Installing the door knobs -- or pulls -- on a bi-fold door is definitely not the most difficult part of hanging the doors; in fact, it's just a matter of drilling a single hole for each knob. The most difficult part of this particular procedure is determining exactly where to drill the hole, and that depends on whether the doors are flat or have panels.
Hang the doors before you install the knobs -- that way you'll be certain to get the knobs centered and at the proper height above the floor.
Installing Knobs on Flat Doors
- Place the knobs a fixed distance above the floor if the doors have flat faces. Measure a distance of [36 inches](http://www.thisoldhouse.com/toh/how-to/step/0,,1176649_1038013,00.html) from the floor with a tape measure and make a light mark on the door 1 to 3 inches from its outside edge as per your preference. Use a pencil that can be easily erased to make the marks.
- Measure the width of the door and make another light mark in the center at the same approximate height as the first mark.
- Hold a level on the first mark; center the bubble to make the level horizontal, then make an "X" at the point where an imaginary line from the second marks intersects the level.
- Drill through the center most point of the "X" mark using a drill bit larger than the shaft on the door knob. Work from the front side of the door to the back. Wipe off any sawdust and wood debris with a rag.
- Insert the threaded shaft of the knob through the hole in the door, adding a washer and a nut to this bolt on the back side of the door. Tighten with a wrench.
To prevent tear-out on the back of the door, watch carefully as you're drilling, and as soon as you see the bit starting to protrude, stop drilling and finish making the hole from the back of the door.
Positioning Knobs on Paneled Doors
- Find the [center of the middle rail](http://www.homedepot.com/catalog/pdfImages/f5/f5ab4561-3f03-48cc-92a1-c0573e63bb31.pdf), if the leading door has panels. To so this, start by placing a straight edge diagonally from one top corner of the rail to the bottom corner on the other side and drawing a light line. The line doesn't have to extend very far -- it can be only 2 or 3 inches long -- but it must be near the center of the straight edge.
- Place the straight edge on the opposite pair of diagonal corners and make a small "X" on the point at which it intersects the first line.
- Make an indentation at the intersection of the lines in the "X" with an awl, then erase the pencil lines.
- Drill through the center of the "X" using a drill bit that is slightly larger in diameter than the bolt attached to the door pull. In most cases, a 3/16-inch drill bit will do the job. Drill through the front side of the door.
- Insert the bolt attached to the door pull through the hole from the front of the door and screw on the retaining nut from the back. Slide a washer onto the bolt before screwing on the nut to protect the wood from the nut. Tighten the nut with a wrench.