Saturday, 26 May 2012

DIY CNC milling machine

...or cartesian robot.

I've been researching building my own CNC mill for a few months now (read: trying to decide if its too much hassle to make my own or to save up £500-1000 and buy one...). In that time I've bought a few cheap stepper motors from Ebay and even a couple of 99p scanners and printers to disassemble for parts. I started putting together a motor driver board based on three L293D chips, an output multiplexer (need five digital lines per axis channel, three axis add up to 15 channels) and an ATMEGA328P (with Arduino bootloader etc)

I'm now at the stage where I need materials too build the system. This is the tricky bit as I don't have a workshop or any bench tools. So I looked around for DIY builds that were simple in their approach and that didn't need fancy machining or (too much/accurate) metal cutting.

Two options presented themselves:

Profile aluminium/aluminum section to create the frame (pros - easy to build up, Al is fairly easy to cut to size and drill and will provide a stiff frame. Cons - cost, once you add up all the section and fixtures. Difficulty making a cost effective linear slide without resorting to expensive rail-and-truck systems)

Wood (pros - really cheap, easy to cut, can glue, screw bolt or whatever suits. Cons - not as stiff, may deform over time, looks a bit rubbish)

A couple of example designs:

Aluminium section frame design with linear rails and trucks

Wood design using silver steel rods and Oilite bushes
After finding the mantis CNC machine design, I decided to go with wood and the desgin above.

A few design considerations:
  • The linear bearing is basically a pair of hardened, ground steel rods with Oilite (oil impregnated) bushes glued to a wooden truck. It would be really easy to misalign these rods and jam the axis movement.
  • Stiffness of the design is OK for a wood structure and the steel rods help to reinforce it, but there still may be a few mm flex, particularly on the y-axis (green truck)
  • The maximum cutting area is around 150mm in X by 225mm in Y by 75mm in Z. 
  • The end-mill motor will probably not be very powerful, but OK for milling copper clad board or wood. Hopefully it'll do aluminium as well :)
 Oh, a note on the steel rods - in the UK you can get something called 'silver steel' which is like 'tool steel' elsewhere. This stuff is intended for making tools (duh) and is fairly stiff. It is ground to a reasonable precision making it better than stock steel rod intended for machining to size. I hope.

First build update here

Sunday, 6 May 2012

Radio meteor detection

OK so its been a while since I posted up here...

I've been busy with work, children and other distractions resulting in a neglected blog :(

There are a few projects on the go at the moment, but I'm going to put up some details on detecting meteors using a PC sound card, a handheld radio scanner and some wires :)

The end results look a bit like this:

These screens are generated by SpecLab. The bright blobs on the top left are meteor trails. There is a great website here that explains what the blobs might mean. Basically, anything travelling left-right is showing a doppler shift (ie speeding up or more likely for a meteor - slowing down). Anything that appears in a vertical line is persistent over time. The vertical bands are radio interference (I think!) Occasionally there are tracks that might be satellites, but to be honest I don't really know!

More to come on how this was put together...