Help Needed: 3-Piece Take-down Recurve Limb Disaster

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Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Jumpster » Fri May 20, 2016 7:33 pm

Hello All,

I've got a problem that, hopefully, someone here can help guide me through to a solution...

I have recently started building a new 3-piece take-down recurve for the upcoming season ahead. As such, I think that I will post this as a build-along so that others may learn from my mistakes.

So, to begin with, I went to a local sawmill and bought a hunk of hard-maple. It was a 9/4 (a tad over 2 1/4" thick) block 7" wide and 70" long. From that block, I cut about 38" off for laminations. Then I cut another 20" block which was then split in half to make two risers and the final section was reserved for wedges. Then I cut out 8" slats, roughly 1/8" thick, using my table-saw.

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Then I spent, what seemed like an eternity, grinding them down to approximately .065" at which point I ordered my black glass. On a whim, which was probably a good thing actually, I ordered some uni-weft glass too. My reasoning was because as I was grinding, I noticed that more and more the lams started bowing into a u-shape as I was grinding them down. That started a voice in the back of my mind that there was certainly going to be limb-twist to deal with. I was hoping that the uni-weft would help alleviate that...

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So, ultimately, I ended up with 2-lams at .065" and two at .064" plus .030" black glass on front and back with .030" uni-weft. Combined with a 9" wedge and a 16" riser, I'm hoping to get a bow capable of hunting weight (~40#/55#). The other four lams will be used for another bow at a later date.

Ok, so then I glued the limb all up (no pics to show), let it cook @ 160-degrees for 6-hours and cool off before taking it off of the form. That was when I was able to take a closer look at the limb and was rather surprised with what I saw...

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I know that the image quality isn't the greatest, but just know that the entire right side is not "just" glue! That's right, somehow even after taping to the form, the whole thing slid to the left about an 1/8" or so. Here's a better image as shown from the end...

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First off, I'm not sure what happened. How does this happen? I paid special attention to fill the hose slowly - adjust the lams, fill it some more - adjust the lams some more and final fill-up before a final adjustment. Yet, at some point during the cooking process, it slid again. My guage showed 60psi...

Secondly, how do I fix it? My idea is to take my calipers to the sides to find and mark exact-center. Then take limb width from 2" (I ground the lams to black-glass width before glue-up) to maximum width capable of squaring up the sides. At this point, I will begin the limb shaping process. Of course, that means that no-matter what happens with the second limb (still in the oven), I will have to at least, at a minimum, grind it down to the same width before continuing.

Does this sound like a plan or should I consider something else?
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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby KsBow » Fri May 20, 2016 7:49 pm

Sounds like that's your only choice to me. I don't use the air hose as I don't make glass bows....but what you've outlined should work. Keep me posted. Ralph
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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Jumpster » Sun May 22, 2016 3:31 pm

Update: And, here goes...

So, I got to take a look at the second limb the other day. Got a pic to show you but didn't touch anything until today.

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As you can see, it too slid some but not nearly as bad as limb one. I wanted to keep a close eye on the two limbs as I was trying to clean them up so I've labelled them each in accordance with which was first and second to be cooked up.

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So then I did some preliminary measurements on both ends of the limbs. Since the lams were 2" wide (roughly 50mm) I was able to get a better idea as to how much they slid. Limb one slid a whopping 5mm (nearly 1/4")...

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whereas, limb two slid roughly 3mm or so.

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I did this on both ends of both limbs and was surprised to see it was a constant slide across the limb (5mm and 3mm respectively).

Using limb one as the basis (as I was expecting to do), I marked center on both ends of the limbs. Then I found and measured the closer of the two edges and marked lines accordingly on each side of center. In the case of limb one, that was 23mm. I was actually able to get closer to 24mm with limb two but since that would have made it wider, I stuck with 23mm for limb two.

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And the other end...

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Then I spend the next hour (or two) grinding them down slowly on my belt/disk sander. When I got done, I was pleased with the results. Now they are looking workable.

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Now that it looks like I can save them, I took the tape off to have a peek.

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Next, I have to work on the riser so that I can begin mount the limbs and get an idea of how they are bending...

More updates to come...

Jumpster

Edit: BTW, I measured both ends of both limbs to get an idea of how much width I lost. I was expecting 2" at glue-up but after they slid, I was hoping for 1 3/4". When it was said and done, limb one ended up being 1.895" on butt-end and 1.812" on tip end. A touch over 1 3/4" so I'm happy. Limb two ended up at 1.925" on butt-end and 1.745" on tip end. The limbs at tip end is 0.223" both. Whereas, the butt-end of limb one is 0.662" thick and limb two is 0.667" thick. I guess that can be attributed to not squaring off the butt-end quite as perfect as I would like... lol

Oh well, still something to work with. Now, I hope that I can still get a hunting bow (40# or more)
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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby KsBow » Mon May 23, 2016 12:15 pm

Looks like you've got er whipped. Patience is a virtue and just by your pictures you look to be in good shape. Continue my Friend. :applaud:
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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Aeronut » Mon May 23, 2016 8:43 pm

I've had a couple of longbows slide and I use fender washers on the sides of the form to keep them in place. You are doing fine on your limbs.

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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Jumpster » Sat May 28, 2016 4:52 pm

Aeronut wrote:I've had a couple of longbows slide and I use fender washers on the sides of the form to keep them in place. You are doing fine on your limbs.

Dennis


Thanks for the comment and support. I do have washers on both sides of the form. Maybe they fell to far down under pressure of the hose... I'll keep a close eye on them next limb.

