Chain pitch mystery (somebody please enlighten me)

[Arky217]

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

I measured a length of STIHL 3/8 low profile chain and 12" came out at the end of 17 drive links (33 rivets)!

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

Philbert


Philbert

Philbert,

If what nmurph says is true ( all .375" chains are actually .365"), then your measurement, if you measured accurately, would be approximately 11 & 13/16" rather than 12".
(.365" * 2 * 16 = 11.68")
However, if you measured that chain accurately, and got exactly 12", then that is one .375" pitch chain that is indeed .375" pitch.

I can understand my Stihl 63PMX being .365" even though its box says (3/8"), since that is also like the low profile chain that Baileys sells is marked.

However, until I get a chance to measure some other full size .375" pitch chains other than this Woodsman Pro 33RP, I'll have to reserve my opinion that all .375" pitch chains are really .365". If, like I said, you measured accurately, you have proved that they aren't, at least not that one.

Arky

 

[J.W Younger]

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

I measured a length of STIHL 3/8 low profile chain and 12" came out at the end of 17 drive links (33 rivets)!

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

Philbert


Philbert

I just measured both(new) same here.91v 33 72lg 33 that not counting 1st rivet.

 

[J.W Younger]

Heres the deal, i think. The low pro ripping chain should have the full size drive tangs. If it does it should work. If it has the smaller drive tangs it wont fit the nose sprocket.

 

[Arky217]

Ok, I did some searching on earlier posts, ( which is what I should have done to start with, but who would have guessed that manufacturers would state a dimension to the thousands of an inch and the actual measurement be .007 difference ?); it appears that those who have researched this subject have discovered that there is no such thing as a .365" pitch or a .375" pitch, but that both those stated pitches are really an actual .3669" pitch.

This explains the chains that I have measured, and I can only assume that the sprockets for those chains are also .3669" pitch.
But that could be just that, an assumption; anyone know for sure ?

One last thing, the stated .325" pitch on my Stihl 26RS actually appears to measure .325". So, some sizes appear to be as stated and some not. Is there any rhyme or reason to all this ?

Arky

 

[Philbert]

I Stand Corrected (and Confused)

Had to run after my last post, and went back down to re-measure the chain.

12 inches does fall on the 34th rivet (counting the first one), depending upon which rivet you start from (front rivet or back rivet of the drive link)! My 12 inch measurement included an extra drive link, and not a complete drive link/tie strap pair.

Shifting the ruler over 1 rivet, 12 inches fell at 33-1/2 rivets (again, counting the first rivet). This is consistent with Arky217's original statement that they are actually a bit less than 3/8 inches.

Philbert

 

[Fish]

In my shop in Lawrenceburg, I had a chart that you could lay the chain
across and quickly count the drive links when making chains.

The 3/8 and the 3/8 lo pro were the same lengthwise.
The last shop I worked at had a similar chart, it only had 1/4, .325, 3/8,
.404, you used the 3/8 silhouette for both chains.


The microscopic accuracy of the measurement I have never explored.



That does not mean you can use the chains interchangeably though.

 

[SawTroll]

....

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.

....

All 3/8" chain should be .367 pitch when new, so this is no mystery!

3/8", .375 and .365 is just "names", not reality.

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

Close!

 

[ray benson]

This picture is off the stihl site. Doing the metric conversions
6.35mm= .25"
9.32mm= .3669"
8.25mm= .3248"
10.26mm= .4039"

 

[Philbert]

All 3/8" chain should be .367 pitch when new, so this is no mystery! . . . 3/8", .375 and .365 is just "names", not reality. Close!

(Maybe rulers weren't so good when standards for chain saws were first established . . . ?)


(Philbert)

 

[Fish]

(Maybe rulers weren't so good when standards for chain saws were first established . . . ?)


(Philbert)

Hitler/Mussolini?

 

[Brmorgan]

Something's drastically wrong... I've logged many hours milling with 3/8 low-pro on a standard .050 bar and standard 8-pin rim sprocket on an 066 and never once had one break on me. Yes, it stretches quite a bit more than standard 3/8 but has never broken or derailed (yet). Of course I'm dealing with softwoods most of the time. Is it getting enough oil when milling? Also how long of a bar are you trying to run the low-pro on? I probably wouldn't recommend it over 30" or so at the very most.

