Primitive Archer
Main Discussion Area => Bows => Topic started by: Marin on October 08, 2023, 07:43:06 pm
-
Hello,
I've been tillering a sinew backed bow as of recently and it seemed to be going well. Just today, I was bending it once again to a point I have already bent it to last weekend. It bent fine last weekend and this weekend it still seems to be bending evenly (even checked the bend with a block and ruler to measure along the curve and see if it's bending evenly). I heard very quiet snaps and cracks as I pulled it today and noticed the formation of several horizontal cracks on the back today. I was expecting this to happen at some point as I tend to add a bit more glue than most and I read about it in TBBI being something fairly normal when making backed bows. However, the cracks seem to be concentrated along a short 5" section and there are quite a number. I checked the bend at this area with my gizmo and ruler and it does not appear to be bending any worse than any other part of the bow, plus this bow is only being bent at about 5" in total currently. I don't mind having these cracks, but I am only curious if this is something that is worse than I think it is? Would this lead to performance issues?
I've attached pics of the cracks in question as well as bow tiller at this point from two different angles. I should note that this bow is heavily reflexed with some slight recurved ends, so at this low level of bending, more reflexed portions are going to look stiff and unbending when in reality they are bending. The cracks in question appeared on the back of the portion closest to the handle.
-
Unstrung profile for reference
-
Id say you need to string the bow to see how its bending,, braced it may show that area as week,,
then proceed to even it out and go from there,,
-
So the cracks themselves aren't anything to worry about? Just as long as the bow is bending evenly
-
Also, isn't it still to early to brace this style of bow? I thought I should at least get it tillered up to about 10" of bend or so before I try to brace it.
-
That usually means you just used just a bit too much glue and the glue itself cracked a tad. Nothing to worry about in my experience.
-
looks pretty even to me,, it will probably shift when you string it,, you need some weight to even it,,
I would string it,,
-
looks pretty even to me,, it will probably shift when you string it,, you need some weight to even it,,
I would string it,,
I agree. Low brace it at least and then look at your bend from low brace. It makes a difference on how the bend will look. You will have a clearer idea on the potential weak spots if any. Also you will have the confidence to continue also from low brace. Best of luck. So far it looks good.
-
Thanks, I guess I can try to low brace. I'm a little worried though as the last time I braced one of these bows too early, one of the inner limbs ended up getting too much strain and chrysalling really bad. I chopped this up to being poor wood (made this narrow style bow from a piece or low ensity ERC with bad Hair-pin grain), but wasn't entirely sure if this had to do with bracing one of these bows too early on in the tillering process.
Any tips on how to string this type of bow at low brace? I've strung one of these before with help, but admit I am still learning, and with these types of heavily reflexed bows, I find trying to do low brace increases the likelihood of it flipping back around on me.
-
Tie some temporary nocks below your nocks,,put long string on those pull the bow using your foot on long string,,
string the bow,, if it looks really uneven,,unstring and even it,,try again,,till the braced bow looks good,,
you can cut the long string off if needed,, after you get it evened out,, you can probably step through and get it strung,,
-
Those cracks are just excess glue. I would be very surprised if your sinew failed here. My experience is that the wood will fail first. The sinew may lift off or pull away or delaminate from the wood due to a sizing issue or something but the sinew is crazy strong. If the sinew was of good quality and not pounded to death or over heated it will be fine. I would consider also making yourself a stringer if you don’t already have one. Here’s a few pics of one I made last year. I got the idea to make my own like this from bowEd on here. At the time I was neck deep into a highly reflexed bow and needed a specific stringer for this bow. Here’s a couple pics. Hope this helps ya. Good luck.
-
Well I was able to figure out a way to string it at low brace. These reflexed-recurved bows are pretty hard to string at low brace without them flipping on you, so I first put it on the long string, then tied the shorter string before taking it off of the long string and having it partially pulled back with this shorter string. It's thus quasi-low braced, as otherwise it would flip on me.
Tiller still seems good, though would like second opinion if you guys think the recurves should be bending more at this point or not. I wouldn't be surprised if they are too stiff. What do you guys think?
Also, in pulling it yesterday on the long string to get these photos, I saw that more cracks on the glue formed on top of the cracks that were there. Don't think this indicates that its bending more in this area, especially since these form in the area around the handle only on the long string, and I keep checking with my gizmo but the bend in this area is not more than the bend on the other limb in the same respective area.
-
Looks good to me. Bend looks good too. Ya those cracks are scary looking but sinew just doesn’t break that way that I’ve ever seen if that helps ya.
-
Thanks, I'll just assume I must've put too much glue in these spots where its cracking
As to the tiller, so you think the recurves are bending enough for this amount of bend? I don't think I mentioned it, but this bow will not be a contact recurve but a working, non-contact recurve.
-
Ya Ed I made that assumption too. It looks good so far to my eye. We won’t know what this thing will do till you bend it a little more. The first few bending pics it’s almost to brace height and from the pic it’s pretty close to being contactless on the recurves. It’s hard to always tell from pics. I’d be hesitant to remove any material till you bend a little more past where you’ve already gone. I suspect you’ll see those tips working a little then. Best of luck.
