Why do longer bars require more power?

[brages]

Thanks, I think I'm starting to understand; I'm going to have to think about this for a while...

 

[romeo]

now my brain hurts

 

[JohnL]

let think about this your saying if you have a 20 tooth chain or a 200 tooth
chain the speed is the same .the moore teeth the slower the speed.
i will put any amount of money you guys wish to wager.Mark a tooth an
a 16'' bar and count the number of times you turn the sprocket until it gets back to the point were you starte now do this with a 32'' bar. now we know
the saw operates at the same rpm with the 2 bars:monkey: :monkey:

For the same rpm of the drive sprocket, (forget about the load on the motor from increased drag), the 200 tooth chain makes a complete revolution once for every 10 revolutions of the 20 tooth chain. BUT, both chains will have the same linear velocity (chain speed).

You are mixing up the difference between the rpm of each chain,which will be proportional to the chain length, (like in gears, where chain length = no. of teeth) and chain speed, which will be equal, no matter the length of chain, for a given sprocket speed.

 

[bigjake]

Yes i was confusing the 2.And was wrong .I seen a very old chainsaw that
had a kinda open loop round bar i would guess thats what this was tying
to combat.And i know the friction would be greater on a tight circumference
tip and sprocket .i know different size gears with the same ratios have different
torque multiplication's. My brain hurts to

 

[pbuehning]

I'm glad I stayed out of this one and just listen - I learned alot. Very funny, "Shutup and listen" actually works.

Maybe I'll have to listen to the little woman, more often.

I only said listen.!!!!

 

[PaulDaisy]

I found it easy to understand the subtle effect of a longer bar by comparing what the engine does trying to drag twice the chain to what a person would do, trying to drag 100 ft of bulk 3/8", semi-chisel saw chain, unwrapped, behind you through the forest, vs. dragging 200 ft of the same chain through the same forest... friction DOES matter.

 

[lab-rat]

now my brain hurts

No kidding Nasa called, time to go home:hmm3grin2orange:

 

[juststumps]

anothrter thing you guys are forgeting is the sproket and gear are different sizes ??????? .Remember we are talking chain speed how many reveloutions
it takes for the chain to make one complete revolution as to the engine rpm??I gues the term ratio wasnt quit right.But you still loose distance covered by the chain per crank revolution.

you just proved what i am saying rpms are time .how can they be the same speed.your saw runs at a given rpm .the smaller chain passes through its whole cycle more in one minute now how can that be the same.

if i go a mile at 60 MPH, or if i go ten miles at 60 MPH... i'm still going 60 MPH !!! it just takes ten times longer to get there ...

if i have a 20 tooth chain running at 10,000 RPM and a 200 tooth chain running at 10,000 RPM... i'm still running 10,000 RPM ... same chain speed !!!! just takes ten times longer to make a complete loop...


DOH !!!!

 

[GASoline71]

Well there's 15 minutes of my life I will never get back...



Gary

 

[Haywire Haywood]

Technically, no power is going into accelerating the chain once it has reached a steady speed.

If that was the case, once I got my truck up to speed on the interstate, I could take my foot off the accelerator and coast down to Georgia.

Ian

 

[M.R.]

There has only been a few times when in mistle-toe [sp?] in pine & doug fir that threading around with a shorter bar Might have been a little bit handier.

Size wise at my heigth & build a 28" bar fits. The logging crews I started with all sized their bar lengths by -standing straight and square and being able to touch the tip a couple of inches out/from or off of the right toe.
Granted it'll take a certain amount of powerhead to pull it. :monkey:

026 Pro 24" Doggy compared to the DCS540
DCS540 20"
064 28"
153 28"
DCS6401 nib 20" waiting for 7900kit then 28"



Heck, even the short barred Texans on here -
Walk up and put it in
Instead of putting it in and walking up.

 

[Modifiedmark]

Well there's 15 minutes of my life I will never get back...



Gary

It took you 15 minutes to read that? :jawdrop:

 

[stihlloggin]

so a 4" drill bit is faster than a 10" !!!

 

[lab-rat]

Well there's 15 minutes of my life I will never get back...



Gary

Forget oil, what beer should I be drinking -dave-

 

[GASoline71]

It took you 15 minutes to read that? :jawdrop:

Forget oil, what beer should I be drinking -dave-

...and 5 Bud Light's...

Gary

 

[timberwolf]

Here is a high speed photo of a chain, if I remember right it was a 10 tooth gear on 066 going about 15,000 RPM. Forget exactly what it worked out to 80 or 90 MPH chain speed.

If you look at it carefully it's possible to see where the chain is hitting the bar and pulling off away from the bar telling a little about the accelerations, when things are going in a straight line the want to keep going in a straight line and when spun they want to go in a circle. Chain was snugged good and tight with no slack what so ever.

Not beating a dead horse here, just thought it was a cool photo shot at about 1/4000 th of a second.

 

[B_Turner]

when things are going in a straight line the want to keep going in a straight line and when spun they want to go in a circle.

Cool shot.

I'm not the sharpest spoon in the shed (just ask Lakeside) but I thought all things basically want to go straight. Got to convince them to go round.

 

[timberwolf]

Yes, but spin a chain loop in free air and it wants to form a circle, thats why the chain rises on the center of the top rail. On the lower rail though it's held in tight by the pull of the motor. Also once things are spinning they want to to keep spining It's a little harder to see but the links around the tip show this a bit.

 

[mtfallsmikey]

Is that blood on the bar?...Deer processing saw?

 

[timberwolf]

No bar oil, spent quite a bit of time running it out of the wood to get photo set up right.