On Mon, Feb 1, 2010 at 4:07 PM, David Griffith <
dgriffi@...>wrote:
>
>
> Here's yet another question on the photographic method. Has anyone tried
> making their own spinner for applying resist? It seems like it would be
> simple and straightforward to create one.
>
I've used a old 12V computer fan running on 6V with a baby-food jar lid
hot-glued to the the fan spindle (The lid is glued upside down). I then
place a dab of hot glue on two or three places on the jar lid lip and after
quickly eye-balling the centering I put a piece of copper clad on it and it
sticks very well until I pull it off after coating. I apply some photo
resist in a fairly thin layer, spreading it out so it's reasonably even and
then spin up the fan until the resist appears to be a sky blue. I then let
it air-dry for an hour or so before putting it in a 250 F oven for a couple
minutes and it's done. It's a little fiddly because if you don't put the
resist on fairly evenly it will cause lines of thicker and thinner resist to
appear. I suppose you could put more on and have it flow over the surface
more evenly but I hate to waste 90% of the resist especially when it's about
$76 for a quart. I've had better luck thinning the resist with water (since
it's water-based) and then air-brushing it on with a Harbor Freight "pro"
airbrush which allows you to adjust the feed rate of the resist on the fly.
This results in a very smooth, even resist coating that dries quickly and is
easy to apply once to get the hang of it, always starting the flow before
you are over the board and halting if after you're off the board and only
going in one direction, horizontally across the board. If you mess up a
little you can always back the feed rate off a bit and go over it on places
that didn't get as much as they should. I use resist I got off of eBay
(Item 300386143218) which seems to work quite well and resolve fine lines
and so forth nicely.
Larry
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