How to Sharpen Wood Band Saws Correctly
How to sharpen a band saw so that it saws up to 100 cubic meters!
In previous publications, we started talking about the specifics of the acquisition and subsequent operation of sawmills, tape-dividing machines for moldings and band-sawing machines for furniture enterprises. We elaborated on the consideration of the classical method, in which the grinding of teeth is carried out by the grinding wheel. And reflected two factors that affect the quality of sharpening. technical and instrumental. The third factor, the last in the list, but the main one in fact, is the human factor.
When choosing a person to work as a sharpener, first of all pay attention to his character. A hot, explosive person, trying to make everything quickly, will never become a good sharpener. Here you need a calm, attentive, assiduous, responsible person, capable of long-term monotonous work. But even this is not enough. Good sharpeners are obtained only from those who can literally feel the saw and only by hearing set up the grinding machine. No wonder the people say that a good sharpener must be born. And indeed it is. Since it is simply mechanically good to sharpen a band saw in this way for the reasons stated above and below it is practically impossible.
Now we show what exactly the sharpener needs to do in the process of work.
The sharpening process must begin with an inspection of the machine:
- It is necessary to check the alignment of the grinding wheel and the plane of the band saw so that they are strictly perpendicular. Otherwise, the tooth will be sharpened sideways.
- Set the grinding wheel to the desired angle relative to the plane of the saw, that is, set the front angle of the tooth along the limbs of your machine. Since these limbs never correspond to reality, having turned a saw, check with a goniometer the obtained real angle. If it does not suit you, slightly change the angle setting in the necessary direction. Cut the saw again and check the resulting angle. And so on until you get the necessary angle. It is advisable to do this with great hardness so that during installation the circle does not lose its shape. Otherwise, you will have to edit it and thereby bring down the presets. After you get the necessary angle on the saw, make a note of the risk on the machine. Then it will come in handy for new reinstallations to other angles.
- All moving parts should have minimal backlash, and it is better that they do not exist at all, otherwise the tooth profile and the grinding wheel will be broken up more quickly.
- Coolant must be supplied in such a way that the entire sharpened tooth is washed, otherwise the part of the tooth that the liquid does not enter will be set on fire.
- The grinding wheel should be set to the right size and sufficient hardness so that its profile does not change at least one full passage, otherwise the saw along the entire length will have a different tooth profile.
- During sharpening, you cannot change the adjustment of the grinding wheel until a full passage has been machined, otherwise a different profile will be obtained at the transition points and during subsequent passes the circle will either burn the profile or pass without touching it.
The grinding wheel is adjusted with two screws:
- a pusher screw that regulates cutting along the leading edge and the passage of the tooth profile;
- depth adjusting screw.
After preparing the grinding wheel, install the band saw and, scrolling the circle by hand or at minimum feed, check how accurately it goes along the profile. If necessary, re-profile the circle.
After completion of work, it is necessary to clean the saw clamping mechanism and the coolant tray from dirt, metal filings and rust; check fluid level and add if necessary; wipe the entire machine.
The main reason for incorrect sharpening a band saw is the loss of its shape by the grinding wheel.
If the technical problem can be solved with the help of high-quality manufacturing of the machine itself (for example, Vollmer produces very good machines), if the tool problem can somehow be solved by choosing the right grinding wheel, then the problem of forming the profile of the grinding wheel cannot be solved even theoretically.
Only very experienced sharpeners or people with an inner instinct can come close to understanding and maximally accurately profiling the end face of the grinding wheel. I will explain this with an example. Draw a horizontal line on a piece of paper. Now from this line to the right side of the eye, draw two vertical lines: one at an angle of 10 °, and the second through 3 mm at an angle of 40 °. Now connect the left fishing line with a horizontal line through a radius of 1.5 mm, and the right fishing line through a radius of 1-2 mm. Do this several times and check with a protractor what happened. For clarity, these sheets can be combined. Note that only a 0.5 ° difference in data already leads to inaccurate profile drilling. And the inaccurate connection of the left straight line also leads to a change in the pitch of the saw. Now imagine that the sharpener should not do all this on paper, but on a rotating circle, where it’s even more difficult to sustain the exact dimensions. But it is not enough to form it once. It is necessary that during repeated sharpening after sawing, the profile of the end face of the circle should be exactly the same as with the previous sharpening, which is practically impossible. Therefore, it is not so important what quality you grind around. Even if you have a very good circle and you can grind a set of band saws for a whole shift without additional profiling, you will almost never be able to repeat exactly the same profile of the end face of the circle at the next sharpening, which means you will not be able to precisely grind the profile of the teeth of the saw after her dullness. Now you understand why the exact formation of the end face of the circle profile is not just a difficult, but an extremely difficult task. In order to somehow facilitate its solution, it is possible to sharpen with bakelite reinforced circles 3-4 mm thick. But it is difficult to find the right workmanship.
