The Perennial CSM Question: How Much Does Powerhead Size Matter?

[duffontap]

Ok, so I've got a little more than a year of experience working with my Granberg mills (MK 3 and Mini), and I'm always fighting the temptation to buy a bigger powerhead (comes with the territory--I know).

My Current Setup:
I currently have a 268xp and a 272xp that both run a 32" bar on a 36" mill with an aux. oiler and Carlton A3 chain. I know that even my 272xp is a featherweight for CSM work but I mostly milling softwoods and I get along fine with patience. I didn't pay much for either saw so I'm just planning on wearing them out--i.e., longevity is not an issue. But--here it comes--what about milling speed? At full capacity (about 24-26 inches wide) I can cut about a foot a minute with a sharp chain in good, dense Douglas Fir. At half the width, I can about double the speed, and at 6" wide I double it again--about 4 feet per minute.

The Dream:
As I'm creeping my way through wide cuts, I sometimes dream of buzzing along at 2-3" per second with a 395xp, waist deep in sawdust before I get a sore back--but is this within reason? My question is--all other things being equal (same chain, same mill, same operator, same wood) how much speed would I gain by laying out $1,000 on a new powerhead? Would I see a huge difference with a 385, or would I wish that I had sprung for the 395...or the 3120? Or, should I consider just picking up an old Husky 2100 for $200 and calling it good?

I know a lot of you guys are milling with monster saws, and I'm wondering if anyone who had started with a smaller saw like mine and worked their way up had any advice for me. What are reasonable expectations with an upgrade?--etc.

J. D.

 

[oldsaw]

Depends on what you are milling. I miss my 3120, but the 066 does a good job. Never put the 372 on the mill, but it would be okay for smaller stuff.

Mark

 

[duffontap]

Thanks Mark,

Like I said, I'm milling softwoods up to the full capacity of my mill.

Is there a significant difference in speed between the 3120 and the 066?

J. D.

 

[woodshop]

In wide stuff like you are milling in that pic, you will never get 3 inches per second, just not gonna happen. In that size, more like 3-5 seconds per inch in hardwood, less in softwood. I'm using a 395. Now in 8 inch wide stuff, yes you can often get an inch per second in ideal conditions with a sharp blade, but even that is fast for a csm.

 

[Kicker_92]

I'm not very experianced with milling yet, but started out with using a 385xp 30" bar on the 36" mk3, so very similar to your setup.

I've now added an ms880 (~120cc) with a 41" bar, still with the same 36" mk3. The main differance is when your cutting full width, where the 385 would drop RPMs, the 880 keeps pulling through. For the less than 12" wide cuts, I've started switching back to the 385, it's much lighter, burns less gas / oil, and seems to go just as fast in the thin stuff.


I'm finding though that quite little time is actually spent in the cut. The time to setup, move pieces, and prep for each pass is taking much longer than the cut itself. I'm now looking to save time in these areas rather than making the sawing any faster.


By the way, on that Fir make sure you wash your air filters well. I was having problems with the fine red dust from the bark building up and choking the airflow.

 

[Brmorgan]

You'll definitely notice a difference going to a 90cc-class saw, but perhaps not as much as your (at least self-admitted) "dream" scenario. I've never timed the cuts with my 395 but I'd say about 1/2 to 1 inch per second in ~24" D. Fir would be about right. With the low-profile chain on my 660 though, I'd say I can cut a 10' board from a 6" cant in less than half a minute. In 4" it'll cut almost as fast as I can walk it down the cant.

The first cuts I ever made were with a very rudimentary home-made mill and my old Pioneer P41 (66cc) which I found dreadfully slow. Mind you, I didn't know what the heck I was doing at the time and couldn't sharpen a chain worth stink compared to now. I've never spent a significant amount of time milling without getting sore somewhere. You'll save some time moving up to a bigger saw, but then they're heavier to lug around and can vibrate more so that can introduce other issues. If you plan on milling very much though, I certainly would recommend at least keeping your eyes open for a good deal on a used bigger saw. They show up in the pawnshops around here fairly frequently in the $300-$400 range.

 

[BobL]

Is there a significant difference in speed between the 3120 and the 066?

This depends on the size of the cut and the type of wood. If you can keep the 066 a full rpm it may even be faster in small wood. My guess is there will be no difference in small to medium width stuff but like kicker says in wider and harder stuff you will notice a difference since the bigger saw won't bog down.

It would be interesting to know the width of softwood that the these two saws would cut the same.

Duff on tap. I'm probably twice your age and my milling speeds in some Aussie hardwood are as slow as 8s/inch but I rarely get a sore back using a CSM. What I get is sore shoulders and arms from moving the slabs

If you get a sore back your setup is not right.
Some tips Tips
- get your log up off the ground and on a slope,
- put wheels on the mill to make contact with the log so the mill doesn't continually jam up against the log
- put slippery skids on the bottom of the mill rails
- add an aux trottle to the wrap handle so your hands come closer together. Put high handles on the cross tube handle on the mill. All commercial mills have their handles way to low.

