Keith do you have experience in this field i.e. CNC costing?
I do agree that some of the asking prices are way over the top.
I did buy some exotic steel, in round dollars about $100.
I did get a quote of $400 to turn it manually, cheapest so far,
but I would
prefer CNC for accuracy of the eccentricity and repeatability.
Then there's the grinding - cost ?
and the Heat Treatment - cost ?
So your estimate of $1,000 is not far off the mark, however I
would like to
get it done cheaper if I can - I'm still working on it.
George (down under)
If a cad file were available I could approach the machine shop I
do business
with for a quote.
They have a nice large cnc machine and typically charge me just
for the lathe
time at $150 an hour if I bring the material.
Anyone out there good enough with a micrometer and cad to knock
out a cnc file
and GPL it to the list so we can get quotes from our local
machine shops?
--
Thanks,
Brent Hasty
Brent,
I've been trying to convince Jerry to take on the single e-shaft
project, I
have a rough AutoCAD drawing ( to nearest mm) but nothing that can
be fed
directly into the CNC - unless they have software to convert
AutoCAD into
the machine language.
$150 an hour is a bit steep, but as you alluded to, the biggest
cost is the
programming cost which is at the same rate, even though they may be
programming while the machine is in production mode, doing
something else. I
just can't quite come to terms with that practice.
Is there a way of programming off a sample i.e. coping an original
e-shaft -
leaving out the centre bit !?
George (down under)
George, producing e-shafts is beyond my ability. It is not a
simple thing. BTW, I took the problem to the local technical college
to a guy who builds small steam engines that are works of art. His
opinion is that a one-inch crank throw is about maximum for a manual
lathe which is far less than an e shaft would require. I cannot
imagine a way to do it on a lathe but I would be pleased to learn if
anybody knows how. People have been building cranks for years but I
could not find a description of the process anywhere including
google. There are cast cranks and forged cranks. Are there also
billet cranks turned out by CNC lathes? Jerry
Yes on the billet cranks. You take a huge chunk of steel
and use a large four jaw chuck with the chunk of steel off set
the same as the stroke. The other end has a center off set as well.
You support that end with a live center. Start hogging the rod journal
or rotor eccentric at very low speed due to the off set mass. Leave a
large flange on the live center end. When the rod journal is done.
Reposition the chuck around the center of the main bearings and cut
the mains. When finished cut off the temporary flange on the live
center end. Needless to say it takes a very robust lathe.
The Wright Brothers mechanic Charles Taylor started with
a thick flat slab of steel 6" by 31" by 1-5/8". Drilled a lot of
holes in the slab using a drill press. Then knocked out the unneeded
pieces with hammer and chisel. Wound up with the shape of a single
plane, four cylinder crank. Then used something similar to the process
I mentioned above. He built this on a 14 inch lathe. The crank
stroke was four inches as was the bore. He machined and assembled the
motor in six weeks once he had the aluminum block casting.
This was extensively described in a book called "Charles E. Taylor
1868 - 1936 The Wright Brothers Mechanician"
by H.R. DuFour Limited 1997 First Edition signed by the author
belonging to my wife Robin. ISBN 0-966 9965 -O-X
BTW the Wright Brothers totally understood the relationships
between HP, Torque, Thrust, RPM and speed.
Paul Lamar ...No rotor no motor.
Thanks Paul, that is a book that I would like to read. It is
amazing and inspirational what truly talented people can accomplish
even with primitive equipment. I might try a single rotor e-shaft
as a turning project, working out the process in mild steel
first. Jerry
In an E-shaft case you would do the rotor bearing first
with the chunk on centers. Then cut the mains with off set
centers.
Rather than cut it with a cutter you might try a cheap
bench grinder mounted on the cross slide. The problem with
cutting it is the tool has to dig in each time the chunk
of steel comes around. It will never be in a continuous cut
until the main is almost the right size. That causes a severe
vibration. Maybe a grinder would be a lot smoother as it is
only taking off a thou or so on each rotation.
This is why engine makers start with either a casting or
forging that is roughly the right size to begin with.
Conceivably on an NC lathe the cross slide could move in
and out during each revolution to keep the cutter in proper
depth contact most of the time. I don't know if this is done
or not. It is a lot of monkey motion. I have never even seen
a crank grinder. Here are a few pictures from the WWW.
Looks like the chucks are on rotating cross slides and the grinding
wheel is very large diameter. http://www.alsblowers.com/grinder.html
If it were me I would not bother doing it from scratch.
Let them come up with a two rotor e-shaft and cut it down.
Richard Sohn made one that way. Perhaps he will describe
how he did it.
Paul Lamar ...No rotor no motor.
When I was at Federal Mogal 26 years back I laid my hands on a lathe for
making cranks for engines. It had a grinding wheel about 3/4" wide and
about 24" - 30" in diameter. There was a diamond to dress the wheel on
the spot. The wheel would be used to grind all journals. The lathe
itself had special chucks at both ends - at first you would center the
work as a convential lathe, then would move the work away from center
with the "slide". The work would turn slowly as the large grinding wheel
what brought in to cut the journals - both main and crank. The stock had
to be fairly close to the correct shap or you would be grinding all
month ! :-0 I would think local engine building shops have these
machies still for regrinding damaged cranks.
-dave
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