First of all, let me tell you about taper and taper turning on lathe.
And finally I will show you 6 methods to cut angles on a lathe.
What is a Taper?
Taper is defined as a uniform increase or decrease in the diameter of the cylindrical workpiece measured along its length.
What is Taper turning?
In a lathe, taper turning is a process of obtaining a conical surface by gradually increasing or decreasing the diameter of a cylindrical workpiece.
In a lathe machine, the taper is turned by feeding the tool at an angle with the axis of rotation.
The angle measured between the rotation axis of workpiece and feed axis of tool is considered as a half taper angle.
Now let’s discuss the taper turning methods.
How to Cut Angles on a Lathe?
There are total 6 methods for turning a taper on a lathe machine.
- Taper turning by swiveling the compound rest
- Taper turning by using taper turning attachment
- Taper turning with tailstock set over method
- Taper turning by using a broad nose form tool
- Taper turning using double feeds
- Taper turning by using numeric control lathe
Let me give you a little information about these methods so you will know exactly how you can cut angles on a lathe.
#1) Taper turning by Swiveling the Compound Rest
This is a simple method of taper turning in which the workpiece rotates on the lathe axis and the feed is given at an angle to the axis of rotation of workpiece.
The single point cutting tool is mounted on the compound rest and this compound rest is attached with the circular base which is graduated in degrees.
Because of this, the compound rest can be easily swiveled at the particular angle (see above image).
One important thing to note here is that the angle required to be set for the compound rest should be the half of the taper angle.
Once this compound rest is set at the required half taper angle, the tool will be automatically fed in the angular direction when the compound slide screw is rotated.
In this way, the taper is formed on the workpiece.
The cross slide has limited movements, hence the taper that can be formed using this method is short but steep.
In this method of taper turning, the feed is given by hand. So there are changes that poor surface finish can appear on the tapers.
If the half taper angle is known, then it can be easily set on the compound rest. But if it is not known, then it can be found out from the diameter of smaller end and larger end.
You can see the line diagram of complete setup for taper turning by swiveling the compound rest. (See above image)
#2) Taper turning by using Taper Turning Attachment
Taper turning attachment method is generally used for generating external tapers only.
As you can see in the above image, the taper turning attachment is bolted at the back side of the lathe machine.
This attachment has a guide bar which can be set at the desired angle as per the required taper.
As the carriage moves parallel to the axis of the lathe, the guide rod causes the tool to move in and out according to the settings of the guide bar.
This way, the taper settings on the guide bar are replicated on the workpiece.
The main advantage of using this attachment method is that the lathe centers are kept in alignment.
#3) Taper turning with Tailstock Set Over Method
This method of taper turning is generally used for the external tapers only.
Small tapers can be done on the longer workpiece by using this method.
In this method, the set over of tail stock is calculated by loosening the nut from the center axis of the lathe. Following formulas are used for these calculations.
Tail stock set over = Taper length × Sine of half of taper angle
(D – d) / 2 = l × sin (α/2)
D = diameter of larger end of cylindrical job (in inches),
d = diameter of small end of cylindrical job (in inches),
l = length of taper to be done on cylindrical workpiece (in inches),
α = taper angle
When a part length of the job is to be given taper,
Then the tailstock set should be
Tail stock set over = ((D – d)/2)) (total length of the cylindrical job/length of taper)
= 1 × sin (α/2) × (total length of the cylindrical job/length of taper)
#4) Taper turning by using a broad nose Form Tool
The Form Tool method is used only for turning short tapers.
In this method, the broad nose form tool is used which forms taper on the workpiece.
The edge of the fo tool must be straight for the accurate tapers to form.
#5) Taper turning using Double Feeds
Double feed can also be used to obtain a taper on the workpiece.
The double feed includes two feeds
- Perpendicular to axis of rotation and
- Parallel to the axis of rotation
The resultant of these two feeds will give a taper section on the workpiece.
For performing this type of double feed operation on lathe, the feed rate can be changed by using the apron mechanism of the lathe.
#6) Taper turning by using Numeric Control Lathe
In Numeric control lathe, the programme is set to make the taper on the workpiece. The cutting tool moves as per the programme set for the taper cut and finally the taper is formed on the workpiece.