My crossbow project

ZigiMan wrote:1) As I know, waxing the string is recommended but except from slipping the sting, does it has more benefits?

Wax protects string from wear and moisture.

ZigiMan wrote:
What are other waxing materials can be a substitute to bee wax?

Regular candle wax. Just take any candle and rub the string with that.

btw. ceremonial candles used in orthodox christian churces are usually real bee wax. They often sell those for souvenirs.

Thanks Nerd, that's helpful!

And if anyone else can pour some light regarding my other questions and also for that one:

5) What is the recommended strength of string in ratio to the draw weight? I saw somewhere says 4 times stronger and in other place 8 times...)

Glade to read your feedback and opinions...

ZigiMan

Got some more answers concerning the string at a separate topic: some questions about strings.

Built a string serving jig:




(sorry for the blurry pic)







But then I noticed that the bend I made was on the wrong direction!
So I straight it down, and made grooves with a file:

The string serving jig hasn't been functioning so well since the hole in the wood thread holder isn't perpendicular. Even the other two I made weren't accurate no matter how I tried. This is influencing the thread tension when you are preparing the string. I found two plastic sawing thread holders, glowed them together:



Along with a small plastic tube which coincidentally perfectly match the hole (in order to narrow it), I made a new string serving jig:



After about there string that were too short for the prod, this is the one that was good:

Took the most suitable steel around me - a 9 mm (11/32 inch) round steel bar (a little bit rusty):



using my forge and a lot of hammering, made it square:



bent it into a tickler:



Found a round plastic cylinder (probably Delrin, but not sure):



With some cutting and filling made the nut:

Lots of great progress! I really like the pully system you set at your workbench, got me thinking about setting something like that up. I noticed the railroad rail section anvil, my father had one just like it.
Gnome

ZigiMan wrote:The string serving jig hasn't been functioning so well since the hole in the wood thread holder isn't perpendicular. Even the other two I made weren't accurate no matter how I tried. This is influencing the thread tension when you are preparing the string. I found two plastic sawing thread holders, glowed them together:



Along with a small plastic tube which coincidentally perfectly match the hole (in order to narrow it), I made a new string serving jig:



After about there string that were too short for the prod, this is the one that was good:

Are u sure that the string is strong enough?
I made a endless loop with 24 strings in it and even that whas comsidered " A bit thin" by a experianced guy.
Your strimg isnt even half as thick az mine.
Just wondering, dont want u to get a slap in the face by a broken string!!

Gnome wrote:Lots of great progress! I really like the pully system you set at your workbench, got me thinking about setting something like that up. I noticed the railroad rail section anvil, my father had one just like it.
Gnome

Thanks Gnome! I wish I could advance even more... As for the railroad anvil, it belongs to my father as well. Probably something fathers have

ferdinand wrote:
Are u sure that the string is strong enough?
I made a endless loop with 24 strings in it and even that whas comsidered " A bit thin" by a experianced guy.
Your strimg isnt even half as thick az mine.
Just wondering, dont want u to get a slap in the face by a broken string!!

Well Ferdinand, that's a good question and I'll give you my answer in my next post...

Hey guys!

It depends on the material used for the string whether it is strong enough or not.

With natural materials (ore new materials I dont know the strength of) I always try to test the breaking point with weight applied to a single strand.
Because the string has some bends I reduce the measured weight (50-70%) and build a string 4-5 times stronger than its appropiate draw weight.

This should give enough room for a shot.

With synthetics like dacron it is more convenient because its high durability (39-55 lbs per single strand).
When using this it comes more to the point of string thickness (too narrow with calculated poundage) so I often build strings capable of !much! higher draw weights.
So a sting with 8mm diameter from dacron comes to a minimum breaking strength of over 2500lbs.

Let me estimate 24 strands of 0.5-1mm linen or hemp could be a bit weak.
Consider making a stronger string.

Remember breaking strings deliver brutal force into the prod and can result in breaking and danger to everyone around.
Stress during a shot is multiple times higher than in rested or spanned position.

Otherwise: good luck with your tests.

Greetings Rizzar

Hey Rizzar!

What I did was similar to what you wrote. I measured the strength of s single strand of linen:



It holds about 20kg (44 pounds). My prod has a draw strength of 50kg (110 pound). I thought that 4 times stronger string will be enough - 200kg (441pounds), that means 10 strands of string. But hang on to read more about it...

There is more progress I would like to show and also I want to answer to Ferdinand. But since this page of posts is prolonged, I'm gonna continue in the next post.

ZigiMan

This is the test tiller, it is made from pine. Not the usual wood for a tiller, but it's the best I could find in my backyard (and a common wood in my country). I believe that I'll probably change it to more beautiful and suitable wood.

