Setting the height of the cutter when making a spur gear
When cutting a spur gear using a Browne and Sharpe type cutter it is essential that the center of the cutter is at the height of the middle of the workpiece. Gears with offset teeth will not mesh properly.
How not to do it
It is very easy to set this up visually so it looks ok. However it is only when it is too late the error is found. This can be easily shown by setting up the cutter on a stub arbor and fitting the dividing head with any piece of scrap round material. If a cut is made on one side and the workpiece is turned round 180º and another cut made then it becomes clear the two are at diffent heights.
fig cut on first side
fig cut on second side
It is hard just by looking to see if both of these are at the same height.
Even more convincing is to make a cut on one side, turn the workpiece through 180º and then move the workpiece round to the other side of the cutter.
It is not obvious from this photo that the cut is the same height as the cutter. This can be tested by moving the cutter so it is right next to the cut. Though this is better it might not be as easy to do due to the lack of space .
How to do it
It is easy to measure the diameter of the workpiece. It is easy to measure the overall thickness of the cutter. It is also possible to use the height of the axis of the dividing head.
If the center height of the dividing head is known then for the center height of the cutter to be correct, the height of its top surface is half the thickness of the cutter plus the center height of the dividing head
center height of dividing head 3.75 inches, ie 95.25mm
the cutter is 0.53mm thick, the half thickness is 0.265mm
the height of its top surface has to be set at 95.25 + 0.265 which is 95.515
This is done by using a height gauge. The table is raised so that a piece of cigarette paper placed between the cutter and the height gauge cannot move freely. The paper is removed and the table raised by the width of the paper.