Chain Pitch/Gauge - Let's Have Some Fun

Birdyman88

Well-Known Member
I have a question for all of you, but first let me give you the base assumptions:
1) The chain is 20" loop and of the same model (say Stihl RM)
2) The sprocket is 7 tooth
3) The guide bars are of the exact same design

Okay the task ... rank the following chains in order of MOST to LEAST effort of saw to pull chain .. and briefly (or not) state the reasoning for your rank.
A) .325 pitch, .063 gauge
B) 3/8 pitch, .063 gauge
C) 3/8 pitch, .050 gauge

I know this may seem stupid, but I just had a chain manufacturer tell me something that I believe is total B.S. Let's see what everyone thinks.
 

Birdyman88

Well-Known Member
.325 pitch. Cutters are smaller.
Smaller in what way? Width, height, length? How does that affect the saw?
BTW, this post is just for fun. I had a 1.5 hour discussion with a rep this afternoon, so I've already confirmed that what I was told by their front line was not rooted in actual fact and disagrees with their internal data.
 

ATH

Well-Known Member
Define "pull" - just for the saw to pull the chain around the bar or buried in wood?

Just around the bar, I'll guess the order you have them:
.325 is most effort. The smaller pitch should have more drive links...right? That seems like it would be ever so slightly more friction in the bar.
.063 is more metal (more mass) than .050 so it takes more effort to move it.

I'm assuming these are minuscule differences...but curious to see other responses!
 

Birdyman88

Well-Known Member
ATH, that is a perfect analysis of the chain as it pertains to the links. You get a gold star from the rep! So why then does everyone say that 3/8 is harder to pull? And when I say "pull", I mean under load - sorry, I should have clarified that in my OP.
 

ATH

Well-Known Member
Through wood: 3/8 has a larger (wider and deeper) tooth, right? So that would make it harder to pull through wood as it is pulling more wood out with each tooth. The trade off is more wood per tooth = fewer number of teeth that need to pull chips out. The balancing act is to get a minimal bump up in how hard it is to pull that wood out, but get as much wood out as possible with each pull. Go to the extremes to think about that: pull a serrated knife across a tree trunk. Very easy to pull, but you don't get much wood out. Now pull a 24" excavator bucket through. If you can, you'd take out all the wood at once and be done in one pass, but very difficult to pull
 

Birdyman88

Well-Known Member
ATH, I thought I was the only one who used "extremes" to explain stuff. So, all of what I'm about to say was discussed and verified with a rep from a large chain manufacturer. I cannot guarantee the validity other than to say he is the most knowledgable person I've ever run across when talking chains.

So, the 3/8 and the .325 IN THE SAME GAUGE are similar widths, but not the same. He didn't have the exact numbers in his head, but he said the width difference was minor as far as cutting performance.

Changing to a different gauge changes the width of the cutter in both pitches, and takes less wood, so it has a larger impact on cutting performance (but we all new that). But still, for the same gauge, minor difference in width between .325 and 3/8 in those gauges.

Both cutters only take .025" slices if the depth gauges are set properly, so the taller cutter on the 3/8 makes no difference in that respect. Wood clearance of the taller cutter may have minor impact but not enough to make headlines. If anything it would increase performance.

The taller cutter of the 3/8 will encounter more friction in the cut than the shorter cutter of the .325. But there are more .325 cutters per length than in the 3/8 chain. He wasn't able to elaborate how much those factors offset each other than say they did offset to a degree.

The length of each cutter was a non-factor because once the leading edge made the cut, the travel of the cut wood along the remaining length of the cutter itself had no effect other than the ability of the cutter to clear the wood - which wasn't a factor as far as the length of cutter is concerned. Think new cutter versus cutters that are almost gone.

The weight of the chain plays a minor role. But the added drive links of the .325 offsets the additional weight of the tall cutters and generally beefier components of the 3/8. The 3/8 may be slightly heavier and thus harder to accelerate, but once going, over factors discussed take over.

Pitch plays a role in chip clearance, and the larger pitch should clear better and INCREASE cutting performance.

So, besides chain sharpness, and assuming you're using the same type of cutter, the number one and major factor affecting cutting performance between the .325 and 3/8 is [drumroll] ........ sprocket diameter. Specifically the distance from the center of crankshaft to the dynamic center of the drive link. NOT to the out edge of the cutter, as some believe, as the sprocket is not contacting and driving that part. The .325 has a smaller diameter and can generate more torque to offset a loaded condition. Think about putting a larger diameter tire on your car, or reducing the gear ratio in the rear end. Same basic principle.

So this is where it gets interesting. Every saw has it's own personal power band and the sprocket diameter and other chain attributes have to play well with that band. Talking chain pitch, it is not always perfect and may be only slightly biased toward one pitch and not the other. But, make a muffler mod, advance the timing, modify the ports, or change gas and you may change that bias the other way. A saw that once liked .325, may get a good tune and actually prefer 3/8 in the same kerf, and/or .325 in wider kerf, or even an increase in sprocket teeth. The 50cc mark is roughly the changeover point for pitch, but that is not set in stone by any means and is very saw specific. They have proven this over there and that's why, for their particular product, they may recommend a longer maximum chain and bar length than the manufacturer of the saw did. They don't preach pitch change that much, but not because of reduced performance, but because most people want to stay with stock pitch, and for them that's where the money is. But, there may be performance gains for you if you want to change pitch and you have the right saw, and they have proven it with some modded saws.

Anyway, the funny part was that I suspected all this to be true based on all the data I've collected over time, but every time I even hinted at putting 3/8 on "a particular .325 saw", you would have thought I had just shot the pope. Funny that the only answer most people have is "it's bigger chain". Anyway, an hour and a half with this guy and I feel totally enlightened. Best part is he gave me all the part numbers to make the mod I've been thinking about. So, now you know the rest of the story.
 
Last edited:
Top