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Laminating Wood #1: Laminating Wood, Part 1 - laminating curved parts in wood

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Blog entry by GnarlyErik posted 123 days ago 1320 reads 5 times favorited 11 comments Add to Favorites Watch
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Laminating Wood

The word ‘laminate’ comes from the Latin ‘lamina’ meaning ‘thin slice, plate, leaf or layer’ which is pretty close to our modern meaning. Funny how that often works, eh?

During my career I have learned a fair amount about laminating wood. There are surely others out there who know far more about specific sorts of laminating than me and I do not pretend to know it all, but am happy to share what I have learned.

There are several reasons for laminating or glueing separate pieces of wood together, to wit:

1. To construct a curved shape in wood with a shorter radius bend or curve than a solid piece of wood can achieve without breaking;
2. To make a larger and bigger construction out of smaller pieces, as in a tabletop;
3. To make a stronger construction, as in a laminated beam;
4. To make a shape curved in three dimensions, as in boat hull or bowl;
5. To construct something more dimensionally stable than something made from a solid piece;
6. To apply a ‘finish’ layer to less attractive stock;
7. To economize on material use in curved parts by eliminating waste sawn from solid pieces.

Often a lamination is made for a combination of the above reasons. But generally speaking, many laminations are done for one of the first two reasons. That’s where we will start.

CONSTRUCTING A LAMINATED CURVE IN WOOD

A general rule of thumb: The more layers in a lamination, the better it will hold its shape, and no lamination with less than three layers can be depended upon to keep its shape (unless it is flat!). In other words, more layers are better for dimensional and shape stability. And, no matter how many laminations there are, there is always some amount of ‘spring back’ as the wood attempts to return to its original orientation. I sometimes glue in several hardwood dowels or pegs at right angles to the laminations after clamping the lamination to try to combat slippage and spring back.

Some allowance must usually be made for spring back, and unfortunately forecasting how much comes only through experience, trial and error and observation. Alternately, a lamination can be made oversized and trimmed back to the desired curve after the glue is set, but this can present problems with appearance and always seems very amateurish to me.

Bending form or jig: First, the curve is laid out graphically on a bench top, plank, or piece of plywood, making due allowance for anticipated spring back. (See Fig. 1)

The surface used must be sufficiently strong and dimensionally stable enough to withstand the considerable strains which will be imposed by the material being clamped. It is also wise to draw your curve somewhat beyond the length you need so that the ends go ‘fair’ when bent and do not end up with flat spots. Some sort of form is then constructed along this (new) line to hold the laminations to the desired curve(s) when glued. This must be on a flat surface (unless making a three-dimensional curve!) The ‘jig’ or ‘form’ can be as simple as nails or screws driven along a curve drawn on a bench top to which the layers are bent and/or clamped as they are glued up. This kind is useful only for very slight curves and generally not strong or secure enough for tighter curves. More often simple or elaborate clamping blocks are used. Sometimes a curved shape is sawn into a piece of blocking to serve as something to clamp to, especially in the case of multiple curves of changing radii. (See Fig. 2)

Sometimes sawn blocking is made for both the inside and outside of the desired curve, but generally not necessary unless the finished thickness of the part is critical. Whatever kind of form is used it must be strong enough to withstand the strain of pulling the layers to your curve(s) and then holding them in place until the glue sets. A considerable amount of force is usually needed to force multiple layers into place, especially on tighter curves. It is very frustrating to have a clamping block tear out as all your glued layers are being pulled to your desired curve!

I do a fair amount of laminating with different curves on my projects, so I have made myself semi-permanent clamping blocks which are securely screwed down to the bench top along any desired curve drawn there, and then removed after each use. (See Figures 3 thru 5). Note these have a PVC nose to allow the laminate to bend across the face without danger of getting flat spots. The nose is also tabbed through a larger bored hole to allow alignment to the line being curved to. They can be used on either inside or outside curves. These also have the advantage of holding the lamination clear of the bench while the glue is setting.

