When I do short production runs like these stair treads I generally try to do as little fitting as possible, relying on good stock prep and accurate machine settings to allow cutting multiple parts to size that mate properly without fussing around. Sometimes it doesn't work out that way and painstaking incremental steps have to be worked through for a good result.DSC_0598.jpg
These treads are 4" x 13" x 53" lock mitered boxes, 16 of which have mitered end grain endcaps. The material is unfinished "engineered" flooring with a 1/4" white oak veneer on a 1/2" veneer core ply substrate that appears to be Baltic Birch. It matches the prefinished flooring on site and the assembled treads will be shipped to the mfr's facility to be finished with a 2k poly over whitewash. The trick is that the treads are to be delivered to the site with a dry-fitted bottom so that the upper part can be scribed to a wall, slipped onto a steel tube projecting from the wall, secured with bolts through the structural tube to the balusters and finally glued to its prefinished mate.DSC_0612.jpg
The material was problematic from the start- something about the manufacturing process caused all the 25/32" x 7 1/2" x 60" blanks to be significantly bowed, on the order of 1/4" and some very stiff in deflection, also cupped slightly. Wide belt sanding took most of the cup out but not all. I wound up kerfing all the material halfway through on 3" centers to make the subsequent machining and assembly a bit easier, but some of the pieces were still quite stiff. Putting the lock miters together took some persuasion. The pieces were beveled on one end and the crosscuts carefully checked and trued up with a block plane and sanding block before gluing up the top and sides with the ends aligned.DSC_0599.jpg
The end caps were made of 1/32" thick endgrain laid up on 3/4" PlumaplyHD, veneer core ply with hardboard faces. Needless to say the short endgrain undercut by a 45 degree bevel all around was fragile. The fits had to be close to perfect and despite the care taken with preparing the beveled surfaces simply sawing out 16 beveled rectangles the same size was not going to give the required results. The lengths and widths were dialed in using flip stops and shims on a modified Fritz and Frans jig on a sliding table saw. Cuts that would exit on a finished edge were stopped before the end and sanded out to prevent spelching. The fits were customised using a 12" disc sander and 80# hard block. The caps were glued up with epoxy and packing tape.DSC_0603.jpgDSC_0601.jpgDSC_0609.jpgDSC_0608.jpgDSC_0615.jpg
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Originally Posted by Warren Lake
