PTFE is one of the easiest plastics to machine and one of the easiest to ruin. It is extremely soft, very slippery, and has a coefficient of thermal expansion roughly ten times that of steel. Each of those properties dictates a rule.
Support it fully. Because it is soft, the workholding pressure alone can deform it, and because it is slippery, normal clamping forces are not enough to hold it. A collet or a soft jaw machined to the part profile solves both. Keep tools very sharp with high rake and a large clearance angle, because a dull tool pushes the material instead of cutting it and leaves a smeared surface.
Control heat and measure late. PTFE grows about 0.12 mm per metre for every 10 C rise, so a part machined warm and measured cold will be out of tolerance. Let it stabilise at 20 C before the final measurement, and if you are holding a tight tolerance, machine, rest, then take a finishing pass. Finally, deburr gently — PTFE burrs are soft and fold over rather than break, so a light scrape rather than a rigid abrasive is the right tool.
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