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    Universal standard Crossbow nut

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    jaeger22
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    Universal standard Crossbow nut

    Post by jaeger22 on Tue Jun 17, 2014 3:07 pm

    OK I am talking about the part here not us X bow builders and shooters! Laughing 
    So I was thinking about why there are relatively few people building their own crossbows. It seems like crossbows are becoming more popular and we see them more and more in both the large and small screen as well as in the woods. So why are there not a ton of DIY builders?
    My theory is that many are stopped by the need for some basic machined parts and the lack of tools or skills to make them. Many have the skills to build the stock, bows and strings are available for purchase at entry level prices. And there are several low tech ways to make bows like the car springs and the multi slat system KenH used so effectively. But try to buy a nut or trigger module.  Sad 
    I think the availability of a low cost high quality set of trigger parts and/or assembly would open the door to a lot of new builders. So I may be a Don Quixote tilting at windmills but I want to take on that problem. But I need the help of you more experienced builders here.
    My son owns a machine shop and I am an engineer and I plan to coerce him into using his fabulous CNC machines to produce some parts for us. I am thinking two levels; The first level is a simple nut and trigger/tickler set. Maybe a set of side plates. These could be a kit or individual parts. The idea is to have standard parts to keep the price low but give the builder maximum flexibility to do his own design and construction. This should work for entry level first timers on up to fairly serious recreations of antique crossbows. So low cost and high quality are needed. That is the domain of CNC machines. Smile 
    The second level is a drop in cartage of a modern type based on my own design with the hammer. (See new member and new trigger design). More on that later.
    So I am thinking 1.5” diameter nut made of black Delrin,  ¼” axel hole and a small hardened tool steel plate for the trigger notch. Here are some pictures of an aluminum prototype I made last night. (I have some 1.5” delrin rod on order)
    I would love to get your thoughts.

    Rough cut on the band saw (from .875" stock).

    After a quick run on the lathe:


    Here is the tool steel wedge has been pressed in but not cut off and trimmed yet.

    This picture is a bit fuzzy but it shows the trigger notch. It is wide enough to accommodate up to a .375" trigger.


    Here the machining is basically finished.  It just needs hand file clean up:

    Please let me know your thoughts.
    Thanks,
    John
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    Re: Universal standard Crossbow nut

    Post by Todd the archer on Tue Jun 17, 2014 4:25 pm

    I have made several like that only using hardwood (walnut), and not having a lathe used a drill press to get it round.Cut the slot for the metal plate and used J-B weld to glue it in. Just make sure to keep the grain vertical when the nut is in the set position.


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    Re: Universal standard Crossbow nut

    Post by Todd the archer on Tue Jun 17, 2014 4:27 pm

    I think you are right though that a "drop in" trigger assembly would make people less hesitant to start their own project,


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    Re: Universal standard Crossbow nut

    Post by kenh on Tue Jun 17, 2014 5:57 pm

    Yup.  More or less drop in "actions" or "locks" as they would be called elsewhere, at reasonable prices, would be a god-send.  I've kinda been saying that ever since I got started in this.  A nice Delrin nut & tickler, something more modern, and perhaps another olde style lock like a top lock or something.  Available both unassembled and ready to polish as well as assembled and totally ready to inlet into the tiller.  There are a lot of interesting but simple designs available if you have a machineshop and the training to use the tools therein -- many of us don't have.  And CNC means short production runs of pieces are easily doable...

    I'll certainly buy some as long as they don't cost more than my boat!

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    Re: Universal standard Crossbow nut

    Post by rolynd on Wed Jun 18, 2014 2:26 am

    That would be a Good Idea, I think. I know of no place where I could  buy a complete Crossbow Trigger. 
    Making the trigger assembly  (esp if you want a multi stage one)  is the most time consuming part in a build. 

    Since I am one of those who does not have a lathe I made the trigger for my little project from flat bar stock.  If a lathe had been avaliable I would have probably made something different..



