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CANADA'S LEADING INFORMATION SOURCE FOR THE METALWORKING INDUSTRY

CANADA'S LEADING INFORMATION SOURCE FOR THE METALWORKING INDUSTRY

ASK THE EXPERT: Tips for sawing pipe and tube from L.S. Starrett Company’s Jay K Gordon

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Sawing pipe and tube has its challenges. But our expert will help guide you through it as we delve into the most important things to consider in “making the cut”.

SHOP: What are the most important things to consider when cutting thin wall pipe?

GORDON:The biggest issue with thin-wall pipe is that you are either cutting a pipe one at a time or you are cutting pipes in a bundle — both scenarios present challenges. The second issue is getting a good tooth match, so that you’re not slapping or hitting the teeth on the material and chips are not sliding down into the gullet. You want the saw blade actually taking a “bite” of the material, so technically what you need is a minimum of three teeth in the material at all times. In thinner walled applications, a blade with finer teeth would typically be the go-to blade. The heavier tooth back provides more strength and better shock resistance to each tooth. This provides longer blade life when the teeth are constantly going in and out of the material, traversing across thick and thin sections. In addition, blades for thinner walled pipe usually have a wider tooth set with a larger kerf. This minimizes stresses in the material that tend to pinch the blades. In most cases, a wider set blade can eliminate pinching altogether.

Another issue, and this is one operators often don’t think about, is the challenge of cutting a larger thin-wall pipe, such as maybe 8 inches around but still only an eighth or sixteenth of an inch gauge thick. If you clamp that incorrectly and it compresses the material, then when you cut it and release that clamp the cut is going to be crooked, even if the pipe being cut looked fine. 

Sawing tubes is difficult because you’re always sawing in and out, and problems will show up quickly if you don’t know the material and it’s not something close to what you guessed. PHOTO courtesy L.S. Starrett Company.

SHOP:  What are the things to consider when cutting thick-wall pipe? 

GORDON: Thick wall pipe is a little bit easier to deal with because you’re not going to compress it, and it is typically easier to match with the right tooth pitch. Generally speaking, you have more options for your blade pitch on thicker walled pipe than on thinner walled pipe. Look for a blade designed specifically for interrupted cuts such as one that offers a heavier tooth and that will take abuse because it will repeatedly be in and out of the material. If you go into a fabricating shop cutting these types of materials, you will hear the saw screaming and making all kinds of noise, which is one of the biggest complaints among operators. In the new Starrett TENNAX-PRO Bi-metal band saw line, which features a variable set, we’ve significantly reduced the noise and vibration to provide a smoother, quieter cut specifically when cutting tubes, pipes and structural shapes.

SHOP: What are the challenges involved with cutting bundles

GORDON:  Your cross sections obviously increase from one piece to multiple pieces, so again blade selection and tooth pattern are very important. For example, if the piece being cut is a simple 4” square pipe with a 1/4” wall, depending on desired results, a 4/6, 5/8 or even 6/10 tooth blade will work. When bundling, based on the size of the bundle, the cross section that needs to be cut changes. For example, using the 4” square pipe in a bundle of 4 pieces side-by-side and 4 pieces high, the blade is now cutting across a 16” solid depending on the angle of the head each time it travels through the tops or sides of the tubes. In addition, the 1/4” wall has in effect become a 1/2” wall. Both 6/10 and 5/8 tooth blades are now much too fine to cut the material efficiently. So, moving to a 4/6 or even a 3/4 tooth blade would offer better cutting rates in this scenario.

Spinning or vibration is one of the biggest issues when cutting round tubing bundles. Usually, a few tubes in the middle of the bundle will start vibrating and that will cause some deleterious effects to the blade itself. It will literally chew the teeth up, so you have to be careful about that. Clamping is an issue every time you cut a bundle. Most of the band saw machines designed for bundles will have what are called nesting clamps so the clamping is along the sides, as well as on the top. Now if the bundle is odd shaped, like some bundles are, that’s where nesting clamps really come into play so that the bundle cannot move. If it moves, you’re going to destroy the blade at some point in the cutting operation.

Spinning or vibration is one of the biggest issues when cutting round tubing bundles. PHOTO courtesy L.S. Starrett Company.

SHOP: Blade speeds are typically determined by the type of material being cut. Sometimes, however, the exact type of material is not easy to identify. In such cases is it safe to guess at the material or should you always know exactly the type of material you’re cutting before setting your speed?

GORDON:  In theory, yes, you should absolutely know what it is you’re cutting. In reality, that doesn’t always happen. I do not recommend making a “best guess”. The disadvantage of tubing is that you can’t read the chips the way you can with a solid to make adjustments. You’re probably going to get more “pieces” as opposed to chips, depending on the material. Tubing is also more difficult because you’re always sawing in and out, and if you don’t know the material it will show up real quick if it’s not something close to what you guessed. I like to use the box analogy. You have a box that a particular material will cut well in and there is some wiggle room within that. As long as the material is similar to what you are accustomed to cutting, it will at least get you started and then you can make small adjustments. The blade will tell you quickly if you’re wrong because you will hear the teeth hitting the material instead of cutting the material. Listen for a slapping or banging type sound. It should not sound like the machine or the blade is coming apart. It shouldn’t be screaming so loudly that everything is shaking, and the blade is vibrating. 

SHOP: Another issue with piping is that it’s not always straight. What problems does that cause and from your experience does the average fabricating shop operator take the time to ensure that every pipe they put through the process is measured and straight?

GORDON:  Let’s start with the last question first: No! There are times when tubing comes off the truck and it is hastily thrown, which can damage the product. The biggest issue with crooked pipes is that if you have a machine that shuttles and feeds the material automatically into the blade, pipes could jam the machine. Crooked pipe could also cause length issues. When you cut it, it won’t be the right length. The material should be straight up against the fixed vice, which is 90 degrees to the blade so that you get a nice straight cut. If the bar is bent a little bit or compressed a bit or you didn’t clamp it right, the blade is still coming down straight, but the material is coming in crooked. Once you’ve cut it and put a square on it, it’s going to be a crooked pipe. 

SHOP: Tube exposed to the elements can develop a layer of rust. What issues can this present for sawing? 

GORDON:  In general, rust is not a huge issue but there are exceptions when the rust is excessive. In the case of excessive rust, keep in mind you are cutting through that layer of rust, and it will add wear and tear to the blade. There may be a 5-10% decrease in blade life depending on how rough the rust is. If the rust is really crackly and thick on top of the material, you may want to change some cutting speeds and feeds. One issue rarely considered is about what happens to the oil that a lot of shops use on tubing to prevent rust. When you start cutting, the oil on that pipe goes down into the coolant tank. Eventually, your coolant tank will become partially filled up with the oil you applied to keep the tubes from rusting. That will kill your blade life too. Hydraulic or lubricating oil is not a coolant and if used it will not work and the coolant tank will ultimately have to be changed. I’ve made calls where that’s exactly what has happened. For six months or a year, pipes might have been cut with no problem, then suddenly there is a problem. The coolant tank has three inches of oil in it. SMT

Jay K Gordon is the North America sales manager, saws and hand tools, with The L.S. Starrett Company.

Jay K Gordon is the North America sales manager, saws and hand tools, with The L.S. Starrett Company.

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