If there isn't one there should be...formula for horsepower required per tooth and bar lkength

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calamari

calamari

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Maybe there is one but I don't think I've seen it. It seems like there should be a simple formula that you'd use to calculate the appropriate horsepower or cc equivalent to use for determining the appropriate sized saw for cutting various diameters of various species of trees. I've seen guys on here say you just can't cut 20" oak for example with anything less than a 70cc saw. I've cut lots of oak that size with a much smaller saw and did it quickly.
Each tooth being pulled through X amount of wood should take Y amount of horsepower. The larger the diameter the more horsepower you need because more and more teeth are in the wood or a reduction of teeth to keep the saw in the sweet spot. For example, I had the opportunity this summer to rip and buck up a very dry 28" diameter oak that I initially used a full toothed chain on. It was 104 degrees and the saw labored and the bar oil smoked. I went to a full skip chain and it cut faster and easier because the chain speed increased due to fewer teeth putting reduced drag on the engine. I'm surprised that manufacturers don't have a simple matrix for their saws that gives the break off point where a particular sized saw has reached the limit of its ability to cut with a bar of a certain length and tooth number in the wood. It would have more application on bigger wood but it would also show that 50, 60 and 70 cc saws just aren't needed if you adjust the tooth count on the saw you already have.
 
MontanaResident
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There are lots of variables to consider in B&C length. IMO, better to go larger on the saw, and shorter on the B&C til you get some practical experience for your general situation. You got a lot invested in the saw, so don't abuse it out of the box with some extra long bar in some nasty sticky overly large hardwood with a homeowner saw.

The manufactures do have recommended lengths, so start there. In my situation, I can go longer and with a more aggressive chain, because I am 100% softwoods. YMMV.
 
calamari

calamari

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There are lots of variables to consider in B&C length. IMO, better to go larger on the saw, and shorter on the B&C til you get some practical experience for your general situation. You got a lot invested in the saw, so don't abuse it out of the box with some extra long bar in some nasty sticky overly large hardwood with a homeowner saw.

The manufactures do have recommended lengths, so start there. In my situation, I can go longer and with a more aggressive chain, because I am 100% softwoods. YMMV.
Using my Makita E6100 as an example, Makita says that the longest bar for the saw is 20". My old Homelite 330 pulled a 20" bar through hardwoods with a regular chain with no difficulty and at a good cutting speed. The Makita has 1/3 again as much horsepower for the same bar length. I used the 20" bar a little and found it worked fine but didn't begin to bog the saw even a little. I put a 28" bar on the saw, turned the oiler to high and the saw still cuts just as good as before with only a slightly reduced cutting speed due to the bigger diameter logs I can now cut.
It just seems that manufacturers under rate their saw to have the buyer think it is exceptionally powerful while what is really happening is that you've paid more for a saw that isn't being used to its full potential when a smaller less expensive saw would run the same length bar just as well for what you're cutting. Your softwoods in Montana are a great example of requiring a smaller saw to cut the Lodgepole or whatever you're after as opposed to Live, Black or White oaks and Madrone like I have to cut.
Yes there are variables in woods of the same species but mostly due to number of limbs on the trunk that create twisted wood and dryness of the wood. What type of cut you're making can vary from type to type but it's pretty consistent within the same wood and type of cut. Ripping a 16" long round that is 20" in diameter cuts as fast as one 36 inches in diameter it just takes longer because you're cutting more wood.
If there was a chart that said for example that a sharp tooth of specific design takes .000x amount of horsepower to be pulled 12" in green oak, you'd know what size saw to buy and what bar and chain based on how many teeth would be in the wood. You'd know that a 45cc saw with a 20" bar would work for oaks up to X diameter and you wouldn't be stampeded into buying a 70cc saw when it wasn't needed.
Just a thought since I'm trying everything I can to avoid going outside to spray weeds.
 
