michael wendt on tue 23 jan 01
Penni,
One key: Make sure the weight of the flywheel is as much at the rim as
possible. If you live near a scrap yard, you can look for a large spoked
pulley with a heavy outer rim. They are already perfectly machined and
balanced.Typically, scrap price in the U.S. where I live is $0.01/lb if you
are selling and $0.10/lb if you are buying. I buy scrap components whenever
possible, especially since I fabricate mostly in stainless steel.
Get a large one (30-40 lbs) with a taper lock hub ( your local machine shop
will tell you what that is) since then you need only buy the correct bushing
for the shaft size you choose.
Two flywheels of the same weight will have vastly different performance
characteristics if one is a uniform solid disk and the other is a rimmed
flywheel with most of its weight at the rim. No math lesson here, just ask
someone who knows.
Best of all, such a flywheel is easy to remove and reattach with an end
wrench and some shim blocks, so the kick wheel can be very portable yet
useful.
Good Luck,
Regards,
Michael Wendt
wendtpot@lewiston.com
Penni wrote:
I am hoping to build a kick or treadle wheel that I can use at historic
re-enactments I go to in the summers.
Penni Stoddart on tue 23 jan 01
I am hoping to build a kick or treadle wheel that I can use at historic =
re-enactments I go to in the summers. Originally I wanted to get a York =
Kick wheel from Axner but the duties, exchange and taxes were more then =
a little overwhelming! I have found several plans for wheels on the net, =
that is not the problem. What I need to know is how small can the fly =
wheel be without being unproductive? Also what else can I use as a fly =
wheel besides concrete (ie, round metal car parts) The wheel will need =
to fit into the back of my Sable Station Wagon - along with everything =
else I take to a re-enactment. And it needs to be portable enough that =
I can lug it around. I am able to lift quite a bit of weight as long as =
it is not going for great distances. I really want to combine both of my =
hobbies this year as well as be able to interpret pottery of the early =
1800's accurately (ie no electric wheel). Thanks in advance for your =
help.
---
Penni Stoddart of Penelope's Pots
President, Artisans London (Ontario, Canada)
LPG web site Manager
www.members.home.net/londonpotters
Everyone has a photographic memory. Some don't have film.
RSteigmeye@AOL.COM on wed 24 jan 01
the flywheel on my homemade kickwheel is 26" in diameter, made of 2 discs of
3/4" plywood and 4 firebricks. i stick to fairly small pots, 10-15 pounds
tops. i would not want to have less weight, but i think you could make the
flywheel a littlebit smaller if you made it heavier. too much smaller and
you don't have the leverage to slow it down. i built mine from internet
plans, and i've been using it almost every day for a year, it works great.
it's not hard to move around with two people, but i don't know about putting
it in a station wagon. best of luck
zak steigmeyer
cashmere WA
Bill and Sylvia Shirley on wed 24 jan 01
Michael,
I'm not a physics expert, but I'm not sure I agree with your theory about putting
as much weight as possible at the rim of the flywheel. A few years ago, I built my
own wheel. I made the flywheel out of a circle of plywood surrounded by garden
edging, with a drilled block in the center to accept the shaft. Being overly
clever, I made a second smaller form and attached it to the center block. This
created a void which was sort of a wide flat u-shape. That void was filled with
concrete, which meant the weight was mostly at the rim.
Once assembled, the kick wheel worked OK, but not great. It would spin a long,
long, long time, but did not really spin fast enough to suit me. Especially for
centering and trimming. Oh, I got used to it, and used it for a long time, but I
always thought it was a mistake to make it that way. I thought about the way ice
skaters extend their arms while spinning to slow down. When they pull their arms
in, they go faster. I always planned to make the flywheel solid if I ever built
one again. I figured solid would be the best of fast spinning and long spinning.
But what do I know.
Sylvia Shirley
Pittsburg, Kansas
michael wendt wrote:
> Penni,
> One key: Make sure the weight of the flywheel is as much at the rim as
> possible.
>
> Two flywheels of the same weight will have vastly different performance
> characteristics if one is a uniform solid disk and the other is a rimmed
> flywheel with most of its weight at the rim. No math lesson here, just ask
> someone who knows.