-
Okay, I'll bend it down 2 more inches and inspect the curve, and take some pics for you to see.
-
Pulled it two more inches. Still getting some cracks when I pull it on the long string to string it, but not cracking noises occur with the low brace tests still.
Checked bend and it still appears to be bending evenly. Even bent it back and forth a bit to see the movement of the outer limbs, and they appear to be bending evenly compared to the rest.
Any thoughts?
-
With a bend like that I would proceed. Unbraced looks good too. What powndage are you at low brace?
-
Haven't measured it exactly yet but it feels close to 20 lbs, maybe slightly above. Am targeting 40 lbs at full draw, which for a short bow like this will be around 20". Even if I can't make that, most of these bows were probably close to 35 lbs in draw weight.
Good to hear about the tiller. So you think the cracks occurring only in this one spot are not indicative of overstressing of this limb portion?
Also, was curious about your take of how I should proceed. I was thinking about tillering further with the short brace like this till I get the tips bending around 10 inches or so, before trying to brace it fully. Should I stick with short brace for longer?
-
Marin. I haven’t made a shorty this small yet myself but based on my experience with slightly longer bows say around 55-60” ttt I would get the brace looking as close to perfect before proceeding on a bow like this. I would not worry about those tips bending yet till further in the draw. It’s hard to tell if they are working much now at your low brace but I suspect once you get out to the last few inches of your draw you’ll see them bending a little. I would get the bend looking balanced on both limbs at your desired brace height. I have found with my more reflexed bow with sinew I have better luck taking my time on getting to perfect or near perfect looking brace then proceeding from there. Doing it this way may be a lot more work initially but saves time later on in the tiller. I’ve had it on some where very little tiller scrapes were needed for tiller and balancing the limbs out to almost full draw if the time is taken to get to brace with perfect looking bend. As for the cracks… it’s likley not an issue but it’s hard to know from pictures really. Typically sinew dose t fail across its fibers this way. The failures I e had with sinew bows is usually not sinew related. I’ve had some sinew lift off of limbs and delaminate on me but never fail itself. It very strong. The wood will fail before the sinew. I ussaully stick to 1/3rd sinew thickness or under to 2/3rds wood core. On these bow I would use a long yard stick method for tillering to brace for perfect brace tiller. I can’t remember where I saw this method but it’s great. I did a quick google search and can’t find it now but basically it’s taking the length of your limbs and measuring to find your mid limb point and make a mark. In your case use from the middle of where the handle would be to just before the recurve tip bend at the belly. As you bend it get it to the point initially where both limbs are straight at the same time using long string. I know you are passed this point now but for future reference. In your situation now you would just get it to your low brace again on your tiller stick and use the measurements marks at mid limbs using your yard stick or ruler and hold it up to the belly and having a look to see if the bend looks balanced on both side of the mid limb mark on each limb independently. This hyper focused approach has saved me on some of my more complicated projects. I also measure the depth from the belly mid point mark to the ruler or yard stick. This measurement I compare with the other limb doing the same thing. I hope this make sense. It’s not a tiller method I use all the time but for these highly reflexed bows I do. My bamboo bows I sometimes do as well as they are static levers/ siyahs. Try it you might like it and it’s pretty simple method. It may seem overly tedious initially but it’s a good method that takes some of the guess work out of such short bows where it can be tougher to see potential problems in the bend. By hyper focused attention on each limb using measurements too small for your eye to always catch could be a good alternative for ya. Hope this helps. Any more questions just message me
-
Those cracks are just excess glue. I would be very surprised if your sinew failed here. My experience is that the wood will fail first. The sinew may lift off or pull away or delaminate from the wood due to a sizing issue or something but the sinew is crazy strong. If the sinew was of good quality and not pounded to death or over heated it will be fine. I would consider also making yourself a stringer if you don’t already have one. Here’s a few pics of one I made last year. I got the idea to make my own like this from bowEd on here. At the time I was neck deep into a highly reflexed bow and needed a specific stringer for this bow. Here’s a couple pics. Hope this helps ya. Good luck.
Hey superdave, would you make a post about how you make those bowstringer cups? I like them better than the stuff I am doing.
-
Those cracks are just excess glue. I would be very surprised if your sinew failed here. My experience is that the wood will fail first. The sinew may lift off or pull away or delaminate from the wood due to a sizing issue or something but the sinew is crazy strong. If the sinew was of good quality and not pounded to death or over heated it will be fine. I would consider also making yourself a stringer if you don’t already have one. Here’s a few pics of one I made last year. I got the idea to make my own like this from bowEd on here. At the time I was neck deep into a highly reflexed bow and needed a specific stringer for this bow. Here’s a couple pics. Hope this helps ya. Good luck.
Sure I can do that.
Hey superdave, would you make a post about how you make those bowstringer cups? I like them better than the stuff I am doing.