Yep, the belt made from the small tubing works well Ned. The original woven
sheath over a corded core would likely be the best solution (the machine
that made those types of belts must be fascinating to see).
Ideally, a drive belt for a high speed light duty machine would exhibit high
flex and grip, with low stretch properties (other than just having the tool
direct-driven by the motor).
Just general observations..
I tried common O-rings and they expand too much with the motor speed being a
little over 10k RPM.
I bought some leather round belt material but haven't tried it yet.
There is a fine balance between the power of a light duty motor and a good
belt material that's not too stiff, but also doesn't stretch too much.
When I've used the previously mentioned round PU belting, it needed to be
cut short enough to create considerable tension to compensate for the
stretchy characteristic of the PU compound, since there isn't any
reinforcement cords in it.. which works kinda/sorta well in certain
applications (as a lathe drive belt, the stretchiness can lead to
oscillations resulting in a resonant chatter-like behavior in the cutting
tool/workpiece contact, for example, although the motor and bearings are up
to the task).
With the low power and light duty bearings of small machines like the
engraver, I'd like to find a good balance since just increasing the belt
tension tends to slow down the motor due to the friction and stiffness
properties of a tight belt.
I've pondered using a somewhat soft tubing with heavy thread laced thru the
center for several passes, then drawing the ends of the thread to pull the
ends of the tubing together.. followed by a drop of rubbery adhesive to lock
the thread cords in place and glue the ends of the tubing together.
Or, just looking for a soft belt reinforced with cords.. or maybe using
different pulleys and a flat belt (like Hermes and other machines utilize).
--
WB
..........
"Ned Simmons" wrote in message
...
On Sun, 11 Mar 2012 05:01:46 -0400, "Wild_Bill"
wrote:
There are round polyurethane belting products available for using as
replacements for light/medium V-belts.
The recommended pulley sizes are possibly being stated for power
transmission, as in round belting in a V-belt pulley groove needs a
minimum
surface contact area to transfer a certain amount of power (definite
maybe).. and V-belts exhibit nearly full surface contact in V-pulleys.
Since you're not wanting to use a round rubbery product for delivering
power, I believe you can disregard those recommendations, within reason
(not
trying to run a fat belt around a tiny wheel).
The urethane product I'm familiar with is supplied on spools so any length
of belt can be fabricated.
There was a "special" heating tool.. a fairly large soldering iron with a
thin flat plate mounted as a tip.
The belting would be cut slightly shorter than the circumference of the
V-belt it was to replace.
The ends need to be cut squarely, then placed into a small jig/fixture to
hold the ends in proper axial alignment and the hot flat tip of the iron
was
used to heat both ends simultaneously.
When the ends showed sufficient melting was taking place, the iron was
pulled out and the ends were jammed together until the joint cooled..
plastic welding basically, very similar to bandsaw blade welding.
The nicest splicer I've used held the belt ends in alignment in a
pliers-like arrangement while a radiant heater between the ends warmed
them up. When the ends swelled indicating proper temperature, you
squeezed the handles, which caused the heater to snap out of the way
before bringing the ends together. I don't remember the brand, nor
have I ever seen another. The radianat heater seemed to do a better
job and require less skill than the hot paddle type.
For prototype work, I weld the stuff with a heat gun, vee block to
hold alignment, and a scotch-bright deburring wheel to remove the
flash.
This is the best place I've found for welded to order urethane belts,
as well as belt stock in various diameters and durometers.
http://www.pyramidbelts.com/
WB: It occurred to me as I was about to send this; I think there was a
belt I made out of urethane air tubing on that engraver I sold you.
--
Ned Simmons