Primitive Archer
Main Discussion Area => Bows => Topic started by: stuckinthemud on September 06, 2016, 09:00:56 am
-
Hi All,
so I am in work at the moment and can't post a photo till later but I have just about finished tillering a hazel bow, 2" wide limbs, parallel width to half-way then straight taper to the tips which have been left stiff for the last 6". 66" ttt with a 6" stiff handle and hollow-limb. The stick was cut and split last September and when I started working it I thought it was fully dried out but it has lost a lot of weight during tillering, so it couldn't have been as dry as I thought. After roughing out, and before tillering, the stave had a little heli twist, which I heated out, and about an inch of deflex, evenly spread along its length. Currently the bow is 45# at 24" with 2" of deflex evenly spread along its length. Is this what is known as 'set'? I am going to heat treat it, so should I straighten the stave at the same time, or leave it alone?
-
How do you mean hollow limb? Hazel has really thin and narrow pith, easy to avoid as it goes away during tillering and btw, it doesn't need to be removed at all. Its not elderberry
-
That "hollow limb" thing is just confusing and makes me think of PVC bows, I think concave belly makes much more sense
edit: Not really, but the first thing I thought was that it must've been two laminations hollowed out and then glued such that it'd be like a tube. But no, it makes sense, like hollowing out a canoe or something. I think I like how "hollow limb" sounds more than "concave limb"..
isn't it usually recommended to clamp bows to a form when heat treating, or something else? or otherwise heat treating ends up inducing more deflex..?
-
Yes its set, but a little set is to be expected. IMO it's a rare bow that has none*.
Would you rather have set, chrysals or a broken bow (I'll go for the set!)
Pulling it straight and heat treating will reduce the set and increase the draw weight. I think the stiff tips don't help, ideally if all the limb is working (obviously the last few inches can't do much) it helps spread the stress, reducing the risk of chrysals or set.
Have a good look and see if the set is evenly spread along the limb, if it is mostly in one place, then it's telling you the rest of the limb should flex more to take the load off the area that is over stressed.
Del
* some of the bows that are ram rod straight, started out with a bit of reflex, and those bows with 1" of reflex probably started with 2"
-
Yes, that is set based on your description. Evenly along its length is preferable to localized in one spot. 2 inches is bordering on too much imo. Too short, too heavy, to wet, so let that information guide you on the next one. On this one clamp it past dead flat by an inch or so and temper the belly. that is what I would do.
Cross posted with Del, but it looks as though we agree.
-
thanks guys, I like the concave belly in hazel because I think that it might reduce the risk of crysals (just the opinion of this novice), the actual set is about 1" as the stave was deflexed before I started to flex it.
-
"One more thing" ( I love Columbo), once I clamped a high-crowned bow down to my bench to apply heat via a hot air gun and the air wash was trapped by the bench against the back of the bow and scorched it (the bow), so any advice on how to avoid this happening would be welcome.
-
"One more thing" ( I love Columbo), once I clamped a high-crowned bow down to my bench to apply heat via a hot air gun and the air wash was trapped by the bench against the back of the bow and scorched it (the bow), so any advice on how to avoid this happening would be welcome.
Clamp thin slats of wood to the sides of the bow.
This does several things.
1. It protects the back.
2. It spreads the heat along the belly avoiding the hot spots you so often see on heat treated bows.
3. It shortens the time to do the job substantially.
http://bowyersdiary.blogspot.co.uk/2015/02/two-steps-forward-one-step-back.html (http://bowyersdiary.blogspot.co.uk/2015/02/two-steps-forward-one-step-back.html)
Very short video here:-
https://www.youtube.com/watch?v=kM1_A2A0_TI (https://www.youtube.com/watch?v=kM1_A2A0_TI)
You may need a few layers of masking tape along the edges to help stop hot air leakage between the side cheeks and the limb... but trust me on this one. It really is a big improvement.
In fact if you are not 100% satisfied, I'll give you your money back :o
Del
-
"if you are not 100% satisfied, I'll give you your money back :o
Del
From a man as generous as you, I'd have thought you would have doubled it (my money, that is) >:D
-
Excellent advice Del! I will apply that for both hazel bows I am making (currently being dried though).
-
OK, some pictures: the set is not so bad as I remembered at 1.5"
(https://stuckinthemudsite.files.wordpress.com/2016/09/dscf3703-e1473197647939.jpg)
something weird going on with the tips: if you look really hard at the right tip you might see the twist and a kind of hinge at the beginning of the stiff section 3" from the end - think I'm going to narrow the tips, maybe go over to an eiffel tower shape instead of the straight taper?
(https://stuckinthemudsite.files.wordpress.com/2016/09/dscf3707-e1473197763859.jpg)
-
I think also its possible hinge there
-
Left limb looks a tad weak out of the fade and stiff over the outer 2/3 to me.
Right limb maybe a tad stiff on the inner 1/3?
It's all very subjective and subtle....If you draw it until it breaks... that will show you where the weak spots are >:D
If you take a tad off the outer 2/3 , strap it down and temper it, it will prob be a lot better.
I think its perfectly good to adjust the tiller, straighten and temper when a bow is still young... gotta teach it some manners :laugh:
Del
PS I don't see that as much set.
