Converting a Point to Point CNC into a Flat Table

      Here's a discussion of the practicalities involved in modifying a pod-and-rail point-to-point CNC with the vacuum and spoilboard flat table required for cutting parts out of large sheets of material. December 28, 2010

Question
I have had a Biesse Rover A point-to-point CNC for 3 years, and am looking for anyone that has tried to convert a point to point machine into a flat table. I don't intend to make this a permanent change - just when we need to cut several small parts. I think one big concern is the increased suction you need from the vacuum. Any thoughts?

Forum Responses
(CNC Forum)
From contributor D:
I made one with two sheets of 3/4" MDF. First I arranged as many pods as I could in a 96" x 48" area, evenly and close to the perimeter all the way around. Then drilled holes in the first sheet to allow vacuum to pass through. On top of this sheet I routed a groove around the perimeter for a gasket, then a grid network of grooves which connected all the holes and covered the surface, leaving no areas greater than 6" x 6". Think of it as one giant pod. This sheet was then painted to stop any parasitic loss of vacuum through the material itself. You want 100% of your vacuum in your grid. The second sheet, or spoilboard, is basically a sponge in use, so I use Trupan Ultralight to get maximum air bleeding through it. You'll want to paint the edges only of this sheet. It will swell and also not be perfectly flat yet, so you'll need to skim the surface, which will be your new Z. It should be skimmed occasionally to true it up and erase your through cuts. There are spoilboard cutting tools made just for this that are worth buying for the time savings.

The limiting factor in suction will not be your pump as with a flat table, but the smaller diameter lines in your rails and pods, which restrict CFM. I currently am experimenting with increasing vacuum by utilizing our powerful central dust collector directly connected to our grid board. Not looking to automate it, just routing a mechanical valve within easy reach.



From contributor M:
You said, "just when we need to cut several small parts." Do you mean that you need to cut them out of a 4 x 8 or larger sheet of material, or smaller blanks of material? Did you know it's fairly straightforward and easy to create a vacuum fixture for through-cutting small hardwood, or odd shaped pieces of Corian, aluminum, etc.? I couldn't tell from your post what your intention is. I have a flat table machine, but still use fixtures for tiny parts or very large solids due to holding ability.


From the original questioner:
The intention is for cutting parts out of sheets of plywood.


From contributor I:
You could just onion skin the small parts in a sheet. Then finish the cutting with a flush-trim router. I've used this method in the past on point to points. It works well and you don't have to screw around with any temporary setups.


From contributor M:
That being clarified, I would see what options Biesse has for you with conversion tables. I would bet they will want to supply you with at least one more vacuum pump in order to get enough flow to hold down parts. The small pumps on pod and rail machines are designed to pull a vacuum in small localized areas, not large footprints like a 4 x 8 sheet presents. I looked at a conversion kit for a pod and rail machine about 10 years ago, and part of that included a pump. I ended up not buying it for a number of reasons. We ultimately bought a used flat table router to handle the nesting duties.


From contributor A:
I have done several of these conversions. It is accurate that an additional pump may be needed if the intention is to run standard sheet sizes. If you only want to run offsize or smaller sheets, your existing pump might be adequate.

It really is applications specific. I am not sure I understand the end result desired here.

One company I worked with converted an older Biesse to a flat table to make very small, ornamental product. They run 4 x 4 sheets in a pendulum fashion. They could have run 4 x 8 sheets, but the 4 x 4 sheets nested better and appeared to be much less of an ergonomic issue for them. They onion skin to within .1-.15 mm, then run the sheet through a wide belt sander with individual components dropping into a box on the other side. Typically you will use some Y axis travel on a point to point, so yield could be a factor to consider.



From contributor C:
We currently have a Biesse CFT (convertible flat table) on the floor. These large pods in conjunction with a high flow manifold and a larger pump convert a standard pod-n-rail machine into a nesting machine. The matrix top for pods is not necessary if your only intent is nesting. Note: Aluminum was used for stability. Definitely something you can do on your machine. Our door is open if you want to see them.


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