[AT] OT pocket knives

[rlgoss at twc.com]

I just now pulled my pen knife out and tried it, and found I couldn't do it -- the knife blade is too dull and it just wants to skip around over the paper rather than slice in.   I'll dig a stone out tomorrow to whet things a bit and try it again.



Larry
---- charlie hill <charliehill at embarqmail.com> wrote: 
> I guess it's one of those things you have to see to grasp.  I just can't 
visualize it working out.
Seems to me like if you traced a circuit around a lake or field or whatever 
that both blades would
end up back at the starting point.   I'm not questioning what you are 
saying.  I just can't
visualize it.

Charlie

-----Original Message----- 
From: rlgoss at twc.com
Sent: Monday, July 13, 2015 8:04 PM
To: Antique tractor email discussion group
Subject: Re: [AT] OT pocket knives

You let the knife edge ride on the paper surface of the map.  As you trace 
the outline of the lake, field, plat, etc., the knife blade glides along and 
slowly gets offset from the base line.  When you have completed the circuit, 
the offset distance gets multiplied by the effective length of the knife 
(straight-line distance from the "tracing pin" to the point of contact of 
the open blade with the surface of the map.)  It is tempting to grip the 
"tracing pin" too tightly and make the knife edge skip across the paper 
rather than to "slice" as you navigate the periphery.
For large areas, you simply break them down into smaller enclosures and add 
them together, just like you do with the professional instrument.  Try it 
with simple geometric shapes or on a piece of quadrille (graph) paper so you 
can get the hang of it.

Sorry you won't be in Portersville, Dave.  It's around 90 miles from where 
we now live, and my grandkids enjoy that show.  Maybe we'll touch base at 
SIAM next year in Evansville?



Larry
---- Dave Rotigel <rotigel at me.com> wrote:
> I'm with you on this Charlie. I was lost right after Larry said "All 
> kidding aside…." I can't get to Portersville this year, but looking 
> forward to the "live demonstration" when it happens.
> Dave
>
> On Jul 13, 2015, at 10:09 AM, charlie hill wrote:
>
> > 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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