Universal standard Crossbow nut

First topic message reminder :

OK I am talking about the part here not us X bow builders and shooters!  
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.   
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.  
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

jaeger22
Your Chinese trigger look very promising. I am a fan of this mechanism since many years. I used those fore modern crossbow with very good result whatever could be the draw weight . I used aluminium for some of them or steel ,I don't have lath or grinding machine and no welding capacity's  so I used, saw,file and rivets to put them together. The first picture is a small fancy crossbow I build years ago(near a real Chinese nuts),you can see the mechanism in details in the following pictures.  

;this one is steel near a real one

With Trigger housing (folded steel band)

Other but alloy, for the first versions of the early two shot crossbow. You can see I double the upper "ear" and make it shorter. like this it can be used like a sight. for me Chinese  can match modern trigger. It is easy to build very cheap reasonably safe (safe can be added) and don't need spring.

Early version Finished

The one for my han crossbow

With the crossbow.

Thanks Jeep! Very nice work. If you had machine tools you would be dangerous! LOL  
I like the way you made the case by bending flat bar around. Cleaver!
Here are the first two parts of my next experiment. For this version I am using brass for the claw and case and steel for the fork and trigger. The claw was machined as a single piece. It is a bit of a pain to machine this way but it is very solid.
First test fit of the claw and fork:


This is just a close up of the fit:

Here are the parts separated for a better view:

Lookin' good there, jaeger.    I just noticed you're up in Orlando, while I've over in Fort Myers, FL.  Small world, eh?

Ken, yes small world. We should get together and shoot sometime.

Well I had a bit of a set back. The main claw part failed. I cut a bit too much off the bottom sides in an attempt to lighten it. Then I when to lock it into the mil vice and it crushed and broke. 
I spent most of the day machining a new one.
But then that is why we build prototypes! LOL  
That one part is a real pain to machine.
Here is a picture of the failed one and the new one next to it:

Thats unfortunate, but things like that happen. The new one looks quite sturdy though. 
I dont know how much time and effort it takes to machine the claw part, maybe you should give the  soldering option another thought?  Hard soldering will take quite some strain before faliure and with a little experience its done quickly with minimal need for cleanup. A short pickling to get rid of the scale + flux residue would be all it takes.
But you obviously know what your doing. From the responses in this thread it seems there is quite some interest in this project, so your efforts are very much appreciated! Keep up the good work!

Nice work jeep and jaeger22 enjoyed the thread

Chaz

I'm wondering if brass is just that much more brittle than bronze, and if that contributed to the fracture of the claw.

Thanks Guys! Yes I am keeping the soldering option mind. It would definitely be a faster method in my shop.  But if my son can work out a CNC process that does not involve to much operator labor, the one piece would be nice. I am not sure which would faster for a small production run.
The aluminum and steel one with the 1/4"bolt is still working fine. I did add locktight to the threads. But the brass one has a much nicer feel. The movement feels slick compared to the aluminum. I hope to get the new brass one mounted in the test bed today and try it out. 

When you get this action worked out and ready to sell, I know a number of folks, outside of the Arbalist Guild, who would be interested in buying them as well.

I finished up both the brass Chinese lock and the Delrin nut drop in trigger assembly and got to shoot them so I thought I would share the results so far. Here are the three:

I had to re-drill the through holes for the brass Chinese so I could not go back to the aluminum one but I did make the drop in nut assembly the same size box as the brass so I can go back and forth in the same cheesy test stock and compare. It was interesting and the results were not exactly what I expected.
First the brass Chinese. This is the solid one piece claw. It is a pain to machine by hand but seems very strong and it is noticeably slicker than the aluminum one. The trigger pull is actually very light and crisp.  It was TOO light at first. It got lighter as the parts smoothed each other out until it reached the point that it would not hold. I locked back the bow string and about 4 seconds later it just let go all by itself and dry fired.  
Not at all good on a pine stock! LOL


But not a major issue, a little glue over night and it was back in business. And I cut the notch in the trigger deeper and it was better but still light. It might be OK, even good for the experienced folks here but I would not be comfortable giving it to a new person. I may be able to play with the trigger notch and make it stiffer but the notch is very deep now.
I learned that there are few drawbacks to this lock style. First it makes a hell of a loud CLACK when fired because of the metal on metal impact that stops the rotation. It sounds about like some one hit it with a large hammer. Not a deal breaker but a bit annoying. I didn't notice it on the aluminum version, I assume because it is lighter and aluminum deadens the sound. But brass, not so much. . .
 
Second issue is that because the fork is in the front of the lock and near the top, I can not cut a deep notch for the fletch to clear. I tried it on the aluminum version but it did no good because of the fork. You can what I mean here:
This results in difficulty

This results in difficulty using most of my existing arrows. You can see the issue here:



To get around it, you could 180/90 degree fletch like this:


That is what I did as I happened to have an old bolt of this style in my junk box. Or you could use just two fletch. . .
You could move the fletch forward but that would place them a bit too far from the rear where they would do the most good for my taste. Still I expect it would work.
And the third issue is that I don't see an easy way to add a hold down spring and of course no way if you use the 180/90 degree fletch.
I would love to hear feed back from those of you that have actually used this lock and how you solved or get around these issues.
So next is the roller nut.