    Instead of selling it with a tickler  I would prefer  just a nut together with a well for it to sit in. Roller nuts are mostly used by people  who build traditional  or exact replicas so I think most of them would prefer  a Nut&well design. Nut with an central Axle is not  traditional.
     Tickler can be easily made with minimal Tools but Nut&well parts would require a lathe for perfect fit. I`d also prefer SS over Delrin If I were to buy something. Delrin can take a lot but I dont know about its max capability.  A medium sized SS Nut could be used from light to also very heavy crossbows. I guess traditionalists also would rather have a metal nut over a delrin one. At a reenactment fair  others would point out to them that they used "plastic"  but metal is accepted even if its SS. Well, these are strange folks...

    You could start with a basic roller nut design then expand to other designs.

    Me personally would like to see a trigger unit based on the famous Chinese crossbow trigger. Its another  proven concept that has stood the test of time and was mass produced  almost without alteration over a long time period. Only three moving parts an a housing.  The tough part for me to make without macining ability would be the housing. Its a simple, compact, contained unit that could be used as a drop in unit in a wide range of builds, not just traditional ones. 
    It doesnt have to be made from bronze - too expensive nowadays - but  moving parts from SS and an Aluminium housing are ok.  If something like that were avaliable at a reasonable price I would definitely buy one.








    But you already said it in your  post : there are not many people who make their own crossbows, so I think you couldnt expect it to sell in real quantity. If it can be made without great cost of initial investment by you I would give it a try. I also have no Idea what people are willing to spend on a premade trigger unit. You could decide to make less on them and sell more or  pricing it higher and probably sell less.

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Wed Jun 18, 2014 4:07 am

    Great ideas here guys, thanks for the input.
    I did think about SS but thought it would be too heavy. But you are right I am sure that some would like that better. So maybe a SS option. It would be almost the same CNC program. I will talk to my son about it.
    And good thought about making a drop in option. I will work on a design for a low cost drop in roller type.
    Right now my son has my latest drop in design of the modern overhead claw type with the hammer. I made it a bit more compact and also made the hammer smaller. It is now 1"wide.
    Here is a shot of the prototype for that one: 

    You can see some of his other products in the back ground. I think they are custom frames for custom 1911's but notice the difference in quality between my hand machined hack and his CNC produced parts.
    He is trying to work on the programing in his spare time. As Todd said, this will probably never be a high volume thing but he can use it to fill in between his real jobs. My main concern is keeping the cost down and touch labor is the big cost driver. As you can see above there are 5 internal and 2 outer case parts that have to be machined plus 5 springs and 8 washers, so it is never going to be cheap. But is will be a complete drop in with a very nice trigger and the hammer is an automatic safety.
    But I was wanting to create a lower price option for someone just wanting to give it a try and thus the nut.
    Thanks again for all the good input.
    John

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Wed Jun 18, 2014 6:25 am

    I forgot to address the point about the nut in the well. I was assuming this could be used that way also, as it will be perfectly round and smooth. The hole in the middle should not hurt anything. Also don't some of them use a string through the middle to keep the nut from coming out of the well?
    Question, I don't know much about the nut in well, I used an axle on my few previous projects, so is the well a machined part? I thought it was just cut into the wood with metal sides. But I can see that a metal on metal set up would be better.
    I do see that one design will not work for all builders. But I would like to come up with the design that works for the most, especially the new builder.
    Thanks again for your insights.
    John
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    Re: Universal standard Crossbow nut

    Post by kenh on Wed Jun 18, 2014 10:52 am

    I agree with Rolynd -- If you can make a version of that Chinese lock, that would be the cat's meow!   I've been looking for a builder for that action ever since I first saw it.

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    Chinese Trigger

    Post by jaeger22 on Wed Jun 18, 2014 3:32 pm

    I think you guys are on to something with this Chinese trigger! I hate to publicly confess my ignorance but I did not know anything about this type of trigger except that it existed.  Embarassed 
    But your post got me to look into it and I have to say that  I see why you like it. Only three moving parts and no springs right? Any down side?
    Questions:
    It looks like the long tab sticking up behind the claw has several purposes. First, for the string to push it back into locked position when you cock it. Second, to hit the stock and stop the forward rotation when you fire, and leave it in the ready to cock position. But It doesn't look like it could rotate too far anyway. Is that right? But is it also that long to act as a weight? It seems excessively long unless it has a use as a weight to rotate the lock forward when the stock is pointed down or something else like that. What am I missing?
    Similarly, the trigger looks thick and heavy but I am thinking it is done on purpose as a rotational thing, causing the trigger to rotate to the locked position when the X bow is pointed down to cock it, and there by eliminating the need for a spring. Does that sound right?
    I am going to try to design and build one based on these principles and see if I can make it work.  Smile 
    I need more time!!! tongue 
    Thanks for the great idea!
    John
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    Re: Universal standard Crossbow nut

