Feathered end 5:1 slope Routed scaft Clamp work piece to fixture Edges are guide for router base Slope fixed as appropriate 10:1 to 12:1, etc. Figure 6-26.  Scarf cutting fixture. Figure 6-23.  Tapered faceplate.  Figure 6-24.  Beveled scarf joint. Figure 6-25.  Making a scarf joint.  New section to be spliced in Guide board Undamaged section Correctly beveled pieces A Incorrect beveled pieces B Gap Slope 10 to 1 in solid wood should not be used in spar repairs. A longitudinal crack in  a solid spar may be repaired using doublers made from the  proper thickness plywood. Care must be taken to ensure the  doublers extend the minimum distance beyond the crack.  [Figure 6-27] A typical repair to a built-up I spar is illustrated using  plywood reinforcement plates with solid wood filler blocks.  As with all repairs, the reinforcement plate ends should be  feathered out to a 5:1 slope.  [Figure 6-28] Repair methods for the other types of spar illustrated at the  start of this section all follow the basic steps of repair. The  wood used should be of the same type and size as the original  spar. Always splice and reinforce plywood webs with the  same type of plywood as the original. Do not use solid wood  to replace plywood webs because plywood is stronger in shear  than solid wood of the same thickness. The splices and scarf  cuts must be of the correct slope for the repair with the face  grain running in the same direction as the original member.  Not more than two splices should be made in any one spar.  When a satisfactory repair to a spar cannot be accomplished,  the spar should be replaced. New spars may be obtained from  the manufacturer or the holder of a PMA for that part. An  owner-produced spar may be installed provided it is made  from a manufacturer-approved drawing. Care should be taken  to ensure that any replacement spars accurately match the  manufacturer’s original design.  6-18