What is Thread Grinding?
Thread grinding is a process of either cutting or finishing the threads on a workpiece by using a specially dresses grinding wheels.
The principle of thread grinding is similar to thread milling, but here the grinding wheel is used instead of milling cutter.
The grinding wheel consists of abrasive particles on the periphery that cuts the threads on the workpiece.
Thread grinding is a process which can also be used to get good finishing as well as accurate threads which is not possible by other thread cutting methods (like threading chasing, threading with taps, threading with dies, etc).
Types of Thread Grinding Process
There are 3 types of thread grinding process;
- Pass over grinding
- Plunge grinding
- Centerless thread grinding
Let’s discuss each of these thread grinding processes one by one.
#1) Pass over grinding
The pass over grinding is a process similar to the thread cutting operation that is done on a metal lathe with a single point cutting tool.
The only difference is that here the single point cutting tool is replaced by a grinding wheel.
Thread grinding with a single rib grinding wheel is shown in the above image.
During the threading operation, the grinding wheel spins against the rotation of the workpiece.
Apart from the spinning, it is given a relative axial feed with the help of a lead screw.
To get the desired depth of cut, the grinding wheel is passed multiple times on the workpiece.
Because of this reason, the pass over grinding is also known as transverse thread grinding.
In this process, a multi-rib grinding wheel is also used for speedier thread grinding operations.
#2) Plunge grinding
Plunge grinding is a type of thread grinding process that uses a grinding wheel with multiple ribs that are usually longer than the length of the thread.
This grinding wheel is fed into the workpiece upto required depth of thread and at a same time it is also fed axially equal to the distance of pitch of the thread.
Plunge grinding is generally used for making threads of a shorter length.
This type of thread grinding is basically used when the production is more important than accuracy.
#3) Centerless thread grinding
Centerless thread grinding is used to make threads on headless screws.
In this process, the workpiece is fed between the grinding wheel and a regulating wheel.
The complete process of centerless thread grinding is shown in the above image.
You can see that the unthreaded workpiece enters from the right side and the threaded workpiece is out from the other side.