String jig, was String and brace, again

Well, here we go again. After the string break I decided to try making a string jig and string. I want this thing on its feet and shooting, and even my best string source is a week out. Besides, it's one more thing I'll have to do anyway, so why not now. The string is 40 strands of B50 served with twisted nylon serving thread.

This Alchem bow is supposed to be braced at 3 1/2", and after all is said and done, my second string has it braced at 4" plus a skosh. I'm letting it sit overnight to see if it relaxes any, but is this too much brace for this prod? (String number one was loose in spots and, somehow, ended up being 2" too long.)

A few pics follow, of my minimalist string jig, the bow strung, and some leather pads to protect the loops.

As always, any feed back is appreciated!
Frode

Your on the right track. Try rubbing the string (while still braced on the prod) with a piece of leather with some wax on it. Go back and forth vigorously to the point it gets hot. This should help the string settle in. Plus shooting it some will help. I don't think 4" is excessively high in my opinion.



Todd

Thanks, Todd! Sorry for the delay in responding. Looks like it settled just a bit overnight maybe 1/8", maybe. I just did the wax rub, and it looks better, if not any lower. Tonight I'll shoot it, and we'll see how much more it changes.
Fingers crossed,
Frode

Frode: Geezer here. 4 inches is a perfectly good brace-height for an Alchem prod with a new string. It should settle down to @ 3.5 inches with a bit of shooting. Dacron is a good choice for bowstrings... you're doing fine. Carry on!

Thanks, Geezer! Just a couple of hours away from a test run.
Frode

Some where I heard about a brief microwaving of a string to get it to settle in, maybe 30- 45 seconds.
Has anyone else heard of this? Tried it?

Considering the inconsistant heating a microwave seems to do on food, I would be concerned about it creating a weak spot if it didnt just melt the string outright. I believe that they heat foods using moisture, without moisture they just seem to burn things. (I get the dubious honor of cleaning microwaves at the end of the day at work every day ) A string failure on a crossbow can be embarassing at the least, dangerous at best. Just my 2 cents! Simply stringing it up and using the crossbow will work out the string enough I would think.

Interesting idea, I wonder if it might work better on a natural fiber like linen or hemp? I don't know how hydrophilic Dacron is, but I do recall hearing somewhere that gut and linen strings gain and lose tension depending on humidity.
Frode

Maybe a blow dryer would help relax a string enough to get the initial stretch resolved?. For someone with more foresight than myself, hanging weights from a string in waiting would prepare it for use.

Dacron is a thermoplastic.

http://en.wikipedia.org/wiki/Polyethylene_terephthalate

Personally I wouldn't actually heat it as it would just make it pliable and allow it to stretch and when molecules lock up again, you'll be looking at the same stretchy polyester you had before...it's the cold stretching that does the trick (similar to work hardening metal). If you watch some videos of modern bow manufacturing facilities...they really like to tell how they make bowstring...but basically everything is a same old story - strings are kept under tension during each and every step of the process and then a final cold stretched at the end.



I've made numerous strings and have been seeing better results when I kept strings under tension . I still make the string bundle on the two posts, but I also made another jig just for servings - it's a wooden version of Boo's (Don Katsumi's) jig from the videos.

serving Part 1

Serving Part 2

Cat Whisker & Jig

Yeh, that's a Flemish string.

Anyway, I built a similar wooden version of the jig and kept everything stretched during serving stage. Then hung a weight almost at the jerk strain limit for an hour. The last string I made for a friend was *solid* , the eye-loop servings didn't show any separation after a night of shooting and center serving was like a stick that sprung back into shape the first few times I tried to bend it. I know...sounds amateur, but these are my observations. Didn't really pay attention to how much it actually stretched during the process (but the 1/4" that everyone is talking about sounds like the deal) still...Definitely worth looking into the material data sheet for B-50 or whatever we're using for some clues.

And definitely worth building a few good jigs...perhaps even in metal.



Ivo

Ivo, thanks for the videos.

I can't, though, envision the jig the guy is using, and reconcile it with the CAD drawing. It looks like he is able to dial in tension at one or the other ends of the sting, so I presume he has slipped the string eyes through some sort of holder or rod or something. But this jig her looks like it would be impossible to serve at the center, as both ends of the string are being pulled by one hook and the center is being pulled by the other?

Any photos of your jig in action and Boo's jigs would be really helpful.

Dane

[EDIT] Ivo, if I had bothered to watch the final video, I wouldn't have posted my last question. Never mind

Dane

Ivo, thing are a bit clearer now, but not much lol. The tensioning part of this jig is simple. The H frame part has me feeling dumb or ignorant or both in equal measures. How does one use it to serve the eye loops? I would appreciate photos (you are a busy guy, so only when you can), possibly even of the jig in action (or simulated action).

Dane

Yes, the jig is basically a "U" frame with some supports. The tensioning mechanism is as simple as it gets - a 3/4 ~ 1/2 way threaded rod with a hook bent on one of the ends and a nut/washer on the other end. The frame doesn't have any threading in it, nor the nut welded to anything, just a hole - all the tensioning is done by tightening the nut. That way you can do both - tighten to stretch the string and give it some twist(by turning the hook a few turns).

Boo does Flemish strings, but I made an "H" frame to allow me to serve eye-loops on endless strings while still keeping everything under tension.

