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Spar milling

Ted Robinson

Ted Robinson

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Oct 1, 2023
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This is the first time I have encountered an octogonal spar center.
I want to mill down the flats using my Dremel Workstation and an x,y table.
My problem is that I don't know how to calculate the width of the flats other than divide the circumference of the dowel divided by eight.
Both views in the drawings show the flats being level with the center portion of the tapered spar. (I believe that's an error.)
The width of the flats on the plans won't work as that width times eight flats exceeds the width of the supplied materials.
My plan is to mill the flats and then taper the remainder. Building up the center flat portion to f necessary.
I've ever used a milling machine other than full sized and don't know how to index the flats.
I have some ideas but am not confident and have no spares to practice with.
A third idea is to cut out the center portion, mill it the pin/dowel it to the outer portions. Looks fiddly and prone to error
I could use so.e advise.
IMG20250802092607.jpg
 
You can glue some sheet material onto the spar material where the octagonal area is before you mill it.
To practice, you can go to home depot and get some dowel material and make new spars that way.
For that matter, you can buy larger dowels that would be sufficient to do the octagonal area and make total new spars. :)
 
A spar is made square for it's length, tapered where needed, then 8-sided. Some sections may remain 8-sided, like the center of a yard, or the bury of a mast; while other sections go to 16-sided, 32-sided and on to round.
Personally, I find it easier to do it the way it was done than start with a round stick and work in reverse.

The ratios for making it 8-sided are 7-10-7. I'd suggest a spar gauge, but it's near impossible to make one that works in scales like 1:64 without an electron microscope.
 
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I agree with Jerry. If you mill the flats on the dowel then the area of the cross section will be less than that of the adjacent round sections. That is incorrect. The corners of the octagonal section should be slightly proud of the adjacent round sections. Follow Jerry’s sequence: square billet, cut taper, make it octagonal, then round sections on either side.

Roger
 
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Corsair said:
You can glue some sheet material onto the spar material where the octagonal area is before you mill it.
To practice, you can go to home depot and get some dowel material and make new spars that way.
For that matter, you can buy larger dowels that would be sufficient to do the octagonal area and make total new spars. :)
Click to expand...
Duh. Good point
 
Roger Pellett said:
I agree with Jerry. If you mill the flats on the dowel then the area of the cross section will be less than that of the adjacent round sections. That is incorrect. The corners of the octagonal section should be slightly proud of the adjacent round sections. Follow Jerry’s sequence: square billet, cut taper, make it octagonal, then round sections on either side.

Roger
Click to expand...
I'll get some spare dowel and start learning. I think I have figured out how to index the blank due to the notch in
Yini vise on the x,y table
 
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Ideal way would be having a square dowel. Then remove the square edges with plane to make it an octagonal shape. Then machine off the sides to round them and tapering them off leaving the middle section octagonal. This is the way I did most of my spars for Victory model. See reference link below. The largest spar was so long that I did as you described in your first post. I made an octagonal middle section separately and also made separately the round tapered sides. Then I joined them with wooden peg of smaller diameter.
 
I got out the dowel stock provided. The lower main and fore masts are made of 8mm dowels and have enough for me to make the center sections out of the excess as well a a.little for practice.
I'm looking forward to this exercise.
 
This is the mini vise Im using to mill the spar flats.
Since the Dremel Workstation doesn't have an incremental or easily adjusted elevation function I'm going try milling the flats on the side of the dowel instead of the top.IMG20250803204621.jpg
 
Get an octagional drawplate, after you get your octagon shape then measure off for your tapers, use a couple of laps of tape over your centers so you don't lose your shape.
 
I got the x,y table anchored to the Dremel Workstation and the mini vise attached.
I have a sample dowel in the vise to experiment on the flats.
I still need to put in a milling bit.
New tools always provide joy and excitement at the prospect of precise parts and hours of enjoyment.
This table is sloppy in the x axis but stable in the y.
IMG20250805133903.jpgIMG20250805133914.jpg
 
This question keeps coming up. My preference is to mirror the process that is used for real spars:
  • Start with a square stick (one with nice straight grain and minimum runout)
  • Cut the required tapers
  • Shave off the corners to make it 8-sided
  • For the portions that should be round, shave off the corners (16-sided) and smooth to round
Requires a few simple tools: finger plane, hobby knife, sanding block, sandpaper.

Fair winds!
 
AndyA said:
This question keeps coming up. My preference is to mirror the process that is used for real spars:
  • Start with a square stick (one with nice straight grain and minimum runout)
  • Cut the required tapers
  • Shave off the corners to make it 8-sided
  • For the portions that should be round, shave off the corners (16-sided) and smooth to round
Requires a few simple tools: finger plane, hobby knife, sanding block, sandpaper.

Fair winds!
Click to expand...
Thank you
I don't have any square stock and am trying to make the octogonal area with the parts provided in the kit.
 
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