I reckon when you put it down with the tips on the floor, if you can get one finger between floor and grip, that's good. Two fingers is ok, three is a bit much and I'd really call that set.
If the tips are off the floor then it's probably had a load of reflex heated into it.
-
Starting to struggle with the tiller on the left limb. Am also 10# over my preferred weight, and when I heat treat it that may rise to 15# or more. Any thoughts?
(https://stuckinthemudsite.files.wordpress.com/2016/09/dscf3711-e1473268604794.jpg)
-
I'm a tad confused. How far are you drawing it and at what weight. What is your target weight.
The tiller looks better, just taken an even few rasp stokes off the entire belly... that will increase the draw length at target weight.
Del
-
Hi Del, thanks for all your advice. I want 40# at 26", currently she's drawing 45# at 24". When I heat treat the bow, I am anticipating the draw weight to rise to about 50# - I think that either this is a really good hazel stave, or hazel works really well with this type of design but the other hazel bows I have built have ended up much thicker than this one and been much lighter in draw weight. I am wondering whether to take a 1/4" off the width, or radius the corners more, or to scrape down the belly, or do a combination of all three. What is really foxing me is the little bit of twist about 8" in from the left hand tip, I don't want to put a hinge in trying to get rid of it but hopefully if I'm very careful when knocking the weight down I should be able to deal with it.
-
Btw, only now I noticed you left bark on, looks really good!
-
Not the bark - I stripped that off and then patterned the xylem with a small gouge, but glad you like it :D
-
OK, so I hit it pretty hard with dry heat, got it all nice and straight, draw was 57# at 24". Have taken it down to 52 - long way to go to get to 40#. Thing is an inch of the set has come back, so I guess I'll just have to put up with it?
-
Say if you want a 40 pound bow don't pull it to 57 pounds.Don't pull it over your intended final draw weight.You might have to tiller it down with a combination of side tillering and belly tillering if you refer to Badgers mass formula to help guide you there.Your doing fine so far but don't pull beyond your intended draw weight no more.
-
Yeah, stuckinthemud, that causes unnecessary set. That was my first mistake on my first bow, at the end it had almost 2" of set, because I pulled it more then intended draw weight of 40#.
-
OH! So, you chase the weight out to the draw length, not get the draw length and then reduce the weight :-[
-
OH! So, you chase the weight out to the draw length, not get the draw length and then reduce the weight :-[
Exactly... drawing past the intended poundage is a recipe for set, chrysals, global warming, recession, bubonic plague etc >:D.
Del
-
we can tolerate the plague, but please don't afflict us with Crysals!
I spent the last hour reading all the various threads on the mass theory I could find - I have no idea how heavy this bow is, but anyone have any idea how heavy it should be - stiff handle, parallel side, hazel, high crown, concave belly, 66" ttt
or should I just go with my instinct and leave the thickness alone and reduce the width - currently 2" (50mm), although Del's wonky hazel bow was also 2" wide
-
Give me email and I will send you excel type document with mass calculator. It is a gift from heavens. It says how much grams or ounces bow should weigh at intended draw weight, draw length, length ntn and reflex/deflex.
Then you weigh your bow during tillering every once and a while and you see how much till that calculated weight.
-
email sent (hopefully)
-
Don't forget to calculate that hollow limb design into that calculator.
-
Thanks PD, will do. Maybe if I post my results someone might check them. Am looking forward to getting to grips with the calculator, I think it will make a big difference to my bow-building
-
Thanks Stalker, that was really quick :)
I have run a calculation which comes out as 15.75oz. As I understand it, heat treating means a 10% deduction - so 14.18oz. Should I subtract a further 10% for the hollow limb?
-
Can you put photo that shows how yours hollowed limbs look like? I don't know about 10% reduction because of that as I don't completely understand how limbs look like.
-
Stalker - will post a picture soon but can't post pictures from work.
PD - I ran the mass calculation for the bow at its current draw weight and it is bang-on, so I'm thinking the hollow limb counters the extra mass of the high crown and in effect the calculation is run as though the bow is flat, so, no adjustment is necessary??? I also need to lose 1/3 of its total mass to get down to my target weight - I'm 8oz (200g)over at the moment
-
Hi Stalker
hollow limb is also known as concave belly. Works well on sapling bows where the crown on the back is really high
(https://stuckinthemudsite.files.wordpress.com/2016/09/dscf3716-e1473927961649.jpg)
-
Looks really cool, how did you hollowed it out and how did you know how much can you do it before it weakens the limbs?
-
I used a wood-carving gouge at first, then switched to a curved scraper. I am using the mass calculator to keep an eye on the weight of the bow, but mostly it is by feeling limb thickness between my finger and thumb - weak spots still show as twist or hinge on the tiller in the same way as a flat bow - I have not gone deep enough in the centre, and I need to take the hollow more out toward the edges - the biggest draw back is that it takes a lot longer than building a flat bow, but, I think it reduces the chance of getting crysals (compression fractures) and it does look good
-
My second bow was elderberry one and it has naturally hollowed out limb that looks cool. Too bad that bow was underweight.