Primitive Archer
Main Discussion Area => Bows => Topic started by: Christian Soldier on July 11, 2013, 03:47:45 pm
-
In a nutshell: "Never settle for an imperfect tiller."
Here's the back story. I've got this hickory pyramid bow which is coming out to be pretty much my dream bow. Perfect length, draw weight, good looks even pre-stain, and everything about it was great except the lower limb was a little weaker but it had some reflex so I figured it'd be alright.
This bow was a rebound off of a hickory west coast bow which fretted and that was a rebound off a black walnut bow which just snapped because of a slight error in ring chasing.
So today I was just about to put a finish on this hickory bow and I see what I thought were rasp marks that I just neglected to sand out when it fact, they were frets. :(
I've made a dozen or so hickory self bows with very few problems and now two in a row with cryssals. >:(
So, that dream bow goes in the utility room of remembrance and I'll start on a new one and I definitely won't settle for anything but perfection on this one.
I'm guessing pretty much all of you more experienced bowyers knew this lesson well but I figured it would help with the coping process if I shared it with others. :)
-
R.I.P hickory pyramid bow, atlease you dont have to rest in pieces lol.
-
A good trick to find them earlier is to take a damp cloth and wipe the belly down under a good light. It will darken up frets, scratches or any other imperfections.
-
A good trick to find them earlier is to take a damp cloth and wipe the belly down under a good light. It will darken up frets, scratches or any other imperfections.
Oooh! Gonna steal that for my trick bag! Nice tip.
-
what are frets and why do you get them?
-
what are frets and why do you get them?
Fret or "stress fractures" happen when the wood cells on the belly side of the bow collapses and makes little horizontal wrinkles.
-
what are frets and why do you get them?
Frets are caused by belly compression- if you have a hinge in the bow, the belly is compressed quite a bit in that area, usually it is compressed more than the wood can take- most wood fails at about 1% compression(according to several sources I have read). in a well-made wooden bow, the compression is lower than that. horn fails at about 4%. Softer woods are GENERALLY weaker in compression, but may be more elastic, compensating for that- Yew is one.
-
Thanks guys http://www.primitivearcher.com/smf/Smileys/default/smiley.gif
-
You said your lower limb had reflex but was acting weak so you left it. Well if a limb is more reflexed than the other it should look proportionately stiffer not weaker.
Squirrelslinger - Horn can take a lot more deformation than 4%...have you made a horn bow?
Yew is an exception among softwoods (apart from junipers) so you really can't use it to describe the properties of softwoods.
Pines are actually quite often stiffer than hardwoods....if you don't believe me try making arrow shafts from various timbers. Would you believe that redwood arrows of the same diameter spine out at about the same as ipe shafts.
-
Are you sure it was tiller that caused the frets and not an under designed bow pulled to far? What are all the stats...length,widths,draw weight and draw length? Just trying to solve your problem and make sure it wasn't something else....an imperfect tiller+under designed can easily lead to frets as well...
And use osage next time ;)
-
A good trick to find them earlier is to take a damp cloth and wipe the belly down under a good light.
You can use mineral spirits if you are concerned about adding moisture to the wood.
-
2 thoughts.
Some crave that photo of a great tiller. The picture perfect tiller is not aways the best one for that particular stave. For example, knotted areas (weak) should not bend as much as the rest of the limb but should bend slightly. Dips and bends need to work as do areas of reflex. All of those affect how the tiller looks to the eye.
Frets (large) and chrysals (tiny) are cracks across the grain on the belly.
There are 2 causes. First, is an imperfect design for the stave. The stave is too narrow or 2 short and then the chrysals will appear all along the limb. Second, localized chrysals in one area mean the limb is bending too much in that spot. In this case the fix is too retiller leaving the chrysalled area alone. Retiller the other limb to match. I've had some success gluing on some rawhide over that spot.
The eventual end result is the bow will fold up like a book if the chrysals are not fixed and even if they are.
Christian Soldier, look at the chrysals as learning tools. They'll show you a poor tiller or design to be avoided on the next stave.
Jawge
-
I take it that this is the same bow that you just heated reflex into a couple days ago? Are you sure they're compression fractures and not tears from reflexing a shot in bow? I too would like to help in the post mortem so you will be sure to avoid repeating whatever caused it. You always learn more from the screw ups than the successes. Well at least I do anyway. ;) Some pics would certainly be helpful. Josh
-
When you've found them, it's too late. They never go away. But the damp cloth wiped on the stave is a good finishing technique because it raises the grain and shows unsightly nicks which can be sanded.
