How to bend wood like this - Outdoor furniture project

[Alan Lightstone]

So, been busy working away on this (when I have time, which lately has been not enough). Ran into some interesting issues.

1.) I was getting very poor resaw pieces. Big variation in thickness. Looking more closely, my tall bandsaw fence really was making things worse in a way. My resaw fence had the same tall height past the blade until the end of the table.
Bandsaw Tall Resaw Fence 1.jpg
Made attaching it easier to the factory fence, but I clearly was running into the issue of the wood's internal tension pushing against the fence after the cut and moving the wood. So I cut off the fence about 2" or so after the blade, and that seemed to help. Thanks, Derek for that tip (and others).

2.) Processing 8' long 8/4 white oak is way too heavy for me. Really a bad idea. I was worried about more waste using 5/4 or 4/4 boards. But after several resaw cuts are made, the 8/4 board becomes a much lighter, thinner, easier to handle board. Really will use that approach in the future.

3.) I think, looking at the quality of the resawed boards as they come off the bandsaw, that my blade must be dull. I'm able to fix that with MULTIPLE runs through my wide-belt sander on a sled I built, but that also really reduces yield. I've had to make about .25" resaw cuts, and then sand them down with multiple runs through the wide-belt sander to get to a final thickness of about 0.15". Really wasteful of wood. I chose 0.15" thickness of the laminations as it's an even multiple of 1.5" final thickness, and it seemed I needed to go that thin to get smooth boards off my lousy resaw cuts (and should be able to bend, I hope, considering the kiln-dried white oak I am using.)

3.) I did get double-sized tape to work well keeping the wood on the sanding sled. I remove it with a squirt of denatured alcohol. Amazingly, I called the company's tech support and asked which solvent to use, and they had no idea. Eventually he through out mineral spirits, which does nothing, BTW.

4.) Steaming the pieces (I'm trying a few now to test) is annoying, and it is a massive rush to get them in the bending jig, but I can do two at a time.

5.) Now, my biggest issue. When on the bending jig, I tried for the first time two pieces at a time. But there is a big gap between pieces, despite tightening down the clamps and tightening the winch. How can I fix this? I have a piece of metal going all the way around the jig, in theory pushing the wood towards the form, but those gaps between pieces (which are sanded very smooth), are preventing this from being built.
Bending Wood on Frame with Gap 1.jpgBending Wood on Frame with Gap 2.jpgBending Wood on Frame with Gap 3.jpg

Now when that Australian woodworker was using a similar setup, he made a packer (I think that's what he called it) of multiple pieces of veneer and had that inside the metal sheet to even out the pressure. I didn't use that. Is that necessary? Is that what I need? It looks like I need more pressure on the wood, but I don't know how I can do that. Physically, I don't have the strength, for sure, and mechanical advantage doesn't seem to be enough here.

[Kevin Jenness]

Have you considered using air pressure? A section or two of firehose and a caul trapped between a two piece form will supply higher and evenly distributed pressure. Short of that, use cauls and more clamps. Drill more holes, offset from the first ones, and use two clamps in each hole, one up and one down. Use bending plywood and cross-blocks to spread out the pressure.

[Mike King]

If you are getting gaps, then your laminates are likely too thick for the radius of bend you are attempting to get. What is the width of the laminates you are using? Why not use a planer as opposed to the wide belt sander to thickness the laminates?

[Alan Lightstone]

If you are getting gaps, then your laminates are likely too thick for the radius of bend you are attempting to get. What is the width of the laminates you are using? Why not use a planer as opposed to the wide belt sander to thickness the laminates?

The laminates are 0.15" thick. They bend without breaking, fortunately.
I can get very consistent thicknesses from my wide-belt sander. My jointer is a little off side to side (long story). I've also heard that running very thin laminates through a planer can sometimes end in quite the destructive scene.

I'm thinking of using either some wood laminates inside the bending steel to provide a less flexible backing for the bend, or using wide ratchet straps as I've seen some people do. I hate the concept of having to rebuild that jig again.

