Numbers from Half Models 'n Such

[Dave Fleming]

Capt Nat, had devices made to his specs by the well known tool makers Brown and Sharpe.
I reproduce here the drawings shown in LFH's bio of his father.





Lets not forget Proportional Dividers either.
A good pair of dividers and a Engineers Scale Ruler works well too.





[ 07-10-2003, 04:45 PM: Message edited by: Dave Fleming ]

[Bayboat]

John Gardner had a nice little machine for taking lines off a halfmodel, that he kept upstairs in the small boat shop at Mystic. I don't recall that he published or described it anywhere...? I wonder what happened to it? Maybe it's still there.

[Wild Dingo]

Thanks Dave... I have a set of the last but have never seen anything like the first two... so thanks

[Dave Fleming]

For those of you wondering how a pair of Proportional Dividers works here is a description ***lifted*** from the Bridge City Tool Works web site.

Utilizing the holes on the arm marked “Proportions” there are 15 distinct settings to choose from. They include:

1:1
1:1.5
1:2

1:1.1
1:1.6
1:3

1:1.2
1:1.7
1:4

1:1.3
1:1.8
1:5

1:1.4
1:1.9
1:6


Of all these settings, 1:1 has no practical use—it is a reference used for factory calibration of the points. All of the other settings are very simple to understand and use.

Traditionally, proportional dividers are used to increase or decrease the size of a measurement and/or project. As an example, you may want to enlarge a drawing or project by 50%. By using the 1:1.5 setting, you can position the narrow end of the PD-11 Precision Proportional Divider on your art or drawing and the opposite end is exactly 150% of the narrow end (100% is the original measurement plus 50% = 150%). This is the fastest way to increase or decrease measurements without calculations and without errors.

Here is a pretty good web site with a description of use of Proportional Dividers

How To Use

[ 07-11-2003, 07:59 PM: Message edited by: Dave Fleming ]

[Lucky Luke]

Dave,

The 1:1 is essential for checking the "zero " of your instrument (and the adjustement of your points). You know that!

The "Capt. Nat" setting you describe here, I used a long time ago with the intent to
....built a model of the model! I was not able to make it of any acceptable accuracy, so did my little model by eye. It would have needed very precise machining of all parts and no play.

To day, you can just sent the model to a CAD-CAM office that has a 3D sensor: they will "measure" it and translate in any "CAD format" your (various) 3D programs can read. But that may not be your style, hey, old salt [img]smile.gif[/img] [img]smile.gif[/img] [img]smile.gif[/img]

[Dave Fleming]

Yes Luke, I am well aware that the 1:1 scale is for calibration, thank you.
<insert big wink here>

I suppose if a person today wished to duplicate Capt Nat's device it would not require the facilities of a precision tool maker like Brown and Sharpe, Moore and Wright, Shur Temico(sp).

Obtain a nice slab of Aluminum Tooling Plate and have your neighborhood friendly machine shop mill that dovetail on the front edge, mill a mating slide out of Aluminum Bronze ( keep the potential of galling to a minumum ) and relieve the underside of the plate for a set of counterbored holes for fasteners for the model to be measured.
Instead of a toothed rack a fine threaded precision ground rod could be used to carry the dial indicators.
We are not working to 1/10,000 or even 1/1000 thou. here 1/100ths is plenty good enough.
Even taking into account Al. tendency to move a bit with temperature changes.

Nothing else a fun exercise for a good Home Shop Machinist I'm thinkin'.