Vacuum Hold down for wood.

[HomeCNC]

Does anyone know anything about building a vacuum hold down setup? I would like to have one for my CNC router I am building. I know I will need a vacuum source. I just got a vacuum pump on Ebay.

Should I add a tank to this so I have a resovoir of, I guess (no air)? How do I build the vacuum plate that will hold the wood?

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[cncadmin]

One way is to make a air tight box that has many 1/16"-1/8" holes in it. Than a very strong vacuum source. You can place tape or alike around the object to provide max suck. A industrial vacuum clearner I belive would work.

[balsaman]

I have heard you don't need the little holes. Just use a MDF box. The mdf is porus and will hold the part. Use 3/8" or 1/2" MDF on the top. Add supports inside the box to keep the top flat under the suction.

Eric

[cncadmin]

Originally posted by balsaman
I have heard you don't need the little holes. Just use a MDF box. The mdf is porus and will hold the part. Use 3/8" or 1/2" MDF on the top. Add supports inside the box to keep the top flat under the suction.

Eric

Yes,but that will take alot of vacuum.

[Laff Riot]

Call a local sign shop. Ask for a piece of Coroplast that is scratched and unsellable. If they try and charge you more than 15 bucks look for another one.

Coroplast is basically plastic cardboard. If you have ever seen a Real estate or Polical sign up close you know what I mean. Coroplast has a series of hollow tube flutes 1/8" that run the length of the material. Block off one end of the coroplast with Duct tape. Grab a shop-vac with the wide pickup nozzle and using a copious amount of duct tape and cardboard seal the other end onto the shop-vac nozzle.

Use your CNC machine to pop a couple hundred holes into the Coroplast tubes for the vac.

You now have independently suctioned tubes. You can block off sections with tape when not in use. Make sure you allow enough air into the shop-vac to not stress out the motor - you can always block off holes again. Block only as many holes as needed to give you hold down. On the plus side you also get dust collection

If the coroplast does not have a smooth enough surface for the type of work you want to do ask the signshop for AlumaCore. It is the same thing as coroplast except that it is skinned with .020 aluminum on the face and back and the tubes are about 1/4" thick. Absolutely smooth. About double / triple the cost of corpolast though.

The coroplast is cheaper but IMO go for AlumaCore if you can get it. If you cannot find either locally I can give you a list of suppliers.
Let me know the type of materials you mill - I have several specialty bases that I built to switch out in seconds on my work system. If you need a sketch, gimme a shout.

[balsaman]

Yes,but that will take alot of vacuume.

He said he bought a vacuum pump, which is perfect for this setup. A vacuum pump is usually low volume, so the holy board doesnt usually suit it. The holy board is better for a shopvac, as you pointed out.

Eric

[hardmill]

Give me a day and illl sketch something for you.
What size are you looking at.
Not much vacuum is req. Ill let you know what you
need, pretty simple actually.

[ger21]

I work in a commercial cabinet shop with a large cnc router with a vacuum pod system. We have a VERY large pump and it will draw through MDF a little, but not enough to hold parts still. Most large commercial routers that draw through MDF spoilboards use even larger pumps. I'm not sure exactly how they are rated, but these pumps are larger than the cnc's we're talking about here and VERY expensive. I think I have a better solution. Last year I built a vaccum veneer press with a compressed air powered vacuum generator for under $100. This will draw much more vacuum than a shop vac. Go to http://www.joewoodworker.com for the article on how to build it. Then get a copy of ShopNotes issue 40, which has plans for various hold down jigs and a vacuum table, which should be a good starting point for a cnc vacuum hold down table.
http://www.shopnotes.com/
This is what I plan to use on the router I'm getting ready to start building.

Gerry

[HomeCNC]

Thanks to everyone for the advice on vacuum clamping. I have also been searching the Internet and have found some information.

Gerry, I have been a subscriber of Shopnotes for about 3 years now. I have that issue and forgot about it!!!

This site has some vacuum plates that they sell. I like the way they use the vacuum tape on plastic plate. Just make one ¼” hole and with creative use of the vacuum tape you can open gates or close them to fit your work size.
http://www.qualityvak.com/kaccess.html

[HomeCNC]

This is my idea for my Vacuum hold down plate. I will start with two plates that are 12" X 24" X 3/8" Alum. (I was going to have a 24" X 24" until I saw the price!!) I cut an o-ring grove in the lower plate (you can get o-ring stock in a roll from McMaster Carr). I drill a cross hole and place a hose barb in it. I make a 1/8" pocket in the upper plate so I have a vacuum chamber inside the two plates. I drill and thread 1/4-20 holes in a 2.25" hole pattern in the top plate. I plug the holes with rubber sealed cap screws. Now I built about 10 or so, small clamping plates that are about 2" square and 1/2" thick Alum. I cut an o-ring grove in both sides and drill a 1/4" hole through the middle of the plate.

