Rigging Cord Measurer Plus by Jerry G

Bill of Materials:

Base plate - l/4" by 6" by 6" Plexiglas1X

Base Block - l" by 2" by 3" tool steel lX

Spacer Block - l/4" by l" by 3" Plexiglas lX

Upright Indicator Mounting Plate - l/4" by 3" by 5 3/16" Plexiglas 1X

Gusset Plates - l/4" by 2 5/16" by 5" Plexiglas2X

Indicator Mounting Angle Bracket - 3/16" by 3/16" by 1 3/8" by 7 1/8" Extruded Aluminum 2X

Drop Dial Indicator - .001" divisions 0 to 1.000" stroke lX

Flange Mount
Legs Pads
5/16" by 3/4" by 3/4" self stick pads - Composition/rubber 4X

Indicator Mounting Bolt
l/4-20 by 1" Allen Socket Head Cap Screw Steel lX
1/4" Flat Washers Stainless Steel 2 X
1/4"-20 Acorn Nut Stainless Steel 1X
l/4"-20 by l" Allen Socket Button Head Screw Steel 4X
l/4-20 by 3/4" Allen Socket Button Head Screw Steel 2X
l0-32 by l/2" Allen Socket Button Head Screw Steel 4X
# l0 Flat Head Washers Stainless Steel 4X
6-32 by 3/4" Phillips Flat Head Screw Stainless Steel 8X

So I have supplied you with a Bill of Materials and working drawings (in case anyone would like to make one of their own). And now it is time to give you a little history on why I developed and built this unit. In trying to determine the exact sizes of rigging cord, I found that there was a great variance in the actual diameters of the cord supplied by manufacturers and kit sellers. It seemed to me there was no standard.

One of the more popular methods of determining the size is by wrapping the cord around a dowel that has been premarked in linear dimensions, such as l/4" or up to I ". After wrapping the cord around the dowel carefully, so as not to distort it, or stretch it, one then counts the number of turns and divides the length by the number of turns to arrive at the diameter. For example; A cord is wrapped or a length of l/4" and has ten turns. So, l/4" x .250"..... .250" divided by ten is .025", which would be the diameter of the cord.

To me, that was not a real solution due to the possibility of inaccurate length measurements and varying tension when wrapping, etc. And that led to the design, development and fabrication of the "Rigging Cord Measurer"

There are a couple of places where I tried to nullify the action of the anvil (spindle) of the Drop Dial Indicator to "crush" the cord when measuring it. First, I removed the internal extension spring that was used to cause the spindle shaft to return to the rest position. Secondly, I made a new larger platen/anvil point to distribute the weight of the spindle shaft when it is used to measure the cord. That is self defeating to a point because the larger platen adds a small amount of weight.

To really measure a cord accurately requires either an optical comparator that projects a magnified mage of the cord upon a screen where you can compare it to a known standard or scale, or a Toolmaker's microscope where you can measure the cord with the optics against a known standard or scale, without any physical contact. However, I think that is beyond the scope of the normal hobbyist /ship modeler.

The only thing left is to calibrate the "Rigging Cord Measurer" by comparative measurements against known diameters from commercial suppliers. It’s like zeroing in a rifle with adjustable sights.

There was an unexpected bonus with this tool. Since it can measure any height from.000" to 1.000" by .001"'s (one thousandth's' of an inch) it can be used in lieu of a micrometer without the possible errors introduced by the operator's feel, which is a prime requisite of using/reading a micrometer.
Now, before I describe how I built it, I would like to say that the heart of this unit is the base block which is a commercial item used for set ups on the 'Moore Jig Boring Machines'. It is a block 1.0000" by 2.0000" by 3.0000" that is held to size, flatness, and parallelism within .0002" (two ten thousandth's of an inch). Equally in importance is the Drop Dial Indicator, which is mounted with the angle brackets to "read" the base block. It has a one inch stroke with a dial that reads in .001" (one thousandth of an inch) per division.

Instructions:

The base plate is drilled, using the coordinates found on the drawing. Two of the holes are for the 6-32 Flat Head screws that hold the gusset to the base plate. Four of the holes are for the l/4" Button Head screws that hold the base block to the base plate.

Next, the upright is drilled. It has a total of twelve holes. Six are for the 6-32 Flat head screws that secure the gussets. Two are for the l/4" button Head screws that hold the spacer block in place. Four are for the 10-32 Button head screws that hold the brackets to the upright.

Then, the gussets are drilled and tapped for the 6-32 Flat Head screws. There are four holes in each gusset.

To make the aluminum angle brackets, drill and tap two holes (each) for the 10-32 Button Head Screws that hold the brackets to the upright. Drill one hole (each) for the Indicator Mounting Screw.

The rest is assembly. Now, since I discovered the bonus (height measurements), I am changing the name of the unit to "Rigging Cord Measurer Plus" - Jerry G