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Advice on using strap clamps for bent lamination

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Forum topic by jtrz posted 04-07-2017 05:42 AM 1150 views 0 times favorited 6 replies Add to Favorites Watch
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jtrz

69 posts in 1012 days


04-07-2017 05:42 AM

So, it’s been a few years since I first tried bent lamination and I’ve got some ideas for some projects floating in my head so I figured it was about time to give it another go. Instead of going the route of making a male and female form and a ton of clamps I am thinking of just doing a male form and using some strap clamps.

The strap clamps should, in principle, provide even pressure. I’ve seen some photos of people using them for bent lamination and for steam bending they seem to be the go to method. So does anyone have any experience using strap clamps in this way or just any experience with strap clamps at all? Any advice on the best type of strap clamp? Aside from strapping things to the top of a car I don’t have any experience working with them, especially when it comes to using them in the woodshop.

I am always trying to find the easiest way to get things done, mostly because I’m lacking a proper woodshop and the tools to fill it. This includes finding a good source for thin strips of wood. I am really thinking about just going out a getting a benchtop planar but until that happens I’ve got to figure out something else. I have an old craftsman table saw that is definitely not going to give me nice 1/8” thick pieces of wood and no band saw either.

What I do have are a bunch of rolls of paper backed edge banding that I found in an old warehouse buried under a pile of who knows what. I found the rolls maybe 8 years ago and I would say they were sitting in that warehouse untouched for at least 10 years. But they are in surprisingly good shape, if not a little dry. Just playing with a stack of 5 or 6 I can roll them up into pretty tight radiuses.

The problem is that it is edge banding and three pieces put together are only about a 1/16”. That means I’m gonna need 12 ply’s just to get a 1/4”. And 12 ply’s is a lot of work for a 1/4” thickness. I’m probably just going to make small little objects not furniture or anything so I’m pretty sure a 1/4” will be strong enough. Bent plywood is crazy strong. I think I’ll try laminating a bunch of strips that are 3 layers thick and then laminating those together when it is bend time. I really don’t want to deal with aligning 12 flimsy veneer strips covered in glue. What a nightmare.

So it most likely won’t work as well as I hope or at all. I’ve been trying to think of where I can come across a wood product that is fairly thin. I was thinking maybe of looking at cabinet toe kicks but they may be too thick for bending. Trying to think outside the box here. Anyone have any ideas of some wood that is usually used for some entirely different purpose but may work?

At this point I would say I am in experimental mode and not necessarily project mode. Once I stumble across the right material and method, I’ll let that guide my design process.

Thanks


6 replies so far

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runswithscissors

2565 posts in 1864 days


#1 posted 04-07-2017 07:17 AM

I might have some suggestions, but would need to know how wide your lamination needs to be, and how long. You can make thin strips quite easily with a ripping sled. Also you can do a combination of heat bending and laminating that lets you make a strong lamination without an excessive number of laminations. Note that it’s heat, not moisture, that allows wood to bend. If you have a heat gun (HF has a cheap one), you can experiment around with that.

I’m not sure what you mean by strap clamps, at least for laminations. For heat bending, you do want to use a metal bending strap on the outside of the bend. Otherwise, you’ll splinter the outer face of the wood. The best I’ve found is the steel strapping they use for sling loads of lumber. Check the dumpster down at the lumber yard.

More on this later. I’ve gotta run.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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Fred Hargis

4764 posts in 2332 days


#2 posted 04-07-2017 11:06 AM

I’m only guessing, but the times I’ve done bent lamination’s (never tried with edge banding) the glue squeeze out was significant. I would think you could do it once with a strap clamp, after that it would be such a mess with glue you wouldn’t be able to use it. But that is just a guess.

-- Our village hasn't lost it's idiot, he was elected to congress.

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EricTwice

230 posts in 372 days


#3 posted 04-07-2017 12:12 PM

When you are cold molding (bent laminating) you need to do it all at once and not in steps. I have had great success with an inner and outer form and trapping the lamination between. I use cleats along the side of the form to control pieces and to mate inner and outer forms. If the forms are substantial it only requires a couple of clamps.

For small tight curves thin veneer is great. Your edgebanding will work well. If you don’t have a thickness sander (even a planer isn’t good enough to get 1/16 for bending) you might want to try a steam box. they are not difficult to make and working with a hot noodle might be easier than the glue on uneven layers in a form that isn’t exactly perfect.

-- nice recovery, They should pay extra for that mistake, Eric E.

