bkrpr team mailing list archive

[James Vasile <james@xxxxxxxxxxxxxxxxx>]

I've built enough parts for 5 book rippers in the last couple weeks
and I've experimented with several different options and
configurations for each part.

Friction fingers work if we add adhesive-backed rubber bumpers and
drill little depressions for them.  They keep the whole thing square,
but they don't actually provide enough friction to prevent slippage.

We can dispense with the routing.  The routed prototypes were more
complex to make and gained us little.  Ian, can you pick up two sheets
of plexi that are 11 3/4 x 11 x 1/4?  I'd like to just screw them on
to the cube and remove the routed sheets.  1/4 is better than 1/8 for
rigidity and to give us a little room for countersinking.  I think
we'll get enough rigidity that way and let the cube sit flush on the
book instead of needing to hang over the edge.  We lose the guide, but
gain a simpler manufacturing process and the ability to do larger
books.

I redid the handle a few different ways and finally settled on a
simple piece with the light screwed on and hanging from the bottom.
It's a little janky, but it works for now.  If the light is sufficient
for our purpose, I can work on ergonomics and making it look better.

Camera mounts are solid.  I was too lazy to drill them straight after
making six different designs, so they won't be perfect on the
prototype, but they're an easy redo when I have more time.

And all the wood pieces can be made out of the same 1" thick material.
We can robofab this if we want to.  And we limited things to one wood
screw and a standard 1/4"-20 bolt size.  So that gives us a simplified
things list of parts and tools:

Bill of Materials:
50  1 1/4" wood or dry wall screws (90031A298) ~ $3
2   11 3/4 x 11 3/4 x 1/4 plexi (Canal Plastics) ~ $15
1   6 x 12 x 1 board (HD) ~ $15
2   1/4"-20 x 4" bolt for the camera mounts ~ $0.50
4   1/4"-20 cross dowel nut for the camera mounts (90835A200 or HD) ~ $0.80
2   1/4"-20 thumb screw for the camera mounts (90181A542 or HD) ~ $0.85
6   1/4" adhesive-backed rubber bumpers ~ $0.50
1   GE 8" slim line flourescent light (no. 10167) ~ $15 at Amazon or HD
2   Cameras

Tools used:
Saws (table/circ/chop)
Drills (electric, press)
Tape measure
Ruler
Triangle
Speed square
Palm sander (optional)

One could probably get away with a circular saw and no table saw.
Precision would suffer, but it could be done.

Unfortunately, this design cannot be built without a drill press.  The
camera mounts depend on that hole being true and of course it's
impossible to line up with the dowel nuts if things are askew.

Anyway, it's $50 worth of materials, maybe $60 if this project is a
one-off and you're going to trash the leftover nuts and screws in the
packages.

COST CUTTING: There are some places we can look to cut costs.  I don't
tend to work in ply for anything that requires end-grain drilling, but
it might be possible to replace the pine board with plywood, which
would allows us to get 4 or 5 rippers per sheet and cut the wood cost
in half.  It would also let us source standard 12x12 sheets of plastic
from,
e.g. http://www.vipplastics.com/product_info.php?currency=USD&products_id=462
and that would cut our plastic costs in half.

We might be able to lower the cost of lighting.  There isn't $15 worth
of parts in the GE unit.  We could buy the parts and assemble it into a
unit.  I tend to think this wouldn't be cost effective on the labor
end, but I could be wrong.

The other alternative is to test some LED units, but while LEDs are
cheap, bright ones aren't and transformers add to their cost.


One of our goals was to make the thing portable.  I don't think that's
realistic.  Removing 8 screws makes the base flat, but disassembling
the cube would take another 14 or 18.  Anything that requires 20+
screws to break down cannot be called portable.  We can ship it flat,
but once it's setup, it's not going to be broken down for daily
commutes.