Monday, March 19, 2012

straw chopper 3

Turns out two stroke gasoline powered chipper, not a good choice. But what else was i going to work with? One of the students found an old lawn edger and gave it to me thinking it might work for this, or perhaps for something else. I took a look at it, it was better than the chipper for sure, but not quite ideal. I wasn't sure it could do the job, and the thought of another false start was pretty unappealing. I mean, you have to get used to that kind of thing, it takes a lot of experimentation and, necessarily, failure to be able to produce something successful. But even knowing that, it still sucks when something just flat out doesn't work.


I contemplated the edger for a while. The blade set up wasn't great, actually it was more or less identical to the chipper minus the giant rusty bludgeoning wheel. I didn't have a clear sense of how to go about utilizing it for straw shredding. I took a look around at some other random pulleys and things, thinking i might find some inspiration there, but i didn't.


At a loss, i decided to take one last look at the scrap pile. I started digging around, clearing brambles and flipping over sheets of corrugated metal.


I honestly didn't expect to find anything. But I'll be damned, enough digging produced a reel mower, the exact thing that i had envisioned for the machine in the first place. It was covered in rust and seized up, who knows how long this thing had been sitting outside. Excitedly, I carried it down to the shop and started pulling the thing apart.


It was even better than i expected- the blades weren't frozen at all, nor was the gear that spun them- actually, they spun great. It was the outer wheel that was frozen and once that was off everything else worked beautifully.

video


The blades themselves were pretty dull, but it didn't even matter, this was the most exciting thing to happen in weeks. I knew right then that it was going to work- this mower was the key.

The first thing to do was to get rid of the side walls that the wheel fit onto. I envisioned using the pulley and belt again, and the easiest way to provide access would be to grind off the wall.



At first i imagined that the corresponding pulley made for the belt might fit snugly onto the axle of the blades. It was close, really close. So close you can't even tell looking at them side by side, but it was just a hair too tight.


That left me with the original gear to work with. This was a good thing. The gear, obviously, was a perfect fit, but it also had a little sliding piece inside that acted as a freewheel- allowing the blades to spin in only one direction, and the gear to rotate freely in the other (or more accurately, to be stopped while the blades still spun). So the gear was it. But how would i keep the belt on?


Maybe this?


Nope.

How about this?


Yeah, that looked pretty good.


I found that when i put it all together the belt kept pulling the gear off. I tried twisting the bike so that the angle of the belt would pull the gear in the other direction. That worked but wasn't ideal- extra friction= loss of efficiency= bad.

I imagined a guide to hold it in place. I drilled a hole in a piece of flat stock, bent it, welded a nut to it, found an appropriate bolt to go through it, ground the end into a point and welded it onto the mower. This way i could turn the bolt in to keep a guard on the gear. I made sure to leave a small buffer of space between the bolt and the gear, ideally the gear wouldn't touch the bolt at all, but realistically it would touch it sometimes. I positioned the bolt with enough proximity to keep it engaged, but with enough space the the gear only bumped it sometimes. It worked really well.


And now it was ready for a test, with legs. Would it spin? Would it all come flying apart? Could it chop straw yet?


video


I know this is just a crappy pixelated video that's probably not all that exciting to watch, but this was a very exciting moment. The chopper went from a sad sack of engine block to a whirring set of blades ready to be built around and brought to life.