Getting serious about lo-pro

[mtngun]

By width I meant the distance to the edge of the cutter from the centerline of the chain. So in theory, if the cutter was filed near 0°, it would make a cut that is the width of the chain.

That's kinda what I meant by "keft width", but it's difficult to measure. I've measured it several times using several different methods and get different results each time.

I just did it again using what I think is the best method so far -- I laid a loop of chain on a bar, zig-zagged the loop back and forth across the bar 4 times, laid another bar on top of that, and then measured the entire "sandwich". Subtracting the combined thickness of the two bars yields the theoretical kerf width.

LP ripping = 0.223" keff

3/8 x 0.063 ripping = 0.265" kerf

LP kerf is 15.8% thinner....... on that round of measurements.

On a power-limited CSM, like my lame 066, I suspect the smaller kerf will translate into faster cutting speed. Not so on BobL's 880 that drives an 8 pin 9500-10,000 rpm with aggressive rakers to boot.

 

[SilverBox]

I think your first numbers were closer, when i cut with lo pro I get around 1/4 inch kerf and with I cut with regular .375 I get around 3/8 inch kerf. My rough guess estimate was 33% savings before you posted your numbers.

See how it does in the wood and measure that.

 

[BobL]

Don't forget that actual kerf is also slightly dependent on top plate filing angle.

 

[mtngun]

Don't forget that actual kerf is also slightly dependent on top plate filing angle.

How is that ? I presume the chain is going to wiggle side to side in the cut and the kerf will end up being wider than the chain ?

Anyway, as promised, here is a pic showing the lo-pro cutters. This 3/8 chain has a few miles on it while the lo-pro is new. Note that the cutters on Bailey's 3/8" ripping chain seem to be a little narrower than the typical cross-cut chain.

 

[BobL]

How is that ? I presume the chain is going to wiggle side to side in the cut and the kerf will end up being wider than the chain ?

That's right. The top plate filing angles force the cutter sideways a little. It's most noticeable going from a 35º to a 5º top plate filing angle.

For cross cutting this slightly wider kerf is produced by the side plate angle. It also varies depending on the type of wood. Wood with tough fibers is more likely to show this up.

 

[mtngun]

Time to generate some hard data ........

A 12.5" ponderosa pine cant, 95" long. I would rather have a cant that is more representative of the wood I typically mill -- doug fir in the 16" - 24" size, however, the logging roads are not fit to travel at the moment, so I had to make do with this pine log that I had at home.

The CSM now has a stopwatch for timing cuts.

First up, Woodsman Pro 0.063" x 3/8" ripping chain, brand spanking new.

ON YOUR MARK, SET, GO ! ! !

After cutting two boards, the 0.063" chain had stretched and would have needed to be tightened. This is typical behavior for Woodsman Pro chain -- it stretches a lot when it is new, but after snugging it up once or twice, then it settles down and behaves.

Continued in the next post ...........

 

[mtngun]

Now here comes the Woodland Pro lo-pro ripping chain, again brand spanking new. The Stihl bar was also new and the chain was a tight fit in the bar, with noticeable drag. A new rim sprocket was used, too. Break-in consisted of running the chain at part throttle for a couple of minutes before beginning the cut.

After cutting two boards, the lo-pro had stretched and needed to be tightened.

5 boards plus an odd sized leftover. The boards have nice character, but they are too punky and have too many checks to be suitable for furniture. I think I'll use them for closet shelving. The odd sized leftover will even get used as a backer for "no trespassing" signs. The saw dust will get used to clean up oil spills in the shop. I don't like to waste natural resources.

I suppose you want to know the results ?

With the 3/8" chain, the saw was running in its powerband, at 8500 - 9500 rpm. Even if I pushed it hard, it wouldn't drop below 8500. Compare that to my last trip to the woods where the saw was struggling to maintain 8500 in a doug fir and would bog unless fed oh-so-slowly.

In other words, the 12.5" pine cant was not much of a challenge for the saw, and that's a problem for this test, because lo-pro shines in situations where the saw is underpowered with 3/8 chain. Oh, well.

With the lo-pro chain, the saw started out running 10,000 - 10,500 rpm. Cool, that's exactly the rpm I had hoped to attain with lo-pro chain. However, by the second cut the rpms had dropped, and by the 3rd cut it would only hold 9200 with a modest push. Either the chain had dulled quickly, or else the saw was getting tired (or hot). I didn't let it cool off between passes except for the few minutes it took to get set up for the next pass.

