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Crossbows - Everything about Building, Modding, and Using your Crossbow Gear

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Basilisk120
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    Post by Pavise Thu Mar 04, 2010 5:09 pm

    Another program I have explored is to be found at the URL below. It allows you to draw and prove your part/s and then submit the design for a cost estimate and approval. The program is free and in itself is a great learning tool. Anyone contemplating several repeat parts for crossbows, goat's feet, cranequins etc., might find this service to be a reasonable solution.

    http://www.emachineshop.com/

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    Post by Basilisk120 Thu Mar 04, 2010 7:06 pm

    Just downloaded the software so can't tell how it works yet but if it is as good as it claims. Could be handy. May end up using it at work as well.
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    Post by Basilisk120 Thu Mar 04, 2010 9:29 pm

    Well the Delrin Roller Nut I drew up had a quote of $330 for 15. Larger orders means a better price per unit. (Ordering 2 nuts costs like $120 per). Would be nice to if I could make a drawing to better control what is important and what isn't. Of course the real price might be a bit lower if I could request making it out of 1.5" Diameter Delrin rod. But still If I had a crossbow company might be cool. Hmm someday.
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    Post by Ivo Fri Mar 05, 2010 2:21 am

    Very interesting app and a very nice touch with the tutorial videos and a dedicated forum.
    The prices are quite interesting too ...but again it does mention that there a numerous factors that have a dramatic influence on production costs...one small setting and you are looking at hundreds added to the total. From dealing with dental milling centers where custom zirconium parts are fabricated, I can safely agree with Pavise and say that this just might be a very nice option for a some of us. E Machine Shop Icon_smile
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    Post by Geezer Fri Mar 05, 2010 6:36 am

    Geezer here, following up on a comment concerning making locks from Delrin round-stock. I make plenty of roller-nuts (perhaps half my production) from Delrin round-stock, either 1 & 1/2 or 1 & 3/8in. round. From observation of lots of medieval roller-nuts, I can say they average around 1 & 1/4 to 1 & 1/2 in. diameter, with the ends of the bell-curve at about 1 inch and 2 inches.
    Since I generally work from a fairly close-fitting round socket without an axle, or at most a nussfaden cord through the roller, I prefer to use slightly larger diameters, since the nut-in-socket fit on smaller diameters can be trickier... particularly when you get swelling of the stock in high humidity/temperature. A little too tight and they jam in hot weather, a little too loose and the nut rattles around and accuracy suffers.
    Some renaissance bows line the sides and even the bottom of the socket with leather, which I suspect was probably saturated with grease. I figure the grease made the leather swell a bit, keeping the nut fairly tight and adding lubrication. When temp and humidity went up, the grease was pushed out and leather compressed, leaving the nut free to turn. When humidity goes down, you add more grease/oil and the leather swells again. When the leather goes entirely flat, you replace it. That's the theory anyhow. I have used leather spacers in a few bows, but can't report any results at this stage one way or another. Geezer.
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    Post by Pavise Fri Mar 05, 2010 10:59 am

    basilisk120 wrote:Well the Delrin Roller Nut I drew up had a quote of $330 for 15. Larger orders means a better price per unit. (Ordering 2 nuts costs like $120 per). Would be nice to if I could make a drawing to better control what is important and what isn't. Of course the real price might be a bit lower if I could request making it out of 1.5" Diameter Delrin rod. But still If I had a crossbow company might be cool. Hmm someday.

    Hi basilisk120,

    Wow, the estimate you received is way out of line IMO and I would not entertain it for one minute.

    If I wanted to make a number of Delrin nuts I would buy a length of round rod of the desired diameter and then make a hardwood jig whereby I could reference this long piece to a router mounted in the normal fashion. If we look at the profile of a nut we can see that there are very few cuts necessary to remove unwanted material. A pie shaped piece needs to be removed in order to establish the intial claw section and then another similar cut at 180 degrees or so from this position to provide the tickler interface and sear. (The latter can be done in other ways as has been described on this forum.)

    After we have routed the claw profile it is only a matter of setting some kind of a stop fence on our router table so that we can repeat the half cross-cut at 90 degrees to define the two claws. A three eights diameter, carbide tipped, straight router bit would be ideal for all cuts. But it would be easy to test my theory with a piece of thick wooden dowel first.

    Sorry if my reply post is now in the wrong section Ivo and please move it accordingly.

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    Post by whiteraven Sat Jun 02, 2012 11:26 am

    Would a roller nut out of say, cast brass, be strong enough to with stand the pressures asked of it?
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    Post by Gnome Sat Jun 02, 2012 5:03 pm

    Whiteraven,

    Brass would be strong enough, the problem is the weight- a solid brass nut would rob a lot of efficiency and cause a lot of misfires. I think Geezer could tell you all about it from firsthand experience. You'd have to engineer it with a lot of cut outs or holes to lighten it up without compromising the strength where it's needed, and of course still be balanced. I've been thinking about milling one, but casting one might be a better approach for a complex shape. I use brass wherever I can, I just like how it looks. Don't know much about casting it, though.

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