Guide Bar Maintenance
The guide bar on every pro saw lives a tough life. First, it supports a saw chain zinging around it at over fifty miles-per-hour. Second, the bar often finds itself inserted in cuts that twist, bend, and pinch. So a pro saw user needs to know how to inspect a bar for both wear and damage -- and he needs to know what to do when he finds either.
Inspecting For Wear
The body of most guide bars wears in two places: On top side of the bar rails and on the surfaces inside the rails. Since the tops of the rails are easy to see and the inside surfaces hard to see, start your inspection by looking at the tops. Pay special attention to the area just behind the bar nose. This is the location where the rails often show the most wear. Saw operators who do a lot of limbing will notice pronounced wear here, because for them, this area of the bar does the most work. Also look for chipping or any other type of rail damage.
Notice the flattened area developing behind the closest sprocket point. This is still a useable nose, but it is showing wear.
Notice the flattened area that is developing in the area behind the oil hole.You can also see some wire edges developing in the same area.
If the nose area of the bar looks good, inspect the rails on the bar's heel. Can you see evidence of excessive wear? It is also a good idea turn the bar so you can view its profile at the heel. A worn bar will have a narrow tail. If it looks like the tail is getting narrow, a good way to determine how much wear is in the heel is to compare in to a new bar. Lay a worn bar on top of a new bar. This will show you how much material has worn away.
Next, look at the depth of the bar groove. A bar heel with a lot of wear may have shallow rails. In extreme cases, the groove will get so shallow, you may see where the chain's drive links have rubbed in the bottom of the groove. If you find this at any location on the bar, your inspection is over. The bar is worn out and needs to be replaced.
If the bar has passed it's inspection so far, next test the bar's inside rails. These are hard to see, but there is a simple method to determine the amount of wear on them: With the chain on the bar, hold a straight edge against both the bar body and a cutter tooth's side plate. Good side rails will hold the chain straight, causing a small gap between the straightedge and the bar's body. If the groove is worn, the chain will lean. With enough lean, there will be no gap between the straightedge and the bar's body. If you find the latter, the inside rails are worn out and the bar needs to be replaced.
A good bar rail will hold a straightedge away from the bar body. Worn bar rails will not. This is a good test to determine how much wear is in the rails and if the bar is still serviceable..
If you were to cut a new bar in half, you would see the groove is “U” shaped. The opposing surfaces inside the rails are parallel with each other. During use, the chain’s drive links rub against these “walls,” causing wear. Bars tend to wear fastest in the top of the groove, slowly turning what was once a “U” shaped groove into a looser “V” shape.
Grinding The Bar Rails
Usually the tops of both bar rails wear at the same rate, but not always. Some cutting, like the bias cuts you make when putting an under-cut in a tree puts more pressure on one bar rail than the other. Over time this can cause extra wear on one rail. When this occurs, the chain will not sit square on the bar. The fix for this is to grind the tops of the rails with a special grinder to even the rail height and make the rails perpendicular (90º) to the side of the bar. .
While grinding the bar rails makes the rails perpendicular again, it is a sign a bar is nearing the end of its working life.
What to Do with Wire-Like Edges
During your inspection, you may notice a wire-like edge on the outside of the bar rails. Be careful, these edges can be sharp. If you have a fine-tooth flat file, use it to remove these edges. A burr on the side of the bar causes drag in a cut. Another reason to remove wire-edges is to minimize chipping. A wire-edge left on the bar eventually breaks off, but sometimes it takes good rail material along with it. Removing the edge before it breaks off prevents this.
Sharp edges on the side of the bar should be removed with a fine-toothed file or with a disc sander.
If you have an electric or pneumatic disc sander, you may use it instead of a file to remove the wire-like edge. If you do, remember to sand with the head spinning in the direction that sends debris away from the bar. If you sand with the disc traveling towards the bar, you will send little pieces of abrasive grit and steel into the bar groove. Once you put the bar and chain back on the saw, any abrasive that remains in the groove will damage the inside of the rails. Abrasive that finds its way into the bar nose bearing is also harmful.
Is The Machining Plug Is In Place?
There should be a small aluminum plug in the machining hole near the bar tip. This plug fills a small “blanked” hole that was originally used to hold the end of the bar during manufacturing. If this plug falls out, the hole tends to collect chips. Almost no one checks this. You wouldn't think loosing this plug would make much difference, but surprisingly, when the plug is missing, the tip will hang up in the cut. Few saw users realize how important this plug is. If you need a replacement plug, contact us, we've got some extras.
The machining plug is missing from this bar. When this plug is gone, chips will get in the hole making it more difficult for the bar to slide through the cut.
Bar Groove and Oil Hole Cleaning
Any time you inspect a guide bar, take a minute to clean the wood chips from the center of the rails and make sure the oil hole is open. This can be done with a groove cleaner or even a pocket knife. Having clean bar rails will allow oil to easily move down the bar. This is good for both rail and tip lubrication.
In our shop, we observe that saws used by operators who hand file their chain tend to have more problems with plugged oil holes and dirty bar rails than those who sharpen with a grinder. The reason for this is they do not remove the chain from their saw very often. Even if you don't remove your chain to sharpen it, occasionally remove it to clean the bar groove and oil hole.
How to Tell if Your Chain Tension Has Been Too Low
Many pro saw users don't run enough chain tension. Most think that if they aren't throwing chains, their tension is OK. This is only partially true. If you find your bar has excess wear on its heel and in the area behind its nose, this may be a sign you are running your chain too loose.
