[chbot] chemical milling

[Mark Atherton]

David, Andrew,

Comments and links appreciated.

I have heard similar warnings about laser-cutting Cu before, but am not 
sure if it is urban legend or not.

The beam out of a 70W or so CO2 LASER emerges as a cylinder a few mm 
diameter (maybe 4mm?), and around 10um wavelength. The light then 
bounces around fixed and movable mirrors until it hits the final mirror 
where is is directed down, towards the bed. On it's way down, it passes 
through a convex lens, focussing the beam, and increasing the power 
density at some focal point - maybe 50mm.

This is where you now have many tens of watts of coherent light arriving 
at a final diameter of perhaps 50 microns. This is an incredible power 
density, and the very reason that the laser-cutter can do useful work.

So now we hit a piece of reflective material; some of the energy does 
useful work, lots gets reflected. The focus has been lost with this 
reflected beam, and it rattles around inside the cutting chamber. Some 
of the energy hits the perspex observation window. Perspex however is 
opaque to 10um and converts any remaining reflections into heat.

Even directly under the cutting head, perspex can only be cut to maybe 
10mm (if you are using a slow head), but the reflections are going to be 
several orders of magnitude lower than this.

I am not advocating using an LC with the lid open and the safeties 
disabled, but I can't see many problems with running a LASER over 
something reflective within the context above.

Anyway, appreciate anyone pointing out holes in my argument since this 
is a safety issue.

Regards,

Mark




Thanks for you comments.

On 7/12/2020 12:13 PM, David Closey wrote:
> Mark
> I have tried exactly as you suggest
> Paint over copper then laser off and etch
> It is written up in a few places on the web (see below)
> 
> I had some success but resolution was a bit to be desired
> (I couldn’t do smd parts) so was not much of an advantage over std methods
> 
> I found the same with milling pcbs
> Résolution was limited to through hole
> 
> I think Russel’s method with screen printing resist and using the 
> transparency from rs components is most exciting for home prototyping
> 
> Be interested to hear how you get on
> 
> https://www.instructables.com/Custom-PCB-Prototyping-using-a-Laser-Cutter/?amp_page=true
> 
> 
> David
> 
> 
> Sent from my iPhone
> 
> On 7/12/2020, at 10:43, Mark Atherton <markaren1 at xtra.co.nz 
> <mailto:markaren1 at xtra.co.nz>> wrote:
> 
>> Thanks Andrew,
>>
>> The hydrogen peroxide/hydrochloric acid solution looks most 
>> interesting; never heard of it before.
>>
>> My largest complaint back-in-the-day when using Ferric Chloride was 
>> the indelible orange-stain that the spills caused.
>>
>> Anyway, I am looking into chemical-milling some thin copper sheet, and 
>> you may have solved one of the issues.
>>
>> Just wondering about spraying a thin layer of paint on the copper. 
>> Removing the 'resist' using a laser cutter, then etching the remaining 
>> piece.
>>
>> Anyone have any experience with a similar process ??
>>
>> -Mark
>>
>>
>>> On 07 December 2020 at 09:14 Andrew Errington <erringtona at gmail.com 
>>> <mailto:erringtona at gmail.com>> wrote:
>>>
>>> Ferric chloride is nasty, and becoming increasingly difficult to get.
>>>
>>> Try hydrogen peroxide and hydrochloric acid (or hydrogen peroxide and 
>>> vinegar). Instructions on the web. I have tried it and it works.
>>>
>>> Andrew
>>>
>>> On Mon, 7 Dec 2020, 08:56 Marshland Engineering, < 
>>> marshland at marshland.co.nz <mailto:marshland at marshland.co.nz>> wrote:
>>>
>>>     Is this Ferric Chloride still available in NZ ?
>>>
>>>     I have some ammonium persulfate but FC works at room temperature
>>>     which makes
>>>     it easier.
>>>
>>>     Cheers Wallace