# Looking for someone to make me a Parabolic cone



## Amonra (Jun 27, 2008)

Im looking for someone who can precisely machine and polish a parabolic cone similar to this: http://www.lightcrafttechnologies.com/news.html ( the bottom part of the craft ) some better pics here http://images.google.com.mt/imgres?...24&prev=/images?q=lightcraft&gbv=2&hl=mt&sa=G 
but with a 2 inch diameter.

This cone should reflect light transmitted from the direction of the cone apex into a very narrow ring to the sides of the cone.

Anyone interested ?


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## Amonra (Jun 28, 2008)

anyone ??


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## PhotonFanatic (Jun 28, 2008)

I think you'll need a CNC lathe to come close to making one of those. 

And if you were to get one, what will you do with it?


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## HEY HEY ITS HENDO (Jun 28, 2008)

oo: oooOOOooo .... was that you posting in the BST for a 10Kw laser?


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## Amonra (Jun 29, 2008)

it is for a little experiment involving solar power not laser power


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## Amonra (Jun 29, 2008)

so does anyone have a CNC ?


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## LukeA (Jun 29, 2008)

I think you will get better results focussing the sunlight into a point using a normal parabolic reflctor than you will get by focussing it into a ring. Higher energy on the point than in the ring.


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## Amonra (Jun 29, 2008)

it is a combination of both


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## Amonra (Jun 29, 2008)

When i saw this light craft i started thinking of some other applications and came up with this.
Here's what i'm thinking:






The craft used a 10Kw laser to 'explode' air in a 6" diameter cone. 
The approximate solar energy that hits the earth is 1kW per square meter.

A 3 - 3.5 sqm fresnel lens will converge 3 - 3.5 kW of solar light into it's focal point. The aspheric lens will then turn the light back into a 1.5" - 2" diameter concentrated laser like beam. The 2" parabolic cone which is a third of the diameter of the craft thus the third of the energy required will then reflect this now concentrated light into a still concentrated tight ring which should then 'explode' the air within the ring.

Assuming there are no losses and that that the air will actually 'explode' it will create a pressure which can be used to drive a turbine or engine of some sort. The light from the fresnel should be pulsed in some way to allow the expanded air to go out and the fresh air to go in.

It might be a bit far fetched but i think it is worth experimenting.


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## climberkid (Jun 29, 2008)

that is some sweet engineering. keep us updated, if you get the cone...


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## Amonra (Jun 30, 2008)

Thanks but it looks like it's not going to be easy


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## PEU (Jun 30, 2008)

I have a small CNC lathe, can you post the profile of the part to be turned? or better, can you provide me with a DXF with exact dimensions?

I *may* be able to do it, depending on its final shape. 


Pablo


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## Amonra (Jun 30, 2008)

I have none of the information required as i have no idea when it comes to parabolics. i was hoping that someone ( like you  ) who has turned reflectors before knew what needed to be done.


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## PEU (Jun 30, 2008)

mmm... its the 1st time I see a reflector like that one 


Pablo


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## LukeA (Jun 30, 2008)

The profile of the cone depends on the intended height of the light-collecting ring.


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## Amonra (Jul 1, 2008)

im not fussy about that as long as it is collected in a nice tight ring


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## McGizmo (Jul 1, 2008)

Amonra,

I think I can provide you with a drawing generated from solid works. You state a 2" diameter but do you have any target on the distance of the focal point from the rear or base of your assembly? Keep in mind that you have not drawn a parabolic cone in your example. The curve will reach its lowest point (far to the left in the drawing) below the focal point and at the very outside diameter. As you have drawn it, you have a low point and then the curve comes back up, if that makes any sense.

In the image of a real part, I can't guess where the focal ring is but it could well be shy of the full diameter of the part. You are asking for the ring to be on the inner surface and not inboard in free air, right? If you want the energy to be focused in the air and not on the surface of the device, might you be better off having your focal ring at a diameter less than as you have shown it?


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## McGizmo (Jul 1, 2008)

Uh...

