Chain pitch mystery (somebody please enlighten me)

[Arky217]

Here's my story and I'm sticking to it.

I have been milling with a muffler modded 395XP on a Logosol M7 for the past year (see my post in the 'Milling and Sawmills'
forum, "Logosol owners and CSM users in general").

I begin using the Stihl 63PMX72 chain (3/8" pitch, .050 gauge, low profile) that Logosol sells. After breaking a number of
them, I switched to the Woodland Pro from Baileys, #33RP (3/8" pitch, .063 gauge) along with a slightly longer .063 gauge bar. The first 33RP has broken twice. I'm still using the second one; it hasn't broken yet.
I just ordered a couple of Oregon milling chains from Madsens, #75RD (3/8" pitch, .063 gauge); I'm hoping these will be
stronger.

Now that I've covered a little background, here's the mystery:

I've always understood that the pitch of a chainsaw chain is one half of the distance between center to center of any 3
rivets (this measurement being used because the tie strap holes are spaced slightly longer than the pitch and the drive link
holes slightly shorter than the pitch, thus both added together equal exactly twice the pitch).

When checking the pitch of an unknown chain, I've always just measured center to center of 3 rivets and divided by 2.

Well, the first of the Woodland Pros (the one that broke twice), really stretch a lot at the beginning of its use. So much, in fact, that I had to take the slack out of the chain after nearly every pass.
The second Woodland Pro, however, did not stretch nearly so much. I was looking over the chains today before I placed the order to Madsens, and I decided to measure a length of the first Woodland Pro just to see how much it had stretched.

Well, here is the mystery, at least to me.

I decided to measure 16 drive links of the chain since that amount should equal 12" in length. (3/8" * 2 * 16 = 12")
Expecting to see 16 links measure somewhat over 12", I was baffled when I measured 11 & 13/16", and this on a chain that
really stretched a lot.

I measured again and again with the same result. That figures out to an effective pitch of .369 which of course is less than
the .375 (3/8") pitch it's supposed to be. How can that be, I wondered.

Well, I then measured the second Woodland Pro chain that I'm still using, same 11 & 13/16" for 16 drive links.

Now, I was determine to find source of this mystery (at least to me), so I then measured a couple of the Stihl 63PMX72
chains that I had used. Same result; 11 & 13/16" for 16 drive links for an effective pitch of .369 instead of .375 plus stretch that I thought it should be.

I thought, "There's just something I'm not seeing here". Then I thought of my MS290 Stihl that uses a .325 pitch chain (26RS).

I'll just measure that and see what I come up with. For .325 pitch, 16 drive links should measure 10.4" (.325" * 2 * 16 = 10.4"). Well, the measurement turned out to be 10 & 1/2" for an effective pitch of .328. Now that makes sense, I thought,
since it shows a little stretch from the .325 pitch it's suppose to be.

Then I measured the original chain from the Stihl MS290 which I wore to the point where the cutters were almost gone.
It measured 10 & 5/8" over 16 drive links for an effective pitch of .333, even more stretch which makes sense as well.

So, what's the deal with these 3/8" pitch chains. After considerable usage and stretching, how can they measure less than the 3/8" pitch that they are suppose to be ?

Somebody please enlighten this ignorant, old man !

(Here's something that may or may not be related to this mystery. When the chains on both the 395 and the 290 are tensioned properly, I've always noticed that the 26RS on the 290 always seemed smooth as silk when rotated by hand whereas all the chains on the 395 always seemed not near so smooth to rotate.)

Again, somebody chime in and tell me why I'm measuring what I am on these 3/8" pitch chains.

Thanks,
Arky

 

[Fish]

There is a 3/8 low profile chain, and the a big 3/8 chain.

The first chain you mentioned was the Stihl 63pm=3/8 low profile.

 

[hotshot]

There's only thirty one links. Are you measuring center to center on the 16
drivers?

 

[Arky217]

Yes, I'm aware that the 63PMX is low profile, however, what has that got to do with the pitch ? 3/8" pitch is 3/8" pitch.

Arky

 

[Arky217]

There's only thirty one links. Are you measuring center to center on the 16
drivers?

I am measuring the distance from one drive link to another times 16 (in other words, the distance from drive link 1 to drive link 17), which should equal 12" on a new 3/8" pitch chain. Not sure what you mean by "only thirty one links".

Arky

 

[Fish]

Yes, I'm aware that the 63PMX is low profile, however, what has that got to do with the pitch ? 3/8" pitch is 3/8" pitch.

