ignition reference

[Kalle Pihlajasaari]

Hi Tom,

> >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').

The sulphuric is just to add a bit of bite to the etchant.  You will
often find it used by normal FC etch people.  The thick material 
undercut problem we would minimise slightly by the use of the
electrical help which speeds the process up and allows you to 
keep the time short enough to actively monitor (read eye ball)
stop etching as soon as you are ready.

We were planning on 0.2 mm to 0.5 mm copper or brass shim.

Cheers
-- 
Kalle Pihlajasaari     kalle at data.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751