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

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.

Thanks Geezer! Great input. Yes you are correct the photo was intended to illustrate that I could not get the butt of the bolt back against the string due to the fetch interference. And you are also correct that I didn't round off the claw as much as I should have. Just in a hurry.  
I think part of the problem with the loud clack was because I made the slots in front of the claw too long. So the left tab didn't actually hit before something down inside hit it's limit. I will fix that on the next one. That may help the clack a bunch.

On the "clack" issue: Well I dont see anything in the original lock construction that would stop the forward momentum of the claw part other than the  longer Bar being stopped by hitting the end of the slot.  

But I also dont see  wear at that point in the photographed originals.  If they were fired a couple hundred times with the  relatively "soft" bronze at least some wear marks at that spot should be visible. Maybe these were not actually in great use or corrosion is hiding something or else? Hard to tell.

Another possibility would be that the downward travel of the "fork" part was linited by the depth of the inlay cavity in the stock so its not hitting metal on metal but metal on wood. But thats still not entirely satisfying because  wear would be just in another part and you dont get rid of the shock also. Does anyone know if the inlet part in the stock  was with a bottom  or if it was just a through hole?

Maybe extending the case a bit downwards and adding a third pin with a rubber sleeve at a point that limits  fork travel downwards so that the claw part is not hitting on the case? But thats not how the originals were done...

When I get back I will make another one with the correct slots in front of the claws. They are way too long so it could not work as originally intended with the long bar hitting the top at the end of the slot. That may greatly reduce the noise problem, or not. . . We will just have to see. You can see the way too long slots in this photo:

They should just clear the claw.
Dumb amateur machinist!  

I put a cock feather groove in my most recent build, and extended it all the way back to the roller nut. I should have referenced the commercial aluminum bolts I bought first, though, as the plastic vanes are actually farther forward than I thought- about 1.75" of shaft behind the vane. I could have material there around the nut socket. I think if you wanted to add that cutout it would work, provided you did shorten the claw cavities a bit. Or end users could file it out, if you wanted to keep the design more traditional.
Gnome

I'd leave it traditional, for two-fletch bolts.  The user can modify if necessary. Just as the user can add a bolt clip or not as desired.

Is brass really suitable for crossbow mechanisms?
I would have thought it's too soft, in terms of both wear and breakage.

The original Chinese locks were Bronze, not Brass. Brass is more brittle than Bronze and not as strong as steel.  Bronze resists saltwater corrosion and metal fatigue better than steel.  So yes, Bronze is suitable for crossbow actions, and historically accurate - for those of us who care about such things.  Brass is not quite as suitable, and if jaegar22 and his son can access bronze - rather than brass - at a reasonable price, I would strongly recommend they do so.

Yeah, just what I had in mind. Moreover, I think brass is heavier than bronze.

For that little bit of metal I don't think the difference in mass between brass and bronze would amount to much.  Certainly nothing as significant say as the difference between aluminum and steel.

Edited:
Comparison of brass and bronze mass

Metal                            Kg/cu. meter
-----------------------------------------
Brass - casting              8400-8700
Brass - rolled & drawn     8430-8730
Bronze - lead                7700-8700
Bronze - phosphorus       8780-8920
Bronze - 8-14% Sn         7400-8900

I totally agree that bronze would be the preferred metal for the Chinese design and will look for some when we get ready to do a production run.  I used brass for the initial development because I could not find bronze at the local scrap metal dealer and I was too cheap to spend big bucks for a commercial order. But that would not be a problem for a small production run. The beauty of this CNC stuff is that the mill does not much care what metal we feed it.   
For example here is a picture of the current state of development of the drop in round roller nut cartridge.


These are aluminum for working out the CNC programing but steel, bronze, anodized aluminum and brass are all possible and each has it's advantages.
It is killing me that I am not there to do some testing and refining the design.  But I hope my son has all three designs fully programed in by the time I get back in mid August and some samples ready to test.  He plans to do a build for himself and I will be interested to see which lock he chooses.
In the mean time I am having fun riding my motorcycle across country (Albuquerque now) and thinking about my next build.
John

Drop in roller block side view:

And from the bottom showing trigger detail:



I am not sure what he used for the trigger in this setup (stainless steel?) but the roller and case are aluminum, with a hard steel plate for the trigger striker in the roller. Aluminum might work well if it was hard anodized to avoid the oxide issues. But what color? Black? Maybe some kind of bone / antler like off white?

off white would be good, and more traditional looking.

How are the Chinese locks coming?  I have seen several people on the ATARN site co-incidentally enquiring about the availability of such actions.

Ken, I haven't gotten any updates from my son for several weeks now but I am hoping he will have a prototype ready when I get home. I am leaving here tomorrow (Portland OR) but it will take me 9 days to get home due to a 3 day stop in Albuquerque for work. Just a little 3,400 mile motorcycle ride!   
If he has the Chinese ready, I will move it to the top of the list for testing.

Didn't realize you were still galavanting out West.  Say Hi to Portland from me... I worked around the metroplex for several years (lived down in Salem and commuted).  Heck, you'll be home just in time for Labor Day!

There has been some interest -- as in "where can I buy a Chinese action..." on ATARN, as well as here.

Bringing this back to active status.  

Jaeger... haven't heard from you in awhile again.  Any update on the Chinese action development.  

If you can give me the dimensions of the housing, I can start putting together a Ming Chinese style tiller and prod in the right dimensions to include the lock mortise.

Ken, sorry to report that things are dragging out. My son has a major opportunity for a contract with big $ so he has understandably been working that full time with not much left over.  I had hoped he would have all three trigger types ready for me to test when I got back but he only had the basic roller nut done. He was going to bring me that last weekend but said he found a major flaw at the last minute and will have to reprogram and build another one. Unfortunately I gave him all the drawings and prototypes I had build before I left and failed to keep a copy of the drawings so I can't give you the exact dimensions.  The approximate dimensions for the case are, 2.75" long, 1.125" wide and 1" deep. There is a 1/4" top lip at each end that is 1/8" thick so the total length is 3.25" including the lip.
Let me see if I can find some time over the next few weeks to build another Chinese prototype and send it to you to test. I still don't have any bronze so I am thinking brass case and claw and steel trigger and fork. Or would you prefer all steel ? Aluminum case and/or claw with steel fork and trigger?
Please let me know your thoughts.
John

John -- whatever works for you, works for me, with many thanks.  I like the idea of the brass/steel combination, as you suggest.  I understand all about making money - or not - and taking care of body and soul come before other things.  

With those dimensions I can start cutting a mortise, anyway, and leave cutting the lip and flush fitting until I have a lock in hand.  The 1.125" dimension tells me I can use a stock 2x8 or 2x10 as the foundation of the tiller.

Great! Sounds like a plan. I will take a bit more time on this one so hopefully it will not be such a hack job. I am re-drawing it now so will use the exact dimensions I gave you above unless I see a problem.  I will keep you informed of my progress. This should be fun!

Yeah, looking forward to this, myself!

So I thought I would give a progress report and make a bit of a step by step for anyone interested in how to do this build. I will start with the claw as it is by far the hardest part to machine. That darn long left arm just gets in the way.
First step, bandsaw out the right size chunk of brass:


Next, square up in the mill and drill 5/16"axle hole:



Then rough cut the profile with the bandsaw:

Trim a bit more with the bandsaw:


Then back to the mill:



I hope to get to spend some quality time with it on the mill this weekend.
Before I have to go out of town to work next week.
More to come.