Wednesday, September 11, 2013

Multi function CNC, Pen/Laser/Extruder, 16"x20" build area

So now that I have a nice CNC mill what is the most obvious first thing that I should build? Why another CNC of course! In an age where you can 3D print a printer this comes as no surprise, but I am looking for an all aluminum build platform with all metal on metal structural junctions held together with high tension machine screws or flat out TIG welded (if I can bribe someone into letting me use the IMSE welding lab).

Here is 2D of what I am looking at so far

Side View

End View

 Blue is the base, red is the gantry, green/cyan is the sled and yellow is linear shafts. Green is not going to be a permanent fixture as this will be used 90% for a larger laser diode cutting system and the massive amount of weight is a no-no for raster engraving/burning. It will be used for experimentation with a very difficult form of printing that another club member brought to my attention but I don't want to make a fool of myself so progress will be presented when it is made.

There are really only 3 forms of aluminum in the entire thing, 1/4" plate for the gantry sides and the ends of the bed, 1" tubing (1/16" or 1/8" is yet to be decided) to hold everything in between, and probably 1/8" for the bed.

Some consideration is going to have to be made where the steppers intersect the 1" tubing but I think overall it will strengthen the gantry since the supports will be milled individually and precisely square, when the stepper is installed it should force the whole thing into square by making the horizontal bars stay parallel. It should also be noted the linear shafts will have high tension clamp on shaft collars just inside of the gantry sides so when the screws are tightened down the shafts themselves will have a load put on them adding another point of rigidity. These areas are not detailed in the drawings because this will be a one off for the most part and parts/changes will be made when the time comes.

Linear propulsion systems are  belted on the X and Y for laser speed and Z is acme lead screw for precision and a bit more head pressure. I have all of the steppers, belt gears, and the lead screw from the auction (The lead screw is actually the quill adjuster from my mill) so all I have to order is the linear shafts, brass bushings, and belts when the eBay money hits my bank account and aluminum stock when I go to KC.

Control wise I already have an Arduino Uno, 3 Pololu stepper drivers and a breakout board that I am beta testing (link found below).

Protoneer CNC Shield for Arduino

Power supply is a 12v Meanwell regulated PSU. Since the steppers are only 2.4v I turned the adjustment pot on the PSU as low as it goes, which is about 10v. Pololu drivers support active current control and actually NEED higher source voltage in order to effectively use microstepping and allow very fast seek rates when no load is applied (all the time when lasing). Still need to get them some little heat sinks so I can run them up to 2A.

The arduino and the PSU will both be mounted underneath the work surface and pockets will be cut for the arduino USB, PSU 120v chassis mount, and a large E-stop button. Cable will all be inside of cable chains printed on the Replicator 2 that belongs to the club I just joined. In the end it should be very polished, pull the USB and power cord then pick it up and go.

Electric Circuit and Controls homework beckons,

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