Note the extended point set screws are better and easier to machine than
splines. All back lash is eliminated.
Paul Lamar
Hi Paul, can you give an overview on the " Note the extended point set
screws are better and easier to machine than splines. All back lash is
eliminated." I am not familar on this topic.
Thanks, Steve Carlisle
A spline (properly machined) is proud of diameter 1.
The inner shaft is the highest stressed part. So for max strength it
should be as large as possible. There is a shear stress concentration
at the start of the spline and near the root of the spline.
You can make the shaft larger diameter with thinner wall say diameter 2
if you use set screws. The shear stress is then distributed over the
number of screws you use.
Of course it much much easier to machine with no broach or mill
required. Especially the female part. I know no way of doing a female
spline with out a shaper or broach.
Just a drill press and taps are all that is required for extended point
set screws .
Tightening down the set screws removes all slop and back lash.
BTW always sign your last name as we have many Steves on here :)
Paul Lamar
Okay Paul, where in Tracy,s re-drive would you be able to use those screws .
Steve Carlisle
Do I detect a doubting Steve ? :)
Since the pin fixing the input shaft to the sun gear failed twice THAT
IS WHERE THEY ARE SORELY NEEDED :) You will need 8 or 12-- 3/8-24.
Paul Lamar
Hi Paul,
To use set screws to fix the primary shaft into the (hardened) sun gear,
how does one drill and tap that hardened gear ?
Chris.
Get it normalized. Send the parts to me as we have a heat treater here
in Ventura.
You can then get it hardened again. Or try normalizing just the aft end
with a torch.
I was able to cut the un-needed teeth off with a carbide lathe tool. It
is probably only case hardened so a good tap may still work.
Give it a try. I was able to drill it as well without normalizing.
Another way to get the un-needed teeth off is mount a small bench
grinder on your lathe cross slide.
Paul Lamar
Paul, you sent me some pics of Tracy,s PSRU, I am not sure where the
broken bulkhead fits into the PSRU. What have been the failure points in
the PSRU and at how many hours?
Thanks again Steve Carlisle
Take another looks at the jpg's. You can see the bulkhead screwed to the
housing.
I don't know how many hours. The sheered pins were on Dave Leonard's turbo.
Fixed once then sheered off again. Then two larger pins as I recall.
The sheered bolts were on Mark Steitle's 3 rotor P-port.
IMHO extended point set screws are a major development in machine design.
BTW you want a small amount of radial slop in the ring gear mount.
Planetary are self aligning if allowed to do so. I would give about
.050 clearance on the diameter and glue it in with RTV red rubber.
Then install the set screws but don't screw them all the way down.
Paul Lamar
Hi Paul,
Got the teeth ground off the sun gear OK in my trusty old
Colechester, will try and drill/tap it today. Next question, what is the
purpose of installing the set screws but not tightening them down ? how
has Neil done his one ?
Chris.
It provides a bit of flexbilty in the ring gear so it can move around
and balance the load on all six pinion gears.
Here is a dwg of the PT6 planetary. Note the thin cone shaped aluminum
bulkhead. This gives a little so the ring gear can center on the
pinions. A solid 1/2 thick bulkhead found in Tracy's gear box is not
near as flexible. However he did use the powder metal bulkhead with a
loose spline fit that served the propose.
You must respect this and mount the ring gear with a bit of flexibility.
RTV rubber and loose set screws will do the job.
I am not sure how Neal did it yet.
Paul Lamar
Paul,
Not sure if Chris understood that the set screws will be tightened
down on the "Sun Gear"
but not tightened down on the "Ring Gear".............
Kelly Troyer
Yep, understood all of that thanks Kelly.
Chris.
What are you planning for a torsional damper Chris?
Paul Lamar
Hi again Paul,
One other thing that I forgot to mention is that RTV hates oil, it
swells up and loses it's strength badly.
chris
Use inner tube rubber :) It does not need to be strong.
Paul Lamar
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