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How to adjust a Clark patent expansive bit?

Shop for Expansive bits

Close up of the head of a clark patent expansive bit showing the clasp adjuster mechanism This guide explains how to adjust the cutter on a Clark patent expansive bit, which is the type that does not have teeth along the top surface of the movable blade.
Image showing how the diameter of a wright patent expansive bit is adjusted by rotating the adjuster screw Wright patent expansive bits (the ones with the teeth) are extended or shortened by turning the adjuster screw with a screwdriver.
Image to show both types of expansive bit: the Wright patent expansive bit and the Clark patent expansive bit For more information on the differences between the two different patents, see: What are the different types of expansive bit?

Adjusting a Clark patent blade

Image of a Clark patent expansive bit with its second outrigger cutter The process for adjusting the cutter on a Clark patent expansive bit is similar to the method used for adjusting Wright patent bits. The biggest difference is that turning the lock screw will not automatically adjust the bit.
A DIYer using a hexagonal socket wrench to loosen the adjuster screw on an expansive bit

Step 1 – loosen lock screw

Using a screwdriver or a hexagonal socket wrench, loosen the lock screw by turning it anti-clockwise. You will notice that the metal retainer on the body of the bit starts to spring slowly upwards.

Diagram to show that the locking bolt on an expansive bit has been opened wide enough that the outrigger cutter can move freely from side to side This should allow the cutter to move from side to side.
A DIYer showing the location of the guide line on an expansive bit, which tells you which length you have set it to

Step 2 – Set up bit

Slide the cutter so that the indicator line on the body is aligned with the measurement on the expansive bit that you would like your hole size to be.

Image to illustrate that the number on the adjustable cutter of an expansive bit indicates the width of the bore hole rather than the distance between the guide line and the outrigger spur The numbers on the gauge show the total width of the entire hole, rather than the distance between the number and the outrigger cutting spur. This measurement is equal to twice the distance between the tip of the bit and the outrigger spur (i.e. the diameter of the circle that the spur will cut).
Image of a DIYer tightening up an adjuster screw on an expansive bit

Step 3 – Fasten the lock screw

Tighten up the lock screw so that the bit is secure once again. You should see the retainer clamp down on the angled upper edge of the cutter.

Image to show that the expansive bit is now ready for use Your bit is adjusted and ready for use!

Changing the blade

Slide out the cutter you are changing to make a space for the new cutter Changing the blade on a Clark patent expansive bit very closely follows the process for adjusting the cutter that is already in place. At step two in the above guide, instead of sliding the cutter to a new position, remove it from the bit entirely by pulling it free.
Insert the alternate adjustable cutter into the expansive bit Replace it with the second cutter, sliding it into position and securing it with the lock screw as per steps two and three above.