[TheForge] Another Long rambley YAK

Tue Nov 18 11:50:01 2003

Wow!  Now I'm a role model!  It's scarey!

Yes, I suppose I do rather research a problem to death.  Comes from the
same sort of head-slapping episode you report - due to NOT researching
enough.  

In the case of mechanicanisms suitable for treadle hammers, there's a
whale of a lot of information out there on mechanisms.  It's humbling. 
Folks have been thinking about these things for a long time.  I have
100-year old book on mechanisms, and the mechanisms in it are VERY
sophistocated.  Things like continuously speed-adjustable power
transmissions.  Great stuff.  Maybe not entirely practical, but great.

The other thing I do is to study things mathematically.  I think too
many people shy away from doing calculations because they're "too hard."
 Yes, they're hard, but your brain can work through them.  Modern
software helps a lot too, mainly by allowing you to test multiple cases,
one after another.  Even if not programmed in any sophistocated way,
this sort of calculation is powerful in its ultimate effect.

I just spend last Sunday studying the Watt straight-line motion. 
Simple, elegant.  Produces a remarkably good approximation of a
straight-line.  I haven't decided yet whether it's practical for a
treadle hammer.  (There are a number of considerations involved, not
worth going into here.)  But to really study this motion I had to solve
what initially struck me as a rather elementary trigonometric problem -
the intersections of three circles, under certain constraints.  About
eight hours of intense work later, I actually was modeling the motion on
the computer - changing strut lengths and observing the path of the
"straight" line.  Turns out a bit of creative mathematics was needed. 
(For the life of me, I couldn't solve for the intersection of two
circles, unless they were both on the same axis.  I had to rotate the
axes to solve the problem.)  The alternative, of course, was to build
models.  But popsicle stick models weren't accurate enough, and it was
faster to do the math than to build anything more accurate than that,
considering the variables I wanted to investigate.

The analysis I ran to find a pulley shape to render the Grasshopper ram
weightless was another example of this sort of thing.  That was a
tedious calculation.  I don't fully recall how I did it, only that the
equations describing the machine proved impossible for me to solve
directly, and I had to use numerical methods, or maybe "optimization"
techniques to get the answer.  (Those are long-winded euphamisms for
"cheating.")  And then the solution proved so simple - a ROUND pulley,
pivoting on its circumference, and mounted at some specific (~56 deg?)
angle to the hammer arm.  Worked like a champ too, first time.

Actually, reinventing the Scotch Yoke is nothing to be ashamed of. 
Mortified by, perhaps, but not ashamed of!

Anyway, I understand now what you meant by "adaptation," and, yes, I do
quite a lot of that.  It's a polite way of saying that I borrow lots of
other peoples' ideas.  (I do try to give credit, mind you.)

I think people underestimate the Weightless Hammer.  The other day I
was working on my Grasshopper prototype, reattaching the treadle linkage
after messing with it while working on the new kickback mechanism.  The
end of the cable was frayed, and I needed to cut it off.  Having been
through this before, I put a cutting plate on the GH's anvil, put the
cable end on the cutting plate, put the edge of a cold chisel (held with
tongs) on the cable, and brought the ram down at an easy rate by hand
(the treadle was disconnected) cutting the cable like butter.  The folks
watching this were obviously impressed.  That slow-moving mass (>60# for
the GH) does a LOT of work when it strikes.

That's the idea behind the Weightless Hammer.  You can do SO MUCH more
work with it, that it's only peoples' failure to understand that that
makes them question it.  Granted, 16# is nowhere near 60#, but you can
swing the Weightless Hammer pretty fast, and the work done increases
with the square of the speed, and the impact force increases a lot
faster than that.  Perhaps the problem is that so few people work with
strikers these days that they don't comprehend just how much work a
sledge hammer can do.   Maybe I'll have to demo the Weightless Hammer at
a conference someday.  I expect that will wake people up, especially
when they find out how cheaply they can build it.  

Anyway, what with the recent change I'm making in the kickback
adjustment, I think I've probably reached the simplest practical design
for the Grasshopper.  The drawings will look simpler, anyway.

When I finally come up with a final design and prototype for the new TH
design, I expect there will be more people interested - people like me
who will never need or want a power hammer, but who really could use a
striker every once in a while.  I'm aiming for many the same features of
the GH, but lightweight and cheap to construct WITHOUT welding.

Bruce
NJ

>>> [email protected] 11/15/2003 7:22:28 AM >>>

You're surprised I pay attention to your opinions and respect your
ideas
enough to ask myself, "How would Bruce approach this problem?" Just
because
we've disagreed and even exchanged a sharp word or two doesn't mean I
think
you're not worth listening to.

In the last year I've had two head slapping episodes where I would've
saved
myself a LOT of work had I taken a page from your approach <snip>0

<snip>

I could be wrong but I don't picture you takeing a quick glance at a
patent
drawing and making the kind of decision I did. I did poor research and
wasted a bunch of time.

The second example I did better and actually managed to reinvent the
wheel,
Scotch Yoke actually. Still, had I been more persistent researching I
could've saved myself lots of time and skull sweat.

So yes Bruce, I use you to inspire myself to be a more persistent
researcher.

<snip>

You adapt things Bruce. You took an "obsolete" mechanism that produces
linear motion using only swing arms and adapted it to a treadle hammer.
A
wonderful adaptation. Then someone tells you the return spring pressure
is
too heavy for comfort and you adapt a differential pully to completely
neutralize spring resistance at the treadle. Outstanding adaptation!

I don't think your weightless sledgehammer is practical enough to go
very
far but if you simplify your grasshopper so it stops scaring people
it'll
really take off. <snip>

I figure the grasshopper only needs a couple steps in refinement to
become
the workhorse of treadle hammers.
<snip>

--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---