Thoughts on milling saws?

Brmorgan · Jun 19, 2009

That's SAE horsepower, an obsolete rating system now. It produces about the same amount of BHP as an 088 But the torque advantage of the 090 is huge - from a little over 5 ft-lbs to around 7. Probably helps that the 090 flywheel weighs about as much as a modern 50cc saw...

Anyway I saved the following nifty torque/horsepower chart from another thread on this site quite a while ago. I take no credit for it, and I'm not even sure who is responsible for it to give credit to. Hope they don't mind me reposting it.

PS - check out the 090G's torque rating compared the 070, which is the same engine. And some have built 090Gs with the big 137cc top-end so I can't imagine where the torque on one of those would rate.

BobL · Jun 19, 2009

Brmorgan said:
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Anyway I saved the following nifty torque/horsepower chart from another thread on this site quite a while ago.

The 090G torque value is high because it is geared down but don't forget the chain speed then also drops accordingly.

Stihlman441 · Jun 19, 2009

Good work boys very interesting reading, its got me thinking which may be dangerous.

Brmorgan · Jun 19, 2009

BobL said:
The 090G torque value is high because it is geared down but don't forget the chain speed then also drops accordingly.

For sure, but if ya need to pull a 10-foot-plus chain, look no further! That's why they used to come with 1/2" chain quite often.

I'd like to see a few more big saws added to that chart, especially the Jonsereds 111s, Pioneer P60, and Mac 125.

BobL · Jun 19, 2009

Brmorgan said:
For sure, but if ya need to pull a 10-foot-plus chain, look no further! That's why they used to come with 1/2" chain quite often.

Sure but unless you are jungle or deep forest milling, for logs that big I'd be heading for a Lucas or similar.

harrygrey382 · Jun 19, 2009

Brmorgan said:
That's SAE horsepower, an obsolete rating system now. It produces about the same amount of BHP as an 088 But the torque advantage of the 090 is huge - from a little over 5 ft-lbs to around 7. Probably helps that the 090 flywheel weighs about as much as a modern 50cc saw...

Anyway I saved the following nifty torque/horsepower chart from another thread on this site quite a while ago. I take no credit for it, and I'm not even sure who is responsible for it to give credit to. Hope they don't mind me reposting it.

PS - check out the 090G's torque rating compared the 070, which is the same engine. And some have built 090Gs with the big 137cc top-end so I can't imagine where the torque on one of those would rate.

That was my creation! Don't mind you posting it at all. I stopped showing i because people started getting touchy about basing too much on figures, which is kind of true.

I've added a couple since. The 038M and 441 spring to mind. What got me was the torque difference between the 070 and 076 (and 088) - why is the 070 so much higher, and is this correct? Well, now I have both, and will report back after a good shoot out!

Brmorgan said:
I'd like to see a few more big saws added to that chart, especially the Jonsereds 111s, Pioneer P60, and Mac 125.

So would I - care on giving me the numbers? My sources were the German test reports and old stihl manuals (apparently unbiased and accurate)

Brmorgan · Jun 19, 2009

Nope, I don't have any info like that. Only whatever's on Acres' site. I agree about basing too much on numbers - sometimes a saw might not post the absolute best numbers but aesthetics and design end up making it superior to the competition. Much like cars really. IMO the reason for the 070's superior torque is mostly due to the increased flywheel weight. Those saws don't weigh over 30 pounds dry for nothing!

Bob - Yeah I wouldn't want to CSM with a 10' bar, but some folks use bars that long for falling the odd tree still. Search Youtube for "090g sitka spruce" - I'm not sure how big the treeHow exactly can a Lucas mill cut a wide slab? Isn't it limited to slightly less than the diameter of the sawblade (not maximum log size, but slab width)? Sorry if these are dumb questions, I have only seen Lucas mills in passing and have never really researched them much.

woodsrunner · Jun 19, 2009

I want to thank all of you for the great replies and info you have posted in this thread. Special thanks to harrygrey for graphing the torque and hp numbers and to Brmorgan for reposting the graph. That's good info guys. :clap:

I really have enjoyed reading everyones replies. I have alot of good info to process before I make my decision.

Scott

BobL · Jun 19, 2009

Brmorgan said:
IMO the reason for the 070's superior torque is mostly due to the increased flywheel weight. Those saws don't weigh over 30 pounds dry for nothing!

Other things being more or less equal the bore to stroke ratio is one of the most important factor in determining torque.
Here you can see that max torque is very closely related to the BS ratio.
Look at where the 070 plots, it has a higher BS ratio that all saws except the 090.

What is important for cutting speed is the chain speed at the maximum torque. If the chain speed is low, cutting speed will be low. Irrespective of chain speed, if the max torque is insufficient to cope with the size and hardness of the wood the saw will bog down (like driving up a really steep hill in a car) which is where the saws high torque saw shine.

How exactly can a Lucas mill cut a wide slab? Isn't it limited to slightly less than the diameter of the sawblade (not maximum log size, but slab width)? Sorry if these are dumb questions, I have only seen Lucas mills in passing and have never really researched them much.

Lucas mills have an optional slabber attachment, 5 ft blade is the standard slabber but it can fit longer bars. The biggest mills have 30 HP four stroke engines so they can pull 5 skip chains with very low rakers. They also sell a dedicated slabber mill with up to 72" bar, check out http://www.lucasmill.com/OurProducts/SlabbingMills/DedicatedSlabbingMill/tabid/274/Default.aspx

Brmorgan · Jun 20, 2009

Hm, ya learn something every day. Here I thought that Lucas mills were all circular-only.

BobL · Jun 20, 2009

Brmorgan said:
Hm, ya learn something every day. Here I thought that Lucas mills were all circular-only.

