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Just so everyone's on the same page,
Bobby's talking about wear on *the shaft* from the 1mm washer,
which currently rides between the two thrust bearings. The goal is
to get a 3.5mm washer in that central spot.
On 11/12/2018 4:39 PM, Bobby J. Hughes bhughes@qnsi.net wrote:
Steve,
I
think the C drive bearing stack is different than the A
series. I have observed a small amount of wear on the
aluminum’s plant from the 3.5 mm rotating but it’s not
measurable except by feel. For the C drive, reordering the
bearing stack and locking the 1mm thrust washer should
eliminate potential wear at both locations. I’ve inspected
four drives and 2 have some wear at the 1mm washer.
Bobby
Sent from my iPad
As a result of
following the messages concerning the input shaft
thrust bearing, I disassembled the RD1A reduction
drive that was installed on my test stand after
spending 610 hours of flight time with a fixed pitch
prop. The input shaft thrust bearing setup on this
unit appears to be similar those recently discussed.
The attached
photo shows the mounting plate having a pocket 0.006"
deep worn into it by the thrust bearing. As
recommended, conditions where the prop was driving the
engine were deliberately minimized. Possibly I wasn't
conscientious enough about this. In any case, it
would seem to be a good idea to fix the thrust washer
to the mounting plate to avoid the wear I observed.
"Stickum" or a pressed fit into the proposed cup might
be effective. If the wear rate I encountered was
typical, a 2 mm deep pocket would be the result after
about 8000 hrs of operation thus requiring no
additional machining.
😉 The photo also shows that the other
end of the thrust bearing has been turning on the
shoulder of the input shaft. This appears to be
cosmetic as the amount of bearing wear here was not
measurable. The plastic snubber did not show obvious
damage.
The RD1A uses a
single thrust bearing. I have found references to
stacked thrust bearings being used to increase the
axial load capacity of the bearing assembly, but this
involves more than simply stacking normal individual
thrust bearings:
https://www.tackpoint.com/stacked-thrust-bearing-gallery/jtqo7l8j741jy1zvu8abos9hziflyw
If the stacked
thrust bearings are used to extend the reliable RPM
range of the assembly, I have found no references to
this being standard practice. There doesn't seem to
be any guarantee of the relative speed of each bearing
in the stack. What am I missing?
Steve Boese
◆
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Charlie,
Sounds simple, but to cut the
depression in the plate accurately will take a lot
of setup time. Then whatever depression you cut
will have to be added to the nylon snubber washer
and the whole gear train will be moved backwards as
well. Couls end up time consuming and very messy
IMHO.
Neil.
Could the same effect
be achieved by milling a depression in the 1/2"
plate? How thick are the thicker washers; 2 mm? If
so, mill a 1mm depression in the plate, and
replace the thin 1 mm washer with a 3rd 2 mm
washer. IIRC, Locktite makes a 'stickum' that
could keep the washer embedded in the plate, so it
doesn't un-nest when the shaft is unloaded. Would
this excessively compromise the strength of the
plate?
Charlie
On 11/12/2018 7:10 AM, Bobby J. Hughes
bhughes@qnsi.net wrote:
Neil,
Looking good. The cup ID may
need to be a few thousands over 52mm so not
sure if there’s room for a mounting spigot.
Depending on material thickness, the cup
will fully enclose one of the 2MM bearings
and part of the 3.5mm thrust washer.
Possibly add oil path grooves to the front
and rear of the cup at 45 degree clocking.
Depending on the material thickness the
channels may need to be offset. Oil channels
may not be necessary.
Too early for wine but well
caffeinated!
Bobby
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net]
Sent: Monday, November 12, 2018
2:26 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: 1mm
thrust washer
Kelly, I really should not draw freehand ---
see if you can make sense of the scribble.
Neil.
Neil and All,
Not sure I am
visualizing the shape of the of the cup
to encapsulate the
1mm thrust washer
but would certainly be a customer if
Randy Kempf were
to gear up to
produce them........How about sketch of
the proposed shape
for those of us
that are somewhat mechanically
inept...........<:)
Bobby,
Sorry I
misunderstood you. By all means
contact
Randy as he may be able to fit you
in. He has a complete reduction
drive of mine there to measure, and
certainly has the machinery to make
same.
Neil.
On 11/12/2018 7:41 AM, Bobby J. Hughes
bhughes@qnsi.net wrote:
> Neil
>
> I was asking if Randy would
consider making the 1mm washer
mounting cup. I have a chip detector
but removed it due to the 1mm washer /
shaft wear creating fuzz every few
hours and setting off an alert. I
also measure the gearbox oil temp
output.
>
> Bobby
>
> Sent from my iPad
>
>> On Nov 11, 2018, at 3:15 PM,
Neil Unger
12348ung@gmail.com <flyrotary@lancaironline.net>
wrote:
>>
>> Bobby,
>>
>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
      Another way is what I
did, was to put a temp sensor in the
pSRU which will let you know if all is
not well with elevated temps. This
is standard in heavy trucks, One in
the gear box, and one each in both
diffs. Simple and effective.
>>
>> Neil.
>>
>>
>>> On 11/12/2018 6:58 AM,
Neil Unger wrote:
>>> Bobby,
>>>
>>> Â Â Â Â Â Â Â Â Â Â Â Â Â
        I put a magnet in the
return line to catch any metal, but
only got the "fuzz" you are talking
about so simply removed it.
>>>
>>> Will discuss with Randy
re stocking a chip detector. That
will be his commercial decision.
>>>
>>> Neil.
>>>
>>>
>>>> On 11/12/2018 3:29
AM, Bobby J. Hughes
bhughes@qnsi.net wrote:
>>>> Neil,
>>>>
>>>> That should work. I
believe Tracy has suggested the same
solution. It would allow for replacing
the 1mm washer if needed. I’m
thinking aluminum instead of steel to
minimize any wear on the washer outer
edge if it rotated. I would like to
start using my gearbox chip detector
again. The 1mm washer shaft contact
caused enough fuzz to activate it
every few hours so I removed it. Would
this be an item Randy Kempf would
consider supplying? We need four in
Austin TX and I’m sure others would
retrofit if the part was available.Â
The cup OD would need to increased but
I think we have plenty of room to
accommodate modification.
>>>>
>>>> Thanks,
>>>> Bobby
>>>>
>>>> Sent from my iPad
>>>>
>>>>> On Nov 10, 2018,
at 4:01 PM, Neil Unger
12348ung@gmail.com <flyrotary@lancaironline.net>
wrote:
>>>>>
>>>>> Bobby,
>>>>>
>>>>> Â Â Â Â Â Â
           Â
 Tried my bearing blokes with no
joy, over that size they are all
1.5mm. There is another way
however if there is room. I
suggest a small alloy (or steel) "cup"
with mounting flanges like the washer
you want, except in the middle the 1mm
washer fits flat against the mounting
plate as usual, and the cup then
tapers upwards (after the 1mm thick
retaining hole at the bottom ) and out
slightly (for say another 3mm?) to
prevent the 1mm thrust washer to "jump
out of bed" and moving sideways. If it
does move forward the taper will force
it back into place when the load comes
on again. My $0.02 worth,
>>>>>
>>>>> Neil.
<thrust bearing s.jpg>
image1.png
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