New Member and new trigger design

Hi Guys, a newbie here, I have been reading some of the great posts here and I am blown away by some of the beautiful projects you guys have done. I am especially impressed with the RDT that Palandjali built using hand tools. Those cams would make me proud if I had done them with a full machine shop!
Just as a quick introduction, I have been making my own recurve and long bows for many years and also black power rifles (including making and rifling the barrels). I have also made a few simple crossbows along the way. I recently got the urge to do a serious crossbow build. So glad I found this site! Most of the crossbow building stuff on the net is junk. But there is nice work and interesting ideas going on here.
So I have to say up front I am not normal. I never just build a kit or a copy of an existing design like a rational person. I always have to design my own. In this case I am starting with the trigger assembly. There are a lot of usable designs out there but I have a couple of goals in mind. I want it to have a very light pull and at the same time be ultra-safe. (I know that sounds like a contradiction) Something like a set trigger on a BP rifle but one that is easily put back to safe.  So here is what I have come up with so far. I added a hammer. The overhead claw is the same as a conventional setup and the latch is also similar except that it takes a 90 degree bend up at the pivot pin. If the hammer was allowed to strike the latch directly, it would be unsafe because any inadvertent blow to the back of the hammer would cause it to discharge. So I incorporated an inertia transfer bar. The transfer bar is just a bit too short to make contact with the latch with the hammer down. With the hammer up, a spring pushes the transfer bar out just a bit so that the hammer will strike it when it falls. That will cause the transfer bar to fly forward and inertia will cause it to strike the vertical arm of the latch. The Latch will then rotate and release the nut.
I built a wood mock up to test the action and work out the 3D fit issues.
Here is a picture:
 
And here is a video showing its operation;
 https://www.youtube.com/watch?v=SkQ-zTVrxFU
I welcome any comments even if they point out flaws. Better to know before I cut metal!  

Cut two!

Looks like a good design, keep us up to date with your progress.

Todd

Thanks guys, and will do.
So I thought I would start with the "nut" or in this case overhead claw (Do we still call it the nut?) because it looks to be the hardest part to make and is key to everything else. I cut this out of a block of 4140. It is tough stuff and a bit of a pain to machine. It is still a bit rough and I will smooth all the edges. I am also thinking about drilling lightening holes in the down arm.

jaeger22 wrote:Thanks guys, and will do.
So I thought I would start with the "nut" or in this case overhead claw (Do we still call it the nut?) because it looks to be the hardest part to make and is key to everything else. I cut this out of a block of 4140. It is tough stuff and a bit of a pain to machine. It is still a bit rough and I will smooth all the edges. I am also thinking about drilling lightening holes in the down arm.

I have those top-releasing claws in my Middleton; they are superb as long as the backside and radius edges are polished.
Jack ><>

Thanks Jack, yes I have a lot of polishing to do. I am actually on a business trip at the moment and I packed the claw and some sandpaper so I can polish on it in the hotel room when not working.  
I realized that the mock up was too big and bulky so I redesigned it to shrink it down about 25%.
Here is the a picture of the rough main block and side block clamped together in the mill being drilled, counter sunk, and taped for 8/32 screws. There are 6 screws total in it now holding the two parts together, but in this picture only one is installed and one being tapped.

When I get home, I will drill undersize and then ream the holes to finished size for the pins so that the pins will have a good tight fit. I plan to do the drilling and reaming in the mill through both parts at the same time with all the screws installed  holding the two parts together in their final position. That should insure that all the holes are perfectly aligned. I will drill them all in the mill at the same time without taking them out of the vice so the holes should all be perfectly parallel. At least that is the theory,  I sure hope it works or I will never be able to get the side plate on and off of the 5 pins. 
The main block is 1" thick. The side plate will end up 1/8" thick but is 3/8" at this point to allow for the areas that need to protrude into the inside to support moving parts. The rest will be milled away down to the 1/8". So the finished assembly will be 1 1/8" wide.
This has been fun so far but there are still plenty of challenges ahead. 

The inertia mechanism is quite amazing, hope it works with a 2 or 3 hundred pound load on the nut.
I guess you thought of some kind of screw adjustment to increase or decrease the spring tension.

