Pond Monster: 0 --Prop Saver: 1

[fun4ej]

Snapped a flex shaft today.

Thanks to a drive dog I modified, my prop didn't get kidnapped.

 

[Ron]

Been there done that. Only I lost a $70 Andy Brown prop.

Lessoned learned! Glad your experience turned out better!

 

[RaceMechaniX]

The failure was probbaly caused by the setscrew in the collar though......... Looks like it twisted apart inside the collar?

 

[Rigged]

yup thats how it looks. Someone else had that happen using a wheel collar with set screw up by the collet.

 

[fun4ej]

The failure was probbaly caused by the setscrew in the collar though......... Looks like it twisted apart inside the collar?

It looks that way from these pictures....I should have taken a shot from the front of the collar.

Where the set screw locked on was at the very end of the weld and the flex shaft broke just ahead of the collar....maybe 1/32"-1/16". At first inspection, I too thought that the set screw had maybe caused the failure, but after disassembly, it appeared to not be the case....there were no separations in the cable where the set screw met the flex. What caused the failure? Could have been the rough water I had been running in, could have been internal fatigue caused by the set screw or could have just been time for that shaft to go...tough to say.

 

[Roxyflash]

Looks like the stuffing tube is way to big?

 

[Mark Bullard]

The failure was probbaly caused by the setscrew in the collar though......... Looks like it twisted apart inside the collar?

It looks that way from these pictures....I should have taken a shot from the front of the collar.

Where the set screw locked on was at the very end of the weld and the flex shaft broke just ahead of the collar....maybe 1/32"-1/16". At first inspection, I too thought that the set screw had maybe caused the failure, but after disassembly, it appeared to not be the case....there were no separations in the cable where the set screw met the flex. What caused the failure? Could have been the rough water I had been running in, could have been internal fatigue caused by the set screw or could have just been time for that shaft to go...tough to say.

Was the shaft soldered at the motor?

 

[Don Ferrette]

The failure was probably caused by the setscrew in the collar though......... Looks like it twisted apart inside the collar?

It looks that way from these pictures....I should have taken a shot from the front of the collar.

Where the set screw locked on was at the very end of the weld and the flex shaft broke just ahead of the collar....maybe 1/32"-1/16". At first inspection, I too thought that the set screw had maybe caused the failure, but after disassembly, it appeared to not be the case....there were no separations in the cable where the set screw met the flex. What caused the failure? Could have been the rough water I had been running in, could have been internal fatigue caused by the set screw or could have just been time for that shaft to go...tough to say.

While it might have "looked" ok where the set screw made contact, the pronounced side load you placed on the cable strands when you tightened it down right at the joint to the stub shaft weakened and/or broke a few cable strands free from the solder to the stub shaft. The reason the damage appears "in front" of the collar is that is the first point the cable was not contained by that same collar so that is where it began to come apart. This is not the first time I've seen this happen either. If you really are dead set on using a collar to try to keep the shaft from going bye-bye, notch the actual strut blade in the middle of it just a little larger than the collar. As you slide the shaft into the strut hold the collar in the notch so the cable slides through it, then tighten it down once everything is in place. That way you will be tightening down on the hardened stub shaft and not the cable. And BTW this is not my idea, I saw this a number of years back on one of Bob Morton's boats.

 

[fun4ej]

Looks like the stuffing tube is way to big?

Yea, the boat originally had a 67 or larger motor and 1/4" shaft. I put in a 45 with 3/16" shaft.

 

[fun4ej]

Was the shaft soldered at the motor?

Yep

 

[fun4ej]

While it might have "looked" ok where the set screw made contact, the pronounced side load you placed on the cable strands when you tightened it down right at the joint to the stub shaft weakened and/or broke a few cable strands free from the solder to the stub shaft. The reason the damage appears "in front" of the collar is that is the first point the cable was not contained by that same collar so that is where it began to come apart. This is not the first time I've seen this happen either. If you really are dead set on using a collar to try to keep the shaft from going bye-bye, notch the actual strut blade in the middle of it just a little larger than the collar. As you slide the shaft into the strut hold the collar in the notch so the cable slides through it, then tighten it down once everything is in place. That way you will be tightening down on the hardened stub shaft and not the cable. And BTW this is not my idea, I saw this a number of years back on one of Bob Morton's boats.

Thanks! I have seen that modification too. I wonder if a small piece of silicone tubing could be used in place of the collar....

 

[RaceMechaniX]

I was going to suggest the same thing. I nice piece of silicone or gas fuel line tightly pushed onto the front half of the stub.

TG

 

[Mark Bullard]

Was the shaft soldered at the motor?

Yep

Your shaft log tube is very much out of line from your collet. I would set the strut up to where the tube plugs into or runs all the way thru to the end of the strut. The next thing is that by soldering the cable at the motor stops the conductors in the cable from moving. This causes cable failures. I know that there is a lot of racers out there that will say otherwise. But I have shafts that are over twenty years old. I have not had a shaft break this way in that amount of time. I have lost some due to running over something.

 

[fun4ej]

Your shaft log tube is very much out of line from your collet. I would set the strut up to where the tube plugs into or runs all the way thru to the end of the strut. The next thing is that by soldering the cable at the motor stops the conductors in the cable from moving. This causes cable failures. I know that there is a lot of racers out there that will say otherwise. But I have shafts that are over twenty years old. I have not had a shaft break this way in that amount of time. I have lost some due to running over something.

Interesting, this is new to me...to not solder the motor end of the flex shaft

 

[dwb2620]

Your shaft log tube is very much out of line from your collet. I would set the strut up to where the tube plugs into or runs all the way thru to the end of the strut. The next thing is that by soldering the cable at the motor stops the conductors in the cable from moving. This causes cable failures. I know that there is a lot of racers out there that will say otherwise. But I have shafts that are over twenty years old. I have not had a shaft break this way in that amount of time. I have lost some due to running over something.

Interesting, this is new to me...to not solder the motor end of the flex shaft

I have been soldering my flex cables at the motor end since 1985 and have never broken one. <_< What about the prop shaft end? Aren't those welded on?

David

 

[Mark Bullard]

Your shaft log tube is very much out of line from your collet. I would set the strut up to where the tube plugs into or runs all the way thru to the end of the strut. The next thing is that by soldering the cable at the motor stops the conductors in the cable from moving. This causes cable failures. I know that there is a lot of racers out there that will say otherwise. But I have shafts that are over twenty years old. I have not had a shaft break this way in that amount of time. I have lost some due to running over something.

Interesting, this is new to me...to not solder the motor end of the flex shaft

I have been soldering my flex cables at the motor end since 1985 and have never broken one. <_< What about the prop shaft end? Aren't those welded on?

David

Yes they are welded on. This is my point totaly. You weld both ends of the cable and then put the shaft thru a S-bend and over time the outer conductors will fail or break either at the motor or the stub. It is like bending a coat hanger. Now you say that you have never broke a shaft. But how many shafts have you had fail and lost the prop?