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Point to NotANumber blog for another idea how to create cone mirror.
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@hzeller
hzeller committed Jun 21, 2017
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Expand Up @@ -64,14 +64,19 @@ keeps the focal plane of the laser exactly on the exposed surface.


![](./img/anim-cone-arc-scan.gif) ![](./img/anim-cone-arc-scan.gif)


However, making custom mirrors in such a shape at home is not really feasible However, making custom mirrors in such a shape at home is not easy.
(Someone who has access to a lathe: this would essentially be a 45° bevel
on the inside of a large diameter stainless steel pipe with a wall thickness
of about 2-3mm. Then mirror finish polishing this bevel. I don't have
access to a lathe though :/).


We want to build this machine with minimal accessible tools, so this Possible ways:
is a hurdle. * With a lathe: this would essentially be a 45° bevel on the inside of a
large diameter stainless steel pipe with a wall thickness of about 2-3mm.
Then mirror finish polishing this bevel. Stainless steel or aluminum are
both nicely polisheable, so these could be materials of choice.
* [John M. suggests on his blog][NaN-cone-mirror] to build such a mirror using
laser cut parts that, snapped together, defining the shape.

We want to build this machine with minimal accessible tools, so these techniques
have to be explored if they can be done with minimal tools. Till then, let's
see what else we can do.


#### Straight mirror line exposure #### Straight mirror line exposure
We can simplify and use a straight mirror to project downwards to get a line. We can simplify and use a straight mirror to project downwards to get a line.
Expand Down Expand Up @@ -259,4 +264,5 @@ go inside the case.
[arc-project-vid]: https://youtu.be/8tyT4CI-1io [arc-project-vid]: https://youtu.be/8tyT4CI-1io
[ldgraphy-vid]: https://youtu.be/G9-JK2Nc7w0 [ldgraphy-vid]: https://youtu.be/G9-JK2Nc7w0
[hardware]: ./hardware#cut-pattern [hardware]: ./hardware#cut-pattern
[f-theta-images]: https://www.google.com/images?q=f+theta+lens [f-theta-images]: https://www.google.com/images?q=f+theta+lens
[NaN-cone-mirror]: http://notanumber.net/archives/228/circular-mirror-idea-laser-lithography

6 comments on commit 333bb2e

@david65536
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Hi Henner - I'm curious, have you considered trying these cone shaped reflectors used in lighting? Obviously there are many varieties!
image

@hzeller
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Good idea. No I have not considered that, but I did build a cone mirror using an acrylic first-surface mirror that I forced into the right shape after heating it. I think after a bit of refining, that technique can be pretty reproducible.
I think I posted a bunch of images to Google+ back then, but these are all gone now :/

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Ok I just ordered an aluminum cone reflector and will try it! Also good to know heat forming of mirrored acrylic is also promising.

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For reference this is a 6” HALO 426. It would be nice if it works since it is a mass produced part. The aluminum surface is quite smooth in quality although could be polished further. I will try cutting a vertical slit.

As an aside - do you happen to have any extra of the driver PCBs or made any updates? I hope to get this working and set it up at Noisebridge.

IMG_8210
IMG_8208

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This looks like it needs some polishing, indeed. And it needs to be a cone with exactly 45 degrees, this looks almost straight.

So, if you're at Noisebridge ... maybe we should meet, as I am local in SF (I actually made the laser-cut encasing on the Noisebridge laser cutter...).

I did some updates, but don't know if I have still PCBs. I can bring some parts and various proto-type intermediate stages that we can play with when we meet. Mail me at h.zeller@acm.org

@hstarmans
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@hstarmans hstarmans commented on 333bb2e Jul 21, 2023 •
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I agree, the cone needs to be exactly 45 degrees. You can calculate the Rayleigh length for a given spot diameter via https://en.wikipedia.org/wiki/Rayleigh_length. This determines how perfect your cone has to follow a circle.
From the distance from the cone to the exposure plane and geometry, you can calculate the impact of angular deviations.

A further complexity is the cross scan error. Each facet is tilted slightly differently. How did you solve this @hzeller, did you use one facet?
I am still impressed by your litho results.

The problem I have with this approach is that the mirror can be seen as a lens and will become more expensive if you target higher resolutions.
The argument this is cheaper than f-theta lens is not clear to me.
The prism I use now cost 20 USD a piece.

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