It really depends on how you define "viable". For most technical writers book sales are very poor return on the investment in time and effort. Far less that w

It really depends on how you define "viable". For most technical writers book sales are very poor return on the investment in time and effort. Far less that what you could earn in doing programming work. But there non-financial benefits that keep people going. When you look at print on demand (POD) and eBook publishing angles, you might be able to eke out some revenue. IMHO the only reason to publish a book is to support your consulting and related activities. There still is some kudos in being a "published author". With a bit of googling you should be able to find some war stories by people who have gone ahead and published their own technical books. I encourage you to read about their experiences before making your decision.