MontanaResident
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Using my Makita E6100 as an example, Makita says that the longest bar for the saw is 20". My old Homelite 330 pulled a 20" bar through hardwoods with a regular chain with no difficulty and at a good cutting speed. The Makita has 1/3 again as much horsepower for the same bar length. I used the 20" bar a little and found it worked fine but didn't begin to bog the saw even a little. I put a 28" bar on the saw, turned the oiler to high and the saw still cuts just as good as before with only a slightly reduced cutting speed due to the bigger diameter logs I can now cut.
It just seems that manufacturers under rate their saw to have the buyer think it is exceptionally powerful while what is really happening is that you've paid more for a saw that isn't being used to its full potential when a smaller less expensive saw would run the same length bar just as well for what you're cutting. Your softwoods in Montana are a great example of requiring a smaller saw to cut the Lodgepole or whatever you're after as opposed to Live, Black or White oaks and Madrone like I have to cut.
Yes there are variables in woods of the same species but mostly due to number of limbs on the trunk that create twisted wood and dryness of the wood. What type of cut you're making can vary from type to type but it's pretty consistent within the same wood and type of cut. Ripping a 16" long round that is 20" in diameter cuts as fast as one 36 inches in diameter it just takes longer because you're cutting more wood.
If there was a chart that said for example that a sharp tooth of specific design takes .000x amount of horsepower to be pulled 12" in green oak, you'd know what size saw to buy and what bar and chain based on how many teeth would be in the wood. You'd know that a 45cc saw with a 20" bar would work for oaks up to X diameter and you wouldn't be stampeded into buying a 70cc saw when it wasn't needed.
Just a thought since I'm trying everything I can to avoid going outside to spray weeds.

Good points, but... Most people can't understand cubic-displacement, 2-stroke vs. 4-strock, DLs, pitch, gauge, mixing oil and gas, etc. Now you want them to consider types of wood.

You are an advance user. If you can even ask the question, you can find the answer and don't need a chart. And that chart would still have to be more general then exhaustive else be of little use to most of the 99% that might even look at it.

Consider the general users here, that are more concerned with ounces of weight, or tiny bits more of vibration in 0.325 vs. 3/8s, and argue constantly about different brands of 2-stroke oil, etc. We got more little old ladies on this forum, arguing the finest points of every aspect of using a saw, that it is a wonder the industry even attempts any recommendations.
 
cscltd

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I think there are so many factors come into play on trying to get that to happen.
How much power you need is subjective. Do we need 250hp in our cars just to haul some groceries in back, or to merge on to highway? I got speeding tickets easily with my old 80’s Jeep cj7 with 4cyl engine with 33” tires.
Wood is not a constant, species, time of year, area that it grows in, and health of tree would factor In cutting speed.
Chain would make difference, not only pitch, but whose chain? A small saw sub 30cc using low kickback low profile chain like 91sg then putting on 63ps will see a speed drop imo.
Max bar length is not always attributed to power. Operator comes into play also.
Operator ‘A’ may be able to use a 40cc saw with 20” bar and will work fine, operator ‘B’ on same setup may smoke clutch and cover cause saw is constantly gets stuck in wood from improper cutting force.
Hence we could only sell certain larger saws to heating installers as the always popped mounts out of certain smaller saws that fit the bar length they were using and only cutting softwood 2x4 etc.
As saws work into higher rpm range, torque is less of a factor for the experienced user. Torque is more about acceleration in which we rev saw to full beans before hitting wood.
 
northmanlogging
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Should be fairly easy math to convert wood hardness (readily available in the machinery's handbook) to depth and width of each tooth, multiplied by number of teeth in the cut, plus a certain percentage for associated drag and friction from the chain and what not.

Then figure out the torque required, and apply that to each saws set up.

Its a lot simpler to just keep a sharp chain and good running saw.

