Real Kerf sizes

Today I was using an 880, not mine - one from the milling yard - and it had a 404 chain on it. After using it to cut some fat cookies as bases for placing logs on for milling I noticed the kerf width was not as wide as I remember. So I then got completely distracted by kerf width testing.

What I discovered was it was quite tricky to measure the kerf with a digital caliper because the chain dances around a bit when it starts the cut and the start of the cut is wider than once it stabilizes some ways into the wood. The other thing I noticed is the kerf is slightly opened up by the other side of the chain as it passes through the wood so one cannot just measure the kerf of a shallow depth cut. I tried using a feeler gauge but that did not work as it could not get down into all the little ridges and just rides the tops of the narrowest gaps, so it underestimated the actual kerf.

What I ended up doing was making a cut deeper than twice the width of the bar. Then I cut across the first cut at right angles and used a digital caliper to measure the kerf in the cross section where both sides of of the chain had passed through the cut. The digital caliper inside measuring knife blades were also able to get into all the little cutting grooves made by the chain as it cuts.

The real kerf is even bigger than this because the cut wanders slightly back and forth across the average cutting line and it is not the width of the cut being made but the extent of the wander that defines the real loss of wood due to the kerf - anyway that was too hard to handle so I stayed with the method above.


I made at least 10 measurements and averaged the results

a) 404, semi-chisel, near new chain, kerf width was 0.337"
b) 3/8 new semi chisel, new, 30º top plate angle, kerf width 0.327"
c) 3/8 LP, new, chisel, 30º top plate angle kerf width 289"
d) 3/8 LP, new, chisel, 10º top plate, kerf width 0.280"
All of the above were cross cuts in very hard, cross grained wood.

At the last minute I also tested chain d) in milling cross grain mode and got 295" !

The tolerance on the results (twice standard error) were all about 0.010"

Leaving the tolerance aside for the moment
1) The 404 has a kerf that is only 3% bigger than the standard 3/8!
I have to say I am somewhat surprised by that 404 has a gullet that is more than 3% bigger so it can carry more sawdust so that explains why 404 cuts more effectively than one thinks.

2) Lopro reduces kerf by 13%
One problem with this comparison is the chain cutters are not same - the std 3/8 is semichisel while the lp is chisel. Maybe the lp semichisel would have s slightly smaller kerf
In terms of reach inches of thickness saved, using LP will save a whopping 1" of wood after making 21 cuts. This raises the issue of whether it is really worth using lp to save wood

3) 30º top plate cuts a marginally wider kerf than a 10º toplate
Perhaps not unexpected since the higher top plate angle have the cutter diving slightly wider to make the cut.

4) Cross cutting cuts narrower than cross grain by 5%
I have heard this before, cross cutting leaves small torn wood fibres in the cut which pads out the kerf. The real kerf is the same as for mill. This should be less of an issue in straight grained softer woods.

Now if one take tolerance into account then there is no difference between 404 and 3/8; no difference between using different top plate angles, and no difference between cross cuts and milling. The only significant kerf difference is between 3/8 and 3/8LP but is the 13% worth it?

I would be interested to see what some of you straight grained softwood millers get.

Hopefully I can now get back to milling ;-)

Cheers

BobL. Was the 404 chain new or somewhat worn down compared to the 3/8 chains? I have noticed that my 3/8 chain kerf gets noticeably narrower as it wears down. Just a thought of why the difference may not be as big as expected.

BobL said:

The only significant kerf difference is between 3/8 and 3/8LP but is the 13% worth it?

I would be interested to see what some of you straight grained softwood millers get.

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My motivation for the skinny chains is speed, not conserving wood.

We may be coming at this from different points of view because I am dealing with softwoods for construction materials, where waste is not a big issue, but speed is. Furthermore, my milled wood is often used as-sawn.

You are dealing with expensive hardwoods, where waste is an issue. Your wood always ends up getting planed, so you are interested in how much is left after planing it smooth.

I haven't attempted to measure the actual kerf for all the reasons you mentioned.

But ....... I did notice this on my last CSM expedition to the woods. Whereas in the past, with 3/8" chain, I used felling wedges in the kerf (I know, I should really make some better fitting wooden wedges), those same felling wedges no longer fit with lo-pro chain. It was hard to even get the wedge started in the cut, and once pounded in, the wedge was apt to fall out of the kerf because so little of it fit inside.

If I were going to measure kerf, I'd use a gently tapered wooden wedge. Push the wedge into the kerf as far as it will go, and measure the thickness of the wedge at that point. The result would not be what you call "the real kerf," but it would provide a useful yardstick for comparing the amount of work the saw has to do.

Good work, Bob. Thanks for sharing your excellent data.

Thought provoking work Bob! I too am surprised at the lack of difference between 404 and 3/8 chain.

