Thread: HSC Japanese Project - Update

I’ve never done steam bending, but I doubt you’re going to be able to bend that thickness of timber to that small a radius. Is kerfing an option? Or laminating?

You need a steam bending strap to stop the cracking like in the link https://www.instagram.com/p/B-4mLm8HQ_V/. It transfers the tension on the outside into more compression on the inside. You might get compression failure on the inside which might be too unsightly if that is the show side. Lamination might be more work but it is more controllable. You could also do it by joining 2 or three shorter lengths. As Jack said, you could kerf it. I've done that in the past like in the attached. But you have to then veneer three sides.

BILD0001 (1) copy.JPG

Mic-d has nailed it. While it is possible to bend straight-grained timber to surprisingly tight radii with proper steaming and a compression strap, I think you're pushing it. You'd be better off laminating it. If you use 2mm laminates and tinted epoxy the laminations will be almost invisible. You can probably use ratchet strap clamps to bend the laminates around a form.

Originally Posted by jack620

I’ve never done steam bending, but I doubt you’re going to be able to bend that thickness of timber to that small a radius. Is kerfing an option? Or laminating?

I think thats the next plan since all this steam bending isn't working and I won't be able to keep the bends consistant.

Originally Posted by mic-d

You need a steam bending strap to stop the cracking like in the link https://www.instagram.com/p/B-4mLm8HQ_V/. It transfers the tension on the outside into more compression on the inside. You might get compression failure on the inside which might be too unsightly if that is the show side. Lamination might be more work but it is more controllable. You could also do it by joining 2 or three shorter lengths. As Jack said, you could kerf it. I've done that in the past like in the attached. But you have to then veneer three sides.

BILD0001 (1) copy.JPG

I attmepted to use a ratched strap instead of the bending strap and ended up snapping the timber, I think my timber is too dense and doesn't hold enough water to be steam or water bent.

IMG_2525.jpg

Originally Posted by Josh_dennis

I attmepted to use a ratched strap instead of the bending strap and ended up snapping the timber, I think my timber is too dense and doesn't hold enough water to be steam or water bent.

IMG_2525.jpg

Good Morning Josh

I have done a bit of steam bending and curved laminate fabication an offer a few comments.

Kiln dried timber does not steam bend very well - commercial kiln driers rush, dry too fast then recondition the timber, and this impacts on the lignin. Slightly green timber is easier to bend than air dried. Green timber is easiest to bend, partially diiies during the steaming phase, then must be dried after bending. Another uissue. My preference is timber air dried to about 18% moisture content.

Geometry; bend to a circle, the inside radius is shorter than the outside radius. When bending, the outside wants to stretch, the inside wants to compress. But timber does not stretch very well and will break. When you put timber in the bending strap it tightens against the ends and this stops that timber from trying to lengthen during the bending process. Your ratchet strap does not do this.

Bending radius. I agree with the others; you are probably trying to bend too tight a radius. Try bending a piece of laminate around you radius. If it breaks or will not ben, then thin it a little and try again. The laminations are not all that obvious unless you look for them, and then become a design feature. Here is an example with 2.5 mm laminations, not bent as tightly as you propose.

Detail - Lamination.jpg
Detail - Lamination

PS: I have never been able to combine steam bending with laminating. The slightest misalignment and a gap will open in the curves.

hi Josh

Yes Graeme Cook is correct.

Kiln dried timber is extremely if not sometimes imposable to steam bend, depending on the level of the kiln drying, sometimes they over dry and cook the legume into a resin in the timber and then re-hydrate the timber but the resin remains hard.

It looks like you have black ebonised the timber before bending this can also make the timber brittle and is better done after the steaming.

I have always had better luck laminating as part of the bend, but also pre steam bend thiner pieces. (I usually laminate the pieces wider and longer so to compensate for any slippage during glue up and then trim down to size). So as a rule I dimension after bending.

If you use a double sided mould rather than the strap one the outside of the form shown in your image, the form will result in a better bend or use a steel strap with clamps it will also be less likely to break.

The radius is very tight. It looks like you don't need a full 90º bend so I would be reducing the radius you are trying to bend.

But braking wood and the disappointment caused can only make you a more skilled craftsman's in the long run, good try. I have always learnt by pain.

I will run down to the workshop and get a photo of how I do bends with a steel strap and clamps.

Forgot to mention you will also have to allow for "spring back" more laminations = less spring back.

Hi Josh

The attached photo shows the bending mould I used with both a steel strap and clamps, if you notice carefully you will see a slight gap between the mould and bent lamination this occurred after the glue was set and the piece was removed from the mould. This is the spring back I mentioned.