Use waxed paper or plastic sheet to catch glue drips and prevent your lamination from sticking to the bench or the clamping blocks. Hot, melted paraffin wax painted on the blocks or anything else which is in danger of glue sticking to works well too.

Layer thickness and length: Once the cross-sectional size of the desired part and the curve radius or radii are decided upon, the thickness of the individual layers is decided. This is normally done through trial and error, keeping in mind the three layer minimum rule. A trial piece is sawn to an estimated thickness, bent to the curve. If this can be made to bend without breaking or undue force, then all layers (of the same material) can be bent to the curve assuming there are no knots or hard spots in the individual layers leading to breakage. Layers should also be made somewhat longer than the finished part will be to allow for trimming to exact length.

Preparing the layers: Layers should be sawn slightly wider and thicker than their final dimension, typically by 1/8” to 1/4” or so. Individual layers are then planed back to their required thickness, but left wider than the planned finished width of the part. This is so you can dress the edges or your part after the glue sets as there will inevitably be some unevenness and glue drips. If the curved part is structural only and appearance is not a concern, the individual layers may simply be sawn to thickness and left un-planed if very carefully done on an accurate saw.

It is best to hold a ‘trial’ before you commit to glue. Place all the layers on your form and clamp them in place to make sure they can be bent to the form as an assembly. Try to orient the layers so that each layer’s grain offsets the grain of other layers to keep strain equalized as much as possible. This also gives you a chance to orient the layers to take advantage of appearance (best appearing pieces to the outsides!) and alternate by staggering any knots, weak or hard places in your laminates so they do not occur near each other. Once satisfied with this it is wise to number and label each layer in pencil to keep them in order and orientation when applying the glue.

Depending on the absorption characteristics of your wood, there is sometimes a risk of ‘glue starvation’ in some species. Spruce and other softwoods for example, will sometimes absorb some or most of the glue between layers, leaving little to hold them together when cured. To prevent this the layers may be pre-coated with thinned glue which is then allowed to dry before the actual glue-up. This forms a barrier which keeps the final laminating glue from being absorbed in the glue-up and does not affect the strength of the assembly.

Types of glue: Any suitable wood glue can be used for laminating wood. Obviously, waterproof glue should be used for anything exposed to the elements or moisture. Most glues like Titebond™ come in waterproof flavors, as do epoxies. It is sometimes desirable to use a glue which allows thinning (see ‘glue starvation’ above). Titebond™, and other yellow and white wood glues can usually be thinned with water within reason. Some epoxies may be thinned with denatured alcohol, which can effect its strength, but which does not really matter very much when the epoxy is being used only as a sealer. Heating epoxy also makes it thinner, and also greatly accelerates its drying time – which is actually desirable when used as a sealer. You should watch out when sealing to make sure you do not end up with glue lumps on the surface of the laminates which can cause problems unless removed before the glueing process. Another important consideration is working time for your glue and you should use a glue which allows you sufficient working time before it ‘grabs’ or sets. 


Glueing the lamination assembly: This is the most crucial part of any lamination and must be done carefully and deliberately. It should go without saying the laminates should be clean and dry, and the environmental conditions suitable for the glue being used, i.e., not too cold or too hot. The parts are laid out in order and the glue is applied, covering all the joining surfaces (typically, just one side of each layer). The parts are stacked in order off the form as the glue is applied. Since the inside of any curve is shorter than the outside, I like to line up one end of the stack and use a small clamp or nail to hold the layers in alignment. The stack is then placed on the form or bending jig and the clamping begins – starting from the clamped end.

(NOTE: GET ALL YOUR CLAMPS READY BEFOREHAND, AND GET MORE THAN YOU THINK YOU MIGHT NEED! You should also have pre-positioned a suitable number of small wooden blocks to place under the clamps for the protection of your lamination)

The clamps are applied loosely at first, then tightened as you pull your assembly to the form or bending jig. Once everything is snug, but not too tight, use a heavy hammer with a block of wood for protection, to knock the edges of the laminations into alignment, and against the table top or blocking. Wood demonstrates a phenomenon when bent which causes it to ‘cup’ in a slight U shape on the outside of the curve (See Fig. 6).

