Here are some beginning base tips:
If the net length on the rail you are bending is 12-ft, a 14-ft bender rail is best to insure that the ends are pulled around the desired radius in order to hold its form when removing rail from its clamps. If you have 13 "steps or treads", you are safe with a 14-foot bender for an inside radius.
If an outside radius going up a stair, figure 2-foot per step. Bending rail is understood when imagining a standard handrail profile cut into thin strips and keyed together (tongue and groove bead to create alignment). Bending mould should also be included as it is moulded to the outside profile of the handrail and is used to sandwich the handrail and allow clamping without damage to the handrail itself.
Weldwood's Plastic Resin Glue (a DAP product) is perhaps the most ideal glue for bending handrails. It has a curing time of 24 hours, allowing for ample time for one to bend rails without feeling rushed. It also sands easily once dried and works with stains. The best place to find this product is a True Value Ace Hardware Store. I understand that they bought the rights to sell this product, which pulled it off of the shelves at all Home Depot and Lowes. It comes in a one pound plastic container and is mixed with water until soupy. Apply it to both sides of the bending rail keys, tape or shrink wrap the rails together, and you can start bending!
When considering steam bending, Weldwood is best applied once the handrail has been steamed and bent on the forms. Remove it from the forms once dried, apply the Weldwood, and reattach to the forms. Steaming handrail, for most styles, is not an option unless your bending rail is less than an 18-inch radius. For some handrail styles the minimum before steam may be a 24-inch radius.
One key to keeping the stress points on the rail's shoulder from cracking or breaking is to apply vinegar on the stress areas of the wood. Vinegar reacts with the woods fibers to relieve stress. Don't use bleach! It will permanently stain some hardwoods black.
Once a handrail is bent, use an orbital or belt sander to finish the job. Make sure all glue is properly sanded, otherwise one will have blotches where the stain cannot penetrate since glue acts as a sealer.
C-Clamps or bar clamps are the best two tool choices for bending handrail. http://www.preciouslowpricegift.com/