Making Your Own Vacuum Pods

      Lots of CNC owners have successfully machined or molded their own hold-down pods. Here are some detailed explanations and photos. October 26, 2011

Question
Anyone with experience using PVC vac pods? Is PVC too slippery for vac pods? We would be making 4" - 6" - 8" pods for holding down small solid hardwood parts for machining. Before we go to the time and expense of buying PVC sheets and machining our own pods, I want to make sure the result will be satisfactory. PVC seems so slippery so I just wonder if the pods would not hold small parts well.

Forum Responses
(CNC Forum)
From contributor D:
It's not really the pod that's holding the work; it's the vacuum and the gasket. The friction against the gasket material is probably the one thing keeping the work from slipping sideways, but adequate vacuum should prevent that. I think that PVC would work fine for what you are doing, but I would also make a test piece first, before making up a bunch of them.



From contributor B:
We make exact replacement pods and special use pods for our Biesse out of paper core phenolic sheet. We get it from MSC.


From contributor Z:
We made a silicone mold of a pod we liked. Then we poured a soft urethane for the contact surfaces and harder urethane for the body of the pods and they work great. Best thing is that once you have a mold you like, you can make as many as you want.


From contributor W:
Do you mean that you poured a little of the soft into the mold first and then poured the harder mix in on top of it?


From contributor Z:
The mold we made is for a 100mm tall pod. We open the mold and then pour an 80a urethane in the bottom of both halves. That gives you a slightly flexible surface that contacts the table and the work piece. Then we assemble the mold and fill it with 90d urethane. This gives you a solid center to the pod. That way you minimize flexing of the pod during machining.


From contributor H:
Over 10 years ago I made oval PVC pods for holding our curved moulding blanks on the CNC. Although a bit abused now, they are all still in use.

I used 3/4" gray PVC I purchased in 12" x 24" sheets from McMaster-Carr. I cut the pods out in 3 sizes... 1 1/2" x 4", 2 1/2" x 4" and 3 1/2" x 4" for various moulding sizes.

A 3/16" groove 1/4" in from the perimeter on one face receives 1/4" round closed cell foam to form the gasket. The center of the same face has a slight recess to create an air space, beginning abut 1/4" in from the gasket slot. Finally there is a recessed center hole for screwing the pod down to the spoil board. A washer head screw works just fine here but you could use a rubber gasketed washer head screw as well.

In addition to the above details there is a 1/2" slot down the face side of the oval that goes right through the recessed screw hole. The slot starts about 3/4" in from the 4" ends of the pod. From one end I drilled and taped a hole in the 3/4" edge of the pod to receive a 1/4" quick connect tube fitting. The hole goes right into the end of the slot just mentioned. 1/4" polyethylene tubing connects the pods to a vac manifold running along the edge of the table.

These pods have held thousands of mouldings over the years. They were quick and easy to make and have proved extremely durable. If we do nick one with a bit we simply repair it with PC-7 epoxy, which even matches the color of the PVC.



From the original questioner:
Thanks. We just ordered a sheet of 1" thick PVC. We just made a passage door fixture out of our old phenolic table top with the grooves all filled in. The pods work okay, but never again! We probably used a gallon of Bondo filling the old grid lines. Plus at 17mm thick, it was challenging to do piping, especially on double sided pods.


From contributor H:
Here are photos of the vac pods.


Click here for higher quality, full size image


Click here for higher quality, full size image


Click here for higher quality, full size image


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