For each cut, I paused a single time to install one wedge, which took 2 - 5 seconds depending on how many times I dropped the wedge.

The 3/8" x 0.063" times were 151 seconds and 146 seconds in that order. Average = 148.5 or 0.64 inches per second.

The lo-pro times were 137, 139, and 137 in that order. Average = 137.7 or 0.69 inches per second.

Note that both the first and the last lo-pro cuts were 137 seconds, even though it had lost 1000 rpms. How is that, you ask ? Because on the first pass, I did not have a good feel for the optimal feed rate. Practice makes perfect.

Ditto for the 0.063" chain, where the 2nd pass was faster than the first.

The lo-pro cutting speed was 7.8% faster than the 0.063" chain, on average.

I was expecting at least 10% faster, so I'm a little disappointed. However, something happened to slow the speed down quite a bit part way through the lo-pro test -- it could have been the saw, it could have been the chain dulled quickly, it could have been knots (the lo-pro boards did have more and bigger knots), it could have been ice (the log had been sitting out in the weather for 2 years and parts of it was wet and frozen). And so forth.

However, for all its imperfections, this is as fair a speed comparison as I'll ever be able to do, so I have to accept the results. :agree2:

The next step in this saga is just to continue running the lo-pro and see how it holds up. Will it continue to stretch or will it stabilize? Will it continue to dull quickly? Will it's speed advantage be more pronounced in bigger wood?

 

[BobL]

Good work mtngun - it has saved us all a lot of comparative work.

What were the raker depths? The Baileys ripping chain looks like it has seen some use so the real question is were the cutting angles the same?

I also didn't think there would be much difference in cutting speed. Another disadvantage of lo-pro is that it cannot carry as much sawdust although that wouldn't be significant in these cuts.

 

[mtngun]

Bob, brand new chains were installed at the start of the speed test, so they still had the factory angles, factory rakers, and factory sharpness (or lack thereof -- it is not unusual to see glint on the cutters, but they cut OK nevertheless).

Factory spec is 0.022" rakers, 10 degree top plate, 60 degree cutting angle, and 10 degree tilt. Same for both chains.

 

[BobL]

Bob, brand new chains were installed at the start of the speed test, so they still had the factory angles, factory rakers, and factory sharpness (or lack thereof -- it is not unusual to see glint on the cutters, but they cut OK nevertheless).

Factory spec is 0.022" rakers, 10 degree top plate, 60 degree cutting angle, and 10 degree tilt. Same for both chains.

The reason I asked wasa because I saw this picture you posted and the standard chain has shorter cutters.

 

[mtngun]

I used the older chain in that picture to make the slabbing cut while preparing the cant. Then I switched to a brand new chain so I would be comparing apples to apples in the speed test.

The older chain may have 12 degree or 15 degree cutters. It definitely has a more aggressive raker. That dates back from my experiments with different cutter angles and the FOP rakers.

 

[mtngun]

I posted this info on the chainsaw forum, but will add it here, too.

In the interest of science, knowledge, and truth, I cut off one side of a 3/8 rim sprocket so we could visually inspect how the drive links fit on the sprocket teeth.

The rim is a moderately well used Oregon 3/8-7. Made of hardened tool steel, it was tough to cut, however, no effort was spared for the benefit of my good friends on AS.

Showing new 3/8 Oregon chain. Since I have no way to apply torque, the drive links are not necessarily pulled tight against the sprocket teeth, however, you can see that if it were pulled tight, it would fit fairly well.

Showing new Oregon lo-pro. Only 2 drive links make positive contact with the sprocket teeth. The other drive links overshoot the teeth. Even though lo-pro has the same pitch as 3/8, a slightly larger rim diameter would be necessary to compensate for lo-pro's narrower side links (a picco rim does have a larger diameter, but I suspect it would be too large for lo-pro).

Showing used Carlton lo-pro. Again, only 2 drive links make positive contact while the others overshoot the sprocket teeth.

Well, I hate to admit it, but Saw Troll was half right. The difference in the height of the side links does affect the way lo-pro fits a rim sprocket (dunno about how lo-pro fits on a 3/8 SPUR sprocket). The drive forces will be carried by only 2 drive links instead of the usual 3. That's more stress per tooth.

That said, it's not the end of the world. People have done it, are doing it, and will continue to do it until lo-pro rim sprockets are made available.

 

[Philbert]

Nice applied research. Tried to rep you for it, but the rep gods . . .

Philbert

 

[DRB]

Nice investigative reporting.

Keep us updated as your quest continues.

