Is the logic flawed?

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

alleyyooper

Addicted to ArboristSite
Joined
Oct 21, 2008
Messages
2,536
Reaction score
3,050
Location
Michigan
I have two chainsaws. When I purchased the newer saw, I fitted it with the same size bar and chain as my older saw. I figured by doing this I could easily swap the bars and chains between the two saws. But, I digress, this is not my issue.

My issue is both saws run .325" chains, not 3/8" chains. My logic tells me that a chain with a narrower tooth (.325") will be easier on the saw's engine and cut faster than a chain with a wider tooth (3/8"). Giving a set engine size, a narrower cutting tooth would be removing less wood, so it should not tax the engine as much as a wider tooth. And, as a consequence, wouldn't a chain with a narrower tooth move through the wood faster?

:D Al
 
In theory, yes.

You also have to take into account the number of cutters in contact with the wood. While .325" is indeed narrower than 3/8", it will also have more cutters given the same length of chain. It's a math problem, whereas cutter width x depth of cut gives you the volume of wood removed per cutter. That multiplied by the number of cutters (on 1 flat side of bar that would be in contact with wood fully buried) should give you the total volume of removed overall at a time. I've never done the math to find out but I've often wondered this as well...
 
What saws are you running Al?

A saw with modest power will cut faster with 3/8 than .325 with all other variables equal.

IMO .325 is a trade off for smaller to mid size saws such as 40-50 cc saws that are considered too small for 3/8 and too large for 3/8 LP. IMO the only benefit of .325 is that it cuts a little bit smoother because there is less space between cutters and more cutters per given length.
 
Lots of overlap with those two sir. They should both do fine with the same bar and chain in .325. The Dolmar would do fine with a 3/8 setup. The Jonsered would not like it as well. The nice part about 3/8 is it will stay sharp a little longer all other conditions being equal. It will also take less time to sharpen since there are less cutters per given bar length.
 
3/8 chain has more chip clearance and takes bigger chips so the number of slices through the wood per cubic inch of wood removed is less. thus the same hp can gobble out more wood. My 026 would not pull 3/8 but I ported one for my son and then had just enough power that it would pull 3/8 chain so the sum total was about a 25% increase in cutting with the 3/8 chain if it has the power to pull it.
id stay with the .325
 
In theory, yes.

You also have to take into account the number of cutters in contact with the wood. While .325" is indeed narrower than 3/8", it will also have more cutters given the same length of chain. It's a math problem, whereas cutter width x depth of cut gives you the volume of wood removed per cutter. That multiplied by the number of cutters (on 1 flat side of bar that would be in contact with wood fully buried) should give you the total volume of removed overall at a time. I've never done the math to find out but I've often wondered this as well...
This ^^^

I could have sworn this was researched heavily by sawtroll.
I know the narrow kerf chain absolutely requires less energy to cut with than 3/8, as I have tried it extensively. However the amount of wood removed between the two, I’m not sure.. I would think that the amount of wood removed versus the force required to remove said wood is dynamic.

Guess to really find out you need to factor in a couple of variables

Time to cut through a specific thickness of wood
Amount of wood chips (weight) that said cut produced

And your Constants would be the chain and saw
 
Your reasoning isn’t right. .325” vs .375” isn’t the difference in kerf, it’s the difference in pitch. Kerf is the width of the cut. Pitch is the distance between links.

Generally a smaller pitch chain will also have a smaller kerf, but the two measurements are not interchangeable.
 
Get a brand new Stihl 26RM .325 cutter and a 36RM 3/8 cutter in your hand side by side and have a look how much 'bigger' the 3/8 is...they are almost the same. RS might be different but the semi RM are very close in profile. I wonder if 'holding an edge longer' and 'bigger chip clearance' and 'wider kerf' are based on what folks have read or what they have done themselves.
 
As mentioned cutter dimensions between to two pitch’s can be very similar. If comparing actual narrow kerf .325 to full sized 3/8, there is a significant difference. The main difference is a distinctive lack of vibration in .325, especially the narrow kerf, this becomes more apparent in smaller saws and harder varieties of trees. Narrow kerf .325 compared to 3/8 lo pro is equaled a bit however the .325nk is still easier on the arthritis.
 
