Cone made of carbon

[farmersplow]

Cone made of carbon

I would like to present my first experiences with the production of cones from carbon.

In the first attempt I made 2 cones with 90 degrees.

The smaller cone was made with 3 layers of carbon fiber, has an outer diameter of 22mm and a height of 9.7mm (with a 3mm hole for the drive rod). The weight is 0.3 grams.

The second (larger) cone was made with 6 layers of carbon fiber, has an outer diameter of 28mm and a height of 12.5mm (with a 3mm hole for the drive rod). The weight is 0.8 grams.

If you take a closer look at the cones, they can be compressed a little in diameter and are therefore also a little elastic. When glued to the "drive coil", this elasticity does not apply!
The cone is absolutely stiff axially! Even with a load of 80kg (I just stood on the small cone) the shape remains unchanged.

If I look at the rigidity, 3 layers should be absolutely sufficient.
The attempt has not yet been completed. The cones have not yet been finally ground and drilled. The connection with the carbon rods and the coil must also be tested first. But I am confident.

My question to the group:
Is the weight 0.3-0.4 grams good?
What is the weight of your plastic, aluminium or sheet metal cones?
I would be very interested in that because otherwise I won't go on with the carbon (if it's too heavy).

Nice greetings from Vienna
Thomas

Illustration of the size of the cone:

1 Illustration of the size of the cone.png

Illustration of a carbon cone:

2 Illustration of a carbon cone.jpg

Illustration of two sizes of carbon cone front view:

3 Illustration of two sizes of carbon cone front view.jpg

Illustration of two sizes of carbon cone rear view

4 Illustration of two sizes of carbon cone rear view.jpg

Illustration of two sizes of carbon cones on speakers

5 Illustration of two sizes of carbon cones on speakers.jpg

Figure: Small cone 0.3 grams

6 Figure Small cone 0.3 grams.jpg

Figure: Large cone 0.8 grams

7 Figure Large cone 0.8 grams.jpg

[Dogtemple]

they look pretty good, for comparison, I have a cone made from an aluminium coke can, its 25mm diameter and approx 65 degrees, thickness is 0.01mm.

it weighs 0.25g but no where near as strong as yours, I couldn't stand on it without misshaping.

what gsm of carbon fibre are you using? I have been thinking of doing the same and forming a cone from carbon as it has the lightness and strength properties we need for such a task. yours look much better than aluminium

[farmersplow]

Thank you for sharing your experiences with aluminum cans cones. (Very helpfull).


The carbon fibre is a 200g/m².

20211005_163258.jpg

Carbongewebe-200g-Koeper.jpg

Today I have done versions with 2-layer. - It is still strong enought to stand on it.

Here a short video how I have done (Part 1):
(time lapse 1:10 - so in real time it was ~ 7 minutes)

20211006_144856.mp4

The negative pressure is generated with an 800W household vacuum cleaner.



24h later - (Part 2) time lapse 1:10

20211008_122153.mp4

The weight is now for the smaller cone (22mm) 0.28 grams and
for the larger cone (28mm) 0.59 grams.

That means the double of your alu coke can cone. I hope that the stability justifies the extra weight.

Greetings from Vienna
Thomas

[Dogtemple]

thats great, interesting stuff and thanks for the video.

I have planned to do it, essentially, the opposite way.

my idea is to make a cone from solid aluminium and lay the carbon on top, rather than inside a recess.

just a thought on making it lighter. you could try making a cone template and fitting it in to your former, rather than using a whole circle. that should help reduce weight as you would need only around half the amount of carbon fibre and epoxy.

I would also try maybe using only one layer, it would still be strong and save even more weight.

[Fela Borbone]

If alluminum,
¿Maybe a pyramid is stiffer than a cone?
Because of the edges..
I don't know, just asking..

[farmersplow]

Making the stencil in positive form was also my first thought. However, I ran into a couple of problems.

First, I can't reinforce the top. In my negative form, I can put two more layers of carbon fiber on the inside of the tip of the cone. If I now drill a 3mm hole in the finished state to attach the carbon rod (drive rod), I have a larger contact area and not just a thin circular ring (the staff won't hold.).

Second, I can use my negative form to drill the 3mm hole absolutely in the middle (because the hole is already in the form).

Thirdly, when processing carbon fiber (as far as I've tried) it is imperative that there is an overlap so that a dense body is formed. It was hard enough to bring the small carbon fiber mat into the negative form without it breaking up into thousands of small individual fibers. For me, two layers were the minimum number. (In the video you can see that I applied a narrow adhesive strip to the edge of the carbon fiber. I then cut it off before the vacuum process).
With one layer, the individual fibers slipped and it became full of holes. Applying the small mat to a positive form (outside) seems very difficult to me. Especially because it is necessary to apply a peel ply over it. The carbon fiber slips when it is attached to the outside. And then there is also a substance that enables air to be extracted. - slip even more.