>
>
michael wendt on wed 24 jan 01
Sylvia,
The quest was for a light weight, portable kick wheel. All I meant was that
if you want a flywheel with the most momentum for the least weight, that
weight needs to be in the rim. For anyone interested, the math is at the
end. Otherwise, delete now.
Regards,
Michael Wendt, wendtpot@lewiston.com
Sylvia Shirley
Pittsburg, Kansas WROTE:
Michael,
I'm not a physics expert, but I'm not sure I agree with your theory about
putting
as much weight as possible at the rim of the flywheel. A few years ago, I
built my
own wheel. I made the flywheel out of a circle of plywood surrounded by
garden
edging, with a drilled block in the center to accept the shaft. Being
overly
clever, I made a second smaller form and attached it to the center block.
This
created a void which was sort of a wide flat u-shape. That void was filled
with
concrete, which meant the weight was mostly at the rim.
Once assembled, the kick wheel worked OK, but not great. It would spin a
long,
long, long time, but did not really spin fast enough to suit me. Especially
for
centering and trimming. Oh, I got used to it, and used it for a long time,
but I
always thought it was a mistake to make it that way. I thought about the
way ice
skaters extend their arms while spinning to slow down. When they pull their
arms
in, they go faster. I always planned to make the flywheel solid if I ever
built
one again. I figured solid would be the best of fast spinning and long
spinning.
AS PROMISED >>> MATH <<<
from physics we know that if an object weighs 10 lbs and is traveling at 10
feet per second, it will have 10 X 10 units of momentum (in U.S. engineering
practice, the unit of mass is actually the slug which is the weight of an
object divided by 32 ft/SEC^2, but the comparison will still work).
If you double the weight, you double the momentum. Now think of the 2" thick
24" dia concrete flywheel as a series of 1" thick concentric rings touching
each other (I do this calculation in machine design using calculus, but this
will be a rudimentary numerical integration).
The first ring at the center has a volume of 6.28 cu " (2"H X 1^2 X Pi )and
if the concrete weighs 130 lbs/cu ft, the weight would be 0.471 lbs . If it
is uniform in thickness, the whole flywheel made up of 2" tall by 1" thick
concentric rings would weigh about 68 lbs at 130 lbs/ cu ft ( 12X12X 3.14X
2= 904 cu in X 0.075 lb/cu ft) I did the numbers in a spread sheet and got a
total "momentum" value of 902 units (lbs X ft/sec for each 1" ring at its
specific distance from the axis at 180 rpm).
Then I left out all but the three outermost rings and did the calculation
again at 180 rpm and got a total weight of 29.7 lbs for the flywheel, less
than half the weight, but the "momentum still came to 515.4 units. I can fax
you or anyone interested the figures so you can see that getting rid of all
the weight possible in the center will not reduce the total momentum by
much (515.4 lbsX ft/sec= 57% of 902lbs X ft/sec though the weights 29.7lbs =
43.7 % the weight of the larger 67.8 lb flywheel.)
Regards,
Michael Wendt wendtpot@lewiston.com
fax 1-208-746-6968
iandol on fri 26 jan 01
Dear Penni Stoddart,
The first wheel I ever used was one I made. I used a grinding stone =
which was obsolete stock from the factory where I worked. I wights about =
seventy pounds, was 30 inches in diameter and about an inch and a half =
thick. I think the axle hole was about one inch. The bottom of the axle =
was counter bored so that it could be supported by a large ball bearing =
which ran in a cup, supported by three smaller ball bearings. This had =
sufficient impetus of me to produce very small pots which were based on =
ineptitude and ignorance and a total lack of instruction.
The second wheel was made form a flame cut steel ring about fifteen =
inches diameter with a two inch square section which was welded onto a =
steel support plate. The axle passed through the plate and everything =
was turned true to the axle. The crank for the treadle was fixed to the =
base of the axle with a bolt so that it could be passed through the =
supporting thrust bearing. That worked very well and I could throw pots =
over ten inches tall on it.
The main thing about a flywheel is to have the mass concentrated at the =
circumference. Solid concrete flywheels are at fault in this respect. =
Our physicist friends will explain all about conservation of momentum =
and energy distribution, which is what you need for you wheel to be =
successful, in that it consumes the least amount of human energy.
Ivor Lewis, Redhill, South Australia.
Human memory. Never forgets anything. All problems are related to =
recall. (Ed Psych 101)=20
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