Can a 3/4" shaft handle 10-12kw?

[akghound]

I am setting up to power an ST-10 or ST-12 head off the crank shaft of a L275 Kubota tractor (Rated  27-1/2 hp at 2800 rpm. Running 1-1 for 1800 rpm.) The flex shaft off the crank is made for a 3/4 inch keyed shaft, it normally powers the hydralic pump. My question is; Will a 3/4" mild steel shaft be strong enough to turn a 10kw or perhaps a 12kw ST gen head? If not, is there a different metal other then mind steel that would work?
Thanks in advance for your input. Ken Gardner

[Henry W]

I am not sure if it is a good idea to attempt running a ST-10 or ST-12 that way.  Why not go with a PTO setup designed to run off the rear 540 RPM PTO? Here is an ST-15 setup. http://www.ebay.com/itm/ST-15KW-PTO-Gearbox-and-42x48MM-Coupler-Combo-/150475636733?pt=BI_Generators&hash=item23090bfffd

Henry

[akghound]

Thanks for the link.
I would rather run it directly off the front crank. There is a lot of loss driving through the gear train. Every thing geared down inside the tractor boxes to get to 540 then the need to gear back up to return to 1800 rpm. Also the need to run the engine at 2250rpm to get 1800 on the gen head. Besides all that it, would cost a lot more. The tractor I am using was damaged in the fire and is not mobile so I have it set up stationary. All I need is a bracket and a couple bearings to power the gen head. I have the generator frame, belt and pulleys on hand. If a 3/4 inch shaft will stand the torque I am good to go, so back to the question.
Thanks again.   Ken

[vdubnut62]

FWIW Ken, I would give it a whirl since you don't really have any "hammering" going on with either the Kubota or the 4 pole st head.
You mentioned flex shaft, does that mean a rubber biscuit sort of thing? If so I would think that would be an added plus.
At any rate, if it was me, and especially if I didn't plan to repair the tractor, I sure would give it a try.
Ron

[akghound]

Thanks Ron
The flex shaft is the cable looking type. I believe at 3/4" I must be at the upper limit of mild steel. I guess if it don't work I can get something stronger. What type of steel handles more torque? I don't know names, numbers or types.
BTW ... I never did get the Nisson engine going.
Ken

[Henry W]

Ok,

Here is the way I see it since the tractor is toast.   As long as you are not planning to drive the gen-head by a driveshaft you might be ok. If you can get the genhead up close and in line with the PTO shaft and drive it with a good coupling that can reduce shock loads it might work.  Here is a good coupling that will reduce shock loads: http://www.guardiancouplings.com/productline/superflex.htm

If it does not hold up, then dissasemble the front end of the tractor from the rest and direct drive the genhead with stubshaft mounted on the flywheel.

Henry

[Terry]

Stress proof or 4140 will handle more than mild steel. I have used stress proof as tie bolts on large press brakes and parts I make for oil field drilling rigs. A lot of the down hole
tools used in the oil field are made from 4140. You can order from www.speedymetals.com.
Terry

[admin]

I think Terry has it right!

if you can get your hands on a piece of 7/8 sucker rod, you can have it machined to fit your applications
and it must be 4140 stress proof because it is tough as hell and will take a heat treat if you like.

3/4" can handle a lot of power just take a look at the small input shaft of an automatic transmission in a car
some of them can't be more than 3/4 inch and take 50kwatts or more input. 

depending on what length you need one of those auto trans input shafts might be something to work with?

another option is a section of bulk spring stock or spring U-bolt stock, i have no idea what it is made of, but it can
take a butt load of torque in the 3/4" diameter size. it can also take a heat treat so it must be something in the 4000 series steel.

bob g

[LowGear]

How pretty do you need your output?

Casey

[akghound]

Pretty is not important. Functional is a must. Why?

[vdubnut62]

Thanks Ron
The flex shaft is the cable looking type. I believe at 3/4" I must be at the upper limit of mild steel. I guess if it don't work I can get something stronger. What type of steel handles more torque? I don't know names, numbers or types.
BTW ... I never did get the Nisson engine going.
Ken

I'm puzzled about the "cable looking type" and "mild steel"?  Somehow, to me at least, the terms seem to contradict?
If it's a fine strand flex twisted cable, it will probably stand more torque than your engine can develop.
Sorry about the Nissan, I was kind of afraid of that. I hope at the least you can recoup the shipping cost by parting it out on Epay or
C'slist.
Ron

[akghound]

I am coming off the crank with the factory cable type flex shaft. It will key onto a steel jack shaft supported with pillow block bearings. The steel jack shaft will turn a pulley / belt which drives the generator. The body of the jack shaft is 1 5/8" with the power input end turned down to 3/4 to fit into the flex shaft. The reason for the 1 5/8" jack shaft is that is the size of the bearings and pulley hubs that I already have on hand. I need to couple this shaft to the flex shaft which is 3/4" keyed female. Thus the question.
Clear as mud now?
Ken

[LowGear]

Hi akghound,

If you've got McIntosh stereo equipment running on this generator you probably want fairly clean solid sine wave or sinusoid power at a pretty fixed hertz.  If you're rectifying it to DC then those needs may not exist or be worth their extra cost.  You don't need a surgeons scalpel to chop fish heads.

Using the transmission parts rang a bell with me for some reason.

Casey

[akghound]

I'm using the ST head that I once powered with the 20/2 Listeroid. I have given up on that engine for now. This tractor has been sitting around since the place burned down in 2006. My sons and I went out and got it started a coulpe weeks ago. Pulled it up to the house, near the old gen shed and plan on powering the place with it. We will be back on track with co-gen again using the heat from the engine coolant to heat the floor of the house, radient heat from the setup to heat the gen shed. And of course the engine for electricity. When the engine is running we prheat our domectic water with a small electric water heater. This cuts our propane bill way down in the winter. The engine runs off of used ATF and WVO so the fuel bill is almost nill. From this fuel we get almost all our heat & hot water and all our electricity. Wind and solar are on the burner to supply our electrical demands in the near future.

[Thob]

HP = Torque (ft-lbs) * RPM / 5252

In order to produce 12Kw out of the generator, you need something like 24HP (maybe a little less depending on generator efficiency).  That works out to about 70 ft-lbs of torque at 1800 RPM.  I don't have machinery's handbook with me at the moment, but I believe a 3/4" shaft can handle that much torque with ease, and be able to stand up to the dynamic loads as well.