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Monday, September 14, 2009
A Fourth Axis to the Next Level of Machining CNC Index Head
I have to confess this project was wholly inspired by 2 (two) unrelated events.
Firstly as one that is predisposed to the not too uncommon habit of reading while seated in the smallest room in the house, I was browsing the well worn pages of Dave Gingery's 6th installment in the "Metalworking Shop from Scrap Series" - Deluxe Accessories.
Secondly earlier that same day I'd visited the "Association of Backyard Metal Casters" web page, and saw a fantastically simple foam turning lathe made from an electric kitchen mixer. www.abymc.com
With teeth gritted in concentration the idea of making a lathe/Indexing head attachment for the CNC mill was born, and it would be similarly be under the digital control of the mill PC.
These are the handful of parts that I settled on for the framing and spindle of the assembly.
The 1/4" Alum plate was carefully measured and cut to size on the band saw. The saw never balked at the Alum, provided I applied a very light feed and held the work as securely as possible.
What ever time I gained by using the band saw, was lost and then some, in the hunt for a gearing mechanism to drive the spindle.
The approx ratio between the 1.8 degree stepper and the spindle is approx 5:1 giving me 1000 steps per revolution.
The spindle is a length of 1/4" rod that was scavenged from one of the numerous printers that I've husked over the years.
Using a #20 tap and an electric drill the rod was suitably threaded to allow foam pieces to be skewered and then securely held by a pair of wing-nuts & washers.
The simple collet type spindle drive was carefully tuned down on the lathe, threaded and machined.
The clamping collar was in amongst several pieces that were in my general "to be sorted pile"...
The Brass base (just behind the collar) was picked out of a scrap pile from a dead blood centrifuge or some such medical device.
I'm rather proud of this simple drive assembly, mostly as it took almost a whole day to cut a set of identical standoffs, machine the drive and line-up all parts.
Given the fineness of the gears, the counting of the teeth is just not for me, but I'll be able to determine the exact count & ratio once the assembly is interfaced to the PC.
The white plastic gear is from a ribbon positioning assembly used to set the colour band on an old dot matrix printer. The stepper motor is simply from the pile.
All of the measuring, filing, punching, drilling, threading, scratching, burping and farting have paid off.
The axis of the threaded spindle is dead on it's full distance relative to the mill-head.
This mini-project is counter to the methodology I used when building the mill itself. I built the mechanical portion first, and will attack the electronics controller second, and lastly will interface to the PC and figure out how to manipulate 4 axis of simultaneous movemen
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