Thread: Trouble Shooting Splined Bent Lamination

Laminated Bends Using the Insert Method

Laminating and Bending Wood

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I suspect that to get the sharp angle you want you're going to have to look into steaming the splined end and splines before bending.

Thinner splines may help, but you're still trying to put a "sharp crease" in the wood instead of a simple radiused bend... .

I re-clamped the bend trying to see if I could apply pressure more evenly. Against common sense it seems to work better to clamp the laminated bent section and then clamp the solid wood part later. Also I get a better clamp up by bending at the mid point of the lamination's I want to bend.

If I make the tolerance for inserts tighter and lamination's thinner I hope to correct any gaps.

I think steaming is definitely on the table, and using polyurethane glue.

I am arranging to get my splines drum sanded down to 2mm I think that will make the bend easier.

I have seen the sharp crease bend in looks way cool and can be done but it is difficult.

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I see two issues with your setup,

1. The gap at the ends of the inserted laminates appears to be caused by the thickness of the inserted material being substantially thinner than the saw kerf width. It should be a firm fit with only enough clearance to enable a sufficient glue film thickness when clamped under moderate pressure for glue squeeze out.
2. The inner or "male" form must be radiused to match the form and not left as shown. The angle will create compression / bruising of the inner most laminate, and possibly others that may compromise structural integrity. Spending the time to make better forms that match the inner and outer radii will be well spent!

Cold bending wood around a tight radius is a big ask at any time, and always carries the risk that the laminates may fracture in the process. Some species will cold form / hot form better than others. Steam bending is always preferable to cold forming.

In the 1970's we built the frames for 16' sailing skiffs from laminated sections of Australian Red Cedar and Northern Silver Ash that was always steam bent even for a relatively large bending radius. Less risk of fractures and far less or at least more controllable "spring back."

Tessa (ceased trading) is perhaps the best example of bent lamination furniture in Australia - the web site has a short video showing how they bent laminates into very tight radius bends. Tessa Furniture - Quality Without Compromise between 1968 and 2019

At this point I am figuring things out, so its not going to be perfect.
I will work on the bending form and make more accurate inserts.
I am using Elm which has good bending properties.

T'sucker, id put a radius on your inside mould former and start clamping at the point where laminations are staggered where you show your 2nd clamp point, that way the other "open end" laminations are free to move when bent

I made a template from Masonite today. It now has a soft curve that transitions into the 20º angle while retaining the relative straight lines.

I can the use it to route the mdf to build the former.


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Here’s a bent lam I did about 30 years back in Saskatoon.
Looks like NG Rosewood but probably Paduk.
From memory stock veneer about 1mm thick.
Ended up 1” dia inside rad about 30mm.
Can’t remember what glue.
Was in a mate’s ‘shop, we made full inner and outer forms and heaps if clamps.
H.

Here is Alvar Aalto's classic stool #60 that TS is trying to replicate.

Alvar Aalto Stool 60.jpg

I do quite a bit of laminating and steam bending, For such a sharp and precise bend with relatively thick veneers I think that you should use both.

Because of the level of precision needed, you will need constant pressure along the entire laminate, not just the bend. I think that you should make both male and female bending forms. Note: the radius of each bend will be slightly different, because of the thickness of the legs.

Then I suggest that you pre-bend the legs by steam bending. When cool and dry, then do the laminating. There must be absolutely no gaps after clamping.

I usually do 4 or 5 dry runs before I am satisfied with the process before I risk glue!

Timber for bending should be air dried and slightly green with a moisture content of 18-20%. Kiln dried timber is not ideal, especially if it has been "reconditioned".

I have been making the male and female bending forms with the 30mm offset for the stock. Lined with cork to fair the form.
Using the shoddy practice piece I had from before I have been able to close up the laminations much better with the new form.
However I will make the laminations in real piece much thinner at 1.9mm (bandsaw kerf) and I should end up with a near perfect glue line.

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It as been an interesting experience building the former. Still need to plastic wrap it for glue.
I have arranged access to drum sander to machine the shims next week.

Coming along nicely TS but you have really jumped in the deep end. Laminate bending has a real learning curve; quite difficult until it suddenly gets easier... And those little splines are way out there on the "real difficult" end of the spectrm.

I always make the bending forms at least 50mm, preferably 100mm, longer at each end to ensure smooth curves. And cover everything with plastic sheet or lots of parafin wax to stop the glue sticking. A I have always done the glue up in one go.

In your example where the laminate only partially fills the clamping area then you may get uneven pressures and the laminate may spring apart. Its just simple leverage. Over tighten clamp A and it may cause the laminate to spring adjacent to clamp C.

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It might be worth you making a "practice chair" with full length laminates and then when you are happy with your technique re-start the insert spline project. There is a real learning curve involved.

TS , it also looks your cuts in parent stock are inconsistent widths. Are you using a bandsaw with new blade and shims against fence? The purpose of shims is that they are the widths of your cut and parent material so that when you remove one it sets you up for the next cut. You prepare one shim for each cut leaving the fence on one setting.

Originally Posted by GraemeCook

In your example where the laminate only partially fills the clamping area then you may get uneven pressures and the laminate may spring apart. Its just simple leverage. Over tighten clamp A and it may cause the laminate to spring adjacent to clamp C.

A simple solution to prevent that is to prepare a few spacer blocks at the width / thickness of the "parent" stock, or use scrap off cuts from it. Then use them where Graeme has marked ""Gap."

"Problem Solvered."

Originally Posted by Mobyturns

A simple solution to prevent that is to prepare a few spacer blocks at the width / thickness of the "parent" stock, or use scrap off cuts from it. Then use them where Graeme has marked ""Gap."

"Problem Solvered."

No, no, and no. I think that this is one of those "solutions" that is good in theory, but not so good in practice.

When you put the glue between the laminates you are effectively lubricating the laminates and they wish to slide everywhichway, usually where you do not want them to go. One solution is to put a tiny amount of sand or salt in the glue; this minimises the lubrication and makes them a lot more stable, but it is still a "slippery" operation... Adding a loose spacer just complicates an already difficult operation.

I frequently have to add a couple of clamps orientated vertically to resist any attempts at vertical sliding by errant laminates.