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jtrz

69 posts in 1012 days


#4 posted 04-07-2017 11:32 PM

Thanks for the responses.

runswithscissors:

I don’t really have a particular goal in mind at the moment. I am really just interested in seeing how edge banding performs in bent lamination and if ratchet strap will allow me to do away with a bunch of clamps. I am going to set up a real basic form tonight or tomorrow with a decently tight radius. I bought these little plywood circles and ellipses (or they may be ovals) that I came across when I had the misfortune of finding myself in hobby lobby a few months back and I will probably just strap them onto some mdf and flush route to get a form.

The edge banding is so thin I am sure I could get extremely tight radii. I am actually a little optimistic. I think it will work. With the edge banding there won’t be any need for heat or steam. I’ve been trying to find a metal strap of some kind that you can be ratcheted but no luck so far. That would be ideal.

Fred:
Yeah last time I did bent lamination, the first few pieces I went overkill on the glue and man what a mess. I’m definitely going to protect the strap from the glue. My buddy that I borrowed it from probably wouldn’t be to pleased to find that his strap had become more of crusty stiff whip.

Eric:
I am trying to put off making the female mold right now because I want to see what the thickness ends up coming out to. Once I have found a method I am happy with and I actually come up with something interesting to make, then I’ll do it the right way with a male and female mold.

I did find some 1/8” thick oak toe kick at Lowe’s that is pretty cheap. From what I’ve read oak is actually a good wood for bending. And it would be nice to produce something that is wider than an 1.5”. I’d love to get my hands on a thickness sander but I’m more leaning towards a budget planer. I’ve got my eyes on a Wen planer. The price is very right and I’ve actually read a lot of good reviews for it

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runswithscissors

2565 posts in 1864 days


#5 posted 04-08-2017 12:03 AM

To expand on what I said earlier: To heat bend a piece of wood, I always used a steel bending strap, preferably as wide as the wood strip. It (and the wood) should be longer than needed for the finished work. One end I clamp, with the strap, in a bench vise. The other end I clamp with a C-clamp. Then play the heat along the face of the wood. This will be the inner face of the bend. After a few minutes (be careful not to scorch the wood), grab the C clamp and start to flex the wood toward you. Keep steadily increasing pressure on it. You can feel the wood yield as it heats up. Continue heating and bending until you have the desired curve, and then beyond. That is, over bend, as there will be some spring back. This is true of laminations as well. Remove the heat, and hold the bent wood for a few minutes. It really is surprising how quickly it will cool enough to hold its shape. If you bent too far, you may have to reheat the wood to relax it a bit.

Once I needed a 10’ long oak crown molding for my kitchen. The only thing I could find was bent like a ski—seriously bent! I used my heat bending method (no bending strap, however) to straighten the molding out, and it worked perfectly.

Obviously, the thicker the material the less of a bend it will take. If you need to go thicker, you can pre-bend as many lams as you need, and then glue and clamp them for a very strong final product. You can do this with plywood, as well. I have done it with quite broad pieces of 1/8” ply. There is still enough flex after bending that they will “spoon” together nicely, but once the glue is cured, you will have a very stiff, strong result. With plywood, don’t bend across the face veneers, but with them.

I’d suggest experimenting with woods you have. I’ve heat bent white and red oak, yellow cedar, black locust, and white ash.Walnut is so-so. Doug fir, hemlock, and phillipine mahogany do not respond well. I know there are other woods that bend well, but I haven’t tried them. (Elm, for example).

I like this method because it is very quick. No steam box is needed. After bending, you don’t have to wait for anything to dry out. Unless you overdid it and scorched the wood, there is no staining or discoloration. You don’t have to wait for glue to dry; and there is no raising of the grain.

First photo shows an experimental shelf bracket I wanted to try. The bent wood is 5/16” thick white oak, which is one of the best woods for bending. Width is 7/8”

Second photo shows heat bent/laminated plywood “shelves” or bins for under a sink vanity. The plywood was 4 mm, which was a little too thick for this application, but I didn’t have any 1/8” (3 mm) on hand.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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runswithscissors

2565 posts in 1864 days


#6 posted 04-11-2017 04:37 AM

Another thought: steam bending very thin wood is problematic because the thinness lets the wood cool too fast. It will probably be too cool by the time you move it from the steam box to the form. So you’ll just be bending wet wood.

I found this out when building a little model lapstrake dinghy from a Howard Chapelle design. The white ash frames had a section of about 3/32 by 5/32. Heating them in a teakettle only took a minute, but I couldn’t get them bent into the planked up hull (which is how you frame a lapstrake boat, usually) fast enough to avoid breaking them.

But, being winter, I was standing next to my hot stove pipe, so I tried bending them on the pipe. Worked so well that I ended up writing an article on the method for Wooden Boat magazine. That would have been around 1993 or 94, I think.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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