Re: PDP-11/44 gas struts

[Alan Frisbie via cctalk]

Earlier, I wrote:

> 30-pound struts are not strong enough.  They improved things a bit,
> but it still takes a lot of effort to raise the box.  I have ordered a
> pair of 50-pound struts and will post an update when they arrive (next
> week).

The pair of 50-pound struts arrived today, and in my opinion they are
just barely adequate.  If I was trying for perfection, I would use the
60-pound ones, but they currently have a 6 to 7 week lead time.  I can
easily live with these.

In summary, what I have learned about replacement gas struts for the
DEC PDP-11/44 in a 40" high cabinet:

1. The specifications are: 15.24" extended, 9.77" compressed, stroke
length 5.47", threaded ball studs, extension force 50 or 60 (preferred)
pounds.

2. A good replacement is the McMaster-Carr 4138T55 gas strut in either
the 50 or 60 pound force version.  The price as of January 2022 is
$20.29 each.  

3. The threaded ball ends on the 4138T55 are 5/16"-18 threads, while the
original DEC ones are 5/16"-24.  They are easy to swap without
unscrewing them from the cabinet, and this is the method that DEC
recommends and describes on pages 5-5 to 5-7 of the PDP-11/44 System
User's Guide, EK-11044-UG.  You simply unsnap a retaining clip (no tool
needed), pop the strut off the ball end (a screwdriver might help),
and reverse the process with the new strut.  A piece of 4"x4" lumber
does a good job of holding the box up while doing this (stick it
under the rear of the cabinet when it is in the raised position).

EK-11044-UG is available at:
.
(In my earlier posting I gave the wrong DEC P/N for the manual.)

4. The 4138T55 struts that McMaster-Carr sells are manufactured by Suspa
Parts .  The 30-pounds struts are their 
part number C16-24186, and the 50-pound struts are C16-24188.   I

suspect that the P/N for the 60-pound struts would be C16-24189, but
cannot confirm that.  Their price is $32.00 each, so it is less
expensive to buy them from McMaster.

5. Suspa's design guide recommends mounting the struts with the rod end
down, the opposite of how DEC mounted them.  I have verified that they
can easily be mounted with the rod down as long as you connect the
upper (body) end first.  That is the way I have them now in my system.

I hope that this helps someone who might need to replace the gas struts
on their PDP-11/44 system or something similar.  It has been an
interesting learning experience.

Alan Frisbie

Re: PDP-11/44 gas struts

[Alan Frisbie via cctalk]

Chris Zach  wrote:


Jesus. How much does the 11/44 chassis weigh?

On 12/30/2021 3:39 PM, Alan Frisbie via cctalk wrote:


2. 30-pound struts are not strong enough.? They improved things a bit,
but it still takes a lot of effort to raise the box.? I have ordered a
pair of 50-pound struts and will post an update when they arrive (next
week).


The box itself weighs about 75 pounds, plus the weight of the cards.

Remember, however, that the struts are not doing a simple lift of
the box.  The box is acting as a lever.  The box is 24" long, and the
struts are only about 5" from the pivot.  Also, the struts are not
doing a straight lift from directly below their attachment to the box,
but at a point about 11" forward from where they are attached to the
box.  All of this greatly magnifies the force required to tilt the box
up.  Anyone care to do the math on this?

Alan Frisbie

Re: PDP-11/44 gas struts

[Chris Zach via cctalk]

Jesus. How much does the 11/44 chassis weigh?



On 12/30/2021 3:39 PM, Alan Frisbie via cctalk wrote:


2. 30-pound struts are not strong enough.  They improved things a bit,
but it still takes a lot of effort to raise the box.  I have ordered a
pair of 50-pound struts and will post an update when they arrive (next
week).

Re: PDP-11/44 gas struts

[Alan Frisbie via cctalk]

On 12/25/21 3:37 PM, I wrote:


I made a wild random guess and ordered two of the 30 pound struts,
which should be delivered Wednesday (12/29/2021).  The 40 pound
ones have a seven week lead time, and a pair of 50 pound ones seem
way too high.  When they arrive, I'll let you know how well they work.


The 4138T55 30-pound struts arrived, and I have learned a few things:

1. The ball connector ends on the DEC struts have 5/16"-24 threads, but
the 4138T55 struts have 5/16"-18 threads.  Therefore, you need to swap
the ball ends.  This is actually the method that DEC recommends for
replacing the struts and is described on pages 5-5 to 5-7 of the
PDP-11/44 System User's Guide (EK-11024-UG, available on Bitsavers).