 

[SawTroll]

This picture is off the stihl site. Doing the metric conversions
6.35mm= .25"
9.32mm= .3669"
8.25mm= .3248"
10.26mm= .4039"
....

Good info as usual from you!

...and it confirms what I said....

 

[Philbert]

Hitler/Mussolini?

Actually, I was thinking more like hand-made marks on wooden sticks that moved with the humidity, but good to have you, Fish, to keep me on my toes.

Philbert

 

[Fish]

Actually, I was thinking more like hand-made marks on wooden sticks that moved with the humidity, but good to have you, Fish, to keep me on my toes.

Philbert

Some of the folk here may be on the electron microscope level..........

 

[Arky217]

Something's drastically wrong... I've logged many hours milling with 3/8 low-pro on a standard .050 bar and standard 8-pin rim sprocket on an 066 and never once had one break on me. Yes, it stretches quite a bit more than standard 3/8 but has never broken or derailed (yet). Of course I'm dealing with softwoods most of the time. Is it getting enough oil when milling? Also how long of a bar are you trying to run the low-pro on? I probably wouldn't recommend it over 30" or so at the very most.

Brmorgan,

Yes, I agree that something seems to be amiss, causing the chain breakage that I have been experiencing; I just wish that I knew what it is.

I started with a 20" Forester bar and two Stihl 63PMX chains; both came with the Logosol mill. The first chain broke after quite a bit of milling, repaired it, and it broke again not long thereafter. Same story on the second chain. I kept the rakers at .025"; I think that's what they came at. I kept the chain sharp at all times. The oil feed is turned all the way up and it uses probably 3/4+ of the oil tank to a tank of fuel. The trees have all been SYP, the shortleaf variety.

After breaking those two chains twice each, I chalked it up to them being .050" gage and low profile.
So, I got a new 3/8" roller nose, .063" gage Oregon Power Match Plus 24" long bar from Baileys. Along with it I got a new 3/8" pitch, 7 pin sprocket (the first sprocket was 7 pin as well), and (2) 33RP Woodsman Pro milling chains.
Pretty much the same story on the first 33RP chain. Milled quite a bit with it before it broke; repaired it, milled about half that much before it broke again. Now on the second 33RP chain; it hasn't broke yet. All total since I got the mill, I've milled about 7000 bf. Over half of that was with the Stihl 63PMX chains.

On all the chains, I kept the 10 degree top angle, but on the 33RP chains, I started out with two changes.
I gave the top edge a sharper hook, probably some where around 50 degrees, and I put the rakers at .030".
I did the rakers first; don't know if I noticed that much difference in the cut. But when I gave a sharper hook to the top edge, I noticed a significant increase in the speed of the cut.

This last 33RP chain is cutting very well (as did all the chains), but I'm concerned that it also might break, so I have got on order two milling chains from Madsens, the Oregon 75RD.

The salesman at Madsens asked me who made the Woodsman Pro; I told him that I didn't know. He claims that if it is made by Winsor or Carlton, it would stretch a lot. Of course, he says the Oregon is a better chain. I have no idea about that (not yet anyway), but it ought to be, according to the price. It's $25 versus $16.80 for the Woodsman Pro. Anyway, I guess I'll find out.

I intend to start out with the Oregon chains with whatever raker height they come with ( I imagine it will be about .025") and also give them a slightly more hook to the top edge.
Hopefully they will be a tougher chain and won't break.
If they do, I don't know just what I'll do then (there's always the .404" pitch, I suppose).

Will entertain any ideas on why I've broken these chains.

Thanks,
Arky

 

[Fish]

Brmorgan,

Yes, I agree that something seems to be amiss, causing the chain breakage that I have been experiencing; I just wish that I knew what it is.

I started with a 20" Forester bar and two Stihl 63PMX chains; both came with the Logosol mill. The first chain broke after quite a bit of milling, repaired it, and it broke again not long thereafter. Same story on the second chain. I kept the rakers at .025"; I think that's what they came at. I kept the chain sharp at all times. The oil feed is turned all the way up and it uses probably 3/4+ of the oil tank to a tank of fuel. The trees have all been SYP, the shortleaf variety.

