(Note: This is Part 2 of my Chainsaw Basics Series. In Part 1 entitled ‘How Saw Chain Works‘, I went into all the terminology and the concepts of what saw chain is and how and why it works. Check out Part 1 here if you haven’t already.)
Maintenance vs. Sharpening
There is a reason I talk about chain maintenance as opposed to just “sharpening a chain”. In my experience, I have found that anyone can grab a file and scratch the teeth and come away with something that is sharper than when they started. You don’t necessarily need to even understand what you’re doing to be successful. If you don’t really understand the concepts involved, you may be able to get away with this a few times on any individual chain. That’s how I did it for my first few years. I saw other guys filing chains and I said “I can do that”, and I just grabbed a file and started going at ‘er.
The real skill however, comes with being able to take a chain through its entire lifespan, from brand new, all the way down to nothing left, and have it cut efficient and properly the entire way. That requires real knowledge of the underlying concepts. So when I say ‘sharpening’ I am referring to a single occasion where saw meets file, and when I say ‘chain maintenance’ I am referring to the series of individual sharpenings that take a chain through its entire service life.
Another thing I’ve found is that you will get the best results if the sharpening on any one chain is always done by the same person. I find that different people working on the same chain over time gives really inconsistent results.
All of the chain that you will be working on is called “round ground” which means that it is sharpened using round files. You can also maintain these chains using a machine grinder, but that is beyond the scope of this article. I have always preferred hand sharpening using files. I find that using files forces me to slow down and really focus on each individual tooth, and it requires me to fully understand how chain and cutters work. So, for learning purposes and for general skills in the field, hand sharpening is superior.
A note on files – the files that you use MUST be high quality, they DO have a lifespan, and they MUST be kept rust free. So this means, buy good quality files, preferably from a dealer; take care of them; and do not allow them to be exposed to water, because once they rust, their working days are done. And even if you take care of them, they will eventually lose their bite and need to be replaced.
For a filing kit being used in the field, I recommend having at least 2 files of each size on hand. Its the old rule of redundancy: 2 is 1, and 1 is none.
A note on file handles – like I say, files have a lifespan, they don’t last forever. So I greatly prefer a removeable type file handle such as this one, as opposed to having a bunch of regular old-school handles. This way I only need a single handle for my entire kit. You pop the file in, use it, and pop it out. This keeps my kit nice and small.
For the best results with sharpening, you are going to want a vise. At the shop, a good solid bench vise is perfect. In the field, you can use a stump vise, or a truck mounted vise, or a vise mounted to a piece of equipment. I have seen them mounted to bucket trucks and chippers, among other things. Yes, you can sharpen a saw without a vise, but it’s not nearly as easy or enjoyable.
|Bench Vise||Stump Vise|
File and Chain sizes
There are basically 3 sizes of saw that we use, and each has its own size chain which uses its own size file. I won’t get into the measurements of chain pitch and gauge here, but basically we use small saws for aerial work, such as the MS200, we use medium size brushing saws, such as the Stihl 26 or Husky 346, and then we use larger saws, like the Husky 575 with 20″ and larger bars.
So, the 3 basic sizes correspond to 3 different size files. The small chains use a 5/32″ file, the medium chains use a 3/16″ file and the largest chains use a 7/32″ file. Make sure before you start filing that you are using the proper size file for the chain!
One caveat to file sizes is with the larger chain. You can see how teeth are designed to slope backwards, so the more sharpenings they have had, the shorter they get. This is especially significant on the larger chain, which starts out using a 7/32″ file, but once it gets down around halfway, you will actually want to switch to a slightly smaller file, the 13/64″.
I find it best to think about sharpening on a tooth by tooth basis. So I’m not working on a chain per se, I’m just working on a single tooth at a time.
For each tooth, the process starts with inspection. The 2 main factors to consider when inspecting a tooth are: the corner and the chisel edge.
The corner must be very sharp for the the saw to cut efficiently. The corner is what starts the cut, and then the rest of the chisel edge carves it out. The corner is usually what gets damaged the most when a sawyer hits a nail or a stone. It can require quite a bit of filing to get back to a nice sharp corner.
The chisel edge is the leading edge of the top plate of the tooth. This is the actual cutter. This edge must be razor sharp. So the act of sharpening a tooth is the process of filing the chisel edge, which in turn sharpens the corner.
