Trapping

[stuckinthemud]

A comment by Bownarra made me stop and think. I've never built a bow with trapped back or belly.  How do you do this ? I mean how far over weight and at what point in the tillering process? I'm guessing at a good overall tiller at half draw length and maybe 20lb over target draw weight?

[Pat B]

The reason for trapping is to compensate for the difference in the strength of the back or belly so in that situation I think trapping from the start is the way to go. Most woods are stronger in tension than in compression so most trapping with wood bows would favor the belly making it slightly wider than the back.

[Jim Davis]

Here's what I said in another thread:

"I've done a lot of reading about lab testing of woods and have "trapped" a lot of bows, ash in particular. It seems that wood stretches only about 1% of it's length before breaking without yielding first. The only clear gain from "trapping" the back is in the reduction of mass in the limbs.

That is a gain, I admit.

As for ash being stronger in tension, every wood is, though some are worse about giving no warning  before a catastrophe. In fact most woods are 3 to 4 times as strong in tension as in compression."

I made a small pyramid bow with a strip of hickory for backing. The hickory was only as wide as the limb tip (3/8" wide from fade to tip). It's a snappy shooter.

[RyanY]

My usual strategy has been to narrow the width to 60% of the total width. I will get the bow floor tillered or as soon as the tiller is even, I will remove the wood for trapping. I will mark around 1/8” or a bit more from the belly as the “depth” of the trapped section. That leaves enough room for tillering without removing so much thickness that the belly has a knife edge where the belly and sides of the trapezoid section meet. As mentioned above, wood is stronger in tension than in compression but it’s always better to err on the side of the back being stronger.

[mmattockx]

I made a small pyramid bow with a strip of hickory for backing. The hickory was only as wide as the limb tip (3/8" wide from fade to tip). It's a snappy shooter.

Jim,

What were the dimensions of the limbs and the strip? Have any pictures you can share of this? It certainly is an easier way to gain the same end result as trapping.


Mark

[bradsmith2010]

i have never trapped a bow,,

[Jim Davis]

I made a small pyramid bow with a strip of hickory for backing. The hickory was only as wide as the limb tip (3/8" wide from fade to tip). It's a snappy shoot

Jim,

What were the dimensions of the limbs and the strip? Have any pictures you can share of this? It certainly is an easier way to gain the same end result as trapping.


Mark

It was a small bow to be used in the living room. I gave it away recently, so only have one image. The bow is about 3 feet ntn, 1" wide at the fades and maybe 3/16 thick. The hickory backing is only 1/16 thick.
I made arrows that had bulbous tips so a miss wouldn't damage the sheet rock. At least that was my vain hope....

I don't recommend this approach. It was an experiment.

[Dances with squirrels]

When I make a bow I plan on trapping, I do it before it goes on the tillering tree and before I know how heavy the draw weight is. It's part of the initial shaping of the bow.

[loefflerchuck]

Most woods are stronger in compression, but not every wood. Cherry, juniper, incense cedar and perhaps most conifers are stronger in compression. Though I would never trap the belly in these, just back them

[bassman211]

I trap the back when the bow comes off the form, but I check the limbs for straightness before I trap. When I think of trapping Black Locust always pops up in my mind.

[Woody roberts]

On white wood bows,ash,hickory,walnut,red oak etc I trap the back as part of the initial forming. Once tillered to brace height I heat treat. If I scrape quite a bit off I’ll heat treat again near final tillering. I rarely have to heat treat the second time.
This has worked pretty well for me.

[Jim Davis]

Most woods are stronger in compression, but not every wood. Cherry, juniper, incense cedar and perhaps most conifers are stronger in compression. Though I would never trap the belly in these, just back them

Brain hiccup, right?

[bassman211]

Yes Jim, I think he meant say tension.

[bownarra]

What has been said above ^^^^^^
It is the 2nd string bow woods that you notice the difference with most (and b.locust) woods that people don't use much because 'they take too much set'. Red oak pops to mind....out of the native woods to here fraxinus excelcior really likes a good trapping I once made an awesome little flight bow from heavily trapped ash, it was one of the best wooden flight bows i've made.

[Marc St Louis]

Trapping reproduces the effect of a high crown small diameter tree.  Some species, such as Elm, make a better bow when they have a high crown.  One thing to remember is that if the wood you are trapping has very fine rings then it's more likely to pop a splinter