• Samuli.seppanen

    Yesterday I made good progress. The case is now finished and the slider was finished earlier:

    I've reused the old crescent-shaped piece for pragmatic reasons, even though it is not 100% match with the text as it's attached with screws, not with a rectangular wooden tenon.

    The attachment points for the T-clamps had to be reinforced with brass screws - something I'm not overly happy with:

    This is largely because of the pine which I used for the case. While the pine is high-quality it still splits easily. However, this tendency is offset by much smaller weight of the case.

    I also drilled holes to the new field frame bars:

    The straight field frame bars are slightly wider at the middle to increase strength. This is another thing I'm not 100% happy w…

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  • Samuli.seppanen

    Today I was writing an email to a fellow ballista reconstructor when I realized I should probably make the email a blog post. So here are two of the most impressive ballista reconstructions/reconstructors right now as far a I know.

    Their reconstructions are very interesting as they don't use sinew at all. Nor nylon. They've tested various oiled animal and plant fibres and achieved quite impressive results: bolt velocity up to 86 m/s, range 480+ meters. Their most interesting hypothesis is this: they believe sinew was not typically used as spring cord material, at least not in inswingers. This is because it simply is not elastic enough for springs where

    • The spring is relatively thick compared to its length
    • The spring needs to be rotated a lot (…

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  • Samuli.seppanen

    The renovations in our apartment have finally come to a phase where I have been able to resume work on my cheiroballistra.

    A few days back I finished attaching the triggering mechanism part to the composite slider which I created a few months ago. The composite construction can be seen in this image:

    The back-end of the slider is of elm for hardness and splitting resistance, whereas the frontend is of pine to keep the weight down. The two pieces are joined together with a half lap splice joint, glue and two vertical wooden dowels. This type of joint should work well, as the slider has to endure mostly compressive forces. The slider is slightly wider than previously, which gives it additional strength. The angle of the dovetail has been adjus…

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  • Samuli.seppanen

    The cheiroballistra project has stalled for quite a while as we've been renovating our apartment thoroughly since July. Fortunately after Christmas I could spend two days at the forge.

    The results of the ballista-related work are these:

    On the left there is an old ring for the cone and below it is an old 3mm thick pi-bracket. On the right side, from top, two spare 5mm pi-brackets, a new washer, three thick rings for the cones and eight thick pi-brackets with partially formed tenons. They attempt to fix a few mildly annoying issues with the cheiroballistra:

    • The 3mm thick pi-brackets were a bit flimsy, even though they had survived earlier fairly high power tests.
    • One of the old washers could not be easily rotated. This was probably caused by s…

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  • Samuli.seppanen

    New parts

    June 29, 2016 by Samuli.seppanen

    It has been quite a while since I actually published pictures of new cheiroballistra parts, so here it goes. First the new little ladder forged from 6mm spring steel coupled with a better and stronger little arch forged from concrete reinforcement steel. Note how the tenons of the rungs simply project above the beams, instead of being riveted or otherwise attached to the beams. This allow one to bend the little ladder beams outwards when inserting their tenons into the pi-brackets in the field frame bars.

    As can be seen from the picture below, the little arch's retaining pins are significantly stronger (5mm) than the previous ones (3mm):

    Because the little ladder tenons are larger than previously, the wedge system needs to be adapted slightl…

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