İlker Tuğru 503111301 6th Week Unanswered Word

2. Hard Boring

(Previous-Better)

Boring, also called internal turning, and reaming are used to increase the inside diameter of an existing hole. The original hole is made with a drill, or it may be a cored hole in a casting. Boring and reaming achieve three prime objectives: (a) sizing – boring and reaming bring the hole to the proper diametric accuracy with a tight tolerance while achieving the required surface finish; (b) straightness – boring and reaming straighten the original drilled or cored hole; (c) concentricity – boring and reaming make the hole concentric with the outside diameter within the limits of the accuracy of the work holding fixture. This unique set of objectives is not normally achieved in grinding so it is logical to use hard boring and/or reaming as the finishing operation after the work material has been hardened.

If distortion and size variation as a result of heat treatment places unreasonable constraints on the “soft stage” machining, increasing its tooling cost, hard boring will provide a cost-effective, scrap-reducing alternative. The greater the distortion (due to part asymmetry, for example) and the length-to-diameter ratio, the greater advantages of hard boring.

(Davim J. P., Machining of Hard Materials, 2011, p. 16-17)

(New)

A horizontal boring method comprises the steps of boring a small diameter pilot hole, thereafter removing the small diameter bit, then boring the final diameter of the bore hole by advancing a boring bit having a lead-off bar guided within and by said pilot hole, simultaneously advancing a cylindrical casing immediately behind said bit, introducing a liquid into the end of the casing to slurry the cuttings and finally, when the boring step is completed, removing the bit through the casing and cleaning the thus installed casing.

(R.P. Dunn, U.S. Patent, Patent Number: 3902563, Filing date: 23 May 1974)