Project gone bad !!!

Hi Guys,!!!!

Would someone mind telling me what the heck is wrong with my new crossbow, it is overriding the arrows and just dry shoots. here are some pictures and if you see what might be the cause please inform me.

Thank you.

Hi William Tell,

I respectfully suggest that you visit Robin Allen's site where under his Tips you will find "Track Dimensions". There I think you will find some answers to your problem.
Are you using a double claw latch where the bolt end goes between them to touch the string?
And you might find that your latch cover has too much clearance above the rail and thus allows the string to jump over the nock end. Even though the latch moves very quickly at the release, the string still attempts to climb the then angled claws on its rush to escape!
Hope this helps.

Pavise

Hi there Pavise,

Greetings to you my new friend, I truly appreciate your help.

No, I am using a single tooth latch and in no way the string touches the nook. I have no idea of how the locks look on modern crossbows. I have been trying to see a close up of one but couldn't find.
Ah!! I see what you mean. is it this part? marked in the picture.


I will view Robin Allen's site and see. thanks once again Pavise

Yes, that is the area where there is too much clearance. The gap between the latch cover and the rail should only be a little bit more than the diameter of the string. This not only controls the brief upper movement of the released string but also provides a safety feature inasmuch as it prevents the string from being accidentally dislodged off the claw when the crossbow is cocked.

Again, you will find a goldmine of good and reliable information at Robin's site if you are willing to navigate through it.

Glad to be of any help at any time my friend,

Pavise

Hi there my friend,

I managed to fill the gap and tried it. Ha ha !! It did catch the arrow but hell the arrow was cast out without control at very high velocity. I in fact the arrow got bent.
I did contact Mr Allen and he was ever so kind to have contacted me, He said that probably the arrow groove is a little over sized and too deep.
I shall be calling him soon .
Today I started an alteration on the trigger mechanism and started machining a twin toothed string catch out of solid brass, instead of the single one. I have grooved the center so that the string shall be touching the nook now.
I shall be sending a picture of it soon. Anyhow thank you once again my friend for your much needed help.

Sincerely
William

William: You're experiencing a phenomenon I call 'string-hop' in which the string jumps out of the release and over the bolt. Your string-snubber... the device that covers your lock and incidentally holds the bolt in place, is too high. If you lower it so there's barely enough room to clear the string, things will return to normal. Geezer

Hi my friend,

Yes, you are perfectly right. In fact yesterday I devised an additional 1/4 inch to the string snubber, tried it and it did catch the bolt, but flunged it out of control. So what I did was i remade another trigger release, instead of a single tooth release i made a claw one, so that the string would touch the nook. Also Robin Allen told me to use flat nooks instead of the half moon ones. Today I have tried it and BINGO shot out beautifully.
However I'm not too happy with the prod. At the moment I have a 180 pound steel prod, but I think I would do better with a carbon fiber one. Well at least would be faster. What do you think?
Thanks for your help Geezer, Much appreciated.
Will post some pics when I mount up the scope.

Thanks

William: You are correct, a carbon-fiber or even a fiberglass prod will shoot faster than steel. Steel prods are very durable, but they are heavy for the amount of power produced, hence they are slower than lightweight modern materials. You will also find that bowstrings made of modern fibers, like fastflite will give you better performance than flax or hemp, or even Dacron b50. The downside of very hard, non-stretchy strings is that they reduce the working life of the prod, since any energy that doesn't go into the bolt gets re-absorbed by the prod, rather than the string. The constant shock eventually damages the prod... by delamination or fatigue, or what have you... depending on the material.
Medieval bolts almost always have flat butts without any sort of nock or cap. Sometimes a slight hollow in the butt can correct a misfire/string-hop problem, but if so, it probably means your string is flying too high, over the bolt, or getting under it.
Going to a two-lug release rather than a single-lug in the center will allow your string to push the bolt from the start, rather than striking it. If possible, you'll want the string to push the bolt at its center, neither high nor low (center of string pushes center of bolt). You will note that roller-nut medieval bows are set up to make this fairly easy. Yes indeed, there's wisdom to be gained from looking how the professionals did it for a thousand years.
Keep up the good work, it's great hearing about others' experiments for a change, rather than having to manage all the disasters myself. Geezer

Hi my friend, WHEW!! What an experience this was, At last all is normal just as you have said buddy. I had a few hours of fun with it today. Thanks to you and Robin Allen.
Now do you have any suggestions of where I can get me a good quality 180-200lb carbon fiber prod and a good string for it please, well I can actually build the string myself, only don't know which kind of strings to buy.
This was a truly exciting experience I tell you. The only disappointment is that where I live there is nothing to hunt for except birds. the animals live on the roads here not in the forest, you know what i mean Geez.

Well thanks once again my friend. I'm so glad and proud to be a ,member of this guild. So much experienced no nonsense guys here.

