Chip-out on HPL panels

      Solving problems with chip-out during CNC machining. August 12, 2001

Our shop cuts doors and drawer fronts from 2-sided HPL on 11/16 pb using a 2 flute 3/8 compression bit. They are cut good side down, as the CNC does the machining for the European hinges we use, as part of the milling process.

The laminate is so abrasive that we experience chip-out on the bottom after cutting only 2 5x8s of sheet goods. At this point, we lower the Z offset to get a sharp edge to cut with. We get approximately 6 sheets per bit, as well as using up a sacrificial 1/4 MDF spoilboard.

Anyone else have experience with this?

Forum Responses
I have seen the same problem. I use a solid tungsten "up-cut" spiral for this. I also have an up+down cut with interchangeable tips that gives a good finish on both edges.

Contact your tooling supplier. Tell them what you're cutting and get the recommended feed rate and RPM for the tool.

Try oscillating your cut depth as you are cutting, so that from the side it looks like hills and valleys. This may extend tool life as well as spoil board life.

Oscillating the router spindle will not increase the life of the spoil board. It could, in theory, help extend the cutting life of the router bit. Using a spoil board on a router, you can extend the amount of time between fly cuts of the spoil board by minimizing the penetration of the bit into the spoil board. With bit penetration of .2mm you can cut 70 sheets of average cabinet parts. When you begin to penetrate into the spoil board even an additional .2mm for a total of .4mm you will have to fly cut as often as thirty to forty sheets.

The key to cutting more sheets of two-sided plastic laminate material is the proper combination of spindle speed, feed speed and number of flutes on the router bit and its diameter.

The other issue that causes problems with compression bits and good two-sided material is the lead-in that your post processor provides. A straight plunge lead-in even when it is not along the actual finished edge of the work piece will quickly dull the bottom cutting edge of a compression bit. To get the best performance from compression bits you need a ramp lead-in with a lateral move into the finished edge of the work piece. The ramp minimizes the heat buildup on the tip of the bit. The lateral move into the finished edge keeps the tip of the bit that has an up cut and tends to chip on entry away from the finished edge of the work piece. The point along the finished edge where the compression bit entered the side that was up and plunged through on the side that was down is where I had a problem with chipping, even with a new bit.

Iíve cut as many as twenty sheets of 5 x 8 two-sided hpl material with a bit that had already cut thirty five sheets of 5 x 8 melamine covered particleboard. At twenty sheets I started to see some chipping on both sides of the board. In this case, I was cutting standard grade plastic laminate, not vertical or post form grade.

The above is pretty right on. A tooling supplier should be able to provide the customer with this information. If not, go to a company that understands what a CNC machine does or what a panel saw does, etc. Today there are a few good firms that understand what the machinery does and what the material being cut does to the tools.

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