octagon portion of a yard/mast

[Juan Carlos]

looking in the download section of the site, i found the article ¨Making a mast (or spars) from square stock¨

i need to make an octagon portion of a yard but i dont understand the 2-3-2 thing i saw in the article.  can anybody here explain that to me?  point me to where to find a chart, template, or any other tool to help me here?  i remember reading about that some time ago, but now that i want to do the yards i realize i am lost.  

thanks for the help!

 

[Jim Lad]

Juan,

 

The "2-3-2" rule refers to the correct proportions to mark on the sides of your square stock in order to get the correct octagonal shape on the finished spar.  If you mark a line 2/7th of the width of the square stock along each side of the of the piece and then cut the 45 degree angles to those lines, you should end up with a good actagonal shape.  These proportions aren't exact, but are very close.

 

John

[Juan Carlos]

aahhh!  thank you!!!!  2/7th from the edge of the square  stock in(towards the center) ?   i can do that.  but then, why is it called 2-3-2? 

[Juan Carlos]

got it.  2-3-2 = 7 . so it ends up 2 units from the outer edges in and that leaves 3 units at the center!   haw!  thank you for showing me the light!!!!!

[Jim Lad]

Glad to help, mate!

 

John

[Juan Carlos]

Thank you Jim!!!!  i remember seeing a template somewhere with a fan shape or something like that for the 2-3-2 proportions.  can anybody here give me the link to get there?

Edited May 10, 2013 by Juan Carlos

[druxey]

A more accurate proportion is 7-10-7. Another way of saying this is that the width across the spar when square at any point is 24 parts. Measure in 7 parts of the 24 from each edge and this will, when planed off at 45 degrees, give you a perfect octagonal cross-section.

[Jim Lad]

You're right Druxey.  Quickly doing the arithmetic, 7-10-7 is almost exact!

 

John

[Garward]

Here still information: octagon portion of a yard can be done on the lathe of such preparations

http://modelshipworld.com/index.php?/topic/1734-manufacturing-of-laths-of-an-octahedral-profile/

[Juan Carlos]

tried to mark the yards for the 7-10-7  or the 2-3-2 proportions but i could not do it on a 5 mm wide square stock.  i guess i will try it by eye.  will know how well calibrated are my eyeballs.  is that how you do it Garward?  judging by eye and experience?  any tips are wellcome..

[Garward]

Octahedral preparations and yards become by the sizes specified on drawings. The method of production of octahedral preparations applied by me allows to supervise their size (for example, side width) with an accuracy of 0,1 mm.

[Juan Carlos]

ok.  found the template for 7-10-7 proportions on page 8 of the document ¨Planking Tutorial DRAFT r6.pdf ¨, located in the building, framing, planking section of the forum.  its pinned under the name

Planking instruction/tutorial by jack nastyface

here the link:  http://modelshipworld.com/index.php?/topic/353-planking-instructiontutorial-by-jack-nastyface/

[WackoWolf]

Jack had a lot of good walk trues but most all of that stuff got lost in the great crash.

[druxey]

One way to mark out small spars is to take a strip of card stock and mark the 7-10-7 proportions on it's edge to the maximum spar diameter. As you mark along the spar, turn the card at an angle so the outermost marks coincide with the edges of the foursquare as it tapers. Pencil the inner marks on the flats at intervals. Make sure that the pencil point is very fine! That will be sufficient guide to cut the octagon accurately.

[Juan Carlos]

thank you Druxey!  will try that!

[twintrow]

At many hardware and some auto  parts stores you can buy octagon nuts in many sizes.  I put one at each end of the dowel and file a perfect octagon each time.  If unable to get a nut with a large enough dia to fit the dowel, I reduce the dowel to the smaller dia for about a 1/4  length of the dowel then put on the nut.

 

Seems to work for me.

 

Tom

Edited May 11, 2013 by twintrow

[Juan Carlos]

did it by eye using a board with a grove to hold the square stock.  turned out very nice.  maybe not perfect, but very nice.  it gives the illusion i was looking for.  thanks to all.  next time i will try the nut trick.  it sounds interesting.

[druxey]

An example of an octagon cut using the method I've described is shown here. The overall length of this windlass at 1:48 scale is about 4".

[druxey]

It's the real thing, Janos. 

[druxey]

Castello boxwood, Janos.

[Juan Carlos]

how did you get such clean low areas? (dont know the proper name)

[druxey]

The low areas are the basic windlass. Juan Carlos. The high areas are all thin wood added on afterwards. It's how the original was built: these wear areas can be replaced.

[Chuck Seiler]

Juan,

 

    The reason for 2-3-2 or 7-10-7 is geometry, specifically triangles.

 

 

   A squared + B squared = C squared.  In the above diagram you want to shave off the corners (A and so that the remaining side © is equal to D.   (2x2)+(2x2)= 4+4=8

                                                                   D=3 so 3x3=9

                                                                   Close

 

                                                                   (7x7) + (7x7) = 49 + 49 = 98

                                                                   10 x 10 = 100

                                                                   closer

 

Then there are hexes.  :-|