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Justice asks : Mr Grant , What is the correct angle for a drill bit for steel to be sharpened to and are there different angles for drills to be sharpened for different uses ?
Hi Justice , yes , there are different angles one should use when sharpening a drill . The angle that you should use depends upon the material that you are drilling into . When a drill is dull or chipped , sharpening is done to the point only . There are three aspects that must be taken into consideration when sharpening a drill , namely :
• Lip-clearance angle
• Even length and degrees of cutting edges
• Point angle
It is the point angle that your question refers to , but consideration should also be given to the lip clearance angle .
The point angle for general work is at an included angle of 118 degrees .
Like single point cutting tools , the only part of the cutting tool to come in contact with the material machined , is the cutting edge .
Lip clearances must therefore be ground to the point of the drill to ensure that only the cutting edge comes in contact with the material , thus preventing the rest of the drill to rub against the material . You can see the lip clearance angle in the sketch .
The table included here gives you an indication of the point angle and the lip clearance angle that should be used for for drilling various materials .
Thank you for the question Justice , the sharpening of drill bits requires some practice but this is a skill all technicians should master .
Thank you for all your questions . Send your problems ( and sometimes your creative solutions ) to acra @ netactive . co . za with ‘ Solutions Page ’ in the subject line . You may include pictures . RACA
REFERENCES : 1 . ACRA 2 . SANS 10147
Supplied
Point and Lip Clearance Angles
ENGINEERS AND JOKES
young engineer starting at a new office was escorted to his
A new cubicle by the engineering manager . He was given an assignment to work on , cautioned to be as efficient as possible and left to get to it .
After a few minutes of quiet in the office , someone from out of one of the other cubicles shouted out a number : " two-seventythree ." Everyone in the office full of cubicles started laughing for a few moments and then all was quiet again , except for the sound of computer keyboards clicking away .
A few minutes later someone else shouted out another number and the office responded in the same way . The new engineer stepped over to the next cubicle and asked what all of this was about .
“ Well , said the veteran engineer , “ in order to be more efficient around the office we have numbered all of the good jokes we know and whenever we want to tell one , we just call out the number . Since you ’ re new , you ' ll want to download the list from the server and get acquainted with our humor data base as soon as possible .”
A couple of days later , the new engineer decided it was time to try his hand at this form of humor . He checked the database , again assuring himself that joke number 39 was very funny and then called out “ thirty nine .”
The office was silent . This didn ' t seem to work at all , so he leaned over and asked the veteran engineer , “ Why didn ' t the office respond with laughter at joke 39 , isn ' t it very funny ?"
“ Oh yes ," said the veteran engineer , " joke 39 is quite hilarious , but you know , some engineers just can ' t tell a joke .” RACA
www . hvacronline . co . za RACA Journal I June 2022 53