No I wasn't that smart.   But you hit on the BIG question and I think only experimenting will answer that question for sure. The hammer spring I am using is actually  a hammer spring from an AR-15 rifle. It is a coil type something like the spring on a clothespin, but with coils on both sides of the spring. It looks like this:   


I can adjust it somewhat by the amount of pre-load but but not quick or easy, For sure no screw adjustment. That would be very nice indeed but would add complication and should only be needed for the initial set up if at all. I could also adjust the mass of the inertia transfer bar. I am starting with it made of a single thickness of 3/8" tool steel, the same as the latch and the hammer. If I find I need more mass, I can make another one that is "fat" in the middle up to 7/8" if needed. But honestly, I expect that the hammer will have quite a snap and will transfer more than enough energy to overcome even the large force on the latch. I hope so, but only building it and experimenting will tell for sure.  
But then again that is the FUN part!!  

It is an interesting concept, and you sure packed it tight together!

Looking forward to seeing more

Well I got the rough machining mostly done. I still have to cut the scope mount into the top. This is turning out to be more work than I expected, but that is normal.   I count 22 parts so far. 7 machined parts and 15 purchased like screws, washers, and springs.
I got all the machined internal parts done and cut the main body out of a 1" thick chunk of aluminum and the cover from a 3/8" slab. The 3/8" cover is cut away to match a mirror image of the main body so that the edges are 1/8" thick. I still have a lot of detail work to do but it is basically working now and I plan to do some testing soon. Just putting pressure on the claw with my hands, it works fine and has a crisp hair trigger. But I want to test it with something pulling at 100 to 200 LB and see if it will still release reliably.
Here is the latest pictures:


Close up:



Other side and assembled:

Very nice progress !

Chaz

Thanks Chaz, I got the Picatinny style scope rail cut in last night. I got in too much of a hurry or was just ham fisted on the mil and got a couple of the spacings off a bit but I think it will still still hold a scope just fine. I ordered a cheap red dot scope last night for it.
Here is a picture with the rail cut.

Be careful now you wouldn't want it to look like a "tackticle weapon"  ........do you intend to blue it?...
might look good with a case hardened finish ........ something different. Obviously you have a plan and it seems to be coming together.

Chaz

Not a "tackticle weapon" for sure! LOL
No I am just feeling my way along here. I ordered some recurve limbs and I bought some wood for a stock but no clear idea yet of what I will end up with. I figured to get the limbs, come up with some way to mount them up front to allow a center shot configuration with the string just touching the barrel. (like I have made before) Then test the bow for draw length and then design the stock around the bow and release. I am not even sure if I want to go old school rifle stock or more modern pistol grip.
What do you guys think?  
The body of the release is Aluminum so bluing is out. I could anodize but that is a lot of work and I am impatient so I am just going to paint it.   
My main goal, at least for this phase, is to get something together to test out the release/trigger design. Then maybe plan out a more advanced build for the next go around. Maybe a reverse draw set up.  

Yes Sir I got caught up in the pictures ( worth a thousand words ) should have read the words. At any rate ........... sure looking forward to following your progress.

Chaz

Well I panted the release and did what I hope is the final assembly.   It is a bit of a pain to put together with all the springs, pins and washers. You have to hold the part with one hand, hold the spring in place with the other hand and push the pin in with the other hand.   
I think I had it apart and back together about a dozen times before I got all the interference and binding issues resolved because I could not see what was binding or hitting when it was together. So I had to guess, cut and try.  
Here is a picture of it with paint. Sorry it is a bit fuzzy.



I made a cheap and dirty stock blank from 3 poplar boards from Home Depot, laminated together. 2 are 1" X 6" and one 1/4" in the center for a total thickness of 1.75". I cheated and used the my ancient milling machine to do the inletting for the release before the final glue up. Almost too easy. But I like easy!   



Here it is with both sides of the blank together checking for fit.


The 1/4" board is in the center and dropped down 5/8"  from the other two to form the grove down the center.
Now I have to wait for the glue to dry before I can shape the stock.
Then it will be "fun with a wood rasp" for some time. . . .

It shoots!  I got it rough shaped last night but I discovered that my limbs that I ordered from The Crossbow Store.com did not get included when my order shipped. The good folks there are fixing it and have another set on the way but I was impatient to see if the trigger/release would work so I pulled the bow(prod) off an old Xbow I made sometime back. That bow actually was made from the limbs from a recurve bow I made. The handle on that bow de-laminated leaving me with an extra set of limbs. It is very long and has a long draw for a xbow. Like 25".    Fortunately I left the new stock very long until I see what the draw length turns out to be on the new bow.
Anyway here is what it looks like with the long prod.


