On 23/12/2017 13:32, Ed Huntress wrote:
On Sat, 23 Dec 2017 09:31:23 +0000, N_Cook wrote:

Metal tape with round or square holes in, engaging with balls or pegs
set in pulleys. Firstly any generic name for this?
I'm after design criteria, for steel tape, 1.25 or 1.5 inches wide,
flexible enough to wrap around 1 foot diameter pulleys.
So the trade-off between tape thickness , size and spacing of
holes/sprockets for maximum tension/torque transfer and tape integrity.

That sounds like a prescription for fatigue failure, if I understand
you correctly. A lot depends on how big the pulleys are and how long
they're expected to last. Bandsaw blades are made to take it, but the
wheel size has to be large enough to keep the flexing within bounds.

Have you worked that into your design?


Its actually very very slow action.
Trying to get some insight into a failure mode of this type and model of
tide gauge, this pic and the original in a 1920s publication is other
wise the only info.
http://trigtools.co.uk/data/2GL_AutoTG.JPG
The relevant pair of pulleys are the wide ones , one under the mainframe
and one with the brass cogs.
But resolution in that pic , or the original book , not up to seeing the
sprocket spacing.
The plotter drum records 24x1inch paper for 1 days record, so
circumference of 24 inches, for overall sizing.
The band may well have been bronze as a marine context.
There is surviving plot of when this machine "broke" in service as well
as another one. Both subjected to an extreme tide surge.
The traverse pen mechanism hit the designed-in endstop .
The perforated tape jumped some sprockets and resettled , neatly still
drawing , but displaced downwards. What was the surge level that in a
sense , it recorded. One insight would be the spacing of the teeth, if
only we knew, as it could only be an integre number of the spacing , for
the jump slippage. It was of the order 2 inches to 2.5 inches from
meteorological data etc.