Results 1 to 19 of 19

Thread: OPINION on broken shaft

  1. #1
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default OPINION on broken shaft

    Last edited by Speedfreek; 02-10-2019 at 03:53 AM.

  2. #2
    Join Date
    Feb 2008
    Location
    GB
    Posts
    2,726

    Default

    My guess is you ran an out of balance prop and/or prop nut and a crack propagated from the bottom left in picture 3 which allowed the shaft to bend and threw it further out of balance and quickly snapped the end off.

    Why are the step downs in shaft diameter there? Deleting them would make for a stronger shaft, or if they have to be there putting a raduis on there inside edges would spread out the stress load a little and make it a bit less failure prone.
    Paul Upton-Taylor, Greased Weasel Racing.

  3. #3
    Join Date
    Aug 2010
    Location
    uk
    Posts
    2,887

    Default

    What is the diameter of the step down & prop size on that shaft ? is it a 3/16" bore prop. As you are running very large powerfull TP 5850 motors on 12s, also as said a step down with no radius will also break easier. It also looked like there was not enough gap between the drive dog & the stinger to allow for flex wind up.

  4. #4
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by NativePaul View Post
    My guess is you ran an out of balance prop and/or prop nut and a crack propagated from the bottom left in picture 3 which allowed the shaft to bend and threw it further out of balance and quickly snapped the end off.

    Why are the step downs in shaft diameter there? Deleting them would make for a stronger shaft, or if they have to be there putting a raduis on there inside edges would spread out the stress load a little and make it a bit less failure prone.
    Prop was a Andy brown ? I would think it would be balanced , Not my shafts and yes I agree that there should be a radius there

  5. #5
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by martin View Post
    What is the diameter of the step down & prop size on that shaft ? is it a 3/16" bore prop. As you are running very large powerfull TP 5850 motors on 12s, also as said a step down with no radius will also break easier. It also looked like there was not enough gap between the drive dog & the stinger to allow for flex wind up.
    Yea 3/16 , I have gone up to the next size now and I machined it so I can have more of a gap too.IMG-20190210-WA0007.jpg

  6. #6
    Join Date
    Aug 2015
    Location
    MI
    Posts
    199

    Default

    to me looks like of scarring on that shaft (maybe more grease or more frequent greasing)

  7. #7
    Join Date
    Aug 2015
    Location
    MI
    Posts
    199

    Default

    although after thinking about it, it would effect the flex shaft not where it broke, but still in all looks like it should have some grease in there

  8. #8
    Join Date
    Mar 2011
    Location
    BC
    Posts
    7,629

    Default

    Quote Originally Posted by Johnc View Post
    to me looks like of scarring on that shaft (maybe more grease or more frequent greasing)
    That is from the bearing. BTW Speedfreak I run two bearings at each end to carry the load and last longer. Once they wear they could cause a wobble and that may happen quickly with only one bearing. Something I’ve been doing on the step down shafts is run a 1/4” drive dog which locks the prop. Just a theory but I haven’t had a stepdown shaft fail.

  9. #9
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by srislash View Post
    That is from the bearing. BTW Speedfreak I run two bearings at each end to carry the load and last longer. Once they wear they could cause a wobble and that may happen quickly with only one bearing. Something I’ve been doing on the step down shafts is run a 1/4” drive dog which locks the prop. Just a theory but I haven’t had a stepdown shaft fail.
    This drive does have two bearings at the prop end , I have put the 1/4 drive in there now and I have allowed 6.4 mm of gap too where before it would not allow me to do that , that's what I think happend.

  10. #10
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by martin View Post
    What is the diameter of the step down & prop size on that shaft ? is it a 3/16" bore prop. As you are running very large powerfull TP 5850 motors on 12s, also as said a step down with no radius will also break easier. It also looked like there was not enough gap between the drive dog & the stinger to allow for flex wind up.
    Yep that's what I think

  11. #11
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    So how much would you say a 1/4 drive flex approx 8 in long would contract on eceleration ?

  12. #12
    Join Date
    Mar 2011
    Location
    BC
    Posts
    7,629

    Default

    Quote Originally Posted by Speedfreek View Post
    So how much would you say a 1/4 drive flex approx 8 in long would contract on eceleration ?
    I would not think it would be much. 8” is fairly short. I know my 6” 3/16” have as little as 2mm gap with no issue. It’s all a matter of experimentation to find it. The little white thrust washers can help with this

  13. #13
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by srislash View Post
    I would not think it would be much. 8” is fairly short. I know my 6” 3/16” have as little as 2mm gap with no issue. It’s all a matter of experimentation to find it. The little white thrust washers can help with this
    it's 7" long close enough i have 6mm gap now and 1/4 dog drive shaft , it better not brake now these props cost to much to loose.

  14. #14
    Join Date
    Jan 2019
    Location
    MO
    Posts
    15

    Default

    whats it out of probably not balanced prop could be a bad bearing too

  15. #15
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by MARK FORREST View Post
    whats it out of probably not balanced prop could be a bad bearing too
    Bearings are three runs old , prop was a Andy Brown.
    I might just put in oil-immersed sintered bronze bushings front and rear less headaches , expecialy in salt water...
    Last edited by Speedfreek; 02-16-2019 at 04:39 AM.

  16. #16
    Join Date
    Mar 2011
    Location
    BC
    Posts
    7,629

    Default

    Quote Originally Posted by Speedfreek View Post
    Bearings are three runs old , prop was a Andy Brown.
    I might just put in oil-immersed sintered bronze bushings front and rear less headaches , expecialy in salt water...
    End of season last year I stuck bushings in on the back of my HPR. I was having a hard time keeping bearings glued in for whatever reason. Plus... they aren’t $15 a pop every month and half.

  17. #17
    Join Date
    May 2009
    Location
    AB
    Posts
    483

    Default

    I think I did the same thing on my 10s mono, 1/4” shaft stepped for 3/16” props, I had a 3/16” drive dog and that’s where it snapped. I’ve gone to a 1/4” dog now.


    Sent from my iPad using Tapatalk
    Namba District 16
    1/8 Miss U.S., 1/8 59 Maverick, 1/8 Executone, 1/8 Smokin Joe, 1/8 Bud, MLGSX380, AC Pro40II Q Sport, AC Pro40II nitro,Twincraft mono 10s, Vision AOPC, VS1 FE, M34.

  18. #18
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by srislash View Post
    End of season last year I stuck bushings in on the back of my HPR. I was having a hard time keeping bearings glued in for whatever reason. Plus... they aren’t $15 a pop every month and half.
    The ones that I ordered have graphite dots in it to lube the shaft .s-l400.jpg
    Last edited by Speedfreek; 02-18-2019 at 04:26 PM.

  19. #19
    Join Date
    Apr 2018
    Location
    OZ
    Posts
    276

    Default

    Quote Originally Posted by pescador View Post
    I think I did the same thing on my 10s mono, 1/4” shaft stepped for 3/16” props, I had a 3/16” drive dog and that’s where it snapped. I’ve gone to a 1/4” dog now.


    Sent from my iPad using Tapatalk
    Way to go for now.
    Going to centre drill on the lathe and press the prop shaft in that way it has no week point.....20190212_145641.jpg
    Last edited by Speedfreek; 02-18-2019 at 02:39 AM.

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •