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A guide to hole saw teeth and TPI

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TPI

TPI teeth per inch, saw blades, hole saw TPI stands for ‘teeth per inch’ and is a way of measuring the frequency of teeth on a saw blade. Usually abbreviated to TPI, as in, “a blade consisting of 18TPI.”
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How does TPI affect how a hole saw cuts?

The TPI of a hole saw blade can affect:

1. How fast it can cut

Hole saws cutting tools, smooth cut, rough cut, holes, wood wonkee donkee tools DIY guide 2. The quality of the finished cut e.g. smooth or rough
hole saws, cutting tools, DIY guide, wonkee donkee tools, How to use ahole saw 3. The material it is best suited to cut

Speed and quality of the cut

hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw The number of teeth a hole saw has per inch varies from type to type, but is typically between 3-14 TPI.
hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw As a general rule, the fewer teeth per inch a hole saw blade has, the faster it will cut through a workpiece. However, because the teeth are larger and more coarse, they are more likely to tear the fibres of the material you are cutting and will ultimately leave a finish that will be rougher. This would be fine for jobs where the neatness of the hole is less important and where it will not be visible once complete.
hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw The more teeth a saw blade has, the slower it will cut through a workpiece. However, because the teeth are smaller and finer, they are less likely to tear at the material’s fibres and so the finished cut will be smoother. A neater hole is needed for jobs where the hole will be visible and where precision is needed like making holes for a lock set.
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Low TPI hole saw blades (1-4 teeth per inch)

Saw blades with a low TPI tend to have larger teeth with deeper gullets in-between. Saw blades like these will cut quickly but much more aggressively, leaving a rough finish to your workpiece.

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Medium TPI hole saw blades (5-9 teeth per inch)

Saw blades with a medium TPI are generally a balance between fast, aggressive sawing and slow, smooth sawing.

High TPI hole saw blades (10+ teeth per inch)

Saw blades with a high TPI tend to have smaller teeth with shallower gullets in-between. Saw blades like these will cut slowly but will produce a much finer, smoother cut.

Measuring TPI

hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw To find out a saw blade’s TPI, start measuring from the middle of a gullet (usually its lowest point). However many teeth fall within an inch from this point is how many teeth per inch your hole saw has.
hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw It is worth noting here that not all hole saw blades have a round number of teeth per inch. Some hole saw blades may have, for example – 3 ½ TPI.
hole saws, annular saws, hole cutters, cutting tools, TPI, teeth per inch, wonkee donkee tools DIY guide, how to use a hole saw It is also worth noting that some variable pitch hole saw blades fluctuate and will have a different number of teeth per inch compared to the next inch along its saw blade. This may, for example, be expressed as 4/6 TPI. Which means it has between 4 and 6 teeth per inch.

Materials

hole saws, cutting tools, DIY guide, wonkee donkee tools, How to use ahole saw It is difficult to say with any accuracy that a particular number of TPI is suited to cutting a certain material as there are other important factors to consider such as the material that the hole saw teeth are made from.

For more information on which hole saws are best for cutting certain materials, see the page entitled: What are the different types of hole saw?

Hole saw teeth

hole saws, cutting tools, DIY guide, wonkee donkee tools, How to use ahole saw Some hole saw teeth are often made from or coated with a material to increase their working properties. Typically to improve hardness, wear resistance and cutting ability. For more information see the page entitled: Which material should I choose?
Gulleted teeth, hole saws, cutting tools, DIY guide, wonkee donkee tools, How to use ahole saw

Gulleted/square teeth

Gulleted or square teeth are a little different from standard saw teeth but you can still work out their TPI (teeth per inch) by measuring an inch from the middle of its gullet (usually its lowest point) and counting how many teeth fall within that inch. This particular image shows a square toothed hole saw with 3TPI.

Hole saws and core drill bits with gulleted or square teeth are for use on hard abrasive materials such as concrete, brickwork, ceramic tiles, glass and stone.