In addition to the wandering issue you already described, another reason that I can think of for why it is hard to measure the true kerf width is that the chain will dive into the wood whenever the chainsaw stops cutting. (Like if you have to stop to add gas or oil, get hung up on the edge, get a sore back - sorry Bob, I know this last one never happens to you!) So from a "getting the most wood" perspective, then it is the depth of this deepest gouge that matters, as well as other things like making sure the cut is straight.

From an 'amount of work done' perspective, since we are not going to measure the actual number of joules we use in cutting, I think we just need a consistent way to compare. Your drawing measures the worst case, mtngun proposes to measure the best case. My guess is that it won't matter, the result should be about the same.

Bob, I also think that it'd be pretty tough to keep the calipers exactly vertical as you have drawn. My guess is that they would tend to nestle into the valleys at the top and bottom, thus slightly exaggerating the actual size?

DRB said:

BobL. Was the 404 chain new or somewhat worn down compared to the 3/8 chains? I have noticed that my 3/8 chain kerf gets noticeably narrower as it wears down. Just a thought of why the difference may not be as big as expected.

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The 404 was fairly new - I will check how new today.

Daninvan said:

Thought provoking work Bob! I too am surprised at the lack of difference between 404 and 3/8 chain.

In addition to the wandering issue you already described, another reason that I can think of for why it is hard to measure the true kerf width is that the chain will dive into the wood whenever the chainsaw stops cutting. (Like if you have to stop to add gas or oil, get hung up on the edge, get a sore back - sorry Bob, I know this last one never happens to you!) So from a "getting the most wood" perspective, then it is the depth of this deepest gouge that matters, as well as other things like making sure the cut is straight.

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I agree. If I go by the biggest individual gouges measured in the 10+ measurements I took then
1) the 404 cross cut was 0.365"
2) 3/8 regular cross cut was 0.341"
3) LP 30º top plate cross cut was 0.316"
4) LP 10º cross cut was 0.320"
5) LP 10º cross grainer was 0.314"

The difference between the 404 and 3/8 increases from 3 to 7%, but the difference between the 3/8 regular and LP drops from 13 to 8%.

Although they apply to cross cutting I wouldn't place a lot of faith in these individual measurements for milling. One thing I now realise is that these were hand held cuts. A CS mill running on solidly mounted rails will hold a CS firmer perpendicular to the cutting direction than what an operator can so I really need to repeat these tests on kerf cut by a mill.

You point about gouging the wood as the operator moves unevenly or starts and stops cutting is absolutely correct. This is why I like to keep milling, even if its only lightly, when putting in wedges. I do this by leaning on the saw wrap handle with my knee/thigh which leaves my arms free to put the wedges in. When stopping and starting I ease the saw into the cut and avoid constantly see-sawing the mill sideways down the log.

From an 'amount of work done' perspective, since we are not going to measure the actual number of joules we use in cutting, I think we just need a consistent way to compare. Your drawing measures the worst case, mtngun proposes to measure the best case. My guess is that it won't matter, the result should be about the same.

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Yep - as long as like is compared with like it should be OK.

Bob, I also think that it'd be pretty tough to keep the calipers exactly vertical as you have drawn. My guess is that they would tend to nestle into the valleys at the top and bottom, thus slightly exaggerating the actual size?

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If you look again at my diagram you will see I only put one side of the caliper in a valley, the other side is not necessarily in the valley. I did this by slightly joggling the calipers as I widened them and hold the caliper atr angles to the cut. The real kerf is bigger than this anyway.

mtngun said:

My motivation for the skinny chains is speed, not conserving wood.

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We may be coming at this from different points of view because I am dealing with softwoods for construction materials, where waste is not a big issue, but speed is. Furthermore, my milled wood is often used as-sawn.

You are dealing with expensive hardwoods, where waste is an issue. Your wood always ends up getting planed, so you are interested in how much is left after planing it smooth.[/QUOTE]
Correct

I get a lot of people asking me about the wasting wood with 404 v 3/8 chain and I always assumed that 404 would cut a much wider kerf than a 3/8. I don't know why this is happening. Just going by gut feel the 441 seems to cut quicker with (and even use less gas) with the lopro compared to the regular 3/8 but I now realize I need to do some timed cuts to convince myself of how much quicker that is.

In my milling operation, even though my cuts might take 20 minutes, gaining 10% in cutting speed doesn't speed up my overall operation anywhere near as much as as I thought. Sharpening, log setup and moving big slabs even with a forklift still seems to be the time limiting steps.

If I were going to measure kerf, I'd use a gently tapered wooden wedge. Push the wedge into the kerf as far as it will go, and measure the thickness of the wedge at that point. The result would not be what you call "the real kerf," but it would provide a useful yardstick for comparing the amount of work the saw has to do.

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Yep - that would work. I try that.