All this helps makes it easier to put the saw through the log. I'm standing closer to upright, arms straight and leaning on the saw like this.

 

[BobL]

An 3/8, 88 ft/s chain with 9 cutters per ft cutting 0.025" slivers per pass should cut

88 x 9 x 0.025/12 = 1.65 ft/s

However, it is well known that when the chain is fully embedded in a cut the chain porpoises its way along the cut/bar and only every third of fourth cutter actually cuts (bandsaw blades don't do this). This then reduces the max cutting speed for chains to 0.4"/s or 5"/s.

Still sounds good doesn't it but there is another serious restriction to cutting speed.

The volume of kerf immediately behind each cutter that sawdust can occupy for a 3/8 regular chain is about 1.25" long, 0.25" wide 0.12" deep. This is = 0.038 cubin.

A cutter cutting at it's max depth of 0.025" generates this amount of sawdust in 0.038/(0.025 x 0.0.25) = 6 inches of cut length. This does not take into account that sawdust occupies ~2 times the volume of the wood that it is cut from so the cutter can only make make a 3" long cut before it reaches it max sawdust carrying capacity. After the kerf is full, if sawdust cannot spill across the bar (and it does a little - or a lot depends on the bar to chain thickness) that cutter can no longer cut and just carries sawdust. I really notice this effect on wide cuts in softer hardwoods, I see a lot of sawdust packing in behind the bar. In harder hardwoods the 1/8" sec cutting speed means the the kerf easily clears even in wider logs, with minimal packing behind the bar.

This is another reason why skip chains supposedly work better, (they have bigger kerf volumes and can spill sawdust past the bar easier) and they do in softer woods, but don't forget they also have fewer cutters per ft.

This is also why Brad can literally walk with a 4" wide cut (he's able to reach close to the max theoretical speed, but slows to 4"/s at 6" wide and drops off increasingly after that.

Chains are fundamentally limited devices. In practice, maintaining chain sharpness and keeping up the max RPMs are the two best things you can do. Your skill and knowledge largely deals with the first and a bigger power head helps with the second.

 

[mtngun]

I sometimes mill with an 80cc saw (Oly 980) when my regular milling saw (Stihl 066) is down for maintenance. Yeah, I can tell the difference.

I bring just as many boards home with the Oly, but it takes a sensitive touch to feed it into the cut.-- if it is pushed too hard, it bogs down. The line between bogging down and not biting at all is pretty narrow.

The 066 requires less finesse. It's easy to maintain a steady feed and RPM, only pausing to wedge the kerf and slide myself along the slab (I sit on top of the log while I mill). Not really faster, just easier.

Because of the 4500' altitude, my 066 does not make as much power as you might expect. It seems inadequate to me, even in softwood like douglas fir.

But, as Kicker_92 pointed out, setup and material handling are the big time eaters with a CSM. That, and stopping to sharpen/swap chains and clean the air filter.

I keep saying I'm gonna modify the Granberg so that the chain can be swapped without removing the saw from the mill.

BobL, if you ever visit the US, please drop by and we'll do some CSMing together, Rocky Mountain style. I've tried propping up the log to make it easier to mill. Propped up log promptly rolls down the mountain But I do appreciate some of your other tricks and tips.

 

[Kicker_92]

After the kerf is full, if sawdust cannot spill across the bar (and it does a little - or a lot depends on the bar to chain thickness) that cutter can no longer cut and just carries sawdust.

Based on this theory, would less raker depth along with fewer cutters lead to a better cut in wide slabs?

Say you were doing 24" slabs, would a 0.010" raker depth allow the cutters to work more effectively, or is there a minimum "bite" that they need to keep shaving off the wood?


This is a good topic for discussion, perhaps it should be a seperate thread?

 

[BobL]

SNIP!

But, as Kicker_92 pointed out, setup and material handling are the big time eaters with a CSM. That, and stopping to sharpen/swap chains and clean the air filter.

Agree 100%, especially when you have to sharpen after every slab.

I keep saying I'm gonna modify the Granberg so that the chain can be swapped without removing the saw from the mill.

I can do that but am increasingly touching up chains on the mill. Most commercial CSMs have the long tubular handle too low and too close to the bar and it gets in the way when retouching, and it also means bending over that little more. If you are considering modding the Granberg thats another mod I would really recommend.

BobL, if you ever visit the US, please drop by and we'll do some CSMing together, Rocky Mountain style. I've tried propping up the log to make it easier to mill. Propped up log promptly rolls down the mountain But I do appreciate some of your other tricks and tips.

