Drum Shaft Design w/ Reinforcing Plates

[zbreeland]

Hello all. I am working on my first winch design and feel like I have a solid design, but I'm struggling to prove the results. I've attached an image showing the winch. I'm looking at the shaft and drum at the moment and I'm using a side insert to act as the main support for the drum through use of roller bearings. This takes a lot of the stress off of the shaft so it is primarily, if not all, torsion loading. I'm looking to handle 85,600 in*lbs @ 38.5 RPM using a gearbox straight to the shaft. To do this I'm using a 4.5" OD x 0.5" WT central splined shaft. This will be welded to half inch reinforcing plate welded to the drum. There will be 3 of these plates, with a maximum of 6.5" between plates. No other stress concentrations along the shaft.

One problem I'm having trouble proving is the torsional deflection. Looking at this as a standard shaft puts me at 6 degrees over 6.5", which is the max distance between plates. The problem I see with that is these plates are all welded to the same drum, so I don't see the plates rotating independently of one another. At least not that much, especially since the gearbox shaft will be placed centered on the first plate so there is no gap between the end of that shaft and the start of the drum shaft.

I know I have to do a shear calculation on the welds for the plates to drum and plates to shaft, which I'm starting on today, but I don't see really anything else that would be an area of focus. The shear stress in this shaft is under 8000 PSI and I'm looking at hardened 4140 steel so that's nothing.

Is there something I'm overthinking in regards to this shaft deflection, or something I'm missing in terms of stress concentrations?

 

[Compositepro]

Almost all of the torsional stress will transfer from the shaft to the drum at the first plate. A conservative assumption would be 100% for purposes of your calculations.