11 Feb 2019
February 11, 2019

HOW-TO: Select A Bandsaw

When looking through the many different horizontal bandsaws on the market it can be difficult to know which machine will best fit your needs. Scissor type, dual-column, single mitering, auto material feed, capacity… the options can be overwhelming. Use this handy guide to find the right saw for the job!

Fully automatic, semi-automatic, or manual? What do I need and what is the difference?

Manual bandsaws require the operator to use their physical strength to lift the head after each cut. Bandsaw heads can weigh 200 pounds or more. The wear and tear on operators from repeated lifting, workmans comp claims, and the time required to manually move the head are things no shop or production facility wants to pay for.  As a result, KAAST Machine Tools does not sell this type.

All bandsaws sold by KAAST are at least semi-automatic, meaning the head movement is controlled by a hydraulic piston, and can be raised and lowered by the operator activating the up/down switch. To run the machine, the operator tightens material in the vice and pushes the Start button. The saw will make the cut, then lift the head back to the upper position. Semi-automatic saws are a good fit if you need to make a few cuts in a length of material.

Fully automatic KAAST bandsaws have a hydraulic piston to raise and lower the head and are either equipped with driven rollers in the vice or a shuttle vice to advance the material. Most fully automatic saws also feature a digital piece counter.

The standard vice on fully automatic saws tends to be the powered roller style, which holds 3-5 cylinders vertically against each side of the material. One side is grooved, to assist with catching and advancing the material, and the other is smooth, containing a limit switch activated by the pressure of the material inside the vice.

Your other option for advancing material through a horizontal bandsaw is a shuttle-vice style. Shuttle vices work by the vice head moving away from the saw blade, clamping around the material, and pulling the material forward to be cut. Shuttle vices are the best option when bundle cutting, as they are typically stronger than their roller-style counterparts, enabling larger, heavier materials to be moved, and prevent slippage within the bundle.

Fully automatic horizontal bandsaw operation is as follows:

  1. Material is placed into the roller vice and the vice is tightened
  2. The operator sets the desired cut length, typically activating a limit switch
  3. The number of desired parts is entered into the digital counter
  4. The operator presses the Start button
  5. The saw will make the cut and the part will fall out of the back of the machine and into the parts
    collection bin.
  6. The machine raises the head and the material is advanced until the length limit
    switch is activated
  7. The cycle continues until the numbers of cuts entered into the control is reached

There are three things that will stop a fully automatic saw cycle. The first is completing the job. The second is running out of material. When this happens, most saws will pause and wait for more material to be added, then complete the cycle. The final is if the bandsaw blade breaks. (All KAAST saws feature auto blade-breakage detection.)

Fully automatic saws (indicated by the letter “A” in the model number e.g. HBS A 320) are best suited for production lines which need to cut multiple pieces to the same length.

All KAAST bandsaws raise and lower the sawing head with a hydraulic piston. The fully automatic saws also advance the material to be cut.

Semi-automatic machines are better for applications where only a few cuts need to be made in a length of material.

Fully automatic machines are better when many shorter cuts are required.

Scissor type vs dual column set ups: more cuts per hour = more money up front.

 

With horizontal bandsaws, there are two common configurations. The first is scissor type, which as the name implies, pivot on a bearing on one side of the head, similar to a pair of scissors. Dual column machines raise and lower the head on precision ground linear guides.

In a pivoting scissor head machine, the blade enters the material at an angle and traces the circumference of the material being cut, which results in a longer cutting cycle [fig. 1]. The down feed pressure on a pivoting head will be greatest closer to pivot point and will lessen as you get farther away. On structural shapes such as I beam or square tubing, the pivot saw will produce a better cut as the blade wanders less when it enters these materials at the more severe angle provided by the scissor head. Scissor type bandsaws tend to require a smaller investment than their dual column cousins; they are typically a good fit for smaller job shops or as back up or one-off machines for production facilities.

With dual column bandsaws, the blade enters the material at an angle, typically smaller than the scissor style machines, but cuts along the diameter of the material [fig. 2]. Dual column saws are much more rigid than their pivoting counterparts due to the dual columns holding both ends of the head, resulting in near constant down feed pressure and feed speed across the entire width of the cut. This rigidity also reduces vibration, resulting in a better cut quality and a longer blade life. Dual column sawblades also take the shortest route through the material, decreasing the time required per cut and increasing production numbers. While dual column machines produce better cuts faster, they also tend to have heavier price tags. However, the increased cost can be quickly recovered by the increase in production numbers. This larger investment usually makes sense for more demanding production lines working with larger materials.