That's very kind of you.

Hey - if you have a mountain you don't need to waste time making a slope - just point the log and the CSM downhill. I've done that myself. Not on a mountain, but on a hillside. We are seriously flat here. we have one 4000 ft and one 3000 ft hill, and the rest of the million square miles of my state (Western Australia, did I say we were bigger than Alaska plus Texas? ) is all less than that!

 

[duffontap]

Thanks everyone for bringing all your years of experience to bear on my question. It sounds to me like my lighter saws are getting me down the road just fine for what I really need. I might just keep my eyes open for a steal on an old 288xp or something along those lines, but as long as I know I'm not milling at 1/4 the speed of most of you I'm not going to really sweat this.

Bob,
I really appreciate the rigor of your answer. That was exactly what I was hoping for. Now, as for my sore back (I don't actually have back problems--just fatigue), I do need to do a few mods on my mill for my comfort--your suggestions are very helpful. Whenever I can I get the cant up into my comfort zone, but there are times when I just don't have the tools and ingenuity to get the big stuff high enough that I'm not hunched over (I'm currently working on a 34" Doug Fir log 18' long).

Thanks again to everyone for the help!

J. D.

 

[BobL]

Based on this theory, would less raker depth along with fewer cutters lead to a better cut in wide slabs?

Say you were doing 24" slabs, would a 0.010" raker depth allow the cutters to work more effectively, or is there a minimum "bite" that they need to keep shaving off the wood?

Correct, The rakers need to be set so that the starting raker/cutter wood angle is optimized to grab enough wood and to make a reasonable cut.

Except when noodling, cutters also cut into the wood in a short arc, I believe noodling has longer arcs because the the grain holds the cutter in place for longer. Because cutting happens in an arc, and because the raker penetrates the wood very slightly during the start of the cut, the cutting angle is not constant during the cut. A 0.01" raker depth does not dig the raker into the wood as much so it never reaches the higher cutting angles achieved by normal depth rakers, so removes a disproportionately shallower arc than 0.025" rakers. I also wonder if because shallow rakers don't cut the wood as quickly users push harder which just makes rakers compress more wood ahead of the next cutter so that the next cutter is having to cut through compressed wood compounds the problem.

All this is why a 0.01" depth makes dust rather than chips. This is also why a constant raker depth is not as good a system as constant raker angle. As the cutter - raker distance or gullet width increases with every sharpening the raker height needs to be lowered even more to maintain the same cutting angle. I use a raker depth which is 1/10th of my gullet width. For a 3/8 chain this equate to 0.025" when the chain is new and as much as 0.045" just before I junk the chain. This is not new, it is the same as the Carlton fileoplate system and there are other similar systems around. This system and retouching after every big slab makes a significant difference to cutting speed when slabbing big Aussie hardwood slabs.

BTW if you have a saw with a lot of power you can just run greater raker depths and get faster cutting speeds , up to the point where the amount of sawdust clogs the space between cutters so if you do this then skip chain appears essential.

Will Malloff recommends 0.045" rakers on a new when using an 090. This puts a significant stress on the chain and makes it very grabby and I would not do that with anything less than 404 chain, but there are people out there that do it on 3/8. The other more subtle factor is raker shape, make them pointier and narrower (Danger Will Robinson!!) so they penetrate the wood further. Everyone has their view points and you can fiddle until the cutter tips just snap off.

This is a good topic for discussion, perhaps it should be a seperate thread?

Good idea - I leave that decision to the mods.

 

[OhioGregg]

Duffontap
Im a newbie at this, so can't speak from alot of experiance or comparison. I run a 385xp, If money was no consideration, I would have preferd a 395 or 660, but I must say the 385 is no slouch! You can bog it down, especially in the wider stuff if you apply to much pressure. I find its like walking a tite rope, just hace to keep a steady light pressure and it sings right along. I personally don't think speed and chainsaw mill go together at all, LOL Sure, narrower cuts go faster, but like some one mentioned, on bigger cuts, i will pause a little for a rest so to speak, when sticking in a couple kerf wedges. Like most things in engine related activitys, there is no replacement for cu. in. or horse power and a sharp chain! But, its a slow steady go, no matter what saw you run.

Gregg

 

[oldsaw]

You can bog any saw in a decent sized log, the bigger saw just needs less "finesse". The whole idea is chain speed and a sharp chain. BobL has put some incredible info up here, and others have put up some very useful "got to know" stuff that gets forgotten by the "old timers", but automatically done as a routine.

Yes, a 268 or 272 can mill a lot of wood, you will just have a slower feed rate. Keep the chains sharp and you will have a lot of wood. The most important thing is to remember it's going to be slow, but the wood in the end is worth it. Nothing like the satisfaction of making something from wood you milled.

