Discussion in 'Quitters' Club' started by ITLKSEZ, Oct 29, 2021.
As long as it sticks out past the wood, you could put a bulkier ball bearing/sprocket out there.
When ripping with a circular blade , ones blade should not penetrate more than 3/4" past the thickness This allows less resistance drag on the blade & motor .
This is different physics though......So I'm out
Aaaaaaaaand… it’s dead.
Like my jeep in Moab, the part that I’d feared would fail has failed, but this time, I don’t have a spare and I’m not sure it’s worth making another one.
I’ll explain later when I have time.
It's not dead, it's just resting... pineing for the fjords...
That wouldn't vroom if you put 4 million volts through it.
That seems like a lot of work to stop already.
Ok, so here’s the dilemma. There was one part of this build that I purposefully left out of public view, because it was a bit of a hack job just to get me running.
I got a 7 tooth rim sprocket from the tractor store for a chainsaw.
The ID of this piece was ~22mm and had teeth to fit over another cog. It is super-hard material that my carbide burrs wouldn't even touch. I had to grind it out to the shaft’s diameter of 25mm with a stone in the die grinder, then cut a tiny groove in it for a makeshift key out of 1/4” round stock. The material at the keyway was so thin, I thought for sure the fail point would be there - a split at the thin point at the "key."
Well, the integrity of the sprocket turned out to be adequate, but the sprocket was so thin, the teeth of the chain now protruded deeper than the depth of the sprocket, riding on the shaft, and not allowing a tight mesh inside the sprocket. This little bit of interference became the problem. The teeth wanted to ride up on the sprocket and skip if the chain wasn’t kept tight.
Over the course of yesterday and this morning, they skipped enough that it stripped out the sprocket to the point that it would no longer grab.
And here’s the rabbit hole:
I can get a 25mm keyed sprocket that would fit this engine perfectly, but it's 11 tooth minimum (57% increase!) and .404 pitch. That would be way too big of a chain and too fast for this engine, so I would need a bigger engine. A bigger engine’s torque will put too much stress on the other weak point, the aluminum track. When I bought the aluminum, I had laser focus on the straightness it offered, but I hadn’t put enough thought into just how much torque would be transferred to it. It’s marginally strong enough as-is. It has quite a bit of flex under torque.
So a bigger sprocket needs a bigger chain which needs a bigger engine which needs a stronger track.
And that’s where I’m at: upgrade none, or upgrade all. Upgrading everything would nearly triple my investment in this. A .404 sprocket is $80-120, a decent bar is $100 minimum, rip chain is $50, engine is $50-100, and an I-beam is probably $150 if I can find what I need at the yard.
Here’s how much I got done before it quit (include the three whole rips I cut up to make the stickers).
If I'm reading this right, what about turning down the shaft of the motor, to fit the 22mm sprockets?
I admire your Spring Pile......
If I was in love with this engine, I’d probably go that route, but tearing down the engine to get the crank out to a machinist sounds like a lot of work. The engine is a bit temperamental with not enough flywheel weight (stalls without warning under load), and starting it with a drill each time is a pain.
For now, I’ll probably try the same process with an 8-tooth sprocket, which *should* leave enough meat to avoid shaft interference with the chain. Hopefully the motor will have enough snot to turn it since it’s only a 14% increase.
Long term though, the flex in the aluminum will need to be addressed if I’m going to keep this thing for any real production work. Sourcing trees won’t be an issue; my neighbors are getting wind of this and are offering up all their standing dead trees that they don’t want to deal with.
I have a hunch that this thing could really plow through some wood if set up properly. Before (and probably the reason) it died, I filed down the raker teeth a little to get a more aggressive cut, and it easily doubled the cut rate, but the power suffered, and the flex in the aluminum was horrible due to the added bite. With all the aforementioned mods, this thing could be a monster.
Plot twist! The sprocket is fine. It sheared the lame key.
Also, I found the reason the bar tip was melting. I took the chain off and part of the sprocket fell out. The rest is missing. I’m wondering if the missing piece jammed and was the cause of the sheared key.
I’ll grab another cheap bar/chain and put this thing back together just to finish my pile of logs. I’ll work on accumulating parts for a rebuild.
hmmmm-it died on the 13th slab
On the 13th! What time did it die?
What an awesome project saw!!! Keep up the great work.
I’m back in business. I dug out an old bar from storage and it fits the rip chain! It’s a shorter bar, but I made the bar mount with a ton of adjustment; it just mounts further from the shaft. Shaft to tip is nearly the same as the old bar (the Stihl bar is wider, so I lost about 1/2” of length).
Are you just dripping oil on the chain or pushing it through internally,could be the reason for sprocket failure....could you put oil in the bar and pressure the tank with air to push the oil through ?
Me, I'd just start the engine and hold a file against the shaft. You (being better at rocket surgery) could probably rig a lath tool holder.
It’s just dripping with gravity feed, but it’s definitely getting enough. It slings it everywhere. In fact, I just moved this thing to behind the shop at lunch because half the shop driveway is now covered in oil.
I think it failed because (1) as I mentioned, it’s pulling all the torque across it, and (2) that bar is cheap, inferior garbage. The nose sprocket on this Stihl bar is huge in comparison.
You’re giving this engine a lot of credit. It vibrates like a jumping jack!
Separate names with a comma.