Saturday, March 29, 2014

Project CNC - RIP for the Rotary Tool

Parting out Dead Rotary Tool

I was finally able to get my desktop CNC mill to run well enough, with a new carbide end mill, to finally level out the bed. First, though, I had to replace the bed I thought was MDF with actual MDF (turned out that what I thought was thin MDF was really Hardboard which does not mill well).

I generated G-Code to level the bed with SketchUCAM and then fed it to my mill using Universal G-CodeSender – and it worked great. Well...., except for setting my feed speed and depth of cuts poorly (I set it up for multiple passes cutting down only 0.5mm each pass, down to 2mm – so at least 4 passes). Leveling the bed ended up taking about 20 hours – due to my not optimizing my settings but since I was in bed sick I wasn't too concerned.  After the leveling was done I was able to cut out a layered pocket for milling PC boards (I put it in the upper right corner of the bed).

Since I finally had a flat and level surface to work from I figured I could start cutting out some 2D shapes: stars, squares and circles.  These ended up working fine (can't find my pictures though).

Finally, I thought, it's time to cut out something real.  I decided I'd cut out some 2D figures for my daughter.  Surprise --- my $15 "Tool Shop" Rotary Tool finally gave up. Even after completely dis-assembling it (cleaning all dust and corrosion, at least twice) I finally gave up trying to repair it. I eventually realized that my hours of work, trying to repair this tool, are worth more than the $20 cost of a new tool for the spindle. So... I ended up buying a "Cut Out" Tool from Harbor Freight. After discounts and a coupon it only cost me about $18.  It is a bit larger, heavier and more powerful (3.2A instead of 1.5A).  So, as a result, I've had to modify my tool mount to fit the Cut Out Tool.  At present it is holding steady (with the help of a few zip ties - I am currently re-designing the Z-axis to make it stiffer/more stable and allow more travel).
New Tool - Chicago Electric Cut Out Tool

Work Holding:
Not wanting to have to keep putting screws into the bed I wanted a way to secure materials so I could mill them without the piece moving or being dragged by the end mill. Tape definitely didn't work, push pins didn't work, couldn't find any clamps that would work (tried binder clips, etc). I finally settled on using T-Nuts on the bottom of the MDF bed. This, of course, involved making holes through the bed, as well as countersinking holes on the back side of the bed for the T-Nuts.
  • T-Nuts #6-32 screw size
  • 7cm x 7cm grid 

T-Nuts (counter sunk in bottom of waste board)
Top of leveled waste board
 Currently every thing is working as it is supposed to.  I writing some G-code to callibrate the steps per mm for each axis as well as determining the optimal feed rate and depth of cut for MDF and Acrylic.