Help! Recurves keep breaking

[recurvebreaker]

I am having problems...

I have made three attempts at a three pc recurve and none have worked. I am attaching pics to help explain the proccess I have been going through. The first pic is of the bows profile. I know that too much recurve or reflex will make th limb unstable, so I would like to know you opinions on this design. The tiles are all about 17"x 17" if that helps.

The real problem though is that after I put the limbs on the riser, make a good centerline using a block of wood with a hole drilled in it and a pen sticking through, and then I profile the limbs and string it to about 7", the string is always sitting off to one side or both of the limbs and the limbs are twisting, and the tip of the limb is going to the side that the string is sitting on. For a reenactment of how it looks when stung (because I can't sting them anymore do to delaminating) look at the second picture, taken from the view of looking down the belly of the limb from the limb tip. Ok, here goes the reenactment...

The string will be sitting off the right (fingertip side) just like in the picture. The limb tip will be moved to that side too. The limb is twisted in a was like if my fingertips were angled up higher than my wrist.

So I figure that the wrist side is the stronger side and I unstring the bow and grind material off that side of the limb, then restring it, pull the string back a couple inches to settle it at the spot is will naturally go, and check for any difference... Not much difference. I do this three times with the last set of limbs, and after that I decide to pull the string back a bit more just to see what happens...

The sting flies off the side of the bow (same side as before, fingertip side), and the bow gets a nice good minor dryfire, delaminating one of the limbs a bit.

I know the riser pads and the limbs are square and true becuase I use a router on everything to square everything up (including how I make the press) but I just don't seem to understand why getting that string to go down the center of the limb without twisting and flying off is so hard and hazardous. I use .050 glass on back and belly, .030 veneers under the glass back and belly, and one taper lam at .002 taper under the wedge.

Can anyone help?

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[Leo L.]

 

[snag]

You have limb twist. With a recurve it is critical to have the limbs marked to center before tapering and grinding your limbs down to the shape you want. I have been taught to put a clamp on center that you can put a string on. Then string it. When strung put the bow on the floor and slowly lift the string up and let down. If the string is not tracking on center you will notice the limb tips twist. Then you can move the clamp accordingly until the string and limbs track in line. Mark that as center. Then when you put a templet on the limb to trace out the shape you are square to the riser.  Just what I have been taught. I don't know how others do it.
Also when the limbs are glued up if the laminations turn under pressure just a little bit that can cause big problems.

[razorback]

Ask Terry if you can change your user name. Might help  

[Trux Turning]

You have the right idea on the strong and weak side and how to address them. One of your problems may be how you lay out the center line on the limbs using a center line block- you may not be getting the actual center line of the limbs (tip to tip) which could be causing you to not be able to correct the alignment problem. You might want to use a string or laser line to mark that straight line before you do any limb tapering. After that you can taper and then make any adjustments-sanding the stronger side and/or making the weaker nock deeper should work then.If you feel the design is to radical you can change the pad angle and lower the limb tips-that will provide some stability also.

[BenBow]

recurvebreaker that bow looks like it's pretty extreme. What is the width of your limbs and the overall length of your bow? It's hard to tell from the picture but it appears like your limbs are too narrow. They need to maintain the full width to the last curve before tapering to the tip. IMHO BTW great looking riser.

[recurvebreaker]

Thank you so much for all the quick and informative replies. I want to go straight back into another one with you advice and make this one and the rest turn out to be good working recurves!

I have a few questions or replies to all of the posts to clarify some things because I don't want to go into a fourth recurve with misunderstood advice. If anyone else has the answers to thes questions I would love to hear your opinion or answer. These don't HAVE to be aimed straight at the person who posted them.

Leo L. --- Can anyone tell me how he posted my pictures directly to the page because when I do it I just get a URL up there and not the actual picture.

SNAG --- Can you clarify what you mean by "clamps that you can put a string on"? Are you talking about tillering blocks that hook over the ends of the limbs and have a hook for a string to hold onto? I have a nice set of tillering blocks I picked up from Mark Horne of Horne Archery about 10 years ago but have trouble stringing the bow with them. Do you have a suggestion as to how to string the bow with them? And when you say put the bow on the floor do you mean putting the back of the riser on the floor as if you would be shooting the floor point blank? Do you just hold it down with one hand and pull the string with the other?

RAZORBACK --- I am considering changing my username to recurvebuilder for an added boost of phsychological confidence. Thanks

TRUX TURNING  --- The first two sets of limbs I used the weighted string method but found it hard to mark the line because everytime I would move down to mark a spot for the centerline my body would move and so the angle that I was looking down at the string and bow limbs would shift and make me second guess myself. I tried putting a light above the string to make a shadow of the string cast onto the bow limb, but if the bow was tilted even a fraction of an inch, the shadow would not be straight anymore on the curves of the limbs. The lazer line idea sounds good but what do you use to cast a lazer line down the entire bow?


