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T-REX 600 › How Bent is too Bent (Main shaft slightly bent)??
10-25-2011 05:04 AM  6 years agoPost 1
lazerface

rrNovice

Michigan

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Rebuilding from a crash i found that the main shaft was bent slightly. With the shaft laying flat on a hard even surface I can insert and .005 inch (.127 mm) feeler gauge along the ends, middle being the part the touches the even hard surface. What do you think replace it? Leave it Be?

Using "H60159 Main Shaft (10x201x29.3mm)"
"H60031 Three part Bearing Block"

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10-25-2011 05:17 AM  6 years agoPost 2
dkshema

rrMaster

Cedar Rapids, IA

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Bent is bent. Kind of like being pregnant, either you are, or you aren't, no middle ground.

Replace it and go fly, otherwise you'll have a heli that won't track, will shake, and you can watch the hardware loosen and fall off piece-by-piece. The vibration is no friend of your electronics, either.

While you're at it, make sure the feathering spindle is straight. Nothing's worse than compounding problems because you think you're saving money.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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10-25-2011 05:26 AM  6 years agoPost 3
lazerface

rrNovice

Michigan

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I guess What i am asking is, is it really bent? I mean what are the tolerances for the shafts out of the factory? Sorry kind of new the the hobby.

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10-25-2011 05:44 AM  6 years agoPost 4
cdrking

rrElite Veteran

Seattle

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I mean what are the tolerances for the shafts out of the factory?
Just because they come from the factory doesn't mean they are straight. I at least do a "roll on a flat surface test", even with a new shaft.

.005" is a lot. .002" is a lot. Less than a half a thousandth is acceptable in my book (main shaft). Also if it's a tail shaft then it should be almost nuts on straight.

Jeff

Very difficult to measure unless you have a good dial indicator and some v-blocks.

To hover is divine, the alternative is rather PLANE.

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10-25-2011 05:53 AM  6 years agoPost 5
lazerface

rrNovice

Michigan

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Thanks... Sounds like a plan.. Get a new shaft compare it with the old for reference, the just use the new one...

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10-25-2011 06:03 AM  6 years agoPost 6
cdrking

rrElite Veteran

Seattle

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Also worth noting is you can really drive yourself crazy chasing vibes for a slightly bent shaft. Just not worth it to not change shafts after a significant crash and sometimes just a tip over.

Jeff

To hover is divine, the alternative is rather PLANE.

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10-25-2011 10:23 AM  6 years agoPost 7
Stephen Born

rrElite Veteran

USA

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When in doubt, throw it out.

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10-26-2011 05:05 AM  6 years agoPost 8
Evan03

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Idaho

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Any kinda bent is to bent

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10-26-2011 05:09 AM  6 years agoPost 9
dkshema

rrMaster

Cedar Rapids, IA

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Any kinda bent is to bent
Amen

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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10-26-2011 05:34 AM  6 years agoPost 10
KevinB

rrKey Veteran

Saskatoon, Saskatchewan, Canada

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Bent is bent. Kind of like being pregnant, either you are, or you aren't, no middle ground.
+1

KevinB

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10-26-2011 05:38 AM  6 years agoPost 11
AKPhill

rrApprentice

Soldotna Alaska United states

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Yes I am with these guys just replace the shaft and the feathering shaft in a set 10 thousandths is a lot of bend and will do more damage to your heli jmho

AKPhill

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10-26-2011 01:44 PM  6 years agoPost 12
steve9534

rrKey Veteran

yakima, wa.

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Bent?
I wouldn't be surprised to find that .005" is within the manufacturer's tolerances and a new one may or may not be better. A .005" runout probably won't produce a noticeable vibration in your heli, but it does increase the stress on the airframe and may predispose to failure. You can straighten them easily enough. I often do and use a dial indicator to assess how straight they are. If I can get it below .002" I'm generally satisfied. Hope this helps. steve.

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10-26-2011 05:59 PM  6 years agoPost 13
fastflyer20

rrKey Veteran

N. Tonawanda, NY

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A new shaft with new bearings will have around .001" of runout. I ditched the flat plate and always use a dial indicator to check main and tail shafts after a crash.

IMHO .002" is too much.

Rest assured, if the main shaft is bent then you will also need to replace some of the grip bearings.

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