The Dreaded Octagonal profile from a round dowel

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SgtSpiff

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Hello all:

I am working on the yards and spars for my 1:64 “Granado” (Victory Models) and I’m at the stage where I have a few yards that require an Octagonal profile on dowels (8mm and 6mm.) Before I dive in based on my suspicions, I am interested in learning what techniques have worked - or not - for other modellers.

For context, I am largely working with basic hand tools. I do have a tabletop vise at my disposal.

Any and all guidance (or thread redirection) appreciated at this end.
 
Allan (post #3) is on the right track. Going from round to octagonal is backwards. The way wood spars were made (and still are in some cases) was to take a tree of appropriate size and cut it square. I admit that seems to be contradict what I wrote, but stick with me. The square stick is tapered as needed while retaining the square cross section. Then the corners are taken off to make it octagonal. Next it is cut 16-sided and so forth until it is round.

For models, it's much easier to taper a square stick than a round one. Then it can be made octagonal with a finger plane or sanding block, depending on the size. Going to 16 sides and round can usually be done with a sanding block. In some cases, a portion of the spar is left with 8 sides or 4 sides. Another consideration is that dowels are often of birch and have significant runout. Rectangular stock of basswood or pine is easier to work and you can control the run of the grain to be parallel with the spar. Pics below are of a bowsprit on a Chesapeake bugeye (round outboard, octagonal in the middle, and square inboard) and some oars that are square on the inboard portion of the looms. The square ends on the oars give some additional weight to offset the weight of the outboard portions and keep them from rolling around in the boat. Fair winds!

oars 3.jpg
bugeye bowsprit.jpg
 
What Allan said above. That said, two points may also be helpful:

1. To the greatest extent possible, straight grained wood is best for getting out masts and spars. There's a lot of planing involved and straight grain will minimize grain runout and avoid inherently weak cross-stick "double runout" where a spar might break across the grain, usually when you're in the middle of setting up the rigging! :oops: For this reason, if you have the opportunity to mill your own building stock, it's best to split the log to create a billet in which the grain runs the way the tree grew, and runout will be negligible when milled parallel to the grain.

2. While recognizing that it is a luxury unavailable to many, tapering spars is probably the best rationalization for buying a nice small lathe with a tapering attachment, a traveling back rest, and hollow spindle bore that can accommodate the length of the largest spar you anticipate ever making. I know that's a substantial expense. (E.g., https://www.grizzly.com/products/grizzly-7-x-14-variable-speed-benchtop-metal-lathe/g0765) Until then, a shop-made lathe that will accommodate a drill motor turning the stick with a steadying holder at the opposite end will serve for sanding the round sections to the desired taper will, with care and a good pair of calipers, serve almost as well.

The tedium of sanding all the masts and spars on a three-masted square-rigger to their proper shapes, particularly in smaller scales, is not to be underestimated.
 
I have a drill press that I use for tapering spars by putting them in the chuck and using sand paper. Having said that here is another option for making the octagonal center section in the middle of the yard. Start with a slightly oversize dowel, say 1/4" for a 3/16" yard. Wrap a piece of paper around the dowel and measure the perimeter preferably in millimeters. Make ticks on the paper to divide it into 8 sections. Lay a straight edge along the dowel length and draw a line to use as reference point. Starting at this line, wrap the marked paper around the yard and transfer the ticks marks at two different locations. Connect these points with your straight edge. The dowel has now been divided into 8 sections. Use a file to make flats between the lines then taper the remaining round length.
 
Just to add to this discussion to get an accurate as possible octagonal shape from square stock use the ratio of 7-10-7. What I mean by that is draw two parallel line down the length on each of the four sides of the stock. The space between the between the edge of the stock is 7 and the space between the lines is 10. That’s the 7-10-7 ratio. (For example. 7mm 10 mm 7 mm or 3.5 mm 5 mm 3.5 mm). Do this on all four sides. Then plane or sand the corners down to the lines
If you need a tapered octagon, that you would find on a windless, first taper the square stock to the correct dimensions and then proceed as above.
NOTE: It is impossible to taper an octagonal after the eight sides have been cut.
 
polydoc said:
I have a drill press that I use for tapering spars by putting them in the chuck and using sand paper. Having said that here is another option for making the octagonal center section in the middle of the yard. Start with a slightly oversize dowel, say 1/4" for a 3/16" yard. Wrap a piece of paper around the dowel and measure the perimeter preferably in millimeters. Make ticks on the paper to divide it into 8 sections. Lay a straight edge along the dowel length and draw a line to use as reference point. Starting at this line, wrap the marked paper around the yard and transfer the ticks marks at two different locations. Connect these points with your straight edge. The dowel has now been divided into 8 sections. Use a file to make flats between the lines then taper the remaining round length.
Click to expand...
Hhmm. Again, as a way to produce an octagonal portion of a spar, this seems to me to be backwards and extra work. Starting with a square stick is much easier and can produce a stronger spar with attention to the run of grain. See post #5. Fair winds!
 
I use my homemade CNC mini mill to make the central octagonal section and the tapered ends. It took me a while to get the G code correct, but now I can produce a finished spar in about 10 minutes. Yes, CNC is not for everybody. But they were saying that about using electricity in the workshop in 1900. BTW, tapered octagon or hexagon, no problem with CNC.

First Thread? Making a Mini CNC Milling Machine

Do you think it could do a hexadecimal Centre on an 8mm dowel? I would love to see its capability there!
shipsofscale.com
 
This is Clink. First time I've seem a Spar Gauge. I'm build the Flying Fish Clipper semi from scratch (I have Plans), can a Spar Gauge be made for my undertaking?

Dave Clink
 
Clink said:
This is Clink. First time I've seem a Spar Gauge. I'm build the Flying Fish Clipper semi from scratch (I have Plans), can a Spar Gauge be made for my undertaking?

Dave Clink
Click to expand...
Brother Dave:
Hard to imagine a gauge that small working but you won't know unless you try. I've always equalized the sides by eye on miniature work. Marking out 7:10:7 as suggested by BarrySR (post #8) should help too. I used the gauge in the photo (post #11) for full size oars, paddles, and small spars. It's 5 inches long and accommodates a stick 2 inches wide.
Fair winds!
 
If you want to really keep it primitive in terms of tools, one might consider tapering the spar in the round. Then, take a square piece of straight grained wood as long as the flat-sided section of your spar and drill a hole straight through the center of it parallel to the grain. (A drill press and drill press vise would be a big help here, but not essential if you can drill a straight hole.) Coat the inside of the hole and the length of the spar that you want flat-sided and slide the piece of wood down the spar to where you want the flat-sided section (e.g., the center or a yard.) Let the glue dry. Plane the glued on square sided piece down on one side to the level of the rounded spar, Do the same on the other three faces, keeping the corners square. (You may want to devise a jig for squaring it.) Once squared to the dimension of the rounded spar, knock off the four corners to create an octagonal shape. Mind you, I've never done this, so if anybody tries it, comments are welcome.
 
here is one way i did it

Colonial Schooner Sultana

yes this is an up grade kit of their solid hull Sultana. the plans are CAD drawn for the hull the original rigging plan will be from their solid hull kit, Instruction in the kit will be a revised version of this build log. The new Model Expo Sultana kit is 1:48 scale. When will the kit be...
shipsofscale.com
 
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