I've seen 4" ratchet straps, but can't seem to find 6" wide ones.

[Mike King]

The way I was taught bent lamination (by Michael Fortune and Adrian Ferrazzutti) was to thickness the laminates on a planer. Michael uses a lunchbox planer to thickness his laminates; he thinks that the rubber feed rollers provide an optimal amount of pressure for thin laminates. If you are using a larger planer and the laminates are as thin as you state, then you can use an auxiliary bed for the planer: it's simply a piece of melamine with a cleat on it that is less than the width of the planer bed. The cleat goes down on the infeed side of the planer bed and holds the auxiliary bed in place -- wax it, and you have transformed your planer into a thin laminate thicknesser.

The issue isn't whether the laminates bend without breaking; it is whether they bend sufficiently to follow the shape of the form. That's not happening at the moment. Looking at your form and clamping process, you do not have a sufficient number of clamps to apply pressure throughout the entire assembly. Pressure moves from the clamp at a 45 degree angle. With the minimal number of laminates you have and the spring steel cover, you have big gaps where no pressure is being applied to the laminates.

One thing you could try is to use strips of ⅛" thickness hardboard as the cauls on top of your laminates. You'll need a fair number of them to spread the clamping pressure to more of the laminates, say 6 or more. Cover the one against the laminates with packing tape to keep it from sticking to the laminates.

A firehose blown up pneumatically with an outer form could also work. But somehow you need to distribute the clamping pressure over more of the form and laminates.

Mike

[Maurice Mcmurry]

All of my fixtures have as many spots for clamps that the space allows. This fixture looks excellent but there is room for more clamps. For something this wide I make the form flippable and put two clamps in each spot, top and bottom, both of which press on a stiff caul. Commercial set ups for this type of press are massive iron forms with hydraulics.

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circular laminating press snip from the web

[Alan Lightstone]

Thanks Maurice, and Mike. Not sure I understand the firehose, though.

Another thought I'm having and am planning on trying is with two 3" ratchet straps. Have to figure out how to use them with this, connection points, etc...

I agree and will have to figure out using some 1/8" wood or hardboard as cauls on top of the laminates. I think this is also a large part of the problem. I didn't realize that hardboard could bend. Never use it or thought about it. The thin metal banding I am using (the thickness was suggested by the metal supplier) is also an issue. Thicker might not bend, but this thin it is not transmitting the force evenly.

Still wondering if not pre-bending the laminates with steam will make gluing up the laminates FAR easier to glue up as opposed to having to spread glue on pre-bent laminates.

I could run my laminates through my planer on the sled I'm using on the wide-belt sander. Outside of saving time and steps, is there some other advantage to that? The wide-belt provides finished laminates that are quite smooth and consistent in thickness. The planer would leave some blade marks. I could see running through the planer once and then the wide-belt, but still not sure of the advantage to using a planer for that.

[Jerry Bruette]

I haven't been following the whole thread but checking in once in a while. It's a pretty interesting project you've taken on.

You could gain some mechanical advantage by going with multiple reaving with your pulleys. Put double pulleys where you have the singles now, then mount singles closer to the winch. Run the cable from the winch through one side of the double sheave, then through to the single sheave and back through the other side of the double and out to your attachment point on the metal. This should reduce the amount of force you need to turn the crank on the winch.

[Mike King]

There are two advantages to using a planer as opposed to a sander to thickness the laminates. The first is speed. The second is that sanding embeds grit from the belt in the wood and that grit will affect any edge tool you use thereafter on the bent lamination.

Pre-bending the laminates isn't going to help you with the issue which is distributing the pressure over the laminates when they are glued up -- you still need to think about the pressure lines off of the clamps.