Hi there my friend. As I was saying to Geezer. I fixed the problem, had hours of fun today. Thanks to you and Geezer. You are terrific guys. Much appreciated.

Hey Hey Hey

Love the topics where there is live stuff going on....

William more Smilies are coming your way once I get a minute to upload them

Any way I have something to add to the String-hop....so we've mentioned lowering the string clearance, using double tooth nut, what I'd like to add is that the a top latch nut design practically eliminates the string-hop.


Also an interesting story with the full nocks vs. moon nocks vs. flat nocks and the string/arrow/track stuff that happens if we change anything in the equation, but I guess this will be another topic.

I noted recently that someone was worried about a crossbow that lacked a deep to accomodate a third feather. Generally speaking, medieval crossbows were built for two-fletched bolts. I recently took a bunch of photos and measurements of a medieval military bolt. I hope to post pics of that, but for a teaser: Length 15.5 inches, diameter, @5/8 inch. Tapered to about half that in width at the tail, but full height, and Flat-butted. The fletchings were thin, flexible wood (limewood?) vanes, about 5 inches long, set into parabolic grooves in the sides of the bolt... Precisely opposite one-another. Yes, they spin.
I have been making two-fletched bolts for my medieval copies for years. They fly beautifully if properly maintained and fletched. Three-vaned bolts are generally more forgiving of fletching-errors. The two-vaned variety aren't so forgiving.
So why not put in a deep groove for a third fletch and avoid the inherent problems with badly fletched two-vane bolts? Among other things, if you have a traditional one-piece prod/lath, the prod will have to be mounted deeper in the stock, thanks to the groove. This in turn requires that the prod be made either very asymmetric or pitched forward to avoid excessive string-drag on the track. Sufficient forward pitch in the prod tends to promote string-hop. It's amazing how many problems you can discover with such simple technology.
Geezer.

I meant a deep GROOVE, dammit. Silly old Geezer can't type straight.
Geezer

Hi IVO,

Yea !!!!! That's for next crossbow Ivo. OK OK we know that's not your drawing ha ha !
Hey !! Geezer c'mon we know what you wanted to mean, you are right in the Groove no problem. Don't have to describe yourself like that buddy !

Hey fellas. I found a Jaguar 175Lb Carbon Fibre prod. what can you tell me about it?
I also would like to know from where I can get some carbon fib 16inch bolts.

No searches came up when I looked for a carbon fiber prod thou I do remember one guy talking about buying one from some italian company in 150lb weight...I don't know how much lighter prod will improve the arrow casting ability, but I do know that regular 150lb fiberglass replacement prods(like the one I use in my build) is plenty powerful to take down deer sized game...most importantly they are widely available...cheaper than steel or carbon prods...and they are more resistant to changes in climate. ...by the way what draw length does your crossbow have?

As for arrows...there is an archery supply shop on e-bay that I have saved in my bookmarks...they sell every component needed to make your own arrows from fletching jigs to carbon shafts, various nocks, different size fletching and much more. I liked their prices, so I'll be placing an order with them soon...let me look them up and I'll be back with their webpage. Good Luck!

Hi Ivo,

I had problems with it again, I noticed that it kept casting the bolts downwards, this was due to a piece of leather which I placed behind the prod to act as a dumper. However I am going to place a Riser with split limbs on it now. I have contacted Robin and he gave me some suggestions. I have managed to make a cardboard plan of the riser. However I do have some crucial questions to ask and have to have the limbs in hand before I can go ahead and machine the riser.
What thickness of wood should I leave on the stock nose to use as a rest step for the riser? Oh by the way it has a draw of 15inches but to install the riser I would have to chop 3/4 inch of the stock nose off to make it strait. Maybe you have some suggestions my friend.
Thank you, and looking forward to the arrows e-mail address buddy!

Hi William Tell,

Sorry to learn that you're still having a problem with your project. But since you have decided to use a pair of limbs instead of your one-piece steel prod you now have the opportunity to reduce the parasite string drag by positioning the riser and limbs higher. Notwithstanding the strength of any fastening bolts, the riser shelf you leave on the fore-end of your stock must be as much as is posssible. Not only must this amount of material (wood, in your case) be enough to resist the pull weight of your prod but it is also very important to keep everything as rigid as you can. Robin reminds us that final "string jerk" is 5 times the weight of the prodd when released and this unused energy is then dissipated through the riser and the stock. For an interesting observation of what really happens, try and find the high speed video clip on YouTube of a crossbow being released. You will be amazed at how the entire crossbow flexes and vibrates.

