Purchased a commercially manufactured Hand Tapper a couple of years ago and overall it is a well-constructed unit. The only complaint was the way the tap was held in the adapters and the way the combined adapter and tap was held in the spindle. Installation of adapter and tap in the spindle went well, the removal was the problem. Every time the machine was used regardless of the size tap used it was a fight to remove the adapter. First the tap slipped out of the adapter and then the adapter would not come out of the spindle without disassembly of the spindle, spring clip and steel detent ball. Occasionally I ended up chasing the ball around on the shop floor. Replaced the slotted set screws with more traditional hex socket set screws with minimal improvement.
The modification I eventually used came about after Tony Foale’s thread on building a Homemade hand thread tapping machine. His use of two Irwin Tap Adapter’s was an excellent solution to the problem. Tap installation was accomplished with simple hand tightening or loosening.
The Spindle was modified to accept a machined adapter with a set screw spring plunger to act as the detent and then drilled and pinned to the spindle.
So far so good.