Racking a PDP-11/24

[Rob Jarratt]

Thank you for the reply.

> -----Original Message-----
> From: pbirkel at gmail.com <pbirkel at gmail.com>
> Sent: 26 February 2022 08:48
> To: rob at jarratt.me.uk; 'Rob Jarratt' <robert.jarratt at ntlworld.com>;
'General
> Discussion: On-Topic and Off-Topic Posts' <cctalk at classiccmp.org>
> Subject: RE: Racking a PDP-11/24
> 
> 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).

I saw something somewhere that suggested the RL02 should be at the top with
the disk accessible without pulling out the drive. I don't think the cabinet
I have was intended to do that, but I will have a closer look.

> 
> 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 did try raising the CPU as high as possible. Will have another look to see
if the RL02s can be dropped a bit lower, but I don't think they can go lower
in terms of using lower slots, not unless I want to leave a gap and possible
interfere with the space at the bottom where there will be some cables I
think. I would like to avoid filing though!

> 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").

There *is* a bit of play in the big black sheet that is screwed onto CPU
enclosure.

> 
> 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