Modern Rack Rails in Classic Racks?

Zane Healy healyzh at
Sat Apr 27 18:15:12 CDT 2019

> On Apr 27, 2019, at 3:31 PM, Steve Malikoff via cctalk <cctalk at> wrote:
> Zan said
>> How safe is it to put modern rack rails (HP) in a classic DEC Rack?  The DEC racks have small holes, while the new HP racks, IIRC, have big square holes.  It looks like the rails will work, they just won’t clip flush.
>> Zane
> I have been modifying quite a few hodgepodge pairs of modern server rack slides for
> H960's. It's the same set of steps to go through on each one.
> The very first consideration is to pick a pair of slides that are firstly a) strong
> enough construction to hold heavy (Unibus) gear and b) thin enough so they will
> accommodate the gear widthwise. Not all slides I've done could have worked for an
> PDP-11/15 in a 19" rack as the box was really taxing the maximum width. Measure the
> slide widths and gear with some degree of accuracy before committing time and effort
> to modifying a pair of slides.
> The next thing is to remove all the modern quick-release latches, levers, buttons, pins,
> pivoting plates and other crap. Also the riveted rear bracket has to come off, so I use
> a die grinder and cutoff wheel to do all these. It's very satisfying to end up with a bare
> set of slides.
> All ,modern slides are too long, so I set them up on the H960, scribe the length at the
> back then disassemble and cut the outer rails to length then drill the outer ends for a
> removeable backstop screw so the inner rails don't slide out the back.
> Using the rear bracket removed in step 1, I cut to size and refit these at the back with
> small countersunk screws so the inner rails can traverse over them. Often an extra pair
> of rack unit-spaced holes are required to be drilled. Use an engineer's square to check
> things are really square and accurate, or the slides will bind a bit when in use with heavy
> equipment (you can almost bet on this).
> The next inner rail is then fitted, 90 deg scribed and trimmed at the front. I use an air body
> saw for this but sometimes also a plain old hacksaw. Each pair needs to be modified
> accordingly to its locations of the front and rear roller guide wheels, the latches and
> so on. Wipe everything clean of metal shavings.
> The innermost rail is then fitted and cut to length at the front. Sometimes some extra
> retract length can be obtained by repositioning something, or cutting away an indented
> stopper or spring-lock latch. Again a stopper screw may be required to prevent the
> gear falling out the front this time.
> Then the mounting holes for the gear are drilled in the inner rails. For the PDP-11/15
> I needed to have a pivoting arrangement so I machined a pair of thin stepped bushes
> which worked well.
> I use modern M6 server rack screws as they are easy and cheap to buy on eBay. Even some
> of these need occasional fitting, for instance the Digitronics paper tape reader had
> inset mounting screw holes in the front panel that were a tiny bit small for the pan-head
> screws, so I machined the head diameter down a fraction.
> For the square holes, I use soft aluminium washers which the rack srew draws into the
> square and centres up when it is tightened.
> In summary - you can adapt modern rack slides to fit old gear and racks, but it's a
> surprising amount of metalwork even with a good arrangement of tools. I still have a lot
> of them to do.
> Steve.

I was going to say I’m lucky, in that I’m looking to mount a modern system (HP DL380).  Plus I found a really cheap, and easy to move modern rack that I’ll pick up, mid next week.  Then it hit me, I’d sort of like to drop a MicroVAX III in the bottom of this rack, in part to allow the use of the system, and in part for weight.  It might also be nice to rig a PDP-11 in there as well.  I have four DEC Racks, two of the short ones that house my PDP-11/44, a taller rack intended for RA7x and RA9x drives, then there is the tallest, the H960.  All these racks are basically full (static storage, if I’m honest).  I’ve used a Gorilla Rack for years to house all the desktop systems that have made up my “home datacenter”, but now I find I need to think about a real rack.  

Actually I don’t need a modern rack, in writing the above it hit me, prior to the Gorilla rack, I’d been using some wooden racks, and based on a quick check, they should just fit.  I have a ton of these, that I no longer use, and they’ve been sitting disassembled taking up space.

Problem solved, for now, and I don’t see me adding more than a couple modern rack mount systems out in the garage due to power and cooling constraints.  To land this server, I’m retiring two older DEC systems, which will be virtualized.

My thanks to you and Adrian for your answers, at some point I’m sure I’ll put this knowledge to use, thankfully it looks like it won’t be today.


More information about the cctalk mailing list