Steam bending Iroko

waynes world

waynes world

Well-Known Member
Joined
7 May 2011
Messages
1,569
Location
Manchester
Visit site
Morning all

I am going to try and see if i can make this frame for the Houdini hatch from some Iroko i have left over from an old school lad table..

The frame will be done in four sections then overlapped to join them on the straights, the sections being the corners that are 100mm radius.

Know after much reading i have decided not to even bother with trying to bend the 25mmx25mm i need to so it will be laminated with Cascamite ( unless other glues are advised )

So i am thinking on five 25mmx5mm laminations being steamed and bent INTO a former of ply and see how it goes, oh and it will be soaked in the bath for 2 weeks ? Not told T yet :)


Question is, how long should i steam it for at around 210 deg, i know of the 1hr per inch but as it is only 5mm thick and i dont want to over steam it as it can dry the wood out to much how long would you suggest for steaming ?


Thanks guys n gals

Wayne :)
 
Problem with iroko is the short and often curly grain which means it is poor for bending to that tight a radius. The other problem you have if you get it as moist as you plan is then getting it dry enough to glue reliably. You could waste an awful lot of timber getting 4 good corners that way. I would be tempted to laminate a longer length, stepped into the straight bits with an overlap of each lamination by 25mm. Build a jig that will hold the straight bits firmly with a former for the curve and do the lamination one layer at a time, gluing the ends to the rebates in the straight bits.

This is an awful lot of work and cutting the corners out of solid stock would be easier and more reliable!
 
Tranona is right.

I tried this with old work top iroko, its a pig to bend.

I would say cut it into strips, glue strips into a brick and bandsaw the corners.

Note that iroko will dull blades fast, its noticeable.

For a few quid it would be worth buying an alternative timber. I had a big stash of iroko and found it hard to find uses unless you want straight bits!
 
Iroko actually steam bends pretty well provided it's not dry. Dagless for example used Iroko for the stem-bent timbers of their motor yachts very successfully. And when used for planking it steam bends well.

Air dried Iroko doesn't steam bend so well of course and kiln dried Iroko doesn't really steam bend at all. As timber dries the lignin in the cells dries out and hardens; this is especially so with kiln dried timber. Soaking it won't restore the lignin to its former state, so, once dried, the elasticity is essentially gone forever. This is true of all timbers, not just Iroko, though some like Ash don't suffer as badly.

You will do just as well to warm the laminates gently with a hot air gun as you will steam them. Soaking them beforehand may help - but of course once bent, you will have to let them dry again before you can glue them.

I would use WEST epoxy to laminate the Iroko strips - the very act of wetting the timber out with the unmodified resin before applying the thickened resin for bonding will help to make them more flexible. Five or more strips together, all wetted out and then coated with thickened resin will bend around a tighter radius than a single strip alone will. And a backing strip of spring steel on the outside will assist greatly.

However, I would think you will need to reduce the thickness of the strips to maximum 3mm to get around a 100mm radius – even so about 120mm is probably the smallest safe radius for 3mm material.

Timber usually fails because the cells collapse in compression before it does in tension – even though it looks as if the tension side is what has broken.

Hope this helps!

Cheers -- George
 
Would not steam bend
You will have notice how thin veneer can nearly go around any corner
Could it be made using bought veneer
If the section is 25 x 25 could you not surface and rip on table saw 20 times using a sharp blade
Construct a good jig for holing and clamping leave oversize to trim back
Use uf adhesive a lot for laminated shore based parts resintite until they stopped makin g it��and now semforite
Glued up two wood blocks with semforite they have been at the bottom of a freshwater barrel for two months still ok
Cannot recommend for marine use as no experience in using it in that eviroment myself
Sometimes colour the adhesive to match the wood as well
It's not the easiest way to make this part but if you want a challenge go for it !
 
Thanks for the replies. All advice is welcome and always appreciated ;)

I know it is not an easy timber to bend at best of times, but a lot of folk do manage it and as i have spare Iroko lengths left i mite aswell give it a try before i actually do the job then.

Be good to have a small experiment really with it.




So still

how long would it need steaming for if i go down to 3mm thick instead of 5mm ?

I may well try both thicknesses while i am at it.
 
Rule of thumb is 30 minutes per inch thickness - so not long at all. Probably another experiment for you. However I think you will be able to bend 3mm dry.
 
Tranona said:
Rule of thumb is 30 minutes per inch thickness - so not long at all. Probably another experiment for you. However I think you will be able to bend 3mm dry.
Click to expand...

Are you sure, i have always gone with 1hr per inch.


I agree that 3mm will bend but to steam it, will that not make less chance of snapping ?
 
Seems like you want to try steaming
Select your wood carefully try and get as straight grained as possible and have you allowed for springback
On a small visual compent errors on miss matched radii will be easily seen
Other woods are easier such as ash
dried wood has its cells collapsed and should dry out quickly enough
 
waynes world said:
Are you sure, i have always gone with 1hr per inch.


I agree that 3mm will bend but to steam it, will that not make less chance of snapping ?
Click to expand...

About 1 hour per inch is the usual rule of thumb. I don't really know how that would translate to 3mm thick - which is basically a veneer – I'm not sure it is a straight-line rule! The whole purpose of thin veneers is to produce a curved result without steaming - so it seems a bit perverse.

You usually bend veneers in a group rather than individually. I think steaming and bending individual layers will not produce a nice even set of curves unless you bend each one to a increasing or decreasing radius.

You could make a male and female former for the lamination – that usually works well if you don't have a length of spring steel to use as a backer.

Cheers -- George
 
I often make laminated knees, 25mm x 5 mm radius is pushing it to go round a 100mm radius one at a time but 3mm thick will be far easier. Go thinner & you will do the lot in one go with glue on them. Top tips, Always make sure the strips are smooth & have a small radius sanded on their outside corners. If you have any nicks in the grain they will break at that point as you bend them. Also put a few pins through the stack at one end, this ensures they stay together as you clamp them up.
 
Morning all, i will go with just laminating the strips then, i did fancy steaming as i made a box a while back but that will still come in handy for when i make the strakes for the dinghy when i get around to it.

I am going to invest in a new set of clamps and make a decent former and experiment a little , first with 5mm then 3mm veneers.

Thanks for all the tips and help guys ;)
 
You must log in or register to reply here.

Share this page

Top