driving a shaft with threads?

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AllenH59
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driving a shaft with threads?

Post by AllenH59 » Sun Nov 12, 2017 5:18 pm

I want to drive something with a diesel engine that will make about 100 ft lbs of torque. Is there any reason not to drive on threads that will take about 300 ft lbs? nothing will ever reverse to loosen the threads and I will put a taper to keep things centered. Thanks

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BigDumbDinosaur
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Re: driving a shaft with threads?

Post by BigDumbDinosaur » Sun Nov 12, 2017 9:18 pm

AllenH59 wrote:I want to drive something with a diesel engine that will make about 100 ft lbs of torque. Is there any reason not to drive on threads that will take about 300 ft lbs? nothing will ever reverse to loosen the threads and I will put a taper to keep things centered. Thanks
That's not something I would do. The engine's torque rating is an average. All internal combustion engines produce torsional vibration, more so with Diesel than gas, which causes the instantaneous torque to rise and fall as each cylinder fires. Coincidentally, this cyclic torque output is the principle on which an impact wrench operates. I'll leave it to your imagination to figure out what is likely to happen to your drive, especially under load. Needless to say, the fewer the number of cylinders, the greater the impact wrench effect.
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John Hasler
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Re: driving a shaft with threads?

Post by John Hasler » Sun Nov 12, 2017 9:43 pm

You'll be fine as long as you make sure that the peak torque actually transmitted by the drive stays well under 300. The engine presumably has a flywheel which will smooth out vibration but it also makes it possible for the engine-flywheel combination to briefly deliver much more torque than the engine's continuous rating.

You're never going to get that coupling apart, though.

AllenH59
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Re: driving a shaft with threads?

Post by AllenH59 » Mon Nov 13, 2017 12:44 am

it will be running a boat, so there is no opportunity for a shock load. never getting it apart is ok

Harold_V
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Re: driving a shaft with threads?

Post by Harold_V » Mon Nov 13, 2017 4:48 am

For the prop?
I used to own a boat. I recall hitting something with the prop on one occasion. I would classify that as a shock load, assuming you'd be driving the prop.

H
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John Hasler
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Re: driving a shaft with threads?

Post by John Hasler » Mon Nov 13, 2017 9:10 am

Harold_V wrote:For the prop?
I used to own a boat. I recall hitting something with the prop on one occasion. I would classify that as a shock load, assuming you'd be driving the prop.

H
Better that the coupling fail than the prop break.

Depending on the taper and how well matched it is much of the load may not be on the threads at all.

10 Wheeler Rob
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Re: driving a shaft with threads?

Post by 10 Wheeler Rob » Mon Nov 13, 2017 6:11 pm

You could make a coupling with threads in side it spilt one side with a ccouple of clamping bolts so its clamps on the threads to take up the thread clearance,

On second though why not due coupling with key ways,
And use the standard soft keys normally used in boats for protection of the prop.

Rob

John Hasler
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Re: driving a shaft with threads?

Post by John Hasler » Mon Nov 13, 2017 6:46 pm

10 Wheeler Rob wrote:You could make a coupling with threads in side it spilt one side with a ccouple of clamping bolts so its clamps on the threads to take up the thread clearance,

On second though why not due coupling with key ways,
And use the standard soft keys normally used in boats for protection of the prop.

Rob
That's a better idea, if feasible.

Ironman1
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Re: driving a shaft with threads?

Post by Ironman1 » Fri Nov 17, 2017 7:38 pm

There is a tractor puller in my area with two Ford 427 engines coupled together with a 1" pipe nipple threaded into a plate attached on each engine.
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AllenH59
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Re: driving a shaft with threads?

Post by AllenH59 » Sat Nov 18, 2017 12:20 am

Ironman1 wrote:There is a tractor puller in my area with two Ford 427 engines coupled together with a 1" pipe nipple threaded into a plate attached on each engine.
Wow

AllenH59
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Re: driving a shaft with threads?

Post by AllenH59 » Sat Nov 18, 2017 12:25 am

changed plans and will spline a shaft to go into the clutch

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BigDumbDinosaur
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Re: driving a shaft with threads?

Post by BigDumbDinosaur » Sat Nov 18, 2017 12:27 am

AllenH59 wrote:changed plans and will spline a shaft to go into the clutch
Sounds like a wise choice.
Science makes it known. Engineering makes it work.

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