As for long vs short bar, its mostly wifes tails and hookus pokus, it has more to do with what a given power head can oil then overall horse ponies, granted some reasoning is involved a 36" bar on a 50cc saw is just foolish, but I do know guys that regularly run 28-32"s on a 50cc saws, mostly for limbing on log trucks, but they can buck with em when needed. (personally I have an 036/360 with a 20" and wish it was a 28" but I keep it in the cab where the loader won't be as likely to smash it..) admittedly the guys I knew that would use the little saws, were all in their 60's and 70's and lugging around 30#s of saw to knock limbs off was just foolish to them... But I've also seen them fall timber and cut their way in/out of a windfall mess with the very same saws.

as for recommended bar lengths... its simply a liability for the saw manufactures to suggest otherwise, but folks will take that as gospel truth.
the factory recommends that a 461 should not use a bar over 25", though I've ran a 36" without issue, in hardwoods too, and mine generally wear a 32" standard, in which they are more then happy cutting everything I've thrown at them, including maple, walnut, cherry, and the occasional oak, not just "softwoods" the PNW is famous for. I only have 3-4 different bar lengths after all... 20" for saws that live in machines, 32-36 main failing saws, and 50" for the big block lets make the earth shake failing saw.

In the end it has more to do with oiler output and clutch ability than anything. Bigger saws have bigger oilers, and bigger clutches, more oil means they can keep a longer bar lubed, a bigger clutch can pull a longer chain without too much slipping.

Anyway, there are a great many variables involved, and dead reckoning is probably as accurate as spending a lifetime gathering data only to have some moss backed logger say... yup this here will do it...
 
calamari

calamari

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Should be fairly easy math to convert wood hardness (readily available in the machinery's handbook) to depth and width of each tooth, multiplied by number of teeth in the cut, plus a certain percentage for associated drag and friction from the chain and what not.

Then figure out the torque required, and apply that to each saws set up.

Its a lot simpler to just keep a sharp chain and good running saw.

As for long vs short bar, its mostly wifes tails and hookus pokus, it has more to do with what a given power head can oil then overall horse ponies, granted some reasoning is involved a 36" bar on a 50cc saw is just foolish, but I do know guys that regularly run 28-32"s on a 50cc saws, mostly for limbing on log trucks, but they can buck with em when needed. (personally I have an 036/360 with a 20" and wish it was a 28" but I keep it in the cab where the loader won't be as likely to smash it..) admittedly the guys I knew that would use the little saws, were all in their 60's and 70's and lugging around 30#s of saw to knock limbs off was just foolish to them... But I've also seen them fall timber and cut their way in/out of a windfall mess with the very same saws.

as for recommended bar lengths... its simply a liability for the saw manufactures to suggest otherwise, but folks will take that as gospel truth.
the factory recommends that a 461 should not use a bar over 25", though I've ran a 36" without issue, in hardwoods too, and mine generally wear a 32" standard, in which they are more then happy cutting everything I've thrown at them, including maple, walnut, cherry, and the occasional oak, not just "softwoods" the PNW is famous for. I only have 3-4 different bar lengths after all... 20" for saws that live in machines, 32-36 main failing saws, and 50" for the big block lets make the earth shake failing saw.

In the end it has more to do with oiler output and clutch ability than anything. Bigger saws have bigger oilers, and bigger clutches, more oil means they can keep a longer bar lubed, a bigger clutch can pull a longer chain without too much slipping.

Anyway, there are a great many variables involved, and dead reckoning is probably as accurate as spending a lifetime gathering data only to have some moss backed logger say... yup this here will do it...
I have to say I like a guy who starts out saying it could be done and ends up saying it can't. I'm not picking on you but you did make me laugh for the first time today. With you and not at you.
What I suggested would be a good thing was probably triggered by reading posts about "moding" a saw by cutting a hole in the muffler. It's easy to think more noise means more power. There is a lot of science that goes into exhaust design on air cooled 2 strokes that doesn't seem to baffle motorcycle riders when you look at their sites. i still think that there is useful information that could be made available to the public both inexperienced and old moss back loggers about teeth numbers, chain design and bar length horsepower ratios. I guess always remember heat is bad and oil is good. Maybe that's all you need to know.
 