    Post by kenh on Wed Jun 18, 2014 6:10 pm

    Here is a definitive article by Stephen Selby, one of the preeminant experts on Chinese archery in all its forms.
    http://www.atarn.org/chinese/bjng_xbow/bjng_xbow.htm

    and other mentions of the same basic action:

    http://www.atarn.org/letters/ltr_feb99.htm

    http://www.atarn.org/letters/ltr_nov99.htm

    Here's a scaled drawing on graph paper:
    http://atarn.net/phpBB2/viewtopic.php?t=2591&highlight=qin+crossbow

    A build-along discussion:
    http://atarn.net/phpBB2/viewtopic.php?t=17&highlight=qin+crossbow

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Thu Jun 19, 2014 4:59 am

    Thanks Ken!!  cheers You saved me a ton of research trying to find all this. A LOT of good information here. And my question about why the rear tab seems so long was answered. It server as a crude rear sight! Interesting that it is only on one side but I assume that was to keep the weight down and it would be easy for the shooter to compensate for. Probably made it easier to cast also.
    Question for all, how wide should the claw be? I was thinking a 3/8" slot for the arrow and 3/16" wide for each claw for a total width of 3/4". 
    The trade off is that the wider the claws, the less stress on the string but the overall width goes and makes it harder to install in a stock unless you make the stock very wide.
    Thoughts???
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    Re: Universal standard Crossbow nut

    Post by Geezer on Thu Jun 19, 2014 2:18 pm

    On the subject of the traditional Chinese bronze lock, they look great... a proven design that's simple, strong, and should give a good release.  Unfortunately, I don't have to the tools to build them in my shop... though a friend just bought a milling machine, so that could change.  If somebody made a bunch of them, I suspect there would be a market.  The design is great.  Geezer.

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Thu Jun 19, 2014 5:34 pm

    Thanks Geezer! Doing them in bronze should be no problem. And the amount of material is small so it should not drive costs too much. Any particular dimensions you would like to see? I am working on a prototype using aluminum and steel just because I have it on hand. I am drawing it up now and I am thinking 3/4" wide nut (if that is what it called on this type), 1" high "sight", 1/4 inch axles, and all in a drop in box that is 1.25" by 2.75" with a .25" lip at each end.
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    Re: Universal standard Crossbow nut

    Post by kenh on Fri Jun 20, 2014 7:16 pm

    Those sound like good dimensions to me anyway...  I'll take one!

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Sat Jun 21, 2014 3:50 am

    So I wiped one up from scrap in the shop just to figure out the subtleties of the deceptively complex geometry. Very small changes in the dimensions make a huge difference. For example, very small changes in the length of the retainer fork's lower arm where it goes into the notch will make it go from won't hold to won't fire. Shocked  But once those are worked out it should be relative simple to replicate. 
    Here is my prototype so far:


    From the other side:


    Here are the parts:


     
     This shot is with it in the fired position:



    I went with 5/16" pins just because looking at the pictures, that seemed closer to what they used.
    A few notes: I assume the pins are all that hold it in the stock. The notch in the back of the trigger was just because I was lazy and used a chunk of medal I found in my scrap box that was close to the right size except for the notch. I didn't like the look and it also needs the weight so I JB welled  another piece of scrap to fill it in.
    The claw is made of aluminum from 3/16 plate. The two sides are held together with a 1/4" bolt with a 3/8" sleeve over it inside.
    Question, what about a groove for the arrow and/or Fletch in the front? What size would you all like to see?
    I wish I had some bronze, that would make it look cool.  Smile  I am going to try to get to the metal scrap dealer today if possible.
    Please let me know your thoughts.
    Thanks,
    John
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    Re: Universal standard Crossbow nut

