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    Roller Nut design / reinforcement.

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    Basilisk120
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    Roller Nut design / reinforcement.

    Post by Basilisk120 on Tue Jun 21, 2011 3:18 pm

    I have a question about the design of the roller nuts in particular how the trigger/nut junction is reinforced.
    I know of two styles of reinforcement; adding a metal plate or a treaded insert, and I was wondering about the differences. Does one provided more wear resistance, lasts longer than the other? Does one style provide a smoother release? Is it possible to replace the metal bits in the roller nut?
    Examples:
    1. The steel plate.


    2. The Treaded rod

    Sorry for the hazy pic but is should be sufficent.



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    Todd the archer
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    Re: Roller Nut design / reinforcement.

    Post by Todd the archer on Tue Jun 21, 2011 7:51 pm

    Hey that top one looks familiar. I came up with that method on my own, seems logical consider the directional strength of wood. The other method does seem more common though and probalbly easier to change out. Not sure how well that would work out on a wooden roller nut.

    Todd
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    Geezer
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    Re: Roller Nut design / reinforcement.

    Post by Geezer on Wed Jun 22, 2011 6:54 am

    Geezer here, concerning sears for roller-nuts. When I started making crossbows, most of my rollers were made of rock-maple, and fitted with a slotted plate-sear, much like the one shown above. They're surprisingly durable, though occasionally a roller will split along the axis of the plate. The down-side is that they occasionally come adrift and score the nut-socket. And of course, they're a lot of trouble to replace.
    Medieval and Renaissance bone rollers usually employed a block-sear, something like a truncated pyramid or wedge, with a little spud on the top that usually shows between the lugs of the nut.
    I tried glue-in sears of mild steel round bar... flattened off on the bottom, to take the distal end of the tickler. Those work well enough, if you can get them in straight to begin with. Eventually I hit on using all-thread rod, with a flat and screwdriver slot cut in the bottom. I drill and tap a hole for the threaded sear and simply screw it in place. On rare occasions, I put some glue on the threads, but usually I leave it alone.
    Threaded sears can be removed for repair or replacement. Usually I use plain allthread for sears, but Some very strong bows get the stainless allthread. Stainless is harder, more wear-resistant, but of course that means the end of your tickler wears more instead. Generally, repairing a worn trigger is a lot more trouble than replacing a sear.
    Now that I have a mortising machine to make life easier, I have considered mortising a square hole in the bottom of the roller-nut and putting in a solid block of steel for a sear. One could drill into the block from the side to mount a set-screw to hold the block in place. So it could be removed for replacement or repair. That would potentially allow a much more substantial sear than is convenient with 5/16 or 3/8 inch allthread that I usually use.
    Just thinking out loud. Geezer
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    Basilisk120
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    Re: Roller Nut design / reinforcement.

    Post by Basilisk120 on Thu Jun 23, 2011 3:01 pm

    Thanks Geezer, I was definatly interested in the why of the different concepts.
    So your saying the sear is a part that is expected to wear out and be replaced?



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    Re: Roller Nut design / reinforcement.

    Post by Geezer on Fri Jun 24, 2011 7:06 am

    Wear is an inevitable consequence of use. The trick is to arrange things so the wear happens where it's easiest to fix. On some strong bows, I prefer to use the stainless steel allthread, but that stuff is much harder. So what happens? The end of the tickler wears instead. Removing a screw-in sear is much easier than re-shaping and surfacing the end of the tickler, so unless I expect the sear-wear to be exceptionally fast, I'd rather replace it it need than re-work the trigger. As an added bonus, my customer can simply send the roller-nut in for repair, rather than ship the entire bow.
    In medieval times, materials were expensive and labor was cheap. Today materials are cheap and labor is expensive. Screws were doubly expensive, since they required materials AND expert labor to manufacture. Thus Medieval bows were usually assembled with rivets, which are an absolute booger to remove if anything goes wrong.
    I use screws to make assembly/disassembly easier, though in fact, they are very rare on medieval bows. Occasionally you see a big round-head or oval-head screw holding the bolt clip in place. I've also seen a few on cranequins. Otherwise, it's always a rivet. So if you wanna make your bows absolutely authentic, use rivets. If you want easy assembly/disassembly, use screws, but that's a business decision rather than an authenticity decision.
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    Re: Roller Nut design / reinforcement.

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