PDA

View Full Version : Vacuum Fixtures for CNC Router



Stepside
12-06-2014, 02:50 PM
The following pictures are of a vacuum fixture I made for a local High School. In this case it was for a wood router. The problem in school shops is the number of students compared to the number of machines. The one hour work window is the second issue, because if the student can't remove and replace the project, the machine is tied up until the next day. This means the other classes do not have access to the machine.

With the Melamine board and the foam cord one can hold the fixture with vacuum. This is a much larger fixture than the one I described in the latest issue of Digital Machinist.

The 3 pegs sticking out of the Melamine are used to index the fixture. The Fixture locks the parts in with the 1/2-10 Acme bolts.

The pictures are 4 legs for a stool.
http://i1148.photobucket.com/albums/o563/72stepside/SHOP/photobucket/DSC_0990.jpg
http://i1148.photobucket.com/albums/o563/72stepside/SHOP/photobucket/DSC_0986.jpghttp://i1148.photobucket.com/albums/o563/72stepside/SHOP/photobucket/DSC_0976.jpghttp://i1148.photobucket.com/albums/o563/72stepside/SHOP/photobucket/DSC_0974.jpg

gundog
12-06-2014, 05:20 PM
I have built several vacuum tables for my CNC routers here is a post I made on another forum about one of them. I recently upgraded routers and built another table I will see what pictures I have for that one.

http://www.talkshopbot.com/forum/showthread.php?t=19277&highlight=vacuum

gundog
12-06-2014, 06:19 PM
This is my current machine a Shopsabre IS 510 it has travels of 75" x 125" x 16". I am setting it up with a 54" x 96" vacuum area with 5 zones that can be turned on or off or can be all on at the same time with 2 vacuum motors that can run parallel for twice the CFM or ran one at a time if both are not needed and usually they are not. I used the same manifold system shown on my earlier router. The vacuum manifold is made from ABS sewer pipe and the valves are also ABS sewer knife valves made by Valtera. The ABS pipe and valves are rated for vacuum. The mount the vacuum motors outside because they are quit noisy. The switches to turn on and off the vacuum motors are mounted on my control stand. I use a vacuum gauge to monitor vacuum pressure.

The vacuum plenum is machined in place on the machine from dense particle board I then sealed it with varnish. The spoilboard is made from fiberboard the type I use is LDF light density fiberboard made by Trupan. I have used standard MDF from the big box stores and it works ok to. The vacuum is sucked through the fiberboard and holds sheet goods in place. One of the pictures shown is machining 1.25" UHMW held in place by this vacuum system.

The new table when complete will have an aluminum extrusion clamping area in an L shape around the vacuum zone for clamping fixtures and vises for maching parts that can't be held very well by vacuum.

There are a couple schools of though on vacuum clamping one is high vacuum low CFM flow like they use in vacuum pods and then there is what I use lower vacuum high CFM flow for larger parts. I machine mostly plastic and aluminum and most of my plastic parts are not machined all the way through so holding vacuum on a full sheet is easily accomplished with one vacuum motor drawing only 7.5 Amps @ 240 volts. The vacuum motors are built in house vacuum motors and cost a little over $100 ea and last me several years before I change them out. The secret to longer life is allowing some air flow that is how they cool if your vacuum is so tight they can't flow any air they burn out due to heat.

http://img.photobucket.com/albums/v292/millnut/IMG_20140727_132012_927-1.jpg (http://smg.photobucket.com/user/millnut/media/IMG_20140727_132012_927-1.jpg.html)

http://img.photobucket.com/albums/v292/millnut/IMG_20140727_131923_070.jpg (http://smg.photobucket.com/user/millnut/media/IMG_20140727_131923_070.jpg.html)

http://img.photobucket.com/albums/v292/millnut/IMG_20140728_165512_597.jpg (http://smg.photobucket.com/user/millnut/media/IMG_20140728_165512_597.jpg.html)

http://img.photobucket.com/albums/v292/millnut/IMG_20140712_104244_7091.jpg (http://smg.photobucket.com/user/millnut/media/IMG_20140712_104244_7091.jpg.html)

I think your bigger problem might be how to remove parts and get them zeroed back with your machine. You would need some type of permanent fixture and a way to re-zero to exactly the same coordinates to go back and continue machining the same part without leaving a watermark from the different cuts. I would think you might need an electronic probe to get your coordinates the same. Maybe it is time for the school to get a bigger machine to allow you multiple fixtures so the parts may stay in place. It has been my experience the hardest thing to do is remove a part and find the zero point exactly again. It is easier with my new machine with servo drives than my old stepper driven machine and I would expect your to be like my old one.

Do you have limit switches you can use to get your zero set to the table?

J Tiers
12-06-2014, 07:58 PM
That's a nice way to reverse the problem!

The router we had at my old work pulled the vacuum right through a piece of particle board.... but it had about a 15 HP pump. Reversing the vacuum makes replacing the "carrier" easy. I like it!

Stepside
12-06-2014, 07:59 PM
Gundog

Thank You for the pictures and the information. My purpose is slightly different with this setup. By using fixture boards the students project stays in position for a series of removes and replacements on the router. The little vacuum holdowns in the magazine write-up are both locating devices and holding fixtures combined. This is not to say that the small holding devices could not be combined with the larger fixture boards.

For a pump we are using a 110 Volt 1/8 Horsepower Gast unit. The pump pulls 23in/hg and due to the small volume of the plenum clamps the fixture quite quickly. The plenum is the space created by the 1/8" diameter"closed cell foam" cord. Cost with gauges and fittings jusr over $400.00-$450.00. The pump will be used for Vacuum Bag glueing as well so built a partical trap for anything that can get sucked up the 1/8" ID hose.

Pete

gundog
12-06-2014, 08:16 PM
I am not sure how your machine is setup but with my old stepper driven machine shutting the machine off and back on say one day to the next which is what I assume you do for the student work my old machine would be off. On that machine I used the limit switches in X & Y to give an offset to my 0,0 corner but it was never completely perfect close though. In wood that may work because it can be sanded out for plastic it shows up real bad. If it is working that is great I was just going by what I had experienced. The newer machine has to be homed when it is turned on and returning to the same zero is no problem as long as you have a way to return the part to the same place or not remove it from the table.

With the old machine if I started a file I finished it all before removing the part or turning off the machine or it was hard to get everything lined back up perfect. Now I can just turn off the machine and start it again the next day no problem but I still don't move anything off the table.

I machine some parts on both sides and that takes a little time to get them lined up but that is another story.

Mike

Stepside
12-06-2014, 09:06 PM
Gundog

The three pins are there to put the part close to the same place each time. There is a X and a Y location on the fixture that the student has to align to before starting each day. I agree that it would be best to go from start to finish without shutting the machine down or removing the fixture. This is not possible in the school setting due to time constraints. The same school has a 48 x 96 inch machine as well, so it would be possible to put several parts on at one time, but the same old time restraints are still in effect.

Pete