BENBOW  ---  The overall length of the bow is looking like 62" AMO. You made a great comment about the width of the limb staying the same until the last part of the curve. Currently, the width at the riser is 1 3/4" and tapers to 1 1/2 right before the curve starts, then it tapers down to 1" at the tip which is about 7" worth of curve. Should I be keeping that same 1 3/4" width for the whole length until closer to the tip? When should I start tapering it down and what do you think would be a good tip width to taper to?

Once again, thanks you everyone so, so much for all the great information. This is what I love so much about the traditional community. Fully willing to share the bits and pieces of knowledge about our craft. Fully unselfish. Thank you.

[razorback]

go with the mojo. Good luck and make sure you show us the successes as well as the learning experiences. It is all good and we learn more from the troubles than the triumphs.  

[razorsharptokill]

On the bingham video I have it shows putting 2" masking tape on the glass( non glue surface) to protect from glue but to also draw a true center line on it before it is ever glued up. Good theory.. but if lams shift in glue up true center is no more. Now that I put fender washers along the length of the form to stop the lams from shifting this isn't too much of a problem anymore. When I get the limb out of the form and cleaned up THEN I find center and draw a center line the length of the limb. I haven't had the best of luck lately either with centering my limb and riser holes. I feel your pain.

[snag]

Exactly! Tillering blocks. The man I am learning from says you must find center to where the string and limb travel are true. You can always adjust the string grooves when you file them in to help with this too. But first make sure, even before grinding the limb tapers, where the true center of those limbs are. If you have the string off to one side or the other the limb(s) will twist, you will see this. Then move that clamp until they don't and you have good string travel. Yes, put the bow on the floor face down, not belly down, and just pull the string up high enough to get the string off the limbs and then lay it down. Try and do this straight up and down. I just put my foot on the riser where my grip will be.

[recurvebreaker]

Thank you SNAG, that gives me a fresh boost of what will work next time! I can actually see how the next recurve will be true.
Do you have any good preference about where on the limb I should start tapering down to a tip from the full width of the limb?

[recurvebreaker]

Ha! I figured out how to put the photo straight on the post and feel like a dummy for not figuring it out earlier! Good times. Much easier then getting a recurve to stay as a recurve and not firewood.

[Trux Turning]

On a recurve the string will find the center and marking it where it contacts the limbs is the easy part. I will usually mark those points and then take my laser level line and shoot it from tip tp tip and that gives me the line the total length of the bow.When using just the string you can mark out the limbs with a series of dashes while sighting down the string and once you sight down and everything lines up connect the dashes for a straight line-if any dots or dashes are out of line cover them with a piece of tape and remark. Tillering blocks are also a great way to find the center for true limb travel as snag says and are fairly easy to construct out of washers- you still need to mark the limb center to align your tapers. If you can find some build alongs from Hera- there are a lot of helpful ideas there also. Keep building and get rid of the limb twist and you will have a winner.

[lostshot]

That's right bolt that thing together and find the center line, I use a laser,it might be the right side of one limb and the left of the other but that is your center. Work to that. Also do not get your tips to thin.  If you still get the twist you might think about shorting the limb tips. you will get a heaver bow weight but it will be more stable.

[recurvebreaker]

So keep the limb tips wider, huh? That sounds like great advice to me! I think I will try a little bit of everyone's centerline ideas. Start with string, check with lazer, use tillering block for confirmation.

I still don't know a good way of bending the limbs so that I can put the tillering blocks over the tips, but I am thinking of constructing some kind of bow press. What do you think?

And I will redesign the limb layout to be wider. Can anyone think of anything else? Thank you so much again!

[snag]

When you find the true center with your tillering blocks then we took templates he had made for the outline of the limbs and laid it on the limb. The templates have center drawn on them. So we lined up the center marked on the limb with the mark of center on the template. Trace the template and then you can start grinding. You may want to make a template...? If there is a bow you like you could make a template off of it...or you could get ideas from measurements taken off it's limbs.

[Bow-n-Head]

Breaker: PM sent

[snag]

Leo here is some pics of the blocks I was taught to use when finding center on the limbs. Keep in mind that these are put on the limbs before tapering and shaping the limbs!
 

[snag]

At the bottom of the clamp is a nylon screw. Remember the limbs at this point are 2" wide! It won't damage the limb when screw up against it. So, I screwed them onto the limbs and strung the bow up. Placing the bow face side down onto the floor lift the string until it comes off the limbs only! Watch the limbs to see if they twist or if the string doesn't travel straight and lay down straight. If one or both do twist I need to unscrew the clamp and move it to the opposite side...slightly, go a 1/16" at a time. When you find good string travel and limbs are going up and down straight you are at center! Then scribe marks on the belly of the limb where the edges of the clamp are...this will be your tip diameter!

 

[snag]

Sorry for the poor pictures. You can see the marks where the sides of the clamp where hopefully. I got lucky and the center was only off slightly. How you place the string grooves can take some of a slight twist too.

 


I've also scibed where the string laid when at rest. That will be filed out slightly.