2. 30-pound struts are not strong enough.  They improved things a bit,
but it still takes a lot of effort to raise the box.  I have ordered a
pair of 50-pound struts and will post an update when they arrive (next
week).

3. The 4138T55 struts from McMaster-Carr are made by Suspa, Inc. in
Grand Rapids, MI.  According to their design guide, the rod part of the
strut should be installed lower than the body.  This is the reverse of
how DEC installed them, which may be why they don't last.  When the new
struts arrive, I will see if they can physically be mounted that way
(I think they will), and will let you know.

I'm learning a lot about gas struts these days, as the ones on the cover
of my sand blast cabinet also failed after only a few months and the
seller (Eastwood.com) can't supply replacements.  Yet another learning
experience!  :-)

Alan Frisbie

Re: PDP-11/44 gas struts

[Alan Frisbie via cctalk]

Mark J. Blair  wrote:

> When I need gas struts and cannot identify a source for exact original
> replacements, I usually look at McMaster-Carr first:
> https://www.mcmaster.com/gas-struts/

Thanks for the McMaster-Carr suggestion, I should have thought of that.

I removed the gas struts from my PDP-11/44 and found the following
markings:

Gas Spring Corp.
Colmar, PA
1216166-0-0
22/81/3  (the "1" might be an "I")

I measured them, and found a compressed length of about 9.8" and an
extended length of 15.25".   The threaded studs are 5/16"-24.

I can't find the company, and Google turns up nothing with either
of the number strings.  Nor do the numbers seem to indicate what
the specifications might be.  Perhaps someone with better Google
skills than I have might find something.

It is, however, an almost perfect match for McMaster-Carr P/N 4138T55.
The big unknown is the extension force.  After cleaning and oiling them,
one of the bad ones measures about 12 pounds, and the other is about 23
pounds.   The 4138T55 is available in 15, 20, 30, 40, 50, 60, 90, and
120 pounds.

I made a wild random guess and ordered two of the 30 pound struts,
which should be delivered Wednesday (12/29/2021).  The 40 pound
ones have a seven week lead time, and a pair of 50 pound ones seem
way too high.  When they arrive, I'll let you know how well they work.

Worst case, I will have wasted $20.29 each, plus shipping, and have
to wait seven weeks for the 40 pound units, or go whole hog and try
the 50 pound ones.

Thanks for the help and suggestions.

Alan Frisbie

Re: PDP-11/44 gas struts

[Adrian Stoness via cctalk]

take them off and take them to a specialized automotoive shop.

On Fri, Dec 24, 2021 at 2:22 PM jim stephens via cctalk <
cctalk@classiccmp.org> wrote:

> There was a Basic four system I had which was a small amount taller but
> you get into having to have a really big counterweight.  I could imagine
> a smaller amount and the rear placement of the 11/44 Power supply weight
> would allow RL02s and such pulled, but leave the system where it is and
> raise the lid.
>
> All w/o having gone to look it up, so I'm guessing.  Also the H960 has
> small feet that support the weight as well when you pull things for
> service.
>
> thanks
> Jim
>
> On 12/24/2021 12:16 PM, Zane Healy wrote:
> > Out of curiosity, is there a manual for this style PDP-11/44 online?
> This is the style I have, but I’m pretty sure my manual is for the pull-out
> enclosure.
> >
> > A manual on this enclosure might give some idea on the gas struts.
> >
> > Zane
> >
> >
> >
> >> On Dec 24, 2021, at 11:58 AM, jim stephens via cctalk <
> cctalk@classiccmp.org> wrote:
> >>
> >> I have the same system cabinet, but have not looked at it in detail.  I
> think from some of the replies, they are thinking about the H960 tall
> cabinets and systems that are pulled out, then rotate on the slides.
> >>
> >> This I think is  like the hood of a car, then the system tilts up, as
> the cabinet isn't that tall that you can't work on it on top.
> >>
> >> As to sources, either automotive sources and match the fit, or a
> supplier like McMaster Carr.  I don't think any NOS on these would be any
> better than the ones  you have that rotted out.
> >>
> >> I only just got the 11/44 and didn't poke at it yet, just moved it from
> the original owner's storage to mine.
> >>
> >> I hope it to be one of my first 'big' projects after some PDP8s are
> tackled.
> >>
> >> thanks
> >> JIm
> >>
> >> On 12/23/2021 8:43 PM, Alan Frisbie via cctalk wrote:
> >>> I have a PDP-11/44 system in the DEC 41" high cabinet.
> >>> It is designed to be tilted up for service, aided and
> >>> supported by two gas struts, one on each side.
> >>>
> >>> Unfortunately, after all these years, the struts have
> >>> failed and do not provide any assistance. That box is
> >>> heavy!
> >>>
> >>> Does anyone know where I can get replacement gas struts?
> >>>
> >>> Thanks,
> >>> Alan Frisbie
> >>>
>
>

