Wednesday, June 11, 2014

Project CNC - Weekend CNC Adventure

(This post is from  about 3 weeks ago - I posted it to my draft folder instead of Publishing it to the blog - so here it is finally.)

Z-axis fixed and functioning perfectly. So, that's a good thing. I figured that I can finally cut out my redesigned Y-axis guide rod supports for my 3D Printer build. 
With everything set: 
  1. wiring connections (check)
  2. 1/8” single flute end mill tightened in spindle (check)
  3. added “%” and homing to G-Code generated by MakerCAM (check)
  4. previewed G-Code in OpenScam (check)
  5. secured HDPE piece (from kitchen cutting board) to work surface (check)
  6. tool zeroed to work surface (check)
All ready to go, using fast shallow passes, I started the run (I set it to cut out the outer edges of 4 supports and then return and cut the hole for the rod and slot for tightening mount after – I've had some issues with MakerCAM when I want to add tabs to pieces and have found that if I do my profile cuts first with tabs I seem to get fewer freezes in MakerCAM).

While the second piece was being cut out I saw that the end mill bit was going to cut into one of the mounting screws for the piece – as fast as I could - I hit pause in Universal Gcode Sender followed by shutting power to the steppers and spindle/router.  I was to late – the bit hit the edge of the screw head sending some sparks out. After removing the end mill all I could see was one faint scratch part way up the side of the bit.

It turned out that small defect was enough to render the bit useless.  I tried using it - first shallow pass was Okay but the next pass the bit did not remove the cut material (acrylic chips built up around the bit) and overheated causing the the cutting area to melt.

Having no other recourse, I ordered new single flute end-mills (for milling plastics) - this time I ordered 2 each of 1/8" and 1/16" (the 1/16" I got to cut acrylic for edge lighting).

Monday night I decided to try cutting out some acrylic to make an open top box – I wanted something that would fit my wallet and phone that I could place in a drawer to keep them both separated from everything else (I generally end up losing one or both at least once a week so I was hoping this might help).
After determining what size box I would need, and the thickness of the acrylic I have on hand, I laid out the pieces in Inkscape – imported into MakerCAM – and finally edited the code. The piece for the bottom of the box came out fine but when the cut began for one of the side pieces the Y-axis stopped moving (motor was moving but not the bed).  I paused Universal G-Code Sender and cut the power to the spindle and stepper motors again.
After checking everything I determined that the nut on screw drive was partially stripped and the mount for the nut was worn down allowing it to spin a bit.

So... I cut a new mount for the anti-backlash assembly, this time using Poplar instead of Pine (in the hopes that a hardwood will stand up better).  I have been learning to cut dovetail joints and my practice with that paid off in making a clean and tight anti-backlash assembly.  So far it has worked perfectly (I did replace the lead screw and swapped the brass nuts for stainless steel ones).