How to tell if a main shaft is bent or not

[Md001]

my 1st 2 crashes were pretty hard....and was still using the stock main shaft and i am 90% sure it was bent...but for some reason heli was very stable.........but i was able to change the feathering shaft without any trouble.

For future reference, if you've had three crashes with the same main shaft then I think it's fair to say that it will almost certainly be bent. There's also a good chance that the feathering shaft will be bent. Obviously depends on how hard the crashes are and how lucky you are.

You will get the hang of all this eventually by the way! There's just a lot to take in when you start out.

[mole hunter]

Someone showed me this once....
Put it back in the heli, without the head. Spool it up so it is turning very slowly.
Then very very slowly and gently touch the side of the shaft near the top with a felt tip pen.
As soon as the pen touches take it away.
If it left a smooth circle of ink the shaft is straight. A bent shaft will have ink on one side and not on the other.

Nice one Trev. This is a standard check I do after any sort of doink. Any run out is amplified x 2 as it rotates. I've also straightened many a very slightly bent shaft by mounting it in a rotating chuck and taping it where the marker pen touches it. Basic engineering.

Cheers, Marty

[Md001]

you can repair bent shafts?????

Nice one Trev. This is a standard check I do after any sort of doink. Any run out is amplified x 2 as it rotates. I've also straightened many a very slightly bent shaft by mounting it in a rotating chuck and taping it where the marker pen touches it. Basic engineering.

Cheers, Marty

[parksy]

Little concerning that shaft needed hammering out of OWB, I would imagine it will have damaged the one way, try spinning and pulling next time. Maybe a little tap to get it going. Quickest way to tell if it's bent is take off head, spin it up (careful of tail blades) and touch top of spinning shaft with your fingernail, you will feel if it's smooth or vibrating. Putting in a drill is fine if the chuck is true, unfortunately you can't always rely on that these days!!

[dillwhacker]

If you had to bash the shaft out of the OWB I reckon it will be ruined - the shaft should slide in and turn silky smooth in one direction. If it was locked solid and needed hammering I bet the outer shell has got grooves from the rollers and it will be no good.

[Md001]

Ok guys i just tried the drill and felt tip thing.........looks very confusing because when i turn the drill quickly and touch the tip of the felt pen slightly it makes half circles. However when i turn the drill slowly and touch the felt pen tip a bit longer it makes full circles...

also tried feeling the edge of the shaft while its spinning cant tell the difference.....

i am pretty sure out of 3....1 is definitely faulty, 2nd one got a bit of hammering , 3rd had very little hammering( i expect at least one to be good)

but looking at the results all 3 feels same in the drill......

Btw can shafts be repaired or if they are damaged straight to the bin???

[electricsceadu]

i will not do it
but i've known of them being straightend and work

[parksy]

The pen and drill trick will only work if you have a steady hand, a good eye and a decent drill, unless shaft is like a banana. When spinning slow you may well have pressed a tad too hard and made a full circle. If you can't tell if it's bent, it either isn't bent or it isn't bent enough for you to worry about. If heli flies ok and isn't shaking like a spanked jelly butt then don't worry about it.

[parksy]

Roll it on a dusky maiden's thigh. Might take your mind off a bent shaft.

haha I find that this will usually straighten out a bent shaft!!

[Md001]

Hmm gut feeling from the rolling technique tells me maybe I hammered them slowly so chances of being bent less....but the stock one is surely bent! but THANKs everyone at least I know what to look for in the future

[dillwhacker]

Roll it on a dusky maiden's thigh.

Oohhh yes now we're talking.
Halle Berry lightly dipped in Maple syrup please...

[WildWake]

If your not sure if they are straight,
Just bin them and buy a new pack.
What's the point in setting up a heli with parts that your not 100% sure are fit for purpose.
A bent main shaft will end up knocking you bearings out.
I think I'd change the main shaft bearings while I was at it.
Best of luck.