Occasionally, the tapped holes for jets (in the castings) are damaged to the point they must be repaired.
Repairing Destroyed Tapped Holes in Casting for Jets
- First, it must be pointed out that this is often a difficult procedure to implement.
- Make and prepare a special plug from 1/4 inch brass rod stock. Cut a plug 1/4 inch length long and smooth both ends, reducing over all length to .200 - .225 inch. Reduce diameter of one half the plug length to .220 inches
- Drill out damaged threaded jet hole first to .189 inch diameter. Progressively drill hole out to .200, .225, and finally to .245 inch. Thoroughly blow out all debris and dust from passage and casting.
- Apply Loctite to the sides of your special prepared plug and press plug in for a tight fit, keeping top of the plug flat for good jet interface. It very important to let Loctite thoroughly dry before proceeding.
- Start process of taping your plug for a jet by very carefully marking with a center punch in the center of your special plug. Extra long drills will be needed for some casting hole locations. First drill a hole to 1/8 inch diameter, being careful to keep drill centered and perpendicular. Secondly, drill hole out to .155 inch diameter. Carefully tap hole with an M5 x .75 (metric) tap. You should remove tap after about every thread cut to remove debris (to prevent pressed in plug from coming loose. Thoroughly blow out all debris and dust from passages and casting. Verify that jet will thread in properly and bottom out correctly.
- If casting needs to be blasted later in your restoration process, tag casting with a note to use caution not to damage brass plug.