Capacity: How much saw do you need?

KAAST bandsaws come in sizes ranging from 9”— 60” (230 mm to 1500 mm) with model numbers correlating to their max capacity in millimeters when cutting at 90°. E.g. an HBS 320 will fit Ø320 mm round bar stock. Larger capacity saws generally have larger motors providing more torque and allowing the operator to cut faster, not just larger, and to increase the speed at which the blade can get through the material. But as size increases, so do prices. How big is big enough? That all depends.

What size and type of material are you cutting on a day to day basis? We typically recommend getting 1-2” more clearance than your most commonly cut material. This allows you to squeeze in those one-off cuts but keeps you from buying more machine than you need.

Want to make your corners tighter? Then miter!

For some fabrication projects, miter cuts will help to give you a more professional product, but when you’re trying to cut corners (pun intended), mitering is the only way to go. KAAST offers an assortment of horizontal mitering bandsaws, with options for a swiveling head or a swiveling vice, each combined with either a scissor type or dual column set up and offered in fully or semi-automatic..

KAAST Bandsaws built primarily for mitering include the letters G or DG, in their model name. E.g. HBS A 325 G or HBS 440 DG.

But what do G and DG stand for and what does that mean to you? Long, long ago an angle was known as a gore, which progressed to an angled cut being known as a gore. On KAAST horizontal bandsaws, G indicates the ability to cut at an angle (aka to miter) in the positive direction (+30°, +45°, etc) (Fig. 1); while DG stands for double gore, indicating the machine’s ability to cut in both the positive AND negative direction (+60°, +45°, +30° -30°, -45°, etc)(Fig. 2).  All G and DG bandsaws feature a swiveling head as opposed to a swiveling vice..

Swiveling head vs swiveling vice: What are the differences?

With a swiveling head (a key element of the G and DG KAAST bandsaws) the material is fed into the vice perpendicular to the machine base and the entire blade and housing can be moved to set and cut the desired angle. (Fig. 1) What is the advantage to this? Production lines can be set up with minimal clearance (dashed line around Fig. 1) as the material will always move in a straight line. Disadvantages to this? Price. Enabling a saw head to rotate requires a larger, stronger frame. This increases the price of the machine. However, if you are making a lot of unique miter cuts in a shop with limited space, a swiveling head is worth the investment.

A swiveling vice (offered on some HBS models) will clamp your material at the angle you wish to cut, requiring additional space around the machine for the material to extend. (dashed line around Fig. 2) The saw blade and housing do not rotate, the positioning of the vice (and as such the material in the vice) dictates the angle at which the material is cut. If mitering is something that is not needed on a regular basis and you have the room to move your material, then a swiveling vice is most likely the way to go, as they typically require a smaller investment.

Fully automatic mitering vs semi-automatic mitering: How many angled cuts are you making?

For making repeated mitered cuts, a fully automatic mitering saw is the way to go. While these machines typically only offer mitering in one direction, this is not commonly a problem as fully automatic mitering saws are usually installed into production lines where material consistently needs to be cut at the same angle. However, the fully automatic mitering band saws offered by KAAST feature an NC control with digital display of the angle as well as the ability to program multiple cuts for multiple lengths at the same angle (eg. Two sections 8” long, four sections 10” long, twenty sections 2” long, all at 15°). This programming allows the machine to run continuously. The more time a machine runs, the more money it makes.

It’s time to get bundled up!

Many shops assume that bundling material will reduce production time and cost. Let’s walk through the process of cutting a bundle to see how this is both true and false.

Effective bundle cutting requires the bundle to be securely held together. If the material in the bundle does not have adequate pressure holding it together, vibration via chattering will result. This vibration results in the saw blade life being reduced by up to 25%. No savings there! Typically, securing the material into a tight bundle is done by placing straps just behind each of the cut locations or by tack welding the ends of the material. Both of these methods take that most valuable shop resource: time. Time for the operator to stack the material efficiently, secure the material together, and get the secured bundle into the saw. If materials are purchased pre-bundled, some of that time can be recouped and saws with hydraulic top clamping (available on most KAAST HBS bandsaws) can help to secure the bundle during the cut by applying additional downward pressure to keep individual pieces secure.