Sorry, no pictures. ~ I've spent this entire week at the lab and it doesn't look like I'll be out for a good few more days...lol, there comes a time when I break down and just drop everything to get back to my projects and visit some friends - THE GLORIOUS WEEKEND!

"still...I manage...":

I will take some pictures when I get home though.

*BUT, basically... ...it's kinda like this:



The "H" frame is 3 layers with top and bottom parts being 1/2 plywood and middle spacer a piece old scrap maple I had laying around. The grey dots in the tips of the "H" frame are polished metal rods that I epoxied in place (wanted to slip bras tubes over the rods to act as bearings, but couldn't find the right size)...and everything sits on two metal posts that slip into the main frame. Frame itself is bolted to the bench.

I really wish I had a picture to post because I'm really proud of the result...so *coming soon*

Ivo

PS: If you ever feel like you missed something, just go ahead, click *edit* on your last post and add an [EDIT] tag at the bottom and write down the updated thoughts.

PPS: CAD? ...
No...
...I mean.... MSPaint.

stoneagebowyer wrote:Ivo, thing are a bit clearer now, but not much lol. The tensioning part
of this jig is simple. The H frame part has me feeling dumb or ignorant
or both in equal measures. How does one use it to serve the eye loops? I
would appreciate photos (you are a busy guy, so only when you can),
possibly even of the jig in action (or simulated action).

Dane

Dane (and guys),

I'm straying away from the technology actually.

The *right* way of doing it is the way dude in the Grinch shirt does it in these vids.

Part 1 - Endless-loop string layout

Part 2 - String loop serving

Part 3 - Closing the loops

Part 4 - Center serving

Glimpse at the *stretcher* jig

That's how you actually do it...but I, being me, just like to experiment with things (even if it means finding out why people don't do it that way ), but this time it turned out ok.
The "H" pretty much plays the same role the two posts ( forks ) do in Part 2, only with added benefit of everything being under tensioned of the stretcher. While it's not really necessary to have everything super stretched, I just thought it would be cool to have rock hard end loops ...also I just hated the idea of making those forks - so the H thing can be called the *lazy spacer*.

Anyway, as Robin Allen used to say - "Won't know if it works till you try it." ...and there are always more than one way that works.

Good luck to you all.

Ivo

I am just putting together a little jig, and this info is useful, so thank you. Mine will be red oak (cheap to buy). It should be in operation this weekend.

Dane

Hmmm. Didn't see these until after I got my new string on and tested. Originally, I used the same twisted nylon serving on loops and center. After just a few bolts it began to fray (sorry, no pictures). The loops looked fine. I then replaced the center serving with a heavier waxed natural (linen) thread, probably close to the .036 mentioned in one of the videos. I thought I had it wrapped pretty tight, and I gave it a good waxing. Then I waxed it again, and later a third waxing (guess I wanted to make sure it was thoroughly waxed). After a couple hours of shooting, this is how things looked.
Is it just not enough tension? Wrong kind of materials?
Thanks,
Frode

Ahh that looks familiar, I have seen this problem before. I put a little knot/twist in the servings as I was serving the string and that seemed to help. I did that on all the serving around the nocks and about an inch on each end of the serving on the bow string. Its kind of like the knots on the sinew you used to tighten the cords hold the prod on.

Sorry I don't have pictures, cameras not working. That would make this so much easier to describe. I'll see if I can find another camera and get some pictures.

Serving is a very interesting topic in my opinion. It's not just to protect the string, there are a couple more interesting uses for it here and there. Reason why it comes in so many different diameters for the same material, but more about that later.

I never really thought about it until now that it's right in my face. My guess is, to avoid such drastic separations in the loop, a thinner serving should be used to get a tighter wrap pattern. This will give less separation in tighter bends that the string is dealing with when thrown over the prod tip. Not sure how you serve the loops closed, but think it's worth mentioning that serving *towards* the loop will help put pressure on the ends of the loop's serving too.

As for the center serving, like in the videos - serving over a stretcher is the cure. I also battled these separations at one time and it's all good now.

---

Now about the variety of uses. It mainly applies to fine-tuning the center serving and it's relation to the nock of the bolt.
Since we are dealing with different diameter bolts, different bolt groove dimensions, and different overall string dieters due to different strength prods and string materials - all of this has to be calculated to work properly - so the string contact the bolt dead center (theoretically correct approach, but I've also heard it should be just a tiniest fraction above center, but again - *heard* ) Now to fine tune this contact point is where different serving diameters come into play. A thicker serving would give one a string with that sits higher on the track and is used to adjust the string center to bolt nock center contact if the string contacts it too low. Same for the smaller diameter serving - which brings the string lower as opposed to the thicker one.



...kinda like that, but that's match grade stuff. Still, it's something to throw something on the forum...if it comes in handy in the process, all the better.

Good Luck.

PS: Basilisk's stuff sounds very interesting. Now you did it man, now you *have* to find a way to show us.
...just messing, anyone heard of this before?

Well, after seeing all the fine examples of string jigs here, I figured I'd better just go ahead and bite the bullet. Here's my interpretation, in wood. I have to say, it puts some scary tension on the string, with no complaints! Tomorrow we'll see how the first string off of it works.
Frode