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Author Topic: Anybody heard of skeleton molds?  (Read 6564 times)

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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #90 on: September 07, 2008, 02:50:55 AM »
Quote
So all round the Wrekin, to arrive at the point of departure. This topic has shown an impotent lack of progress, the height of archeological necromancy, that is akin to fortune -telling, and now we know less about so-called skeleton moulds, due to a lack of consideration for the opinions of glass-makers.

Archeological necromancy?  Akin to fortune-telling?  How so?

How do you figure we know less about skeleton molds, and who has shown a lack of consideration for the opinions of glass-makers?


Even though this is off-topic, I just gotta respond... ;D

Gear or direct drive?

On a lawnmower or an outboard motor, a cord works because there is a flywheel to which the cord is attached.  The purpose of the flywheel in those examples is to make it easier to pull.  The purpose of a flywheel is not to make it easier to pull; that wouldn't make sense, since flywheels are heavy and resist movement.  The are used to store kinetic energy, as Patrick pointed out.  It may still be true that they function as gears as well.   The flywheel in those examples works as a gear, which means that not too much effort is needed to start the motor.  Which is why you perceive it to be easier to pull a cord.

The whole point is that the diagram shows a cord attached to the drive shaft and as Patrick pointed out originally, relatively the flywheel looks rather heavy. It doesn't make sense to use a cord to start it.  It made sense to the filer of the patent!   It will require much more strength than a lawnmower.  Now this is conjecture!  Do you have a car, or a bike? Do they have gears or are they direct drive?

In the Hamada example, there is a weighted flywheel underneath the working surface.  Why?  If his wheel is heavy enough, it wouldn't need a flywheel.  I don't get that.  His wheel was a pre-cursor to the kick start wheels that you refer to. He managed to work out that by pushing the edge of the wheel, it required less torque or strength to turn the wheel than to put crank it from a central drive. This is also a form of gearing.  No it's not.  Imagine if he had a hole near the centre of the wheel to put his stick into. Which would have been easier?

You are quite right, attaching a string to the pedal would not work. Well spotted! As you say, you would need to attach the cord to the sprocket, which, again is a gear!! Maybe, what you should do is to attach a piece of steel to the axle of the bicycle and then wrap the cord around that. See if you get a better result than spinning the wheel from the edge.  Betcha I could make it spin faster with a cord around the axle! ;D

I am not really an expert in this, but so far as I know, direct drive requires more effort than gears.  Why raise the issue of gears?  There are no gears in this picture. But I am not an engineer, so I am not going to add much more. Instead, I am hoping that there is an engineer out there who will be able to confirm that it would require less effort and torque to spin the fly-wheel from the edge, rather than pull the cord.  Yes, agreed, but how do you get it to go fast?

However, I would be equally happy if an engineer can show that that pulling a direct drive cord requires less force.  Smiley  I don't think anyone is arguing that.  It would take exactly the same force (or rather work - ergs - to use the proper physics term) to spin the flywheel at a given speed no matter how you do it.  Well, unless you weren't spinning it constantly, in which case friction would tend to slow it down each time you stopped, so you'd have to regain that ground.

I would also be very interested for that engineer to provide an explanation that shows that a using a cord would give a more constant speed than spinning the flywheel, because my very basic memory of studying this stuff about 35 years ago is that the fluctuation of the speed will be primarily related to the weight of the flywheel and any variation to the speed will be related to that as soon as the force is removed.  True.  The heavier the wheel, the greater the inertia.  The change in speed will also be related to the friction, which in turn may be dependent on the weight of the flywheel.   In other words, when you stop pulling the cord, or spinning the flywheel, the deceleration will follow a constant curve.  Exactly!

 :hb1: ;D



 ;D ;D ;D
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline aa

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Re: Anybody heard of skeleton molds?
« Reply #91 on: September 07, 2008, 09:07:33 AM »
http://www.youtube.com/watch?v=7eCsUQAjcI0

Please explain why the crank handle shown is this funny shape rather than being straight. :)


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Offline Patrick

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Re: Anybody heard of skeleton molds?
« Reply #92 on: September 07, 2008, 09:28:28 AM »
Hi Adam,
 I hope you see me as a good friend of yours but all this talk of egg wisks and now crank handles has me baffled.
 Are you saying his original idea that may or may not have been made, would NOT WORK ??????