To guard against this being an issue in the finished part, it is good to stagger the clamps up and down along the curve and/or place strong blocking under the clamp across the full width of the lamination. Cupping on wider laminates (over 3 or so inches) is harder to deal with and sometimes I resort to the use of ‘stretchers’ which can be clamped to the face of the last lamination to force it back into plumb. This is normally female (as illustrated in Figure 7), or male if needed on the opposite side of the curve.

The stretcher is merely a piece of stiff hardwood as wide or wider than the laminate, with appropriate ‘rocker’ cut into the profile to offset the cupping. It is OK to over-curve stretchers a little to allow the clamps to pull things right again. Stretcher spacing depends on the needs of the lamination being done. Occasionally, and especially in a repeat manufacturing type operation a long metal band the same width of the laminate is utilized to both combat cupping and protect the clamping surface of the lamination. Metal bands are normally not part of a one-off lamination operation however.

Now, the clamps are tightened and everything carefully examined for gaps, alignment, etc. When you are satisfied, go pour yourself a celebratory libation and allow the glue to set.

Finishing up: When the glue has set you may remove your part from the form. Just be sure to allow plenty of time for the glue to completely cure. Carefully note the amount of spring back you see as you remove the part. This will give you important empirical information to file alway in your mind for your next laminating project.

The part can now be cleaned up and planed back to its desired width and used or given whatever finish you need.

Lykke til!

-- Candy is dandy and rum may be fun, but wood working is the best high for me!



11 comments so far

View shipwright's profile

shipwright

4846 posts in 1402 days


#1 posted 122 days ago

Good information Eric.
The cupping bit made me smile. When I used to build working boats with round cornered timbered sterns we used to change up the guard (rubbing strip) material from 2” gumwood along the sides to 1” oak around the bends and across the stern. The pieces were almost 12” wide and we had to cup the timber under where the piece would bend by at least 1/4” to make the piece fit down nicely. There is just no way in God’s green earth you were going to force the edges down to flat. Of course we planed the outer surface to flat after they were all fastened up.
You’ve likely had similar experiences. It’s great to have another boat builder to BS with.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View GnarlyErik's profile

GnarlyErik

179 posts in 739 days


#2 posted 122 days ago

Hi Paul – yeah, great to swap sea stories!

Heavily built round stern wooden work boats may be great sea boats, but that part of them is sure hell to maintain in frost country. It’s really hard to keep things together back there in a marine environment through frost-thaw cycles. Everything seems to want to just come apart and spit out the caulking by Spring, especially in a stacked or layered build, and most especially if left on the hard through a winter. The standing joke in the shipyard was ‘Well, here comes another one of those national forests floating all by itself’!

Savvy owners know keeping the vessel in the water, and a little down by the stern if possible is the best way to protect such sterns in heavy frost country through the winter. My biggest yard repair dread was replacing bad pieces in a round layered timber stern with rake! Even dealing with rotten stems, frames and garboards seemed better. But, you just gritted your teeth and went for it anyway.

Stave built sterns on frame seems to work better than stacked timbers but never seem to look as good. Guards at the stern are the very devil to refit, and they always seem to need replacing sooner rather than later .

-- Candy is dandy and rum may be fun, but wood working is the best high for me!

