CNC vs P2P

      Defining the difference between P2P and CNC. June 13, 2001

Please define the difference between P2P and CNC.

Forum Responses
Not so long ago, the distinction between a CNC router and P2P was as simple as how the parts were held in place.

A CNC router used a vacuum table and a sacrificial piece of LDF (low density fiberboard), to hold the part while it was being machined. If running the same parts over and over, the LDF can last a long time (weeks). If lots of different parts are being machined, the LDF only lasts 8-10 sheets of material in nested base operations. The CNC router had no "standard" origins, so the part(s) can be programmed to be machined essentially anywhere in the working field of the machine.

The CNC router does what it is told, and the program is normally stepped through to verify the program at slow speed. There is additional software available for most routers to verify that the program part is not exceeding the physical limits of the machine, or hitting the vacuum table.

A P2P used a pod and rail system, making setup faster and easier. The panels have to be accurately cut before they can efficiently be machined. Normally, pins are used to index the part to fixed origins, and automatic mirroring can be accomplished by selecting a mirrored field.

Horizontal operations are much easier to accomplish with a pod and rail system. However, since the pod(s) only hold a percentage of each part, the part may not be pulled flat for machining operations. This normally doesn't show up unless there is a profile on the edge, or horizontal operations.

Now, the CNC machine can be called a machining center, regardless of if it is a "CNC router" or a "P2P", or has been called one or the other in the past. There are numerous variations of work holding currently available--rails and pods, vacuum tables, both of these with dedicated jig fixtures, both of these with flexible jig fixtures (a matrix or grid that can be customized by where the vacuum seal is placed). There are "shoes" or supports that can be placed on a table to hold the part above the normal work surface to allow horizontal operations to take place or profiling. Then there are clamping options for parts that can't easily be held by a vacuum system. Parts can be clamped to aid a vacuum system, or totally clamped, eliminating the use of a vacuum system.

If you are interested in a machine, have your product run on the machine, from start to finish. Pay attention to the programming and setup of the machine. It doesn't accomplish very much to be able to machine parts at 30 MPM if it takes a factor of 30+ to program or set the machine up to run that same part.

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