Tuesday, 14 August 2012

Cheap linear CNC rails

Well, our CNC drilling machine challenge is certainly generating a bit of interest, both across the 'net and down at BuildBrighton, our local hackspace.
Nowhere in our "rules" does it state that outside help is not allowed - in fact, we even encouraged other people to get involved - so it was great to have a link sent by one of the group asking if it was of any use. The link was to a laser-cut CNC linear rail on Thingiverse at http://www.thingiverse.com/thing:3554


As we've not really given much thought to our z-axis, we figured we could build this on a gantry over our moving bed (y-axis) to give us an x-axis movement, then simply mount something either on the underside, or on top, overhanging one edge, with a simple raise/lower mechanism on it for the drilling head.

The first job then was to make up the laser cut linear rails:


The carriage bolted together quite easily, and with the cogs and gears held in place by only a few turns of a screw, we thought we'd try the carrier assembly on the rails:


A neat trick we learned (well, it would have been neat if we'd had the proper tools and not spent four times longer than we needed to trying to cobble it together) was to create the holes in the acrylic at 2.5mm, not 3mm, to accept the M3 bolts.
Running an M3 tap through the hole (this is where we needed the proper tap-and-die sent, and not just a single tap and a pair of rusty pliers!) created a lovely threaded hole in the acrylic, so all the bolts held themselves in place and didn't simply fall out when you picked the whole thing up!



The green cog in the centre is the one that will be connected to the stepper motor. As this centre gear turns, it causes the other gears to turn against the rails, causing the entire carrier to move left/right.

All we need to do now is stick the lid on and hook up the stepper motor and we're good to go!

And why the garish green/orange colour combo?
Simply put, they were was the first two sheets of acrylic in the pile.