Shop-Built Vacuum Pod Solutions

      Here's a detailed discussion of making your own vacuum hold-down pods, with a side discussion on laser positioning and router control. February 19, 2013

Question
I have a flat table router I'm hoping to start using for door parts, necessitating pods, or the like. I've read all the threads on the subject and would like to manufacture my own, and possibly use a smaller pump to operate them. I like the rubber-top pod idea. Does anyone know what the material is and what the durometer might be?

If I run them off a smaller pump, what size is adequate, assuming good seal? I notice that they are rated by hp, cfm, and other criteria. Interestingly the cfm and hp don't seem to have as direct a relationship as one would expect. I wonder if there is some fudging of numbers going on. Any other advice about pod/system design would be welcome.

Forum Responses
(CNC Forum)
From contributor H:
You really need a soft rubber to seal it up. There have been previous discussions about making your own and using gasket tape to seal up the cup. You can also purchase some ready-made cups from Better Vacuum Cups. In regards to the your question about the vacuum pump. If everything is sealed, you don't need a large pump. It also depends upon what the maximum number of cups your plan to use. If you have a smaller pump and a lot of cups it can take it two-three minutes to get to full vacuum. The larger capacity for the pump, the quicker it builds up vacuum and can handle any vacuum loss.

I would recommend using at least a 10hp pump. I tend to recommend Busch or Becker vacuum pumps. The hp to vacuum isn't related due to the type of vacuum pump. There are different types and some require a more powerful motor.



From contributor B:
We run screw down vacuum pods on our MDF table almost exclusively. The MDF spoil board is just for screwing down the pods, not for through vacuum. We use 3/4" thick PVC pods I made about 15 years ago and have yet had to replace. The pods are oval shaped, about 5" long and 1 1/2" wide, 2 1/2" wide and 3 1/2" wide for different parts holding. The PVC is available from McMaster-Carr. Round 1/4" closed cell gasketing is inserted into a 3/16" slot around the perimeter of each pod. They are also available from McMaster-Carr. I made the pods right on the CNC.

For a pump I currently run a 5hp Gast pump on a 30 gallon tank. However for years I ran this system with a 3/4 hp Gast pump and a new and "empty" propane grill tank for vacuum storage. A large volume of air pull is not nearly as important here as inches of mercury pulled. I believe the 3/4 hp Gast pump is still available for under $100 from Surplus Center in MN. You will need to add a starting capacitor and a pressure switch but both are available at reasonable prices from Surplus Center. A large volume of air is not necessary because you are only removing air from the manifolds, 1/4" tubing and the small space between the top of the pod and the bottom of the wood.

I had a local welding shop put end caps on two 4' lengths of square tubing which I then drilled and tapped for valves - one on either side of the CNC act as manifolds. I run 1/4" tubing from quick connect fittings on each valve to a quick connect fitting tapped into the end of each of the pods. A roll of masking tape hangs on a hook on the end of the CNC for taping the tubing down to the table surface.

Parts positioning is the last part of this equation. I used to draw the parts with a magic marker we keep in T1 on the CNC. We stretch a sheet of 6' wide brown kraft paper over the entire table surface for drawing. We get this from the local cardboard factory as roll ends. We would screw the pods down between the magic marker lines and then put our wood blank in place. If you looked straight down and couldn't see the line we knew the router would cut the part. Now we use an S-L Laser for parts placement but still keep the magic marker in T1 for other uses. This is an incredibly simple to build and efficient to run system. We've cut thousands of our curved moulding blanks with this system over the years.


Click here for higher quality, full size image



From contributor A:
To contributor B: Why would you use this system instead of a pod and rail machine?


From contributor B:
I've never used a pod and rail machine (Point to Point I believe) but have seen plenty of them. The downsides I see are: First - I have my CNT Motion router and it does everything we need fast and efficiently. I could never get a large machine that does not dismantle into our shop space and I think that would rule out most any Point to Point. Also the CNC sits on a wood floor and the all-aluminum CNT machine is ideal given the weight limitations.

Second: My S-L Laser shoots the laser lines down onto the surface of the router. With a Point to Point I think we would have difficulty with this process.

Finally: With the flat MDF table surface we can screw the pods down anywhere - even put three right together within an inch or less of each other if we need. This might be an issue trying to do it on a Point to Point.



From contributor A:
Thank you for taking the time to explain Contributor B. Being able to place the pods so close together makes perfect sense. Does your router have a taller z than normal?


From contributor D:
Which model laser did you get? Do you mind me asking the price? Did it integrate smoothly with your router? Their website didn't give a lot of info, and I'm confused about one thing. If the laser projects the line on the spoilboard so you can set the pods, doesn't the position of the line change when you add the 2" part to the pods? Do you need to reset because of the 2 3/4" height difference between spoil board and the top of your blank? I hope this makes sense. Also, can you project more than one part at a time?


From contributor H:
The question shows perfect sense and a clear understanding on your part of what is involved. The laser has no direct integration with the CNC control. It is an independent product with its own software package. It runs from the same Windows PC as the router control software but like any other Windows program you just switch between windows.

I picked up my unit as a leftover demo so I acquired it for about 40% off. I looked for a long time before finding this deal and consider myself lucky to have found it. Even with this purchase situation S-L Laser was very helpful in the setup, even giving me a call on the weekend to make sure the installation was going along okay.

The laser program gives you a lot of setup options so you can arrange the screen to meet your needs. I have individual on-screen buttons that correlate to the wood thickness we are placing on top of our 3/4" thick pods. When setting up we first "put the laser on the table" and mount the pods between the projected moulding lines. Then we shift the laser to the top of the wood and set the wood blank on top of the pods. A single mouse click is all it takes to make the change.

You can indeed project more than one part at a time. You are limited by the total number of arcs and lines the laser can keep on the table without them beginning to blink on and off. The laser is fast but it can only do one arc or line segment at a time. If you have a circle or square for example it is so fast you would never see the fact that one segment has turned off while it projects the next segment. It continues around the square or circle repeatedly which makes it look like the entire object is always on.

However if you have a 4x8 sheet with dozens of parts drawn it will project one at a time and you might have to wait a half second for the first one to light up again. When we have large sheets like that we will typically either break it into two or three laser files or just project the four corner images to position the sheet. The laser is also plenty bright but in situations like that it can be helpful to turn the room lights off. I'm not sure of the model number of my unit but it is the standard sized unit - about 20" long and 12" high and 6" thick.


Click here for higher quality, full size image



From contributor B:
We're at around 9 1/2" Z-axis clearance with the 3/4" spoil board on the table.


From contributor D:
If there's no integration between laser and router, how does the laser know where to put the part? Are you nesting in the CAD software? Our router has its own nesting program. We just load dxf files and then manipulate them at the router.


From contributor B:
Both the CNC and the laser reference off of x0y0 on the CNC table. When I apply a router bit to a tool path with Enroute I also apply a laser "bit" path. Both the physical router bit and the laser line follow the same cutting edge.

I've never used it but I think the S-L Laser may also read dxf files. If I'm correct then whatever manipulation you do at the router would have to be duplicated in the S-L Laser software.



From contributor S:
I posted a similar question last year and followed Contributor Bís advice and built some out of 30mm gray PVC board. They have worked well. We did some really tall pods (4") to give tool clearance from the tooling hanging over the edge and the air lines. We used our CNC to machine them of course. For fixed jigs we have machined pods out of MDF and then sealed them with Titebond glue on the top, bottom, and edges.


From the original questioner:
I think the higher clearance would be desirable for my intended use doing entry door cope and stick with shaper tooling on an arbor.



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