Back Yard Engineer
We all have to learn, but some of us have to learn the same things more than once.
I bought an old garden tractor years back, it was a Bolens 12HP Wisconsin powered, with a hydrostatic trans and a front loader. Even though it was light on HP, it could do some real work. It spent it's first twenty years at Weber's Nursery in Covington, WA. I'm sure lots of kids used it and abused it.
When I bought it, I found all kinds of reasons to overload the bucket by twice the rated capacity and other foolish things. I'd lower the bucket and take runs at things that caused the whole machine to nearly hop off the ground when it hit... and still the little machine held up.
One day, I decided to overhaul the tired engine which cost $600 dollars to have done. Then I stripped it, removed rust, did some sheet metal work and put it all back together. As I went through the boxes of parts, I noted how rusty and old the bolts looked. Going through my parts bin, I found a wide selection of beautifully plated grade 8 bolts with locking nuts. I figured these would look pretty cool on the ole tractor, so on they went.
The frame rails are tied together fore and aft with massive cast iron pieces that double as mountings for other parts like the heavy eye beam front end, and the hydraulic ram for the 2 point hitch aft.
All together it looked new again, gleaming, shiny paint, and those plated bolts and nuts... certainly a quality job I thought.
With a few hours of work under it's belt, the engine started lugging down, sparks shot from underneath and I quickly shut it off. Upon inspection, I found the massive cast iron piece up forward broke in half which allowed part of the suspension to run up against the drive pulley. Upon further inspection, I found another crack in the massive cross tie aft!
How could this be? Twenty plus years of abuse and no problems, then a single day of work breaks the tractor in half?
Remember those old rusty bolts?.... they were soft, weak, and stretchy, when you took a run at something, those ole bolts absorbed the shock and allowed the rails to move independent of the cast pieces. The shiny grade eight bolts I put on got snugged up tight. and being far stronger and less 'stretchy' transferred all that abuse into the cast parts that couldn't bend or flex enough... it just broke in half!
Moral of the story? Making something stronger is not always a good idea, you could understand the concept, but you've got to be paying attention as well!
The reason I take the time to share this story? Because I want you to give your designs some consideration. Take a drive coupler for instance, do you want to make it stronger than the crank shaft or generator shaft? If something needs to give, what should it be? The coupler?, the crank?, the generator shaft?
I'm always learning.... sometimes, its the hard way.....
Read about couplings... there's more to it than some of us understand.