Noisy Endo Component Tip
Chris L Johnson
Description
Collection
Title:
Noisy Endo Component Tip
Creator:
Chris L Johnson
Date:
1/29/2000
Text:
Noise principle: If it can make noise it will. High force, high cycle
loads following similar loading patterns will bring noises out like
nothing else. In prosthetics, that is exactly the scenario.
Being seriously involved in prosthetic design and a wearer of prosthetic
designs, noise is an enemy I have wrestled for years. Every prosthesis
and every sub component I have had has made noise at some time,
regardless of brand.
I have worked now for 4 years with durability/maintenance/noise
improvement efforts on the College Park TruStep with much success. Foot
improvements aside, I have found the most major source of noise in BK
prostheses to be endo components. I still get fooled some times,
thinking it's either the foot or the socket interface attachment that's
making a noise, when in fact, the vast majority of the time it's the endo
components. I could go into great detail about all the noise generation
sites in endo components, and what you can do to avoid noise, but save
that for later. I have written thing son this list in the past
concerning this issue. Right now, I'll pass a cute, new one I found this
week. Well, maybe not new, but I was able to observe the mechanism for
the noise.
Mike Link, our resident prosthetist, had just made a laminated, half test
socket, half definitive leg for me. I walked on it over night and next
day had these little tinking/popping noises at heel strike and sometimes
at toe on. I performed the usual diagnostics. We both suspected the
socket interface component. We had installed a very light Ortho Europe
(Ortho Enterprises) titanium pyramid adapter with stainless steel wings
riveted on with aluminum rivets directly onto the end of the socket.
This was cast to the inner lamination via Alumilite, a cast able
urethane, then finished back to form a surface for the outer lamination.
We thought maybe this light set-up was flexing a bit and causing the
popping noise. I noticed, however, That the noise would disappear if I
loosened the set screws on the proximal tube adapter, but reappear after
only a few steps. Odd. I removed the tube adapter and found something
interesting.
The evening before I had put Locktite 242 on all the set screws. I'm
pretty hard on legs, and if I do not Locktite the set screws they can
come loose. When they loosen without Locktite, it's a 10-step affair
until the leg falls apart. Not fun if you're out and about wihtout
tools! The noise was directly caused by Locktite.
Uncured Locktite had migrated down the threads and gotten between the
pyramid facets and the set screws. The set screws were contacting the
pyramid adapter facets very flush. The Locktite had wicked into the gap
and kicked off. As you all know, Locktite does not like to cure unless
it in a tight gap. If out in the open, the stuff is very watery and runs
where it wants to. So I had the tight gap between the set screws and the
pyramid facets, and the presence of fresh, uncured Locktite. The
Locktite in the gap cured. Flexing due to load would cause an alternate
breaking and re-curing of the thin Locktite interface, generating noise.
The moral of this tech story is that if you use Locktite on the threads
of tube clamp set screws, make sure none can get onto the pyramid facets.
I wiped off the uncured stuff, then carefully scrapped off the thin
cured layer from the set screw tips and pyramid facets. Noise gone!
Perhaps if there is sufficient interest in this topic, I'll share more of
what I know on this issue.
Chris Johnson
Scorpa 250 EZ Fun/Gas-Gas 160/Fantic 305/Yamaha Virago 1,100 & XV920RH
Euro
and now vintage `74 TY 250 (do I love motorcycles or what?)
<Email Address Redacted> as Director of Engineering at College Park
see www.college-park.com (work) and <Email Address Redacted> (home office
address)
loads following similar loading patterns will bring noises out like
nothing else. In prosthetics, that is exactly the scenario.
Being seriously involved in prosthetic design and a wearer of prosthetic
designs, noise is an enemy I have wrestled for years. Every prosthesis
and every sub component I have had has made noise at some time,
regardless of brand.
I have worked now for 4 years with durability/maintenance/noise
improvement efforts on the College Park TruStep with much success. Foot
improvements aside, I have found the most major source of noise in BK
prostheses to be endo components. I still get fooled some times,
thinking it's either the foot or the socket interface attachment that's
making a noise, when in fact, the vast majority of the time it's the endo
components. I could go into great detail about all the noise generation
sites in endo components, and what you can do to avoid noise, but save
that for later. I have written thing son this list in the past
concerning this issue. Right now, I'll pass a cute, new one I found this
week. Well, maybe not new, but I was able to observe the mechanism for
the noise.
Mike Link, our resident prosthetist, had just made a laminated, half test
socket, half definitive leg for me. I walked on it over night and next
day had these little tinking/popping noises at heel strike and sometimes
at toe on. I performed the usual diagnostics. We both suspected the
socket interface component. We had installed a very light Ortho Europe
(Ortho Enterprises) titanium pyramid adapter with stainless steel wings
riveted on with aluminum rivets directly onto the end of the socket.
This was cast to the inner lamination via Alumilite, a cast able
urethane, then finished back to form a surface for the outer lamination.
We thought maybe this light set-up was flexing a bit and causing the
popping noise. I noticed, however, That the noise would disappear if I
loosened the set screws on the proximal tube adapter, but reappear after
only a few steps. Odd. I removed the tube adapter and found something
interesting.
The evening before I had put Locktite 242 on all the set screws. I'm
pretty hard on legs, and if I do not Locktite the set screws they can
come loose. When they loosen without Locktite, it's a 10-step affair
until the leg falls apart. Not fun if you're out and about wihtout
tools! The noise was directly caused by Locktite.
Uncured Locktite had migrated down the threads and gotten between the
pyramid facets and the set screws. The set screws were contacting the
pyramid adapter facets very flush. The Locktite had wicked into the gap
and kicked off. As you all know, Locktite does not like to cure unless
it in a tight gap. If out in the open, the stuff is very watery and runs
where it wants to. So I had the tight gap between the set screws and the
pyramid facets, and the presence of fresh, uncured Locktite. The
Locktite in the gap cured. Flexing due to load would cause an alternate
breaking and re-curing of the thin Locktite interface, generating noise.
The moral of this tech story is that if you use Locktite on the threads
of tube clamp set screws, make sure none can get onto the pyramid facets.
I wiped off the uncured stuff, then carefully scrapped off the thin
cured layer from the set screw tips and pyramid facets. Noise gone!
Perhaps if there is sufficient interest in this topic, I'll share more of
what I know on this issue.
Chris Johnson
Scorpa 250 EZ Fun/Gas-Gas 160/Fantic 305/Yamaha Virago 1,100 & XV920RH
Euro
and now vintage `74 TY 250 (do I love motorcycles or what?)
<Email Address Redacted> as Director of Engineering at College Park
see www.college-park.com (work) and <Email Address Redacted> (home office
address)
Citation
Chris L Johnson, “Noisy Endo Component Tip,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 5, 2024, https://library.drfop.org/items/show/213465.
