[AT] OT pocket knives

Dave Rotigel rotigel at me.com
Mon Jul 13 17:25:43 PDT 2015


I have reservations for SIAM already, Larry! Will you be at the fall Coolspring show?
	Dave

On Jul 13, 2015, at 8:04 PM, rlgoss at twc.com wrote:

> 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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