Jack screw retention

[Don Y]

Is there a "trick" to keeping jackscrews fastened to the
"bulkhead connector" with which they are associated? I.e.,
so removing the cable attached to that connector -- and
secured by those jackscrews -- doesn't "back out" the screws
in the process?

I've been using Loctite (red) to secure the jackscrews but
even that doesn't seem reliable. Maybe add WD40 to the
mating fasteners prior to engagement?

[Monitors seem to be the biggest problem -- no doubt because
the connectors often aren't convenient located and the
fasteners too cramped for ease of access. Other connectors
often have alternatives that aern't as "pissy"]

[DecadentLinuxUserNumeroUno]

On Tue, 10 May 2016 17:45:48 -0700, Don Y <blocked...@foo.invalid>
Gave us:

If you are talking about the screws that are on the "plug" (moving
element), there are little clips.

If you are talking about the stand-offs on the "jack" (fixed,
panellized element), then you should use the red locktite, however, you
should also STOP cranking the plug onto it like it is a truck tire.

they are only meant to retain the position of the installed plug, NOT
make it some bolstered assembly.

Even a d-sub SVGA connector with extended thumb screws are only meant
to be run down enough to 'cinch' the connection mating.

The torque you apply MUST always be less than that of the retention
feature (stud) of the stand-off (jack screw) itself.

I have seen poorly made chinese types that were undercut at the neck
and would twist off like taffy if one tried to attach then tighter to
keep the d-sub attachment from breaking them loose.

But the really good ones can be locktited in real good. Your locktite
could also be expired and have poor efficacy.

[Martin Riddle]

On Tue, 10 May 2016 17:45:48 -0700, Don Y

I use loctite too, and make sure there is a lock washer on them.

Cheers

[Rheilly Phoull]

I've had success with lockwashers

[Tim Wescott]

You _are_ tightening the snot out of them? To paraphrase my across-the-
street neighbor when I asked my dad about torque on my '48 Chevy's
straight-six head bolts, tighten them until they just break, then back
them off about 1/4 a turn.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

[Rob]

I presume you mean the "DB" types of connector.
(used for serial ports, VGA and DVI monitors, etc)
There are different problems...

Two different types of thread are in use (probably one US and
one metric). The "wrong" thread screws sort of fit, but when trying
to loosen them they stick and take the jackscrew with them.

The materials are also soft (brass), and screws that have been
tightened too much tend to stick as well.

The soft material also means you cannot tighten the jackscrews
very well without destroying the thread.

Of course these DB connectors are being phased out.
Newer connector types like HDMI and USB unfortunately lack
a locking mechanism. DisplayPort has one, not using screws.

[jurb...@gmail.com]

I am curious about just what kind of environment is causing this problem. I have never had nor seen a problem with this in my life, and I been around. This must be somewhere I haven't been around. What ?

[Rob]

jurb...@gmail.com <jurb...@gmail.com> wrote:
> I am curious about just what kind of environment is causing this problem. I have never had nor seen a problem with this in my life, and I been around. This must be somewhere I haven't been around. What ?

I understood he means the locking screws of DB-type connectors used in
the past for RS232 (and parallel on IBM PC) and for monitors (EGA,VGA,DVI).

It was VERY COMMON with those connectors that the locking screws in the
connector took out the receptacles in the chassis part when unscrewing
them to remvove the connector.

[Don Y]

On 5/10/2016 6:41 PM, Martin Riddle wrote:
>> I've been using Loctite (red) to secure the jackscrews but
>> even that doesn't seem reliable. Maybe add WD40 to the
>> mating fasteners prior to engagement?
>>
>> [Monitors seem to be the biggest problem -- no doubt because
>> the connectors often aren't convenient located and the
>> fasteners too cramped for ease of access. Other connectors
>> often have alternatives that aern't as "pissy"]
>
> I use loctite too, and make sure there is a lock washer on them.

That (lockwasher) hasn't seemed to help, either. (I have variants of
the MF standoff that are a tiny bit "shorter" to accommodate the
thickness of the lockwashers without "disengaging" the cable by that
amount).

I spent some time sorting through the various types of cables that
I regularly use (I move kit around often so it's not uncommon
for cables to be mated/unmated many times). Without crawling
under/over/into anything, I came up with:

- DE9 ("abbreviated" EIA232 connector, old CGA)
- DA15 (old ethernet, old apple video)
- HD(e)15 ("VGA" cables -- monitor and computer end)
- DB25 ("real" EIA232 connectors; old PC parallel port; wonky SCSI)
- DC37 (reading machine)
- DD50 (old Sun SCSI)
- "DVI" ("digital" monitors)
- HPDB68 ("SCSI-3" [sic])
- VHDCI (SCSI)
- 13W3 (Sun/SGI monitors)

Of these, the only ones that seem to have caused problems (with the
jack screws coming off the bulkhead) are the "VGA" (HD15) connectors.

