Back Elasticity, Overwhelming Rawhide; Tillering Reflexed Bows

[kbear]

Hi everyone. I'm based in Australia, and fairly new to the bow making scene; I have experimented with a bunch of Australian timbers with some luck (just some mind) and had recently experimented with a timber—Queensland Silver Ash (Flindersia Bourjitiana). I built a 66" 40# trapped, heat treated, and backed with a very thin Black walnut veneer (less than 1/16) (more cosmetic than anything). I took it to the range and put 200 arrows through it. It shot nicely, didn't take too much set (maybe 1") and showed no evidence of chrysalling, or splinters. "Hmmm, I like this wood" I thought and went bought some more. Yes, boards (Gasp!)

The next bows I made from this wood, I backed with goat rawhide. It was very thin, but extremely strong. Whilst the first one was curing I profiled, floor tillered, heat treated, and rawhide backed three more. All were given approx. 2" of reflex during the heat treat. The reflex was held whilst the backing was applied.

So I get to near finishing the tillering on the first one today, and to my dismay, numerous chrysals have appeared!

It is my thought that the original with the Black Walnut veneer had enough elasticity in the back that both Back and Belly worked in harmony to produce a decent bow, whereas the rawhide on this latest one (and three more aside) even though trapped to favour compression, seems to have overpowered the belly, crushing it before achieving my target of 40# at 28".

I am going to try thinning the rawhide on the remaining three, and hopefully get some functional bows from them. Any suggestions?

Has anyone else had this experience with Rawhide or other backings? Are there any woods that you'all are aware of that favour a naked, or more elastic back?

[Ryan Jacob]

This might help http://www.wood-database.com/queensland-maple/

Also, I can’t tell what’s the problem right now but there could be several factors. What is the length of the bow that failed? What was the tiller like? Did you heat treat properly without any scorching? Where were the chrysals? What was the quality of the wood? less dense or perhaps containing more moisture? Or perhaps the first board you used was of supreme quality? Also some pictures could help.

As possible solutions, you could shorten your draw a bit or trap the back some. Also, another solution would be to put a belly wood on the bow. Wood is much more stiff than rawhide so I can’t believe that rawhide, especially thin hide, would be the cause. Good Luck!

[kbear]

Thanks Ryan. Its not Queensland Maple mate. Cheers though. Flindersia Bourjotiana. Bow was well within length spec 69". The tiller was fine, no hinges. Even heat treat, no scorching. The chrysals were mid limb. A grade wood, 12% MC, no knots or pins, straight grain. The back was already trapped. Not into making laminate bows. Bow was in spec for a 28" draw.

Perhaps Rawhide with a 2" reflex over-stressed the belly?

[Ryan Jacob]

Yeah, I just picked that because it redirected me when I typed “Flindersia”. With what you said, the reflex is the only cause I can see. That or the walnut was doing something weird...

[Badger]

     I doubt the rawhide had any affect at all. It has very little resistance to stretching, it helps to keep splinters down but doesn't do much otherwise. I have never been one to use trapping. I think it is the equivalent to just making a bow narrower and concentrating stresses. If the bow wasn't trapped it would be thinner and less likely to chrysal. I could be wrong on the trapping as I have never really used it.

[Ryan Jacob]

I agree with the trapping bit, it doesn’t make sense in most situations. In this case however, koreybear is already done with heat treating, removing wood from the belly could mess that up a bit. Also I don’t know what kind of cross section he has.

[George Tsoukalas]

The back is under tension and the belly is under compression.

If the chrysals are localized to certain spots they were caused because that part of the limb is bending too much in relation to the rest of the wood. The tiller is off.

If they are spread out along the limb  it is a  design issue. The bow is too narrow or too short.

I don't use rawhide much but I don't think it could  overpower the belly.

I've never worked any of the woods you mentioned so I don't know if they are compression weak.

