Primitive Archer
Main Discussion Area => Bows => Topic started by: arachnid on February 22, 2015, 06:59:39 am
-
Hi Guys.
I`m working on a tri-lam, ipe, walnut, boo with a eflexed design.
I`ve reached 26" with a long string (yes, I know it`s too much...) and the thing doesn`t want to get braced!
Each time I put a string on it`s eather tears or flips to the back of the bow, like so:
(https://lh5.googleusercontent.com/-BIs3WUiDy9s/VOm0E-vQDhI/AAAAAAAAFKA/JlV1nOuVAzM/w1153-h865-no/20150222_124649.jpg)
The bow isn`t too heavy, it pulls about 45#@26" (my target weight) with long string so it`s not over stressed.
So I really need some help.... what can I do?
-
Oh, looks like a heavy reflex. Always hard to bace.
Often back- flipping happens due to a misalignment of the tips? Maybe the string is to long?
A backview would be helpful.
Michael
-
That unfortunately is one of the problems when putting too much reflex near the handle. You will have to raise the brace height. Give us a view of the bow on the long string at 26", shorten your long string though till it's taught.
-
Need to make sure you don't have a stretchy Dacron string.
Got to a go for a reasonably high brace straight off, can't mess with low brace... it's all or nothing.
Hold on real tight as you are stringing it and try to see if it's bending sideways... I'm working on one that's trying to that at the moment.
The limb alignment was a little out, I managed some sideways correction by clamping it up and heating the belly. I had slats of wood clamped to the sides to keep the heat off the glue line.
Del
-
If its flipping, your not straight. Either the glue up or your side to side thickness on each limb.
-
I don't think it is a problem with limb alignment. Your stringer doesn't look up to the job, too short.
I got old and started having trouble stringing bows to go to the short string. I started leaving my tips clunky and putting a stringing groove in the top nock overlay and a wider groove in the lower limb overlay.
I could use a parachute cord stringer and string any poundage bow this way easily. As I finished the bow I would file off the clunky tips and get rid of the stringing grooves.
Later I realized I liked stringing a bow this way and made my finished overlays with the stringing grooves.
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/curlyosagetip_zpsb2a4f00a.jpg) (http://smg.photobucket.com/user/ekrewson/media/bow%20making/curlyosagetip_zpsb2a4f00a.jpg.html)
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/doublenockwithstringer.jpg) (http://smg.photobucket.com/user/ekrewson/media/bow%20making/doublenockwithstringer.jpg.html)
(http://img.photobucket.com/albums/v181/ekrewson/bow%20making/bottomnockwithstringer.jpg) (http://smg.photobucket.com/user/ekrewson/media/bow%20making/bottomnockwithstringer.jpg.html)
-
I have an adjustable bracing jig I use with wheels on each end. It gives me a lot of control over the bow so I can see what is going on when I have a problem bow. Same thing as a bow press but I push it down by hand.
-
If its flipping, your not straight. Either the glue up or your side to side thickness on each limb.
Here`s a pic of my limb alignment, back side up:
(https://lh4.googleusercontent.com/-QnTmtbSCYRM/VOnmDoL2kTI/AAAAAAAAFKU/i9xAaL4aElw/w415-h553-no/20150222_162051.jpg)
It`s the first time I have such a problem (guess there`s a first time for everything....) so how do I fix it?
Dor
-
Remove belly wood on the right side, cut your nocks deeper on the left side.
-
Like I said, you can put in small lateral correction with heat as long as you clamp on some side pieces of hardboard etc to contain the heat on the belly. Clamp it up with 1" of sideways bend apply heat over about a foot in that centre section, just a minute at a time over a 3" section at a time, so it doesn't take too long.... let it cool for an hour, job done.
I apply a couple of layers of masking tape along each edge before clamping the hardboard strip to really make sure there is no hot air blow by.
If the hardboard, hangs down beyond the belly by about an inch it channels the hot air along the belly giving good even warmth.
I'd make sure the bow isn't thicker than it's wide at any point too, that really makes it try to go sideways.
Del
-
How wide is it? In my limited experience the narrower they are the more sensitive they are to string mis-alignment.
-
Depending on the type of glue you used, it's hard (or impossible) to heat correct a lam bow. Get it hot enough, and it will delaminate. I believe your problem is a design flaw. Too narrow, and too highly reflexed = lateral stability issues. I ran into this problem trying to make reflexed warbows. As a result, I either use a small amount of reflex or none at all.
-
The bow is pyramidal, 1 1/4" wide at the fade and tapering to 1/2" tip. I glued in about 4-5" of reflex 'cause I thought it'l take set and sattle at about 2". But that sucker bearly took any set!
I think the reasonable option is to scrap from the sides as PatM suggested but I don't have much width to play with and I don't want to screw this bow (I've worked a lot on it so far and it looked so promising...)
I'll be greatfull if you can give me detailed instruction on how to do it right.
