Dear Thomas and Katie,
This page is intended to give you a flavour of some of the engineering work that Dad is involved in. We manufacture a wide range of diverse components but particularly specialise in parts for excavators and refurbishment operations. Today we are going to be making bushings and pins to repair a worn-out dipper arm casting.
We start with a steel ‘blank’; that is a piece of rough metal that we must shape on special machinery to the required shape. You can see the blank stock- in this case round bar- on the top right of the photo above, and the finished products we made from it lined up on the left and foreground of the picture.
First the steelstock is roughly sawn to size on a machine called a power hacksaw, or donkey saw. It’s called a donkey saw because of the ee-aw ee-aw sound it makes when it’s operating! The metal is flooded with a special coolant to stop it overheating during the cutting operation, as it will be for many of the processes shown here.
The round bar is then put into a machine called a lathe. All our large machine tools are made in England because even today with cheap far-eastern imports the English, northern european countries and America still make the best quality machinery for our industry. This lathe was made in Essex, near where you used to live!
The lathe shapes the parts to the correct precise dimensions. It is very important that all the parts we produce are made extremely accurately (we call this tolerance) in order for them to fit correctly into their housings or mesh with each other.
Any imperfections or burrs that remain on the work are removed on a machine called a band surfacer:
Then, when all the measurements have been checked and double-checked, it’s time for some heat treatment!
This is done in a special furnace that can heat the metal to over 1,000 degrees; the parts become glowing red-hot and are then cooled rapidly in a special oil tank in a process called hardening. They are then reheated to a lower temperature in a process called tempering. The end result is a very hard but non-brittle component that will last for many years when it is fitted to a digger.
While the parts are cooling we can bring in the dipper arm to be machined ready to accept the new pins and bushings we have made. We use one of these…
The holes, more correctly called bores, in the white circle are the ones we have to repair. Service wear has distorted and damaged the shape of the original bores to the point where they are no longer round, so we must enlarge the original diameter by using a special drill called a boring head and then finish with a tapered reamer to an exact dimension.
Again, we do this to precise measurements and of course the parts waiting in the furnace are designed to fit into the enlarged bores to a specific tolerance also. Once everything has cooled down we use a special hydraulic press to pressfit the parts we have made into the arm. The press pushes the parts in with a force of 50 tonnes- rather like putting 50 small cars on top all in a column!!
So, especially you Thomas, when you are playing with your Christmas present I hope you will look at the parts you are assembling and think of Dad and his work!