Ozbow

Good evening.

Today I had my first go at steam bending. I'd made a form recently and was keen to have a go.

I had a couple of spotted gum billets ready to go so I cut the thickness taper and left them at a full width of 35 mm. I left them in a bucket of water for a couple of days.

The limbs are only 8 mm thick at the end with a fairly subtle taper.

I steamed one of the limb tips for 20 minutes over a fairly fiercely boiling pan of water. I had soaked and steamed a longer section than would actually be bent on the form.

I had the billet clamped to the metal support strap prior to steaming so that when the time came, I could just go. I was pleasantly surprised by how easy it was to bend the limb around the form. What I was unfortunately surprised by was that the belly side, about four inches from the tip, seemed to fracture across the outside of the curve. Quite disappointed about that.

I think my steam time for the thickness was alright. I moved quite quickly when the limb came out of the steam. The only thing I can think of was that the steel strap was not tight enough before much of the bend was achieved.

If anyone has any insights, I'd be most glad to hear them. I'm planning on setting glue into the cracks and putting a thin underlay around the curve and hope it all stays together. I'll also try to fit the steel strap tighter on the next one.

The limb, once cool, did not retain all of the curve of the form. It still puts the tip 3" forward of what will become the handle though.



Doesn't look too bad from a distance.


But when you start to get closer:


Things aren't so brilliant.


Fractures run right across the belly.


And on to the other side.


New adventures for me!

yeoman wrote:.......I steamed one of the limb tips for 20 minutes over a fairly fiercely boiling pan of water.......

Dave,

Although I have not steamed spotted gum before I would have given it 45 minutes to 1 hour and using a cover / steam tunnel covering the pot.

yeoman wrote:......The limb, once cool, did not retain all of the curve of the form. It still puts the tip 3" forward of what will become the handle though.

As mentioned in my previous posts regarding steam bending around 50% of the curve will pull out.

Daryl.

I put a lid over the limb, and plugged the gap it made with a tea towel, which I think was almost as good as a steam box. I would have preferred a proper streaming setup though.

I'll try steaming the next one for longer and see what happens. I'll report back of course.

What have you stream bent, and what we're your early experiences like, Daryl?

Hi Dave.

I have used Daryl's set-up to steam American Ash. It worked well however the curve did slowly pull out over a few months. So I did the appropriate thing and did it again using the same caul. The curve came back and once again it slowly pulled out over a few months.

I am of the opinion that the problem is that I need to use a caul with great amount of curve and bend more of the bow.

That was a few years ago and the bow is still shooting well and it has shot a lot of arrows. My recollection was that it was in the steamer for a bit longer than twenty (20) minutes probably 30 minutes plus and when it was placed on the caul and bent it was very pliable.

There should be a post on the forum about it.

edit and here it is. http://www.ozbow.net/phpBB3/viewtopic.php?f=3&t=8668

Thanks Grahame.

Was your recurve a working recurve? I commonly hear of working recurves pulling out over time.

I was expecting the limb to lose some of its shape coming of the caul. It still has sufficient curve in my opinion. Well within the realm of usable recurve. Currently, the curve occupies eight inches of limb length. I was thinking of making another caul that gives a bend that occupies more of the limb.

Hi Dave

yeoman wrote:Was your recurve a working recurve?

Essentially 'Yes', the limb was working before it was curved. Irrespective it was a good experience and it still has some recurve in it years, and many arrows, later. That original post was 6 years ago.

edit: Dave read this http://www.ozbow.net/phpBB3/viewtopic.p ... ilit=steam

Dave,

I have used steam bending when making some Osage Orange bows of mine but I did not recurve the tips. I do mine over a boiling pot of water and I seal it all off as best I can with alfoil.

I too think you would need to steam the limbs for longer than you did. If it was me I would also narrow the limb tips before recurving them. One last comment is that I don't think Spotted Gum, with the type of grain structure that it has, is the best wood to be steam bending.

Jeff

yeoman wrote:What have you stream bent, and what we're your early experiences like, Daryl?

Dave,

Timbers that I have steamed are, red ash, pink ash, hickory, hard rock maple and osage.

I have not had any issues with my steaming setup as I had other bowyers advising me before my first attempt.

Rounding the edges of the stave may help to minimise splinters raising on the edges.

As I have mentioned before and it is personal preference that timbers such as spotted gum and ironbark go to the bottom of my list of bow woods.

Daryl.

I found a couple of resources that may be of use to others:

http://www.vccaq.org/BendingTimber.pdf

http://www.dpi.nsw.gov.au/__data/assets ... Timber.pdf

I've also read elsewhere on the wide internet world and found that Spotted Gum can be suitable for steam bending, but small imperfections in grain can be problematic.

I think my sample suffered from slight grain runout near the sharpest part of the bend, as well as not having a tight enough strap.

The literature seems to suggest an hour per inch of thickness, meaning my 20 minutes for 8 mm might have been about right.

Morning Dave.

yeoman wrote:The literature seems to suggest an hour per inch of thickness, meaning my 20 minutes for 8 mm might have been about right.

You need to spend a bit of time working in a boatyard where they are working on wood boats, Oz timbers and check out how they do it and some of the issues.

Dave

Text was taken from the links you provided.

Softening the Timber. The most commonly used method of softening or plasticizing wood is steaming, using either atmospheric or low gauge pressure.
When steaming at atmospheric pressure, one hour for every 25 mm thickness should be allowed. Over steaming of the timber can cause problems such as excessive shrinkage, checking and warping during re-drying.

With regards to ‘one hour for every 25 mm of thickness’ this is probably a bit of a generalization for bending planks on shallow curves or large radii.

Daryl.

Dave,

Grab yourself a Red Oak board from Masters and give it a crack! My experience is that it bends well if steamed for an hour per 25mm thickness... Might be worth trying to get your confidence up. Just remember to round the edges!!

Should work really well with a bamboo backing I reckon.

Colin

Good point Daryl! That picture with that text superimposed should become the standard object lesson in what not to do!

I may in fact, have a go with red oak.