Friday, March 28, 2014

The search for precision...

"The search for perfection is all very well.  But to look for Heaven is to live here in Hell"
- Sting "Consider me Gone"

Alright, perhaps the above quote is a touch extreme, but only a touch.  After failing to achieve an acceptable degree of accuracy for my block lifting mechanism with laser cut parts I've started down the path of 3d printed parts.  Many thanks to +Duane Johnson for the use of his delta printer and for putting up with my endless revisions.  The first part I designed and printed was this:

This is the carriage piece that will attach an articulated block to the rest of the lifting mechanism.  Unfortunately, my design had insufficient and/or no tolerance so none of the hardware apertures we're large enough.  Thus ensued a bunch of sanding, grinding and filing until the hardware DID fit.  So, back to the drawing board.  Before I wasted a bunch of PLA on another failure I decided to design a calibration sheet (stepping bore holes up by 0.5 mm for a few iterations).  Designed and printed, it told me what I needed to know about tolerance.  Next came this:

The lift head, a piece that keeps the power screw and alignment shaft in place and stops the carriage from lifting to far.  Made a mistake assuming that a 1 mm wall of PLA was sufficient to hold the nut for a set screw in place, the part broke as soon as I tightened the set screw.  Back to the drawing board.  Undeterred I redesigned the lift carriage and came up with this:

Success, everything fit and was lined up, the linear bearing even pressure fits into its bore hole (eliminating the need for a set screw, wee).  Emboldened by success I redesigned the lift head and printed this:

A good enough part, it warps a bit when the set screws are tightened, I'm probably going to shrink the bore holes a smidgen so the hardware will pressure fit.

Coming soon, I get too fancy with a part's design and need to go back to the drawing board, again.