The Hole Story
Posted on November 10 2017
As the name suggests, a hole saw is a power tool accessory that makes circular cuts.
Hole saws are generally made out of a strip of bandsaw blade welded onto a cap to create a cup-shaped body with teeth on the edge.
Hole saws are distinguishable based on what tooth edge material is used Morse produce bimetal (featuring an 8% Cobalt M42 cutting edge with low alloy steel backer), carbide tipped, carbide grit and diamond hole saws.
It is vital to choose the right tooth edge for your application. In fact, one of the leading causes of lowered tool life is choosing the incorrect tooth edge.
Bi-metal hole saws are an excellent general purpose saw that are used to cut metal, wood and plastics.
Carbide tipped hole saws and carbide grit hole saws are well suited for difficult to cut material such as fibreglass, ceramics and stainless steel. See our hole saw selection guide to help you find the right saw for your particular application. Here
However, the most commonly used hole saws are bi-metal due to the variety of the materials they can cut at a lower cost.
If premature failure of the saw occurs where the cutting edge is electron beam welded onto the backer then the operator should consider using a different tooth edge material such as the carbide tipped hole saw or if the failure is sudden then check the drill is not in reverse as when directional teeth are run in reverse this causes tooth strippage.
The accessories you use with a hole saw can also effect the life of the saw. Hole saws are generally used with a pilot drill. If they are not used then the hole saw can move laterally ‘walk’ before engaging in the cut. This creates a larger elliptical hole and lowers the life of the saw.
Along with the tooth edge material, the tooth design, such as the tooth spacing, tooth angles and gullet design can affect the cutting performance.
In a typical hole saw design the side slots are used to remove the slugs from the hole saw. Recent research at the MK Morse R&D lab has shown that the tooth design plays a critical role in slug removal.
To improve the cutting process slug removal should be closely observed. In some applications, operators may notice that the cut time might be shorter than the sluf removal time. In such situations, an operator should consider shifting to a hole saw with a better slug removal system such as the new MK Morse’s new patent-pending tooth design on their MHS hole saw.
Combined with the innovative side slot shape, the MK Morse tooth design offers the easiest sluf removal feature in the market. In fact, tooth design has a significant effect not just on sluf removal but also on the ease of cut, tool life and cut surface finish.
Another option to make slug removal easier is by not using a pilot drill. As described earlier by not using a pilot drill the saw walks which increases the kerf and therefore reduces slug diameter so making it easier to remove. However, this can decrease the life of the saw.
In general, hole saw performance is evaluated based on the cut time, tool life, ease of slug removal and cut finish.
Although hole saws should not be considered precision tools, often, operators have high expectations. They expect a good cut finish and easy slug removal, which are influenced just as much by the type of material being cut as the tooth design.
Typically to meet cut finish expectations, reducing the feed rate is a good option/ Remember however that there are a few expectations to this rule, such as cutting thin metal sheets. As many operators know, achieving a good cut finish while cutting thin sheets of metal is challenging.
Therefore using a rigid work holding device, proper drill extension/arbor and a relatively high feed and RPM are recommended.
In some instances, cutting fluids can also improve the overall performance of a hole saw. A cutting fluid helps improve the cut finish and easy of slug removal while also giving the tool longer life and reducing vibration that can be harmful to the operator over time. A semisynthetic cutting fluid is recommended because it has the capability to reduce frictional resistance and temperature build up.
Selecting the correct RPM and feed rate is another essential approach for achieving better hole saw performance. If an operator experiences higher vibrations or harmonics while using a hole saw it can be an indication of incorrect RPM and feed rate. However, higher vibrations can also be due to improper tooth design.
One way to reduce the vibration or harmonics is to reduce either the RPM or the feed rate. Also, the combination of the tooth design (angles and pitches) and the kerf variations will reduce the harmonics. The new MK Morse Hole saw (MHS) has been designed to optimize tool life and harmonics. Also, the patent-pending tooth design has been rigorously tested to prove that it has the best slug removal feature on the market.
In summary, a good hole saw should be able to make an annular cut with ease while also delivering on quick slug removal. Hole saw accessories such as pilot drill and arbor play an essential role in the hole saw performance. Furthermore cutting conditions and workholding can have a significant effect on everything from vibrations and harmonics to tool life and cut finish.
We supply a wide range of MK Morse Hole Saw kits on our website including the Morse BiMetal Master Cobalt Hole Saw kits - find out more here.