Therefore, the profile of the circle must be monitored very carefully. Otherwise, this leads to the following changes in the body of the band saw:
- A change in the radius at the base of the tooth, which entails a change in pitch and the impossibility of already on the next pass of the normal sharpening of the saw. The circle begins to unevenly cut into the front face, without touching the back, or vice versa, that is, it becomes impossible to grind the full profile of the saw immediately. The grinder already in two or three passes tries to pierce at least the cutting edges of the teeth, while a microhump or microcavity appears at the transition point, which leads to microcracks, and microcracks that have already arisen during sawing are not removed, which leads to premature saw breaking in the body.
- Changes in the angle of sharpening, the height of the tooth, the shape of the cavity, which affect the performance of the sawmill and the quality of the resulting lumber.
The grinding wheel should be as shown in fig. 1a. Thickness. 5-8 mm. But in practice, working with such a profile is very difficult. We recommend using circles with a profile, as in fig. 1b. Thickness. 3-4 mm. Then the sharpener will not need to very often form the profile of the grinding wheel, but only occasionally slightly correct it. This greatly simplifies the work of the sharpener.
As will be shown below, only 3-4 mm of the grinding wheel thickness can participate in the grinding process. thickness is needed only if you have the perfect machine. But this does not exist in nature. And also if you want to sharpen at accelerated feeds of the tooth, then the circle will not bend and bend. But at the same time, you are almost guaranteed to receive major risks and burns, and thereby greatly shorten the life of the saw, and you can hardly cut it well. The cutting time of one whole passage of a band saw 4 meters long should be 10-15 minutes. At a minimum, two passes are needed: the first is sharpening, the second is finishing for taking scans.
In practice, it is rarely possible to grind a saw well in one pass. often, two or three are needed. So, if the sharpener now tells you that he will bring the sharpened saw in 15 minutes, you can imagine what quality it will be.
Possible violations of the shape of the end face of the grinding wheel and the resulting saw tooth profile are shown in Fig. 2.
Under numbers 1-7, the red dotted line shows the model profile, the solid line shows the resulting profile.
- The correct shape of the end face is an ideal version of the resulting tooth profile.
- Grinding while sharpening the front radius. There is a change in the radius of the cavity with a subsequent change in the pitch of the saw.
- Too small or missing radius of the left side. During sharpening, the front radius of the tooth is not formed. This leads to a change in the pitch of the saw, as well as to an increase in tension during sawing at the root of the tooth, which leads to microcracks and an accelerated rupture of the band saw in this place. This shape of the end face of the circle can be obtained during initial formation or during sharpening.
- Incorrect preparation of the right side. Filmed too little. During sharpening, the cavity will increase, the tooth will be shortened and set on fire at the exit. This state of the grinding wheel can also occur during sharpening.
- Incorrect preparation of the right side. Too many taken. During sharpening, the stroke of the grinding wheel will be smaller than the cavity, that is, the back of the tooth will not protrude.
- Improper preparation of the right side. the angle is greater than the posterior angle of the tooth. During sharpening, the back of the cavity will not protrude, since the right end of the circle will more quickly rest against the back of the tooth than the right radius will reach it. The tooth will be shortened and set on fire at the exit.
- a. Incorrect preparation of the right side. the angle is set smaller than the posterior angle of the tooth. The circle almost exactly runs along the tooth profile.
Video: How to Sharpen Wood Band Saws Correctly
As can be seen from the above examples, it is almost impossible to perfectly prepare the grinding wheel due to problems with the right side. Therefore, we must try to form the working surface as shown in paragraph 7a. A circle of the required hardness with such a profile will allow the sharpener to grind several tape saws to the edits, the number of which depends on the thickness of the material being removed. But at the same time, you still need to monitor the work of the circle, since as the end of the circle is grinded, the angle of the right side will increase and the circle needs to be profiled.
If you immediately put a circle 3-4 mm thick (paragraph 7.b), the profiling of the right side is practically not needed, you need to monitor only the left side, and this greatly simplifies the process of forming the profile of the end face.
It is also necessary to remove so much metal in one pass so that there is no cauterization of the body or the cutting edge of the band saw. Sometimes, even with a small metal removal, blackness still appears. In this case, it is necessary to clean the grinding wheel with a straightening pencil from adhering metal particles and grind the saw again.
You can’t leave big risks as well, you must go one more round and grind them.
So, it is necessary to give the end face of the grinding wheel the correct shape and sharpen the band saw only along the entire tooth profile, using a harder circle, remove as little metal as possible in order to prevent burns, sharpen the saw in several passes, so that in the end barely noticeable white risks remained. The tooth profile should be the same along the entire length of the saw and match the specimen.
