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A method of reducing the diameter of round blanks for spar, using a thread cutting die and a drill.
I've been wanting to try this, having a good size set of threading dies. I always want them tapered, though, but thought of doing this with various size dies only so far along the spar, giving a tapered but "stepped" spar, then hand sanding the steps. I think it could work.
What a great way to quickly rough out a taper. I think I could then take the rough shape and put the piece on the lathe for final shaping and smoothing.
If I had a lathe, I don't think I'd be looking for other ways to taper the spar.
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That doesn't look tapered to me, just reduced in diameter. I usually just power a square strip through a metal drill gauge, which doesn't thread the dowel.
This doesn't thread it either. The teeth are used to cut the size, not thread it. Admittedly, I expect the finish won't be as smooth as other methods, but I think it would be fairly constant in diameter and finish up easily with sandpaper. Just my opinion, though, I've never tried it.
I've used 0.5 & 0.6 mm carbon fibre.
Since I only have a small hobbyist lathe, I can't do long spars on it, and I find anything that long and skinny to be too unstable to do well on a lathe. Rather, I just figured out how to use the technique in the video to do tapers in a fraction of the time it takes to do it by hand, but I'm interested to hear how others do their tapers. Full disclosure: so far, I have only tapered a test piece, but it came out great and my next piece will be the real article.
Here's how to use a set of dies to taper a mast:
Metric thread inside minor diameters (in mm) for my set of dies are:
I set my calipers for the diameter of the largest die that is smaller than the diameter of the base of the mast and find the spot on the plans where the diameter of the mast matches the calipers. Moving a couple of mm up the mast (to allow for slop), I mark this spot on the plan and annotate the size of the die. Repeat for each subsequent die size until you get to the smallest die that is not smaller than the minimum diameter of the mast.
Now transfer the markings on the plans to the dowel. The markings show how far to go with each die as shown in the video. I go with a slow drill speed to control things better. You will probably have to redo your lines for each subsequent die, since the previous one will chew off the lines for the smaller diameters.
Now it's back to hand-sanding to get the final shape. I use a long sanding board with a fence on one edge to turn the stepped profile the dies leave into a smooth taper. By selectively applying pressure at high spots, I can control the rate at which material comes off at any point along the profile.
Yes, the technique in the video did leave me with a very rough-looking stick, but I only had to spend a couple minutes hand-sanding to the final shape, rather than the couple of hours it normally takes.
Here's how to use a set of dies to taper a mast:
Metric thread inside minor diameters (in mm) for my set of dies are:
| M3 | 2.459 |
| M4 | 3.242 |
| M5 | 4.134 |
| M6 | 4.917 |
| M7 | 5.917 |
| M8 | 6.647 |
| M9 | 7.647 |
| M10 | 8.376 |
| M12 | 10.106 |
I set my calipers for the diameter of the largest die that is smaller than the diameter of the base of the mast and find the spot on the plans where the diameter of the mast matches the calipers. Moving a couple of mm up the mast (to allow for slop), I mark this spot on the plan and annotate the size of the die. Repeat for each subsequent die size until you get to the smallest die that is not smaller than the minimum diameter of the mast.
Now transfer the markings on the plans to the dowel. The markings show how far to go with each die as shown in the video. I go with a slow drill speed to control things better. You will probably have to redo your lines for each subsequent die, since the previous one will chew off the lines for the smaller diameters.
Now it's back to hand-sanding to get the final shape. I use a long sanding board with a fence on one edge to turn the stepped profile the dies leave into a smooth taper. By selectively applying pressure at high spots, I can control the rate at which material comes off at any point along the profile.
Yes, the technique in the video did leave me with a very rough-looking stick, but I only had to spend a couple minutes hand-sanding to the final shape, rather than the couple of hours it normally takes.
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