How to cap framerate to 60fps in QT opengl

Question

I used to cap the render framerate in GLFW using the function.

glfwSwapInterval(1);

Now i am building a Opengl project in QT using the Qt opengl features.

in the main function i set the global value.

QGLFormat  format;
    format.setDepthBufferSize(24);
    format.setStencilBufferSize(8);
    format.setSampleBuffers(true);
    format.setSamples(4);
    format.setSwapInterval(1);
    QGLFormat::setDefaultFormat(format);

This is how the Qt opengl class header looks like.

   class GLWidget : public  QGLWidget
{
    Q_OBJECT;
public:
    explicit GLWidget(QWidget *parent = 0);
    void initializeGL() override;
    void paintGL() override;
    void resizeGL(int w, int h) override;
    QTimer timer;

};

In the constructor for the class

 GLWidget::GLWidget(QWidget *parent) :QGLWidget(parent)
{
    connect(&timer, &QTimer::timeout, this, [&]() {  
        QElapsedTimer elapsedtimer;
        elapsedtimer.start();
        updateGL();
        qDebug() << elapsedtimer.elapsed();
    });
    timer.setInterval(0);
    timer.start();
}

But still the render loop is not synced the Qdebug values keeps varying from 8 to 16.