I have two chainsaws. When I purchased the newer saw, I fitted it with the same size bar and chain as my older saw. I figured by doing this I could easily swap the bars and chains between the two saws. But, I digress, this is not my issue.

My issue is both saws run .325" chains, not 3/8" chains. My logic tells me that a chain with a narrower tooth (.325") will be easier on the saw's engine and cut faster than a chain with a wider tooth (3/8"). Giving a set engine size, a narrower cutting tooth would be removing less wood, so it should not tax the engine as much as a wider tooth. And, as a consequence, wouldn't a chain with a narrower tooth move through the wood faster?

:D Al

Hi Al!

There is nothing wrong with your logic! The narrower kerf makes a big difference! In fact, Stihl offers an upgrade for their MS261 (if memory serves) which claims that the saw will cut about 30% faster than stock. All they did was offer the bar and chain combo in a .325 as opposed to the stock 3/8! A professional sawyer on YouTube timed the upgrade, and it turned out to be almost exactly 30% quicker - all due to the narrower kerf! I'll see if I can find the clip....

Welcome to the beginnings of SCTD a.k.a Sawchain Cutting Theory Disease.... You're off to a good start. Pretty soon you'll be custom hand-filing your chains to your own spec, and spending sleepless nights wondering how to make things better.... :surprised3: :happybanana::crazy2:
 
Ok, so I had a brain fart.... I found the clip - Stihl calls it a "tuning kit" and replaces the standard chain with a PS3, and claims a 20% increase in "performance". Bit of a marketing ploy, if you ask me, but it works. I run a PS3 chain on my MS170, and it's quite happy!

Here are the links to the two vids: Stihl's official one here....

and the other guys here....

Enjoy!

Mike
 
An MS170 is a small saw that’s mostly going to be used to cut small wood. For it, a narrow kerf chain with small teeth is ideal. Put that same chain on a 60cc saw with a 20” bar and you probably won’t see any difference in cutting speed at all. A bigger chain can pull more wood out, not just a wider kerf, but because the teeth are taller there’s more space for shavings to be pulled out with each pass...if there’s enough power to do it.

Which is faster is going to depend on how powerful the saw is and what you’re cutting. Put a .404 chain and a 24” bar on your MS170 and it’ll be a dog. There’s simply not enough power for it. An MS660 on the other hand would handle it well and a ps3 chain would only slow it down.
 
These ideas only holds true with brand new chains only.
Then the chain gets sharpened. All the math is needs recalculation.
Because once you touch the cutter and reduce its height,
getting every depth gauge perfect it impossible. So, everything changes.
Or dirt. Or saw tuning. Or ambient temp. Or barometric pressure.
I would think, what the manufacture installs most likely is the best
performer. And that varies in locations. How many swamp maples in the Yukon?
Stihl used to use 3/8 on an 026 and 029. Then changed to .325.
They didn't do it the reduce performance.
 
These ideas only holds true with brand new chains only.
Then the chain gets sharpened. All the math is needs recalculation.
Because once you touch the cutter and reduce its height,
getting every depth gauge perfect it impossible. So, everything changes.
Or dirt. Or saw tuning. Or ambient temp. Or barometric pressure.
I would think, what the manufacture installs most likely is the best
performer. And that varies in locations. How many swamp maples in the Yukon?
Stihl used to use 3/8 on an 026 and 029. Then changed to .325.
They didn't do it the reduce performance.

Stihl86 touched on an important point here - as the chain gets sharpened.... The main reason chains start to perform better as they "age" is because the kerf width narrows. This is a function of the shape of the cutter, which is tapered from front to back to provide cutting clearance. All thing being equal, and assuming proper sharpening techniques and depth gauge maintenance, a chain nearing the "end" of its life will outperform a new one every day of the week. Just ask the racing guys - all their chains are on the very limit, since this gives the best speed. Here is a pic of just such a chain from another thread on this site: race_chain.jpg
 
Most stock 50cc saws will run better with .325 at an appropriate bar length. They will cut more smoothly and allow more control at the nose of the bar. Stock 50cc saws can’t hold the RPM with a 3/8” chain unless they have short bars. Some 50cc can pull 16” 3/8. Most would do better with .325.
 
Back
Top