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posted Apr 6, 2014, 4:37 PM by Taylor Peterson   [ updated May 20, 2015, 12:47 PM ]

   Bill of Materials
Generating CAD from preliminary design

  • CAD model of Pilot G2 0.38
  • This dictated internal diameter to be nominal G2 diameter plus 0.001
  • This in turn dictated the minimum standard tap diameter - 5/16
  • We want to use standard tap sizes because this drastically reduces difficulty in finding tooling of actually making the part (vs. machining the threads on or acquiring custom tooling)
  • We've typically used 5/16-18, so went with that
  • Outer wall thickness was set by the tap to be major diameter (0.3125") plus 0.05" - 0.365" (I can't add apparently...)
  • The slot heights were set to barely recess the pen tip, slightly over-extend the pen tip, and fully extend the pen tip
  • The width was arbitrarily chosen
  • A countersink was put on the slot edge 
  • Angles on slot were chosen for appearance
  • The clip bolts were separated by 0.25" arbitrarily
  • Clip holder was given its shape because it looked nice
  • Tip angle was chosen because it was snubby but still looked good
  • Tip hole set by the ink cartridge
  • Interior angles and diameters also set by the ink cartridge and spring
  • Length stolen from Rotring 600
  • 0.25" of threads kind of arbitrary
  • Thickness guessed
  • Profile eyeballed
Bolt Carriage
  • Length set by slot
  • OD set by the ID of the body
  • Threads set by the width of the slot
  • Shaft set by width of slot
  • Ball made to look pretty

Changes from preliminary design once experimentation began
  • Vibration while reducing diameter of body -> live center
  • 5/16-18 threads don't work! or 5/16-24 -> 5/16-48 (specialized tooling!) & smaller interior diameter (.243")
  • Drilling out the body tube required janky use of the drill bit -> acquire longer drill bit
  • 4-40 screws didn't fit on the clip -> 2-56
  • Using die difficult -> die holder from Paul
  • Machining the slot with collet means can't countersink slot -> indexing head
  • Want to remove minimal material when countersinking, but still break edge nicely -> 60 degree countersink (using combination drill and countersink)
  • Putting holes in clip -> basic jig
  • Threading endcap, wat -> no endcap (also allows more threads on the clip)
  • Want to stick on manual lathes for alpha -> using machine screw and sleeve for bolt
  • Stainless is harder to work with -> aluminum for alpha prototypes (want to figure out the basic design and how to make it first)
  • Tapered tip also protects our body
  • Thinking of doing hex -> change outer diameter to 3/8" b/c that's what suppliers have
  • Clip too much spring strength -> make long part 25% thinner
  • Clip not slide on easily -> make lip longer and at higher angle
  • Bolt could catch on pants -> rotate it so it is offset by 90 degrees from clip
  • No drills for ID -> tweak dimensions to fit closest size
  • Bolt hard to machine -> purchase solid rivets and use die to add threads
  • Best size of solid rivets 1/8" -> move bolt and carriage threading to 5-40 and widen slot in body
  • Machining diagonal clip relief on body difficult -> use vertical relief
  • Carriage binds up inside body -> tighter tolerances and rounded edges
  • Wasted space for clip threads -> shorter body
  • Knurling double-tracking -> change tip OD to 0.373"

Miscellaneous Notes:
  • For these dimensions, the hex body looks hideous...
  • Slot difference -> 60 degrees (70 too much visually and for hex)
  • Using precision ground 3/8" stock saves a ton of time on the body
  • Using the Haas machining center produces better results (particularly for the interior) due to greater rigidity