Scroll bars with QScrollArea

I've created two scroll areas in Qt Designer. Each of them has size [(31,48) 1141 x 161] and [(31, 310) 1141 x 101], respectively. Then I've created two widgets copy of TimeDiagram class, I've set them sizes that are bigger than sizes of the respective scroll areas. And then I've set the objects to the areas. Vertical and Horizontal scroll bars are enabled.

Constructor of the window:

GraphicScaleDialog::GraphicScaleDialog(OutputData *outputData, QWidget *parent) :
    QDialog(parent),
    ui(new Ui::GraphicScaleDialog) {
    ui->setupUi(this);

    data = outputData;

    commonSAGridSpacing = 120;
    commonSAScale = 15;
    resultsSAGridSpacing = 120;
    resultsSAScale = 15;

    ui->commonSAGridSpacing_line->setText(QString::number(commonSAGridSpacing));
    ui->commonSAScale_line->setText(QString::number(commonSAScale));
    ui->resultsSAGridSpacing_line->setText(QString::number(resultsSAGridSpacing));
    ui->resultsSAScale_line->setText(QString::number(resultsSAScale));

    commonArea = ui->commonScrollArea;
    commonArea->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    commonArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    resultsArea = ui->resultsScrollArea;
    resultsArea->setVerticalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    resultsArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);

    commonDiagramWidget = new TimeDiagram(20, this);
    commonDiagramWidget->setGeometry(31, 41, 2000, static_cast<int>(data->outputSettings.flowQuantity * commonDiagramWidget->rowHeight));
    resultsDiagramWidget = new TimeDiagram(100, this);
    resultsDiagramWidget->setGeometry(31, 114, 2000, 101);

    commonArea->setWidget(commonDiagramWidget);
    resultsArea->setWidget(resultsDiagramWidget);

    commonArea->show();
    resultsArea->show();
}

The problem is to create two grids with timeline axis.

Is it right that I need to use QPainter for this problem?

UPD: May be problem in methods of TimeDiagram?

void TimeDiagram::paintEvent(QPaintEvent * /* event */) {
    QPainter  painter(this);
    draw(&painter);
}

//--------------------------------------------------------------

void TimeDiagram::draw(QPainter *painter) {
    painter->setRenderHint(QPainter ::NonCosmeticDefaultPen, true);
    QPen* pen = new QPen();
    pen->setWidth(1);

    pen->setColor(Qt::black);
    painter->setPen(*pen);
    for (int i = static_cast<int>(rowHeight); i < this->height(); i += static_cast<int>(rowHeight))
    //for (unsigned int counter = 0; counter < static_cast<GraphicScaleDialog *>(this->parent())->data->outputSettings.flowQuantity; counter++)
        painter->drawLine(0, i, this->width(), i);

    pen->setColor(Qt::lightGray);
    painter->setPen(*pen);
    for(int i = 0; i < this->width(); i += 30)
      painter->drawLine(i, 0, i, this->height());

    delete pen;
}