Quick mill update

A project log for Servicing and Upgrading a Harbor Freight Mini Mill

Years ago, I converted a Harbor Freight mini mill to a CNC using a CNCFusion kit and stepper controllers from HobbyCNC. Time to fix it!

james.moranjames.moran 06/28/2015 at 00:310 Comments

We did a bit of work last weekend, primarily on getting the mill itself ready. Here it is cleaned off and setup in it's new home:

Once everything was connected (mill, CNC1000, GRBLWeb laptop, etc) we had to calibrate it. GRBL has a bunch of settings used to determine things like how many steps of a motor equal 1 mm of travel or limits on movement rate. The main ones we had to worry about where $100, $101, and $102 - the steps per mm in X, Y, and Z respectively. There's a formula given on that GRBL page for working it out based on the motor and controller being used. With that done, we used a set of magnetic dial indicators (specifically this set) to test both the accuracy and repeatability of commands. Below we see the indicator set to measure X-axis movement:

With this in place we sent a series small commands (like "move 2 mm in +X" five times, then "move 2 mm in -X" five times) to check our setup. We had good and bad results here: good being the repeatability (each individual command moved the same amount and we could always reliably return to 0) and bad being the accuracy (a 2mm command resulted in ~1.7mm of travel). Our results were consistent across all 3 axes, with the Z being slightly more troublesome than the others (expected since it has to deal with gravity).

We didn't finish the setup and calibration - after a couple of hours we hadn't made any progress and decided to cut our losses for the day. We did find an error in the step/mm calculations, so next time we get a chance to work on this we'll put in the new value and see if that fixes it.