.325 faster than 3/8?

[ol'homey]

This is my first post and I have a question re. 3/8 and .325 chain. Madsen's site talks about the reasons 3/8 is faster than .404 chain. Those reasons (narrower kerf, lighter chain, less HP required etc.) lead me to believe .325 should be faster than 3/8. For a while I thought the .325 was not strong enough to take the torque of the higher HP saws without breaking. But my new GB books lists .325 sprockets for an MS460 which is a good size saw.

I'm thinking that the lightest, narrowest chain that will withstand the torque your saw produces, combined with a sprocket that allows your saw to run at its peak HP rpm should cut the fastest right? IOW your saw is running at peak HP (doing as much work as possible), is concentrating that energy into the smallest kerf size possible (want to go down through the wood as opposed to removing material on the sides) and has the least parasitic losses possible (less rotating mass in the chain). Am I right?
Has anyone actually done the work and compared chisel .325 to chisel 3/8 by setting them up with the same bar length and varying the rim sizes so that the saw is taching as close as possible to its peak HP rpm in the cut? IOW .325-7T isn't going to put as much load on the saw as 3/8-7T so you would have to go a larger sprocket to get close to the same load. I think once you get the load dialed in so your saw is running around its peak HP rpm in the cut with both chains you will find the .325 cuts faster than the 3/8. Can anyone confirm or deny this theory? This is a great forum and I'm glad to be here! Thanks, Lee

 

[Lawn Masters]

If running a larger saw like a 460, the .325 chain will cut slower because its a lower profile cutter tooth than 3/8 chain is. if you're running a 346XP though, the .325 will perform much better.

 

[glens]

OA you're not reading enough.

ol'homey, this is factual: http://www.arboristsite.com/showthread.php?p=236813&highlight=.325#post236813

 

[rmihalek]

I'm not sure what Oldsaw-addict means when refering to a low profile cutter on .325 chain since the depth gauges on .325 and 3/8ths can be set to the same height. Therefore, each cutter should take the same bite.

 

[WRW]

There's some chainsaw millers that have switched over to .325 for milling. They claim that it cuts faster and leaves a better surface. I'll just take their word for it.

 

[Crofter]

The narrower part of the idea is legitimate, but the fact that generally the .325 chains have a smaller (height wise) tooth and so a relatively smaller gullet capacity, they start to have limitations in getting rid of the chips. This becomes more noticeable as the tooth wears back. Some .325 chain is quite small to start with compared to the Stihl chain (which may have the largest profile, correct me here) and wont even be in the race with a 3/8 chain on a larger saw. If you are square filing both chains, the .325 is almost too tight to get proper angles and the 3/8 can easily be made to skin it except perhaps in the smallest saws. Timberwolf has done some experimenting with 10 pin sprocket .325 on an 066 Stihl and I believe he found it pretty quick indeed on smaller wood.

 

[WRW]

Crofter,
I would rather think that the gullet would merely allow the shaving to peel off of the uncut wood and that the space between teeth would carry the chips.

 

[Stumper]

WRW, Unfortunately the space between the teeth is also smaller on .325. There is really no need for anything other than 3/8ths lowprofile on small saws and regular 3/8ths for larger saws. Many pitches have come and gone. >404 and .325 still linger but I suspect thta they are going to fade away also. >325 may linger on simply because it looks aggressive but is pretty smooth cutting on a 2.5-3.0 cid saw-The manufactureas stick a lot of it on homeowner models. I converted a Husky 40 to 3/8ths low pro years ago for the narrow kerf-seemed about equal in performance. I have converted a couple of 3.0cid class saws to standard 3/8ths- I like stocking less chain and fewer file sizes-It works great.

 

[WRW]

WRW, Unfortunately the space between the teeth is also smaller on .325. .

I was aware of that fact. The ability to go to a larger sprocket (due to the narrower kerf) should negate that deficit.

None of this is from personal experience, and it may only work for end grain cuttting (milling). Size of the wood being cut may make a difference also (see glen's post on 10" wood).

 

[Mange]

WRW, Unfortunately the space between the teeth is also smaller on .325. There is really no need for anything other than 3/8ths lowprofile on small saws and regular 3/8ths for larger saws. Many pitches have come and gone. >404 and .325 still linger but I suspect thta they are going to fade away also. >325 may linger on simply because it looks aggressive but is pretty smooth cutting on a 2.5-3.0 cid saw-The manufactureas stick a lot of it on homeowner models. I converted a Husky 40 to 3/8ths low pro years ago for the narrow kerf-seemed about equal in performance. I have converted a couple of 3.0cid class saws to standard 3/8ths- I like stocking less chain and fewer file sizes-It works great.

I agree, 3/8 is the way of the future. I have pointed out in earlier threads there is no need for 3 types of chain, this is a fact.
The 3/8 can be shaped to fit almost any bar length and saw power.

 

[ol'homey]

Glens,
Your comparison between .325-8T and 3/8-7T showing that the .325 was faster makes sense. However we don't know the operating RPM's of the saws so we don't have any idea of how much HP was actually being transfered to the wood. My guess is if we have equal HP being transfered to the wood through .325 and 3/8 chain the .325 will be faster. Without access to a chainsaw dyno we can't measure the HP/RPM curve. But we do have access to the max. HP spec listed in the service manual and the RPM it was measured at. BTW, for folks that don't know this, the RPM where max. HP occurs has NOTHING to do with the max. allowed RPM that is quoted everywhere. Max. allowed RPM might be 13,500 no load. Max. HP RPM occurs under load and might be 10,000. So if you put a tach on a stock saw in good condition and it's running around the RPM for max. HP you know that the saw is actually making right around its rated HP. Getting the RPM range right is very important with modern tuned port saws with narrow power bands compared to the older reed valve saws with broad power curves. If you do the test with the saw running close to the same rpm with .325 and 3/8 the load on the saw should be roughly the same and the .325 should be faster. If this rpm is close to the max. HP rpm the saw is doing all it can and should be pretty fast. This may be the case with the test you already did, or you might need say a 9T sprocket for the .325 to get the load/rpms equivalent to the 3/8. If anybody does more testing please post your results and include the RPM's. Thanks!

