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How to Degrease and Clean Machined Parts
Guide · Updated October 28, 2026
Parts need to be clean before inspection, plating, painting or assembly. Oil and coolant films throw off measurements and stop coatings from sticking.
Clean before measuring
Clean parts before measuring them against gage blocks. The free Gage Block Calculator builds the stack.
Step by step
- Blow out chips: Remove chips from holes and threads first.
- Choose a cleaner: Aqueous (water-based alkaline) or solvent, by material and soil.
- Wash: Soak, spray, or brush; ultrasonic for small parts and blind holes.
- Rinse: Rinse to remove cleaner residue.
- Dry: Dry quickly with air or warm air, especially holes.
- Test: Use the water-break test if coatings will follow.
- Protect: Oil or wrap steel parts if they will sit.
Worked example: mixing an aqueous cleaner
A cleaner used at 5% in a 10 gal tank needs 10 × 0.05 = 0.5 gal of concentrate and 9.5 gal of water. Follow the maker's range; too strong can stain aluminum, too weak leaves oil.
Water-break test
ASTM F22: after rinsing, hold the part so water sheets off. A continuous film that holds for some seconds means the surface is clean; water that beads or breaks apart shows remaining oil.
Ultrasonic cleaning
Works well for small parts, threads and blind holes. Keep parts off the tank bottom in a basket.
Aluminum and brass
Strong alkaline cleaners can etch aluminum and stain brass. Use cleaners rated for them.
Common problems
Rust right after cleaning: not dried or protected. Stains: cleaner too strong or left to dry on. Oil still in holes: no blow-out before washing.
Worked example: drying blind holes
A 1/4-20 blind hole 0.750 in deep holds a small drop of rinse water that air-drying may leave for hours. Blow it out with low-pressure air for a second or two, pointing the part away from you, or dry at about 150°F for a few minutes. Wet tapped holes are where rust starts on steel parts.
Order of operations
Deburr, then clean, then inspect, then protect. Deburring after cleaning leaves fresh chips and oil.
Tips
- Rust: rust protection.
- Deburr: deburring.
- Coolant: coolant basics.
Worked example: cleaning a part before inspection
A steel bracket comes off the mill coated in water-soluble coolant and chips. Blow off loose chips, wash in warm water with mild detergent, then rinse and dry immediately with compressed air. Wipe the datum faces with isopropyl alcohol on a lint-free cloth, let it reach room temperature on the surface plate (about 20 °C / 68 °F) before measuring, and apply a light rust preventive if it will sit for more than a day.
FAQ
Aqueous or solvent?
Aqueous for general use; solvent for heavy oils where allowed.
How do I check it is clean?
Water-break test.
Ultrasonic?
Good for small parts and holes.
Aluminum?
Use non-etching cleaners.
Why do parts rust after?
Not dried and protected.
Related guides and calculators
- How to Protect Finished Parts and Gages from Rust
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- Cutting Fluid and Coolant Basics
- Gage Block Care & Wear Blocks
- How to Check Coolant Concentration
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- All free machinist calculators
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