Racking a PDP-11/24

[pbirkel at gmail.com]

The conventional mounting for RL02 drives in a corporate cabinet puts one at
the top with the 6U CPU in the middle *but* that assumes that you have a
corporate cabinet designed for that purpose -- in which case the top is
missing so that the RL02 disk-pack can be directly accessed, and there is a
1U divider below the top RL02 that reinforces the rack (and in effect
replaces the 1U lip on your rack top).

AFAIK you should be able to make your rack plan work; it's just the case
that RL02 are always "top snug" (at least in my experience).  Have you tried
raising the 6U CPU as high as possible *before* tightening the bolts/screws
on the mounting flanges on the slides (to the rack, not to the chassis)?
There's usually ~1/8" of play there.  From your photo perhaps you have
already done that as the CPU-front looks to be snug to the rack-top.  If
anything it looks as if your RL02 instead need to move down.

I would start by moving the bottom RL02 down as far as possible, then repeat
with the second RL02.

Your observation that there is "very little clearance between the CPU and
the RL02 at the front but more at the back" suggests to me that you need to
fiddle move with the front and /or rear mounting flange positioning on the
various slides.  Don't assume that wherever "gravity drops them" is going to
be correct.

If none of the suggested adjustments are working then I would consider
getting out a rat-tail file and enlarging the slots on the mounting flanges
on the RL02 slides so as to let them drop a little lower (assuming that you
have clearance at the bottom!).

Regardless you shouldn't need to play with the slide-to-chassis attachment
points -- those are always "just so" and not really free to fiddle with (no
"slop").

In my experience "racking" is a fiddling-time and clearances can be *really*
tight.  But ... it can be done :->.  Good Luck.

-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Rob Jarratt via
cctalk
Sent: Saturday, February 26, 2022 3:15 AM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: Racking a PDP-11/24

I am wondering if I have racked my 11/24 correctly.

As you can see here:
https://robs-old-computers.com/2022/02/10/pdp-11-24-progress/ I have put the
CPU at the top and the two RL02 drives underneath.

The problem is that the CPU enclosure catches on the RL02 underneath. There
is a bit of play in the mounting bracket:
https://rjarratt.files.wordpress.com/2022/02/cpu-mounting-bracket.jpg. With
a bit of manipulation I can get the CPU to slide in. However, I am wondering
if I have racked it correctly? I don't think there is room to move the RL02s
down and it would presumably leave a bit of a gap below the CPU. There seems
to be very little clearance between the CPU and the RL02 at the front but
more at the back, but I am sure that the rails are mounted horizontally. Is
it just a matter of tightening the big screws that hold the mounting
brackets to stop the play? If so I am not sure I have a big enough
screwdriver!

Regards

Rob