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shipwright

4846 posts in 1402 days


#3 posted 122 days ago

Ah yes but on the west coast we have much better weather…... and we have yellow cedar. I know what you mean about “floating forests” though. I remember a 60’ seiner we built that had a raked timbered stern that was really an igloo made of yellow cedar 4X12. It was all in a day’s work then but man did it ever soak up the lumber pile.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View jinkyjock's profile (online now)

jinkyjock

228 posts in 179 days


#4 posted 121 days ago

Hi Erik, I have absolutely zero experience of boat-building and have a project in mind which would require me to use aforesaid techniques in miniature, so would be grateful for any feedback from someone like yourself.
I was watching an episode of Mountain Men and Eustace built a canoe from scratch. He (and a friend) built a skeleton from USB and 3×2 to get the basic shape and then laminated around this frame, which was taken out after completion. I was thinking of making a cradle/Moses basket in the shape of a canoe using the same basic method, the timbers I have available would probably be Oak/Maple/Cherry/Sycamore/Ash. It will probably be a couple of months down the line but I thought it unwise to miss an opportunity like this to gain some knowledge.
Would be grateful for any feedback from you on my initial thoughts, or even reference to some useful/appropriate information sites.

View GnarlyErik's profile

GnarlyErik

179 posts in 739 days


#5 posted 121 days ago

Hi Jinkyjock- thanks for your comment.

There are at least two basic ways of laminating three-dimensional curved shapes like boats. I’m not sure what you have in mind, but it sounds like something like which is termed ‘strip-building’. In boats this kind of construction is always covered with some sort of membrane for waterproofing. In the past strip built canoes for example, were covered with painted canvas, and a flat sort of close-set framing was installed for overall structural integrity. The strips themselves are actually clinch nailed to the framing with copper tacks, and the whole built over a rigid temporary ‘mold’. Glue was normally not a part of canoe building, so that was not actually ‘laminating’. This kind of canoe construction is still being done by a few builders today.

There is a second strip building method for boats which uses thicker strips glued and nailed or screwed edgeways to each other, using little or no framing. Nowadays fiberglass cloth and resin is usually the waterproofing medium in either case. Fiberglass has the advantage of becoming nearly transparent so the wood still shows through and the fiberglass fabric virtually disappears. Fiberglass is a very nasty stuff to work with however, and requires a second set of skills, tools, learning curve, etc. I personally stay as far from that stuff as I can, though do admit to using it on rare occasions when I absolutely must.

Another more modern technique is something called ‘cold-molding’. Essentially this is multiple thin layers (at least three) installed in offset directions, and usually using epoxy as the adhesive, although other glues might work almost as well, particularly in something not continuously exposed to water like a boat. Cold-molding requires careful planning in the layup, but done properly can be extremely strong. Pound for pound it can be much stronger than steel in fact. In a way it is sort of like the layers in plywood, but curved in three dimensions which makes it exceptionally rigid. The result is called 'monocoque' construction, and in practice is normally also covered with a waterproofing membrane.

I intend to cover both types (strip-building and cold-molding) under ‘laminating’ in my Lumberjocks blog in due time. If you can let me know the direction you are headed I will try to cover that sooner.

Cheers,
Erik

-- Candy is dandy and rum may be fun, but wood working is the best high for me!

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shipwright

4846 posts in 1402 days


#6 posted 121 days ago

This is likely heavier construction than you are looking for but I did a blog about a couple of cold moulded sailboats I built. You can find it here.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View jinkyjock's profile (online now)

jinkyjock

228 posts in 179 days


#7 posted 121 days ago

Hi Erik/Paul, thank you for your swift replies to my enquiry. From the info in your posts it would appear that the monocoque/cold-moulded construction would be my best option scaled down to the appropriate size.
The finished piece will never need to float so waterproofing is not an issue, and as it will only bear the weight of a child I don’t anticipate any great thickness of stock. My initial thoughts are to build the frame/bulkheads from 3/4 USB and 2×2 or 3×2, build a skeleton, and then begin to apply the horizontal laminates. Hopefully I would be able to find some process to allow me to shape the laminates in pairs to apply equally to either side.
I would need to build some kind of “box” to house a child in the centre and then perhaps have a kind of deck on either side, so I suppose it would resemble more a Kayak in that respect.
As you can see I am still very much in the research stage but the info from your posts will I feel be invaluable when I do commence, and you can never have enough preparation, preparation, preparation, as my old lecturer often said.
Once again, thank you for your help.

