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Friday 9 December 2016

A balancing act for the business end of cutters

Secret lies in getting the rotor head stable

Bruce Lett

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.

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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.

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"You then weld on the required balance weights onto the shaft at the indicated position to correct the imbalance," Nicholas adds.

All of this sounds relatively easy but, generally, there is a bit of damage done to the rotor shaft, necessitating repair.

"Vibration can be caused by the flail mounting holes, worn out from the retaining bolts not being kept tight or bent, or damaged rotors or shaft ends. Whatever the case, maybe we can straighten rotor, profile out the lugs (flail mounting brackets), weld them on and repair shaft ends," Nicholas states.

His workshop is equipped with a 600t press, lathes, gas and plasma profilers, which means he can pretty much repair any rotor within reason.

"We can cut the profiles out of mild steel or Hardox. For normal users, farmers generally, we use mild steel and for high usage, contractors, the Hardox because it's hard wearing," Nicholas says.

"Hedgecutters involved in road work are not too bad. You might get a few bearings problems. It's when you get into fields and hit stones, tree stumps or gate piers you find that the real damage is done."

Nicholas can provide a full rotor repair service as well as repairing rotor hoods, fitting new liners or whatever needs to be done.

Not restricted to just hedgecutter rotors, Nicholas can also balance the likes of combine harvester secondary drums and grass mower conditioner units.

His current balancing machine can handle items up to 3m long and up to 120kg in weight. When the current rush of harvest repairs are finished, Nicholas will commissio a new Schenck balancer.

"The new machine can cater for parts up to 5m long, 3t weight and up to 1.6m in diameter," he says. This means changes to the way work is done.

"We will be able to balance the rotor with the flails on and also we will be able the handle the new mulcher rotors," he says. "It's a big advantage to be able to run a rotor with its flails still attached, though we would always maintain the base rotor has to be right first and then put on your flails."

A sizeable investment has been made in buying the new machines. "It will have to run a lot of rotors to pay for itself," Nicholas says.

Nicholas quotes an average price of around €300 + VAT for the balancing of a hedgecutter head but prices vary.

For more information contact Nicholas Gainford on 053 925 5713 or check out his website, www.gainford.ie.

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