Steam bending advice

[COWS]

Morning...

Does anyone here have experience in steam bending?

What I'm trying to achieve is a pretty tight bend. 180deg over 50mm diameter on 45deg angle. To create a twist for want of better explanation.

Material is maple cut into 4mm thick strips for laminating to 20mm thickness.
Its quite difficult getting the bend around the curve and I'm getting some minor splitting on the edges. I think this can be rectified with making sure compression is constant on the outside. Would steaming for longer make the wood more pliable? Does steaming too long have a negative effect on the wood? I've been steaming about 30 mins a piece for reference.

Also, bending the 2nd piece over the 1st goes ok but coming to the 3rd, I cant follow the same path. Is my approach to this wrong? If I were to bend each piece over the same former, would they fit together well enough for glueing up?

The realms of bending are new to me so any experienced folk here that can help me succeed would be appreciated.

Thank you

 

[Tris]

You may have already heard of him, but Tom Raffield is worth looking up for information on steam bending.
I can't help thinking you may have to go down to 2mm to get that sort of bend, although I've never done anything with that tight a radius

 

[deema]

If it’s been kiln dried it will be very difficult to get that bend, if it’s air dried, as you suggest you need a metal strap support. You need to make sure that it gets as hot as possible, insulation around the box and lots of steam.

 

[Fitzroy]

I happened to be watching this build last night, I think he is doing what you are thinking about?

 

[COWS]

@Tris Thanks for the memory jog on Tom Raffield. I have seen his stuff. I will look more into his techniques and try and learn a bit. My first test was with 2mm and made the bend with ease just using water. I'll have a couple more goes with 4mm as I have them cut already. It's very nearly there. If this is not successful I will go to 3mm.

If it’s been kiln dried it will be very difficult to get that bend, if it’s air dried, as you suggest you need a metal strap support. You need to make sure that it gets as hot as possible, insulation around the box and lots of steam.

Yes it's kiln dried. But I think it will take the curve ok. Just need to refine my method. I'm using a lorry strap for support. Would you recommend including a metal strap too?

@Fitzroy Thats pretty much what I'm aiming for in terms of leg shape. My former is a slightly different setup but using the same idea. A nice build.

 

[profchris]

From my experience bending guitar and ukulele sides, you need to try to avoid runout. Ideally, looking at the thin (3 or 4mm) side, the grain lines should run the full length of the strip. If they are angled so they meet the sides, that's where it might lift when bent. The steeper the angle, the more likely to fail.

A metal backing strap when bending helps, I've used strips of sheet aluminium (from a dead caravan).

At 2mm maple usually bends nicely with dry heat, in my case from a heat pipe. It's so easy that 3mm might work too. Hand hot enough to be uncomfortable, but watch for scorching!

You might try clamping the metal strip to the wood at either end, heating it with a heat gun (played on the metal) and gently persuading the wood to take the curve. 4mm would be a challenge dry, though.

I'd consider bending all on the same form, clamping them together to the form, and then heating dry again with the heat gun. That could allow you to close the gaps.

Finally, with dry heat you need to over bend a little as the wood springs back after cooling.

 

[Keith 66]

Im my trade boatbuilding steaming timbers is a common activity, First selection of stock, try to avoid grain runout on outer edges, Always sand the outer edges as the slightest nick in the grain will encourage a break.
Green timber is best for steaming but if all you have is kilned or air dried soak it for a few days first.
As to steaming time, i have hear all sorts of times suggested, in my experience many are far too long.
If i was steaming an oak rib into a dinghy a typical rib would be a max of 3/4" x 1/2" on which size i would go for about 10 to 15 minutes tops.
Your 4mm maple shouldnt need more than 5 to 10 minutes max.
If you leave them too long you cook the life out of the timber & will break loads more when putting them in.
Trick to do is to allow that you will break some, Pull one out of the steamer & try it, if its too stiff put it back for another 5 minutes, then try it again, you will know when its ready as it will go really floppy.
I seem to remember steaming some maple once & it steamed quite well.

 

[COWS]

From my experience bending guitar and ukulele sides, you need to try to avoid runout. Ideally, looking at the thin (3 or 4mm) side, the grain lines should run the full length of the strip. If they are angled so they meet the sides, that's where it might lift when bent. The steeper the angle, the more likely to fail.

A metal backing strap when bending helps, I've used strips of sheet aluminium (from a dead caravan).

At 2mm maple usually bends nicely with dry heat, in my case from a heat pipe. It's so easy that 3mm might work too. Hand hot enough to be uncomfortable, but watch for scorching!

You might try clamping the metal strip to the wood at either end, heating it with a heat gun (played on the metal) and gently persuading the wood to take the curve. 4mm would be a challenge dry, though.

I'd consider bending all on the same form, clamping them together to the form, and then heating dry again with the heat gun. That could allow you to close the gaps.

Finally, with dry heat you need to over bend a little as the wood springs back after cooling.

Thanks for this different approach @profchris I'm a long way down the steam method now so will possibly look at this another time. Although I will try bending them one at a time over the same former before forming them again all together.

Thank you @Keith 66 Great explanation on your method. I will take this on board.

 

[COWS]

Been back on this again today so thought I'd post an update.

Ended up using 3.3mm thick stock to give me 20mm finish, and steaming for 10mins a piece worked well. The first one I steamed for 6 mins and had splitting issues as you can see in the pics. I can loose this in the finishing so leaving it in.

I bent each piece over the last to keep the form correct. This also went to plan.

Finally glued up with epoxy and a well thought out clamping plan... which I had to frantically adapt on the fly. Standard!

Let's see how it comes out in the morning.

 

[The_Yellow_Ardvark]

Tidy.

A few years ago I was infilved in bending some oak to fit onto a canal boat, to act as rubbing strips.

We built a steame, double ended, with a drain. Insulated with foam and ex MOD blankets.
The steamers were 2 Ex Navy steam gennies

 

[Yojevol]

View attachment 151418
That last picture reminds of the game TWISTER

 

[yetloh]

Maple wouldn't be a first choice for most steam benders- ideally a ring porous species like oak or ash., but at small thicknesses you should be able to get away with maple. I have used steamed lamination (albeit at 10mm each and in ash) and found that bending them all at the same time is a much better approach, that way you are bending each laminate to the correct radius, which will be different for every piece. Speed is vital so forward planning is important and it helps a lot if you can recruit an assistant to get the clamps on fast. Some sort of fence at either end of the bend will also help a lot in keeping all the pieces aligned. As others have said, straight grain is important for success and air dried or, better still, wet timber gives you a better chance of success. Your steaming time should be ample - excessive steaming weakens the structure of the wood.

Good luck and don't forget to post pics of the finished item.

Jim

 

[stuckinthemud]

Small stuff reacts well to being boiled. Realise the job is done, just thought I’d mention it for reference purposes. Ever play with a coffee stirrer in a take away coffee??