Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

okay so everyone knows your not supposed to hit stuff with their lawnmower (treeroots,survey markers,rocks,small cars ect)

but did you ever wonder just what happens when you run over something .

we had an ariens tractor come in friday with a complaint of a terrible noise in the deck.

so we remove the deck and flip it and check it out. it had 2 blades and they are timed,they run from a cog belt and are designed not to pass each other .i guess you could say they overlap .

anyway the operator ran over somthing and 1 blade skipped over its cogs on the belt.

now most of you know that ariens is pretty good gear and they have a very heavy duty set of blades on this particular mower .they are almost a 1/4 inch thick,has to be more than 3/16 at least.

anyway the blades met each other and as a result one blade ended up badley bent and the other lost at least 2 inches off each end...thats a lot of smash and crash with some heavy blades.

so here is why it happens.

there is a regulation  of blade tip speed,comes from the guys that put the stickers on the mowers. i beleive its ANSI in the US.

they have determined that 18000 feet per minute is the maximum safe speed a blade can travel.

this workes out to about 3200 rpm on a 21 inch walk behind mower.

a tractor is set up the same way,blade speed is regulated the same.

the number used to be higher ,but was slowed a few years ago not sure of exact date.

so you say whats that 18000 mean to me ,its kinda hard to relate to.

lets put it in perspective.

we know that a mile has 5280 feet 

we know the blade travels at 18000 feet per minute ...

so the blade tip actually travels at  3.4 miles a minute. here is where it gets interesting.

3.4 miles a minute gets us over 200 miles an hour.

no wonder blades get bent and cranks get twisted and lawnmowers get junked.

hmm makes me wonder if i should start wearing some extra safety gear when working on them.

later chris