ZoSharp, LLC

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Working with chainsaws

Aug 09 2015

            When I am out in the field sharpening or making deliveries, I get the opportunity to talk with people about many different things that we do in the shop. When asked if we sharpen saw chains, I always say yes. This will lead to questions about why chains act the way they do. Recently, I was asked why a new chain would not stay on the bar. The chain was tensioned according to the paperwork that came with it, but as soon as he squeezed the trigger on the saw the chain would fly off. The original chain would no longer cut in a straight line, so he bought another chain. He said he picked up the same size chain for the bar, but it seemed to be too tight when he took the slack out of it.
            I had him bring the saw over so I could check a few things for him. As soon as I took the chain off I realized what the problem was. Although the chain was for a 16” bar, the one that was needed was a .325 pitch, .050 gauge and 56 drive links. What we had with this chain was 3/8 pitch, .058 gauge and 56 drive links. Although this was close it was also way off. The pitch was not allowing the drive links (those nubs on the underside of the chain) to fit properly into the drive sprocket. This was causing the chain to lift around the sprocket, and not follow the groove in the bar. The gauge was only .008 larger than the original, but this was enough to make the fit in the bar groove tighter than it should be. This also caused the chain to lift instead of riding in the groove as it was designed to do. The result was the chain would drift instead of aligning into the groove allowing it to disengage the bar when running.
            Each bar size or length could have any pitch or gauge. Depending on the style of the chain, the drive links could be a give or take one or two. To explain this a little when buying spare or replacement chain, check your owner’s manual, or look up the saws model on the chart usually found where chains can be bought. It will give the three numbers that you will need. On the package there will be a picture of a cutter showing three rivets on the side of the chain. There will be a number showing the pitch. The pitch is the measurement from the center of the first rivet to the center of the third rivet divided by two. The nest will be a picture of the drive link. It will give the width of the link that rides in the groove of the bar. The last number will be the numbers of those drive links within the chain loop.

            I still looked a little deeper into the problem, as running this may have caused some damage to the bar or drive sprocket. In this case he did not run it long enough to damage the bar groove or wear the drive sprocket excessively. So putting the right size chain on was all that was needed. Had the bar been damaged, he would have had to replace that one as well. When the sprocket gets damaged then it is finding the right size (pitch), and replacing it. If you can’t do it yourself it can get costly taking it in. As we do not do small engine repair, anything other than taking a chain off and putting the next one on is all we will do. The other repair would have had to be done elsewhere.

            Since he was getting his original chain sharpened, I was able to get him back cutting in a few minutes. He did need to pick up another chain as a backup for the original. Once he learned the difference in chain sizes, he understood what the problem was, and was able to find the correct chain for his saw.

            With the way the chain kept coming off while the saw was running, this could have been a very bad situation for this person. The chain could have wrapped around his leg or arm instead of just coming off. Sometimes we get lucky when things go wrong.

            Stay safe with your cutting tools, and until next time happy cutting.

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