The default assumption that machining needs flood coolant is a metal habit. Most engineering plastics machine dry or with air blast, and adding fluid often creates a new problem — thermal shock, contamination, or a material that swells.
Where coolant genuinely helps is deep-hole drilling, sawing thick sections, and any operation where chips cannot clear. It helps because it evacuates chips and controls heat, not because the plastic needs lubrication.
The risks are contamination and absorption. Nylon and acetal will absorb water-based coolant and swell, so they are machined dry or with air only. PEEK and PEI tolerate water-based coolant but should be dried and, where the end use is medical or food contact, cleaned afterwards because residue in a machined surface is difficult to remove. Do not use chlorinated or sulphur-based cutting oils on any polymer — they cause stress cracking that appears weeks later. Clean, filtered water-soluble coolant at reasonable dilution is the safe general choice where a fluid is required.
Need a material recommendation?
Send us the application and we will reply with two or three candidate grades and a price.
