Why standard tip angle is 118 degrees? 6

[pratyu]

I would like to know why "118 degrees" made the standard tip angle for a drill bit hole.

I looked up in internet and didn't find a convincing answer

 

[cloa]

Not an Aerospace question- its a machining question.

http://www.eng-tips.com/threadminder.cfm?pid=1529

Use translation assistance for Engineers forum

Note the rules include No Student posting

 

[WKTaylor]

pratyu... [Twist-] Drills/reamers are essential aerospace tools.

Each material type... soft/hard metals, plastics, composites, etc... requires different drill/reamer types. The tip configuration (among many cutter features) is one of the most important for clean material penetration [angle, rake, split, etc]

CAUTION...
"Drill-point gemometry" for metal cutting comes in generally (3) flavors... 118-deg is generally for aluminum and other soft metals.

P-3 135-Deg general purpose
P-5 118-Deg light duty
P-9 135-deg heavy duty

NOTE. there are also quite a variety of shank-styles and drill-bit alloys at our disposal.

See AIA specs for single diameter drill bits and stepped diameter drill bits...
NAS907 Drills, High Speed Steel and Cobalt, 1/16 Inch thru 1/2 Inch
NAS937 Drills, Double Margin Stepped, High Speed Steel and Cobalt, 1/8 Inch Thru 1/2 Inch

and, for giggles... check-out reamer bits...
NAS973 REAMERS, CHUCKING, RIGHT-HAND CUT, 0.0938 THROUGH 1.5000 INCH

NOTE. There are corresponding ASME standards for twist drills, reamers, etc that I have NOT mentioned.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[Sparweb]

To summarize Will's excellent answer:
There IS NO standard tip angle.
Just conventions, determined empirically, about what works best under different circumstances.
Also see Machinery's Handbook: hundreds of pages of drilling/reaming bit designs.

STF

 

[GregLocock]

You'll probably get better answers on a machining forum, but it varies by material, for instance for rubber I use 90 degrees.

The reasons you might change it would be structural support for the point, heat conduction away from it, tendency to form swarf (ideally you want chips not coils usually) and about a zillion other things.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[pratyu]

Greg,

You gave an insight of what I was searching for! Will post the same on Machining forum and will let you guys know if there is something new added to your info!

Thanks all!

 

[pratyu]

I posted the query in Machining Forum :

http://www.eng-tips.com/viewthread.cfm?qid=347145