Arky

yes, that is the measurement between the rivets.

So any hard questions about the measurements of long stretches must
be asked before you have stretched the **** out of them to be relevant.

The bottom side of the 3/8's chains are not the same, so you cannot interchange the chains...

Well, I guess you can............

 

[Arky217]

yes, that is the measurement between the rivets.

So any hard questions about the measurements of long stretches must
be asked before you have stretched the **** out of them to be relevant.

The bottom side of the 3/8's chains are not the same, so you cannot interchange the chains...

Well, I guess you can............

Not sure what you mean by the above.

The puzzle is, since the measurement of a .375" pitch chain from a given point on any drive link to the same given point on a drive link 17 drive links away (16 spacings from drive link to drive link) should be precisely 12 inches, then it doesn't seem to make sense for that measurement to be less than 12 inches on a new chain, much less a well used, stretched chain.

Arky

 

[J.W Younger]

Not sure what you mean by the above.

The puzzle is, since the measurement of a .375" pitch chain from a given point on any drive link to the same given point on a drive link 17 drive links away (16 spacings from drive link to drive link) should be precisely 12 inches, then it doesn't seem to make sense for that measurement to be less than 12 inches on a new chain, much less a well used, stretched chain.

Arky

fish musta got an early start

 

[J.W Younger]

low profile is .365 pitch

 

[Fish]

Sorry, I have not followed the thread too close, as there is something very
wrong, as breaking more than 1 chain in a year should throw up a bunch of
flags, whether milling, ethnic cleansing, or whatever.......

You have gone into a long tale of measuring and so on, but I think the
real question has yet to be made known.......

After many years of trying to figure out what the question is, I put this thread
in the same model.....

Post some pics of the remains of your sprockets.....

 

[Arky217]

low profile is .365 pitch

I'm aware that some low profile chains are .365 pitch, such as the 30LR Woodland Pro from Baileys. On Baileys website, the 30LR is described as [pitch 3/8" low profile (.365)] However, on the box that the Stihl 63PMX came in, it states [3/8" pitch] only.

If it were .365 pitch even though the box states 3/8" pitch, that would explain the measurement of 11 & 13/16" for 16 drive links, as that would be an effective pitch of .369, which would account for some stretch from the new .365 pitch.

Now, on the Woodland Pro 33RP, the box states .375 pitch and it is definitely not low profile. However, if it were made to .365 pitch also, even though the box states .375, that again would explain the measurement of 11 & 13/16". However, I have never heard of a full size 3/8" pitch chain being manufactured to an actual pitch of .365"

However again, unless there is a better explanation, I will have to conclude that the 33RP is indeed an actual .365 pitch even though it is a full size chain and the box indicates .375. There seems to be no other explanation for it.

Arky

Fish,

The current sprocket was installed new with the first Woodland Pro. The sprocket it replaced had seen much more use yet was still in very good shape.

Arky

 

[nmurph]

all 3/8' chain actually measures .365"....mystery solved....

 

[MS260 Fan]

I think the trouble is in the equation 3/8" * 2 * 16 = 12".

It takes the first 3 rivets to calculate the 3/8" pitch. Call that length S. The next two rivets (4 and 5) use rivet #3 to make length S. Now you have 5 rivets and 2*S. 7 rivets is 3*S. It's really that first rivet that messes everything up.

For your measurements I would suggest measuring an odd number of rivets.

Say 15 rivets. The magic number for 15 rivets is 7 [(15-1)/2 = 7]

The distance for 15 rivets should be 7*2*0.375

Maybe I'm missing the point here but that's my $0.03. I threw in a penny extra with the example.

 

[nmurph]

all 3/8' chain actually measures .365"....mystery solved....

i repeat, all 3/8" is actually .365".....niko, where are you???

 

[synness4]

switching to 404 would help right? some one tell me if i'm wrong

 

[Arky217]

I think the trouble is in the equation 3/8" * 2 * 16 = 12".

It takes the first 3 rivets to calculate the 3/8" pitch. Call that length S. The next two rivets (4 and 5) use rivet #3 to make length S. Now you have 5 rivets and 2*S. 7 rivets is 3*S. It's really that first rivet that messes everything up.

For your measurements I would suggest measuring an odd number of rivets.

Say 15 rivets. The magic number for 15 rivets is 7 [(15-1)/2 = 7]

The distance for 15 rivets should be 7*2*0.375

Maybe I'm missing the point here but that's my $0.03. I threw in a penny extra with the example.