Fourth, in the vacuum process, the air is sucked off (in order to compress the carbon firmly and "push away" the resin). This is where the tip is squeezed the most. This makes it even thinner and the effect (as described in the first point) is even worse.

Fifth: So that the cone on the side where it has to be attached to the coil body can be made absolutely at right angles to the drive rod, a good idea is necessary. I also need the negative form with its 3mm hole for this. The cone is put in and screwed tight with a screw. Then the negative form with the cone can be fastened in a vise and a plane level can be milled (filed) with a milling cutter or file. It is then absolutely at right angles.

And finally one last point. The cone just looks a lot better when you can see the smooth carbon side. (The bottom is ugly). After all, the eye is listening.

But try it with the positive form and report how it was. Maybe I'm wrong and I'll do it like you do.

Greetings from Vienna
Thomas

[farmersplow]

If alluminum,
¿Maybe a pyramid is stiffer than a cone?
Because of the edges..
I don't know, just asking..

Maybe. I don't know. Somebody should try ?!
But my goal is to get from a large round coil tube to a small round diameter of the drive rod.
If the coil were square, I could imagine a pyramid shape. But since it is round, I don't know how to mount a square shape on it? Ask for an idea how the transition should take place.

Nice greetings from Vienna
Thomas

[Dogtemple]

Making the stencil in positive form was also my first thought. However, I ran into a couple of problems.

First, I can't reinforce the top. In my negative form, I can put two more layers of carbon fiber on the inside of the tip of the cone. If I now drill a 3mm hole in the finished state to attach the carbon rod (drive rod), I have a larger contact area and not just a thin circular ring (the staff won't hold.).

Second, I can use my negative form to drill the 3mm hole absolutely in the middle (because the hole is already in the form).

Thirdly, when processing carbon fiber (as far as I've tried) it is imperative that there is an overlap so that a dense body is formed. It was hard enough to bring the small carbon fiber mat into the negative form without it breaking up into thousands of small individual fibers. For me, two layers were the minimum number. (In the video you can see that I applied a narrow adhesive strip to the edge of the carbon fiber. I then cut it off before the vacuum process).
With one layer, the individual fibers slipped and it became full of holes. Applying the small mat to a positive form (outside) seems very difficult to me. Especially because it is necessary to apply a peel ply over it. The carbon fiber slips when it is attached to the outside. And then there is also a substance that enables air to be extracted. - slip even more.

Fourth, in the vacuum process, the air is sucked off (in order to compress the carbon firmly and "push away" the resin). This is where the tip is squeezed the most. This makes it even thinner and the effect (as described in the first point) is even worse.

Fifth: So that the cone on the side where it has to be attached to the coil body can be made absolutely at right angles to the drive rod, a good idea is necessary. I also need the negative form with its 3mm hole for this. The cone is put in and screwed tight with a screw. Then the negative form with the cone can be fastened in a vise and a plane level can be milled (filed) with a milling cutter or file. It is then absolutely at right angles.

And finally one last point. The cone just looks a lot better when you can see the smooth carbon side. (The bottom is ugly). After all, the eye is listening.

But try it with the positive form and report how it was. Maybe I'm wrong and I'll do it like you do.

Greetings from Vienna
Thomas

lots of good points there, thanks for sharing.

something I have been thinking about is the drive rod and having enough material at the point for it to adhere to. it is something I have been trying to work out how to do best.

looks like your method is likely the best way of accomplishing this

[farmersplow]

Weight reduction by half thanks to additional drilling like a Swiss cheese. The stability remains almost the same.

b094647c-c0b8-40b9-a906-8a16cf472fb9.jpg

f16f7564-114e-452f-8b13-27d142b25ede.jpg

15b76fc8-e65d-4ad0-abf9-3b540829f3bd.jpg

During a stress test with a firm blow with the big hammer, a bridge broke. (The cone without holes has no damage). But I think this load will not occur on the cutting head.

38431e92-9594-4a2e-a7f8-7c44f974d923.jpg

Nice greetings from Vienna

[Dogtemple]

that looks great, that should be more than strong enough.

[leemichael]

I’ve often wondered if making holes in the cone would affect the audio and resonance of a cut.

[farmersplow]

Drilling holes definitely has an impact on sound and resonance. But I think that the influence of a stable carbon cone is much smaller than the gain that arises from the lower weight.
As far as I can remember, there are many solutions to get to one point from the large diameter of the bobbin. For example, four rods were also used. This would be comparable to a cone that has been drilled so much that only four rods remain.
I believe the advantage of drilled carbon over relatively soft and resonance-prone aluminum is greater than the influence that the holes have on the resonance.
But to believe is not to know anything.
The truth is, I don't know either.