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star washers

 
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kenryan



Joined: 20 Oct 2009
Posts: 324

PostPosted: Thu Dec 13, 2018 1:22 pm    Post subject: star washers Reply with quote

Bob,

In the recent weeks/months I "think" I saw what appear to me to be contradicting posts regarding the use of star washers.
In one discussion I thought you said that star washers are never used in the current path on any certified airplanes. I think the reason was that they prevent the gas tight seal that will inhibit corrosion.
Then, in a second discussion about bus bar construction using brass bars, I thought you said to be sure to use a star washer under each terminal.
Could you clear up my confusions as to your approach to using star washers in an aircraft electrical system? 
Thanks,
Ken


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PostPosted: Thu Dec 13, 2018 10:11 pm    Post subject: star washers Reply with quote

Hi Ken;
I think star washers would make good electrical contact, but I don't like them against aluminum, as they can initiate cracks.
Cheers! Stu.
From: "Ken Ryan" <keninalaska(at)gmail.com>
To: aeroelectric-list(at)matronics.com
Sent: Thursday, December 13, 2018 1:21:13 PM
Subject: star washers
Bob,

In the recent weeks/months I "think" I saw what appear to me to be contradicting posts regarding the use of star washers.
In one discussion I thought you said that star washers are never used in the current path on any certified airplanes. I think the reason was that they prevent the gas tight seal that will inhibit corrosion.
Then, in a second discussion about bus bar construction using brass bars, I thought you said to be sure to use a star washer under each terminal.
Could you clear up my confusions as to your approach to using star washers in an aircraft electrical system?
Thanks,
Ken


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PostPosted: Fri Dec 14, 2018 6:54 am    Post subject: star washers Reply with quote

At 03:21 PM 12/13/2018, you wrote:
Quote:
Bob,

In the recent weeks/months I "think" I saw what appear to me to be contradicting posts regarding the use of star washers.

In one discussion I thought you said that star washers are never used in the current path on any certified airplanes. I think the reason was that they prevent the gas tight seal that will inhibit corrosion.

Then, in a second discussion about bus bar construction using brass bars, I thought you said to be sure to use a star washer under each terminal.

Could you clear up my confusions as to your approach to using star washers in an aircraft electrical system?

Thanks,

Ken

I spent a few minutes searching the term
'star washers' in the list archives. Generally,
the use of star washers in the electrical path
was discouraged. If used at all, they were
for mechanical security (i.e. used under a nut).

Couldn't look at all the search hits, but the
few I found were consistent with the above.

Just for grins, I checked a Brand-C parts
catalog for battery contactor installations
and found this image:

[img]cid:.0[/img]

Here we see a lockwasher called out as part
of the assembly. It's used under a nut that
secures a terminal post to the 'wing' of
an H6041 mil-style contactor. It doesn't
have a numerical call-out meaning its not
a cataloged spare part as far as Cessna
is concerned. In fact, it's part of the
contactor assembly as supplied by Cutler-Hammer
(item 15). I'm not sure why the catalog
illustrator chose to explode these parts
off the as-supplied assembly. From an OEM
service manual perspective, there was no
reason to disassemble that stud.

I also found some un-flagged star washers
on vendor-supplied assemblies but in each
case, the washer was under a nut . . . not
part of the current path. As a factory
policy, metal locknuts were the
preferred anti-loosening technology for
threaded fasteners.

Electrical conductor pathways were made
up with flat, clean and sometimes malleable
conductors (crimped terminals) being brought
together in gas-tight union with no
intermediate enhancements. Sometimes a
service manual would call out moisture
proofing by painting the finished joint
with some suitable coating . . . these
were joints located out on structure subject
to moisture incursion by drip, splash
or condensation.

B&C supplies star washers with the firewall
forest-of-tabs ground block. All the circuit
breaker manufacturers supply lock washers under
the heads of their screws for terminal attachment.
Again, these are intended to enhance mechanical
integrity of the fastener outside the current
pathway.

An interesting aside . . .

While cruising through the electrical installation
data I found this image I had forgotten
about . . .

[img]cid:.1[/img]







Somewhere in my archives, I have a letter from
the head-shed of single engine electrical systems
rejecting my proposal for replacing the too-warm,
panel dimming rheostats with a remotely mounted
array of power transistors on heat sinks. This
would have been about 1964 or thereabouts.

He offered a litany of down-sides . . .

A about 5 years later, the same idea cropped up
across town on the light twins . . . a short
time later, solid state dimming migrated into the
single engine airplanes. We COULD have beat
the twin engine line to this enhancement by
several years. Oh well . . .

Bob . . .


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kenryan



Joined: 20 Oct 2009
Posts: 324

PostPosted: Fri Dec 14, 2018 9:01 am    Post subject: star washers Reply with quote

Thanks. I now understand how a star washer under the nut is not in the current path (a concept that had eluded me). As an aside, is there any preference as to inside vs outside teeth on the washer?


