How to be sure of your excavator bucket size
A common issue for many sites is getting excavator bucket sizing right. It seems straightforward on the face of it – you order a given size and that’s what should arrive. In practice, it’s not that simple. Typically, GP buckets for 30t excavators can vary by more than 12%. If you’re working to a 10% margin, that could mean the difference between making or losing money.
When excavators are hired for a site, it’s important to stipulate bucket sizes and then run a check to see if you have what you paid for (no one wants to pay for an optimum bucket size only to find that something smaller has been fitted). Assuming your bucket size has been agreed on prior to the machine arriving on site, how can you know if the correct version has been fitted?
The easy option
Buckets are a mixture of curves and tangents, which make measuring a cross section difficult. In the past, we’d sketch it up and try to overlay a grid of known sizes (typically 100mm x 100mm). We’d then count the squares fully within the bucket’s perimeter, and group ones only partially within the perimeter. The addition of the two gave us an approximate cross sectional area such that, if we knew the throat width (easily measured using a tape), we could approximate the struck volume. This method works, but accuracy is variable. You could measure the volume of water required to fill the bucket but, while it’s very accurate, it takes time, requires a serious workaround to measure the volume of water, and it’s not overly sustainable.
The advanced, precision option
What we do is slightly more advanced:
Take side-on photos of the bucket, trying to ensure the camera is centred and level
Measure four or five easily identifiable points (eg the distance between pins, the depth of gum protection, a tangent length etc)
Put the photo into autocad and trace the bucket’s outline
Use the measurements taken earlier to scale the drawing to suit
Use the autocad measuring tool to get a surface area and then use the throat width to calculate the volume.
We’ve found this method gives good, repeatable results. From start to finish, it typically takes about an hour to go from taking the photos to producing the report. While you might wonder if you can be bothered, like many of the disciplines we follow at CEA, it’s a small investment up front that makes a huge potential saving down the track. Take this hypothetical – if your 75t bucket is off by 8%, and you’re managing 75,000m3 of cut, it’s going to take you 2,000 more bucket loads than you planned. That’s at least 2.5 days of unplanned work. Suddenly that 1-hour effort at the start is a smart and time-saving investment.
