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3 posters

    Adding a steel sear insert?

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    fester
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    Adding a steel sear insert? Empty Adding a steel sear insert?

    Post by fester Sun Sep 10, 2017 3:00 am

    Whats the best method of adding a steel seer insert to a delrin nut. I've been through the wiki but cant find any info. Also whats the upper limits of prod draw weight for building a bow that is comfortable to draw by hand for an average guy.
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    Adding a steel sear insert? Empty Re: Adding a steel sear insert?

    Post by Geezer Sun Sep 10, 2017 8:43 am

    Geezer here: re steel sears for Delrin nuts.  I make a lot of Delrin nuts.  My standard method is to drill a 1/4 inch hole from between the lugs, out the bottom (preferably slightly behind bottom center) I thread the passage with a 5/16 in. tap and then make a sear out of 5/16 in. allthread.  (threaded steel rod) I cut a notch and a step into the bottom of the allthread section, so I can get a flat-head screwdriver into the slot.  Then cut a square keyway at the bottom for the end of the trigger to fit.  It's easy, quick, looks professional. Given a choice between mild steel allthread and the harder stainless, I prefer the mild steel unless the bow is Very Strong.  Why? Because wear is inevitable at the point of contact. If you make your sear out of hard stainless, most of the wear will take place on the distil end of the trigger. If your sear is slightly softer, it will take most of the wear.  It's a 10 minute job to pull out a nut and install a new sear pin.  Reworking the trigger will take half an hour on the forge, plus filing.  If your bow is really strong... say over 200 lb. you might want to look at 3/8 in. allthread in stainless.  Good fortune.  Geezer.
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    Post by Andy. Tue Sep 12, 2017 4:29 am

    Thanks Geezer, had wondered this myself, knowing how repellent Delrin is to adhesives and such.

    Like the idea too of a sacrificial/soft nut sear of sorts for the reasons you outlined.
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    Post by Geezer Tue Sep 12, 2017 7:45 am

    I do ususally put a little glue into the passageway... gorilla glue or superglue, to help prevent the sear from turning in use.  The glue doesn't stick well to Delrin, I don't know a glue that does, but I think a bit of glue helps make the threaded sear a tight fit.  You can still unscrew it easily enough, and if by some miracle it actually sticks, just heat a piece of iron rod with a torch, then set the end of the rod against the end of the sear.  That will heat it enough to make the glue fail.  Geezer.
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    Post by Andy. Fri Sep 15, 2017 3:39 am

    Geez... have you played with brass as a sear on low poundage bows?

    Granted it's softer than steel, but thought it's self lube properties may make it suitable for light crossbows, and improve trigger feel?
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    Post by Geezer Fri Sep 15, 2017 7:13 am

    In the early days, I made a lot of paraffin/impregnated wooden rollers for lite bows (60 lb. or so) and fitted them with brass triggers and simple brass-plate sears (set in a slotted keyway in the bottom of the roller) If properly peened and glued in place, the brass sears lasted surprisingly long and had smooth release.  When I changed to steel triggers, I still made some wooden nuts with brass sears and they gave good service.  So yeah, if you don't go for excessive power, a brass sear can serve you well.  Just keep an eye on it for wear.  Geezer.
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    Post by fester Fri Jan 19, 2018 3:11 am

    Geezer could you please clarify does that mean you actualy drill between the lugs that hole the bow string
    infront of the axle pin and angle backards exiting the nut under the axle pin bottom center?
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    Post by Geezer Fri Jan 19, 2018 7:38 am

    I use a drillpress and 1/4 in. bitt to drill a nearly vertical hole thru the nut, starting between and at the back of the lugs, and coming out just behind bottom-center.  The allthread sear, properly prepared, screws into the passage.  
    If you look at Payne Gallwey's pattern, you will see he suggests making his wedge-sear come out at bottom center.  If you move the bottom of the sear back about 1/4 inch Behind bottom-center, you will move some of the stress of holding the nut in place to the trigger, rather than the nut socket.  This reduces stress on your socket, and substantially increases the useable life of your nut socket.  Of course, if you manage to break or wear out the socket, you can always reinforce the edges of the socket with slabs of bone or antler, and re-cut your nut-socket.  Does that all make sense?  Geezer.
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    Post by fester Fri Jan 19, 2018 10:48 am

    The bit i cant understand Geezer is how you avoid drilling through the path of the axle pin? I'm sat now with my delrin in front of me and the only way I can see to do this is to move the start point of the hole forwards and angle the drill backward in order to emerge just behind bottom center. That would have the drill at a considerable angle , far from near vertical.
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    Post by Geezer Fri Jan 19, 2018 11:12 am

    Simple answer: I don't avoid drilling thru the axle pin's path.  I fit the sear, then re-establish the axle for the lock... it doesn't really bear any load, so it need not be very thick.  In fact, you can use a broken axle... small headed tacks that enter the roller from both sides, but don't meet in the center.  The real purpose of the axle in a nut of proper depth (about 2/3 buried) is just to keep the roller from falling or hopping out on release.  Easy, huh?  Geezer.
    ps: of course you can set the path up, so the sear goes thru just behind the axle.  Later bows, 16th century, often have the sear far up the back of the roller, with the trigger (often multi-axle trigger) adjusted accordingly.  G
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    Post by fester Fri Jan 19, 2018 12:53 pm

    Ahaa!!! Now it makes sense thanks Geezer.

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