Ross Kirkland
I assume you mean replacement of an existing, rather than assembly of a kit. This can be a tricky job, even for a skilled carpenter. It requires precise measurements and skilled use of chisels and or power router. I would not recommend attempting this as DIY, you could post this in the jobs section and get some quotes. If you do attempt, then after removal of the existing post, use as a template to mark out the recesses required to accept the riser and tread on stairs onto new post. It would be better to make the new recesses slightly tighter than the original, as you can always remove a little more wood but cannot replace it if you remove too much. Using a combination of router, wood drill, chisel etc, carve out the recesses. Check the new post fits, If you are installing a hand rail, you may want to mark out and cut any mortice hole into the upper post on a bench, before final fixing of post. Apply good quality glue into recesses and then re assemble, with hand rail, make sure it's roughly plumb, fix with a few countersunk screws and fill, or plug holes. Job done, expect it to take a carpenter most of a day, or DIY 2 days.
