wacky chain sharpening theory

I'm taking a US forest service approved chainsaw certification class at my college so that I can run saws with our Appalachian trail maintenance crew/woodsman team/whatever.

The instructor advocated sharpening each cutter as far back as required to remove any defects, and then individually adjusting each depth gauge to the desired .25 or .30.

This went against anything and everything I've ever heard, so I suggested that this would cut with more vibration and potentially off to one side or another. He said that as long as everything had consistent depth gauges, the chain would still cut straight.

I think the main reason they advocate this is because these saws get rocked a lot and I guess they're trying to save on chain.

Has ANYONE heard this before? Do people agree?

MGF

I don't do it that way but it does make some sense. As long as each raker is the same setting to its own tooth they should all remove the same amount of wood.

Ww

Now that you mentioned it....

If you rock like 3-15 teeth, then take them back to "sharp"...then use a depth gauge on the rakers...it would end up being just like he does.

Never gave it much though but kudo's to you for thinking it out like that!

I have not enough time the way it is...I'm not going through and mic'ng every cutter and raker...if it cut's crooked...it all burns the same.

my experience with chains and bars up to 24" is that it works with different length on the cutters as long as adjust the depth gauges individually.

He's right. And if you pick up the little Husky filling jig, it makes it a lot easier. The jig regulates how much to take off the depth gauge depending on the length of the tooth.

I've been thinking about this for awhile. I think he's correct. However, I believe you have a typo. I think it should be .025-.030 instead of .25-.30.
:agree2:

Dan

The reason the unequal cutter lengths still cut is because not every cutter is cutting to its max depth during every pass of the chain. The chain porpoises on and off the bar with only every 2nd or 3rd cutter grabbing a maximum raker depth of wood. The others only cut a little or not at all. When the cutters are of unequal length they still grab and cut, perhaps not evenly or with minimal vibe, but they will cut. Where that method won't cut straight is if most of the cutters on one side of the bar are longer or shorter than the other - then you will definitely end up cutting crooked. That's why it's always better to keep the cutter lengths more or less equal across the board.

The overall amount of chain vibration will depend on the extent of the variation in cutter length and raker depth and the direction of the variation. For example having a few cutters much shorter than the others, or a few rakers much shallower than the others will have little effect on chain vibe, but the reverse is not so. On a long bar, this vibe and a slightly loose chain can lead to chain drop out. These are all good reason to keep everything reasonably constant.

The constant 0.025" and 0.030" raker depth spec is so old school I don't see how it continues to get all the air time it deserves. I reckon it's a ploy to get people to buy new chains well before they are needed. What is needed is a constant cutting angle or gradient between the the top of the cutter and the top of the raker. This needs to be about 1:10 or 6º. Thus as the chain wears through sharpening the distance between the cutter and the raker increases, so raker needs to be dropped accordingly more - in fact much more than 0.025 or 0.030". It's very easy to figure out - it's 1/10 of the gullet width. So when the gullet is 0.35" the raker needs to be 0.035" and when the gullet is 0.45 the raker needs to dropped to 0.045". This maintains a constant cutting angle and is automatically done using guides like the Carlton filoplate but not using the oregon raker guides. I use a digital caliper to check mine - I don't worry about getting them all exactly the same, as long as they are within 0.005" of the required depth they seem to work fine although the closer they all are to the same value the less chain vibration and the smoother a cut I get. It may seem a bit scary to file a 0.045" raker depth when there is not much cutter remaining but boy does it make a big difference to cutting speed.

Here's the sort of thing that can be done in moderately hard Aussie hardwood which is as good a test of chain sharpness as anything. This is done with full comp 3/8" 2º top plate angle with a 0.040" raker depth. It's slightly bit slower to cut than 10º top plate angle but it is very smooth cutting on the operator and saw and can reduce the amount of work that needs to be done in the woodshop afterwards.

BobL said:

What is needed is a constant cutting angle or gradient between the the top of the cutter and the top of the raker. This needs to be about 1:10 or 6º.

Click to expand...

You've probably mentioned this on here somewhere before but this is the 1st time I've read it. It makes perfect sense. Thanks for the info.

mikefunaro said:

I'm taking a US forest service approved chainsaw certification class at my college so that I can run saws with our Appalachian trail maintenance crew/woodsman team/whatever.

The instructor advocated sharpening each cutter as far back as required to remove any defects, and then individually adjusting each depth gauge to the desired .25 or .30.

This went against anything and everything I've ever heard, so I suggested that this would cut with more vibration and potentially off to one side or another. He said that as long as everything had consistent depth gauges, the chain would still cut straight.

