"Jim Wilkins" wrote in message ...

"RogerN" wrote...

I'm wanting to make a display for load cells, ...
Anyone here done anything like this? RogerN

What I had in mind was to make a 10:1 lever divider for a bathroom scale
mechanism so it would read to 3000 Lbs instead of 300. I haven't dissected
one to figure out the specifics.

I've been thinking about similar setups. There are lighter hanging scales
in the 300lb to 600lb range with a little mechanical advantage they could be
used for heavier weights. It could be a lever with a solid link at one end
and a scale at the other with various attachment points to get a leverage
from maybe 2:1 to 10:1. This would have friction inaccuracies like you said
but I'm mainly wanting to get ballpark figures to test and not overload.
Another idea is to use a snatch block or pulley (wire?)rope to expand the
scale of the lighter duty scale.

http://en.wikipedia.org/wiki/Steelyard_balance

You could set up an unbutchered bathroom scale with a lever to confirm a
modified one or calibrate a homebrew cell.

The problem with a lever is frictional hysteresis. I would try needle
bearings and take the average of the reading with the load increasing and
decreasing. A strong spring deflection element like the Dillon avoids it.
On a stationary test setup you could let the pin of a chain shackle roll on
the lever bar.

The Dillon's gain can be adjusted by rotating the hexagonal plug with the
ramp, the zero by moving the indicator stem clamp or the dial scale ring,
http://wagner.securesites.com/produc..._xc_dillon.jpg

Here's another geometry if you can find some thick-walled tubing, perhaps a
scrap hydraulic cylinder.
http://2.imimg.com/data2/WO/ST/IMFCP...pg-250x250.jpg
Make it too long and adjust by shortening it.

jsw

At work we have some very heavy duty tension gauges on our commercial
vehicle tire curing presses. There is a link like a connecting rod,
estimating 10 feet long, 2 feet wide by about 4 inches thick. There is a
dial indicator attached near the top of the rod and a free floating rod at
the other end. This measures how much the almost 100 square inches of steel
stretches over a distance. Expanding on that idea I could have a steel link
with a dial indicator to measure how much the link stretches, using
different sizes of links for different ranges.

RogerN