Lathe Tips & Tricks : Finding the centreline
Ensuring your cutting bit is at the centerline of your workpiece is a basic skill needed to ensure optimal cutting performance.
If the cutting bit is too high, the cutting angle of the work bit will be too steep, and the bit will tend to rub more than cut, generating heat and reducing bit lifespan while cutting the work piece more slowly.
If the cutting bit is too far below the center-line, the cutting angle will be too shallow. Rather than rubbing against the side of the insert, the work-piece will be pushed to roll-over the work bit, leading to breakages and jams.
For super precise work special measuring devices are advisable, but if you want to avoid the time and cost of a dedicated set up, here is a quick trick to easily find the center-line on any workpiece:
1. Put the tool holder and cutting bit you intend to use in your tool post and align it roughly to the center of the work-piece by eyeball.
2. Advance the cutting bit until it is about 1-2cm away from the work piece.
3. Take a 30cm/12 inch steel rule and slide it between the work-piece and the tool-bit so that the center of the ruler rests between the bit and workpiece. It is not necessary for the ruler to be dead center.
4. Gently advance the cutting bit until the ruler is clamped between the bit and the workpiece.
5. Now, look end on (from the tailstock to the chuck). If the tool bit is on center then the rule should be sticking up at a 90 degree angle. If the tool bit is too high then the top of the rule should be leaning over the lathe. If the tool bit is too low, the top of the ruler will be facing away.
6. If the bit is too high or too low, adjust the height and repeat steps 3-6 until the ruler is pointing directly up at a 90 degree angle. You can use a set square on the lathe carriage
If the cutting bit is too high, the cutting angle of the work bit will be too steep, and the bit will tend to rub more than cut, generating heat and reducing bit lifespan while cutting the work piece more slowly.
If the cutting bit is too far below the center-line, the cutting angle will be too shallow. Rather than rubbing against the side of the insert, the work-piece will be pushed to roll-over the work bit, leading to breakages and jams.
For super precise work special measuring devices are advisable, but if you want to avoid the time and cost of a dedicated set up, here is a quick trick to easily find the center-line on any workpiece:
1. Put the tool holder and cutting bit you intend to use in your tool post and align it roughly to the center of the work-piece by eyeball.
2. Advance the cutting bit until it is about 1-2cm away from the work piece.
3. Take a 30cm/12 inch steel rule and slide it between the work-piece and the tool-bit so that the center of the ruler rests between the bit and workpiece. It is not necessary for the ruler to be dead center.
4. Gently advance the cutting bit until the ruler is clamped between the bit and the workpiece.
5. Now, look end on (from the tailstock to the chuck). If the tool bit is on center then the rule should be sticking up at a 90 degree angle. If the tool bit is too high then the top of the rule should be leaning over the lathe. If the tool bit is too low, the top of the ruler will be facing away.
6. If the bit is too high or too low, adjust the height and repeat steps 3-6 until the ruler is pointing directly up at a 90 degree angle. You can use a set square on the lathe carriage