“Excuse me sir, can I ask you what kind of band saw blade you are running right now?”
“Sure it’s the blade I had laying around when I needed to cut some material.”
Okay, so how many times have we all heard a reply similar to that? In this blog we are going to address the “great mystery” of band saw blades for metal applications.
The poor old band saw, sits in a dark corner of the shop and don’t get no respect. This band saw is rarely — if ever — serviced, is filthy, has chips all over it and is probably located by the overhead door where it’s always cold.
This old band saw only gets worked on when it breaks. Operated by an individual who wishes he or she was anywhere else. The operator wants to know why their being punished by having to run this old band saw machine. Sound familiar? Unfortunately, this sad story is repeated in company after company, large or small all across our great nation. There’s an old saying in the band saw blade industry, “if a company takes steel off a semi-trailer they have a band saw”, can you imagine how many band saw machines that is? Whether they are horizontal or vertical, the poor old band saw is the “Red Headed” stepchild of the shop. Relegated in stature to the forklift and the air compressor, right?
The process of metal removal has experienced constant improvement virtually daily for the last 30 years. Now companies employ as much as 5 axis milling machines, numerous axis vertical machines, the highest quality consumable cutting tools, with the latest technology that can be seen in every direction. Well, quietly the leading metal saw blade manufactures are deeply involved in the constant improvement in today’s latest technology saw blade. Yeah that’s what I wrote, “latest technology” band saw blades! It was probably the early eighties when the leading suppliers of band saw blades began to realize that a general purpose blade will cut a lot of different materials, only problem was the general purpose didn’t cut very many of them well.
It was the early 1990’s when the major band saw blade producers began to test and market what I like to call “material specific” saw blades that were designed to cut certain materials with much increased production. The first of these new blades was designed specifically to cut stainless steel, this blade succeeded very well in the field and all the other blade manufacturers took notice and rushed to their drawing boards. As this scene replayed its self over and over again on different cutting jobs where there was now a specific blade to cut bundles, a blade to cut aerospace materials, a blade designed to cut tool steels and on and on.
The general purpose band saw blade wasn’t dead. In thousands of shops across this country there are small to large band saw machines that have to provide total flexibility for the company’s needs. These saws might cut ¾ inch rebar one minute and a piece of angle iron the next. What kind of a blade do you give a consumer when he says “I don’t care what kind of blade you give me; we break them all!”
Correct band saw blade application has been something of a mystery to the majority of the metal working industry. For some reason a large manufacturer let’s say who has a 5 axis milling machine all programmed up with the latest technology in cutting tools, is producing an unbelievable part but can’t figure out how to run a band saw? Yes, believe it or not there is an industry accepted method of properly conducting cutting on your machine. Now, before I go any farther let me make a distinction here, the new wave of band saw machines coming out from the leading builders of band saw machines have solved this problem. They, simply put, introduce a computer into the overall design that takes over proper application and running of the band saw blade. Ta da! What about the rest of us that don’t have a computer on our saws? The remainder of this blog is for you.
Pick any kind of material (metal) you can think of, 1 piece at a time 12 pieces at a time or a solid bar 36 inches in diameter, they all have to go through the same process of band sawing setup. What is band sawing setup anyway? It’s the process of determination that is implemented to insure your band saw blade is:
The proper type saw blade for the material being cut is selected.
The proper pitch (number of teeth on the blade) you need to cut the material.
The blade manufactures speed chart is consulted and the correct band speed is implemented.
This is the tricky one, accurately compute the square inches of material in the cut piece computation. You need to access how many square inches of material you have in the cut job.
Then go to the blade manufactures square inch per minute cutting rate chart to see how many square inches of material per minute the chart recommends can be cut.
Simple right? You may have never heard of these resources in relationship to band saw blades yet almost all, if not all, blade manufactures have them in hand out form for years. Yes, folks, your handy dandy band saw blade sales representative probably has a box of these in the trunk of his car. A speed chart, a blade pitch selector chart, a catalog that shows all his available band saw blade types. He would also carry a square inch per minute cut chart (this chart would describe how many squares per minute a given material can be cut at.). Lastly he should be able to convey the computation of material area (so you can figure out how many square inches of material you have).
We have all our knowledge at hand, let’s determine our next cutting job with all our newfound tools. Let’s setup the band saw for our next cutting job. Just for the sake of discussion, we are using a BMT HBA 330 machine with a 13 inch cutting capacity and a 1 ¼ inch width band saw blade. The material to be cut is A.I.S.I. 1020 solid steel round bar, 6-inch diameter. The first thing I like to check is to see if the correct blade type and pitch are on hand and properly mounted on the saw. You would know that the correct pitch (2-3 variable pitch) was on the saw because you would have verified the pitch selection with your new chart. Next comes blade speed adjustment using the blade speed chart, you go down the row to find your exact material type and then go across the row until you get to the size you are cutting. (275 feet per minute). The next step I take is to get a figure of the area in that 6-inch diameter round. Here is the simplest computation that will get you area of the round in square inches. Take the diameter times itself (6×6) = 36 times .7854. and if you computed correctly, you got 28.27 square inches of area in the 6 inch round bar. Great, now you got this number what’s next? Now, knowing how much area is in you cut piece, you can refer to the square inch per minute cutting rate chart. This chart tells you how many square inches per minute a given type of material can be cut.
(See the end of this blog for an explanation of how to compute other shapes areas.)
O.K. so here we go, the cut rate chart (square inch per minute cutting rate chart) say’s conservatively, you can get 12 square inches per minute in cutting rate, you have 28.27 inches of area to cut in your 6-inch bar, how do you put the two together? We’re almost there! You take your 28.27-inch area and divide it by your 12 inch cutting rate, and come up with the amount of time it takes to cut that 6-inch diameter steel bar. In this case 2.35 minutes or 2 minutes 21 seconds. The cutting rates on charts from almost every blade manufacturer are generally regarded as conservative for obvious reasons. They do not want their blade to wear-out too prematurely so they reduce the cutting rate to prolong the blades life.
Discovery is one thing, implementation quite another. You now have the ability to set up your band saw and run it to an industry accepted norm. Let’s do a quick recap.
I pick the band speed off the chart.
I pick the tooth recommendation off the chart.
I figure the square inch area of the part and write that down.
I pick the cutting rate in square inches per minute for the material type off the chart and write that down.
With all this information compiled you do the math and arrive at your cut time. What do you do then?
Well, the first thing you’re going to need is a stop watch right? Gotta time the piece part cuts to see how long they are taking to cut at current settings. The usual set up of a band saw that has not been optimized tends to slant vastly towards the lower output range. This is not by anyone’s design just happenstance. Cutting conservatively is better than cutting aggressively especially if you don’t know exactly how to set up your machine, right? Sometimes yes, sometimes no. That discussion will be covered in an upcoming blog titled “It doesn’t do any good to buy a quality band saw blade if you don’t get the point!”
Now you are “armed to the teeth”, with information to correctly operate your band saw machine and reap the benefits, save your company thousands of dollars in the first year. If you could only figure out how to get the operators on board with the new program for operating the production band saw machine.
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Round solid- diameter times diameter times .7854 equal the area of a round.
Round tube- do above calculation twice, one for o.d. one for i.d. and subtract.
Square solid/Rectangle solid- Multiply two sides to equal the total area of a square or rectangle.
Square tube/Rectangle tube; do above calculation twice one for o.d. and one for i.d. and subtract.
H beam, I beam, C channel, angle iron; Measure independent planes of material, and add to get total area.