Maintenance supervisor

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5 horsepower is 5 horsepower? But if you want to cut with a 28 inch bar in ( x )amount of time and effort then it becomes end user subjective.
There's plenty of videos of people using an 026 stihl or a 455 racher to cut an enormous log or tree but its what they want to do, just like someone who straps a 20" bar on an MS880.
I'm pretty sure that anyone can come up with a formula that would be a great suggestion but I doubt that anyone would follow that suggestion for a purchase.
There's such a wild variation of 5hp(as just 1 example)saws that I think 50% of buyers would disagree with whatever you suggested in the end TBH.
 
calamari

calamari

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You are in California- so it will be pointless math pretty soon.
You will be reverted back to handsaws and be down to one or two MP (manpower) maximum input. :p
Oh, I was waiting for this. Actually you're probably right but then a lot of the old growth was cut down in the US with handsaws.
The hard part is getting guys willing to man the saws. An example is a roofing contractor I talked to who only hires illegal aliens. He's offered the jobs to citizens but he said they tend to puke, faint and then quit usually before lunch the first day in the over 100 degree heat here. The illegals show up on time, never complain and will work hard all day, every day. They really aren't taking jobs away from anyone at least in the manual labor sector.
I just thought that thinking about this as a solvable engineering problem would be interesting but maybe "Buck'n Billy" videos are as scientific saw owners want.
 
MagraAdam

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Should be fairly easy math to convert wood hardness (readily available in the machinery's handbook) to depth and width of each tooth, multiplied by number of teeth in the cut, plus a certain percentage for associated drag and friction from the chain and what not.

Then figure out the torque required, and apply that to each saws set up.

Its a lot simpler to just keep a sharp chain and good running saw.

As for long vs short bar, its mostly wifes tails and hookus pokus, it has more to do with what a given power head can oil then overall horse ponies, granted some reasoning is involved a 36" bar on a 50cc saw is just foolish, but I do know guys that regularly run 28-32"s on a 50cc saws, mostly for limbing on log trucks, but they can buck with em when needed. (personally I have an 036/360 with a 20" and wish it was a 28" but I keep it in the cab where the loader won't be as likely to smash it..) admittedly the guys I knew that would use the little saws, were all in their 60's and 70's and lugging around 30#s of saw to knock limbs off was just foolish to them... But I've also seen them fall timber and cut their way in/out of a windfall mess with the very same saws.

as for recommended bar lengths... its simply a liability for the saw manufactures to suggest otherwise, but folks will take that as gospel truth.
the factory recommends that a 461 should not use a bar over 25", though I've ran a 36" without issue, in hardwoods too, and mine generally wear a 32" standard, in which they are more then happy cutting everything I've thrown at them, including maple, walnut, cherry, and the occasional oak, not just "softwoods" the PNW is famous for. I only have 3-4 different bar lengths after all... 20" for saws that live in machines, 32-36 main failing saws, and 50" for the big block lets make the earth shake failing saw.

In the end it has more to do with oiler output and clutch ability than anything. Bigger saws have bigger oilers, and bigger clutches, more oil means they can keep a longer bar lubed, a bigger clutch can pull a longer chain without too much slipping.

Anyway, there are a great many variables involved, and dead reckoning is probably as accurate as spending a lifetime gathering data only to have some moss backed logger say... yup this here will do it...
I think you're right that it should be able to be done. Inputs needed would be:

Torque of the engine (eg force applied)
Resistance of the drive links per cutter (eg skip tooth, etc), the resistance of each tooth in the wood (which would need to be made up of the type of wood) (eg resistance applied)
Then you need to know the limit.. eg you don't want as much reistance as there is power, or else the chain won't move. so what's the ratio, and is it constant or is it a curve?

I see a lot of people say "my 026 runs a 30" B&C" but then they are only using it for limbing so the teeth in the wood is no more than a handfull. I think this would need to be built for assuming full bar in the wood.

Another variable would be chain width and depth gauge settings, both altering the resistance. It would be best to assume a new chain (they get narrower as the teeth get shorter, so less resistance) and I'm not sure if Semi Chisel, Chisel, Square, Hex grind will make enough difference, but it could be added in as a resistance modifier too.