[Note that some of the mating SCSI cables had problems with *bent*
mating screws owing to the bulk of the cable and the length of
the thumbscrews. And, once bent, "abandon all hope..."]

So, why the problem with these but *not* the DE9, 13W3, DVI, DA15
(all used in "similar" applications)? Or, any of the (often heavier!)
cables that employ similar fasteners?

Long story short: it appears to boil down to quality (of the
device to which the connector is attached) AND the ease with
which the mating thumbscrews can be accessed ("VGA" cables
tend to "crowd" the thumbscrews making them hard to engage/disengage)
AND the tendency of the mating cable to experience some side motion
while engaging/disengaging.

Removing the (factory installed!) jackscrews from monitors reveals
sloppy fits -- almost as if a metric screw was used in an "english"
boss. By contrast, the 13W3 jackscrews mate to the connector like
a machine screw into a *nut* (no "slop"). Ditto for the SCSI3,
DC37, "serial port", etc. Even the massive DD50 cables were
robust in this regard.

Some monitors had well fitted jack screws; but, those tended to be
part of the HD15 connector itself (not something that could be
separated from the connector without breaking the connector!).

It appears the sloppy/cheap screws are used in cases where the
jack screws are relied upon to secure the HD15 *to* the device's
enclosure. So, if you had to disassemble the device, you would
have to remove the jack screws to access the PCB.

None of this helps me; I have no desire to unsolder HD15's -- and
then modify the enclosure so the PCB doesn't require the jack screws
to support the connector!) just to replace a crappy connector with
one that's more robust.

And, as the jackscrews must be removable (to access the PCB), the idea
of "welding" them onto their HD15's is out of the question.

Maybe a "stickier" Loctite formulation (I also have "green" but I
thought that was for penetration, not hold strength)? Note that
there is a limit to how tight you can make them without the
jackscrew (or its mating female part in the HD15) failing -- in a
big way! (the jackscrews seem to have very low tensile strength;
maybe I can rescue some from the SCSI3 connectors as they seem to
be hardened parts)

[Don Y]

On 5/10/2016 10:02 PM, Tim Wescott wrote:

>> [Monitors seem to be the biggest problem -- no doubt because the
>> connectors often aren't convenient located and the fasteners too cramped
>> for ease of access. Other connectors often have alternatives that
>> aern't as "pissy"]
>
> You _are_ tightening the snot out of them?

There's a limit as to how tight you can get them. The "female" into which
they mate is often a flimsy material that won't stand up to much torque
(without pulling the threads out).

And, often the jackscrew (M-F standoff) itself fails due to low tensile
strength. I learned this using nut drivers to tighten a bunch some
years ago -- far too easy to "overtorque" them and snap a portion of
the screw off inside the "nut" (I put these on little "widget" assy's
that I make as "cable adapters". So, they are being screwed into machine
nuts, not some flimsy connector shell)

The "Loctite epiphany" was a result of that. But, hasn't seemed to
fare well with monitors...

> To paraphrase my across-the-
> street neighbor when I asked my dad about torque on my '48 Chevy's
> straight-six head bolts, tighten them until they just break, then back
> them off about 1/4 a turn.

I'll have to remember that one! :>

[DecadentLinuxUserNumeroUno]

On Wed, 11 May 2016 08:18:27 -0700, Don Y <blocked...@foo.invalid>
Gave us:

>

>That (lockwasher) hasn't seemed to help, either. (I have variants of
>the MF standoff that are a tiny bit "shorter" to accommodate the
>thickness of the lockwashers without "disengaging" the cable by that
>amount).

There are various lengths and they are designed for various panel and
spotface thicknesses so that the mating level of the face of the nut
gets properly positioned with respect to the connector shroud.

The lock washer is supposed to be on the other side (of the panel)
with the nut or threaded hole the stand-off's stud screws into.

[Tim Wescott]

Maybe you need a better grade of jack screw and screw? If you're getting
the cheapest possible stuff then you won't be able to screw it in hard.
OTOH, at the absurd extreme you can get grade 8 hex head hardware -- you
may pull the threads out of cheapo soft jackscrews, but you won't break
the screw itself unless you really, really try.

I'd make sure I'm getting name-brand parts, and I'd buy a few extra to
break on purpose just to get myself calibrated. In a production
environment I'd use a torque wrench or screwdriver, and record how tight
I could go, then instruct my people (even if "my people" were just me) on
what that is. I think that even if I were doing lots of repairs I'd be
tempted to treat it as a production environment.