The saw must be installed on the machine clean and stainless. Otherwise, the pusher may not have enough force to pull the saw and the grinding wheel will hit the tooth. The tooth will be damaged. With a strong cut, a circle may crack.
All the sharpening time, the band saw must be preloaded and the precleaning mechanism clean. The clamping force must be such that the pusher pushes the tooth with a slight voltage, but so that the motor does not slow down. If the saw is clamped loosely, it can move back behind the outgoing pusher or forward from the force of the grinding wheel. The result will be the same as in the previous paragraph.
If there is any doubt about your sharpener’s ability to sharpen the band saw correctly, you can check its operation within a few minutes.
We must take any saw prepared for work and look at it from above the tooth where the grinding wheel passed. The butt should be the same silver color. If the cavity is darker in color, it means that it did not pierce. There should be no blackness at the end. If there is blackness, then when working in the body at these places microcracks are accelerated, which leads to a rupture of the band saw. over, the cutting edge should not be set on fire, since in this case it will instantly become dull and the saw will stop sawing, that is, a wave will go. Only barely visible white risks are allowed.
You also need to check the shape of the tooth according to the sample, which should be near the sharpener. Such a piece of tape can always be obtained at the company from which you purchased the tape.
If you’re already tired of reading how to sharpen in the first way, and you just want to work and make a profit without constantly thinking about all these problems, then only the second method for sharpening a band saw is suitable for you.
All at once
If you carefully read how the work proceeds in the first way, you should have understood how really difficult it is to qualitatively sharpen a saw.
There is constant talk that it is impossible to quickly and well cut narrow band saws. Saws are torn quickly. To properly prepare them, it is almost impossible to find a sharpener. The lumber at the output is obtained with a large wave, which negates all the advantages of a thin cut.
So, in order to radically solve all these problems at once, Wood-Mizer proposed a method not of sequentially grinding each tooth of a band saw, but of the whole tooth profile at once with just one special profile disk entering it.
In this way, three main problems are solved at once:
- No need to look for a highly skilled sharpener. on such a machine almost one person can sharpen a saw in one pass with factory quality. He only needs to bring the disk to the saw. The machine will do the rest itself, which makes it possible to eliminate the influence of the human factor on the quality of the result as much as possible. If the profile of the saw tooth does not match the profile of the grinding wheel, then first, tooth profiles are formed in two or four passes, deepening the disk in one pass by no more than 0, 1 mm. Further sharpening proceeds in the usual manner.
- Band saws work two to three times longer, since the saw along the entire length is obtained with a completely grooved and absolutely identical profile of each tooth without burns, microroughnesses and scratches, that is, without stress points.
- The sawmill can work with its maximum performance, since the saw along the entire length is obtained with the same front and rear angles on each tooth. But, despite all the above advantages, this method of sharpening for a long time was practically not used at the sawmills.
This happened for the following main reasons:
- Very high price. Therefore, such a machine was bought mainly by service centers.
- Not very convenient technical solutions of the grinding process itself. Necessarily required a warm room, special oil, only with which a weak oil pump could work. This oil, when intensively sharpened, began to burn, therefore, mandatory exhaustion and much more were required.
- But the biggest limitation was the inability to grind bandsaw profiles of manufacturers other than Wood-Mizer, since Wood-Mizer made profile discs only for its saws. There were no other manufacturers of borazon grinding wheels.
1. Cheap group (the price of the machine is 15-35 thousand rubles). Some manufacturers of classic tool grinding machines simply change the phases of movement on the cam. Now the disk is no longer moving along the tooth, but only up and down. This gave them the opportunity to grind the entire tooth at once when installing the profile disk. But none of them understood that for sharpening a saw with a profile disc, it was necessary not only to change the phases of cam movement, but also to make the entire machine in a different accuracy class. Many of those who came to us for help have already come across this. Therefore, I want to warn immediately about the pointlessness of the acquisition of such machines. The worst thing for a disk is the backlash of the machine. If they are (and they are on all ordinary grinding machines and, accordingly, remain on those grinding machines that simply, with the help of another cam, try to remake them for working with elbor disks), then the disk begins to unpredictably hit either the front face or the back one, and, accordingly, to break the profiles of the teeth of the saw. Then the sharp tips of the teeth begin to cut the disk, several times reducing its service life.
Backlash can ruin the disc after 500 meters. And it turns out for those who have already purchased such machines. At first, sharpening goes well, but very quickly an expensive sharpening disk becomes inoperative (it simply cuts the front part to the base or cuts the risk). You need to buy a new disk, which is already becoming economically unprofitable.
In fig. 3 shows the phases of movement of the profile disk. It should be included in the tooth profile all at once and sharpened with the entire plane. The thickness of the applied layer of elbor is only 0.25 mm. But this layer is quite enough for a long normal operation. If the front part of the disk, when entering the profile, cuts into the top of the tooth (Fig. 4), then the sharp cutting edges of the teeth pierce relatively quickly in the coating at risk or even rip it off completely to the base in this place, making the disk inoperative. In this case, the tooth profile is also broken.