I think it's probably easy enough to build a calc in Excel, but it's the inputs that are the problem..

I'll end with saying that yes, oiler capacity is a limiting factor, but you can always add external oilers. or you could add a limiter to the calc (eg no more than X inches for Y power (although i wonder if the ideal ratio would already limit it..?)
 
calamari

calamari

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I think you're right that it should be able to be done. Inputs needed would be:

Torque of the engine (eg force applied)
Resistance of the drive links per cutter (eg skip tooth, etc), the resistance of each tooth in the wood (which would need to be made up of the type of wood) (eg resistance applied)
Then you need to know the limit.. eg you don't want as much reistance as there is power, or else the chain won't move. so what's the ratio, and is it constant or is it a curve?

I see a lot of people say "my 026 runs a 30" B&C" but then they are only using it for limbing so the teeth in the wood is no more than a handfull. I think this would need to be built for assuming full bar in the wood.

Another variable would be chain width and depth gauge settings, both altering the resistance. It would be best to assume a new chain (they get narrower as the teeth get shorter, so less resistance) and I'm not sure if Semi Chisel, Chisel, Square, Hex grind will make enough difference, but it could be added in as a resistance modifier too.

I think it's probably easy enough to build a calc in Excel, but it's the inputs that are the problem..

I'll end with saying that yes, oiler capacity is a limiting factor, but you can always add external oilers. or you could add a limiter to the calc (eg no more than X inches for Y power (although i wonder if the ideal ratio would already limit it..?)
Thanks. That's what I was trying to say but didn't. An interesting exercise that might be of interest to guys in saw competitions. I bet there's something or maybe a series of minor somethings that aren't obvious that in combination are a significant limiting factor for saws and their cutting ability. Perhaps it's chain friction like rivet height or maybe where the horsepower peaks in the curve but saw cutting performance isn't treated as seriously as other internal combustion engined tools.
 
northmanlogging
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I think you're right that it should be able to be done. Inputs needed would be:

Torque of the engine (eg force applied)
Resistance of the drive links per cutter (eg skip tooth, etc), the resistance of each tooth in the wood (which would need to be made up of the type of wood) (eg resistance applied)
Then you need to know the limit.. eg you don't want as much reistance as there is power, or else the chain won't move. so what's the ratio, and is it constant or is it a curve?

I see a lot of people say "my 026 runs a 30" B&C" but then they are only using it for limbing so the teeth in the wood is no more than a handfull. I think this would need to be built for assuming full bar in the wood.

Another variable would be chain width and depth gauge settings, both altering the resistance. It would be best to assume a new chain (they get narrower as the teeth get shorter, so less resistance) and I'm not sure if Semi Chisel, Chisel, Square, Hex grind will make enough difference, but it could be added in as a resistance modifier too.

I think it's probably easy enough to build a calc in Excel, but it's the inputs that are the problem..

I'll end with saying that yes, oiler capacity is a limiting factor, but you can always add external oilers. or you could add a limiter to the calc (eg no more than X inches for Y power (although i wonder if the ideal ratio would already limit it..?)
eventually friction of the guide bar, as well as the teeth/chain moving on the opposite side than the cutting side, becomes enough that the power head just looses to much RiPM's to keep the clutch engaged... So that I assume is the real limiting factor.

A direct drive chain with sharp teeth really doesn't need a whole lot of ponies to keep moving, especially when already in motion and supported by its mass to some extent, speed alone would keep it going to some extent, but two smokes are not known for having lots of torque, and rotating mass is difficult to control and heavy,(which is were most torque comes from). so a guy could theoretically loose the clutch and require much less HP to achieve more cut at lower speed...

Anyway, its all for naught as the clutch is pretty important to chainsaw safety lol. improving current clutch design could be a thing? maybe using some uber dense material like tungsten for the weights and placing some sort of friction type material on the drive faces, so that they engage at lower Ri"PM's and hold harder? This is well outside of my enginerding credentials (none) and well into the pipe dream realm, but it does present some interesting possibilities for the 3d printing folks... just sayin.

