20" Oregon 72LG vs. 28" Oregon 72LG chains

[kodiakfisher]

(Times) 20" Oregon 72LG vs. 28" Oregon 72LP chains

Here is my question the two chains have the exact same number of cutters on the chain. If both chains are sharp is there any difference in the amount of drag on my chainsaw to turn each chain in the wood. Say 18 inch for the 20" bar and 26" for the 28" bar. If there is a significant difference of 20% or more between the two what causes the difference.

I will state that both cutters are equally sharp and that the bars are being equally oiled any significant differences are attributed to what is happening in the wood. Can someone explain the significant difference if any. I understand that the cutting speed will be slower due to fewer cutters as a percentage of wood diameter, the question then becomes is it faster to cut with a slower bar and chain or make two cuts with a shorter bar but faster chain including changeover times. I also realize that the setting of the rakers may need to be set different depending on the saw being used small saw < 60cc and >60cc and hardwood vs. softwood.

Doug

 

[Lawn Masters]

somehow, I doubt a 357XP will handle a 28" bar very well. a 20" sure, but a 28, no way.

 

[Diesel JD]

60CCs? Doubt it will push the 28" very well, my Stihl MS390 was a dog with the 28". You might get away with it if you used the full skip version of this chain and kept it very sharp. I've found that the 390 with similar CCs will push a 25" bar 84 DL 3/8" chain just fine. As fast as an 044 or 038 MAG..? No, but it's less saw, and I don't have to set any speed records, just cut big wood without hurting the saw and without having to constantly kneel down.

 

[kodiakfisher]

WHY WHY WHY answer the question unless you can quantify why the significant difference when the number of cutters is the same you have not even provided any useful information. I want to know why if the number of cutters is the same why does bar length matter?

Doug

 

[Billy_Bob]

I don't understand your question...

Are you using two different models of chainsaws? Which?

Different length bars on each? Which model bars if different bars?

Cutting same size logs with both saws? What size log(s)?

And same amount of cutters? One is a full comp chain and another is a full skip chain or something?

[Need input!]

 

[scottr]

Friction

Doug , the longer bar and chain has more friction to rob horse power .

 

[kodiakfisher]

same chainsaw two different bars 20" bar and 28" bar 20" bar has full comp 36 cutters I think, and 28" bar full skip with about 36 cutters also. So why is there a difference in the amount of power required to pull both chains through the wood?

It seems with the same amount of cutters the power required would be very close. From what I can gather on this site this is not the case but nobody can or has explained why this is.

Doug

 

[Grande Dog]

The number of teeth engaged in the wood determines the power required. If your using 3/8 pitch chain making a 20" cut, with full comp. you have 14 teeth engaging the wood and full skip only has 10. Considering most people are using sprocket nose bars, the chain is suspended between the nose sprocket and the drive sprocket. With no load, the power to spin the 28" bar compared to the power to spin 20" is negligible. From past experience I would say all things considered even, a 20" cut with full comp would have the power requirement as a 28" cut with full skip. I don't have any science or numbers to back this statement up but, maybe the Oregon Engineer might be able to shine some light on this subject.

Grande Dog
Master Mechanic
Discount Arborist Equipment and Tree Care Supplies

 

[Billy_Bob]

Seems to me accurate testing conditions would be:

Same saw motor.

Same model of bars, but one longer than the other.
Example: both Stihl ES bars.
(More expensive bars would have less friction than cheap bars.)

Both bars have brand new chains of the same exact type and skip.
(This would assure that they were the same sharpness and rakers were set exactly the same.)

Both bars are used to cut the same piece of wood - same diameter.
(Same number of teeth are cutting the wood with both bars.)

The only thing left to be different in this case would be the length of the bar.

 

[kodiakfisher]

Thank you Grande Dog,

you seem to have confirmed that the differences would be minimal. It seems many will recommend a particular bar length without consideration of the chain being used. I'm sure when the recommendation is made it is made with the assumption of full comp chain in mind. It has been my belief that I could run a longer bar with full skip for the 15% of the soft wood trees I cut that are 25" or so and use the shorter bar with full comp the rest of the time, since the saw is not pulling any more cutters through the wood the saw would't be able to tell how long the bar is only how much drag is created by the cutters. The issue seems to be the number of cutters creating drag on the motor not how long the bar is.

Doug E

 

[kodiakfisher]

scottr,

You have a point about frictional losses but I believe these losses are probably minimal, but I don't know. I believe the greatest cause of friction would be the cutter itself and with the same number of cutters between full comp 20" bar and full skip 28" bar the only thing left would be frictional losses due to the longer bar, I believe this to be minimal but was looking for actual experience if anyone has any.

14 (full comp) cutters in a 18" inch log with 20" bar should be very close to 14 (full skip) cutters in a 25" inch log with 28" bar. Close being the amount of drag on the motor NOT cutting times. I am only interested in be able to maintain RPM in the wood not how long it takes to make the cut, full comp will always be faster.

Doug E

 

[scottr]

Load

Doug , it will be interesting to see if any of the bar companies have measured the load when using a 20" with x teeth in the cut verses the load of a 28" bar with y teeth in the cut . Once the chain in the cut loads up with chips to be moved and severed it becomes a different story . It would be interesting to measure just the difference of the tension to properly adjust a chain on a 20" bar versus a 28" bar . A lot of different factors come into play with your question .

 

[kodiakfisher]

Scottr,

Never claimed it was any easy question . I only claim to be smart enough to understand the answer....this may not be true either it was hard enough to word it in such a manner to keep people from thinking strictly cutting times and think only about the load on the engine.

Doug

 

[PWB]

Don't know for sure, but it seems to me you'd lose power to friction and mass. More drive links to drag around the bar, and more mass of chain to move. Really want to throw a monkey wrench into this? Go 3/8" on the short one, .325 on the longer one!

 

[tonka]

Interesting question. I'd like to know too. It would seem that the number of cutters in the wood would determine how much power is needed. It'd be nice if someone had data to prove or disprove this idea.

 

[kodiakfisher]

Don't know for sure, but it seems to me you'd lose power to friction and mass. More drive links to drag around the bar, and more mass of chain to move. Really want to throw a monkey wrench into this? Go 3/8" on the short one, .325 on the longer one!

The effect of this would be due to the size of the kerf. It has been pointed out on other threads that in many cases the size of the kerf for a 3/8 vs .325 is often the same or very close but i digress lets stay on topic there are pleanty of threads dealing with 3/8 vs .325 and even a few threads with actual cut times of the two sizes. This is really an old dead horse granted the comparison was made with equal number of cutters and not full comp vs. full skip.

kodiakfisher

 

[SawTroll]

.... 14 (full comp) cutters in a 18" inch log with 20" bar should be very close to 14 (full skip) cutters in a 25" inch log with 28" bar. Close being the amount of drag on the motor NOT cutting times. I am only interested in be able to maintain RPM in the wood not how long it takes to make the cut, full comp will always be faster.

Full comp will only be faster as long as chip clearence doesn't become an issue, I think.

I wonder if friction between the side of the tie straps and the wood will be a factor into the equation ???

 

[kodiakfisher]

I wouldn't suspect that the tie straps would create much drag because the cutters are going to cut a kerf slightly wider than the strap and bar.


Thanks,

Doug

 

[jokers]

.........the cutters are going to cut a kerf slightly wider than the strap and bar.


Thanks,

Doug

True, but with the sawdust and chips in the kerf and the waviness(sometimes looks like corrugation) you often see on the cut face I would expect drag to be high even if the saw were supported by a totally unwavering machine.

Russ

 

[PWB]

Try it and time it already!