 

[BobL]

Now that you have cut the sprockets here's a very interesting experiment to try.

Put the sprockets and chains back onto the CS with the exposed sides facing out and apply a normal chain tension.
Take a photo of the drive sprocket and chain, and use a feeler gauge to measure the gaps between ALL the drive links and sprocket teeth. I suspect a moderately normal worn 3/8 chain on moderately worn 3/8 sprocket is not going to come up roses on this test.

You can then repeat the test with a higher tension.

My hypothesis is once a drive link is off the sprocket tooth it's off and a half sprocket of chain is driven once around the sprocket by one tooth only. If this is the case then provided the lo pro doesn't stretch to the point where it jumps a tooth, it is no different to any other 3/8 chain. Remember the forces generated are not that much different to the back force generated on a chain when only one cutter cuts wood which is pretty common in narrow wood.

According to chain and sprocket theory [http://chain-guide.com/basics/2-1-2-engagement-with-sprockets.html] a chain being driven by a sprocket with less than 60 teeth can only stretch 1.5% before it reaches a point where it is largely driven by one one drive link and one tooth on that sprocket.

A chain on a 20" bar (nominally 40" long) can therefore only stretch 0.6" before it becomes driven by one drive link and one sprocket tooth. This translates to the bar needing to be elongated by 0.3".

In the case of a 60" bar this 0.9" of bar movement.

So I wonder if this is the case for just about all chains?

 

[mtngun]

Put the sprockets and chains back onto the CS with the exposed sides facing out and apply a normal chain tension.
Take a photo of the drive sprocket and chain, and use a feeler gauge to measure the gaps between ALL the drive links and sprocket teeth.

That's a good idea, though a standard feeler gauge will be too wide to fit in that little space.

Since I still regard lo-pro as an experiment, I'm OK with using the 3/8 rims for now. If I decide to stick with lo-pro, then I'd get more serious about the drive sprocket.

Wondering out loud :

-- how would lo-pro fit on a 3/8 spur sprocket ?

-- I think a picco sprocket's diameter is too large for lo-pro, but what if I turned it down on a lathe ?

 

[huskyhank]

Further in BobL's post:

http://chain-guide.com/basics/2-2-1-chordal-action.html

I think that as a chain and its sprockets wear in together they mate better than when new. Mismatches in wear between a sprocket and a chain might be similar to what you're getting with your mixed up parts -- i.e. new chain on a worn out sprocket.

 

[Rob D]

Just have to say a great thread and I'd like to stick my neck out a little and add my pennys worth -

Just a few things I've found which are far more rule of thumb:

Low pro chain can break on larger saws (already said I know)

IMO low pro chain seems to me to dull faster when cutting larger trees that have more grit etc in them.

If indeed I'm right and it dulls faster = more sharpening time then there would be less point in kitting a saw out with lo pro in order to save time.

If low pro 3/8 chain is being substituted for .404 chain then there will be more cutters on the same length chain which I have found leads to more drag (albeit a smoother cut) and doesn't give the same chip clearance rate. I have not measured this - it is more just the feel of it.

If using low pro to reduce saw kerf it does beg the question if kerf is an issue (as the timber is valuable) then it is probably worth using/hiring in a bandsaw. If accesss is difficult then break down with a CSM first with standard ripping chain then use a bandsaw.



So in relation to the above does switching over to a low pro system really warrant the effort anyway? As the first post says there seems to be no clear consensus on using low pro chain - that says a lot in itself!

 

[mtngun]

IMO low pro chain seems to me to dull faster when cutting larger trees that have more grit etc in them.

If indeed I'm right and it dulls faster = more sharpening time then there would be less point in kitting a saw out with lo pro in order to save time.

I, too, am concerned about it dulling faster. I need more field experience with lo-pro before I can draw any conclusions.

If low pro 3/8 chain is being substituted for .404 chain

Who uses 404 for milling ?

If using low pro to reduce saw kerf it does beg the question if kerf is an issue (as the timber is valuable) then it is probably worth using/hiring in a bandsaw.

It's about kerf to the extent that kerf width influences cutting speed.

Bandsaws are great if you own timber, but they are not an option on public land in the US.

 

[Kicker_92]

IMO low pro chain seems to me to dull faster when cutting larger trees that have more grit etc in them.

It's the leading edge of the cutter that is critical, and that is about the same size whether it's lo-pro or not. I've got some 16" lo-pro loops to try out, but they are semi-chisel, and I'd be comparing to full-chisel chain for wear, so not apples to apples.