Cutting the stock:





Inserting the tickler:





The side plates with an extra inaccurate hole for the axle:







And finally, the assembled rough crossbow:


I forgot to take a picture how I assembled the irons I made for the prod, but I simply drew a hole for the welded nut, and screw the four screws to the tiller.

The crossbow spanned with a dowel playing as a bolt:

.

Well, I was eager to shoot it, finally, after a long time. I wanted to feel the power of the shot. So I took it outside (in the dark, I couldn't wait) and shot the dowel just to see if the crossbow works. This is the result:



It worked: the broken dowel indicated that the shot was good. The crossbow has enough power to shoot the dowel and smash it against the yard date, few meters in front of me.
The second "evidence" for the shot was the broken string. It broke in the nock, reminding me what Dane wrote about strength in the nock.

Ferdinand, now I'm sure it's now strong enough ! You and Rizzar are right, I need to make a stronger one. Thinking of something like 12 times stronger the draw wieght, i.e. 600kg (1323 pounds).

Back to the working table...

The point for counting the strings strands always have to be the nock.
Otherwise if you count in the middle, you only have half the breaking strength in the nock (where the forces are very devastating).

Another very important point is rounding up and polishing the nocks. any small point and edgy area works like a cutting edge to your string.


Linen with over 40lbs sounds almost fantastic, great material.

I am enjoying to see your progress.

Rizzar

I was also going to mention refining your nocks- I can't see them that well in the photo so you may have done this already, but where the string lies and moves against the metal from rest to armed position should be as smooth, curved, and without edges as possible. Even a very dull edge will cut when there is enough force behind it, and you have plenty of force working there. I might also reccomend adding padding between the steel and string, like thin leather. Some add a leather tube around their string end loop, I wrap the nock ends then put the string over, because that way the string is still visible so I can check it periodically . Either way, you could eliminate string wear from friction against the nock from the equation and concentrate on getting your string strength where it should be.
Gnome

Rizzar and Gnome,
I was failing to see that point... That's how it is, you learn all the time . I think I polished the nocks pretty good but didn't made them round enough. I'm starting to think that the shape of the nocks causes a lot of stress on the side as you can see from the side profile drawing:



Maybe they are too width - 20mm (25/32 inch)...
I think I'll take your advice Gnome, and pad the nock with leather or something else. And maybe make them more rounded.

I'm really glad to know that you are enjoying my progress, Rizzar. I'm also glade to read your comments, both you and Gnome and everybody else who gives feedback. Cheers!

Sorry about the broken string, ZigiMan. Far worse could have transpired, and I think you can never, ever have too strong a string, all things considered and factoring in that performance may suffer with too fat a string. But I'd rather loose a few FPS bolt speed then end up in the ER or have my weapon destroyed.
I was just look at specs for Fastflight, a newer bow string material. It has a breaking strength of about 100 pounds per strand, so if you made a string from 100 strands of this stuff, you will have a string that fails at 10,000 pounds. That is a lot! Even halved at the nock points, you have 5,000 pounds of breakage strength. Fastflight is an expensive material, and you do have to buy special serving material, since the stuff is very slippery, but it may be worth the extra money. It is also I believe smaller in diameter per strand, so you can add more material and still have a thinner string than with Dacron B50 or linen.

Oh, and when you can, get some hardwood for your tiller! I wonder if some sort of palm would work, since it is a local tree where you live. I have seen bows made from palm, and it may look really handsome.
Dane

Dane, I think you are right. It's better to have strong string then breaking the crossbow or get hurt. Fastflight might be good material but probably I will stay with linen in order to keep the medieval look. But I will keep that in mind for future modern builds. For those, I will want to use more modern and thinner string. I will surely get a better hardwood for the tiller, this one is just an experimental one. Tell you the truth, I never heard of using Palm as wood material. From past looking on Palm stock I believe it doesn't seems suitable for tiller. Thanks for the tips!

ZigiMan

Cuts of old Coconut palm trunks are pretty hard - similar to mahogany. Trees that were planted for coconut crop production and have gotten too old to produce fruit are often just ground up as trash, but sometimes are cut into planks for timber. Likewise Black Palm, a native of Latin America; but with it, only the outer few inches of the trunk are hard, the inner core is soft.

ZigiMan wrote:

It worked: the broken dowel indicated that the shot was good. The crossbow has enough power to shoot the dowel and smash it against the yard date, few meters in front of me.
The second "evidence" for the shot was the broken string.

How heavy is that dowel?
If you shoot too light bolt with a massive bow you are guaranteed to break strings. As you are technically dry-firing the bow.

Zigi,

Mr. Flintstone makes an excellent point there. If the energy stored in the bow doesn't get used up doing something useful there is bound to be trouble.

But, that doesn't mean the string loops and the bow nocks don't need attention.

