a downcut spiral bit to cutout your project, it will pack sawdust into the cutout area, further holding it down. In fact, with the vacume off it is hard to lift or move the part. Cutting out a sheet of pie plates would be easy as, well, pie.

Another benefit of this method (with a 1/4" bit) is 2-sided machining. Turn the part over in the cutout, place the 1/4" melamine strips vertically between the part and cutout to act as shims holding the part perfectly centered in the cutout.

[rcnewcomb]

We use a different approach with vacuum since we usually are machining solid wood plaques rather than sheet goods. For our purposes we found this to be faster and more accurate than clamps or screws.

Basically we have drilled a hole in our table which is connected to a shop vac. Then we place AllStar gasket on the table and lay the piece on top. Most of the machining is V-carve or 3D. The only through-cuts are the outside profile. Since we use a downspiral bit on the profile cut the chips tend to pack back into the cut so we don't lose much vacuum

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