CNC pod table

      Homemade pods and more. (CNC Forum) March 23, 2003

Our machine currently has a phenolic table for 3" pods but we do not have enough pods to use it and they are very expensive to buy from the manufacturer. I figure if we are going to spend the money we are best to find a better system.

I'm looking into Carter pods but would like to hear from those who have made their own as well. We do quite a bit of panel production using MDF, plam and melamine sheets.

I'm used to SCM matrix tables with their "Lego block" pods and I quite like that system. I'm new to this company and for the past while they have been using 1/2" MDF bleeder boards, which I find less than adequate. Our feed rates are very slow and we cannot utilize a broad range of the tool when the area cutting the surfaces gets dull (i.e. plam or melamine), as the tool is already on the table surface. I saw an earlier post on a custom made table and delrin pods and I quite like that idea.

Forum Responses
(From WOODWEB's CNC Forum)
Some questions which may help us better understand your problem:
What are the problems with the current setup?
What size vacuum pump are you currently using?
What feed rates and tooling are you using?
Is horizontal boring one of the reasons you would like to see parts placed on pods?

From contributor D:
Bernie Davis has developed his own pod system that uses screw-down pods that fasten to a spoilboard. Perhaps that would work for you. We're just now making some pods for our lab router based on Bernie's design. One advantage is that this system doesn't require a monster vacuum pump.

From the original questioner:
I started at this company in August. It seems before this, both programmer and operator positions had turned over frequently. My predecessor (programmer) seemed to have little interest in trying new things to improve on what was already being done.

The main thing I don't like about bleeder boards is we don't seem to get enough suction and end up cutting 3/4 material at approximately 5-6m/min. I am much more used to being up 18-22 m/min with 1/2" solid carbide spinning at 18k. Our machine has a maximum feed of 12 m/min (another thing I hate), but I feel we should be running at this speed all the time. We cut so much melamine, plam and MDF I feel a pod system would serve our needs much better as we do 90% panel production using full sheets. Parts are usually sized between 6-10 pieces per sheet so there is ample room for 4-6 pods per part. We do not currently use the horizontal bore head and this could be utilized if the part was elevated. Our company uses only dowel construction (no dados). We also cut a large number of door lites and as the size is always different - pods would work well here too. I like having the flexibility of being able to buy tools with cutting edges longer than required so one can adjust where the surface contacts the tool as wear occurs. My tool preference is a 1/2" solid carbide compression spiral with 2 flutes, although I am going to try singles due to the slow feed rate of our machine. Our vacuum pump is a Becker VTLF250 with a rating of 800mbar (?) I doubt vacuum should limit any pod system as this pump seems similar to any I have used previously. Carter pods are starting to look good unless I can find a way to make my own for less money.

I program using AlphaCAM and in previous jobs I would import a table/pod drawing behind a part program so the operator would know where to place pods. That system seemed to work well.

Contributor D, could you tell me a little more about the pods you are building? I would like to build a pod vacuum table but the price to use the Carter systems is a little expensive. It would be nice to find a lower cost method for now.

From contributor D:
Here's some more on the home-made pods:

We're using 3/4" thick rigid vinyl from Laird Plastics from which to cut pod shapes. We're making 4" rounds and 3" x 6" rectangles. The gasket that Bernie used is 1/4" diameter closed-cell (EPDM?) material from McMaster-Carr - about $14 per 100 feet.

Each pod has a groove just inside its periphery to accept the gasket. The groove, I think, is 3/16" deep by 1/4" wide. (I'm not at the shop just now.) The center area of the pod is cut at the 3/16" depth to distribute the vacuum, and a deeper slot across the inside of the pod carries the vacuum from a hole in the end with a nylon tubing nipple for 1/4" semi-rigid plastic tubing from Lowe's.

At the middle of each pod, a counterbored screw hole allows the use of a drywall or deck screw to fasten the pod in place on the spoilboard. Longer pods might require provision for two screws. (If you're concerned about accidents taking out router bits, you might use brass screws.)

The manifold, in our case, is a piece of 1.5" plastic pipe along one side of the router table which is drilled and tapped for 1/8" pipe nipples and capped at each end. We will screw short 1/8" pipes along the length of the plastic pipe and add simple shut-off valves to each line (from Lowes or McMaster-Carr, or your local plumbing supply at about $5 each). 1/8" pipe-to-tubing fittings connect the 1/4" tubing to the valves, and carry vacuum to the pods. The vacuum inlet to the pods is kept as low as possible in order to avoid damage to the tubing and fittings from the router bit. Bernie uses masking tape to hold the tubing down against the spoilboard out of the way of the cutter. That should work for us as well.

