bent lamination

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Bent Lamination http://www.woodonline.com DOWNLOADABLE ® Page 1 of 8 DS-015 ©Copyright Meredith Corporation 2002 Create curved project parts the easy way with strips of wood, glue, and a form We all know that curves are pleasing to the eye. The question for woodworkers is: What’s the best way to make them? In some cases, you can cut an arching shape from a solid piece of stock. Or you can build up a blank with mitered pieces, and then cut it into a curve. But more often it’s best to bend wood to get the shape you want. Why? Because bending usually produces a stronger, better-looking result and wastes much less wood.

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Page 1: Bent Lamination

Bent Laminationhttp://www.woodonline.com

DOWNLOADABLE

®

Page 1 of 8DS-015 ©Copyright Meredith Corporation 2002

Create curved project parts the easy waywith strips of wood, glue, and a form

We all know that curves are pleasing to the eye.The question for woodworkers is: What’s thebest way to make them? In some cases, you cancut an arching shape from a solid piece of stock.Or you can build up a blank with mitered pieces,and then cut it into a curve. But more often it’sbest to bend wood to get the shape you want.Why? Because bending usually produces astronger, better-looking result and wastes muchless wood.

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Gather your materialsConsider wood species, thickness,and width as you plan your lamina-tion. We used quartersawn whiteoak for our rockers; see “Thestraight skinny on bending” at theend of this article for a generalguide to the bending properties ofwhite oak and several other com-monly used woods. If you plan touse a wood not listed in the chart,try this test. First, cut a samplestrip to width and thickness. Then,bandsaw a particleboard form tothe needed radius, and bend thesample strip around it.

To make the gentle curverequired for rockers, we resawed aboard into strips ‹" thick and 3‡"wide. Those dimensions workedgreat, but a sharper bend wouldhave called for thinner stock, andgreater width could have createdproblems in the form of surfacecracks or complete breaks.

Within any species, some boardsare better bending candidates thanothers. Reject any board with knotsor wavy grain. Select boards withstraight grain on the edges andfaces. In Photo A, you see twovery different ash samples.

We recommend standard yellowglue for lamination bending. The“Extend” versions of Franklin’sTitebond glues give you more timeto assemble your lamination andadjust the clamps. For outdoor pro-jects, use water-resistant Type IIyellow glue or polyurethane. (See“Do you need a heavy-duty adhe-sive?” on page 7 for informationabout other choices.)

Particleboard works well formaking your bending forms. It’seasily shaped and inexpensive.You also can choose plywood.Finally, be sure to have plenty ofclamps on hand. Sliding barclamps are the most convenientchoice for the job, and provideadequate clamping pressure.

A

Look for bending stock with straight grain, like that on the right.When grain runs in various directions, as on the left, it’s quite likelyto break.

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Build your formTo end up with a perfect curve,start with a perfect form. Use aplan pattern, trace an existingpiece, or use a trammel to make aradius. We laid out our rockerswith a 48" trammel, a pencil, and apiece of particleboard.

Cut the sheet stock just largerthan the shape you’ve drawn.Now, cut more pieces to the samedimensions, until you have enoughto laminate a form that’s approxi-mately equal in thickness to thewidth of your bending stock. Useyour bandsaw to cut about ¤" out-side of the line you marked on thefirst piece, and then sand to theline. Use this template to mark therest of the pieces, and bandsawthem ¤" outside of their lines.

Now, use yellow glue and screwsto begin building the form. Addone piece at a time, and trim eachpiece to match the previous onewith a flush-trim bit in your router,as shown in Photo B.

After completing the form, applypackaging tape to the bending sur-face, as shown in Photo C. Thetape will keep your glued-up lami-nation from sticking to the form.

Cut the laminationsSlice thin strips of wood fromstandard lumber, using either thetablesaw or the bandsaw. (Thechart at the end of this articlegives you thickness recommenda-tions.) Thinner strips produce abend that holds its shape better.Thicker strips tend to spring backsomewhat after you remove theclamps, slightly flattening thecurve. We got a springback ofabout ›" on our chair rockers, asmeasured at the center of the arch.Make your laminate strips ‹"wider than the completed piece,so you can trim away any rough-ness after the glue-up dries. Alsomake them 2" longer than thecompleted piece to allow for accu-rate trimming to final length.

A well-tuned bandsaw can han-dle most resawing tasks. However,

B

C

Particleboard serves well as material for bending forms because it’sinexpensive, easily milled, and free of voids. Use enough sheets toequal or exceed the width of your laminate strips.

Any kind of tape will keep glue off your forms; this clear packagingtape is wide and easy to remove when you’re done.

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if you need lamination strips lessthan 6" in width, you might find iteasier to cut them on the tablesaw,using a 24-tooth rip blade. Formost of us, the tablesaw producessmoother, straighter surfaces thanthe bandsaw, although it wastesmore stock by cutting a wider kerf.

See Photo D for another goodresawing option. Run the originalworkpiece across your jointer aftereach cut so you always have oneperfectly smooth surface. Scrape,plane, or sand the other surfacessmooth. Cut one extra strip toserve as a clamping surface.

Test a sample strip on your formbefore you cut the whole stack.You should be able to bend it to itsfinished shape with moderate handpressure. When you apply glue, thewood will soak up moisture, andbecome even more pliable.

Ready, set, glueMake a dry run before you openthe glue bottle. First, put your formin a position that will allow con-venient clamping. If your clampswill sit vertically, as in our exam-ple, you may need to set the formon supports to make room for theclamp jaws. (Our clamping blockstook care of the problem, as you’llsee shortly.) Place the stack ofstrips on the form, and then add asmany clamps as it takes to close allgaps, with a scrap of wood undereach clamp head to protect theworkpiece and spread the clamp-ing force.