To use this thing I just remove a screw and place a clamp plate over the screw hole to receive vacuum. This gives me the ability to create vacuum hold down shapes where I need them.

[cncadmin]

Very nice that should work very well!

[paulried]

Here is one I saw while visiting ShopBot in Raleigh, NC. Pretty simple and hooked up to a vacuum cleaner. The plate at the front is what regulate the amount of vacuum. The grooves where sealed with clear varnish bottom and side. The parts are caulked together to avoid vacuum leaks.

[Laff Riot]

I didn't have a pic the last time I posted on the AlumaCorr product. This is a small piece of a 4x8 sheet. The channels run end to end between the faces.



http://www.nudo.com/nudosign/Alumacorr/alumacorr.htm

Cost of a 4x8 sheet of this material 5mm thick is 65.00. I run it off a vac. Im sure a sign shop will sell you mini pieces for whatever size table you need for 20 bucks or so. If you need the same function but in a soft plastic that wont bust bits use Coroplast. $7.90 for a 4x8 sheet.

Im not saying my way is the best way by any means. I reposted on this because I think the pic explains a lot of what I tried to get across last time.

[HomeCNC]

I found a nice web site for the vacuum tape. www.allstaradhesives.com I have ordered two different type of pod tape after talking to the engineer at the company. I will soon have my POD system up and running for my CNC router.

[ger21]

I've been using their stuff for a few years now on the pods on our point to point at work. I thought you already knew what you were going to use or I would have pointed you that way a few weeks ago. Post some pics and let us know how it works.

Gerry

[tsalaf]

You might consider attaching the vacuum hose directly to the pods. That way you can have several pods that will “stick” to any smooth surface. The pods can be permanently attached to a manifold and controlled with simple ball valves. This will also let you dispense with the vacuum box.
If you do decide to build a box, you will need to use braces in the centre as the pressure generated by a properly functioning vacuum pump will easily collapse an unsupported 3/8 aluminum plate.
As an aside, a 2" square pod will generate approx. 40-50 lbs. of holding force (depending on air leaks). This is barely enough for light cutting. To increase the holding force, you have to increase the surface area of the pod, or the number of pods.. Figure on 10-12 psi of holding pressure (allowing for air leaks).

[HomeCNC]

I did not think of the material under the vacuum chamber bending. I will machine the chamber with islands all over the place to prevent the plate from bending.

[Scrit]

HomeCNC your vacuum pump won't need a vacuum reservoir unless it is a very low capacity pump. What it will need, however is a vacuum filter on the machine (workbed) side of the pump. This stops the pump from ingesting dust and crud (and thus damaging itself). You will also need a vacuum gauge. This helps to indicate whether you have sufficient vacuum to hold the piece you are about machine. In a real world scenario (I run a CNC router) I find that I need at least 40cm Hg vacuum (that's about 16in) to hold timber/sheet ply/MDF components, although my machine does have a 120 cubic metres/hour pump.

To hold work I currently use a vacuum pod system, with specials and small pieces being held on purpose-made spoilboards bolted onto the pod bars. My spoil boards are normally machined from birch ply with foam rubber gasketing. I have tried MDF, but it tends to swell with age (it absorbs water and has to be remachined once or twice a day in changeable weather) and requires much more sealing. Remember to seal the edges and surfaces of any spoilboard (I use shellac or a thin coating of UF/RF glue, but then again I have them both in plenty). I also surface any spoil board on BOTH sides with a trepanning cutter before use. My purpose-made spoilboards use hard plastic pipe and plastic push-in connectors. Connections onthe underside are screwed into the bottoms of the spoilboards using air tool connectors (1/8 in thread x barbed pipe end) which have had a slot filed at right angles to the threads - this acts as a self-tapping fitting.

[HomeCNC]

Well I finally had some time to work on my vacuum hold down system. I got the plate finished and built the pluming with the vacuum gauge. I made small rubber washers for all the ¼” screws in the plate and sealed them all. With the pump going I read the gauge and it said 29.65.

It’s now time to make the pods and use the vacuum tape and try it out on some wood. More to come.

[mace]

Here is a system i used back in the day on a koma 5'x12' quad head router.
Depending on size of final part it can hold 3" thk al. plate
You can get good ideas or just purchase from them.

http://www.carterproducts.com/produc..._id=1&cat_id=9