The bow only pulls about 75# so it is not the final test but so far it works great! It has not failed to fire once, and I love the trigger! It feels like the double set triggers on my BP target rifles, crisp and light.
The only problem I am having with it is that when I shoot, the claw ends up bouncing back into the locked position about 1/2 the time. That is annoying because I have to check each time and it if it is locked, I have to push it forward and drop the hammer to get it unlocked.   
I will have to think about that. 
I plan to spend some more quality time with my spoke shave and wood rasp tonight finshing up the stock while I think about how I am going to mount the new limbs. 

Do you have a spring on the string claw? Set to hold it in the open position, you should only need a little tension.

Todd

Thanks Todd. Yes there is a light spring behind the claw. I may try making it stronger. Here is what I think is happening.
When the claw releases the string, it rotates up of course and the bottom rotates forward until it contacts the front wall. I have a small section of hard rubber there on the front wall  to cushion the impact.
It hits hard enough to bounce back to the cocked position. The same I expect as in a conventional trigger. This happens very fast, all in a few Milliseconds. However with a conventional trigger, the shooter still has the trigger pulled at that point so the spring quickly rotates it back to the fired position before we slow humans can let off the pressure on the trigger. So we never see it locked.
But in my set up, there is no direct connection from the trigger to the claw or latch. The latch is just driven by a spring so it locks up anytime the bottom of the claw gets back far enough and it does it very very fast.   
The only way I can release it is to "fan"the hammer. Not a big deal, just a minor iteration  but I would like to fix it. But I have too many other details to work out first, like how I am going to mount the bow limbs.   I have some ideas but need to refine the design and start making the mounting bracket.
Thanks again,
John

Will the stiffer spring behind the claw solved the problem. Thanks for the idea Todd!

Is the spring behind the claw the same set up as in the mock up you made in your first post? The danger is if too strong it may give too much resistance for the hammer to overcome. If you could utilize two independent springs for the claw and the hook I think it has a better chance of working.

Todd

Another solution would be to add a "soft" locking system for the claw to stay in fired position.
Maybe some sort of springy piece attached to the claw, with an angular tip that would fit into a hollow in the block.
Will not bounce anymore, and easily unlocked by the string at the end of the drawing process.

Todd, you are exactly right and I went to two independent springs in the final (so far) design.
You can see the claw spring here:

You can't see it in this picture but the latch spring is in the bottom and pushes the horizontal  leg of the latch up. You can see that here:



Robin, yes that might work but the stiffer spring seems to have solved the problem. It may even be stiffer than I need now so at some point I may want to play with it and see if I can get to Just stiff enough to avoid it locking.

Well I screwed up on the stock big time.   I shoud have know this but when I got the red dot scope yesterday and mounted it, it was immediately clear that the cheek pad was WAY too low to place my eye up high and in line with scope. So I hacked it up and added wood to make the high cheek piece. Looks like crap but it seems to work. I may just paint it to hide the ugliness.   I am glad now I used a cheap piece of wood for this working prototype. I would be really bummed if I had screwed up on a nice piece of wood.

Well I have to say I really like my release and will call this experiment a success!  I got the new limbs in and built center shot bracket. The bow is a short 30" tip to tip. I tested the bow and it pulls #140 at 14". So I cut down the stock to fit and mounted it. Here is what my little test bed looks like:

The hammer spur also acts as a built in hook for the cocking aid as you can see here:

The release has worked flawlessly so far. I think I have between 50 and 100 shots through it and no issues at all. And the trigger feels just like a rifle trigger. Crisp and lite. I did test banging on the hammer with the hammer let down and I could not make it go off. So I feel that is very safe.
Now I can start thinking about a serious build around this release/trigger. I learned a lot building this and it is fun to shoot. But I am not wild about the short bow and resulting short power stroke. Its power stroke is only 9 1/2 inches. Or the very short bolts (18") as they bury in the target deep enough to mess up the fletching a lot. It is nice and handy, like a carbine rifle, but I am only getting 193 FPS from 140 LB with the short light arrows and that is about the same as I was getting with the huge recurve bow with the longer and therefore heaver arrows and it only pulled 75 LB. That is about what I expected because the smaller bow is almost twice he pull weight but only about 1/2 the power stroke. So I am thinking something in the 34 to 36" bow range might be just right. Or maybe I will do a compound or even a reverse compound.   Fun to think about.
John

Great job! I have made a few with similar prods, but go with 3 1/2" brace plus 10" power stroke. I am getting around 210 fps with 410 grain arrows with silencers on the string. 

Good going and am anticipating what you will build next.

Todd