Thursday, March 5, 2009

Another DIY CNC router, Pt. 1: Software, Electronics

Small CNC mills and routers can be a bless for the dedicated tinkerer, but they're expensive, to say the least. No wonder there have been lots of efforts in home-built ones.
Anyway, this is how my dad and i built ours. It's mainly used to isolation route, drill and cut out single- and double-sided circuit boards, but also for engraving signs and milling small aluminium parts.

First, i will show you how to connect unipolar stepper motors to your computer and set up the necessary software.


Setting up EMC2

Many DIY and commercal mills use EMC, the enhanced machine controller. It's free, linux based and as flexible as it could ever be.
The very best way to get and set up EMC2 is to use the Ubuntu EMC2 Live CD. You can try to install it yourself (did that with 6.10), but i tell you, it's a pain.

When you run EMC2 for the first time, you will be asked to choose a configuration. You can pick either stepper_mm or stepper_inch and tell EMC to copy it to your home directory for customization. Download this archive and choose one of the supplied setups (you can switch between them at any time):

2.5D (2 unipolar stepper motors, servo for Z)
3D (3 unipolar stepper motors)

Each setup comes with two .hal-Files. Overwrite the original files of your configuration with these and you're done.


Building a simple Stepper Driver

The next thing you will need are two unipolar stepper motors with up to 250mA current/phase. I bought mine from Pollin
(Howard Industries 1-19-4200), but you might as well salvage ones from old printers.
To drive them, i recommend using the circuit displayed below - it's dirt cheap and really simple, but still sufficient for now. Connect the stepper's common wires to Pin 1 and 2 of the respective connector and the others to the rest. It will propably take you a few tries to find out the correct order.

Hints:
  • Use an ohmmeter to identify the steppers common wires and corresponding coil ends.
  • You can change the pinout in the configuration's standard_pinout.hal.
  • Old printer's axes can be used as a great testing machine.
  • Use an old computer power supply to power the driver.
  • For now, it doesn't matter which HAL files you have chosen.


You should be able to make 2 steppers run now. If you've got problems, just ask.

There may be quite a few posts on this topic in the next weeks, mainly concerning a few details of the mechanical construction, but probably only on request.

UPDATE: Ok, I won't write anything about the mechanical part. Most of the good stuff is already documented elsewhere anyway, e.g. the linear bearings are similar to those.



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Monday, March 2, 2009

DIY ColdHeat-like Soldering Tweezers

Ever tried one of those fancy "Cold-Heat" soldering iron replacements?
I did, and i really liked my Cold-Heat Classic after i got used to it, but then it's cheap crappy electronics died.
Since it's quite limited when it comes to soldering small parts, i tried to find a better solution.

The result is pretty similar to this thingie (read first),
except that i've picked up his idea of building tweezers to be able to adjust the spacing of the leads.
It's quite a failure, but building it was fun.

I just twisted .5 mm² wire end sleeves using pliers until they firmly held .7 mm leads, then soldered them onto old steel tweezers, isolated the halves from each other and applied 5V from an old computer power supply to it. Be aware that this will draw around 8 A, so use thick wires. It's actually a bit too powerful, which is why you have to be quite fast if you don't want to burn all the flux before your soldering connection is nicely set (see the video). Also, make sure that the leads can't touch each other, if they do they will just burn up without sufficiently heating the tin.

video

UPDATE: Don't try to solder SMD parts using this. Crap.
UPDATE2: Using a current source would definitely work much better given that the lead's resistance falls with temperature, but that's far too much effort for my taste.

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