Sorry MS260 Fan,

but that's a negative. The distance between the holes in the drive link are one length (slightly shorter than the pitch) and the distance between the holes in the strap are another length ( slightly longer than the pitch); when you add both of those lengths together, then divide by 2, that is the pitch.


nmurph,

That is very interesting if true. What is the source of your information that all .375" pitch chains are actually .365" ?
If indeed that is true, then it begs the question, are all .375" pitch sprockets actually .365" ? And if so, why ?

Or, if all .375" pitch chains are actually .365" pitch, and .375" pitch sprockets are actually .375", then at any given time, the sprocket is going to be putting nearly all the pressure on only one drive link. If this scenario is correct, it would surely explain why I have had these chains to break on me.

Let's just say that these .375" pitch chains (at least that's what the boxes say) that I have been using are indeed actually .365 (and from the measurements, that appears to be the case), and the sprocket I got from Baileys when I bought the chains is actually .375" pitch, then that, in my opinion anyway, would account for the chain breakage I've experience.

However, I find it hard to believe that:
1) All .375" pitch chains are actually .365" pitch and that all .375" pitch sprockets are just that, .375" pitch.

or 2) That all .375" pitch chains are actually .365" pitch and that all .375" pitch sprockets are also actually .365" pitch as well.
If that were the case why not call them what they are, .365" ?

Arky

 

[Philbert]

I think the trouble is in the equation 3/8" * 2 * 16 = 12".

It takes the first 3 rivets to calculate the 3/8" pitch. Call that length S. The next two rivets (4 and 5) use rivet #3 to make length S. Now you have 5 rivets and 2*S. 7 rivets is 3*S. It's really that first rivet that messes everything up.

For your measurements I would suggest measuring an odd number of rivets.

Say 15 rivets. The magic number for 15 rivets is 7 [(15-1)/2 = 7]

The distance for 15 rivets should be 7*2*0.375

Maybe I'm missing the point here but that's my $0.03. I threw in a penny extra with the example.

Our friend from up north deserves a prize for critical thinking.

I measured a new length of STIHL 3/8 low profile chain and 12" came out at the end of 17 drive links (34* rivets)! **

(* corrected by J.W Younger in post #22, below. It is 34 rivets including the ones on both ends. My first post, stating '33' rivets was incorrect, or at least confusing. Thanks.
** Please also see post #25, below)

Send this man some rep, and somebody submit this to Car Talk 'Puzzlers'!!

Philbert

 

[nmurph]

2) That all .375" pitch chains are actually .365" pitch and that all .375" pitch sprockets are also actually .365" pitch as well.
If that were the case why not call them what they are, .365" ?

exactly, and i don't know......

 

[MS260 Fan]

Hmmm, I've always measured the distance between any 3 consecutive rivets and divided by 2 to get the pitch. I remember reading this somewhere. Maybe even on here. I've never paid attention to the holes in the drive links. I didn't realize all chains had holes in the drive links other than for the 2 rivet holes.

Sorry MS260 Fan,

but that's a negative. The distance between the holes in the drive link are one length (slightly shorter than the pitch) and the distance between the holes in the strap are another length ( slightly longer than the pitch); when you add both of those lengths together, then divide by 2, that is the pitch.


nmurph,

That is very interesting if true. What is the source of your information that all .375" pitch chains are actually .365" ?

If indeed that is true, then it begs the question, are all .375" pitch sprockets actually .365" ? And if so, why ?

Or, if all .375" pitch chains are actually .365" pitch, and .375" pitch sprockets are actually .375", then at any given time, the sprocket is going to be putting nearly all the pressure on only one drive link. If this scenario is correct, it would surely explain why I have had these chains to break on me.

Let's just say that these .375" pitch chains (at least that's what the boxes say) that I have been using are indeed actually .365 (and from the measurements, that appears to be the case), and the sprocket I got from Baileys when I bought the chains is actually .375" pitch, then that, in my opinion anyway, would account for the chain breakage I've experience.

However, I find it hard to believe that:
1) All .375" pitch chains are actually .365" pitch and that all .375" pitch sprockets are just that, .375" pitch.

or 2) That all .375" pitch chains are actually .365" pitch and that all .375" pitch sprockets are also actually .365" pitch as well.
If that were the case why not call them what they are, .365" ?

Arky

 

[ray benson]

Do a search on this site. Many have already said- Both the regular and lo-pro 3/8" chains or .375 chain or .365 chain really have a .367 pitch.