There's a crazy young Queenslander calls himself weisyboy who runs his Lucas slabber with 0.05"+ rakers.

harrygrey382 · Jun 20, 2009

BobL said:
Other things being more or less equal the bore to stroke ratio is one of the most important factor in determining torque.
Here you can see that max torque is very closely related to the BS ratio.
Look at where the 070 plots, it has a higher BS ratio that all saws except the 090.

I'm not following here - for a start, the 1111 (050/051/075/076) has a longer stroke than 1106 series saws (070/090/contra), so that was another reason I didn't understand the higher torque.
Also, it's the higher the stroke to bore ratio the more torque right (always so in cars anyway, and it makes sense thinking about lever lengths)? Well here the 090 has a really low value, becuase of a very big bore and relatively small stroke, in fact all these saws do...

Brownpot Deaton · Jun 20, 2009

well the rpm of the 090 is literally half that of the 075's......

BobL · Jun 20, 2009

harrygrey382 said:
I'm not following here - for a start, the 1111 (050/051/075/076) has a longer stroke than 1106 series saws (070/090/contra), so that was another reason I didn't understand the higher torque.
Also, it's the higher the stroke to bore ratio the more torque right (always so in cars anyway, and it makes sense thinking about lever lengths)? Well here the 090 has a really low value, becuase of a very big bore and relatively small stroke, in fact all these saws do...

Yep, that is correct (I got my B/S mixed up with my S/B). I got out my old mech eng books and also found out that the S/B ratio mainly affects low end or low RPM torque which none of these engines have much off. Low end torque is important for low rpm acceleration and it (and the flywheel on the 070) probably contributes to why some of these older saws take longer to spin up to max RPMs. High end torque is affected more by other things than BS ratios.

As for the rest, I dunno - might post something in the CS forum and see what the tech heads there have to say.

woodsrunner · Jun 21, 2009

Another question

So here's another question for you folks. Looking at the Husqvarna web site and the engine specifications have a "maximum power speed" listed for their saws. How does this magic rpm number match up with max torque and max hp. It would seem to indicate a "sweet spot" on the torque and hp curves. But how does an everyday user utilize this info? I know when I run heavy farm equipment with a tach I can dial in engine rpms for maximum useable power provided I know where the curves tell me to set rpm. Is there a way to maximize useable power with a chainsaw using something other than the "hold it wide open and let it rip" method? If I recall correctly the point where the hp curve and the torque curve cross would indicate the most efficient operating rpm for 4 stroke engines. But efficency is not necessarily my goal. Max cutting power is. Any thoughts on this? Seems like Rail-O-Matic used a tachometer to dial in 2 powerheads to run synchronously on a double ended bar. I'll see if I can find that post.

Scott

BobL · Jun 21, 2009

woodsrunner said:
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But efficency is not necessarily my goal. Max cutting power is.
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I agree once you know the RPM that's giving the optimum cutting speed being able to hold or stay on those RPM is pretty handy.

With any saw it's very tempting to just push harder to improve cutting speed and depending on the saw it may well do this for a short while but the RPMs eventually drop off and the cutting speed drops to less than before or it may bog down completely. The narrower the power band the trickier it can be to stay on optimum cutting speed RPM. This is what happens with saws like the 660 and to a lesser extent with the 880. Although the 076 is slower overall it seems to have a broader power band so this effect is not as critical to stay on or near maximum cutting speed.

When I set up my tacho wrap handle clamp on the 880 I envisaged just using the tacho to tune the saw and then removing it but what I am finding is that I am using it a lot especially when milling big logs. With small stuff you can just sit on WOT and go for it but I don't plan to mill any more small logs with the 880 - it's just a waste of fuel when I can use 441 or 660. On bigger (40"+) harder logs I seem to get maximum cutting speed at around 10000 - 10500 RPM so I keep an eye on the tacho and it does seem to help, at least until I get a hang of using this saw.

woodsrunner · Jun 21, 2009

I have found that I can "feel and hear" a "sweet spot" on my 395 but I am not satisfied with going just by feel. I would really like to have some empirical data that would let me look at torque and horsepower curves with rpm on one of the axis' of the graph and then dial the saw in using a tach and a timer. BTW, I ordered a tach yesterday should be here by next weekend, so maybe I'll make a little progress in my search (obsession) for the true sweet spot.

Scott

Brownpot Deaton · Jun 21, 2009

the "sweet spot" huh...

sounds like an 'informative' article in either the playboy or cosmos magazine.

BobL · Jun 22, 2009

woodsrunner said:
I have found that I can "feel and hear" a "sweet spot" on my 395 but I am not satisfied with going just by feel. I would really like to have some empirical data that would let me look at torque and horsepower curves with rpm on one of the axis' of the graph and then dial the saw in using a tach and a timer. BTW, I ordered a tach yesterday should be here by next weekend, so maybe I'll make a little progress in my search (obsession) for the true sweet spot.

Scott

I agree "feel and hear" is not the same as real cutting speed. Based on the sound alone it feels like the 880 is just spinning its wheels when it's operating at it;s fastest cutting speed. It feels like it should be cutting at a lower RPM but I think it's because I'm just used to the 076 sweet spot. A torque and power curve from a manufacturer are also only going to be indicative and the best way has to be by timing cuts in real situations. I timed some cutting speeds at different RPMs in 42" wide hardwood and I was very surprised since I found the max cutting speed is using relatively little forward pressure on the saw with it sitting @ between 10 and 10.5k RPM.

Brmorgan · Jun 22, 2009

Brownpot Deaton said:
the "sweet spot" huh...

sounds like an 'informative' article in either the playboy or cosmos magazine.

I swear I come to ArboristSite to read the articles! I don't even look at the nice pictures! :monkey:

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