 

[ol'homey]

Just looked at my last post and I don't think I explained what I'm looking for well enough, so here's some more to read or skip over!
If we put a tach on an engine and have it's HP/RPM curve we can look at the tach and the curve and tell how much HP it's making. Each RPM point has a different HP. As you increase RPM the HP will reach a peak and then decline. For example, a saw making say 12k rpms in the cut is not making max. HP if it's max. HP occurs at 10k. If the saw had the right chain/sprocket/bar combo. to get the load up and the rpm's DOWN to 10k it would cut FASTER.
In order to have a valid comparison between to different chains we must run them on the same saw and the saw must be making as close as possible to the same RPM. This is because if the RPM is the same then the HP is the same. Then we can compare how efficiently the same HP gets transfered to the wood by timing the cuts.

 

[Crofter]

WRW. I think if you try it you will find that enlarging the gullet area on the teeth without touching anything else will yield quite an increase in cutting speed.
Ripping is a whole different study than cross cutting. The sawdust (and that is what it is ) is a whole different shape and the volume created in a given time is not nearly so great. The limiting factor is severing not getting shed of the product, so a narrower kerf and concentrating the power is the advantage.
If any speed advantage of the .325 only exists with a new chain and the largest profile cutter, then in the real world over the life of a chain, you cannot say that it is faster than 3/8. You may be able to trick up a situation that shows this, but I doubt if you could prove it is GENERALLY so. When you start to go to oversize sprockets you have to have either non standard chain link counts or alter the tail of your bar and install chain, bar, and sprocket as an assembly. That then might be faster in 10 inch and under wood but slower on anything bigger. Different combinations make some interesting possibilities, but don't bet your rent money without nailing down all the conditions of the race.

 

[WRW]

. Different combinations make some interesting possibilities, but don't bet your rent money without nailing down all the conditions of the race.

Crofter,
That's exactly what I was trying to infer by pointing out that glens was cutting 10" wood.

 

[Mange]

If you would ignore some BS, there is some info on the subject here.

http://arboristsite.com/showthread.php?t=16012

 

[Pioneer]

According to my Stihl dealer, the smaller chain will cut faster because it will not have to cut as wide a groove. He also says that the smaller chain makes the saw more susceptible to pinch because of the narrow grove it cuts. I don't know about .325 vs 3/8, but I can tell you first hand that 3/8 cuts faster than .404 on the same saw, because I have tried it on one with identical bar lengths.

 

[timberwolf]

feel like I am giving away a secret here, but the cutters on a .325 and 3/8 stihl RS chain are the same size. Note some of the other brand .325 chains are not pulling full size cutters.

In the messing about I have done, I found the .325 to start to take over on poplar less than 10". I am thinking that chip clearing is the issue, however with stock stihl chain there is only .005" extra chip space between the cutter and the drive link then with the 3/8 chain. kerf seams to be much the same.

One other aspect that I note is the outside corner of the tooth is consistantly crisper on all the .325 chains I have which gives a finer corner compaired to the 3/8 when square filing.

As far as square filing, I have not had any space problems that impact angles for square filing the stihl .325. With the flat file, I did find the trigular file problematic.

So for my thinking the .325 puts more cutters of the same size in the wood given the same chain speed, this works on smaller softer wood anyway.

unfiled stihl RS.325 chain on left unfiled stihl RS 3/8 on the right.

TW

 

[Crofter]

Looks like there would be just a bit more room in the gullet between cutter and rear of the raker. Could you show the cutters in side view. I never measured but felt the rear of the .325 cutter top was a little closer to the tops of the drive links. (Lower)
I believe Jokers had a picture up a year or so ago showing some different brands of .325 that were quite dinky compared to the Stihl.

 

[ol'homey]

Thanks for the link Mange, some good info there. I liked the post by fencerowphil where he broke the .325 with his 090. It just wouldn't handle the torque which is great! He now knows that the lightest and fastest chain that will work on his saw is 3/8. For lower HP saws and smaller bars that won't develop enough torque to break the chain, my theory is that .325 will be proven fastest for all the reasons 3/8 has been proven faster than 404.
One factor that may throw a wrench into proving this theory is availability of various size .325 sprockets in order to get the load on the saw right so it runs as close as possible to its peak HP RPM. For example, looking at the available rim sprockets in my GB catalog I see that the Stihl saws up through MS390 use the small 7 spline rim sm7 and the only .325 rims available are 7 and 8T. The larger Stihl saws use the standard 7 spline rim sd7 and the only available .325 rim is the 9T. The limited selection of .325 rims may make dialing in the load and operating RPM difficult. What happens if you have an MS390 and need a 9T .325 sprocket?
If anyone has ever tried say an 066 with .325 chain and a 9T sprocket I'd like to hear about it. Be sure to list the operating RPM's with your 3/8 chain/sprocket and with the .325 chain/9T. I bet it would be fast!

 

[Al Smith]

It is probably a personal preference.My saws,up to 5 cu.in,run 3/8" over 5 cu.in,.404.My little "climbers" ,all use 3/8" low profile.I don't have any with .325,so I can't make comment on this size.