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Short chain vs long chain cutting speed

Ford3000

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I read that people comment a short bar / chain cuts faster than a longer setup.
How can this be, surely its the number of teeth that passes through the cut that matters,
up until your input power cant keep up the speed, and as such its rpm multiplied by teeth
through the wood that counts, all else being even, like having enough power to keep up
/ hold the rpm in the cut.
 

ammoaddict

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I've heard the same. Heard some say you shouldn't run a 20" bar on a 50cc saw, not enough power to pull it. Should only run 16". I have a 20" on one of mine and it pulls it just fine. Don't see what difference 4" of bar and 12 driver links makes.
 

HumBurner

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I've heard the same. Heard some say you shouldn't run a 20" bar on a 50cc saw, not enough power to pull it. Should only run 16". I have a 20" on one of mine and it pulls it just fine. Don't see what difference 4" of bar and 12 driver links makes.
It's the same difference in cutting a cookie at 5.6 seconds versus 5.7 seconds. Is there a difference? Yes.


Does it really matter? Not so much, but there's always a point of diminishing returns, one way or the other.
 

Wonkydonkey

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A Longer bar zaps power! With all that added friction It all adds up in The end, that’s why manufacturers have max bar lengths & that can change a bit just by the actual size of the chain.
Eg look at times they quote in cutting speeds when you use a narrower kerf chain compared to the std chain. As well as making an old chain cut well with smaller teeth compared to a new chain.

That said most homeowners can’t get a half used chain to cut even close to a new chain 🙈😉🤔👍 when in actual fact it should cut faster because of the smaller kerf.

And I forgot to add wood species into the equation .

I will add bigger teef are more forgiving and stay sharp longer.

So I guess it’s a balancing act…and…big bar cuts faster with sharp chain compared to smaller bar with blunt chain. 🤪

Look at your chips/sawdust ratio etc, and can you make a blunt chain cut good again (notice I didn’t say blunt chain sharp)

Btw I,m not saying I’m an expert, I just know a few differences and what to look for. And that’s from reading from this place with the help of those many helpful members 😉👍


Edit ; I forgot to add, a bigger bar or/and bigger drive links needs more oil and that also adds to more drag on the power head. thus less power to cut..🤔
I sort of said that in the first sentence but not very clearly enough..🤦‍♂️
 
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sawmikaze

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A Longer bar zaps power! With all that added friction It all adds up in The end, that’s why manufacturers have max bar lengths & that can change a bit just by the actual size of the chain.
Eg look at times they quote in cutting speeds when you use a narrower kerf chain compared to the std chain. As well as making an old chain cut well with smaller teeth compared to a new chain.

That said most homeowners can’t get a half used chain to cut even close to a new chain 🙈😉🤔👍 when in actual fact it should cut faster because of the smaller kerf.

And I forgot to add wood species into the equation .

I will add bigger teef are more forgiving and stay sharp longer.

So I guess it’s a balancing act…and…big bar cuts faster with sharp chain compared to smaller bar with blunt chain. 🤪

Look at your chips/sawdust ratio etc, and can you make a blunt chain cut good again (notice I didn’t say blunt chain sharp)

Btw I,m not saying I’m an expert, I just know a few differences and what to look for. And that’s from reading from this place with the help of those many helpful members 😉👍


Edit ; I forgot to add, a bigger bar or/and bigger drive links needs more oil and that also adds to more drag on the power head. thus less power to cut..🤔
I sort of said that in the first sentence but not very clearly enough..🤦‍♂️

If you own a home you can't sharpen a chain ?
 

huskihl

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60 links on 16” 3/8 vs 72 on a 20. 12 links worth of bar friction makes a small difference but the WOW factor is mostly from comparing a new 16” setup to their dull 20”
 
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Ford3000

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A Longer bar zaps power! With all that added friction It all adds up in The end, that’s why manufacturers have max bar lengths & that can change a bit just by the actual size of the chain.
Eg look at times they quote in cutting speeds when you use a narrower kerf chain compared to the std chain. As well as making an old chain cut well with smaller teeth compared to a new chain.

That said most homeowners can’t get a half used chain to cut even close to a new chain 🙈😉🤔👍 when in actual fact it should cut faster because of the smaller kerf.

And I forgot to add wood species into the equation .

I will add bigger teef are more forgiving and stay sharp longer.

So I guess it’s a balancing act…and…big bar cuts faster with sharp chain compared to smaller bar with blunt chain. 🤪

Look at your chips/sawdust ratio etc, and can you make a blunt chain cut good again (notice I didn’t say blunt chain sharp)

Btw I,m not saying I’m an expert, I just know a few differences and what to look for. And that’s from reading from this place with the help of those many helpful members 😉👍


Edit ; I forgot to add, a bigger bar or/and bigger drive links needs more oil and that also adds to more drag on the power head. thus less power to cut..🤔
I sort of said that in the first sentence but not very clearly enough..🤦‍♂️
This guy does well with a longer bar, 24 inch on 50cc saws.
 