I think the main reason they advocate this is because these saws get rocked a lot and I guess they're trying to save on chain. Has ANYONE heard this before? Do people agree?

MGF

Click to expand...

My understanding is that as the tooth gets narrower, the raker depth gets compromised.i.e less aggressive. Therefore your teachers theory wouldn't work. Carlton explains this situation very well and has a raker gauge that takes into account this cutter length/ raker depth differance.

redunshee said:

My understanding is that as the tooth gets narrower, the raker depth gets compromised.i.e less aggressive. Therefore your teachers theory wouldn't work. Carlton explains this situation very well and has a raker gauge that takes into account this cutter length/ raker depth differance.

Click to expand...

Remember, you are taking a class. With the FS, it isn't production cutting, it is can you safely and confidently cut up or fall a tree. If you are going to be a certified faller, you won't be falling "normal" trees much. You don't have to buck or cut trees to a mill specification. Do what they say to do or forget getting certified.

A friend and I both will say, "There's the real world way and the FS way."
The FS way is probably overcautious, but theres good reason to be that way when you are hiring large amounts of kids out of school who think they are going to work in a park, and maybe haven't even touched a saw before...think that way.

Yes, we rock a lot of chains. At least I did, but where I'm at now, there aren't a lot of rocks so I hit the dirt with the chain. You will be cutting up trees that were felled by nature, and they have landed where they want to. Some are imbedded in the ground. Some are hiding a rock underneath.

Pay attention, run a saw the recommended way, and listen to the crew leader and you'll do OK.

It goes against general theory and advise often given but when I rock a chain and it only gets a cutter or two I give those teeth the same number of strokes as the rest of the chain. If they dont get to a keen edge and point so be it. I dont see or feel a differance in the field. Obviously you cant do this if you rock half the cutters. When I set the depth gages they all get set the same irregardless of tooth legnth.

As for cutters being off a bit side to side and making the saw cut crooked I will argue that point until my saws tell me different I just dont see it in the field. My youngest son has filed his chains since the age of 10 and due to his faulty techniques (bull head) he has always sharpened the RH cutters back faster and to a sharper angle top angle than the LH cutters. Looking down at the chain a person would think, no way its going to cut straight but it does. In my experiance the condition of the bar rails have far more to due with crooked cutting than the chain (given that the chain is sharp) at least on my equipment.

I am not advocating half arsed sharpening and maintainance but it seems to me that the equipment is more forgiving than some make it seem. But then again, maybe I need to time some cuts eh?

My experience is that you can individually sharpen the cutters and adjust their rakers and still get 90% of the optimum performance out of the chain. If you're gonna be milling or doing a lot of bucking, it's worth doing the official way and getting 100%. If you're likely to hit another rock on your next tank of gas, why bother? I haven't noticed any additional vibes from this. Although if one side has been rocked and filed more than the other, it's a bit harder to keep it straight. Although like has already been said, I find straight has as much to do with a tuned bar and tensioned chain as it does with symmetric cutters.

Butch(OH) said:

It goes against general theory and advise often given but when I rock a chain and it only gets a cutter or two I give those teeth the same number of strokes as the rest of the chain. If they dont get to a keen edge and point so be it. I dont see or feel a differance in the field. Obviously you cant do this if you rock half the cutters. When I set the depth gages they all get set the same irregardless of tooth legnth.

Click to expand...

Yep I agree with that. Even completely losing one or two cutters seems to make little difference. If you want some real fun do the reverse ie add one or two new cutters to an almost used chain.

As for cutters being off a bit side to side and making the saw cut crooked I will argue that point until my saws tell me different I just dont see it in the field. My youngest son has filed his chains since the age of 10 and due to his faulty techniques (bull head) he has always sharpened the RH cutters back faster and to a sharper angle top angle than the LH cutters. Looking down at the chain a person would think, no way its going to cut straight but it does. In my experiance the condition of the bar rails have far more to due with crooked cutting than the chain (given that the chain is sharp) at least on my equipment.

Click to expand...

That is interesting and I agree about the rails being more important. One thing that could be the case of your bull head son (I have me one too ) is that greater top plate angle could compensate for shorter cutters, ie shorter cutter grabs a bit less but when it grabs, the higher top plate makes it grab more.

I am not advocating half arsed sharpening and maintainance but it seems to me that the equipment is more forgiving than some make it seem. But then again, maybe I need to time some cuts eh?

Click to expand...

Yeah - it amazes me sometimes what I see still cutting out there. But then it amazes them when you hand them a properly sharpened chain and they say - howyadothat!

as a coincidence I made a related mistake today that give me a nice insight..