This photo is courtesy of the engineers at Oregon Cutting Systems and shows why low chain tension causes excess wear on the bar's heel.
Without adequate tension, the chain does not pull itself straight after it rounds the tip or drive sprocket. This puts the job of reorienting the chain on the bar's rails right behind the bar nose and heel. As a result, both areas will see increased wear. But, don't go overboard with too much tension. Too much will damage the chain, bar tip, and the saw engine's main bearings.
How to Minimize Chain Throwing on a Worn Bar
If the bar you are using has significant heel wear, your saw probably has a tendency to "throw" its chain. If you have wondered why this occurs even with plenty of chain tension, here is what happens. If you compare a worn bar to a new bar, you will notice the warn bar has a much narrower heel. This loss of rail height in the heel area increases the distance your chain travels out of the groove when it rounds the sprocket. The greater this distance is, the more unstable the chain is and the easier it derails.
The obvious solution here is to replace the bar, but if it still has working life try running a “shorter” chain. What this means is, run the heel of the bar as close to the sprocket as you can. If your chain has stretched some, don't wait until you are at the end of the bar adjuster's travel to remove a link. Remove a link just as soon as you can run a shorter chain. This is actually the best practice with all bars, new or old.
How to Extend Rail Life
A simple way to extend the rail life on a guide bar is to rotate it. Whenever you change chains or at some regular interval, remove the bar and put it on upside down. Don’t worry that the logo painted on the bar is upside down. Rails wear faster on the bottom where cutting pressure is, so rotating the bar spreads wear to both sides evenly. You rotate the tires on your truck for the same reason.
How To Inspect A Bar for Damage
Experienced saw operators don't bend bars often, but every pro user will occasionally have their saw's bar in the wrong place at the right time. It can't be avoided. So when a bar experiences “tree trauma,” stop and inspect it. Sometimes it is easy to see it is OK, and you can go on cutting. Other times it is necessary to stoop and take a good look.
To inspect a guide bar for damage, first remove it from the saw. Wipe away any sawdust or debris and look for anything obvious. If all the surfaces look good, hold it level with your eye and look down the rails as if they were a site on a gun. This can be done from either end of the bar. If your bar is bent, you will see sweeps or bends in its body. If you have never looked at a bar from this angle before, you will be surprised how visible even a slight bend is.
To check how straight a bar is, look down it like you would the site on a rifle. From this perspective you can easily determine if your bar is straight or not.
We straighten bent bars in a press. After locating a bend, we work it out slowly.
If you find the bar is bent, take a close look at the bar rails in the bend area. If the bend is abrupt, the rails will probably be cracked. If you find cracked rails, don't spend time trying to straighten the bar. It's ruined.
If the rails are not cracked, try straightening the bar. After, locating the bend, gently bend it in the opposite direction, working the bend out slowly. We do this in a press, but some pro users make a cut in a stump and use this as a holding device. This sounds crude, but some users get surprisingly good results this way.
If the bar is straight, next look for pinched rails. If you find them, repair the damage immediately. Even the slightest pinch will cause a “hot spot” in the rails if you try to run it this way. Hot spots change the temper in the bar's steel, doing permanent damage. To open pinched rails, mount the bar in a vice and gently tap on the bent rail with a hammer and punch. A flat-blade screwdriver is another tool that can be useful for prying open bent bar rails. Once you've got the pinch worked out, test your repair by placing the chain back in the groove. Make sure the chain easily slides past the repair. If it doesn't there may be some burrs inside the rails left from the damage or repair. In our shop, we use a small die grinder with a thin abrasive disk to remove these.
If you site down the bar and find one side is bent more than the other, the bar is twisted. Twisted bars are difficult to straighten and should probably be replaced. And this brings up another important note; most bars can be repaired, but repair may not be your best option. If you decide to take your bent bar to a saw shop, ask what the repair will cost before you authorize it. If the cost approaches half the price of a new bar, consider replacing the bar. Remember, saw shops charge for their labor. Since bars are a low profit item, a shop may make more money on a repair than they would selling you a new bar. Most shops will do what's best for the customer, but not all. Whatever option you choose, make sure you are getting the best value.
What to Do if a Saw Won’t Cut Straight
Logic has it that when a saw won't cut straight, the bar is probably the problem. It is reasonable to assume the bar is not doing a good job of "guiding" the chain. While this can occur, it is rare. The fact is, most of the time when a saw won’t cut straight, it is a chain problem.
A gentle or slight bend in a bar will not affect a saws ability to make a straight cut as much as you'd think. We are not advocating that you run a worn or bent bar. Just know that a “less-than-perfect” bar will perform as well as a “rifle-straight” bar when fitted with a good chain. So, when you are having problems with a saw not cutting straight, take a good look at the chain. More times than not, that is the problem.
• Stop and inspect your bar after an accident. If the rails are damaged, repair the pinch before running the bar again. Pinches cause hot spots, which ruin bar rails.
• Regularly rotate the bar to spread rail wear to both top and bottom rails.
• A bar that is twisted or has cracked rails should be replaced. Repairing this damage is too expensive to be worthwhile.
• If you scrap a damaged bar, don't forget to salvage the tip. You can always use it on another bar.
• Too little chain tension causes excess wear on the bar's heel and behind the bar nose.
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