The third thing to inspect on each tooth is the raker. I personally don’t even look at the raker at all until the chain is at least half way down. Some people put way too much attention into the rakers and file them down too much, which makes the saw bite in way too hard and makes cutting very jerky.
There is one more definition that you need to know before we get into the technique of sharpening, and that is the Witness Mark. The Witness Mark shows you the proper angle to aim for when you are filing. This is one easy way to distinguish good quality chain. Cheap chains don’t always have a witness mark.
The witness mark has 2 purposes:
- by following this angle when sharpening, it sets up a good aggressive corner on each tooth, helping the chisel edge to cut efficiently.
- it allows you to get the maximum life from each tooth. Each time you sharpen a tooth, it gets a little bit smaller. Following the angle of the witness mark allows the tooth to last longer. If you were to sharpen a tooth on too steep of an angle, you would end up running out of top plate at the back before you had run out of chisel edge at the front.
The act of sharpening a tooth is the process of filing the chisel edge, which in turn sharpens the corner. It may look very simple if you’ve seen an experienced person doing it, but it is not as simple as just dragging a file over a tooth.
Now as you can see, the cutter teeth are arranged in alternating fashion, one on the left side and one on the right side. This ensures that the chain cuts evenly and straight. So with the saw in the vise, I can only sharpen the one side. When I get done working on all the cutters on the one side, then I will go back through the chain a second time, inspecting each raker and filing as necessary. I will then take the saw out of the vise and turn it around so I can work on the other side.
So, first things first, it is a good idea to wear gloves when sharpening a chain by hand. If you sharpen enough times you will eventually slip, and you can cut your hand pretty bad. Secondly, the chain must be properly tensioned before you start sharpening it. You will be applying pressure with the file – the chain tension must be sufficient to withstand that pressure and keep the tooth from moving. So, like I said, it is best to work one tooth at a time. There will usually be some teeth that need more attention than others. So it is important to really inspect each and every tooth as you go.
Taking your file, fit it into the tooth, and you will see that the chisel edge overhangs the file a little bit. This overhang is how you know that you have the correct round profile on this tooth. Your goal is to maintain this overhang of the chisel edge throughout the life of the chain, never more and never less of an overhang.
The area where I see the most confusion and the most problems is the concept of the round profile. When you are moving the file through the tooth, you are actually grinding every surface that it touches, but it is only the very top section, the chisel edge, that matters. So, to sharpen properly, you must be able to visualize where you are applying pressure with the file.
|Proper Round Profile||Proper Application of File Pressure|
Consistently applying pressure with the file in the direction shown above will ensure that your sharpening activities properly maintain the correct round profile of each tooth and will allow your chain to cut efficiently throughout its entire lifespan. Countless chains have been ruined partway through their service lives by incorrect application of pressure with the file. Some people push down too much, cutting towards the rivets. Others don’t push inwards enough, leaving the chisel edge with an improper angle, not aggressive enough to really tear into the wood.
Holding the file level, you push all the way through, trying to exactly match the angle of the witness mark. You don’t usually need to apply much pressure with each stroke if your file is good. Applying a lot of pressure takes more material off the tooth and also increases the chances of your hand slipping. With a good file, all you have to do is apply nice, steady, even pressure all the way through. I like to hold the file with both hands: the hand at the back keeps the file level and lined up with the Witness Mark while the hand at the front “pulls” the file through the tooth and applies the inwards and downwards pressure. I will explain more further on in the article about pulling vs. pushing the file when we talk about side dominance issues.
Remember, the file sharpens on the push stroke only. So, coming back, don’t drag the file on the tooth. Just return it to the starting position. If the tooth wasn’t too bad to begin with, just give it a couple swipes and then get down and inspect it. You want the corner to be absolutely sharp, and the chisel edge should be uniformly shiny and sharp.
So, the process looks like this:
- Inspect the corner and the chisel edge,
- file the tooth as necessary,
- manually advance the chain, repeat the process.
So, continue this process, tooth by tooth, until you have gone all the way around the bar. Some people will mark the starting tooth with a black marker, but I just go by colour. If the groove isn’t nice and shiny, then you haven’t sharpened that tooth yet.
Generally speaking, you are trying to keep all teeth equal size. This is not usually too big of a problem, but if you have hit something serious like a nail, it can be an issue. Sometimes you will have a few teeth with bad corners while the rest of them are not so bad. It doesn’t always make sense to file down all of the good teeth just to match the size of a few bad teeth. In those cases, I just focus on the chisel edge on the bad teeth, temporarily ignoring the corner, and over time, the good teeth will nearly “catch up” to the size of the bad teeth.