Hi again

Here is the piece I cut off after I removed the lamination from the mould, as you can see it's 12 pieces in total.

Originally Posted by GraemeCook

Good Morning Josh

I have done a bit of steam bending and curved laminate fabication an offer a few comments.

Kiln dried timber does not steam bend very well - commercial kiln driers rush, dry too fast then recondition the timber, and this impacts on the lignin. Slightly green timber is easier to bend than air dried. Green timber is easiest to bend, partially diiies during the steaming phase, then must be dried after bending. Another uissue. My preference is timber air dried to about 18% moisture content.

Geometry; bend to a circle, the inside radius is shorter than the outside radius. When bending, the outside wants to stretch, the inside wants to compress. But timber does not stretch very well and will break. When you put timber in the bending strap it tightens against the ends and this stops that timber from trying to lengthen during the bending process. Your ratchet strap does not do this.

Bending radius. I agree with the others; you are probably trying to bend too tight a radius. Try bending a piece of laminate around you radius. If it breaks or will not ben, then thin it a little and try again. The laminations are not all that obvious unless you look for them, and then become a design feature. Here is an example with 2.5 mm laminations, not bent as tightly as you propose.

Detail - Lamination.jpg
Detail - Lamination

PS: I have never been able to combine steam bending with laminating. The slightest misalignment and a gap will open in the curves.

Hi GraemeCook,
Thanks for this information, I do think my timber doesn't have enough moisture and would definitely need a timber with qualities that you are mentioning.
I'm at the point now where I'm looking into kerfing to try and achieve the radius I am attempting to bend.

Thanks for all the informaiton and example.

Originally Posted by snowgum

Hi again

Here is the piece I cut off after I removed the lamination from the mould, as you can see it's 12 pieces in total.

Hi Snowgum,
Thanks for all the suggestions and examples.
As GraemeCook has mentioned I believe the moisture content in my timber is too low therefore the other reason for it snapping.
I'm looking into kerfing now so I can keep consistant profie and repeat over multiple times.

Thanks

Hi Josh

Thank you for taking the time to reply.

Originally Posted by Josh_dennis

I'm looking into kerfing now so I can keep consistant profie and repeat over multiple times.

Thanks

If you want to do it by kerfing you can do it very simply by handsaw and a bit of mathematics. If you want to do it on a table saw try and use a blade with no more than a 1.5mm kerf. In fact 1.5mm kerf for the handsaw is good too.

Your bend is a radius of 72.5mm (r). Because the stock is 20mm wide the outside radius is 92.5mm (R). The proportion of outside length to inside length is therefore R/r which is about 1.28. So your segment length on the inner radius is 50mm. The outside radius will have a length of 50 x 1.28 ~ 64mm. So you kerf evenly over a length of stock of 64mm and you need to remove 14mm of material to achieve 50mm length on the inner radius. If you use a handsaw with a 1.5mm kerf, you will need around 9 (14/1.5) evenly spaced cuts to achieve this. Your segment length is 64mm so you need cuts about every 7mm (64/9) along that segment to achieve the bend.

If you go larger than 1.5mm kerf, like say 3mm on the table saw, the kerfs may start to telegraph though to the outside of the curve. If you go smaller, for example the saw in the image I use to kerf has only a 0.7mm kerf, you need a cut about every 3mm. These small segments can become quite fragile and need great care not to break them when bending, although you should use your bending jig for glueup to introduce the curve evenly.

The image shows my jig for kerfing (see how old the photo is by the phone!). Two pieces of stock create a channel exactly the right size for the work to slide through. The saw is made to kerf to the correct depth with a depth stop (this depth you will have to optimise by trial but try around 3mm edit by this I mean leave 3mm short of cutting right through). Once a cut is made, it is advanced to the index finger which sits in a kerf at the distance you calculated, in this case 7mm and the next cut is made and then on until you complete the number of cuts required. It's very fast. Then you just have to glue up on your jig and veneer the 3 sides.

It's best if you leave enough waste on the end to control the bend right to the end, ie don't start cutting 7mm from the end or you will have trouble controlling the curve to the very end and you may find you may want to make a few extra cuts into the waste to help establish the curve. You'll work it out.

BILD0003 (1).JPG

You know, possibly a better way to kerf in this case is on the outer side of the curve. Have a look at #woodworking #builder #build#carpenter #trending #fyp - YouTube

if you colour and grain match the wedges to the wood of the curves you may not even have to veneer.