After breaking those two chains twice each, I chalked it up to them being .050" gage and low profile.
So, I got a new 3/8" roller nose, .063" gage Oregon Power Match Plus 24" long bar from Baileys. Along with it I got a new 3/8" pitch, 7 pin sprocket (the first sprocket was 7 pin as well), and (2) 33RP Woodsman Pro milling chains.
Pretty much the same story on the first 33RP chain. Milled quite a bit with it before it broke; repaired it, milled about half that much before it broke again. Now on the second 33RP chain; it hasn't broke yet. All total since I got the mill, I've milled about 7000 bf. Over half of that was with the Stihl 63PMX chains.

On all the chains, I kept the 10 degree top angle, but on the 33RP chains, I started out with two changes.
I gave the top edge a sharper hook, probably some where around 50 degrees, and I put the rakers at .030".
I did the rakers first; don't know if I noticed that much difference in the cut. But when I gave a sharper hook to the top edge, I noticed a significant increase in the speed of the cut.

This last 33RP chain is cutting very well (as did all the chains), but I'm concerned that it also might break, so I have got on order two milling chains from Madsens, the Oregon 75RD.

The salesman at Madsens asked me who made the Woodsman Pro; I told him that I didn't know. He claims that if it is made by Winsor or Carlton, it would stretch a lot. Of course, he says the Oregon is a better chain. I have no idea about that (not yet anyway), but it ought to be, according to the price. It's $25 versus $16.80 for the Woodsman Pro. Anyway, I guess I'll find out.

I intend to start out with the Oregon chains with whatever raker height they come with ( I imagine it will be about .025") and also give them a slightly more hook to the top edge.
Hopefully they will be a tougher chain and won't break.
If they do, I don't know just what I'll do then (there's always the .404" pitch, I suppose).

Will entertain any ideas on why I've broken these chains.

Thanks,
Arky

Post some pics, and we will entertain you.......

 

[Arky217]

Post some pics, and we will entertain you.......

Fish,

If you mean pics of the broken chains, I don't have any at the moment, but I can say that they all broke out the narrow rear edge of the rivet hole of a drive link.

Thanks,
Arky

 

[nmurph]

All 3/8" chain should be .367 pitch when new, so this is no mystery!

3/8", .375 and .365 is just "names", not reality.




Close!

thank you sensei. lets not quibble about 2 thousandths of an inch!!!

 

[Brmorgan]

Well if not the drive sprocket, normally I'd say first look for a worn bar nose sprocket (or perhaps one with a tooth missing); failing that perhaps a bent bar - but from your story those can't be the case (and since you're milling you'd have noticed many other problems from a bent bar, I'd imagine). I can't believe you're snapping .063 chains that easily though. Have you tried a different drive sprocket just for kicks? I know that sometimes one might not look too badly worn, but sprockets and chains tend to wear to "fit" each other, and sometimes throwing a brand-new chain on a worn sprocket can put excess tension on the drivers. It might not be enough to break the chain under "average" use, but milling puts a LOT more stress on the chain than regular felling/bucking operations. Other than that you might want to check your chain tension - you should just be able to pull the drivers' tips out of the bar rail with fairly light pressure. You should be able to pull it along the bar easily too, but you don't want any sag. Too much tension can cause premature wear of the sprocket and chain quite quickly, including stretching, and the increased workload of milling compounds the effect even more.


Given that the wood you're milling is rather soft pine, you can definitely stand to give the cutters a bit of a sharper hook and take the rakers down a bit on the low-pro especially. The softer wood won't dull the thin cutter edge nearly as quick as it will in hardwoods, especially if you take care to not run it through dirty bark etc. I run my low-pro setup with a fairly deep gullet and aggressive hook (never really measured with a protractor though, just set with a file guide) and set the rakers around .035 - .040. With the 8-pin rim in wood up to 16" wide, it just flies through the Spruce/Pine/D. Fir I usually cut, and the odd green birch log which is just as soft as the softwoods. The only other setup I've used that's faster for slabbing cants is .325 9-pin full-chisel left at 25° - it's a bit grabbier and tougher to control, but the cut is just as smooth in my experience, as long as you don't bog the engine down, due to the extra cutters.