What about operator loading and unloading? Surely it is faster to move 1 bundle than 6 individual pieces, right? Once again, it seems like the bundle would be the faster way to go. However, the more material in your bundle, the heavier and more unwieldly the bundle will be. This increased weight will slow your operator’s movements, and possibly require adding another operator or machine to assist with loading the material into the production line. Also, if your bundle is heavier than your feed system can handle, the saw will be unable to advance the material. Using a shuttle vice (standard on fully automatic mitering KAAST bandsaws, and available as an upgrade to most others) to advance the material bundle will help to keep your bundles tight as the vice secures around the bundle before advancing it.

In summary, bundle cutting can only save you money if you invest in proper equipment.

Top clamp, chip conveyor, feed roller, oh my!

The KAAST HBS horizontal bandsaws have a wide array of options available. Which can you live without and which are necessary?

Hydraulic Top Clamp – Available on all dual column and/or mitering models

The hydraulic top clamp for the HBS line up allows the operator to easily, with minimal tack-welding of the ends or strapping, cut multiple pieces of material by applying pressure in 2 directions simultaneously to ensure a clean and complete cut.

Chip Removal Conveyor – Available on all HBS models

If you plan to run your saw continuously a chip conveyor will ensure your chip chute doesn’t overflow, reducing downtime, saving money. The chip auger especially helps to move larger, heavier chips (e.g. cutting iron with a large tooth blade), which might otherwise sink to the bottom of the chute and not be flushed to the coolant collector. Running your saw 8+ hours a day, every day? You need this.

Roller Tables and Motor Driven Roller Conveyors – Available on all HBS models

Roller tables, as the name implies, feature multiple cylinders which roll as material is moved across them. A little push goes a long way! While they cannot initiate movement, the rollers greatly ease material movement.

Motor driven roller conveyors are recommended for use in conjunction with hydraulic top clamps and shuttle vices in fully automatic horizontal bandsaws. Using a small but powerful motor, the tables help the shuttle vice to move heavy materials into position to be cut. The combination of shuttle vice, hydraulic top clamp, and motor driven roller conveyor results in a machine made for mass production with minimal hands-on time.

How to choose a blade for a horizontal bandsaw

In a perfect world, operators would have a saw and coordinating blade for each of the cuts they need to make. In the real world, operators typically have a single saw with which they are tasked from cutting everything from mild steel thin wall tubing to solid titanium plate. While no blade is perfect for every application, considering a few factors can help narrow your choices from numbering in the hundreds to a dozen or so to consider.

Our friends at Lenox (the KAAST Machine Tools preferred brand for bandsaw blades) put together this excellent guide to band sawing which includes how to select a blade.

Before we begin, here is a crash course in bandsaw blade terminology from the Lenox Guide to Band Sawing:

1. Blade Back: The body of the blade not including tooth portion.

2. Thickness: The dimension from side to side on the blade.

3. Width: The nominal dimension of a saw blade as measured from the tip of the tooth to the back of the band.

4. Set: The bending of teeth to right or left to allow clearance of the back of the blade through the cut.

5. Tooth Pitch: The distance from the tip of one tooth to the tip of the next tooth.

6. TPI: The number of teeth per inch as measured from gullet to gullet.

7. Gullet: The curved area at the base of the tooth. The tooth tip to the bottom of the gullet is the gullet depth.

8. Tooth Face: The surface of the tooth on which the chip is formed.

9. Tooth Rake Angle: The angle of the tooth face measured with respect to a line perpendicular to the cutting direction of the saw.Kerf: Amount of material removed by the cut of the blade.

The first item to consider is your saw. Horizontal bandsaws have tight specifications for the length, thickness, and width of blades. These numbers are essentially non-negotiable.

The length is decided by the spacing and size of the band wheels of your particular machine (Fig. 1). KAAST horizontal bandsaws will not run with a blade that is too loose or tight (too long or short) for the inherit safety reasons.

The thickness of the blade is based on the clearance in the blade support arm blocks (Fig. 2). If the blade is too thick, it will not be able to pass freely through the guide wheels on the support arm blocks. If the blade is too thin, the guide rollers will not hold the blade securely, allowing the blade to chatter (vibrate) as it passes through the blocks. Vibration = deteriorating cut quality.