In addition to rounding the "pins" of the nocks, you should also consider the "shoulders". While the pins can be made quite round and still have enough strength to do their job, the shoulders of this bow are always going to be sort of narrow. This may be a source of continued trouble. A hard leather "washer" placed over the pins will pad and effectively broaden the shoulders. I have used this trick before on a ballistrino, and had good luck with it.

Mac

mac wrote:Zigi,

Mr. Flintstone makes an excellent point there. If the energy stored in the bow doesn't get used up doing something useful there is bound to be trouble.

But, that doesn't mean the string loops and the bow nocks don't need attention.

In addition to rounding the "pins" of the nocks, you should also consider the "shoulders". While the pins can be made quite round and still have enough strength to do their job, the shoulders of this bow are always going to be sort of narrow. This may be a source of continued trouble. A hard leather "washer" placed over the pins will pad and effectively broaden the shoulders. I have used this trick before on a ballistrino, and had good luck with it.

Mac

Good advice!! I did that on my first bow and the last one, same design nocks as u have, heavy jute cloth or thick raw leather will decrease the wear on the loops.
Maybe the string whas a little short to? To much brace? Good luck making that second string, use lots of wax!

Hey guys,
Thanks for the feedbacks!
Been away lately... holidays (Passover)...
I've noticed that I got a Techno Weeny rank Thanks! (I've always wondered how you get those ranks...and still wondering)

kenh wrote:Cuts of old Coconut palm trunks are pretty hard - similar to mahogany.
Trees that were planted for coconut crop production and have gotten too
old to produce fruit are often just ground up as trash, but sometimes
are cut into planks for timber. Likewise Black Palm, a native of Latin
America; but with it, only the outer few inches of the trunk are hard,
the inner core is soft

kenh, I don't think we have Coconut or Black Palm hear... Maybe only for beauty or in botanic gardens but for sure not in plantations... But I believe there won't be a problem buying one of the common woods in use for tiller.

Nerd Flintstone wrote:How heavy is that dowel?
If you shoot too light bolt with a massive bow you are guaranteed to break strings. As you are technically dry-firing the bow.

Nerd, In my rough estimation it's about 30-50 grams, so you can say it's weight almost nothing... So maybe that was one of the reasons for the break.

Mac wrote:Zigi,

Mr. Flintstone makes an excellent point there. If the
energy stored in the bow doesn't get used up doing something useful
there is bound to be trouble.

But, that doesn't mean the string loops and the bow nocks don't need attention.

In
addition to rounding the "pins" of the nocks, you should also consider
the "shoulders". While the pins can be made quite round and still have
enough strength to do their job, the shoulders of this bow are always
going to be sort of narrow. This may be a source of continued trouble. A
hard leather "washer" placed over the pins will pad and effectively
broaden the shoulders. I have used this trick before on a ballistrino,
and had good luck with it.

Mac, That seems like a good supplement for the nock. I think I'll file the edges a little bit more, make a stronger string and add a leather washer as you advised. If that's fail, I'll round the pins a little bit more.

ferdinand wrote:Good advice!! I did that on my first bow and the last one, same design
nocks as u have, heavy jute cloth or thick raw leather will decrease the
wear on the loops.
Maybe the string whas a little short to? To much brace? Good luck making that second string, use lots of wax!

ferdinand, I think the string was in the right size. In the first string I've mad, I followed the the common size of one inch shorter then the nock-to-nock distance but it seems very short with high brace height. Then I made shorter one, and another one shorter until I got to the right size and brace height. Thanks for the good luck! and now that I got bee was candles can wax it well.


Thank you all again for the comments and advices!

ZigiMan

p.s. Speaking of weight, I always saw here that when people writing about the
weight of the bolt they use Grain. If I understand correctly, it's an
old use measurement. Or am I wrong? I'll be glade to know more about it.
I also couldn't find a way to convert it.
And what should be the weight of a bolt for a 60kg (110pound) prod?

1 Grain = 0.06479891 grams

The weight of a bolt, I understand, should be 1/12th of the MASS of the prod, not it's draw weight.

Happy Passover, by the way. The other day, I made a batch of knishes. We are not Jewish, but they are sooo good. You get the various new ranks by the number of posts you have done. I think so, anyway.

kenh wrote:1 Grain = 0.06479891 grams

The weight of a bolt, I understand, should be 1/12th of the MASS of the prod, not it's draw weight.

Thanks, kenh! I wonder why the weight should be relative to the mass of the prod, rather then to the draw weight...

stoneagebowyer wrote:Happy Passover, by the way. The other day, I made a batch of knishes. We
are not Jewish, but they are sooo good. You get the various new ranks
by the number of posts you have done. I think so, anyway.

Cheers Dane Tell you the truth, I never knew Knish before... It seems that there are Jewish dishes that are not so common and well known in Israel and the Knish is one of them. It looks delicious! Well, I learn new things almost everyday