Using a grinding machine often involves the need for workholding. Workholding means anything used to fasten a workpiece to make sure that it can withstand the machining forces. Workholding between centers for cylindrical grinder is one way of doing this.
Ever since the practice of cylindrical grinding came into being, there have been many advances in the system. Today’s cylindrical grinders have modern wheel technology, advanced temperature controls, and precise drive systems.
Despite these developments, the workholding part of most cylindrical grinders have not changed much. If this part of the grinding machine is weak, it will affect the whole system. By learning more about how it works, those who are just beginning to use the machine would know how to use it properly.
What is Workholding for Cylindrical Grinder?
Workholding between centers is the method used by most machinists. Many of them believe that grinding between centers is the most effective way of shaping an object. In fact, most tool designers begin with this principle in their minds.
Advantages of the Method
One possible reason why the workholding between centers method is popular is stability. Even though the object is rotating, the centers will still stay in contact with each other. This stationary position makes this workholding method just like hard tooling.
With this method, even if you stop and restart your work, you do not have to worry about the concentricity of the object. You can also easily transfer from one machine to another. Unlike other methods, it will also involves less time and effort on your part.
Disadvantages of the Method
One disadvantage of workholding between centers is the limitation of diameters and lengths. This is because long parts that have small diameters might lead to deflection. This, in turn, can make it harder to achieve a round and accurate finish.
Moreover, as the diameter becomes smaller, it also gets harder to use the center points on the end parts.
But you can use a steady rest and other accessories to reduce cases of deflection. In any case, you need to make sure that the taper on the centers of the machine are compatible with the center drills.
Another limitation of this method is that there are plenty of shapes that cannot be formed between centers. If your object has complicated end features, it would be impossible to drill centers. In other words, your cutting rate would not be accurate.
With this method, you could still turn most of the object through centers. But then you will need to perform a second operation to cut off prep the end features. This will only make the whole process more expensive plus it could lead to inaccurate results.
Cleaning Your Cylindrical Grinder
To make the most out of the workholding between centers method, you need to make sure that each part of the machine is smooth and clean. Even the tiniest piece of dirt can affect its performance and cause a deflection.
If you are doing a regrind, the effects of dirt and other contaminants are even more noticeable and could cause a runout.
Live Centers and Dead Centers
There are two basic types of centers: the live center and the dead center. You fit a live center on the spindle of the headstock. The live center rotates along with the object you are working on.
Meanwhile, you fit a dead center on the spindle of the tailstock. This type of center comes in handy when you need to support the other end of an object. The good thing about live centers is that they can come with extended points.
The longer points may be less rigid but they can give maximum tool clearance. Shorter points are more rigid but they do not offer as much maximum tolerance as the longer ones.
To choose the right kind of live center, you must first identify the purpose that you need it for. This means that you should consider the weight of the object, size of the center hole, pressure of the tailstock, and the need for tool clearance.
Another thing that you should take note of is the maximum limits of your operation. If you go over the limits of a live center, you are putting yourself in a dangerous situation. In any case, ask your seller or inquire with the manufacturer about these limits.
As for dead centers, when they begin to show wear, you need to reground them as soon as you can. You will notice this once you observe changes in the finish and surface of your work.
These are often acceptable, but when if you see any wear rings and grooves, then you need to replace the center as soon as possible.
Before you use a live center or a dead center, make sure that you check the central hole of the part. If the hole is off center or shallow, this can result into a workholding problem. The same thing applies if the hole is badly formed and drills are not maintained properly.
Furthermore, do not settle for cheap centers because they might break easily after regrinding them several times. After you have finished regrinding, see to it that the concentricity and point angles are the same as before.
Specific Types of Centers
Aside from the two basic types, there are several other specific types of centers. These include the centerball center, half center, inserted type center, ordinary center, pipe center, revolving center, and tipped center.
The type of center that you need will depend on the shape of your object as well as the kind of operation you plan to do.
Regardless of the kind of center that you use, the important thing is that you make sure they are of good quality. See to it that the center is hardened, tempered, and consists of high carbon steel. This kind of center is strong and resistant to wear.
A Final Note
In choosing your workholding method, consider first the size as well as the type of object you plan to work on. You should also take note of the complexity of the design and the number of parts. This way, your workholding operation will be a success.
When workholding between centers for cylindrical grinder, make sure that you understand how the method works. You must also consider how much time and effort your operation will need. In doing so, you will be able to complete your grinding project with great efficiency.