If you have a long piece of cylindrical material which you need to work on a lathe, how do you turn it? The problem is that you need to turn the whole length, and if you use the three or four jaw chuck to hold it, it will be necessary to complete the project in two steps.
Lathe Carrier, otherwise known as Lathe Dogs, are tools that fit on the headstock spindle of a lathe in the place of the regular chuck. Lathe dogs clamp around the workpiece and cause the rotary motion of the lathe’s spindle to be transmitted to the material being worked.
Lathe carriers, colloquially known as lathe dogs, replace a lathe chuck when an object is turned between an active and a dead center. The centers do not produce enough friction force to rotate the work, so a lathe dog is clamped on, providing the rotational force.
Lathe Dogs Are Used To Hold Projects Which Chucks Can’t
As lathe technology improves, lathe dogs are not used as often as previously.
Without using industry jargon, a lathe dog is simply a fitting installed either to the lathe headstock spindle or over the chuck. Instead of the chuck securing the cylindrical material to be worked, the lathe dog holds it in place.
A lathe dog is selected if the cylindrical material needs to be turned for its entire length. If the chuck held it, too much material “inside” the chuck would be left unturned.
If this happens, the section not worked in the first pass would have to be turned around and worked in a second pass from the other side.
The problem with this is that it is difficult to center the material when it is turned around. If it is not centered precisely, the second pass will be off-center and not aligned.
A hole is drilled in the middle of each end of the cylinders to be worked. A “center” is attached to the faceplate and another to the tailstock.
The “centers” attach to the holes at each end of the material to be worked. There are two types of centers, i.e., a live center and a dead center.
- A center that fits into the headstock spindle and turns with the work is called a live center.
- The dead center is used in a tailstock spindle and does not turn.
The lathe dog holds the cylindrical material and has a “bent” tail that catches the headstock spindle’s rotational movement. When the headstock spindle rotates, it causes the lathe dog to rotate on the “centers,” which in turn causes the material being turned to rotate.
The use of the lathe dog in this manner makes it possible for the whole length of the cylindrical material to be turned from end to end while being held by the lathe dog.
There Are Three Types Of Lathe Dogs
Applicable to all three types of lathe dogs is if the rotating mass of the dog setup is not done correctly or adequately balanced, the rotational motion may become off-center, which would cause the work to be rejected.
If this happens, the lathe dog may need to be counterbalanced, or the rotational speed may need to be reduced to complete the project successfully.
Standard Bent Tail Lathe Dog
A standard bent tail lathe dog is often used for cylindrical workpieces.
Standard bent tail dogs are available with both square head and headless set screws. The classic bent tail lathe dog with a headless set screw is safer than one with a square head set screw because there is less chance of the screw catching on the operator’s work clothes and causing an accident.
When a bent tail lathe dog is used, the tail fits into slots on the driving faceplate slot or a chuck.
The potential issue with standard bent tail lathe dogs is they can crow off-center. It means that because the rotational force is being applied to the side of the standard bent tail lathe dog, it can sometimes occur that the work will become off-center resulting in an inaccurate cut.
Two-tailed dogs are lathe dogs with two tails that can slot into opposing slots on the driving faceplate. These will equalize this torque between the two tails and cause the work to remain more centered, which will make it turn a lot truer.
Even if the two tails were not equal, it would significantly reduce this torque as a minor error would quickly reach an equilibrium point.
Straight Tail Lathe Dog
Straight Tail lathe dogs are rotated by catching a stud in the drive plate.
When a straight tail lathe dog is used, it rests against a stud on the faceplate, which drives the rotational motion.
Because the rotational force is applied closer to the straight lathe dog’s center, there is less chance of the work becoming unbalanced. The result is that straight tail lathe dogs can be used for more precise turning.
Clamp Lathe Dog
A lathe dog is designed to hold non-cylindrical-shaped material such as square, rectangular, or odd-shaped work.
Clamp lathe dogs have a moveable portion secured by two cap screws.
Clamp lathe dogs are used to turn abnormal shapes. Spindle speeds must be reduced when working with Clamp Lathe Dogs due to the unbalanced nature of the setup.
Conclusion
Lathe dogs get a bad rap in that very few metal turners still use them. Lathe dogs provide a useful function when the material is being worked between two centers; they cause the material which is being worked to rotate.
If material is being held between a live center and a dead center, there is not enough friction force to cause the material to rotate. Enter the lathe dog, driven by its tail, and the work van commences.