Please ignore the two extra holes. The stupid guy doing the machining got the part in the mil vice backwards the first time and the lazy SOB didn't want to start all over. LOL 
Here is what it looks like mounted in the test rig:


The holes in the stock are for the Chinese lock and not used on this one. The pins are flush with the case are captured and held in place by the wood on the sides. The screw in the back is temporary. I have not decided how I want to tie it down yet but the tight inletting takes all the load. I do have a trigger spring in this one but realized that like the Chinese lock, no spring is really needed if the trigger is made "fat". Gravity will push it forward when the bow is being cocked. But I do like the spring because it is more positive.

Shooting this one is different than the Chinese as expected. The trigger pull is a bit stiff but is very crisp. This is with a 95 LB bow so it could be more of an issue with a heaver bow. I am sure some tuning could get it lighter but for something to sell that is aimed in large part at the new builder, I want it on the stiff side. I would not want it too light for sure. It does make some noise also but nothing like the Chinese. The nut will spin about a second or two after the shot if the trigger is held back, causing a slight buzz due to the imbalance. But to me it is not at all objectionable. The most annoying thing about this lock is that I have to rotate the nut to the pre-cock position by hand every time. I often forget until I have the string pulled back and have to let down and start over.   Just a learning process and it is no different than the Xbow I made years ago.
All in all this one is much nicer to shoot and has no issues with cutting a slot for the fletch so all my old arrows worked.
So I was expecting to like the Chinese lock a lot better and it is a very interesting and cool looking lock but in actually shooting, I enjoyed the roller nut style a lot more. It should also be cheaper to produce. The same basic lock can use the long tickler style trigger for traditional style bows. So I will start on this one first.
As a side note, these locks both work and are fun to shoot but very crude compared to my other design, the hammer lock.

My son is working on getting this in to production now but it will take some time.

On a scale of 1 to 10 I would rate them like this.
Hammer lock - 10
Roller lock - 7
Chinese Lock -5
But this is a personal preference thing and as always YMMV.

Please let me know your thought.
Thanks,
John

P.S. I am leaving a week from today on a coast to coast and back motorcycle trip and will not be able to play with these toys for 6 to 8 weeks.   But I will be online.

jaeger22 wrote:

 
And the third issue is that I don't see an easy way to add a hold down spring and of course no way if you use the 180/90 degree fletch.
I would love to hear feed back from those of you that have actually used this lock and how you solved or get around these issues.

Ancient Chinese did not use bolt clips. Bolt clip is a late medieval European invention.
That is one good reason to use nocked arrows with these.

Nerd, yes understand that the ancient ones did not have a clip. In fact I didn't even know that the  Europeans had them. But I have seen them added to the roller nut type so know it can be done. I was just pointing out that there is no easy way to do it with the Chinese style that I can see. 
Good point about the nocked arrows. But I am not clear on what would need to change to accommodate the nock. Deeper groove? Sideways groove in the claw to hold the string higher? What did you mean by nock groove?
The good news is that I took the locks and drawings to my son and he said it would be no problem to make either or both types in the CNC machines. And the quality will be MUCH better. Once the machines are programmed, the parts can be made from any metal. I left them with him and I hope by the time I get back he will be ready to crank out parts.
This is going to be fun! We may need some of you experienced hands here to test a few samples. 

jaeger22 wrote: What did you mean by nock groove?

That extended bolt groove you allready have here behind the claw ,

space under and behind the string allowing a nocked arrow to be loaded on the the string.

A narrow bolt hold-down spring can come from behind the lock, over the latch, to the right side of the lever where it sticks up.  It can be wider forward of the latch to give a better hold on the bolt butt.  At least that's what I'd do.

Good thinking! I bet that would work. I was thinking the lever was in the way. But of course, just go around it on the right or thin down the center. I should have thought of that.

nerd wrote:That extended bolt groove you allready have here behind the claw ,

OK great. That is why I extended it but was not sure if I understood right.
Thanks,
John

geezer here with some comments on the brass Chinese lock as illustrated above.  First, Chinese crossbows didn't include a groove for a third-feather on bolts... presumably they used two-feathers/vanes at 180 degrees.  You can get excellent flight that way.  Second, the bolt in the illustration is not resting against the string... that may be for illustrative purposes, but beware.  If you don't set the bolt's butt against the string, the chances of misfire go up exponentially.  Third, the upper corners of the release-lug are very sharp.  Round them off a bit and particularly round off the outer corners, or you'll ge extra wear on the string serving.  Fourth: See if you can find some way to soften the strike of the setting lever on the top of the lock when it's released. If it goes 'clack' you're getting unnecessary shock, hence wear on the lock-housing and the pin.  Eventually this will break something.  So try to engineer a way to absorb that shock without damaging things.  Fifth: It looks like medieval crossbows didn't use a bolt-clip... perhaps bolts were made to fit snugly between the lugs of the nut.  That should work out if the bolts are heavy enough.  Renaissance bows... say from 1450 and later, Often use bolt clips.  Some are wide, some are narrow enough to actually fit between the lugs on the nut.  Some are metal, some are made of horn.
Still, I think the brass Chinese lock in particular looks classy and should be eminently workable.  Otherwise Chinese wouldn't have used them for two-thousand years. 
Geezer.

Geezer correction: When I mention 'medieval crossbows' above, I mean medieval European crossbows.