    Post by Gnome on Sat Jun 21, 2014 7:57 am

    jaeger22 wrote:Thanks Ken!!  cheers You saved me a ton of research trying to find all this. A LOT of good information here. And my question about why the rear tab seems so long was answered. It server as a crude rear sight! Interesting that it is only on one side but I assume that was to keep the weight down and it would be easy for the shooter to compensate for. Probably made it easier to cast also.
    Question for all, how wide should the claw be? I was thinking a 3/8" slot for the arrow and 3/16" wide for each claw for a total width of 3/4". 
    The trade off is that the wider the claws, the less stress on the string but the overall width goes and makes it harder to install in a stock unless you make the stock very wide.
    Thoughts???

    Jaeger, 3/8" for the center gap sounds good to me, but I think the claws should be at least 1/4", if not wider. I don't think a stock that is extra wide at the lock area would be a bad thing, and, depending on the metal you finally go with, couldn't the walls of the box be thinner?
    This is an exciting thread and I certainly hope it follows through for you- I certainly want to get my name on the list for one or two or six of these! I don't think I'd ever attempt to fabricate this type of mech myself unless I had access to much better equipment than I have now. On the other hand, I think that a roller nut is not beyond the abilities of anyone with simple tools and patience.
    Gnome

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Sat Jun 21, 2014 12:22 pm

    Gnome, thanks so much for the feed back! I totally agree on the 1/4". It is a trade off of course between lower overall width and lower stress on the string. I went back and forth between 1/4" claws with a total width of around 1 1/4" and 3/16" with total width a bit over 1". I certainly defer to your vastly grater experience! I will go to 1/4" claws and as you suggest, do some stress analysis to determine how thin I can make the walls and still have acquit strength with at least a 50% safety factor at 300 LB pull. 
    I stopped on the way home this morning at the scrap metal dealer looking for bronze. The closest I could find was brass. Would that be an acceptable substitute?  (hope so I just bought $50 worth  Shocked ) Expensive stuff! But it should look beautiful and I am thinking that with a bit of deliberate corrosion,  it would be hard to tell from bronze. What are your thoughts?
    Another question. The originals cast the claw in one piece. Including the pin or bridge if you will connecting the two sides together. For machining, getting that pin round down in there between the two side plates would be a real pain because you just can't get a cutter in there and turn it on either the mill or the lathe. So I used the threaded bolt and sleeve described above. Would that be acceptable? It is not visible unless you take it apart. 
    Thanks again for the help.
    John
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    Re: Universal standard Crossbow nut

    Post by kenh on Sat Jun 21, 2014 9:00 pm

    Looks really good!!!  Like all good engineering, "the devil is in the details" like the length of the sear in the notch Cool .    They probably used larger pins because the material was bronze, not iron or steel.

    Bronze would look cool, but steel and really hard aluminum alloys are stronger.  Isn't there a chemical bath, similar to bluing/browning that can be used to "bronze color the steel bits?  Electroplating?  Steel can be left 'white' to allow the builder to blue/brown or otherwise color the metal to suit.

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Sun Jun 22, 2014 12:50 pm

    Good thoughts Ken. I was also thinking about a combination, shell and claw from Brass and the inter fork and trigger from steel. That could be the best of both worlds. I did a quick analysis and and it looks like I could go down to .1" on the wall thickness and still use any metal except maybe really soft aluminum. (which I would not use any way) Even that would probably work.
    With a .1" wall thickness and a 5/16 " pin we have .03125 Sq" area on each or a total of .0625 for both sides. So with 450 LB of pull (300LB + 50% SF) we have 7,200 PSI of stress.
    All the metals can easily handle that except for possibly soft Aluminum. (Soft AL bearing stress is in the 6,900 to 10,000 PSI range) I found a value for brass on-line and it was 34,100. So even if I am way off in my calculations is should still be safe.