On Fri, Dec 14, 2018, 06:02 Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com) wrote:

Quote:
At 03:21 PM 12/13/2018, you wrote:
Quote:
Bob,

In the recent weeks/months I "think" I saw what appear to me to be contradicting posts regarding the use of star washers.

In one discussion I thought you said that star washers are never used in the current path on any certified airplanes. I think the reason was that they prevent the gas tight seal that will inhibit corrosion.

Then, in a second discussion about bus bar construction using brass bars, I thought you said to be sure to use a star washer under each terminal.

Could you clear up my confusions as to your approach to using star washers in an aircraft electrical system?Â

Thanks,

Ken

  I spent a few minutes searching the term
  'star washers' in the list archives. Generally,
  the use of star washers in the electrical path
  was discouraged. If used at all, they were
  for mechanical security (i.e. used under a nut).

  Couldn't look at all the search hits, but the
  few I found were consistent with the above.

  Just for grins, I checked a Brand-C parts
  catalog for battery contactor installations
  and found this image:

[img]cid:.0[/img]

  Here we see a lockwasher called out as part
  of the assembly. It's used under a nut that
  secures a terminal post to the 'wing' of
  an H6041 mil-style contactor. It doesn't
  have a numerical call-out meaning its not
  a cataloged spare part as far as Cessna
  is concerned. In fact, it's part of the
  contactor assembly as supplied by Cutler-Hammer
  (item 15). I'm not sure why the catalog
  illustrator chose to explode these parts
  off the as-supplied assembly. From an OEM
  service manual perspective, there was no
  reason to disassemble that stud.

  I also found some un-flagged star washers
  on vendor-supplied assemblies but in each
  case, the washer was under a nut . . . not
  part of the current path. As a factory
  policy, metal locknuts were the
  preferred anti-loosening technology for
  threaded fasteners.

  Electrical conductor pathways were made
  up with flat, clean and sometimes malleable
  conductors (crimped terminals) being brought
  together in gas-tight union with no
  intermediate enhancements. Sometimes a
  service manual would call out moisture
  proofing by painting the finished joint
  with some suitable coating . . . these
  were joints located out on structure subject
  to moisture incursion by drip, splash
  or condensation.

  B&C supplies star washers with the firewall
  forest-of-tabs ground block. All the circuit
  breaker manufacturers supply lock washers under
  the heads of their screws for terminal attachment.
  Again, these are intended to enhance mechanical
  integrity of the fastener outside the current
  pathway.

  An interesting aside . . .

  While cruising through the electrical installation
  data I found this image I had forgotten
  about . . .

[img]cid:.1[/img]

 





  Somewhere in my archives, I have a letter from
  the head-shed of single engine electrical systems
  rejecting my proposal for replacing the too-warm,
  panel dimming rheostats with a remotely mounted
  array of power transistors on heat sinks. This
  would have been about 1964 or thereabouts.

  He offered a litany of down-sides . . .

  A about 5 years later, the same idea cropped up
  across town on the light twins . . . a short
  time later, solid state dimming migrated into the
  single engine airplanes. We COULD have beat
  the twin engine line to this enhancement by
  several years. Oh well . . .

  Bob . . .


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user9253



Joined: 28 Mar 2008
Posts: 1394
Location: Riley TWP Michigan

PostPosted: Fri Dec 14, 2018 9:16 am    Post subject: Re: star washers Reply with quote

Inside or outside teeth do not matter as long as the teeth are under the nut. But some outside star washer diameters are big enough so that the teeth are outside of the nut circumference. For that reason, I prefer inside diameter teeth.
Speaking of lock washers, what we know as split ring lock washers are not really lock washers at all. In fact, they allow fasteners to loosen sooner than plain flat washers. There is a YouTube video by Nord Lock demonstrating this.


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PostPosted: Fri Dec 14, 2018 10:24 am    Post subject: star washers Reply with quote

At 11:00 AM 12/14/2018, you wrote:
Quote:
Thanks. I now understand how a star washer under the nut is not in the current path (a concept that had eluded me). As an aside, is there any preference as to inside vs outside teeth on the washer?

Given that the locking effect is really
just a 'friction enhancement' it stands
to reason that you want the greatest
practical torque moment as measured from
the center of rotation. It follows that
external teeth would offer the greatest
impediment to rotation.



Bob . . .


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PostPosted: Fri Dec 14, 2018 10:34 am    Post subject: star washers Reply with quote

At 11:16 AM 12/14/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>

Inside or outside teeth do not matter as long as the teeth are under the nut. But some outside star washer diameters are big enough so that the teeth are outside of the nut circumference. For that reason, I prefer inside diameter teeth.
Speaking of lock washers, what we know as split ring lock washers are not really lock washers at all. In fact, they allow fasteners to loosen sooner than plain flat washers. There is a YouTube video by Nord Lock demonstrating this.