Brand New Chain
Now, this may just be me, but one thing I have noticed with most brand new chains these days is that they are actually ground with a machine profile. I think this means that the manufacturers are assuming that you will be using a machine to sharpen them, as opposed to hand filing. What this means is that the first sharpening with a round file will be as much about establishing the proper round profile as it will be about actually sharpening the chisel edge. So generally, for the first sharpening on a brand new chain, you will need to be pushing a bit harder with the file than normal.
To Recap the Sharpening Process
These are the things to pay the most attention to:
- Chisel Edge
- Round Profile (proper application of pressure on the file)
So now that you have sharpened each tooth, you can turn your attention to the rakers. As the tooth gets filed down, the chisel edge gets lower and lower, until eventually the gap between the edge of the tooth and raker disappears. At this point, the tooth will not cut, regardless of how sharp the corner and chisel edge are. The standard depth setting for rakers is about half the thickness of a dime, or .025″. Like I say, I don’t even look at the rakers until the tooth is halfway done.
The standard way to check the raker is using a depth gauge tool. The depth gauge tool usually has 2 sides, one is the standard .025″ and the other is .030″, just slightly more aggressive. In practice, you won’t notice any difference between them so it really doesn’t matter which side you use.
So you simply set the depth gauge tool flat on the chain so that the raker rests in the groove. If the raker tip is exposed above the groove, then it is time to file it down. We use a good quality flat file for the rakers, and we always go in the same direction as the filing of the cutters. Raker filing is even more subtle than tooth filing, usually just one simple stroke will do, and rarely do you need to use more than 2 strokes. Whenever you file a raker, you will also want to take notice of the profile of the front corner of that raker. It needs to stay rounded to move smoothly through the wood. So you may need to take a swipe off the front corner with your file as well.
Now in my opinion, the depth gauge tool really only has 2 uses: it is for anyone who is unsure of what they are doing, and it is for people who don’t want to bend down and actually look at each and every tooth. I don’t use a depth gauge tool because I don’t find it necessary. First of all, you don’t need to check the rakers nearly as often as many people think, and secondly, when you have looked at teeth for long enough, you start to be able to see that gap between the tooth edge and the raker. So when I am bending down to inspect the tooth, I am seeing how the raker looks at the same time, and I can tell if I need to take a swipe off of it. One additional option to check your rakers is to set your flat file along the teeth which allows you to see the gap quite easily.
When you file the raker, you will be able to see a couple of straight lines on the top of it. This is how you will be able to tell which rakers you have done.
When you file a saw, you WILL file each tooth, even if it’s just a couple swipes to freshen it up, but you may NOT need to file down every raker on the chain. Do NOT over-file your rakers, you will regret it!
So, now that you have finished all the cutters on the one side, you can set the file down, loosen the saw from the vise, and flip the saw around to do the other side of the chain. The process on the other side is exactly the same, except that everything is flipped backwards. This is where a lot of people run into difficulty because of side dominance issues. On the one side, you hold the file with the right hand, but when you flip the saw around, you have to hold the file with the left hand. So a lot of people will end up getting a different result on the one side of the chain than they do on the other.
I had to practice for years to overcome this side dominance issue but I think I pretty much have it licked by this point. My main technique for dealing with this is to use my whole body to move the file, as opposed to using just my arm. I can use just my arm on the right side but I find it much more difficult to push with just my arm on the left side. So, I basically try to lock my arm in position at my side and, bending forward at the waist, I use my whole body to move the file and basically just keep my arm stationary. The other thing that I do, as mentioned above, is I try to visualize myself as “pulling” the file, rather than “pushing” it. This way I can do things the same way on the left side as the right. These techniques have helped me to overcome the side dominance issues that are a part of filing chains, and I highly recommend that you experiment to find out what works best for you.
Well, there it is, Basic Chain Maintenance and Sharpening. I know this article is quite long-winded, but I hope you stuck around to the end and that you can get something out of it. Maintaining a chain properly takes a lot of theoretical knowledge of how chain works, and it takes a lot of practice to do it well. But it is very rewarding to be able to restore your chain at any time and have it cutting like new. It is better for your saw, and it is much better on you, the sawyer. The information in these last 2 articles took me years to understand and appreciate – I hope that I can accelerate that process for you.
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