Meanwhile, I've not got much done in the last few days with holiday preparations and such but my plans are to finish this one over the next week. I've got a weeks vacation with no other to do items from the Mrs... Of course, we'll see how that progresses as well... :lol:

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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Jumpster » Fri Jun 03, 2016 9:18 am

I finally got some time to work on her yesterday...

To begin with, I took my riser block and marked it off where I wanted to cut it. I chose 18-degree limb pads because the trigonometry was easy to mark off. 5" across the top with a 1 5/8" drop down the side gives 18-degrees. Both of those numbers are clearly marked on virtually any ruler. You'll have to trust that my math is right because I don't really want to go into the trig-formula that I used. If you have doubts, feel free to google it. I did just to double check my work... lol

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So, after I got her marked, I used my hand-saw to cut it out. These cuts were easy as they were only one-time cuts. After cleaning up the cuts, I went ahead and installed the hardware. To do that, I made myself a drilling jig with holes 1 1/2" center to center. One was 3/16" for the pin and the other was 5/16" for the bolt. By using the jig on both the riser and limbs, I got the holes to line up just fine. I then went and bored the riser's bolt holes larger for the threaded insert. Glued in the hardware and we're ready to move forward...

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Attach the limbs to admire my work...

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Yup, she's beginning to look like a bow...

So normally, at this point, I would run a line from tip-to-tip to find centerline and mark off limbs for shaping. But this time, there's a problem... The line rides across the riser (instead of above it) because my tips are sitting to low.

What to do? What to do?

I have seen in other posts where they took a couple of washers and cut out angular sections to grip the tips from the belly side. So that's what I did...

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My hack-saw has been getting a serious work-out lately...

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So I tied up two washers on either end of a line applying a slight pressure on the limbs. Not a lot though, don't want the steel washers to gouge the limb-tips.

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Once I got the line to run center along the riser, I was appalled to see just how far off-center my limb tips were. Limb #2 was just fine...

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However, limb #1 - woo-hoo...

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I got the limbs marked and ground down and was once again surprised. As far off-center as limb #1 looked, I expected to see the tip end drift off to the right when stacked up on top of limb #2. This was not the case. Somehow, they both line up perfectly when stacked one atop the other...

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So now it's time for the tip re-enforcements. I sand the tips (about 2"). I wrap two layers of masking tape underneath and place a block of wood over the tape. The wood is there to make sure my tip re-enforcements do not slide down while clamping into position...

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And here's one of the tips when I got done with the glue up. I'm not particularly keen on the smash-spot from the clamping even though I had a block of wood on either side of the limb between the clamp...

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Ugh! Another oops found... Look at that nasty glue line... From a distance it looks like there is no glue even there but upon closer inspection you can see what looks like a piece of glass in there - shiny and brittle looking... Yuck!

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With that in mind, they did clean up pretty nicely tho...

Here's one:

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And the other:

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It's finally time to check tiller...

Limb #1: Just a tad over 4 3/4"

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Limb #2: Just a tad over 4 1/2"

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Not too bad I guess...

So now that I know that limb #1 will be my top limb, I can draw and cut out my riser shape.

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Boy, am I glad I've got a spindle sander. It works wonders when squaring up my mistakes.

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I decided to take a picture to illustrate the process of shaping my riser. I've got a band-saw but for some reason, it just won't touch this hard-maple... So I had to shape it completely by hand and clean-up with my spindle sander... I cut slits using my hack-saw, then break them off with a heavy flathead screwdriver...

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Clean it up with spindle sander and then with the parts that the sander can't reach I used files and rasps... Very time consuming....

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Still got some serious fine-shaping to go with finish sanding but she sure is beginning to look like a bow now...

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I decided to take her out for a shot or two. She flings the arrows pretty quickly. In that regard, I'm pretty pleased but I'm afraid she's to light to be a hunter. I'll verify that later when finished but she feels like she's pulling upper 30's to me... :(

Regards,

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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Jumpster » Sun Jun 12, 2016 6:23 pm

I'm sorry it took so long but here she is, all dressed up and guess what: she's legal! Coming in at 42 @ 28, 60"...

I've got to say that I'm extremely proud of this one given the problems that started from the beginning...

So, without further ado...

Side profile, unstrung:

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Side profile, full-brace:

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Side profile of riser:

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Isometric view of riser:

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And finally, the entire shebang:

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For finishing, I used two-coats of a dark chestnut stain on the riser and limb profiles. Riser has four coats of wipe-on poly clear satin and the limbs have eight or nine coats, I lost count. In order to conceal some of my craftsmanship mistakes, I was trying to back the limbs with mossy oak bow limb tape and seal it inside the poly but as soon as I'd put a coat on, the tape would literally disintegrate and fall apart. I tried three times before finally giving up and just coating the limbs trying to get the same sheen as the riser has.

Since I had some left-over "pleather" material from re-upholstering some of our furniture a few weeks ago, I decided to try and do a handle wrap and arrow-rest piece. I think that they both came out pretty good. For the wrap, I found a youtube video that showed using some reverse wrapped electrical tape (glue on outside) to tack the wrap to the handle and keep it from moving. I then went and super-glued the top and bottom edges and trimmed away the exposed tape underneath. Not sure how long it will last but it was easy enough to apply and looks fantastic...

And there you have it, my latest creation, successes and failures abound...

Regards,

Jumpster
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Re: Help Needed: 3-Piece Take-down Recurve Limb Disaster

Postby Winter Hawk » Mon Jun 13, 2016 9:22 pm

I like! :77:

~WH~
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