Examining Air Cooled ER11 CNC Spindle

Up until this point, almost everything in the home brew vertical mill CNC project has been salvaged or reused from some previous project. But we’ve come to the point where the Z-axis drive has been properly configured for a spindle motor… that we don’t have. We have smaller lighter motors that aren’t strong enough for the job, we have big beefy motors too heavy for our gantry. While we could potentially use a Dremel or a RotoZip as a stepping stone, the decision was made to buy a cheap milling/engraving spindle from Amazon (*) for the project.

The product page proclaims a maximum of 500 Watts and maximum speed of 12,000 revolutions per minute. We’ll measure power draw once we can put it to work, and we have tachometers to measure its speed range. We don’t expect it to actually hit those numbers, but they seemed reasonable. The part that we were most skeptical about was the proclaimed precision: 0.01-0.03 mm of runout. This is a very high level that we doubted was reasonable in this price range.

The first test after unpacking all components was the obvious basic test: does it spin up? Once we established that it does indeed turn, the second test was then to mount a Starrett dial test indicator (*) to measure its actual runout.

Cheap spindle on Amazon getting dial indicator

The results were… surprisingly good! When the motor is not under stress and turning freely, it actually stayed within a very tight range. This specific dial test indicator was in Imperial units, measuring a range within +/- 0.0005 inch. This is in the ballpark of +/- 0.0127 mm, so the product listing was not a complete lie.

For practical purposes, though, we’ll never have that level of accuracy. There is a lot of flex in the system — from the motor output shaft to ER11 collet — to take us out of that range. A single finger press was enough to bend things beyond the technically-not-wrong runout, so we shouldn’t expect very high precision from this spindle after we mount it on our Z-axis and run under real cutting forces.

(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

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