I have put together a Level wind mechanism that uses a 1" steel bar 40" long
with a helix cut into the bar in opposite directions. At each end of the
bar the counterclockwise helix joins up with the clockwise helix. I am
using a 'key' that fits into the helix to travel along the shaft when the
shaft is rotated. The travel speed is about 12 inches per second, and I am
carrying about a 15 pound load on the key mechanism.
I am finding that the key (presently made of brass) wears down very quickly
(about 1000 cycles) and suspect that it may be due to two reasons:
1) The rapid change in direction hammers the key on the end of the spline
2) The key is not positively, centered in the spline when it reverses
direction, and during travel along the bar.
This causes the key to wear prematurely. I am tempted to build a steel key,
but fear that then the double helix bar will wear or fail, and it is fairly
expensive.
Has anyone had any experience that they would like to share on projects of
similar nature?
Thanks in advance,
Andy
snipped-for-privacy@triacengineering.com
Andy K wrote: Has anyone had any experience that they would like to share on
projects of similar nature?
^^^^^^^^^^^^
Printing presses use a similar device to drive the oscillating rollers.
They use a steel follower in a steel groove, and get very long life.
However, the loads are mostly inertial, where the roller reverses direction.
Could you relieve the follower of the radial load by running the shuttle
along a track, parallel to the scroll-shaft, so the tension is not
transmitted to the contact between the follower and the groove?
Could you put collars on the ends of the scroll-shaft, so the shuttle hits
there, and relieves the delicate follower of most of the banging?
You could try making the key out of aluminum bronze instead of brass. I
have some brass "things" that tend to wear rather quickly. I built them
back up with TIG and Ampco 200 aluminum bronze. The difference is
amazing. The aluminum bronze machines nicely, is much harder than brass
and works well as a low friction match with steel.
Ted
Did a job several years ago with the same "slamming" problem at each end.
Is the helix constant in pitch right to each end? If so, change the pitch
every few degrees so it is reduced on approach and increased on exit,
ramping down and ramping up. i.e. assume 1.0 pitch, every 5 deg lose .1,
so your pitch would go 1.0 to .9 to .8, etc. until it goes flat at
turnaround point.
michael
Maybe a system like this would work.
Two parallel lead screws geared together so the rotate in opposite
directions. A traveler with a pair of halfnuts or chasers is mounted on
a third smooth non rotating shaft. When the traveler reaches the end of
one shaft it disengages and rocks over to grab the other reverse turning
leadscrew. some kind of trigger and springs keep it engaged.
Hey it's like 4 am and I didn't work out all the details. But I light
try this since I have some long acme threaded rod and ground shafts.
How about placing sprockets at either end of the 40 inch run. Mount a link
chain (motorcycle type) between the two with a single extended link pin
protruding below that carries a suitable guide through which the cord, rope,
cable, or whatever can be threaded. Drive one of the sprockets from the
winding gear-train and you'd be off to the races. (In theory)(^:
Bill D
PS That's a bit fishing reel!!
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.