A balancing act for the business end of cutters
Secret lies in getting the rotor head stable
Published 06/09/2011 | 05:00
At the business end of all hedgecutters is, of course, the head. Within this, the rotor spins at speeds in the region of 3,000rpm. Bolted to the rotor are the flails, which perform the actual task in hand of cutting whatever greenery, vegetation or trees at which they are aimed.
Anything spinning at that kind of speed needs to be balanced. Otherwise it will vibrate anything from mildly to extremely violently, depending on how far out of balance it may be. This effect is similar to a car's wheel being out of balance and it can cause quite a serious vibration at certain speeds on the road.
With a car, though, speeding up or, more sensibly, slowing down will cause this vibration to cease and can be corrected when the vehicle is brought to a tyre centre and the wheels balanced. A hedgecutter rotor is driven at a constant speed, so if there is a vibration in the head it will not go away until the problem causing the vibration has been rectified. Even mild vibration can cause problems with loosening bolts on the hedgecutter head and boom. More serious vibration will shake it to pieces, making it a dangerous machine to be around.
Curing an imbalance may be as simple as replacing a broken flail or, in more serious cases, straightening a bent rotor or removing a broken flail bracket and welding a new one in place. The latter two will usually require the rotor to be checked and balanced afterwards because the dynamics of the rotor will have changed with the repair.
Who does this kind of work? As it turns out, less than a handful of firms in the country. I only discovered recently that there was one such firm virtually on my doorstep, Nicholas Gainford Ltd, just outside Killane, Enniscorthy, Co Wexford.
Owned and run by Nicholas Gainford and his wife Mary, the company provides both repair and engineering services to the agricultural, plant, truck and forestry industries. Nicholas has had a German-built Schenck balancing machine for a number of years and has been quietly working away balancing hedgecutter heads under the shadow of Mount Leinster.
I visited to see what was involved in the balancing process. To balance a rotor requires it to be removed from the hedgecutter head and stripped of all flails, before being placed in the balancing machine.
"You start out with the stripped rotor and set it up in the balancing machine. The balancing machine spins the rotor shaft at speed and the computer determines where the imbalance is in the shaft," Nicholas says. The Schenck balancer indicates the angle of imbalance and the weight needed to correct it.