Did a bend test of some White Cypress Pine.

[yeoman]

Tonight I finally got around to testing a sample of White Cypress Pine (Callitris glaucophylla) off the back of Nezwin's success using the wood.

I got four fence palings from the local hardware shop. I managed to find some that had at least a short section of straight, unadulterated grain.

I cut one up into 13 x 13 mm sections just over 500 mm long. So far, I've only tested one sample.

The results were interesting...to me anyway!

Modulus of Elasticity: 6.6 GPa
Allowable Strain: 0.85%

Let's see how that compares with some other Australian and other timbers:

Rose Gum:
MoE: 17 GPa
Allowable strain: 0.71%

Spotted Gum:
MoE: 21.6 GPa
Allowable strain: 0.75%

Red Oak:
MoE: 12 GPa
Allowable strain: 0.83%

A quick reminder: the MoE is the stiffness. How hard it is to bend. The allowable strain is that strain the produces a set that is 8% of the total deflection.

So, this sample was about half as stiff as a given sample of Red Oak, and Spotted Gum sampled at about three times as stiff! Regardless, the allowable strain is quite impressive. I did some calculations for a 66", eliptically tillered, bend through the handle longbow. The thickest and widest section is of course at handle center. For a 40 lb bow, this is what we'd need:

White Cypress: 43 x 17 mm
Rose Gum: 29 x 15 mm
Spotted Gum: 19 x 15 mm
Red Oak: 25 x 17 mm

These samples should not be seen as representative of the whole species. My sample tested less stiff than published figures...by a fair bit. I'm confident the moisture content was sufficiently low (though I couldn't measure it), so it is probably just an anomaly of the sample.

The way to make a stunning bow form it would be to back it with some other wood, and add Perry Reflex in the process. This would allow for a narrower bow (by viture of the fact a Perry Relfexed stave is stiffer) while taking advantage of its impressive allowable strain. The fact that Nezwin has recently made a nice bow, and Perry's (not of the reflex phenomenon fame, but our own forum member) reports of the unbreakable bow mean there must be better samples out there. One of my other boards might be one.

For the information of anyone that might care.
[edited to fix the numbers]

[greybeard]

.........The way to make a stunning bow form it would be to back it with some other wood, and add Perry Reflex in the process........

Or back it with clear glass.

Daryl.

[yeoman]

As long as it was clear. If it were possible to maintain vision of the beautiful grain, it'd be a shame to waste it.

How thin does clear glass come?

[greybeard]

..........How thin does clear glass come?

.030 in UL or .043 in ULS.

Daryl.

[Nezwin]

The way to make a stunning bow form it would be to back it with some other wood, and add Perry Reflex in the process. This would allow for a narrower bow (by viture of the fact a Perry Relfexed stave is stiffer) while taking advantage of its impressive allowable strain. The fact that Nezwin has recently made a nice bow, and Perry's (not of the reflex phenomenon fame, but our own forum member) reports of the unbreakable bow mean there must be better samples out there. One of my other boards might be one.

It's an impressive timber, by the numbers, and I think some more examples of builds with it should prove how effective it may be.

I've noticed that not all boards seem to be equal (which is about one of the most obvious comments I've perhaps ever made!), in many ways - the original board I bought (sawed into two lengths, seen resting on my sander in the Hickory backed White Cypress thread) have a very clear & distinct grain, the colours being very stark & contrasting with one another well. I bought another board since then and, despite being the best in the small stack, it was less impressive - the grain was 'vague-er'. I'm not sure if this will impact the strength of the timber in compression (I assume it will) but it could be that Cypress is a species with widely varying properties, dependent on orientation of milling, tree growth, etc.

I'm beginning to favour these softer, elastic & durable woods. They're really nice to work and have a nice feel to them when shooting, White Cypress & Celery Top Pine being examples. They're more in keeping with the Northern Hemisphere timbers like Oak, Ash, Elm, Hickory, Maple and, particularly, Yew. They also seem to take heat a lot better than the dense, stiff eucalypts like Spotted Gum & Ironbark (Ipe also fits into a similar pattern of characteristics as this). My next goal re: Cypress is to get a few clean staves and see how well it works with a sapwood, under-bark back and the richly-grained heartwood belly...

[cadet]

...For the information of anyone that might care.
[edited to fix the numbers]

I care!

That's some really interesting information; any idea whether there's significant difference between heart and sapwood? The stuff is notoriously knotty, so beggars may not be choosers if anything knot free can be found. I did grab a couple of palings to have a play with one day.

[yeoman]

I think you're right there Nezwin: more bows need to be built from it to explore its potential. I'll do some more bend tests too.

I didn't select the samples for sap/heart wood, but I will in future and see if either of them has a beneficial property.

I suspect this timber will have a wide range of variation in quality. Some will be stiffer, some will be able to withstand more strain. Some will do both, and they will be super-specimens.

I was re-reading Marc st Lois' chapter on heat treating. It's fairly evident that as a wood's density goes up, its suitability for heat treatment goes down. There's probably a sweet spot somewhere, as the very sparse woods would probably burn too quickly.

I have some Elm lams to back bows with now. I think I shall use some of that to back one of these palings. It'd be the perfect length for a little wannabe archer that lives around here.

Nezwin, have you made a bow from CTP? Where'd you source the timber?

[Nezwin]

I have some Elm lams to back bows with now. I think I shall use some of that to back one of these palings. It'd be the perfect length for a little wannabe archer that lives around here.

That'll be interesting to see. I don't think I've seen a bow with an Elm backing...

Nezwin, have you made a bow from CTP? Where'd you source the timber?

I made a 72" Hickory backed CTP rectangular section bow which came in grossly underweight at 25lb and a short 58" hickory backed recurve which came in at 45lb after I'd shot it in. The longer bow my wife shoots and the recurve went off to a mate overseas. Few pictures here - http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=15644

I found half a dozen boards of CTP at the back of an old fella's shed - I was just doing a fibreglass patch repair on an old boat of his so he gave me the boards. Nice guy!