On Mon, 19 Nov 2018 13:57:48 +1100, you wrote:
If I remember this properly the following things could be happening:
1) if you manually set the grid size, then 0.025 may be small enough
for the primary grid, and 0.00625 (all inches) may be good enough for
the secondary grid. Tracks when manually routed follow the grid and
snap to it. Your job to manage pad size and trace width.
Now, Eagle's autorouter is set up for PC board houses, not for the
kind of routing either toner transfer or mechanical etching will need.
Trace size is generally set by net class according to the signal type,
however, the spacing between the trace and another trace, trace and
pad, pad and via, all of which the autorouter has to follow, that's
set by the Design Rules.
Check clearance to see what's going on.
As an experiment, set up three parallel pin headers, say about fifteen
or so long each. Connect corresponding pins on the two outer ones,
leaving the inner one disconnected. Set the clearances to 8 mils,
autoroute. ripup, set to 12, ripup, set to 16, then 24, then 32, then
40. Sooner or later, the autorouter will stop putting wires between
pins. Cobble together a board that has at least one surface mount
chip on either side, doesn't have to make sense. Do the same and I
think you'll start to see where the vias get placed.
Generally, when I routed boards that I was going to make (I used toner
transfer), I stuck to 10 mil trace, 10 mil spacing as the minimum
Note that as long as the design rules are followed, the autorouter
doesn't care how close it gets to another trace and has no incentive
to spread them out.
That being the case, maybe switching off Snap to Grid in Eagle will allow it do it properly for you.