Thread: Broken 3/8th chain

Originally Posted by timbertalk

I recently changed to 3/8th chain on a chainsaw mill (4 ft bar) to reduce the kerf loss and the chain broke while milling a 600mm sally wattle. Was I just unlucky or is 404 necessary? At one point I was considering 325 chain to reduce kerf further, but maybe not strong enough?? Any similar experiences?

I use 3/8 up to 5ft bar no problems.

Take the following close up photos,
- break in the chain.
- drive links before and after the break
- the drive sockets in the drive sprocket
And we'll have more of a chance of diagnosing your problem.
Also we'll need to know what CS you were using and how long you had been using the chain for.

had the chain been sharpend?

my lucas and all the others run 3/8 on 1.5m bars no problem.

how about teh pic of the broken link/s

Unfortunately too late for pics of the chain, but I can tell you the following:

• Chainsaw Stihl 084
• Skiptooth chain
• Chain had done no more than one hour full use
• Broken part was a pin (sheared in the middle), but it was MY joint and I had hammered the pin (I made the chain up).
• The angle on the cutters is 30-odd degrees

Maybe I did something wrong at the joint, or maybe its because I still have 30 degree cutters? The drive sproket was slightly older than the chain, but in good wear.

Originally Posted by timbertalk

Unfortunately too late for pics of the chain, but I can tell you the following:

• Chainsaw Stihl 084
• Skiptooth chain
• Chain had done no more than one hour full use
• Broken part was a pin (sheared in the middle), but it was MY joint and I had hammered the pin (I made the chain up).
• The angle on the cutters is 30-odd degrees

Maybe I did something wrong at the joint, or maybe its because I still have 30 degree cutters? The drive sproket was slightly older than the chain, but in good wear.

I have cut ~ 20 wide slabs with 30º angle cutters and they do chatter and vibrate a lot more than lower angle cutters because 30º cutters put a lot of sideways force on the cutters. The fact that it broke at your join is pretty telling so combining the two are probably enough to explain what happened. I would get a decent spinner and try again.

Cheers

Sounds like the join. Cheers MM

Originally Posted by weisyboy

my lucas and all the others run 3/8 on 1.5m bars no problem.

Carl, that's not right, yours might run on 3/8 chain but not all the other lucas slabbers. Lucas manual clearly states 404 chain for slabbing attachments and dedicated slabbers. So every new Lucas slabber will have 404 and mine still does...

i stand corrected i got a 3/8 chian to run on mine but checked teh manual and it has gor 27r witch is 404.

One more question for timbertalk. How many times had you stopped to re-tension the chain in that first use first hour? With new 3/8 chain on a 5ft bar I run about a 1/2 slab, retension, after the whole slab retension, in that first hours I may retension 5/6 times. Only then does it settle. If I don't do that hardwood the chain can easily come off the bar. If it comes off at speed and the chain stays on the sprocket a weak pin could easily breaj. I'd say you cracked the pin when hammering the top. That's why spinning is better than hammering.

Some of you may be interested in some temp measurements using an infrared detector and here is what I found. Excuse me for the inches and F but I researched this for the American site

On a 65F (18°) day a well lubed freshly sharpened chain chain reached ~120F (49°) in softwood and 175 F (80°) in hardwood. If the chain is blunt, lube is poor/limited or a zillion other things the temps will be higher. A 100F (38°) temp rise estimate is pretty reasonable.

I have measured the chain reaching a steady temp under steady cutting in about one minute while the bar takes about 10 minutes to reach a steady temp. This explains why the chain can appear to be very loose very quickly and why it should not be hard tightened , after just one minute of running as the still thermally expanding bar acting on an already thermally expanded chain will just stretch it even further.

After about a minute of running the bar will still be cool and not have expanded much but the chain will have expanded to
2 (chain is twice as long as bar) x 0.018" (0.5mm)= 0.036" (1mm) for a 3 ft (900mm) bar and 0.06" (0.15mm) for a 5 ft (1500mm) bar

This does not sound like much but if you use a simple pythagorean model to calculate chain droop (see "x" in the diagram= SQRT(30.06^2-30^3) for a 5ft bar) from the bar the droop is around 0.6" (0.15mm) for a 18" (450mm) bar, 1.1" (28mm) for a 3 ft (900mm) bar, and 1.9" (48mm) for a 5" (1500mm) bar!

Doubling the temp difference will not double the droop but increase it to 2.7" (69mm) for a 5 ft (1500mm) bar but it's still easy to see why a blunt chain contributes to why chains come off especially in that first few minutes after it goes blunt from hitting something etc.

Now something else to watch out for when adjusting.
The bar is typically 10-15 F (-12° to -9°) cooler than the chain but the bar takes 10 minutes to cool down whereas the chain cools down in about a minute. This means if you stop the saw to adjust the tension you should do it asap or else the chain will shrink and you won't get the tension right.

• Broken part was a pin (sheared in the middle), but it was MY joint and I had hammered the pin (I made the chain up).

Maybe you locked up the link with the hammering, This will cause the chain to fail.

Also remember that the weakest part of the chain is the drive link at the rivet hole so it doesn't matter whether you are using 3/8 or 404 x 63 chain.

The lighter gauge chains are more likely to fail than the .063

Laurie

Thanks guys for the information and shared experiences. The longer bars seem to add a lot of extra considerations - thermal expansion, huge loads on each link, and no room for error with lubrication, chain tension etc. I did not tension my chain frequently in its first hour - I checked it at the completion of each slab, but can't remember how may times it was tensioned. I am confident that it did not come off the bar however. The chain was not super sharp - it had cut at least 3 slabs since last sharpened, so maybe extra load there. I will buy a spinner and try that for joints in future. When I hammered the joint I did test for free movement in the joint when I was done, and all was good. I might also bring the cutter angle back to 10 degrees or so and see how that goes. In terms of heat, I heard of someone dripping WATER onto the chain at the bar tip, not oil, just to keep things cool. I do not have anything atmy bar tip. I am soon setting up a 5.5 ft bar and want to get all this right for it. Sawchain, are you saying that the pins are the same on 3/8th and 404 chain? Ken

Originally Posted by timbertalk

In terms of heat, I heard of someone dripping WATER onto the chain at the bar tip, not oil, just to keep things cool.

Hi Ken, I have experimented with water cooling a fair bit and there is a one thread here on the setups. I am not convinced it's as good as using an auxiliary oiler. the water seems to wash the oil off the chain more than I like. I rather spend $5 a day on a bottle of Coles 2L canola for the aux oiler than use water. It keeps the chain clean and cool. I still use regular bar oil in the saw.

BobL, you didn't happen to do some bar and chain temperature comparisons with and without water did you?? The oil itself does a lot to keep things cool, simply by reducing friction. I remember how hot the bar/chain got when my oiler died

Originally Posted by timbertalk

BobL, you didn't happen to do some bar and chain temperature comparisons with and without water did you?? The oil itself does a lot to keep things cool, simply by reducing friction. I remember how hot the bar/chain got when my oiler died

Bar and chain temps depend on water flow. If you run enough water the bar and chain stay more or less at the water temperature. However at that rate I reckon too much oil is washed off.

This was about the water flow rate I was using. Sort of drops rather than spray.


I prefer a good oil flow over the water - I think there is generally less bar and chain wear using oil than water