Levering hinge cuts

RC1 · 28th May 2007, 06:44 AM

http://www.mydeo.com/videorequest.as...1055&CID=90341

This link is to a video of a treefelling aid of which I designed and now manufacture from the UK. I first posted the link on the US based discussion forum ????????.com. It turned into a very long winded disscusion the kind of which doesn't need to be repeated. If anyone is curious about the main Tool 'BlockDriver' then by reading through the TBuzz/rant and rave/new arborist tool, thread should satisfy the majority of your curiousities. The following is the latest addition to that thread (submitted today) which now also goes out to the Treeworld members:

I?m not great with numbers perhaps someone could advise me if I?m working this out correctly.

Many have seen the Blockdriver video and will now remember the technique.

Although, not a great emphasis was put on the value of the small lever-bar in the thread. It is actually fantasic for step/bypass cuts before the BlockDriver is warranted, ie further up the tree. However, it is suggested in the manual that it should not be implemented in hinge-cuts. I took this measure so to avoid the bars misuse by overloading and inevitable distortion, but that doesn?t mean it won?t work.

It obviously does work very well, so long as you calculate/incorporate the SWL.

By my calcs 25 KGF on the bar handle (mechanical advantage 9.25:1) = 231.25 on the lifting plate, which would then tip an evenly weighted up-right stem (notched by 1/3) of up to 925 KG. This calculation accounts for the pull created on the notched side of the hinge but not the bending factor of the hinge-wood itself, nor the friction caused by the point of contact between bar and wood.

Am I working this out correctly?

The reason I ask is that as things stand at present, I will be exhibiting the Blockdriver and now this latest ?heavy duty? Felling lever (see attachment) at our UK Arborist Trade Fair next month, under the wing of Treeworker.co.uk.

And in a bid to sound semi-intelligent in putting across my own ergo/eco/techno babble, my formulas/factors obviously need to be correct.

I can?t upload videos of the big bar working at present due to a problem with my PC. But for now, I?d just appreciate some input on those calculations. Thanks

Reg

Ekka · 28th May 2007, 02:27 PM

Quote:

Originally Posted by RC1

By my calcs 25 KGF on the bar handle (mechanical advantage 9.25:1) = 231.25 on the lifting plate, which would then tip an evenly weighted up-right stem (notched by 1/3) of up to 925 KG. This calculation accounts for the pull created on the notched side of the hinge but not the bending factor of the hinge-wood itself, nor the friction caused by the point of contact between bar and wood.

Am I working this out correctly?

Reg

First off Reg, great inventions, could've used that ratchet device on those darned cuban logs we had the other day.

Regarding your calculations .... I would just stop at saying there's 231kg of force applied by the lifting plate ... end of story.

The reason is for what you have discovered, friction, hingewood strength etc. Also the diameter of the log plays a difference as well as the height.

Imagine a short fat log weighing 1000kgs and a tall skinny one like a pine ... very different in getting them going over. With the tall skinny one it doesn't take much to get the centre of gravity beyond the hinge but the big one takes heaps.

As you know on a tall spar a wedge lift of 25mm in the back cut can move the tip 25cm but on a shorter fatter log not as much movement would occur.

Just my 0.02

RC1 · 28th May 2007, 02:43 PM

Yeah Eric, I hear what you're saying.
I realise Ive not accounted for the momentum needed to keep the section going, push a tall-skinny or short-fat section past its centre of gravity or bend hinges of different lengths and thicknesses. My calcs only deal with the dead weight of the initial lift. Your right though, its not that simple in reality, but its a starting point. Thanks for your input.

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28th May 2007, 02:43 PM	#3 (permalink)
RC1 Semi-mature vigorous tree Join Date: Jan 2007 Location: Macclesfield England Posts: 148	Yeah Eric, I hear what you're saying. I realise Ive not accounted for the momentum needed to keep the section going, push a tall-skinny or short-fat section past its centre of gravity or bend hinges of different lengths and thicknesses. My calcs only deal with the dead weight of the initial lift. Your right though, its not that simple in reality, but its a starting point. Thanks for your input.