Regards,

Pavise

This is the e-bay store...perhaps someone can suggest a better place, but this is where I will be buying my arrow making stuff...wanted to try these guys for a while now. >>>Link

As for the 15" draw I believe the commercially made fiberglass prods can only go as far as 14" if not less...but if you're building a shoot through riser then you will be cutting the limb in half...right? If so then you will be moving the limbs apart and and that's what can give you a slightly longer draw. This is my guess...haven't seen the riser yet and don't know if you are making your own limbs(you've been talking to Robin so anything is possible)

By the way...I make my test pieces out of styrofoam...I cut it with a hot-wire cutter and assembled it to be cast in aluminum...kinda abandoned this project until I build a better melting furnace(something I've been doing in the back ground lately )

...didn't get the result I was looking for yet, but working on it...any way it is a great way of quickly fabricating models allowing you preview your future crossbow parts.

As for mounting the riser...I believe in wood stocks, it is usually done by milling out a space under the rail right at the end and mounting a block of aluminum that sticks out enough to make a lip. The riser is then mounted to this lip with bolts...with out much knowledge I've been thinking up my own crazy ways of doing it, but since you've been in touch with Robin he might suggest something better.

PS: This is the website that has a nice collection of slow motion videos that Pavise was talking about>>>Link

Hi Friends,

Thanks Pavise and thanks Ivo. I am actually going to buy the limbs from Excalibur. Wish I knew how to make them though. making things yourself is fun and rewarding. I like your way of making your projects out of Styrofoam, great idea.
I don't know how I'm gonna hook up the riser yet, but I was thinkin of hooking it directly to the wood. by 2 1/4 inch hex screws. No offense to you guys cause you are of great help but I'll send the riser plans to Robin and see what he suggests. well I can display them here as well and see what you guys think.




Thanks

Yep...that's what I meant except instead of wood I suggested a block of aluminum that is securely mounted to the stock...a sort of transition piece. Since you've got such a nice riser you might just think about improving the arrow track a bit by either adding some aluminum angles or milling out a hollow space and inserting a properly milled plastic track just as I see Robin and other crossbow builders do.

And don't feel bad in any way about going and looking for stuff in other places...I go to various forums/people for information and talk to them about one or the other technology while looking through the crossbow building prism. Good Luck and let us know what you guys come up with.

Hi fellow crossbowmen!

I thought I would feed you a little bit of the latest info with regards to project gone bad. Well now I am under the tutorial expertise of Mr Robin Allen. He has contacted me and instructed me on what to do to fix the arrow track in order to make it shallow. I would have to mill out the whole track first at about 1"x 1". then I am going to insert a piece of orange wood (very hard) this has been drying for 4 years.
Than when this is done Mr Allen shall continue to monitor the process. This is one thing that has to be fixed.
Secondly, I have ordered a couple of Carbon fiber split limbs from Excalibur. when these arrive I can be able to start working on the riser. I don't know but I was also thinking of constructing a top release mechanism to eliminate the string hop. but have to see about that.
I would like to thank all you guys for your kind interest to help me, that's what I call brotherhood.

Thanks

Really cool stuff William!

Interesting thought came to me...since you teach fabrication of medieval armour and such...do you have any experience with casting metals?

Hi Ivo,

Still waiting for the Excalibur Limbs, Kinda slow but will get there. I was also thinking of extending the Arrow track by another inch, to increase the power stroke. What do you think?
Even though I manufacture Authentic - Functional Medieval Arms and Armour, I don't do any casting accept very seldom with lead. What did you have in mind my friend? May I know?

I would like to post a couple of pictures of the Chapel- de - fer and the Kettle hat both used by crossbowmen, if you'd accept, where should I post them?

Will keep you informed with the project buddy

Willy Tell

Hello William,

Increasing the power stroke is always good, but it is best to stick with the recommended draw length...brace height can be lowered to increase power stroke, but don't overdo it. Good Luck!

William Tell wrote:...I don't do any casting accept very seldom with lead. What did you have in mind my friend? May I know?

https://thearbalistguild.forumotion.com/design-discussion-construction-help-f12/nuts-and-sear-plugs-t62.htm

William Tell wrote:I would like to post a couple of pictures of the Chapel- de - fer and the Kettle hat both used by crossbowmen, if you'd accept, where should I post them?

Very nice stuff William...the "Crossbowman armour"(or something along the lines) will be a great topic A good place for these would be in the History/.../... Section>>>Link

Hi friends,

HURRAY !! I have just received an e-mail from master Robin that he was discharged from hospital. He told me that his German shepherd accidentally stepped on his chatater tube and pulled it out. Well he is weak from loosing blood, but at least he is fine.

I have improved the arrow track and now is much better than before. Unfortunately the Excalibur people are taking too long to reply, for as much as I wished to have the limbs in hand to continue, however i am tempted to make them myself out of fiberglass with incorporated carbon fiber material. I have been watching the pictures of our Russian friend, quite interesting and quite nice of him too. However one thing i could not understand of how could the resin allow him so much time to build laminate over laminate and then place it in the cast and press it. I am lost here !

Thanks

William