The physics is beyond me but it seems that you plan to take the energy of parallel sunlight and convert it to heat to do something to the air? If yes, you have used a fresnel to focus this light to a point and if this point is in air, won't you have the greatest impact at the fresnel's focal point and perhaps already have spent much of this energy?!?!


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## LukeA (Jul 1, 2008)

McGizmo said:


> Amonra,
> 
> I think I can provide you with a drawing generated from solid works. You state a 2" diameter but do you have any target on the distance of the focal point from the rear or base of your assembly? Keep in mind that you have not drawn a parabolic cone in your example. The curve will reach its lowest point (far to the left in the drawing) below the focal point and at the very outside diameter. As you have drawn it, you have a low point and then the curve comes back up, if that makes any sense.
> 
> In the image of a real part, I can't guess where the focal ring is but it could well be shy of the full diameter of the part. You are asking for the ring to be on the inner surface and not inboard in free air, right? If you want the energy to be focused in the air and not on the surface of the device, might you be better off having your focal ring at a diameter less than as you have shown it?



I think that as much as one half of the parabola is revolved, not more. That would put the focal ring at the outer rim of the part.


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## Amonra (Jul 1, 2008)

What i have drawn is basically freehand drawing so nothing is to scale or set in stone. It is just a rough picture of what i had in mind to aid the machinist.

I am trying to find the correct size fresnel for this and it appears that none exist with a 3 sqm area the largest i can find is a 1 - 1.2 sqm area fresnel this greatly reduces the concentrated sunlight and therefore the reflector has to be smaller. I may try to find a parabolic mirror/dish with a larger diameter to achieve the same results. but from some calculations i think that a 18cm diameter reflector might have a better chance at succeeding.
I suppose this makes it a bit harder to make.

Mc Gizmo i think you are right It would make sense that the focal point is just shy of the full inside diameter so that it heats the free air. I am not sure of this but as in the photo of the real part it appears that the focal point is within that small dark ridge. 

I have never personally seen this device but it got me thinking if the laser could be replaced with sunlight at a smaller scale.

The actual device works like this: A paralell beam from the 10kW laser is reflected into a concentrated ring of energy by means of this device. the air within this ring is very rapidly heated by this concentrated energy and 'explodes' creating thrust.

Sunlight comes to earth in paralell beams but is not concentrated.
when it is concentrated with a fresnel or parabolic mirror it is no longer in a paralell beam so an aspheric lens is needed to turn it back into a parelell beam. something like this:




we now have a concentrated paralell beam of sunlight that will replace the laser.


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## Amonra (Jul 1, 2008)

McGizmo said:


> Uh...
> 
> The physics is beyond me but it seems that you plan to take the energy of parallel sunlight and convert it to heat to do something to the air? If yes, you have used a fresnel to focus this light to a point and if this point is in air, won't you have the greatest impact at the fresnel's focal point and perhaps already have spent much of this energy?!?!



I guess what you mean is that the highest energy is at the focal point of the fresnel and if air had to explode it would do it there. I thought of this too and it would appear to be a good reasoning.
but the high powered laser does not explode the air before hitting the device which would prove this reasoning wrong. In this case the device does something to the beam and the air which creates the explosion.
however the laser might not be concentrated before hitting thus not exploding the air before hitting and is then concentrated after hitting which would prove the reasoning right. In this case i would need a lot more solar power to achieve my goal.

Im not sure of what is going on exactly and the only way of making sure is with some testing or some big brained optics expert to explain exactly what is going on in this device and tell me if i'm going in the right direction or into a wall.


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## DM51 (Jul 1, 2008)

You shouldn't necessarily need a fresnel lens for this - a normal lens would work just as well, in fact probably better. The advantage of a fresnel lens is that it is thinner due to the "steps", saving weight / bulk; however with the fresnel, you lose some efficiency due to these "steps". With a large-diameter lens, weight may be an important factor.


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## Amonra (Jul 1, 2008)

Apart from the weight and bulk advantages of a fresnel, cost is a decisive factor. I seriously doubt that I can find a 1 - 1.5 meter diameter lens off the shelf of a couple hundred bucks.

My other 'economic' option if i need to go really big is a polished parabolic dish which i might be able to find or build locally at not too much of a cost..


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