The first toolhead nears completion

There was one major part missing from the assembly thus far.  There is a need for an easily switchable toolhead so that several designs can be experimented with.  I have some rough designs in my head for a much finer extrusion, and hopefully reducing the mass of the extruder significantly.  A switchable design will also let me drop in a tangential knife setup, or other options, more on those in a minute.  The other big thing that I've not seen is a safety system to protect the head in the event of a crash, and notify the system.  Such a system is essential to protect the system during an unattended print if something goes wrong.  The lasers at work have a similar system that if the actual head contacts the work, it simply alarms out, and the nozzle is easily pushed back to precise alignment. 

Good news is that I think I can kill several birds with one stone.  I've basically adopted the same methodology as some simpler 3D probe systems.  The above pictured item is kind of the keystone in this setup.  Three dowel pins are mounted at 120 degrees to each other.  These will set on pairs of bearing balls, providing two points of contact per dowel pin.  With 3 pins there will be repeatable location every time.  By electrically connecting the balls in series, you can sense if the unit is located or not.  By applying spring pressure to the top the extruder will stay still, but if the tip gets knocked away by a warped or attached part the system can safely stop.  By mounting a stylus head instead of the extruder you could scan simple objects into point clouds.  If nothing else you can determine the exact level of the bed of the machine using this method.  

Now I can put together the extruder head.  Except for the #8 bolts I'm missing....doh! At least things have gone together enough for this shot.  Todays work involves drawing and hopefully cutting the PTFE insulators for the heater block.  I'll get the bolts tomorrow.  I'd really like to melt some plastic by the end of the weekend, but there's a long way to go.

After much internal debate I have also decided to go with non RepRap electronics.  I have a viable CNC drive system already done.  The Gecko 4 axis drive that I have uses 9 pin DIN connectors to plug steppers into.  Within these connectors there is a current set resistor installed for each motor, so the drive is set per the motor that is plugged in.  This will make it easy to make a CNC drive box with the stepper power supply, the 4 axis drive, and the USB step pulse generator.   Connections available for limit switches and such available, I'll develop a multi-pin solution so all I need to do is connect 4 steppers and one other plug to switch machines.