The blade width (also called height) is also important to consider. The width of the guide wheel will determine the maximum width that will fit your bandsaw. Typically, for the straightest cut possible, you want to use the widest blade possible; wider blades = less vibration = cleaner cut. Horizontal bandsaws are not typically able to make contour cuts, where a narrow blade would be required.

Now that we know which size blade is needed, we can work on choosing which material our blade should be constructed from. Bi-metal blades consist of an outer layer of high-speed steel teeth wrapped around an inner layer of a high strength spring steel. With the ability to cut up to Rockwell C 40/45 hard materials and a melting point of around 1100°F, bi-metal blades are the most commonly used blades in a machine shop as they have the widest array of applications.  Carbide tipped blades, which can cut up to Rockwell C 78/70, are typically used for cutting harder materials such as tungsten, nickel alloy, or titanium.

Tooth shape needs to be taken into account at this point. The shape will decide how efficiently the blade will cut, and will affect blade life, cut quality, and chip carrying capacity. The common tooth shapes are:

Variable Positive: Variable tooth spacing and gullet capacity of this design reduces noise and vibration, allowing faster cutting rates, long blade life and smooth cuts.

Variable: A design with benefits similar to variable positive, for use at slower cutting rates.

Standard:  A good general-purpose design for a wide range of applications.

Skip: A wide gullet design makes this design best for non-metallic applications such as wood, plastic, or composite materials.

Hook: Similar to the skip design, this high raker blade is best for materials which produce discontinuous chips (eg. cast iron) as well as non-metallic materials.

Our next decision to make is the tooth set. Tooth set is determined by the number of teeth and the angle at which the teeth are offset. The tooth set will affect the cutting efficiency and chip carrying ability. There are 6 basic tooth sets to choose from, and our friends at Lenox break them down as follows:

Raker: 3 tooth sequence with a uniform set angle (Left, Right, Straight).

Modified Raker: 5 or 7 tooth sequence with a uniform set angle for greater cutting efficiency and smoother surface finish (Left, Right, Left, Right, Straight). The order of set teeth can vary by product.

Vari-Raker: The tooth sequence is dependent on the tooth pitch and product family.

Alternate: Every tooth is set in an alternating sequence. Used for quick removal of material when finish is not critical.

Wavy: Groups of teeth set to each side within the overall set pattern. in a controlled pattern. Wavy set is typically used with fine pitch products to reduce noise, vibration and burr when cutting thin, interrupted applications.

Vari-Set: The tooth height / set pattern varies with product family and pitch. The teeth have varying set magnitudes and set angles, providing for quieter operation with reduced vibration. Vari-Set is efficient for difficult-to-cut materials and larger cross sections.

We also need to choose either Single Level Set or Dual Level Set

Single Level Set: The blade geometry has a single tooth height dimension. Setting this geometry requires bending each tooth at the same position with the same amount of bend on each tooth.

Dual Level Set: This blade geometry has variable tooth height dimensions. Setting this product requires bending each tooth to variable heights and set magnitudes in order to achieve multiple cutting planes.

Now we are up to choosing our teeth per inch, or TPI, which correlates to the tooth pitch (eg. 4 TPI = 0.25” tooth pitch).  The factors impacting our TPI choice include the size and shape of the material to be cut.

Obviously, the less material removed by each tooth, the finer the finish will be. So why don’t we just go with the highest TPI available, so all of our cuts come out super clean? It’s not that simple.

As each individual tooth of the blade meets the material, it shears a chip as long as the material is wide and as thick as the angle of the tooth. This chip accumulates in the gullet of the tooth, and then falls out when the tooth exits the material. The higher the TPI, the smaller the individual tooth size and consequently, the smaller the gullet. The smaller the gullet, the less room there is for chip to accumulate. If the chip overwhelms the gullet’s physical limit it will consequently increase the resistance, loading down the machine and damaging the blade. So, we need the gullet (and as such, the tooth) to be just large enough to hold the material accumulated during the cut.

In summary, for maximum cutting efficiency and lowest cost per cut, it is important to select a blade with the right number of teeth per inch (TPI) for the material you are cutting. Lenox has put together these handy charts to help find the correct TPI for your job.

For bundle cutting, Lenox recommends selecting the proper number of teeth per inch (TPI) for bundled or stacked materials by finding the recommended TPI for a single piece and choose one pitch coarser to cut the bundle.

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