Thursday, February 25, 2010

USA at last!

Its been several weeks since I machined the 2008 presidential election mold, and being the bum that I am, I haven't done anything with it.

Last night night I mixed up some Smooth-on two part urethane epoxy and poured the urethane into the purple wax positive mold.  When the urethane cured, I ended up with the orange negative mold below.  The cool thing about using urethane molds is that they are very flexible and thus you can easily remove the final molded parts without damage.

The urethane is also capable of capturing very fine detail.  Even the swirl-like milling marks come through.

After the urethane was fully cured (overnight), I poured some hydro-stone plaster into the urethane negative mold.  Depending on temperature, the plaster requires about an hour to cure.  The plaster/urethane combo is nice because it doesn't require any sort of mold release.

And thus the Mantis V8's first milled/cast part is finally completed!

Monday, February 8, 2010

Making EMC do the printer dance

After a few days of dry spell, I got back on the 3D printer train today.

I really like the simplicity and low cost of EMC, parallel port, A3982 combo for driving machines.  Unfortunately, the existing open source 3D printing projects don't really fit well into that frame work.  There has been some RepRap/EMC stuff done here, but the it seems kinda kludgy to me.

For example: to turn the extruder head on or off, EMC has to parse a custom M code using an external python module, this module then uses another python module to send a serial command to a RepRap extruder controller, the extruder controller microcontroller then parses this serial request and commands the extruder motor off.

On top of all this, the RepRap extruder controller does not automatically do constant current drive for stepper motors.  This limits your choice of motors and hamstrings their performance.

Since the latest RepRap extruder is designed around a stepper motor, and EMC is natively set up to drive stepper motors, it makes sense to me to have EMC drive the extruder motor as just another machine axis.

At first it looked like this wasn't going to be an easy task.  Both the RepRap host software, and Skeinforge want to generate code like "extruder on, move X,Y,Z a bunch, extruder off" rather than "move X,Y,Z and extruder axis 1mm left, move move X,Y,Z and extruder axis 2mm up".  Fortunately though, I stumbled across something called the "5D firmware" for the RepRap.  This experimental firmware for the RepRap motherboard wants G-code very similar to what I want for EMC.  Better still, Skeinforge version 10, released yesterday!!!, added support for generating 5D G-code.

Now that the stage is set, here is how you generate EMC readable (and almost printable) G-code files with Skeinforge.

  1. Launch Skeinforge
  2. Under the Craft menu, click Dimension...
  3. Check the Activate Dimension box, and the Absolute Extrusion Distance option
  4. Click Save
  5. Load and process your STL file with Skeinforge as normal
  6. Open of the generated G-code file with an editor (or make a script to do the next few steps)
  7. Remove all of the M10X (M101, M103, ...) lines from the file
  8. The file will contain lots of lines like: "G1 X4.8 Y17.21 Z0.72 F186.624 E2.43", change all of the letter "E"s to "A"s.  Find and replace will probably work.
  9. Save the modified G-code file
  10. Lastly, you'll need to modify your EMC machine configuration so that the A axis, probably called AXIS_3, MAX_LIMIT travel parameter is a really big number like 99999.
Once you do all of that, if you fire up a 4+ Axis machine in EMC and load your G-code, you should see something like this:


Original STL:

 Time to get the extruder finished and test some of this out!

Friday, February 5, 2010

CAM software, EMC, and brute force

I added/updated a few pages in the Electronics and Software and Machine Components sections of the wiki.

EMC control software tool path generation software
Low cost spindle 1.0

Brute force stepper driver

Thursday, February 4, 2010

Lots of work on the Wiki

Lots of new content has been added to the wiki.  Check it out out...

Wednesday, February 3, 2010

Started working on ABS extruder

Today I started working on an ABS extruder head.  I used a pinch roller design similar to the one used by RepRap here.  Instead of 3D printing the body, I cut one from plywood on the ShopBot.  Here's a picture of the cad drawing:

I'll try to take a picture of the real thing sometime soon.

I ended up knurling the stepper motor shaft on the lathe, managed to get the rollers assembled.  Using a NEMA 17 motor at 50% current, I managed to get about 60 in/min filament feed rate.  Right now the motor stalls before the ABS filament slips which I guess is good.  We'll have to see if it can generate enough force to drive the hot part of the extruder.

I also ordered a bunch of other parts for the rest of the extruder today.  Those should be here in a few days...

About Me

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I'm a graduate student in Information Ecology at the MIT Media Lab interested in the creation of low cost machines that enable personal digital fabrication.