Tethering A Runaway

I have been specialising in stump grinding for the past 18 years throughout Anglia. Over that time period I have experienced loss of drive to the wheels on a number of occassions while on site (a real bummer) and twice while up/down loading from the van. In the past this happend through broken drive chains to the grinders live axle. More recently, loss of drive while downloading in a car park owing to a disintergrating taper lock bushing on the hydraulic motor drive sprocket. The taper lock bush was of the sintered (die-cast) type most commonly sold. These are very brittle, and great care must be taken with their installation. I was lucky on this occassion as my 850 kg runaway grinder trundled down the ramps and eventually came to a stop short of hitting anything. I have now replaced the sintered type of taper lock with a solid steel taper lock---at greater cost--- and as a further precaution, designed a tether connecting one end of the grinder to the vans tow ball as it exits down ramps. This worrying experience needed further investigation. I discovered the woodruff key did not have clearance between its inner face and the bottom of its keyway on the bush. This placed strain on the fragile bush at perhaps its weakest point --- the keyway. This is a heads up to those of you who do your own repairs or rely on outside repairers. It is an easy oversite for a repairer to quickly grab a woodruff key that seems to securely fit without checking for clearance as described earlier. This can lead to disasterous or even fatal consequences when working with heavy machinery. I eliminated the problem of broken drive chains some years ago by going over to higher tensile strength chains, and installing a chain lubricator of my own design. I have now gone over to steel taper lock bushes which used to be common place years ago, but are more difficult to find and seven times the price of sintered taper locks ( what price safety?) Lessons learned!

Hi Gary,

I fixed a 12V winch permanantly to the stump grinder, as well as my own anchor point design next to the van's bulkhead several years ago. The cabled anchor point secures the machine whilebeing transported, and has been used to pull the machine up ramps into the van on past occassions when a drive chain has broken. I don't use it as a precautionary tether when downloading because it takes a long time to set it up and to get the machine to creep down the ramps to ground level. My quick release tether made from a lorry tie down strap is very quick and effective. Further, if the winch cable was in use as a tether while the machine broke away from its own drive while on the ramps , it's momentum and weight will probably tear out the anchor points

Replies

PRO

Gary RK February 17, 2018 at 11:29am

Could you use a 12v Winch (remote lead) mounted on the floor by the baulkhead and use when removing and retreive the stump grinder ?

It would therefore be 'under' tension all the teime and thus would not run away. Some I know has done smilar on a van for a large ride on as they didnt would to be seated while taking up / down the ramps.
Mike Lish February 17, 2018 at 11:49am

Hi Gary,

I fixed a 12V winch permanantly to the stump grinder, as well as my own anchor point design next to the van's bulkhead several years ago. The cabled anchor point secures the machine whilebeing transported, and has been used to pull the machine up ramps into the van on past occassions when a drive chain has broken. I don't use it as a precautionary tether when downloading because it takes a long time to set it up and to get the machine to creep down the ramps to ground level. My quick release tether made from a lorry tie down strap is very quick and effective. Further, if the winch cable was in use as a tether while the machine broke away from its own drive while on the ramps , it's momentum and weight will probably tear out the anchor points
Mike Lish February 17, 2018 at 12:10pm

Further, if the winch cable was in use as a tether while the machine broke away from its own drive while on the ramps , it's momentum and weight will probably tear out the anchor points. Having said that, I am currently trying to source a suitably strong spring to put inline with the tether thus reducing shock load. I have given the details to a few spring suppliers but no advice has been received.

Anyone know where I can get a double closed loop heavy duty extension spring?
- PRO
  
  Gary RK > Mike Lish February 17, 2018 at 12:18pm
  
  I'd talk to one of the UK trailer manufactures - IforW or Wessex Trailers.
  
  They build to spec and/or customise trailers and will probably have come across a similar requirement, so may be able to size/supply ?
  - Mike Lish > Gary RK February 17, 2018 at 12:44pm
    
    Thanks for that Gary, what a good idea. I have looked at some draw bar springs but they are the wrong configuration. Perhaps as you suggest trailer manufactrurers may be able to point me in the right direction.