What drill bits

[JimM]

Gradually building up my stock of tooling etc and for my next job I need to drill some 2mm holes through some brass rod. Do you guys normally just go with standard HSS drill bits or are 5% cobalt split point bits worth the extra expense.

Cheers

Jim

 

[Blogwitch]

If you use a spot drill first, you can use normal drills. But if you have a lot of holes to drill, the cobalt will last longer.

The split point drills are designed to be ALMOST self centring, but I definitely wouldn't trust them on any curved surface to self centre and start cutting straight.


Blogs

 

[Deanofid]

You don't need anything fancy to drill brass. Regular HSS works great.
What you will probably find is, no matter what kind of bit you use, they will want to grab very aggressively, pulling the bit hard into the work. Bits used on brass need to have the cutting lip honed down just enough to get rid of the very sharp edge that is put on regular factory ground bits.

See my post in this thread for further details:

http://www.homemodelenginemachinist.com/index.php?topic=6718.0

Dean

 

[Omnimill]

I get Dormer or SKF drills when I'm buying "specials" for a particular job because that is what is normally available from my local engineering supplies. I use cheap supermarket sets for rough drilling though and the Draper ones are very good for the price.

Vic.

 

[Lew_Merrick_PE]

Jim,

The real issue is the quality of the drill bit. Cobalt adds abrasion resistance and (a bit of) surface hardness that may or may not pay off for you (it depends on what you end up doing with them). Beware of the cheap Chinese drill bits as they are rarely even close to round or straight. I am quite a drill (& tap) snob. Pulling broken bits out of a part gets old in a hurry. Poor (mechanical) surface finish leads to cracking. Well finished bits with a smooth finish that are round and straight will save you a lot of grief.

A reasonably good drill grinding set-up is a necessity for anyone who does more than occasional drilling. The (relatively inexpensive) Darex grinders are "pretty good." [I have a 1972 vintage Pratt & Whitney drill grinder, so my "basis" is set quite high.] If you do the set-up for it properly, the General Tool drill bit grinding support will do an excellent job. A hand honing grind for small (<.100 in or 2.5 mm) is also in order. The one shown in Guy Lautard's The Machinist's Bedside Reader works reasonably well and is not too hard to make.