I gave the girls at the office little curio boxes made from wood that I felled, milled, carried out of a ravine, dried, planed, built, and finished. I was pretty proud of that.

Mark

 

[Freehand]

I run a 268,and find it to be barely enough saw-almost featherweight for a ripping/ milling application.But it gets the job done......

I'm in the market for a 7 hp saw though-maybe a ms660 or a 395.....let's see now , where is that extra 1000 bucks I had laying around here...

 

[BobL]

Nothing like the satisfaction of making something from wood you milled.

I gave the girls at the office little curio boxes made from wood that I felled, milled, carried out of a ravine, dried, planed, built, and finished. I was pretty proud of that.

Most people I give stuff to made out of home milled timber seem very impressed as well. I gave the boss at work a "gavel and sound block" made from wood I milled and she has it on display in her office along with her other curios she collected from he overseas travels. I've gave the ladies in the office cheese and pate knifes with handles made of wood that was home milled and they really seem to like them.

 

[BlueRider]

An 3/8, 88 ft/s chain with 9 cutters per ft cutting 0.025" slivers per pass should cut

88 x 9 x 0.025/12 = 1.65 ft/s

However, it is well known that when the chain is fully embedded in a cut the chain porpoises its way along the cut/bar and only every third of fourth cutter actually cuts (bandsaw blades don't do this). This then reduces the max cutting speed for chains to 0.4"/s or 5"/s.

Still sounds good doesn't it but there is another serious restriction to cutting speed.

The volume of kerf immediately behind each cutter that sawdust can occupy for a 3/8 regular chain is about 1.25" long, 0.25" wide 0.12" deep. This is = 0.038 cubin.

A cutter cutting at it's max depth of 0.025" generates this amount of sawdust in 0.038/(0.025 x 0.0.25) = 6 inches of cut length. This does not take into account that sawdust occupies ~2 times the volume of the wood that it is cut from so the cutter can only make make a 3" long cut before it reaches it max sawdust carrying capacity. After the kerf is full, if sawdust cannot spill across the bar (and it does a little - or a lot depends on the bar to chain thickness) that cutter can no longer cut and just carries sawdust. I really notice this effect on wide cuts in softer hardwoods, I see a lot of sawdust packing in behind the bar. In harder hardwoods the 1/8" sec cutting speed means the the kerf easily clears even in wider logs, with minimal packing behind the bar.

This is another reason why skip chains supposedly work better, (they have bigger kerf volumes and can spill sawdust past the bar easier) and they do in softer woods, but don't forget they also have fewer cutters per ft.

This is also why Brad can literally walk with a 4" wide cut (he's able to reach close to the max theoretical speed, but slows to 4"/s at 6" wide and drops off increasingly after that.

Chains are fundamentally limited devices. In practice, maintaining chain sharpness and keeping up the max RPMs are the two best things you can do. Your skill and knowledge largely deals with the first and a bigger power head helps with the second.

Thanks for running those noumbers for us, and thanks for doing them in imperial rather than the more sensible metric. I do have a question and I think you might be the one to come up with the answer.

because the teeth on a chain are tapered in width, as it is sharpend through its lifespan it gradualy makes a thinner kerf. this smaller kerf requires less power to make but it allso offers less space for swarf. Your calculations show how this space issue is the ultimate limiting factor to cut speed so my question is will an equally sharp new chain cut faster than an almost used up chain?

 

[Brmorgan]

I have no numbers to back me up, but I've found that to be the case when bucking firewood (old chains are slower, that is). I haven't worn any of my milling chains down far enough to have an objective opinion about them yet though.

 

[BobL]

Thanks for running those noumbers for us, and thanks for doing them in imperial rather than the more sensible metric.

I went to school in the 1960's where we still leaned imperial so I am very comfortable in thinking and calculating in this system.

because the teeth on a chain are tapered in width, as it is sharpend through its lifespan it gradualy makes a thinner kerf. this smaller kerf requires less power to make but it allso offers less space for swarf. Your calculations show how this space issue is the ultimate limiting factor to cut speed so my question is will an equally sharp new chain cut faster than an almost used up chain?

Smaller Kerf also means a lightly bigger gullet and slightly less sawdust so they should self compensate but there are other issues. For example the kerf gets narrower so less sawdust can escape past the chain. My gut feeling is that most people experience slower cutting from old chains compared to new chains because the chain is not set up properly. By then many of the cutting angles could be a long way out, cutters of slightly different length etc. I'd guess that unless the user is using something like a Carlton filoplate the biggest factor will be the raker depth will be way too high. I have my raker depths set as much as 0.045" with an old chain to maintain the 6º cutting angle. Despite all this, although I have not made timed cuts, my old chains still seem a little slower than new chains.