Homebrew PCBs

Here is an update of my progress:

The spray on (negative type) photo resist and developer will arrive on
Thursday. In the mean time, I took some nominally 1.125 " diameter copper
pipe and cut off a 1/2" piece. Then I turned some cold rolled steel down for
an interference fit. I left a shoulder on the steel. I was then able to
force fit the soft copper onto the steel using my bench vise. Then I put the
assembly back on the lathe to true it all up and drill a center hole. My
finished outside diameter of 1.125" means my scale must be 3.545" long. 

I then drew a 6" line with my CAD program and printed it out. To my
surprise, the printed line was 6.000" so no correction factor is needed. I
then drew a simple scale with 10 segments and 4 small tick marks per
segment. I also put numbers to the right of each segment line. After
printing out, I taped it to the OD of the copper and it was a perfect fit. 

So next I will print it out on clear plastic, trim the excess, and wait for
the chemicals. If I understand the term "negative type" correctly, what is
black on the artwork will be copper free after etch. If true, that sure
saves toner.

Rick

-----Original Message-----
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of KalleP
Sent: Monday, March 25, 2013 7:45 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Re: etching the OD of a cylinder to create a
graduated dial

This will not work as is for a cylinder but for a conical scale it might
work.

Instead of projecting a line and then indexing the dial you could look at
some of the long wave UV photo cure polymers that are used for 3D stereo
lithography.  You would dip the scale in the resin, pull it out and project
an image with a UV modified DLP video projector, no need to dry the resist
as you would be hardening it in-situ with the UV image.  Have to keep the
projector as far as convenient to maximise the focus depth if you have a
conical scale (long focus lens) but you could have arbitrary complexity of
the artwork that could be changed on every scale.

You would rinse and post cure the resin and then try out various etching
methods to get a good bite.  You could paint fill and then strip the resin
off with a suitable solvent.

This method might have some value in making DIY PCBs as well, I know there
are very (very) expensive industrial machines that do just this and have
many of these projectors and expose a 50mmx50mm square (or whatever) and
scan across the material and have the image track the material motion to get
a continuous scan while having a largish projection area (instead of a
single laser spot or scan line that is too slow).  Imagine a video projector
and a simple jig to position a pcb in 50mm grid, you could manually project,
move, project and expose arbitrary image.  Using the 3D printing resins
might be a way to do a wet photo resist at home but I have not tried it.
The materials are still a bit expensive but the layer required for etch
resist should be fairly affordable.

A Google search found these two interesting hits, the second is just an
abstract unless you pay or are a member of some secret cabal.

http://maskless.com/High_Speed_MLI_TechPaper.pdf

http://www.researchgate.net/publication/24261077_Direct_projection_on_dry-fi
lm_photoresist_%28DP%282%29%29_do-it-yourself_three-dimensional_polymer_micr
ofluidics

Regards

Kalle
--
Johannesburg, South Africa