The chrysals are there and the bow will eventually fold on itself like a book so anything else that is done may forestall that but that's it.

Jawge

[BowEd]

The back is under tension and the belly is under compression.

If the chrysalis are localized to certain spots they were caused because that part of the limb is bending too much in elation to the rest of the wood. The tiller is off.

If they are spread out along the limb  it is a  design issue. The bow is too narrow or too short.

I don't use rawhide much but I don't think it could  overpower the belly.

I've never worked any of the woods you mentioned so I don't know if they are compression weak.

The chrysalis are there and the bow will eventually fold on itself like a book so anything else that isdone may forestall that but that's it.

Jawge

Well put George.That's about the size of it.

[ohma2]

Agree.

[willie]

lots of good possibilities being presented, but it seems you have been fairly careful in your construction and the problem is limited to the new boards you bought? not every tree is the same, nor do you know if the boards were handled the same before you got them. Are the boards easier to tool? possibly lighter in density? maybe mismarked or misplaced? smell the same? etc

[JW_Halverson]

lots of good possibilities being presented, but it seems you have been fairly careful in your construction and the problem is limited to the new boards you bought? not every tree is the same, nor do you know if the boards were handled the same before you got them. Are the boards easier to tool? possibly lighter in density? maybe mismarked or misplaced? smell the same? etc

Willie makes a good point. Even two trees side by side, seeded from the same parent trees will vary.  My first bow was green ash and shot fairly well considering unbalanced limbs, less than perfect tiller, and a sub-optimal design. Every green ash bow since then, despite all the gains I have made in technique and understanding have been dogs. Other bowyers in the area agree that a rare green ash (Fraxinus pennsylvanica) will make a good bow, but in this area they are generally not a great choice for a bow unless you make a sinew backed Lakota style horsebow.

I would say try another one or two UNBACKED of the same exact design as the ones that failed, if you think it was the rawhide that did you a dirty trick. Changing more than one variable at a time proves nothing.

[Bryce]

"Rawhide couldn't overpower a fart"

                                     -Pearl drums

[JW_Halverson]

"Rawhide couldn't overpower a fart"

                                     -Pearl drums

Then again, modern science can't bottle his farts anyhow!

[Badger]

lots of good possibilities being presented, but it seems you have been fairly careful in your construction and the problem is limited to the new boards you bought? not every tree is the same, nor do you know if the boards were handled the same before you got them. Are the boards easier to tool? possibly lighter in density? maybe mismarked or misplaced? smell the same? etc

Willie makes a good point. Even two trees side by side, seeded from the same parent trees will vary.  My first bow was green ash and shot fairly well considering unbalanced limbs, less than perfect tiller, and a sub-optimal design. Every green ash bow since then, despite all the gains I have made in technique and understanding have been dogs. Other bowyers in the area agree that a rare green ash (Fraxinus pennsylvanica) will make a good bow, but in this area they are generally not a great choice for a bow unless you make a sinew backed Lakota style horsebow.

I would say try another one or two UNBACKED of the same exact design as the ones that failed, if you think it was the rawhide that did you a dirty trick. Changing more than one variable at a time proves nothing.

     I think that ash is the most inconsistent of any wood I have ever worked with.

[kbear]

"Rawhide couldn't overpower a fart"

                                     -Pearl drums

Then again, modern science can't bottle his farts anyhow!

Thanks everyone. I am happy now that the problem lies not with the rawhide, but most likely my tiller! These are the first I have made with reflex and now looking at the bow, though no hinges are present, the outer 2/3 of the limbs are pretty straight. Me and my impatience. I said it to my wife yesterday "so frustrated, I haven't made a decent bow for months". That right there is the answer.

Impatience in tillering!

You nailed it Jawge.

The next three I will dunk my head in a bucket of cold water before tillering. I might start the next tomorrow. This one is going through the band saw (like so many before it).

I will post picks of the hopefully successful finished product.

Thanks to you all!