Many, if not most joints on electrical system
threaded fasteners are made up with only
flat washshers. Given aviation's preference
for fine pitch threads, taking a nut up to
design specs for torque probably makes it
as 'locked' as it will ever be.

The #1 antagonist to make up pressure is
rotational vibration imparted by the WIRE
crimped into the terminal under the nut.
This is why I've been partial to welding
cable for fat wires. VERY flexible and
minimal transmission of wire motion
to the threaded fastener.

Most of this is pretty academic. I've
opened joints that had been in service
for decades that took significant break-away
torque to move the fastener. This in spite
of no 'locking' feature on or under the nut.

I.e. the original installer was paying attention.


Bob . . .


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kenryan



Joined: 20 Oct 2009
Posts: 324

PostPosted: Fri Dec 14, 2018 10:44 am    Post subject: star washers Reply with quote

Thanks. Although "academic" I have found the responses quite educational.

Ken
On Fri, Dec 14, 2018 at 9:39 AM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 11:16 AM 12/14/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Inside or outside teeth do not matter as long as the teeth are under the nut.  But some outside star washer diameters are big enough so that the teeth are outside of the nut circumference.  For that reason, I prefer inside diameter teeth.
  Speaking of lock washers, what we know as split ring lock washers are not really lock washers at all.  In fact, they allow fasteners to loosen sooner than plain flat washers.  There is a YouTube video by Nord Lock demonstrating this.

  Many, if not most joints on electrical system
  threaded fasteners are made up with only
  flat washshers. Given aviation's preference
  for fine pitch threads, taking a nut up to
  design specs for torque probably makes it
  as 'locked' as it will ever be.

  The #1 antagonist to make up pressure is
  rotational vibration imparted by the WIRE
  crimped into the terminal under the nut.
  This is why I've been partial to welding
  cable for fat wires. VERY flexible and
  minimal transmission of wire motion
  to the threaded fastener.

  Most of this is pretty academic. I've
  opened joints that had been in service
  for decades that took significant break-away
  torque to move the fastener. This in spite
  of no 'locking' feature on or under the nut.

  I.e. the original installer was paying attention.


  Bob . . .


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rickofudall



Joined: 19 Sep 2009
Posts: 1355
Location: Udall, KS, USA

PostPosted: Fri Dec 14, 2018 3:03 pm    Post subject: star washers Reply with quote

Joe, What about the Rotax split washers that have both ends turned the same direction?

Rick
On Fri, Dec 14, 2018 at 11:23 AM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Inside or outside teeth do not matter as long as the teeth are under the nut.  But some outside star washer diameters are big enough so that the teeth are outside of the nut circumference.  For that reason, I prefer inside diameter teeth.
  Speaking of lock washers, what we know as split ring lock washers are not really lock washers at all.  In fact, they allow fasteners to loosen sooner than plain flat washers.  There is a YouTube video by Nord Lock demonstrating this.

--------
Joe Gores




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user9253



Joined: 28 Mar 2008
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Location: Riley TWP Michigan

PostPosted: Fri Dec 14, 2018 7:27 pm    Post subject: Re: star washers Reply with quote

Quote:
Joe, What about the Rotax split washers that have both ends turned the same direction?

I am not familiar with Rotax split washers. Where are they used on the Rotax?
The prop bolts on my Rotax have wedge-lock washers, no safety wire required. Matco breaks also use wedge-lock washers.
When wedge-lock (Nord Lock) washers are used, it is actually harder to loosen a fastener than to tighten it.


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PostPosted: Sat Dec 15, 2018 8:31 am    Post subject: star washers Reply with quote

I love Nord Lock washers even though they're expensive. I used them on all the battery connections in the truck I converted to electric. I check them every 6 months and have never found one coming loose.
--Rick

On 12/14/2018 10:27 PM, user9253 wrote:

Quote:
I am not familiar with Rotax split washers. Where are they used on the Rotax?
Quote:
The prop bolts on my Rotax have wedge-lock washers, no safety wire required. Matco breaks also use wedge-lock washers.
When wedge-lock (Nord Lock) washers are used, it is actually harder to loosen a fastener than to tighten it.

--------
Joe Gores



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PostPosted: Sun Dec 16, 2018 7:22 am    Post subject: star washers Reply with quote

At 10:27 AM 12/15/2018, you wrote:

Quote:
I love Nord Lock washers even though they're expensive. I used them on all the battery connections in the truck I converted to electric. I check them every 6 months and have never found one coming loose.

--Rick


Those are a pretty cool product. There's
a constellation of youtube videos on the
technology at

https://tinyurl.com/yb7h38kv

This design is not limited by friction
but by the relative hardness of washer
and that of the nut and base
surfaces. The outside faces of the Nord
washer pair must displace metal and
'dig in'.

I suspect that star washers, fabricated
from steels on the same class as Nord
washers would see a quantum jump in
performance.



Bob . . .


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