[AT] OT pocket knives

[charlie hill]

Larry,  I understand how you are tracing the irregular area with the 
secondary knife blade but
how do you allow the main knife blade to behave as you trace?  Do you keep 
it perpendicular to
the straight line?  I don't understand at all.   There are multiple ways it 
could wander including
at random if not controlled some way.  What am I missing?

Charlie



-----Original Message----- 
From: rlgoss at twc.com
Sent: Monday, July 13, 2015 9:40 AM
To: Antique tractor email discussion group
Subject: Re: [AT] OT pocket knives

!!!Dave, All kidding aside, a tape measure is exactly how you get the answer 
out of measuring an area with a make-shift planimeter. You start tracing an 
area with the main knife blade resting on a straight line that is drawn 
outside the area you want to measure.  When you come back to the place on 
the irregular outline where you started, you measure the perpendicular 
distance to the straight line. That distance multiplied by the distance 
between the contact point on one blade and the tip that you use as a tracing 
pin is a direct read-out of the area. The next time I run into you at a 
show, I'll give you a live demonstration.  I'm headed to Portersville in a 
little over two weeks.  Are you going to be there?


Larry
---- Dave Rotigel <rotigel at me.com> wrote:
> Darn, That's NEAT! I use a tape measure in a similar way!
> Dave
> PS, Kidding aside, THAT'S NEAT!
>
> On Jul 12, 2015, at 11:02 AM, rlgoss at twc.com wrote:
>
> > I sold both of the polar planimeters I had in our garage sale yesterday. 
> > They were perfectly  good instruments, but technology has left them 
> > behind. That fact plus this thread brought to mind that I have carried a 
> > two-bladed pen knife for many years specifically because you can use it 
> > as a planimeter in an emergency by opening the large blade completely 
> > and opening the smaller blade to approximately 90 degrees before 
> > starting a tracing. It gives a measure of irregularly-shaped areas that 
> > is better than estimations and requires minimal instruments.  You do 
> > have to keep the blades sharp so they don't slide sideways over the map, 
> > and they need to hinge at opposite ends of the knife.
> >
> >
> > Larry
> > ---- jtchall at nc.rr.com wrote:
> >> Just an update: I bought my son a single blade Case with a 
> >> plastic/composite
> >> handle. The knife has a lockback design. After reading your posts it 
> >> seems
> >> quite a few folks are using single blade knives instead of the 2 and 3 
> >> blade
> >> knives I carry. I carried him to 3 stores and we tried several. This 
> >> one is
> >> fairly easy to open and close, yet the blade is never in a "free" 
> >> rotating
> >> state. Some of the easy opening ones seemed to me they could open in 
> >> your
> >> pocket. The blade is about 3-3.5 inches long and the knife is big 
> >> enough to
> >> get a really good grip on. The handle is also textured. The Kershaw and
> >> Gerber knives some of you suggested were out of stock actually. Anyway 
> >> he
> >> seems pleased and has used it the last couple Saturdays around the 
> >> farm.
> >>
> >> John Hall
> >>
> >>
> >>
> >>
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