RE: PDP-11/44 gas struts

[pbirkel--- via cctalk]

This would be the "11X44" configuration where the 11/44 is mounted in a 40 inch 
top-loading H9642 cabinet ("corp cab").

See http://bitsavers.org/pdf/dec/pdp11/1144/1144_UsersGuide.pdf, Figure 4-5 
(page 4-7)

-Original Message-
From: cctalk  On Behalf Of Zane Healy via cctalk
Sent: Friday, December 24, 2021 3:16 PM
To: jim stephens ; General Discussion: On-Topic and 
Off-Topic Posts 
Subject: Re: PDP-11/44 gas struts

Out of curiosity, is there a manual for this style PDP-11/44 online?  This is 
the style I have, but I’m pretty sure my manual is for the pull-out enclosure.  

A manual on this enclosure might give some idea on the gas struts.

Zane



> On Dec 24, 2021, at 11:58 AM, jim stephens via cctalk  
> wrote:
> 
> I have the same system cabinet, but have not looked at it in detail.  I think 
> from some of the replies, they are thinking about the H960 tall cabinets and 
> systems that are pulled out, then rotate on the slides.
> 
> This I think is  like the hood of a car, then the system tilts up, as the 
> cabinet isn't that tall that you can't work on it on top.
> 
> As to sources, either automotive sources and match the fit, or a supplier 
> like McMaster Carr.  I don't think any NOS on these would be any better than 
> the ones  you have that rotted out.
> 
> I only just got the 11/44 and didn't poke at it yet, just moved it from the 
> original owner's storage to mine.
> 
> I hope it to be one of my first 'big' projects after some PDP8s are tackled.
> 
> thanks
> JIm
> 
> On 12/23/2021 8:43 PM, Alan Frisbie via cctalk wrote:
>> I have a PDP-11/44 system in the DEC 41" high cabinet.
>> It is designed to be tilted up for service, aided and supported by 
>> two gas struts, one on each side.
>> 
>> Unfortunately, after all these years, the struts have failed and do 
>> not provide any assistance. That box is heavy!
>> 
>> Does anyone know where I can get replacement gas struts?
>> 
>> Thanks,
>> Alan Frisbie
>> 
> 

Re: PDP-11/44 gas struts

[jim stephens via cctalk]

There was a Basic four system I had which was a small amount taller but 
you get into having to have a really big counterweight.  I could imagine 
a smaller amount and the rear placement of the 11/44 Power supply weight 
would allow RL02s and such pulled, but leave the system where it is and 
raise the lid.


All w/o having gone to look it up, so I'm guessing.  Also the H960 has 
small feet that support the weight as well when you pull things for service.


thanks
Jim

On 12/24/2021 12:16 PM, Zane Healy wrote:

Out of curiosity, is there a manual for this style PDP-11/44 online?  This is 
the style I have, but I’m pretty sure my manual is for the pull-out enclosure.

A manual on this enclosure might give some idea on the gas struts.

Zane




On Dec 24, 2021, at 11:58 AM, jim stephens via cctalk  
wrote:

I have the same system cabinet, but have not looked at it in detail.  I think 
from some of the replies, they are thinking about the H960 tall cabinets and 
systems that are pulled out, then rotate on the slides.

This I think is  like the hood of a car, then the system tilts up, as the 
cabinet isn't that tall that you can't work on it on top.

As to sources, either automotive sources and match the fit, or a supplier like 
McMaster Carr.  I don't think any NOS on these would be any better than the 
ones  you have that rotted out.

I only just got the 11/44 and didn't poke at it yet, just moved it from the 
original owner's storage to mine.

I hope it to be one of my first 'big' projects after some PDP8s are tackled.

thanks
JIm

On 12/23/2021 8:43 PM, Alan Frisbie via cctalk wrote:

I have a PDP-11/44 system in the DEC 41" high cabinet.
It is designed to be tilted up for service, aided and
supported by two gas struts, one on each side.