Regards Patrick.

Ps. No crank here only works by a cord going round shaft and given a good pull........


Offline aa

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Re: Anybody heard of skeleton molds?
« Reply #93 on: September 07, 2008, 09:36:06 AM »
I'll call you
Hello & Welcome to the Board! Sometimes my replies are short & succinct, other times lengthy. Apologies in advance if they are not to your satisfaction; my main concern is to be accurate for posterity & to share my limited knowledge
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #94 on: September 07, 2008, 04:49:45 PM »
http://www.youtube.com/watch?v=7eCsUQAjcI0

Please explain why the crank handle shown is this funny shape rather than being straight. :)




Sigh.  You know why - you can get greater torque with a greater turning radius.  I don't question that.  But it seems to me speed is the issue here - how to get the thing going fast enough to work.  If the axle the cord is wrapped around has a circumference of 5 cm and the flywheel has one of 50 cm, is it faster to pull a cord 5 cm or move your hand in a 50 cm circle?  At the beginning you could always start the flywheel with your hand to overcome some of the initial inertia, making it easier to start pulling the cord.  Once it gets going faster, can you even move your hand in a 50 cm circle in, say, the space of half a second or a quarter second?

Why do you think mowers and outboards have a cord, rather than a crank?  They need the speed to turn the engine over fast enough that it will fire in rapid enough succession to keep going of its own accord.  Well, I think so, anyway...I'm certainly no motorhead, and if that's wrong, hopefully someone will correct me.


Just so we all know, this is a friendly discussion, right? and not a heated argument.  I enjoy friendly, respectful debates as long as no one takes things the wrong way and gets offended.  It's good brain exercise. :)

 :) :) :)
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein

Offline aa

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Re: Anybody heard of skeleton molds?
« Reply #95 on: September 07, 2008, 05:10:03 PM »
But it seems to me speed is the issue here - how to get the thing going fast enough to work.

Why do you think it needs to go fast?
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #96 on: September 07, 2008, 05:43:10 PM »
Good question!  Partly it's because that's the way it looks like it was designed - how's that for circular reasoning?  ;D ::)  But considering the fact that the patent talks about having different shapes of bars in the mold part, I'm assuming that it works by spinning quickly enough that centrifugal force will expand the bubble around the bars.  The other possibility is that the bars slide over the bubble to shape it, but I don't know why you'd put something like spiral bars into the mold then.

It's also presumably supposed to be a time-saving device, so you'd want it to be quick.

The whole gadget seems sort of a waste of effort.  Why not just blow it in a dip mold for the same effect?  Somehow I doubt it was used in a production capacity.  I bet at that time there were lots of people making up new "time-saving" gizmos and whatzits.

Too bad what we're seeing is a patent abridgement, rather than the whole description.
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein

Offline aa

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Re: Anybody heard of skeleton molds?
« Reply #97 on: September 07, 2008, 08:23:01 PM »
Glad to see you've worked it out. :)
Hello & Welcome to the Board! Sometimes my replies are short & succinct, other times lengthy. Apologies in advance if they are not to your satisfaction; my main concern is to be accurate for posterity & to share my limited knowledge
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #98 on: September 08, 2008, 12:37:03 AM »
What?  Just like that?  Now I feel kind of bad.  I hope you aren't being sarcastic.
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein

Sklounion

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Re: Anybody heard of skeleton molds?
« Reply #99 on: September 08, 2008, 01:06:57 AM »
Hi Kristi,

Adam, being sarcastic? Not at all.

Few of us are actively involved in glass-making. Adam is, and when he has reservations, which are based on many years of first-hand experience. maybe he has good reason.
For the rest of us mere mortals, all the theorising could be merely an exercise in intellectual masturbation.
Regards,
M

 

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