Why standard tip angle is 118 degrees? 1

[pratyu]

I would like to know why "118 degrees" made the standard tip angle for a drill bit.Or for that matter, 135 degrees?

1. Is there anything called "standard tip angle"?
2. What factors determine the choice of the tip angle?

P.S: I posted the same question in Aerospace forum :

http://www.eng-tips.com/viewthread.cfm?qid=347077

 

[Viktor]

KENAT (Mechanical)

"DO NOT BREAK THRU" - is an atavism from the time when we did not use CAD drawings. Nowadays, a normal drawing should show everything graphically with tolerances. For example, in the automotive industry in drawings of the valve bodies, pump covers and other parts of an automatic transmission we have a lot of narrow passages called veins. We use proper GD&T to avoid breaking thru or not no damage anther vain. A CNC machine does not understand "DO NOT BREAK THRU" ( I tried to tell it but the machine controller just refused to cooperate ) - we have to set proper drill length and the length of the working stroke to avoid such a breaking. Properly designed tool layouts help the matter, i.e. selecting the proper drill point and assigning the length of the working stroke.

On the second thought, you might be right for less advanced drilling operations done manually.

 

[EdDanzer]

In some business areas it may be required to dimension every detail of every feature to make sure things are machined as designed. In low volume and repair it is much more common to only put in the required solid model features and dimensions and write notes of details than expect the programmer and operator to waste time looking at several drawing pages with information that just adds to the confusion and cost.

Viktor,
If you read my post we do use high tech drills when the task justifies. Do you also model the thread helix, dimension the thread angle and radius at the thread point?

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[KENAT]

I use proper GD&T too, I just fail to see the benefit in identifying the maximum hole depth (and implied inspection requirement) in situations where so long as it doesn't break thru there is no real functional maximum. After all if you're hung up on 'proper GD&T' presumably one cares about the drawing defining functional requirements not specifying how a part is to be made (unless it directly affects end performance).

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MikeHalloran]

I think "DO NOT BREAK THRU" is irresponsible, in the sense that it shifts responsibility for problems to persons who are not in a position to evaluate the actual situation, let alone do something about it.

Certainly, for pressure containing parts, it implies the existence of a minimum remaining wall thickness beyond the drill point. ... which is what should be specified or dimensioned in the design documents. ... either directly, or indirectly with the usual depth to full diameter plus some indication of the allowed drill point angle.






Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

Um, so in a situation where there is a functional requirement for a certain minimum remaining material thickness then obviously specifying the min hole depth and do not break thru wouldn't be appropriate, in such a case there is a functional maximum hole depth and so it should be specified or potentially the resultant material thickness in some cases.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Viktor]

EdDanzer (Mechanical)

Viktor,
If you read my post we do use high tech drills when the task justifies. Do you also model the thread helix, dimension the thread angle and radius at the thread point?- unfortunately not although a lack of such models creates some problems when we use rigid tool holders for taps. A certain mismatch of the pitches of the tap and than set on the machine creates tread quality problems and sometimes breaks the tap (particularly carbide taps). Synchro tapping holders are expensive and require maintenance. What I did is a model for the proper diameter of the tap drill - it is another untold story for high-tech manufacturing.