You can fix a broken maple chair spindle by replacing the spindle with a strong, new piece of wood. If you still have the broken spindle, you may be able to use it as a pattern for getting the proper dimensions for the new part. Although the original spindle may have been turned on a lathe, you can shape a replacement with a few sharp hand tools and a vice.
Select maple stock that is similar to the damaged spindle.
Use a froe, wooden mallet and hatchet to split 1-inch by 1-inch pieces of maple. Beat the blade of the froe into the wood at 1-inch intervals with a wooden mallet. Use the hatchet to cut through any fibres that do not separate.
Measure the dimensions of your broken spindle with a measuring tape and calipers.
Place one piece of 1-inch by 1-inch wood into a vice.
Shape the spindle with a sharp drawknife. Transfer your measurements as you remove wood slowly to form a new spindle.
Whittle slightly oversized tenons on the ends of the spindles. Make the tenons 1.25-inch long and fashion eight facets around the perimeter of the tenon. These slight angled facets will fit snugly in the sockets of the seat and chair back.
Stain or paint the new spindle so it matches the colour of the original.