Unfortunately, after all these years, the struts have
failed and do not provide any assistance. That box is
heavy!

Does anyone know where I can get replacement gas struts?

Thanks,
Alan Frisbie

Re: PDP-11/44 gas struts

[Zane Healy via cctalk]

Out of curiosity, is there a manual for this style PDP-11/44 online?  This is 
the style I have, but I’m pretty sure my manual is for the pull-out enclosure.  

A manual on this enclosure might give some idea on the gas struts.

Zane



> On Dec 24, 2021, at 11:58 AM, jim stephens via cctalk  
> wrote:
> 
> I have the same system cabinet, but have not looked at it in detail.  I think 
> from some of the replies, they are thinking about the H960 tall cabinets and 
> systems that are pulled out, then rotate on the slides.
> 
> This I think is  like the hood of a car, then the system tilts up, as the 
> cabinet isn't that tall that you can't work on it on top.
> 
> As to sources, either automotive sources and match the fit, or a supplier 
> like McMaster Carr.  I don't think any NOS on these would be any better than 
> the ones  you have that rotted out.
> 
> I only just got the 11/44 and didn't poke at it yet, just moved it from the 
> original owner's storage to mine.
> 
> I hope it to be one of my first 'big' projects after some PDP8s are tackled.
> 
> thanks
> JIm
> 
> On 12/23/2021 8:43 PM, Alan Frisbie via cctalk wrote:
>> I have a PDP-11/44 system in the DEC 41" high cabinet.
>> It is designed to be tilted up for service, aided and
>> supported by two gas struts, one on each side.
>> 
>> Unfortunately, after all these years, the struts have
>> failed and do not provide any assistance. That box is
>> heavy!
>> 
>> Does anyone know where I can get replacement gas struts?
>> 
>> Thanks,
>> Alan Frisbie
>> 
> 

Re: PDP-11/44 gas struts

[jim stephens via cctalk]

I have the same system cabinet, but have not looked at it in detail.  I 
think from some of the replies, they are thinking about the H960 tall 
cabinets and systems that are pulled out, then rotate on the slides.


This I think is  like the hood of a car, then the system tilts up, as 
the cabinet isn't that tall that you can't work on it on top.


As to sources, either automotive sources and match the fit, or a 
supplier like McMaster Carr.  I don't think any NOS on these would be 
any better than the ones  you have that rotted out.


I only just got the 11/44 and didn't poke at it yet, just moved it from 
the original owner's storage to mine.


I hope it to be one of my first 'big' projects after some PDP8s are tackled.

thanks
JIm

On 12/23/2021 8:43 PM, Alan Frisbie via cctalk wrote:

I have a PDP-11/44 system in the DEC 41" high cabinet.
It is designed to be tilted up for service, aided and
supported by two gas struts, one on each side.

Unfortunately, after all these years, the struts have
failed and do not provide any assistance. That box is
heavy!

Does anyone know where I can get replacement gas struts?

Thanks,
Alan Frisbie

Re: PDP-11/44 gas struts

[Mark J. Blair via cctalk]

Like Steve, I don't know about the original application. My own 11/44 project 
pile has the slide out and rotate style of slides, to the extent that it has 
any slides at all. When I need gas struts and cannot identify a source for 
exact original replacements, I usually look at McMaster-Carr first:

https://www.mcmaster.com/gas-struts/

-- 
Mark J. Blair 
Blog:https://www.nf6x.net
Git: https://gitlab.com/users/NF6X/groups
HECnet:  DOGPAK::MBLAIR
Twitter: @nf6x

Re: PDP-11/44 gas struts

[Steve Malikoff via cctalk]

Alan asked

> I have a PDP-11/44 system in the DEC 41" high cabinet.
> It is designed to be tilted up for service, aided and
> supported by two gas struts, one on each side.
>
> Unfortunately, after all these years, the struts have
> failed and do not provide any assistance. That box is
> heavy!
>
> Does anyone know where I can get replacement gas struts?

No idea about original but if aftermarket is ok:
ebay.com   69,448 results for gas strut
Results could surely be narrowed down if dimensions provided.

Also for a given size they come in different levels of compression
force required.
I have replaced a few here and there, and also had them re-gassed
by a mobile service although that did not really last a long time.

Steve