I've never used firehose myself, but have heard of using it to provide pressure. Here's a link that gives you an idea of how this works:

https://www.instagram.com/p/BBTT9F9oK6U/?utm_source=ig_web_copy_link

There's clearly some issues with this approach: a) there's a lot of pressure involved, and a catastrophic failure can be dangerous, b) I don't know of any sources of information on how to do this -- maybe you can find it, but my googling wasn't promising, and c) the width of the fire hose may not conform to the width of your assembly.

The ratchet straps may be your best solution. However, I suspect that you will still need to clamp the long straights as the ratchet strap is unlikely to apply sufficient pressure to those elements.

One thing that hasn't been mentioned yet is that you need to use an odd number of laminates. This puts the pressure of slip once the assembly is dry in the interior of a laminate rather than on a glue line.

Mike

[William Hodge]

I agree, 2" truck straps work great. Pad the laminations with some bending plywood.

The note above warning about sanding wood to be machined is right on. Any sandpaper touching wood will dull your cutters.

Using clamps to bend wood is so hard to do, it's really awkward and next to impossible to spread the force from such a small clamp foot print.

[Mike King]

Alan, I just went back and reviewed some material I have from Michael Fortune. Take a look at how many clamps he has to ensure that the pressure is distributed through the laminate assembly. Also, notice that he has an interesting caul assembly: a strip of bending plywood with blocks, then some padding (likely hardboard or bending plywood), then the laminates.

bending caul.jpg

He does have a reference to using a pressure hose, but warns that it can be very dangerous...

Mike

[Alan Lightstone]

There are two advantages to using a planer as opposed to a sander to thickness the laminates. The first is speed. The second is that sanding embeds grit from the belt in the wood and that grit will affect any edge tool you use thereafter on the bent lamination.

Pre-bending the laminates isn't going to help you with the issue which is distributing the pressure over the laminates when they are glued up -- you still need to think about the pressure lines off of the clamps.

I've never used firehose myself, but have heard of using it to provide pressure. Here's a link that gives you an idea of how this works:

https://www.instagram.com/p/BBTT9F9oK6U/?utm_source=ig_web_copy_link

There's clearly some issues with this approach: a) there's a lot of pressure involved, and a catastrophic failure can be dangerous, b) I don't know of any sources of information on how to do this -- maybe you can find it, but my googling wasn't promising, and c) the width of the fire hose may not conform to the width of your assembly.

The ratchet straps may be your best solution. However, I suspect that you will still need to clamp the long straights as the ratchet strap is unlikely to apply sufficient pressure to those elements.

One thing that hasn't been mentioned yet is that you need to use an odd number of laminates. This puts the pressure of slip once the assembly is dry in the interior of a laminate rather than on a glue line.

Mike

I'm speechless after seeing that firehose picture.

[Alan Lightstone]

The ratchet straps may be your best solution. However, I suspect that you will still need to clamp the long straights as the ratchet strap is unlikely to apply sufficient pressure to those elements.

One thing that hasn't been mentioned yet is that you need to use an odd number of laminates. This puts the pressure of slip once the assembly is dry in the interior of a laminate rather than on a glue line.

Mike[/COLOR]

I agree about the long straights at both ends of the curve. I think that will need clamping and may be the big issue. On the other hand, adding a big piece of wood outside the ratchet straps and clamps I would think would distribute that pressure well.

Been also going through my brain about how this could be done with vacuum bagging, but can't quite get my head around that approach.

[Mike King]

For vacuum bagging, you place the laminates in a bag without a platen (with breather mesh to allow the air to evacuate), draw the vacuum, then bend the assembly in the bag around your form. You need to clamp the bagged assembly around the form. It's best to have a polyurethane bag as opposed to a vinyl bag as they are more flexible. Adrian Ferrazzutti showed us this technique for another student in the workshop I did with him at Anderson Ranch. It was cool.

Personally, I think I'd go with the caul approach Michael Fortune used in the slide I posted above...

Mike

[Maurice Mcmurry]

Here are some forms with access to both sides. I will try to dig the round window form out of the shed. It is set up like a BBQ rotisserie.

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