We're setting up for ten pods to start with.

Bernie makes his pods in an elliptical shape which is better adapted to the curved moldings that he usually cuts on his router. He uses a low-power vacuum pump, but is able to hold parts securely with his system. We have purchased a 3/4 hp Gast pump for this application, and Bernie says it's probably all we'll ever need.

We have a large reservoir tank, and as recommended by Bernie, a whole-house water filter to keep dust out of the vacuum system.

Our router has a 5' x 10' table, as does Bernie's. If you prefer to use a melamine surface on your router table, you might adapt this design by screwing and gluing (use vinyl pipe adhesive) two pods back to back, so that you could eliminate the hold-down screws and let the pods hold themselves with the vacuum against the melamine surface. You'd also get a higher (1.5") working height. If you try this method, let us know how it works.

We're just preparing to cut a nest of pods this coming week. (We've been busy building 5 of our "702" digitizers to fill some orders.)

To the original questioner: What machine do you own?

From the original questioner:
We have an Anderson EXXACT 51 with what I understand is the old style phenolic '3" round pod' table (5x10). We have so few pods we're into a whole set anyway so I figured it would be a good time to look at other options. I'm not concerned about cost of the table (phenolic, UHMW, MDF, etc) but I'd love to find a very cheap pod, to make or otherwise.

From contributor G:
You might want to take a look at a previous post on this forum, "Universal Spoil Boards." The setup pictured allows the use of pods, bleed boards, as well as conventional fixturing. I purchased the 4-1/4" pods for $12.50 each, the 2-1/4" pods for $10.10 each, and the locator buttons for using the small pod in the large seat for $6.25 each.

I have done extensive work with the Carter pod system. While it worked adequately, I found that I had a lot of dead area without vacuum under the part. I use a product for my table that is the best you will find out there for dimensional tolerance over time, such as shrinking and expanding. The product is called Richlite made by Renaier Richlite. As for the Carter pods, I have used the same pod table that I made for them but have designed my own pods that actually fit the part area. I have gained over 3 times the holding power that I had with the carter pods. I drew the new pod up in Alpha Cam then machined them right on the table on top of my current carter pods. Delron is a good product to machine your pods out of, also for the dimensional stability. My biggest suggestion to you is make a layout that suits your specific needs. I have spent a year on different setups and products to find what worked the best for my situation. I also use the gasket material referred to by contributor D that he purchased from Mcmaster-Carr in the tops of my pods for my parts to sit on. It works great and it is inexpensive.

From the original questioner:
We got the Carter video yesterday and since we mainly do panel production using full sheets I think the system would work well for us. The main drawback is the cost of the table material. Seems that a sheet of Richlite 5x12 is approximately $2100 USD! That's over $3000 CND for the table alone. I think I'd have a hard time convincing the owner to go for that. UHMW is much cheaper and it's more likely.

We're looking at all options at the moment and I have stumbled on a very interesting possibility which we are about to test. Let's just say these "pods" look to be costing approximately $3 CND each (if anything, less) and you can find them at Home Depot! They will utilize our existing phenolic table bed but we will have to do some minor machining.

From contributor G:
Be aware that UHMW has a thermal coefficient of expansion over three times that of cast iron. If your shop has a 40 degree swing between summer and winter temperatures, 12 feet of UHMW will grow and shrink nearly 1/8". If you try to use sheets that are too large, they will crawl around and sometimes buckle. A couple of expansion joints will keep a 5' by 12' table from buckling, but any reference bushings or grooves in the plastic will still move around some.

Good luck with your pods. I made some out of PVC pipe with a lip cut around the top and bottom edges for o-rings. This worked very well with warped parts because the o-ring would roll down the outside of the pod when the vacuum was applied. Unfortunately, the o-ring frequently rolled off of the pod when a part was dragged across the top.

As contributor G stated, the Thermal Coefficient of UHMW is terrible. Not only do you have to watch the temperature change in your shop but also the humidity level. UHMW has a large water retention level which will make it expand and contract also. You may want to do a little research on other products before using one or the other that fall into the price range you are looking at.

From contributor D:
Correction: In a previous message, I wrote that our seal cord grooves were 1/4" wide by 3/16" deep. The depth is right, but the width is only 3/16".

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