As an aside sanding chrysals just makes the tiller even worse.
I wipe and sand with 220 grit until the grain is no longer raised. Then finish with 300, 400 and 600 grit. This is an old woodworker's trick. I guess at 65 I'm an old bowyer. Thank God!
Jawge
-
Yes, this is the same bow that I heat treated but, reflecting to the past I remember those 'marks' being there before I heat treated it.
It was right below the fade and it was 2" wide so it wasn't a design thing. Just that the lower limb was weaker and that was the weakest point of the lower limb.
It's one of those light hinges that is painfully obvious now but I just ignored earlier.
My camera would focus on the Frets (definitely big enough to qualify) but here's the profile and tiller pictures. Lower limb is at left and the hinge is just below the fade.
(http://i1214.photobucket.com/albums/cc495/KenpoFighter1/HPIM5821_zps66c95cd9.jpg) (http://s1214.photobucket.com/user/KenpoFighter1/media/HPIM5821_zps66c95cd9.jpg.html)
(http://i1214.photobucket.com/albums/cc495/KenpoFighter1/HPIM5822_zpsb3e0789f.jpg) (http://s1214.photobucket.com/user/KenpoFighter1/media/HPIM5822_zpsb3e0789f.jpg.html)
(http://i1214.photobucket.com/albums/cc495/KenpoFighter1/HPIM5823_zps6479f7cc.jpg) (http://s1214.photobucket.com/user/KenpoFighter1/media/HPIM5823_zps6479f7cc.jpg.html)
I attributed the weak limb thing because the lower limb was an entire 'ring' lower on the belly, I figured I'd let it go.
Live and learn. Maybe someone else can learn from my lesson too. I was also kind of rushing this bow to finish it for hunting this year. Apparently its easy to miss things when rushing.
Debarked the new stave yesterday. Its got some snake to it but no knots so the tillering should be pretty straight forward and I'll be sure to keep this one a little wider too. It'll probably be done in a month or so.
-
Yes sir! I do believe your diagnosis was correct. That's quite a hinge. I hate it when that happens! I agree that your design was more than adequate. For future reference, when you have one limb that is reflexed more than the other, put the reflexed limb on top. Its easy to overthink that situation. But when you break it down to tip deflection(how far the limb travels) the limb that travels further to reach equilibrium with the other limb is the weaker limb. I purposely induce a half inch more reflex in the upper limb so that I have the same effect as positive tiller and yet a symmetrical appearance at brace and full draw. That is, I do that when I bother with such details. Most of the time I just go with whatever the wood offers with no regard for symmetrical appearance. I hope you get the next one dialed in on time for season. Josh
-
That's a hinge alright...next time post pics first so ya don't get a bunch of us saying it could be this or that and such n such....lol :laugh:
Let me "guess"..in your rush you were rasping/scraping from handle down to limb thru the fade? Careful if you do this as most people have a tendency to put to much down pressure right thru that area where you are hinged...its best to rasp/scrape up to the handle and not down from the handle...not sure if that's how you caused it but always be mindful of your thickness taper...do you facet lines down the sides that follow the undulations of the back to reduce down too,so you don't go too far?
-
One other point while we're talking hinges and tip deflection. Ok, I'm the only one talking about it, but this is a good opportunity to cover another important point. When your hinge right against the fade, the natural assumption is that limb is weaker than the other. DON'T start reducing the other limb until that hinge is corrected. Chances are the hinged limb is still the stronger limb. The reason being that the closer the hinge is to the fade, the more tip deflection it causes. Once you correct the hinge, the limb seems to stiffen up. This is one of the many reasons why your first goal when you start tillering a bow is to get the limbs working properly. Once that's accomplished then you can start working it down towards target weight. Josh
-
"DON'T start reducing the other limb until that hinge is corrected. Chances are the hinged limb is still the stronger limb."
That is some solid advice.
1+
Gabe
-
Hickory is pretty bad about chrysalling. Kind of unforgiving of design and tiller flaws.
-
I had a nice hickory bow do the same thing. In my case the back had a small ridge running down it that ran off of the stave and another coming in the stave about 2 in below that. When the bow was dry it showed the tiller to be off very slightly. When the MC of the wood went up this summer it took on some ugly hinge look. :o So I just keep shooting her till she gives out.