How to Get Mill Finish on Aluminum

A mill finish is necessary on high-performance parts.

Adding a mill finish to aluminum is performed as a finishing pass with an end mill. You can use the same end mill to perform the roughing and finishing passes, but you must make sure you are using the right feeds and speeds and leave the correct amount of material to make the mill finish.

Things You'll Need

• Vise or fixture
• Indicator
• Wrench
• Allen wrench
• Mallet
• End mill

Instructions

1. Set up the vise or fixture you will use to cut the aluminum in the milling machine. Blow off and wipe down the work table before setting it down. Hand tighten the T-bolts and use an indicator to straighten the vise or fixture. Tighten with a wrench when the vise or fixture has been indicated.

2. Set the raw aluminum in the vise or fixture and tighten it in using the vise handle or an Allen wrench. This will assure it does not move while being machined. Tap it lightly with a mallet to make sure it is sitting flat in the vise or fixture as well.

3. Rough out the material to be removed. In a CNC mill, the roughing amounts will be calculated automatically. In a manual mill, remove material using a roughing end mill, but no more than half the diameter of the tool per pass. Leave .01 to .015 of an inch of material to get a good mill finish when you run the finishing end mill over the part.

4. Set the finishing pass on a CNC mill. The finishing end mill will leave a high quality mill finish if the speeds and feeds are correct. For aluminum, you want at least .01 to .015 of an inch of leftover material so that the mill cuts just enough to expose a good finish on the part. Excessive feeds will result in a chattered finish, but if you run the end mill too slowly, you will be wasting time. Find the right combination of feed and speed to get a high-quality mill finish.

5. Inspect the finish after you have completed the part before removing it from the vise or fixture. Re-mill the part if the finish is not to your liking. As long as you do not move it, you can re-run the part from the finishing pass and adjust the feeds and speeds to improve the finish.

References

• Cutting Tools Design; End Mill for Alumimun Practice