Thanks
Dor
-
I to have had this problem. Never built a lam bow though. For the most part it's been string alignment. But I tried a highly reflexed bow once for the same reason "set" and my initial "full" brace was somewhere near 10". After finish tiller and shooting in it finally settled in at 7" brace. A little high but it worked till I shut it in a truck door! Good luck, should be a sweet bow when you get it lined out. Patrick
-
You can actually make adjustments with heat as most modern glues will soften with heat. The danger is de-lamination when heating areas where there is some reflex but there is a way of doing it
-
The bow is pyramidal, 1 1/4" wide at the fade and tapering to 1/2" tip. I glued in about 4-5" of reflex 'cause I thought it'l take set and sattle at about 2". But that sucker bearly took any set!
I think the reasonable option is to scrap from the sides as PatM suggested but I don't have much width to play with and I don't want to screw this bow (I've worked a lot on it so far and it looked so promising...)
I'll be greatfull if you can give me detailed instruction on how to do it right.
Thanks
Dor
I did not mean to reduce width but rather thickness of that side of the belly.
-
As I said, I don't want to use heat because of the chance the biw de-laminate. I'll scrap the width of the limbs, I just want to be sure with the shape I want to get and what I'm going to do...
-
Could try this, on a table or bench place a block of 2x6 close to each bow end bow's back facing down. Use a trigger clamp at the bow's center to press the bow's back down to the table while steadying it. Then hook on a string. It will then be bent to about normal brace height. Markus
-
[/quote]
I did not mean to reduce width but rather thickness of that side of the belly
So if I understand currectly, I should get a sort of uneven belly, thicker on one side the the other. Would that help correct the tip misaligment by forcing the limb to bend more the right?
-
That's the idea.
-
I think PatM is on to something there. Patrick
-
What Pat is talking about will make the right side weaker and the limb will move that way. And the string alignment will start to move back towards the center of the bow.
-
when I have a bow with reflex, that is fussy,,, I do not brace it low to allowing for the string stretch etc,,and so it does not flip on itself,, if it looks like it is going to pull to a low brace(when it will flip and try to cut off your finger),, I stop and twist the string up and try again,, if it is a stubborn heavy bow,, I will tie on leather nocks below the string nocks,, and use a long string to bend the bow to put the string on,, you can adjust the limb twist as you tiller,,, making mostly self bows limb twist or alignment issues are just normal,, and once the bow is strung,, can be evaluated and resolved if need be,, i think exercising the limbs is good right now,, you have to move the tips quite a bit to string it,, and getting the wood used to bending is a good idea before stringing it the first time,, :)
-
I would bend the handle to line the limbs up.
-
That's the idea.
Well thats an original way of thinking! Thanks Pat!
Just to be sure, wouldn't forcing the limb to twist cause an uneven stress on the limb? Can't it cause it to chrysal?
-
Depending on the type of glue you used, it's hard (or impossible) to heat correct a lam bow. Get it hot enough, and it will delaminate. I believe your problem is a design flaw. Too narrow, and too highly reflexed = lateral stability issues. I ran into this problem trying to make reflexed warbows. As a result, I either use a small amount of reflex or none at all.
Whoops... my bad I was thinking it was just a backed bow. Forgot it was a tri-lam
Del
-
Well, I got it to lo brace and both limbs kick to the side pretty badly... I`ll post a picture later....
Seems like an easy fix with heat, if it was a self bow... any chance I can fix it with heat and avoid delamination?
Remember its ipe (haven`t seen ipe heat bent before...)
-
Im glad that's your head ache and not mine, this time. I doubt it can be recovered, that's just my hunch.
-
i would try scraping like Pat suggested,, it will still shoot well with a little limb twist :) as the bow settles in it may shift some in your favor,, dont panic, :)
-
If Pat's suggestion doesn't work do you have the length to cut it in half and splice it back together straight. Although getting a straight splice is a talent all it's own.
-
A long v-splice solves that alignment problem. Lots of adjustment that way. Best to remove the riser block, do that and then overlay the splice with the block.
A wrapping set in glue reinforces the lower surface area glue joint.
-
Splicing can be very difficult as I don`t have a bandsaw....
-
A bandsaw is not necessary. I cut splices by hand all the time.
-
Seems like an easy fix with heat, if it was a self bow... any chance I can fix it with heat and avoid delamination?
Remember its ipe (haven`t seen ipe heat bent before...)
I did suggest in earlier post that this is possible, I've done several times. The idea here is not to bend the Ipe with heat but rather to soften the glue enough to be able to reposition the limbs and then let the glue harden back up. PM me if you're interested
-
What kind of glue are you talking about, Marc... or does it work with all glue? I've thought about doing this a couple times, but decided against it for fear of separating the joint.
-
I've never tried it with Urac but I have done it with TB3 and G2.
-
I feel like ive seen somebody solve an alignment problem like marc is saying, with gentle heat, i feel like they used a lightbulb next to the limb for a long period of time.