My statement:

Crooked cutting is related to the difference in angle of the left and right side cutters, not their lenght.

The amount of material taken in the cut is influenced by the lenght of the cutter and the height of the raker.

Why:
the angle gives a outward pressure to the vertical cutter. Look at it as a wedge.

If you have a difference in this top angle (left side cutters versus right side cutters) one side will be pushed more than the other and thus making an arch as the backpressure (or opposite pressure) of the next (and opposite cutter) is less and thus not strong enough to counter the pressure

Drawing: black: is the chain. the cutters are the blue (top plate edge) and red (vertical cutter edge)

Green arrows indicate the forces on the side cutters as a result of the wedge action from the angled top plate




I came to this as i in a hurry sharpened a chain at 30 and 70 degrees on my 361. The result of this was consistantly a crooked cut that bad that i could only cut about 1 bar height deep before the bar would jam in the curved cut. The paint of 1 side of the bar was "wiped" off completely after a couple of cut attempts.


A lot of cursing and looking at the bar, saw, chain and remounting them twice got me to take the 026 to finish the job. back at home during sharpening i all of a sudden realized looking at the top plates.

Dont know if it helps anyone. Took me 15 years of chainsaw usage to realize....:monkey:

mikefunaro said:

I'm taking a US forest service approved chainsaw certification class at my college so that I can run saws with our Appalachian trail maintenance crew/woodsman team/whatever.

The instructor advocated sharpening each cutter as far back as required to remove any defects, and then individually adjusting each depth gauge to the desired .25 or .30.

This went against anything and everything I've ever heard, so I suggested that this would cut with more vibration and potentially off to one side or another. He said that as long as everything had consistent depth gauges, the chain would still cut straight.

I think the main reason they advocate this is because these saws get rocked a lot and I guess they're trying to save on chain.

Has ANYONE heard this before? Do people agree?

MGF

Click to expand...

The instructor is right. The lenght of the cutters really makes no difference as long as the riders are set at the same depth per tooth on an individual basis.

slowp said:

Remember, you are taking a class. With the FS, it isn't production cutting, it is can you safely and confidently cut up or fall a tree. If you are going to be a certified faller, you won't be falling "normal" trees much. You don't have to buck or cut trees to a mill specification. Do what they say to do or forget getting certified.

A friend and I both will say, "There's the real world way and the FS way."
The FS way is probably overcautious, but theres good reason to be that way when you are hiring large amounts of kids out of school who think they are going to work in a park, and maybe haven't even touched a saw before...think that way.

Yes, we rock a lot of chains. At least I did, but where I'm at now, there aren't a lot of rocks so I hit the dirt with the chain. You will be cutting up trees that were felled by nature, and they have landed where they want to. Some are imbedded in the ground. Some are hiding a rock underneath.

Pay attention, run a saw the recommended way, and listen to the crew leader and you'll do OK.

Click to expand...

slowp's advice is dead on. Your goal is to get that cert card so you can work on their projects. Take notes, do as instructed and you'll get the card.

btw, FS and BLM used to have about 5 levels of certs for operating their vehicles and equipment on/off road. Some of the printed study guides had parts that were at odds with some state DMV CDL regs. But, if you wanted the cert for work you studied their guides and did exactly as instructed. Don't know if they still have this program.

I appreciate all the responses.

With regard to everyone who has told me to shut my mouth and get the card--do not worry--I am not bullheaded enough to get in an argument with the instructor or give him a tough time. He's a younger guy and understands that I have a bit of experience, and seems open to my questions. I'm not interrupting the class, or slowing him down in asking him questions. I learned very early on in my career as a student to comply with the instructor for the sake of the final result of any educational endeavor.

MGF

mikefunaro said:

The instructor advocated sharpening each cutter as far back as required to remove any defects, and then individually adjusting each depth gauge to the desired .25 or .30.

This went against anything and everything I've ever heard, so I suggested that this would cut with more vibration and potentially off to one side or another.

Click to expand...

The theoretical vs. practical stuff has mostly been covered above. Technically, you should grind back the most damaged cutter, then make all the other cutters the same. This could take a lot of grinding, but give you the smoothest cut.

And a chain with sharp cutters will still cut, even if they are not all the same length - heck, some guys put their chains on backwards and still manage to gnaw through a log.

But the point not mentioned is cutter height. If you look at your chain from the side, the top of each cutter is sloped, so that there is clearance as the cutter passes. A shorter length cutter will be closer to the bar than a longer length cutter, which could make the bar bounce/vibrate if the difference is significant, and make some cutters really dig in while others barely touch the wood, resulting in a slower, jerkier cut.

Philbert