ignition reference

[tom cloud]

>> Has any thought been given to making the disk from a PCB??  The artwork
>> would be relatively simple using AutoCAD or such.  I can't see how
>> to do it right now -- maybe plate the copper with iron so a hall
>> sensor would work with it.  Long ago I used a similar approach
>> to make optical encoders: encapsulated a film negative artwork in
>> a lexan disk.
>
>You could photo etch a copper or iron disk.  It would probably be
>quite easy to do as well.
>
>We were going to make soft copper head gaskets for high compression
>conversions for older off-beat engines that there are no kits for
>by using sign writing vinyl which can be cut to 0.25 mm accuracy
>without any trouble.  We have a set of vinyl masks which would
>be about right for a chainsaw but have not had time to try out the 
>setup.  With copper it is easier, you take some ferric chloride
>and sulphuric acid and then REVERSE electroplate the  holes into the 
>sheet with the vinyl mask protecting the gasket.

Whoa, dude.  My experience etching thick stuff is not happy.  Also,
what's this with the sulfuric and ferric chloride?  Ferric chloride
or ammonium persulfate are normal for etching PCB's.  Can also use
alkaline ammonia and chromic-sulfuric acid, but they are dangerous.
Just plain nitric acid can also be used.  But, as I said, the most
commonly used for PCB's are ferric chloride and ammonium persulfate.
If anyone cares, I can elaborate on pros and cons of each.  Don't
have much success with anything very thick (that requires spraying
the etching solution to lessen 'undercut').


Tom Cloud <cloud at peaches.ph.utexas>