BoltHobber - a tool for tapping hobbed bolts

thingiverse

The BoltHobber is a tool designed to simplify the process of hobbing bolts with taps of varying sizes. The initial inspiration came from struggling to pass taps through bearings and remove completed bolts without damaging their hobs. To overcome these challenges, the inventor envisioned a hobbing tool that allows the tap to move against the bolt, adjusting cutting depth and enabling easy disengagement of both components once hobbing is complete. The BoltHobber consists of two printed parts (base and slide), four ball bearings for the bolt and tap, a vertical screw/nut elevation system, and a metal sheet for distributing force. Small ball bearings (type 688ZZ, 8x16x5mm) were chosen to keep the tool compact and robust, with minimum groove distance of 23mm from the bolt head. Washers can be added to fine-tune this distance. To use the BoltHobber, secure it in a bench vice and place a metal sheet behind it. Insert an M8x60 bolt with washers and a tap from the front, then tighten the elevation screw until the bolt and tap touch. Rotate the tap while turning the bolt, tightening the elevation screw by 1/4 turn after each complete turn of the bolt to reach the desired hob depth. The BoltHobber has been successfully used with M6 and M8 taps, and smaller sizes like M5 or M4 may also work. For efficient hobbing, use a power drill at its slowest speed instead of turning the tap by hand.