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    Re: Universal standard Crossbow nut

    Post by rolynd on Wed Jun 25, 2014 6:45 am

    This looks real good!  I definively can live with a brass/steel combo for an more original look. But also a All-steel version would not put me off especially if it can be made cheaper than the brass combo version. 
    If you wanted to do a replica it would have to be bronze, but you can always offer this on special demand if you figured out the intricacies of the design and your tooling is set up. If you say Steel you talk of SS ? One thing that would put me off would be  tool steel because of rust issues... 
    The beauty of the bronze ones is that they are  almost maintenance free, do not rust and thats why we have so many well preserved specimens to study even after  2000 years.

    I always wanted to build one of these but lack of tooling equipment put me off (no lathe, no mill)

    I would have fabricated it from flat stock and hardsoldered it together. The housing being the most problematic for me to make. The interior workings are  relatively easy to make once you figured out the dimensions.
    I would also  - like you did-  made the claw from two parts and soldered the round connecting bar. Other than casting I see no easy method to machine it otherwise. 

    Since this bar is the only point that connects the two parts of the claw I am not sure if a threaded connection would be able to hold fast during repeated release. With a strong drawweight  the claw gets suddenly stopped by the longer rear arm hitting the housing and get repeatedly "shocked" real hard.
    Well, the claw is held by the rear retaining pin so its not going anywhere, no fear of that. And also the whole thing is retained in the housing and the threaded rod cannot go anywhere.  But if the threaded connector rod on the front of the claw comes a bit loose over time the two parts could try to change position a bit relatively to another , or make the 2 claw parts have a minute wobble between them , if the threaded bar works a bit loose over time it could begin to  scrape on the housing etc. (not sure of the interior tolerances, but I think you would like to keep it as flat as possible )- hope you get what I mean?

    I would prefer if the connector rod between the  claw parts could be a soldered connection over a threaded one making the claw into a solid part. Well, I am thinking long term durability here, maybe a threaded bar is all it takes. 

    3/8 claw spacing is fine with me.
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    Re: Universal standard Crossbow nut

    Post by Gnome on Wed Jun 25, 2014 11:20 am

    I can't quite tell from the photos, I'm assuming there is a collar built into one side or other of the claw assembly that provides the spacing, and the threaded rod goes through it. Since I can't forsee any reason why you'd ever want to take it apart, I agree with Rolynd that it should be bonded permanently. Also, I'm wondering if the two parts just butt-join with flat surfaces, or if you plan to mill some type of key system so that they positively lock into alignment for tapping the threaded hole? Just thinking that might make that assembly step less fiddly, as well as make the construct more secure.
    While a cast bronze authentic replica would be so awesome to own I might persuade myself to build my first ever historically accruate weapon to house it, right now I'm most intrigued by a working version of this mechanism that can handle the abuse dummies like me are bound to heap on it- stainless steel would work well, IMHO.
    Gnome

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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Wed Jun 25, 2014 7:06 pm

    Wow, a lot of good thoughts here guys! Thanks.
    rolynd wrote:Since this bar is the only point that connects the two parts of the claw I am not sure if a threaded connection would be able to hold fast during repeated release. With a strong drawweight  the claw gets suddenly stopped by the longer rear arm hitting the housing and get repeatedly "shocked" real hard.
    Well, the claw is held by the rear retaining pin so its not going anywhere, no fear of that. And also the whole thing is retained in the housing and the threaded rod cannot go anywhere.  But if the threaded connector rod on the front of the claw comes a bit loose over time the two parts could try to change position a bit relatively to another , or make the 2 claw parts have a minute wobble between them , if the threaded bar works a bit loose over time it could begin to  scrape on the housing etc. (not sure of the interior tolerances, but I think you would like to keep it as flat as possible )- hope you get what I mean?
    Yes I totally get what you mean and spent a lot of time thinking about that very thing. After thinking about it seems like it may be self correcting. The claw assembly has a  pin,  that holds the two sides of the claw and another that the claw pivots on. Think about when the claw is holding the weight of the bow. There is a large but equal force on each claw and a centered counter force on the connecting pin. That should force any misalignment back into alignment. I think the connecting pin could actually be completely free to rotate and it would still work. I had assumed I would use locktight to keep the bolt in tight. But for the moment I have left it loose to see if my theory is right. So far so good but I  have only made a dozen or so shots so far. I think the bolt may back out and hit the side at some point. More experiments are needed here.
     I definively can live with a brass/steel combo for an more original look. But also a All-steel version would not put me off especially if it can be made cheaper than the brass combo version. 
    If you wanted to do a replica it would have to be bronze, but you can always offer this on special demand if you figured out the intricacies of the design and your tooling is set up. If you say Steel you talk of SS ? One thing that would put me off would be  tool steel because of rust issues...
    Yes good point about the rust, The tool steel was to be able to harden but I am not sure it is needed. The good thing is that once the CNC machines are set up they can handle any metal so I could make them out of several different types.
    Gnome wrote:I can't quite tell from the photos, I'm assuming there is a collar built into one side or other of the claw assembly that provides the spacing, and the threaded rod goes through it. Since I can't forsee any reason why you'd ever want to take it apart, I agree with Rolynd that it should be bonded permanently

