Directional pull line for felling

[Ekka]

It must be time for experiments. Why don't we do some and post the results here along with the method.

An idea I had was to set a model in a vice fixed to a set of bathroom scales. Tie off at the top and apply 20kg of pull (measured on a scale) from a 60 degree angle, measure the new weight on the bathroom scale and measure the flex in the spar at the top.

Then do the same but tied off at the bottom.

You'll then know if the there is any difference in the downward or outward force.

Any one else got some ideas on how to set up an experiment?

 

[glens]

I cannot get past the talk of the hinge <i>action</i> being part of the equation, if that's in fact what he's saying...

 

[caryr]

 

[Ekka]

Hey Caryr

Attached is what I was thinking, but I'm not with you mate, a diagram of your idea would be better.

If you're pulling more straight down that's not how we fell trees, we don't want to be under them when they come. Everyone knows that at 45 degrees you're right on the edge so you tend to go that bit further, 60 degrees is fair.

 

[a_lopa]

mike?

 

[glens]

Hey Caryr

Attached is what I was thinking, but I'm not with you mate, a diagram of your idea would be better.

If you're pulling more straight down that's not how we fell trees, we don't want to be under them when they come. Everyone knows that at 45 degrees you're right on the edge so you tend to go that bit further, 60 degrees is fair.

Ekka,

Try it like in this modified version of your diagram.&nbsp; The ruler may not be necessary, however (I can't figure why you want it).&nbsp; Then you'll be able to see first-hand what has been said by some of us all along.&nbsp; Try the same pull direction/distances with the line draped down the back and with it affixed to the top.

When I discussed it, I used 45&deg; because it provides for the greatest downward pull in any situation even approaching sanity with a spar.

I agree that 60&deg; would be a better minimum choice in practice, but it doesn't serve so well to exaggerate/illustrate the point.&nbsp; If the object is not a spar, but has limbs present above the tie-in point, even 60&deg; may be too steep.

Glen

 

[fpyontek]

glens' experiment

Ekka,

Try it like in this modified version of your diagram.&nbsp; The ruler may not be necessary, however (I can't figure why you want it).&nbsp; Then you'll be able to see first-hand what has been said by some of us all along.&nbsp; Try the same pull direction/distances with the line draped down the back and with it affixed to the top.

When I discussed it, I used 45&deg; because it provides for the greatest downward pull in any situation even approaching sanity with a spar.

I agree that 60&deg; would be a better minimum choice in practice, but it doesn't serve so well to exaggerate/illustrate the point.&nbsp; If the object is not a spar, but has limbs present above the tie-in point, even 60&deg; may be too steep.

Glen

I did a physical modeling of your diagram in "diagram.png" and posted the results in arborist-experiment.pdf.
Fred

 

[Ekka]

Hey Fpyontek

Well done on your experiment.

What I'm trying to discover is ... is there any difference between tying the log up at the top only, or going down the backside. In your experiment I'm not sure if you tried both and measured any variables.

Please elaborate, what we are in debate over is the differences. It's killing me!

 

[glens]

I did a physical modeling of your diagram in "diagram.png" and posted the results in arborist-experiment.pdf.
Fred

Exemplary work, my friend!

The discrepancies in the horizontal forces are likely due to the large flat base of the "spar" and those of the (backside) vertical to the extremely large relative rope size and low source tensions.&nbsp; All in all I'd say it was a success and proof of the concepts as discussed.&nbsp; And the quality of your document itself is great.&nbsp; What did you use to produce it?

Glen

 

[fpyontek]

What did you use to produce it?

Exemplary work, my friend!
And the quality of your document itself is great.&nbsp; What did you use to produce it?

Glen

I use the Linux operating system instead of windows. OpenOffice is a MicroSoft Works like program that has an excellent wordprocessor, spreadsheet, drawing prog., etc. . The word procesor has an "Export to PDF" function.

Fred

 

[glens]

I'd figured as much...&nbsp; I'm very near to starting on my 9th year of almost exclusive (easily 99.999%) use of Linux (a couple of those percentage points actually belong to FreeBSD, but not at home; from, but not at).&nbsp; You just can't get the same quality out of MS junk in my experience.&nbsp; They seem to always leave a turd in the pool, floating in a yellow cloud.

I don't use Org, or any of the others.&nbsp; I'll typically scribble it out in HTML in vi, load the page into the browser and print it to postscript, then convert it to PDF from the prompt.&nbsp; Almost takes longer to describe than to do; certainly quicker than waiting for Org to open it's terrible graphical interface.&nbsp; :<tt>)</tt>

At any rate, the pull up the back is lessened by the extra ("abnormal") friction across the top and the horizontal pull is lessened by the tendency of the log to actually rise as it tries to pivot on its forward perimeter.&nbsp; That's my story and I'm stickin' to it!

Glen

 

[fpyontek]

Hey Fpyontek

What I'm trying to discover is ... is there any difference between tying the log up at the top only, or going down the backside. In your experiment I'm not sure if you tried both and measured any variables.

Please elaborate, what we are in debate over is the differences. It's killing me!

This Sunday morning I'll do the same experiment, this time with the rope tied around the trunk at same height and post the results. It has to end with the same values

 

[caryr]

 

[fpyontek]

Nicely done Frank! I only see one small problem that when corrected should fix the mismatch between the calculated and measured results.

It appears you just placed the flat edge of the log on the bathroom scale.

Cary

A notch was cut into the bottom of the log approx. 1/3 deep so as to be consistant with felling. If you look closely, you can read the bathroom scale under the log. I will try a 1x1 though. It'f Fred by the way.
Fred

 

[caryr]

 

[fpyontek]

Hi Cary,

I took your advice and used a 1X1 and balanced the log on it as best I could. This time the horiz. component values were off much less, only 9%. The vert. component was off slightly more than previously, about 4%. My purpose for setting this up was not to confirm elementary mechanics, but answer ekka's original question. Unfortunately, I needed to get the "kinks out" in the setup so, all things being equal, I can try to answer his question. Now that I have the setup correct it shouldn't take long to perform both tests and post the documentation. I think that for the last 2 tests I'll "rip" the edge off of a 2X4 to give me a long triangle with a flat base. Then the center of mass and the pivot point will coincide.

Fred

 

[caryr]