29 Jul
2015
29 Jul
'15
6:11 a.m.
From: Pete Turnbull: Wednesday, July 29, 2015 2:57 AM
On 29/07/2015 07:24, Vincent Slyngstad wrote:
Are you referring to the junction of the post and the block? That would
be easy enough to do (though tedious in SketchUp).
Or are you referring to the bottom edges of the slots? (That one is
easy.)
I've placed a new design at:
http://svn.so-much-stuff.com/svn/trunk/3D/rack-bracket/bracket-new.jpg
That looks pretty good to me, and the only refinements I'd suggest are
these:
Firstly, to add a small fillet to the junction of post and flat surface,
so that there's a small radius, perhaps 0.5mm - 1.0mm, at the
transition. The sharp transition will concentrate any stress, and a
radius will reduce that. I'm not sure how much difference it makes for
a 3D-printed object but it would be significant for injection moulding. 
Secondly, and maybe less importantly, to make the
lower part (maybe half
the length) of the post a slightly smaller diameter - but not to the
extent of reproducing the ball-on-a-thin-post of the original. This
eases alignment, because as Al pointed out, the panel always tilts or
twists as it's removed and that puts a bending strain on the joint - in
this case, now at the post base than than just below the ball.
It troubles me that the whole design is based on the flexibility of the
particular plastic it is made out of, but I'm not sure what to do about
it.
One concern that I had was that the new design might end up trying
to ovalize the (brittle) socket in the mating panel, since the new posts
are only really compressible in one axis.
It would be next week at least before I could print and try any of these,
and then not in ABS. If someone wants to print a couple and see how
they do, that seems to me a logical next step. (Certainly before I'd even
consider ordering 10,000 of the things.)
The posts can not be vertical in the print (for strength in the correct
direction), so a small amount of support will likely need to be printed too.
(And don't forget to convert the inches!)
Vince