2. Dear group (the price of the machine is 120 thousand rubles). These are the manufacturers who simply copied the woodmeiser machine. At the same time, the machine was obtained from them at the price of the original, and the workmanship is the same or even worse. With this option, it seems to me, it is better to purchase a proven original. However, it is up to you to decide.
3. A machine for sharpening band saws with a full-circle borazon circle (price. 75 thousand rubles) (photo 2). This machine stands for sharpening in our service center.
Sharpening in this way when working the saw on tape dividing machines is especially relevant, since the saw there, unlike the sawmills, works all the time, without stopping, and any unstressed voltage points there are much faster.
However, this method of sharpening is now already cost-effective even when preparing a band saw even on one sawmill.
Here is an approximate economic payback calculation provided to us by the owner of one of the sawmills.
- The salary of a sharpener is approximately 10-15 thousand rubles per month. To prepare 10 tape saws per shift requires a full day.
- The small resource of the saw is sawing about 15-25 m 3 of round timber on edged sawn timber.
- If the quality of the saw preparation is poor or medium, the sawmill’s productivity for sawing timber into edged sawn timber is usually 0.2-0.5 m 3 per hour of round timber, i.e. approximately 100 m 3 of round timber per month.
- Five monthly band saws are consumed per month on average. With an average saw price of 800 rubles, the cost of them will be 4000 rubles.
- The average cut of 20 m 3 is multiplied by the number of saws (5 pcs.), We get 100 m 3.
- Let us take the average profit from 1 m 3 of edged lumber equal to 400 rubles, with an average or poor surface quality and, accordingly, not the highest price for lumber.
Profit for the month will be 400 × 100 = 40 thousand rubles.
Total: net profit for the month will be 26 thousand rubles per month: 40 thousand rubles. 10 thousand rubles (sharpener salary). 4 thousand rubles (the cost of sawing).
And how many nerves it will cost, only you know!
- To prepare 10 tape saws per shift, 60-90 minutes are required. No extra person required. Saws can easily be prepared by the owner of the sawmill or frame.
- Saw resource. sawed about 40-60 m 3 or more round timber on edged sawn timber.
- The productivity of a sawmill for sawing wood into edged lumber is usually 0.8-1 m 3 per hour of round timber, that is, approximately 200 m 3 of round timber per month.
- Five monthly band saws are consumed per month on average. With an average saw price of 800 rubles, the cost of them will be 4000 rubles.
- Let’s take the average profit made from 1 m 3 of edged lumber equal to 450 rubles, with good surface quality and, accordingly, a high price for lumber.
Profit for the month will be 450 x x 200 = 90 thousand rubles.
Total: net profit for the month will be 86 thousand rubles: 90 thousand rubles. 4 thousand rubles (the cost of drinking).
With a quiet work of production!
We get the profit difference for the month: 86 thousand rubles. 26 thousand rubles = 60 thousand rubles.
The difference in the price of machine tools: 75 thousand rubles. 25 thousand rubles = 40 thousand rubles.
Thus, in the first month of work, you pay for the grinding machine with a profile wheel and then only increase your profit.
The calculation is made approximately. But he draws on the experience of real work. You can do your own calculation yourself.
Sometimes confusion arises, what distinguishes borazon from elbor.
Borazon, a technical cubic boron nitride (b-BN), was first obtained in 1957. In 1969, General Electric registered the Borazon trademark for crystal.
Elbor is a technical cubic boron nitride (b-BN). Elbor was synthesized in 1959 by a team of scientists from the Institute of High Pressure Physics (IHF) of the USSR Academy of Sciences. Since 1964, the industrial production of elbor and tools from it has been organized.
Thus, this is one and the same material, but obtained in different ways in different countries. It is believed that the Russian elbor in its structure has the best grinding properties.
Today, working with disks of different companies, we have received an average resource:
- Wood-Mizer. ≈5-7 km;
- Polish, Turkish and other unknowns. ≈2-4 km;
- Russian-Ukrainian production. 7-10 km or more.
In conclusion, I want to repeat what I started this article with. Any machines are bought for profit with their help. Everyone wants to supply equipment and work without unnecessary problems. But rarely does anyone really know what they will have to face after installing the main equipment. After reading this article, you get a complete picture of all the pros and cons of the two ways to sharpen a band saw. Now, based on this knowledge, you will be able to independently make a competent choice.
We suggest you purchase a trial batch of band saws with subsequent sharpening in our service center, this will give an understanding of how the band saws work after sharpening with a borazon circle, compare them with your sharpening and not buy an expensive and modern machine.