Building a Balsa Bridge

Building a Balsa BridgePrepared by:Barry Sparrow and Sal IencoCivil/Construction Sault CollegeAssemble Materials

You will need:Balsa woodTapeCutting knifeClampsBooksMath setGlueCardboardPinsSandpaperPencil

Prepare a drawing layout on cardboard

Cut accuratelyTake your timeBe carefulTotal length to be 450mmSave your off cuts (scraps)Cut the balsa piecesCutting VideoCheck all of your cut pieces

Cut both truss sides at the same timeLay out all of the pieces for one truss before gluing

Begin gluing the piecesUse tape to hold parts in placeUse white or carpenters glueBe sure to glue all contact faces

Gluing the pieces

GluingBe neatUse a damp cloth or tissue to clean upPins can hold parts temporarilyUse scraps as spacers

Final truss assembly

Check the alignmentComplete the truss gluingAllow the glue to dryUse more tape to hold parts in placeUse books or similar weights to hold in place until glue has dried (1-2 hours)

Gluing VideoRemove books and tapeRemove booksCut away tape and remove carefully

Truss completeRemove any pins and remaining tapeRepeat process for side 2

Cut the bracing and cross membersNow the truss sides can be assembledMeasure and cut the cross membersMake sure bridge is minimum width (40 mm)

Assemble the two sidesGlue top and bottom cross pieces in placeLine up cross members with truss webbing

Bridge Assembly continuedUse spacers or blocks to keep parts straightSand and trim before gluing to ensure a good connection

Glue truss to cross membersOnce the connections have glue applied the truss can be put in placeApply glue ready for the top cross membersUse tape to keep cross members in place

Apply top cross membersInstall top cross piecesDiagonal bracing installed later after glue had dried

Add weights and let glue dry...Books keep everything in place until glue setsSpacers keep sides straight up (vertical)Let dry for 1-2 hours

Install final cross piecesUse clamps where needed to install final cross pieces

Add pieces on truss endsTo deal with compression forces, extra material is added at each truss end

Add gussets at cornersAdding gussets at bottom corners increases the connection strength

Prepare cross bracingFor this bridge, diagonal bracing material was made from thickness pieces, cut along the length

Prepare end bracingCut and assemble thickness angled bracingThese pieces are used on each end of the bridge to keep it from collapsing sideways Trim to size after they are in place and the glue has dried

Bracing at endsInstall bracingNote gusset added at top cross member

Trim bracingAfter glue dries, bracing can be trimmed and sanded

Install top & bottom bracingDiagonal X bracing is installedCut to fitUse pins or tape to hold in place until glue dries

BracingInstall bracing on top as well as bottom of bridgeNote extra gusset at support point

Youre done!Bridge is completeTouch up lightly with sandpaperIts ready for testing

Testing Video