Speed of cast vs draw weight?

[Woody roberts]

Hello, first post I’m fairly new to archery and bow making so there is a lot that I don’t know. Ive built 5 bows so far. The first and the last are still shooting. The other 3 have broke after a few hundred shots. Well the Elm bow broke the first time I pulled it back.

The first bow is a red oak board backed with rawhide. 64” long ,8” handle section. I would call it a flat bow. Finished it drew 30 lb at my 26” draw and pushed around 115 fps. Heavy or light arrows made little difference.
I piked it to 60” which raised draw weight to 40 lb. Arrow speed went to 118/120. About the same.

The last bow is bamboo backed Ash. The Ash blank had a 1/4” resawed off and turned end for end before glueing up. This bow was more English long bow style 69” long. Finished at 35 lb @ 26” and pushed an arrow about 120’ fps. Very smooth to shoot and as accurate as I can shoot it.

I piked it to 64” which raised draw weight to 46 lb. just what I was looking for. Maybe gained 5’ fps.

I’m confused by the added draw weight not making any difference in arrow speed.

I realize all wood bows are individual but are there any given designs that have a higher ratio of arrow speed vs draw weight without going to reflex/deflex/ recurve design?

Thanks, Woody

[Digital Caveman]

I've only been at this a few years, but here are a few thoughts.

First of all, you didn't mention arrow weight,  but those speeds are pretty good for a target bow shooting 10 grains or more per pound of draw weight.  Considering how smooth and accurate the ash bow is, I can only wish my first few where like it.

As to the piking dilemma, piking a bow puts more stress on it, which causes more set, which in turn reduces cast, so there comes a point when any advantage to piking is lost.  Also, all else equal, shorter bows are slower per draw weight than longer bows because they store less energy per draw weight.  Finally, are you sure you're drawing the heavier weight version exactly as far as you drew the lighter weight?  Sometimes heavier bows are accidentally under drawn. No offence

I hope this helps explains some of your issues. 

Holmegarrds, D-bows, and American Flatbows are very efficient designs when well made.  Heat tempering and Perry-reflexing are tricks that increase cast on almost any design.

[Woody roberts]

Yes that does explain some things. I believe I’m coming to full draw. Both bows shoot best with 550 gr arrows. That’s the heaviest I have right now. A 31” carbon arrow with no field point doesn’t go much faster.

Can I heat treat without damaging my glue? My next bow is already glued up. It’s 3 piece bamboo, ash with a red oak belly.


Ps. Posting here is really difficult.

[DC]

Posting gets easier after a few posts. Speed is a strange beast. Everything affects it. Really. First, decide on the grams per pound(gpp) you want to use and stick to it. The standard is 10 gpp. It means you need a different arrow for each weight bow which is a pain but it gives some consistency to your results. Using one arrow for different DW just confuses the issue. DW and DL must be measured reasonably accurately. Consistency is important and your release is important. Unless you are a speed freak like me don't worry about speed too much. As long as the bow doesn't feel doggy you're good. For target just use the lightest arrow that flies true. 

[Del the cat]

Double the draw weight doesn't double the speed... it's the law of diminishing returns.
A 70# isn't twice as fast as a 35#.
There's a sweet spot at say between 35# and 45# where it's relatively easy to make a good smooth fast bow.
As you go heavier, yes they'll get a bit faster, they'll also throw a heavier arrow.
The skill of the bowyer makes a huge difference too, once you've mastered the basics, you can try all the tricks to build faster bows, but be warned... you don't get 'owt for now't so what you gain in speed you may loose in longevity, stability or smoothness.
Del

[bownarra]

The main thing here is wood combination choice.
A bow feels tension and compression forces.
Wood is normally able to stretch further than it can compress.
This means that you need to balance out the properties of the materials you are using.
Bamboo backings are very resistant to stretching.
Red oak and ash are not great in compression.
A more optimal belly wood to use with a bamboo back would be yew/osage/ipe. All woods that excel in compression.
If you have access to red oak it can and will make a great self board bow. Just get very straight grain (important!). If you can't find any straight grained boards then back them with rawhide or woven linen cloth.
Red oak is more resistant to stretch than it is able to resist compression. To aid it in compression you can heat treat it and trap the back - this is making the back narrower than the belly. On a flatbow the cross section of a 'trapped' limb would be a trapezoid. Both heat treating and trapping will make a big difference to how much set red oak takes.
Look up what a pyramid bow is and stick to that design. The bend should then be an arc of a circle tiller and easier to judge for a beginner.
Your main goal to improve speed should be to tiller slowly and never pull the bow past a problem.
Make a tillering gizmo for help with the board bows.
Make your bows 68 inch ntn for a 28 inch draw. Do not bother piking bows if you come in under weight....pretty much a waste of time.
No you can't safely heat treat a bow with a glueline.
Good luck and post pictures as you tiller to get some expert eyes on your bend

[bradsmith2010]

there are times ,,,bows can be piked to increase draw weight and cast,,

[PatM]

Wood is normally able to stretch further than it can compress.

 Source?

[Selfbowman]

I’ve never had a belly of a bow blow. Does it happen? Does it fail and cause dead mass ? I think so. Interesting topic . Arvin

[Digital Caveman]

Excessive set, frets, and chrysals are all considered belly failures.  If any are too concentrated in an area the back can break there.

Piking works best when the bow is to long to begin with.  I typically leave extra length on my staves for just this reason.

[Woody roberts]

Ok. I have an Ash board with pretty decent grain. The growth rings run side to side pretty square with the board. 6’ long by 2-1/2” wide. I googled pyramid bows and am going to give this a go.
Questions
Should the original outside of the tree be the back?

Should I back this bow with rawhide, bamboo or something I can come up with. I have nothing but plastic Sheetrock tape here at the moment?

It will be 67-1/2 n-n and I’m shooting for 40+ -50 lbs @ 27” draw

All thoughts, concerns, advice, criticism welcomed.
Thanks Woody

[Digital Caveman]

If the grain is straight, the surface of the board will be fine for a back as is.  A little wiggly grain is also fine on a flat ringed board. 

If the grain is marginal, rawhide is a good idea.  From what I have heard, bamboo is much more likely to overpower ash, and it's really more protection than you need.  Rawhide is more proportional, and less expensive.

You may want to start the bow @ 70" so you can pike it if necessary. At around this length, 1" off each limb increases draw weight by 5#. Generally, piking from extra long to ideal length is better than from ideal to too short. 

Anyway, that's how it works for me.

[bownarra]

Wood is normally able to stretch further than it can compress.

 Source?

Common sense matey

[PatM]

Wood is normally able to stretch further than it can compress.

 Source?

Common sense matey

  Unfortunately it's false. 

[Fox]

Wood is normally able to stretch further than it can compress.

 Source?

Common sense matey

  Unfortunately it's false. 

Pat I'm confused I always thought that too... They say something in the TBB along the lines Of, most wood has better tension strength then compression,  excluding yew, ERC, juniper, and a few others... hence why you trap the back on wood such as hickery to take stress of the belly and put it on the back where hickery excels in tension strength and and the rounded/ trapped belly of a elb takes tension of the back and puts in on the belly? .....  also woody Roberts... you should check out a bendy handle bow... There my favorite design...

-Fox