Bow limb broke. Help!

[Del the cat]

It doesn't need much wedge... remember stiffness is proportional to the cube of thickness, so even and extra 1/8"-1/4" will make a big difference to stiffness.
If it's relatively thin, the fade becomes easier and less critical as there is some flex in the wedge itself.
Embrace the problems... if it's a project, then learning and experimentation is part of the process.
That's why we do it... (that and a tiny bit of insanity  )
Del

[WilltheArcher]

Ok folks it's 3AM and I've got 3 days till the school shop closes. Here's where we're at.

Waited 24 hrs after gluing on the new ash lam to the broken limb. Who knows whether it was the lam or the stress at the bolt, hoping it was the latter. I made sure to rough up the ipe with 80 grit sandpaper, and the ash for good measure. Wiped the ipe down with acetone and glued it up, and tried not to squeeze too much glue out. Cut off the excess ash and sanded down to size, then sanded down to thickness - hurray new limb. I machined two washer plates and used gasket rubber to make two (you guessed it) rubber gaskets, one between riser bed and limb, other between the washer plate and limb.


Hoping beyond hoping this does it.

Now some more tillering advice would be great. Got my long tillering string, pulled it back a few times and snapped some pictures.




Think a couple people mentioned before it looks like it's not bending much in the outer limbs, especially on the right limb. I'm thinking start with fifteen strokes of a card scraper on the outer 12" of the right limb and ten on the left..but I've never done this before so advice appreciated.

[Del the cat]

Give us some info.
What is the width taper on the limbs and what is the thickness taper?
The thickness taper is the more important and I generally go for about 1.5-2 mm every 6" along the limb (excuse the mixed units!)

Del

[WilltheArcher]

Give us some info.
What is the width taper on the limbs and what is the thickness taper?
The thickness taper is the more important and I generally go for about 1.5-2 mm every 6" along the limb (excuse the mixed units!)

Del

Happy to Del. The limbs taper from 1-1/4" to 5/8" at the tips. 1.25 to .625 if you prefer decimals. They stay 1.25" along the 3" riser bed, then taper inwards from there. They are 28.5" long. The aluminum bowstring nock you can see on either end gives me a nock to nock length of 70".

They are a uniform thickness of 1/2". Bubby and I talked about that a lot in this thread and he convinced me to go with constant thickness, with some tillering required at the end.

[Del the cat]

Ah! Right.
Constant thickness is fine if the width taper goes down to zero at the tip.
Now obviously this is impractical ... So what I'd suggest is you draw the taper on the limb going from full width (just out side of the riser) to zero at the tip. Then mark a pair of parallel lines from the tip, 1/2" maximum (as skinny as you dare maybe 5/16) running down the centre line of the limb until they meet the taper lines.
Blend these two sets of lines together and cut to that profile hopefully you get a better bend.
Other thing is to shorten your long string so that it only just goes on the bow, then once the tips are pulling back about 6" get it braced.
You may still need some tillering of the belly on the outer limbs, rounding the belly (taking off the corners) may be an easy way to do it.
Del
Those funny clamp things on the end of the limbs look like they are on back to front?

[WilltheArcher]

Del - I'll round the corners. Do you think that the tillering on the belly that Bubby recommended would be enough to get me to a good pull? I'd rather not recut the profile of the limbs at this point.

[Del the cat]

Yeah, sure it will. I just thought re-cutting the profile would be easier than rasping away at the ipe.
You probably have a fair thickness to take off if my guestimate of 1.5 mm every 6" is anything to go by!
Del

[WilltheArcher]

Ok sounds good. Yea I'd rather rasp than recut at this point 

Planning on doing about ten-fifteen scraps on the outer portion of each limb to start, I'll try to take off a bit more at the ends to give it a bit of a taper. Do you have a good reference pic of what the bow should start to look like when I put it back on the tiller jig?

[WilltheArcher]

Ok I spent some time with a card scraper this afternoon, tried to take a bit off the outer half of both limbs. Tried to be a bit more aggressive as I went along the length to get some taper. Probably took about 30 strokes on each limb. This part is hard, I feel like I don't have a great idea what I'm doing. Would really appreciate some input on how it's looking and how/where I should take off more material. Every time I pull it back I'm worried it's gonna break again but so far so good.

[bubby]

Del the whole constant taper / pointy tip thing i know, but with a straight taper and even taper works great, then you tiller and usually end up with a slight thickness taper but it gives a good launching point pre tiller
Will take a six inch straight edge and when you have it pulled like in the pics run it along the belly find the places with gaps and mark them then scrape the areas you did not mark

[WilltheArcher]

Thanks Bubby that was a good idea. Wasn't surprised by what I found - the ends were still a little stiff. Scraped a good deal more on each end, doing my best to taper lightly by taking more off towards the tips. I think it's looking a lot more like a bow now.







Going to scrape a bit more off the end of that last picture, then try to brace it. Lightly. I'll go for the 6" brace height after I've worked the limbs a bit more.

[WilltheArcher]

On Del's suggestion I tapered the limbs cause the curvature just wasn't right. I'm cautiously hopeful we're getting to something at least decent. Hope so, because tomorrow is the last day the woodshop is open for the year.

Not quite comfortable with full draw, might warm the limbs up and taper a bit more.

Suggestions appreciated.

really light brace.


cautious draw

[mikekeswick]

Looking good in that last picture.
Tips on tillering - always work in the bow with 30 pulls when you have removed any wood. This allows the freshly exposed wood to 'settle' it. If you don't do this any areas where you remove wood will just look the same as they did before you removed anything, then all of  a sudden you'll realise you've taken too much off!
Always pull to a specific weight ,decide on this now.
Never pull past a mistake.
Use a tillering gizmo constantly - you don't want an arc of a circle you are aiming for a mild elliptical tiller (bend).
Raise brace height very slowly - no big jumps to a higher brace height.
6 inch max brace height.
Take further pictures if you want help with the tiller 
And most importantly GO SLOWLY now, you have very little wood to take off.

[bubby]

That looks better take it up to 5-6" brace now and let it set for a bit then do as mike said   

[Onebowonder]

Here's hoping you have an awesome 'last day in the shop'!  You're very close now...

OneBow