Highcharts setExtremes overflow issue - highcharts

Question

I have a Highcharts column graph with 10 series on the x axis.
http://qaa.balcroft.com/images/chart1.png
I want to allow the user to zoom in so I added a button to setExtremes:
$('#zoomInButton').click(function () {
var chart = $('#container').highcharts();
chart.xAxis[0].setExtremes(4, 9);
});
However this causes the graph to overflow into the y axis title area on the left hand side.
http://qaa.balcroft.com/images/chart2.png
I've tried amending xAxis.minRange and yAxis.overflow but neither fixes the problem.
Any suggestions?
The function to create the graph is
function inialiseGraphOnLoad(strOrgCode, strLevelCode, currentLevel, strTeamName){
var jsonMimeType = "application/json;charset=UTF-8";
$.ajax({
type: "POST",
url: "ajax/getStaffOnLoad.php",
cache: false,
data: {org: strOrgCode, levelcode: strLevelCode, level: currentLevel},
beforeSend: function(x) {
if(x && x.overrideMimeType) {
x.overrideMimeType(jsonMimeType);
}
},
dataType: 'json',
success: function(dataDepts){
//Create array of employee names
chartWidth = 0;
maxZoom = 0;
var listDepts = [];
for (var i = 0; i < dataDepts.employees.length; i++) {
chartWidth = chartWidth + 250;
maxZoom = maxZoom + 1;
var arrayEmployee = dataDepts.employees[i].name;
var splitResult = arrayEmployee.split("||");
var strEmployeeCode=splitResult[0];
var strEmployeeName=splitResult[1];
var employeeURL = serverURL + strEmployeeCode + '">' + strEmployeeName + '</a>';
listDepts.push(employeeURL);
}
var mainPageWidth = $('#staffMainPage').width();
if(chartWidth > mainPageWidth){
chartWidth = mainPageWidth;
}else if(chartWidth < 500){
chartWidth = 500;
}
$('#hid_lastPage').val(maxZoom);
//Create series array
var seriesArray = [];
for (var i = 0; i < dataDepts.groups.length; i++) {
seriesArray.push({
name : dataDepts.groups[i].name,
dataLabels: {
enabled: true,
rotation: -90,
color: '#424242',
align: 'right',
x: 4,
y: 10,
style: {
fontFamily: 'Verdana, sans-serif'
},
formatter:function(){
if(this.y > 0){
return this.y;
}
}
},
color : dataDepts.groups[i].colour,
data : []
});
for (var j = 0; j < dataDepts.employees.length; j++) {
if(i == 0){
seriesArray[i].data.push(dataDepts.employees[j].rating1);
}else if(i == 1){
seriesArray[i].data.push(dataDepts.employees[j].rating2);
}else if(i == 2){
seriesArray[i].data.push(dataDepts.employees[j].rating3);
}else if(i == 3){
seriesArray[i].data.push(dataDepts.employees[j].rating4);
}else if(i == 4){
seriesArray[i].data.push(dataDepts.employees[j].rating5);
}else if(i == 5){
seriesArray[i].data.push(dataDepts.employees[j].rating6);
}else if(i == 6){
seriesArray[i].data.push(dataDepts.employees[j].rating7);
}else if(i == 7){
seriesArray[i].data.push(dataDepts.employees[j].rating8);
}else if(i == 8){
seriesArray[i].data.push(dataDepts.employees[j].rating9);
}else if(i == 9){
seriesArray[i].data.push(dataDepts.employees[j].rating10);
}else if(i == 10){
seriesArray[i].data.push(dataDepts.employees[j].rating11);
}else if(i == 11){
seriesArray[i].data.push(dataDepts.employees[j].rating12);
}else if(i == 12){
seriesArray[i].data.push(dataDepts.employees[j].rating13);
}else if(i == 13){
seriesArray[i].data.push(dataDepts.employees[j].rating14);
}else if(i == 14){
seriesArray[i].data.push(dataDepts.employees[j].rating15);
}
}
}
// Set up the chart
var chart = new Highcharts.Chart({
chart: {
renderTo: 'container',
type: 'column',
width: chartWidth,
height: 550,
marginBottom: 100,
margin: 80,
options3d: {
enabled: true,
alpha: 5,
beta: 10,
depth: 50,
viewDistance: 25
}
},
title: {
text: strTeamName
},
subtitle: {
text: 'Quality Rating By Employee'
},
xAxis: {
categories: listDepts,
useHTML: true,
minRange: 5,
title: {
text: '<br>(click an employee name for more detail)',
style: {
color: '#6E6E6E',
fontSize: '1em',
fontFamily: 'Verdana, sans-serif'
}
}
},
yAxis: {
min: 0,
title: {
text: 'Quality Rating (%)',
align: 'high'
},
labels: {
overflow: 'justify'
}
},
tooltip: {
valueSuffix: ' %'
},
scrollbar: {
enabled: true
},
plotOptions: {
column: {
depth: 25
},
bar: {
dataLabels: {
enabled: true
}
}
},
series:seriesArray
});
}
});
}