BobL said:

In my milling operation, even though my cuts might take 20 minutes, gaining 10% in cutting speed doesn't speed up my overall operation anywhere near as much as as I thought. Sharpening, log setup and moving big slabs even with a forklift still seems to be the time limiting steps.

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Agreed.

My saw's hour meter typically logs about 2 hours of run time after a full day in the woods. The other 6 - 8 hours is spent skidding, bucking, limbing, positioning, clearing the workspace, setting up the mill, wrestling with the slabs, refueling, taking breaks, etc., etc..

But -- I'm gradually finding ways to be more efficient at those tasks, too. Nothing wrong with striving for better efficiency, where ever you can find it.

I suspect that there is another issue in play here and that is one of gearing and the difference in torque. with something like a husky 385 running 3/8 you will get a chain speed of x but with that same saw running 404 the chain speed will be about 15% faster and that increase in speed comes at a cost, decreased torque. the net effect is that the cutting speed will drop unless the power head has torque to burn. the perception would be that the chain MUST be cutting a much larger kerf with .404 than 3/8 due to a dramatic loss in speed due to the power head not having enough torque to pull the chain at a faster speed. This assumes using a drive sprocket with the same noumber of pins for both sizes of chain, a common thing since many don't understand the corelation between chain pitch and chain speed.

I also have to wonder how Bob's figures will hold up in a milling set up. Keep in mind I run .404 and I have alway maintained that the difference is not as much as it is made out to be compared to the difference in strength. As far as waste goes the wood I mill would end up as firewood so what ever I get out of a tree is already better than the other option.

BlueRider said:

I also have to wonder how Bob's figures will hold up in a milling set up. Keep in mind I run .404 and I have alway maintained that the difference is not as much as it is made out to be compared to the difference in strength. As far as waste goes the wood I mill would end up as firewood so what ever I get out of a tree is already better than the other option.

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Well I made a tapered kerf stick as per mtnguns suggestion and remeasured the kerfs,



404 = kerf is 0.35"
3/8 regular is 0.32"
3/8 LP is 0.27"

My method was 0.34, 0.33 and 0.28" respectively - so pretty similar.

Now - at the milling yard my 3/8 milling chain on one of my 42" bars consistently gave 0.035" on the inboard side and 0.037" on the outboard side"?

The fact that the milling kerf is 0.03 to 0.05" bigger than the freehand kerf is surprising.

One possibility of it being bigger could be that my bar not being coplanar to the milling rails?
I will need to check this.

Why the inboard side has a smaller kerf than the outboard could be due to the increased effect of vibrations on the outboard side. The inboard side is forced up against the log whereas the outboard side is flapping in the breeze.

Will all this ever end?

BobL said:

Well I made a tapered kerf stick as per mtnguns suggestion and remeasured the kerfs,

404 = kerf is 0.35"
3/8 regular is 0.32"
3/8 LP is 0.27"

My method was 0.34, 0.33 and 0.28" respectively - so pretty similar.

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So either way, the LP kerf is about 15% smaller. I'll buy that. Thanks for the data.

Will all this ever end?

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Nothing wrong with using a hobby as an outlet for your creativity and your analytical mind. The nice thing about hobbies is that you don't have to justify everything you do, like in the business world. You don't have to get your boss's approval. No one is looking over your shoulder and micromanaging you. I think it is very, very healthy.

mtngun said:

So either way, the LP kerf is about 15% smaller. I'll buy that. Thanks for the data.

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Yep

Nothing wrong with using a hobby as an outlet for your creativity and your analytical mind. The nice thing about hobbies is that you don't have to justify everything you do, like in the business world. You don't have to get your boss's approval. No one is looking over your shoulder and micromanaging you. I think it is very, very healthy.

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Well said.

Interesting thread.

Regarding the small time spent actually cutting compared to the time spent overall...

Most of a lumber mill is set up to handle the wood. Only a very small part of the operation is required to do the actual cutting.

But...you all know that already.



Mr. HE

Hddnis said:

Only a very small part of the operation is required to do the actual cutting.
But...you all know that already.
Mr. HE

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** WARNING ergonomics Police comment **

Yep, this is why it makes sense to put some effort into ergonomics and work flow. A tired, disorganized miller probably loses way more overall productivity than can be regained by a modded saw.

mtngun said:

If I were going to measure kerf, I'd use a gently tapered wooden wedge. Push the wedge into the kerf as far as it will go, and measure the thickness of the wedge at that point.

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Old thread, but BobL recently referenced it.

Comment made me think of this device from Lee Valley Tools (Veritas® Tapered Gauges - Lee Valley Tools )



Philbert

Bump! (and photo replacement)



Philbert

I've seen those veritas gauges and here in OZ they cost About US$60!
Here's a photo of mine made from a tapered piece of wood.

If there is around 3 - 6% difference in kerf size between 3/8" and .404" there must be close to 2 times the chip clearance room in the teeth right?