[DecadentLinuxUserNumeroUno]

On Wed, 11 May 2016 08:37:02 -0700, Don Y <blocked...@foo.invalid>
Gave us:

>There's a limit as to how tight you can get them. The "female" into which
>they mate is often a flimsy material that won't stand up to much torque
>(without pulling the threads out).

Actually they are design not to strip threads and will even allow
tightening all the way up to the point at which they shear off at the
neck. "often a flimsy material" sounds like the place where you got
your 'experience' bought nothing but cheap chinese CRAP.

[Don Y]

I'm not "getting" anything ("I had to pay $50 and pick up the garbage!")
but, rather, living with the jackscrews that come with the kit.

For example, the jackscrews that IBM (and Sun and some "high end" Sony) use
are much harder steel than the stuff on most "monitors". Ditto for the
"non-monitor" cable uses.

> OTOH, at the absurd extreme you can get grade 8 hex head hardware -- you
> may pull the threads out of cheapo soft jackscrews, but you won't break
> the screw itself unless you really, really try.
>
> I'd make sure I'm getting name-brand parts, and I'd buy a few extra to
> break on purpose just to get myself calibrated. In a production
> environment I'd use a torque wrench or screwdriver, and record how tight
> I could go, then instruct my people (even if "my people" were just me) on
> what that is. I think that even if I were doing lots of repairs I'd be
> tempted to treat it as a production environment.

Small hardware is typically rated well below what an "average person"
can develop in the hands/arms. E.g., you should be able to strip a
#0 and #1 point Phillips-head screw (and even shear the tip off the
screwdriver).

And, the jackscrews aren't intended to carry any significant load; so,
no reason they should be designed for that. I suspect they encounter all
sorts of weird "side" loadings when users try to mate/remove cables
WHILE tightening/loosening thumb screws. E.g., a bending moment
could bind the thumbscrew in the jackscrew and transfer the motion
that the user is placing on the thumbscrew to the jackscrew itself...

I'm guessing the problem is primarily in the "sloppiness of fit"
that seems characteristic of the connector shells -- common on $100-$200
monitors (but absent on $500-$1000+ monitors!). I'm going to
see if there is an "even stickier" Loctite-like product available
and try that.

[George Herold]

I'm not sure exactly what you are doing.
But you could try peening, or otherwise deforming the place
the two pieces join. Both metal I assume.
George H.

[Don Y]

On 5/11/2016 7:07 PM, George Herold wrote:
> I'm not sure exactly what you are doing.
> But you could try peening, or otherwise deforming the place
> the two pieces join. Both metal I assume.

I repair a lot of kit. Some for myself, but most for charities
and other non-profits. Monitors are a big item -- they seem to
have short lifespans (but easy to repair (FETs/caps).

When the monitors come to me, they sometimes have missing
(or broken) jack screws. They may come from the nonprofit
(i.e., something their staff was using when it crapped out)
*or* from some other donor... on their way *to* a nonprofit
once repaired/refurbished.

Regardless, I have to disassemble the monitors to access the
internals. Almost always requiring the jack screws to be
removed in order to free the DVI/VGA connectors from the
metal chassis that provides the support they need for the
cable mating.

So, I end up having to rethread the jackscrews into the connector
bodies. And, want to ensure they don't work themselves loose,
later (sometimes, a monitor is delivered "for repair" and you
realize what has happened is the video cable probably worked its
way loose -- because a jack screw is missing -- and the user
decided the monitor was "broken").

I can't come up with a "permanent" fastening because the
monitor may need servicing again later (doubtful unless I
screw something up; in which case, it would be REALLY
frustrating to discover I have locked myself out!)

Loctite seems easy to undo. But, doesn't seem to be "do"-ing
as well as I'd hope...

[Jasen Betts]

On 2016-05-11, Don Y <blocked...@foo.invalid> wrote:
> Is there a "trick" to keeping jackscrews fastened to the
> "bulkhead connector" with which they are associated? I.e.,
> so removing the cable attached to that connector -- and
> secured by those jackscrews -- doesn't "back out" the screws
> in the process?

I tighten them with a nut driver almost to breaking point.
so long as the socket doesn't flow under that pressure they seem
to have enough friction to stay put, because the thumb screws are
usually only done finger tight. I don't recall ever having to
re-tighten one.

> I've been using Loctite (red) to secure the jackscrews but
> even that doesn't seem reliable.

loctite is a kind of weak cyanoacrylate... you could try the strong
stuff.

most new stuff is USB or HDMI so not so much an issue now.

--
\_(ツ)_

[Cydrome Leader]

Try crushing the threads a bit with pliers, the drive them back in with
threadlocker.