Ford3000

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This is even more remarkable, MS250 with 24 inch bar
 

Al Smith

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You can run longer bars but not cut as fast .Think about a 3 cuber with a 16" then a 20" .A 5 cuber,80 cc it won't make much diff except after a time a short bar will require some file work .Less teeth to dull faster .
 

Ford3000

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You can run longer bars but not cut as fast .Think about a 3 cuber with a 16" then a 20" .A 5 cuber,80 cc it won't make much diff except after a time a short bar will require some file work .Less teeth to dull faster .
Will a longer chain with more teeth need less sharpening, did I pick this up right.
 

Al Smith

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Vica versa .Case in point going back over 40 years .Myself and my father both had Mc bricks.McCulloch model 610 . Dad had a 16" mine a 20" .He could run circles around me but the chain needed filed more often and I caught up with him time wise .BTW I have both of them still .
 

isaaccarlson

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A saw will pull a short bar at a higher rpm than a longer bar, if everything else is the same. So yes, a short bar will cut faster than a longer bar as long as the wood is smaller than the bar.

If you make the chain more aggressive, the rpm will drop. Once you get behind the power curve, the saw will stall, because the power drops off rather than increasing as rpm drops. The goal is to stay in front of the power curve so there is reserve power on tap for knots, or an increase in cutting pressure. Different saws have different power curves, and some will pull a longer bar than others, in the same displacement range.

A longer bar may be too much unless the rakers are higher to reduce load. Drag is exponential, and a longer bar will rob more power than you think, expecially if the bar/chain is a tight fit or new, because the oil film is thinner and resists shear movement.

I had an old worn out bar on a ported 50cc saw. The bar groove was .080" and the chain was .058". It would easily hold 12,500 rpm in the cut and had gobs of power. I got a new bar for it and the power dropped by a lot because of the extra drag. I miss how the older one cut/ran, but it was destroyed by a tree, so I'll just have to wear out the new one, lol.

This is a rabbit hole, so be careful.
 

Wilhelm

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A saw will pull a short bar at a higher rpm than a longer bar, if everything else is the same. So yes, a short bar will cut faster than a longer bar as long as the wood is smaller than the bar.

If you make the chain more aggressive, the rpm will drop. Once you get behind the power curve, the saw will stall, because the power drops off rather than increasing as rpm drops. The goal is to stay in front of the power curve so there is reserve power on tap for knots, or an increase in cutting pressure. Different saws have different power curves, and some will pull a longer bar than others, in the same displacement range.

A longer bar may be too much unless the rakers are higher to reduce load. Drag is exponential, and a longer bar will rob more power than you think, expecially if the bar/chain is a tight fit or new, because the oil film is thinner and resists shear movement.

I had an old worn out bar on a ported 50cc saw. The bar groove was .080" and the chain was .058". It would easily hold 12,500 rpm in the cut and had gobs of power. I got a new bar for it and the power dropped by a lot because of the extra drag. I miss how the older one cut/ran, but it was destroyed by a tree, so I'll just have to wear out the new one, lol.

This is a rabbit hole, so be careful.
Just utilize .050" chains till the bar wears out a bit! ;)
 

Al Smith

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Could you change drive sprocket from a 7 to a 9 and pick up chain speed? :Laie_22mini:
It would depend on the saw .I once tried a 10 tooth rim .404 on a Mac 125 which normally ran an 8 .Really bogged down the big saw ,bad plan .In addition on a large displacement saw you take a chance of breaking the crankshaft .
I did rework an 8 tooth sprocket from a Homelite ,1/2" and used in on a 650 Mac gear drive but with a 32" bar .It sped it up but had it been the 48" bar I'd imagine it wouldn't work real well .
 

Wilhelm

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It would depend on the saw .I once tried a 10 tooth rim .404 on a Mac 125 which normally ran an 8 .Really bogged down the big saw ,bad plan .In addition on a large displacement saw you take a chance of breaking the crankshaft .
I did rework an 8 tooth sprocket from a Homelite ,1/2" and used in on a 650 Mac gear drive but with a 32" bar .It sped it up but had it been the 48" bar I'd imagine it wouldn't work real well .
I have a 3/8" 8 pin and a .325" 9 pin, tried them with chain speed being hyped so much - don't like it.
The loss of torque is noticeable.
Also, the increase in chain speed is counterproductive in dense hard wood species.

There are better ways to keep chain speed up without placing higher wear on ones saw/PH - a sharp quality chain set up for a given PH. :)
 

Al Smith

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It's often not actually chain speed rate .For example running at top speed might seem fast but at higher RPM's usually is not the highest torque rate might be several thousand RPM's lower.
Case in point the two little Partner 49 cc models I'm tinkering with .They are rated at 14,000 RPM's but the cut rate is around 12,000 .One a 5000 plus has a rattle ball governor that would effectively attempt to keep it in the power curve .I'm not exactly certain what kind of a carb the other one,a 500 has.
Haven't got to that one yet .
 
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