Magyar Bow - Predicting Draw Weight

[mikekeswick]

Trying to predict draw-weight from an unbraced reflexed bow....wait till you have the string on before thiunking about measuring the weight.
You have plenty of horn thickness to adjust the draw weight if necessary.
I don't know how many bows you have made so I don't mean to patronise if you already know this but draw weight is measured from brace height onwards. Very reflexed bows intially appear very stiff but once strung it can be a different story.
As for the noises it could be the glue in the sinew layer cracking which isn't a fatal problem but it can be very unnerving! The first ever sinew backed bow I made did this because I had used the glue at too high a concentration....It made those cracking noises every time you drew it...but that was because the glue was very,very thick. Other potential causes are layers delaminating, sinew layers seperating or the core breaking under the sinew. Try to catch where the noise is coming from.

[Edmund Dohnert]

mikekeswick -

Yes, I realize that hanging a weight on the tip isn't the same as putting a fully braced bow on a tillering stick. I just wanted to get a very rough idea of where I was. Based on what you've said, I now realize that since the geometry of a highly reflexed bow changes so much over the draw distance, it's probably futile to try to predict draw weight at this point.

That faint crunching sound certainly is disconcerting. It's hard for me to tell exactly where it's coming from, but it seems to be somewhere in the bending section. I have also noticed that those perpendicular fine lines I previously mentioned appear to be more pronounced, but I have not observed any visible signs of any sinews actually parting. Could this just be the weaker parts of the sinew layer permanently stretching rather than the beginning of a core failure, or is there really no way of telling until something gives way?

I am pretty confident that I have a very good uniform bond between the core and horn layer, but less so about the integrity of the sinew layer. The sinew was applied with the hide glue at around 20-percent concentration. (This was after sizing the upper core with glue at less than 10-percent.)

I suppose I should just very gently and gradually work the limbs onto the tepeliks and see what happens. At the risk of inducing string follow, would it help if I warmed the bow up a bit with a heating pad, to say something around 90 degrees F? My basement workshop is around 68 degrees F and rather dry at this time of year.

[mikekeswick]

If the core was failing then the sinew would be whiter in just that part and it would be obvious.
Yes the only real way to know other than the sinew/glue getting more of these cracks is to pull it further.

[fusizoli]

If the shop is dry, than put the bow at a more humid place for a few days.
After the dry shop if warm it up more, the glue chould be more brittle.

First of all, have to open it and uniform the the two limbs, just than pull on the teplik. Adam wrote the method in his book.

[Edmund Dohnert]

mikekeswick + Zolt?n -

I do have some white sinew, but that is only because I sanded down some of the rough high spots not long after I completed applying the sinew. This white sinew was there well before I started the tillering process and runs totally parallel to the limbs. There are no localizing perpendicular white areas or raised areas indicative of pending core failure.

Yesterday, I got 'Limb B', the slightly stiffer of the two limbs, fully onto the tepelik and left it there overnight. I was expecting the worst during the last part of the bending, but there was no crunching sound at all. After I took it off the tepelik, there was some set, but the bow started to recover to its original shape after a few hours. I am cautiously hopeful, but will hold off on doing the other limb.

I will take Zolt?n's advice and move the bow to a more humid part of the house, namely the upstairs bathroom, before I try the other limb.

What do either of you two think of the idea of making a little 'tent' out of plastic sheet and putting the bow in there with a wet rag (not touching the bow, of course) for a few days? That should really create a very humid environment. Or maybe too humid?

[Edmund Dohnert]

mikekeswick + Zolt?n -

I kept the bow in the upstairs bathroom for almost two days, where it is much more humid than in my basement.

This morning I managed to get both limbs fully tied down on the tepeliks without any problems. There was absolutely no crunching sound or signs of sinew failure when I did this, so I am encouraged. The ears are almost parallel to the grip, so I probably don't have to flex it all that much more to get a string on it.

I still need to make a bowstring for it. (Will use Dacron B-50 from which I've made several self-bow strings.) Should I leave the bow on the tepeliks for another day so, or would it be best to remove the tepeliks and then put them back on once I have a string ready?

[Edmund Dohnert]

Zolt?n, mikekeswick, etc -

I an now at the point where I could really use some good advice.

I put the bow on the tepeliks I had made, and I got both limbs down pretty tight, and there was absolutely no crunching sound as I did this. Whew!

I then managed to get a makeshift bowstring on it, albeit one at a pretty shallow brace height (only about 4 inches), as I am still being rather timid.

While I feel fortunate that I have absolutely no noticeable twist in the limbs, I do have a definite imbalance if the curvature and deflection between the two limbs. One limb (let us call it 'Limb A') is much stiffer than the other and has a curvature that is consistently 1.5 to almost 2 cm deeper than the other. It is quite noticeable.