    Yes that is how it is made. I think I will try one out of brass next and solder in a pin as an experiment. I am sure that is the best way but I want to keep the labor down to hold down cost.
    Thanks for all the good inputs!
    John
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    kenh
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    Re: Universal standard Crossbow nut

    Post by kenh on Wed Jun 25, 2014 7:26 pm

    When yer ready for a field test, let me know.  I'll make up a replica of this one:


    I've got laths for the prod and a nice plank for the tiller...

    rolynd
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    Re: Universal standard Crossbow nut

    Post by rolynd on Thu Jun 26, 2014 3:11 am

    I'd like to see someone tackle this one:



    it used the same trigger.... Wink 

    I briefly experimented with this kind of setup in my rubber  thingy and noticed it had almost no recoil. It was also little faster than the same amount of rubber set up in a "single" bow.  But I dont know if that readily translates to one made with "real" bows.

    There was a thread from Jihaif in the webarcherie forums  - he started a build of a double-bow one but the thread  has disappeared before  he finished the thing. No Idea what happened or how it performed.


    According to the Threaded bar issue:
    I found pics of this one:

     





    Apparently there is no need for a round connecting bar in this one, it seems the claw is made from a massive piece with a protruding part at the bottom conforming to the shape of the 2nd part.  Maybe with CNC machinery it would be easier milling the Claw from a single piece and eliminating all the aforementioned issues and also the additional soldering , cleanup etc.  I dont know exactly what is doable  (If you have 2,5D or 3D machinery or else)or the most economic way but if you can make the claw part from one piece this version seems to do away with the issue of having to mill a round bar in the recess. From the reciever parts shown in the background of one of your photos you can make fairly complex parts... Sorry, Dont want to upset your processes - just food for thought Smile


    Yes, tool steel can be hardened but as you sait it may not be needed. Bronze is softer even than unhardened steel and there seemed to be no issues with excessive wear. The sear lips on the trigger and 2nd part seem to be  fairly crisp on most of the photos I have seen so far. As long as the trigger and 2nd pard are the same materials/hardness  I dont expect much wear.

    jaeger22
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    Re: Universal standard Crossbow nut

    Post by jaeger22 on Thu Jun 26, 2014 4:30 am

    This is GREAT stuff! Outstanding photos! I wish I could see inside the claw and see what they did to accommodate the short upper arm of the fork but I will have to figure that out for myself. It does look machinable. I notice that it does not have a notch in the front for the fletch. I made mine that way but the first time I tried to shoot it I could not get an arrow loaded, so I cut a 1/4"slot in the front. I really like this design. Back to the drawing board as they say! Smile  I want to work out the design details and build a prototype out of brass or brass/steel.
    I have only shot the first prototype a few times. The trigger was TOO sensitive for something with no safety. I could not make it go off banging on the stock but if you breathed on the trigger it fired.
    So I made the notch just a bit deeper changed the angle last night. I hope to get time to shoot it some to day.
    But another delay, I got in 6 feet of 1.5" Delrin rod to make roller nuts from so I want to build a prototype for that style with a simple trigger/tickler and side plates because my son whats to set up for that as soon as he has the hammer trigger design ready and he is almost done with that.
    If I didn't have a job and family I could get something done! LOL Laughing 
    OK if you promise not to laugh too hard I will show you my "engineering test bed":


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    Re: Universal standard Crossbow nut

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