View GnarlyErik's profile

GnarlyErik

179 posts in 739 days


#8 posted 120 days ago

Hi again Jinkyjock

My shop built a number of cold-molded boats over the years ranging from a 31 footer up to the largest ever built at the time (a 92 footer launched in 1979 – and, even larger ones have since been built by others), so I have studied and learned a fair amount about that method over the years. It is by far the strongest boat building method there is, bar none, except perhaps some of the more exotic plastics. However, strength does not seem to be a major factor in your planned project.

If cold-molding is your technique, there is no better guide than “Gougeon Brothers on Boat Construction”. These folks were the pioneers on epoxy based cold-molded wooden boat construction, and still the best and most extensive authority out there in my book.

All that said, cold-molding becomes much less attractive in smaller sizes, although there are a few dinghies down to ten or eleven feet long done in this method. The main reason is, in order to make the tighter curves without breaking, the laminates must be super thin – down to 1/10” or less, and both hard to make and/or obtain. (Perhaps Shipwright // can help you there!)

Might I suggest you consider a less complex construction technique? There is nothing wrong with using old tried and true traditional boat construction methods, which many times can be scaled down to quite small sizes (think model boats!). For an example, have a look at one of my own projects which just happens to be a baby cradle, and a successful one at that. The baby loves it, although it has lately been converted over to a Rocky Boat with which he now terrorizes the family cat!

There are any number of good boatbuilding books available which can take you through all the steps from raw sketches to realizing your project in reality.

And I do also plan a future blog entry under, ‘Laminating Wood’ to cover cold molding fairly soon, so watch for that if that is your method!

-- Candy is dandy and rum may be fun, but wood working is the best high for me!

View jinkyjock's profile (online now)

jinkyjock

228 posts in 179 days


#9 posted 120 days ago

Hi Erik, once again thank you for expending your time and patience in laying out for me the possible construction methods I may use in my forthcoming project. As an introduction to the craft of boat-building I doubt it could have been laid out in a clearer fashion. You (and Shipwright) have pointed me in a direction, and I understand it is now down to me to do the research and development to enable me to understand the processes involved.
As I said before, this is new territory for me and the glimpse I have had informs me of how complex it can be.
Which brings me to your “Rocky Boat”, I just love it and it is just what I am aiming for. Not a toy, not a model, but a small boat built using the same techniques as for a full size traditionally constructed boat.
So for the moment I shall continue my R&D learning curve and look forward to your future blog on cold molding, and perhaps nearer the time I shall come back to yourself and Shipwright for a further conversation.
Many thanks again.
P.S. I should perhaps tell you I am not entirely a maritime novice. My ex-wife and I ran an Orkney Longliner off the coast of Skye in Scotland fishing commercially for Lobster and Brown & Velvet Crabs. They do say the sea always calls you back, hmmm…....

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shipwright

4846 posts in 1402 days


#10 posted 119 days ago

Whoa Eric! You worked on Whitehawk? What an experience that must have been. I am impressed beyond and envious. She is one of the most beautiful boats around. Way out of my league.
Did you have the opportunity to sail her?

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View GnarlyErik's profile

GnarlyErik

179 posts in 739 days


#11 posted 118 days ago

Paul – yes – see my private message to you.

Jinkyjock – wow, Orkneys and Isle of Skye! I’m jealous. I’ve made a few longlining trips in the North Atlantic off Maine, and worked on quite a few longliners and crab boats in the shipyard in Alaska, but most of those are steel and FG these days. When I have a bit more time, I will do something on what I have learned about cold-molding in this blog, and also something on solid laminating (non curved). If you have any specific questions, please just ask.

Cheers,
Erik

-- Candy is dandy and rum may be fun, but wood working is the best high for me!

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