I have taken careful thickness and width measurements along both limbs, and they appear to be almost identical. Yet limb A stubbornly refuses to bend as much its opposite limb. I have scraped some material off the horn layer but have not seen any results, and am reluctant to do much more scraping. (Might this be a problem in the sinew layer, such as the sinew in Limb B perhaps stretching more than that in Limb A?)

I can equalize the curvature of both limbs if I wrap a band around the weaker limb near the string bridge, thus flexing the stiffer Limb A. This seems to make both limbs look the same, but is hardly a permanent solution.

I have done some very preliminary tillering, and right now, I get around a 12-inch draw when the string is pulled to 25 pounds. If the remaining draw is linear, that would suggest something over 50 pounds at my comfortable short draw of 26 inches. I have not pushed the tillering further at this point.

So, should I continue nibbling away at the horn layer of the stiffer limb, use some heat to make it behave, or perhaps even add an additional layer of sinew to the weaker limb? Or should I just accept the fact that one limb is going to flex more than the other?

I don't want to do anything further till I get some advice by you all who know what you are doing.

[mikekeswick]

Personally I would simply remove horn from the stiffer limb. If the two limbs have different strengths they must be made equal. Bear in mind that the lower limb (when shot by hand) will need to be a shade stiffer than the upper (due to the different forces drawing by hand puts on the limbs).
Yes dimensions will certainly get you 'in the ballpark' but tillering is where you either make a good bow....or not!
So make the limbs even and once the bow looks good at a certain draw length then obviously you can draw it a little further.
I would advise drawing by hand once you get to 18 inches or so. It's useful to take pictures of the tiller with the bow hand drawn.
Also it's better to brace it a little higher, somewhere around 6 inches.
Good luck!
You must get a picture of this bow for us!

[Edmund Dohnert]

mikekeswick -

Thanks for the advice.

I scraped some more horn off the stiffer limb this morning, and now the differences between the two limbs is less than 1 cm at my currently shallow brace height, but then becomes almost indistinguishable once I put 15 - 20 lbs on the bow. The curvature of both limbs is also much more symmetrical now. As such, I am inclined not to mess with it anymore for now and will start gently and patiently tillering after I get a tighter string on there to bring the brace height closer to 6 inches.

I will try to get some pictures the next time my son and daughter-in-law come down for a visit.

[Arry]

Edmund,
sounds like a success! But maybe leaving the barshak band on the weaker limb for a few hours, maybe overnight, would have been sufficient, too. It helped me balance my bow, at any rate.
Looking forward to those pics!
Cheers
Jarek

[Edmund Dohnert]

Jarek -

Thanks for the encouragement, but I won't consider it a success until I am able to repeatedly pull it to full draw without something giving way. Right now, I've drawn it to 18 inches, and so far so good. I will be gradually working the bow and increasing the draw. As I'm a short guy, my comfortable draw distance is only 26 - 27 inches, so that's what I'll be aiming for.

I suspect it will be around a 50-lb bow at full draw. At first it felt that it would be a lot stiffer, but after working it and removing some horn to balance the limbs, it no longer feels so stiff. I also have some string follow, but the bow comes back if left unstrung for a day.

Just an indirect question: If the bow turns out to be too light, is it practical to add an additional thin layer of sinew to increase the draw weight even though the original sinew layer was put in place several months before? Any special preparations when doing this?

[Edmund Dohnert]

Well, since I strung the bow a little over two weeks ago, I have been giving it a twice-daily workout, repeatedly drawing it and gradually going further beyond mid-draw.

I've heard a few minor groans along the way, but they have not recurred. I have now been able to repeatedly draw the bow to my intended 26-inch draw length, and so far I've had no problems. The limbs are very symmetric, there is no noticeable twist, and the bow has a nice smooth curve when fully draw (at least it looks that way to me.)

As I've just been hand tillering it, I don't know the precise draw weight, but it feels like about a 50-lb bow at full draw. I've shot it a couple of dozen times, but only down my basement. It appears to have pretty good power.

I need to make a better bowstring, as this one was only makeshift for tillering purposes. And I want to maybe reposition the string bridges that I put on, more or less as an afterthought.

well, I think I've got a bow! Not too bad for my first attempt. I'll try to include some pictures when my son and family visit in a week or so.

I want to thank Z?ltan, mikekeswick, and the others that have generously provided good advice and kept me from of making serious mistakes.

[mikekeswick]

Eagerly awaiting photos!

[Jake Levi]

Edmund this has been a fascinating read !!

Congratulations on your bow !

In the fwiw category the TBB has excellent information on sinewing. I havenot changed my use of it since first reading of it there.

You have had some incredible coaching here, awesome !

Along with your coaches I am looking forward to seeing your pics.

Thanks for posting your progress here.

[fusizoli]

Eagerly awaiting photos! :)

Detto! :)