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    How To Make a Roller Nut?

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    banuvatt
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    How To Make a Roller Nut?  Empty How To Make a Roller Nut?

    Post by banuvatt on Fri Nov 01, 2019 10:56 am

    I am a beginner crossbowmaker, which you can obviously tell. I am having a hard time learning how to make a roller nut. The part I am specifically having the hardest time to learn is how to make the lugs on the roller nut. I am going to make the roller nut out of a piece of delrin that is 1 1/4" wide in diameter, and is an inch thick. The height of the lugs I was going to make them 3/8" of an inch tall.
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    Post by Geezer on Fri Nov 01, 2019 12:28 pm

    Cut a notch in the top with a bandsaw, or frame saw if you'd rather.  cut slots for the space between the lugs and chisel that bit out.  Drill a hole from between the lugs, and out the bottom, slightly behind center.  (I use 1/4 inch bitt for that)  Then tap with a 5/16 tap and screw in a piece of 5/16 in. diameter 'allthread' threaded rod.  cut to fit, making sure there's a notch at the bottom to take a screwdriver.  Cut a keyway behind the notch for the trigger to fit against the allthread.  That gives you a mild steel sear. to work against your mild steel trigger (you could use 3/8 in. brass bar for the trigger) When the sear starts to show excessive wear from shooting, unscrew it, make a new allthread sear and screw it into place.  Cut to fit nice ans smooth again.  Geezer.
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    Post by Geezer on Fri Nov 01, 2019 12:58 pm

    Okay Banuvatt: let's look at this in greater detail.  Take your piece of delrin.  Draw a line across the side, front to back, 1/3 of the way down from the top.  That top third is the part of your nut that will protrude from the nut socket when your lock is set.  Measure from the front of the line, halfway to the back.  Draw a vertical ine up to the top.  One side or the other of the section above the 1/3 line needs to be cut away.  Do it.   
    The 1/2 of the section still standing will make the lugs.  Eventually you're gonna want to smooth off the lugs edges, and maybe give them a little hollow at the back for the string to sit pretty, but that's later.  Now look at the standing lug-section.  Find the center of the section from side to side: draw a center line fore and aft.    The lug section will eventually be divided into 3 parts: the center slot and the lugs on both sides.  Generally with medieval bows, the lug section is divided into equal parts, 1/3, 1/3, 1/3.  That should do with your 1 inch wide nut (in fact, the little Padre Island bow has a nut 15/16 wide, and is divided 5/16-5/16-5/16, so you'll want to do something similar.  Make careful saw cuts fore/aft in the center section, being careful to avoid cutting too deep, then take a sharp chisel (dull chisels are useless, make yours really sharp) and chisel out the center passage.  Take small files and sandpaper to get everything even/smooth so the nut won't eat your string.  
    Now punch a small hole in the center passage, just slightly ahead the rear flat of your nut.  Drill with your 1/4 inch bitt from there to come out the bottom center, a little behind the center line.  Yes, I know Payne Gallwey says to put the sear-plug/trigger meeting at precise bottom center, but in fact, you'll have more success if your trigger engages about 1/8-3/16 Behind bottom center. That way, the trigger takes more of the load and your roller nut won't try to rise out of the socket, stressing the edges of the nut-socket.  Tap the passage with a 5/16 in. threaded tap
    Get some 5/16 inch. threaded mild steel rod from your local iron monger/ hardware store.  Cut off a few inches, then stand your cutoff bit in a vice and hacksaw a 1/4 in. slot down from the top.  Cut away one half of the slot, being careful to leave just a little bit of slot in the bottom.  Now you can screw the threaded sear into your nut.  Trim the threaded sear to fit flush at top and bottom.  
    Using your chisel, cut a keyway behind the notched bit of your nut for the trigger to fit into sear.  
    Make sure everything is nice and neat.  Now you have a good strong nut that should give you years of service.  If you observe too much wear on the sear over time, unscrew the sear plug and make a new one.  
    If your bow is very strong, you can use 3/8 in. threaded rod, made of stainless steel.  It will be stronger and more wear resistant, but you'll now see more wear on the end of the trigger.  I find it much easier to replace a sear than tio re-forge the end of a trigger, so I won't use stainless for a sear unless the bow is a real bruiser.
    You may want a center axle or 'nussfaden' cord to hold your nut in place... just drll an 1/8 in. hole right thru the middle and go to town.  Your nut can take it.
    Does that make sense?  If you get stuck try calling me.  Geezer/DRW Austin Texas, 512 453 2628.
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    Post by banuvatt on Fri Nov 01, 2019 1:14 pm

    Okay thank you, that makes a lot more sense.
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    Post by banuvatt on Fri Nov 01, 2019 3:16 pm

    I know it would make things easier if I just made the lugs on the roller nut straight, but I really like curved lugs on roller nuts. They make the roller nut look more elegant and sweeping. I'm going to share a video that I really liked, but unfortunately it's in German. Does anyone recognize where the guy got that diagram of the nut's dimensions at 5:11? If you watch towards the end you can see how well the lugs turned out on his roller nut, I want to try to make mine like that. https://youtu.be/WgKcbHOgHvw

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