Though heavier clutch weights would also mean lower RPM chain movement (well bellow idle) so a stronger spring would be needed to offset said movement, but would the 2 cancel each other out? Or would the extra weight be more useful at higher rpms? I'm sure someone has done the research on this, but its not something I've thought much about, at least not in relation to friction inertia clutches, Snowmobile variable drive clutches on the other hand, springs and weights are changed regularly and mismatched to get "optimal" performance, but its a different mechanism all together.

Rambling I know... anyway, PNW snow and mountain conditions are very different from atypical US snowmobile stuff, the rocky mountains are close... so we tend to start with sleds meant for there, as the midwest stuff is just not worth messing with, anyway, our snow is denser and wetter here, and arguably the hill climbs are steeper. You won't see many standard length tracks or 2 up sleds around here...

Like chainsaws in many ways, we modified things to work for us, (big felling dogs, full wrap bars, welding bars together to make long bars, paddle tracks, tall handlebars, cut down windows, extended tunnels, jacked up suspension etc) cause the factories were not making things for little ole PNW... (though to be fair, IEW, Titan, and a few others built saws locally... Titan being the first one man saw I think)
 
Valpen

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There has been lots of points discussed here, but not much about chain width.
A narrower chain takes less power to cut with as it is not cutting as much wood (width) with each tooth. So a saw running a narrow bar/chain setup needs a less powerful (heavy) motor.
There is a lot to be said about narrow chain at high speeds. A cut is a cut, regardless of the chain width.
 
MagraAdam

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There has been lots of points discussed here, but not much about chain width.
A narrower chain takes less power to cut with as it is not cutting as much wood (width) with each tooth. So a saw running a narrow bar/chain setup needs a less powerful (heavy) motor.
There is a lot to be said about narrow chain at high speeds. A cut is a cut, regardless of the chain width.
Another variable would be chain width and depth gauge settings, both altering the resistance. It would be best to assume a new chain (they get narrower as the teeth get shorter, so less resistance)
 
muddstopper

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I guess I am just different or have a differrent way of approaching this problem. I prefer comfort over hp or speed. I mostly use 50cc saws for firewood and I prefer full chisel chains. Keep them sharp and you dont have to push them thru the wood. I prefer a 20 in bar because I dont have to stay bent over while bucking. I do have 55 saws with 18 and 20 in bars and some with .325 and 3/8 chain. I dont like any bar on any saw over 24inches simply because I am short and a long bar means holding the saw up to keep it out of the ground. I dont like big cc saws simply because they are heavy and for the one or 2 large dia trees I might cut each year, it just isnt worth the money to have a big saw. I like older saws, 346xp, 55 ranchers and 372xp will do 99.9% of all the cutting I might do but I do have a 80cc saw in the shed, that hasnt been ran even once since I have owned it. Keep the chain sharp and let it cut and I am happy.
 
calamari

calamari

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There has been lots of points discussed here, but not much about chain width.
A narrower chain takes less power to cut with as it is not cutting as much wood (width) with each tooth. So a saw running a narrow bar/chain setup needs a less powerful (heavy) motor.
There is a lot to be said about narrow chain at high speeds. A cut is a cut, regardless of the chain width.
60 years ago I was able to use a McCulloch BP-1 saw that had a unique chain design. You could sharpen it while running the saw by pressing a button on the saw that pushed a stone against the chain. To work, the chain was designed with just vertical teeth offset just a little to give space for the bar. It didn't seem to cut any better because of it being narrow but I think the tooth design was faulty.
I'd like to get a narrow kerf bar and chain for my 6100 Makita but unfortunately they only seem to make them up to 20" for some reason and I want a 28" B/C.
A sharp chain of good design will add apparent horsepower to a saw. An 80cc saw with a rocked chain and high rakers won't cut pudding while a 30cc saw with a sharp chain will throw big chips. I think guys who recommend 70 cc saws to cut 20"DBH oak are probably not consistently using or maintaining that "sharp chain of good design."
 

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