A 'good-enough' H960 |d|i|g|i|t|a|l| PDP11 masthead replica

Noel Chiappa jnc at mercury.lcs.mit.edu
Fri Jul 10 09:34:35 CDT 2015

    > From: Steven Malikoff

    > It appears the top edge projects further than the bottom by a tiny bit
    > leading to a tapered appearance, but I assume the plane of the printed
    > inset panel is parallel to the exterior mounting surfaces.

By top edge I assume you mean the top edge of the unit (we need a common term
for the entire injection-molded plastic thingy), as it would be when mounted
on the rack?  And the distance you're talking about is the distance from the
very front of the unit to the flange that projects out around the unit on
three sides (sides and bottom), right?

OK, I'm measuring mine (with calipers :-), and from the back of the flange to
the front of the rim around the coloured insert, it is 3.80 cm at the top,
and... 3.80 cm at the bottom. So no tapering. (And it's the same on both

    > A common method of determining radii is to use an engineers radius
    > guage.

Which I don't happen to have... something to add to my tool wish-list! :-)

    > Failing that, try fitting a series of circular objects (coins etc.)
    > which can then be measured with calipers or micrometer.

I did try with the butt ends of a number of large drill bits, but I didn't
get really good results. I mean, you can tell when it's way off (too small,
and the object 'lifts' off the surface at the outer edges of the object, too
large, and you get a gap in the middle), but there's a range in the middle
where it's hard to tell - it all depends on where you decide the ends of the
curved part are.

Oh, one note: when I gave the gap between the coloured insert, and the sides
of depression it sits in ("it's slightly smaller than the inset in the
plastic housing, by about .5 mm"), that .5 mm is on each side, not total.


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