Vacuum or wipe the dust fromthe laminate strips, and prepare towork quickly. Apply glue to bothsides of each laminate joint, build-ing the stack as you go. (Don’tapply glue to the outside surfacesof the first and last pieces, or thestrip that bears the clamps.) Placethe stack on the form. All of thatglue makes for a slippery structure,so use a clamp across the strips tohold them in position as shown inPhoto E. Then set a clamp in themiddle of the assembly, alsoshown, and tighten.

D

E

Before resawing wide stock with a bandsaw, try cutting a kerf onboth edges with the tablesaw. The bandsaw blade will tend to followthe kerfs.

With wide, fixed jaw faces, Quick-Grip clamps do a good job of hold-ing the strips in alignment. Place your first bending clamp right inthe middle.

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Work outward from the middletoward the ends, spacing yourclamps at regular intervals, asshown in Photos F and G. Whenwe approached the ends of theform, we attached blocks to thebottom with screws, to compensatefor the clamps’ tendency to slide.

Check carefully for open spots inyour glue-up, and tighten or repo-sition your clamps as necessary.Once everything is set, clean up asmuch of the glue squeeze-out aspossible with a putty knife, asshown in Photo H.

Leave the clamps in place for atleast 48 hours. You want a solid,cured glue-up to guard against anymovement along the joints.

F

G

H

Place a block under each clampto spread the force. Screw ablock on the bottom of the format each end to keep the finalclamps from sliding.

Use two clamps at each end,where the bending distance andresistance are greatest. Tightenone clamp, slide the other down,tighten, and repeat.

Scrape off the squeeze-out beforethe glue hardens completely.Also, it’s good shop practice toclean your forms before storingthem for future use.

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Final machiningRemove the clamps, take the bentlamination off the form, and cleanup any rough spots. You could usea hand scraper or sandpaper, but apass across the jointer, as shown inPhoto I, quickly and easilysmooths a long, gentle curve, suchas our rocker.

We built our bent laminationslightly more than twice as wide asa finished rocker part. That notonly saved time, by doing the workof two lamination bends in oneoperation, but also ensured that thetwo rockers are nearly identical inappearance and characteristics. Ifone springs back slightly, the otherone should move about the sameamount and remain matched. Thisapproach works for other matchingparts, too.

We ripped the completed lamina-tion on the bandsaw, as shown inPhoto J, to get two identicalpieces. After jointing one edge oneach piece, we took them down tofinished width with the planer.Finally, we cut them to length onthe bandsaw, and proceeded to fitthem to our chair. ¿

I

J

Smooth the edges of a bent lamination on your jointer. Make a testpass with the machine turned off to make sure you won’t strugglewith the safety guard.

When cutting a bent lamination on the bandsaw, keep the workpiecefirmly against the table at the point where the blade enters the wood.

Produced by Marlen KemmetWritten by Jim Pollock with Charles I. HedlundGraphic Design: Jamie DowningPhotographs: Marty Baldwin©Copyright Meredith Corporation 2002

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It’s difficult to get good resultsfrom a single form when you builda piece with multiple curves. Inthose situations, press the lamina-tion strips between two or moremating forms.

Here’s the key to making matingforms: Remember that they won’tmatch up correctly if you simplybandsaw them apart, and thenplace several lamination strips inbetween. When you cut your formstock into mating pieces, you needto remove a band of material equalin width to the thickness of yourplanned lamination.

What to know before you try multiple curves

Here’s how we used matingforms to make the sinuous legsfor a bentwood accent.

Some experts recommend using plastic resin glue, modified ureaformaldehyde glue, or epoxy for lamination bending, pointing out thatthose adhesives dry rock-hard, while yellow glue remains slightly soft.We opt for yellow glue because it’s much more convenient to use,and, in our experience, “creep” along the glue lines never has pre-sented a problem.

If you build a curve that will be subject to unusual stress will have towithstand a great deal of outdoor moisture, consider the harder glues.However, remember that plastic resin glue and modified ureaformaldehyde are toxic. Wear gloves and a dust mask when mixingthe powders, and put on the mask again when you sand hardenedsqueeze-out. Also, epoxy generates heat when mixed, and overexpo-sure can lead to serious skin reactions.

Do you need a heavy-duty adhesive?

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The straight skinny on bendingWe tested the bending properties of seven types ofwood, with each sample measuring ‡" wide and featur-ing straight grain. Here you see the results of three dif-

ferent thicknesses and five radii. For each bend, thespecies shown in black made the grade, but the ones inred cracked or snapped in two.

For bends as sharp as this 2" radius, plan onusing strips no thicker than „". Most of oursamples made the grade.

When cut to ‹", this piece of cedar couldn’tpass our easiest challenge. It splintered on aradius of 16".

‹"

16" 12" 8" 4" 2"

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ash, cherry,mahogany,pine, red oak,white oak

ash, pine,cherry,mahogany, red oak, white oak

ash, pine ash, cherry,mahogany,pine, red oak,white oak,cedar

ash, cedar,cherry,mahogany,pine, red oak,white oak

ash, cedar,cherry,mahogany,pine, red oak,white oak

ash, mahogany,pine, red oak,cedar, cherry,white oak

ash,mahogany,pine, red oak

ash, cedar,cherry,mahogany,pine, red oak,white oak

ash, cedar,cherry,mahogany, pine,red oak,white oak

ash, cedar,cherry,mahogany, pine, red oak,white oak

ash, cedar,cherry,mahogany, pine,red oak,white oak

ash, cedar,mahogany,pine, red oak,cherry, white oak

ash, cedar,cherry,mahogany, pine,red oak,white oak

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