From: "William Thornley" 
To: dwightk.elvey{at}amd.com, atm{at}shore.net
Reply-To: "William Thornley" 



Hi All,

Sorry for resurrecting this thread again, but I just read an article on
this subject last night. The article was called 'Why Won't It Fit' in Vol
189 No. 4178 20 September 2002 issue of the UK magazine 'Model Engineer'.

The phenomenon mentioned in this thread of badly drilled holes, due to
drill chatter, is called 'Lobate' and is caused by opening up holes with
larger size drills.

The solution is simple - use 3 fluted drills instead of 2 fluted drills. I
don't know about the rest of you, but I have trouble maintaining a set of
imperial and a set of metric 2 fluted drills let alone another set each of
3 fluted drills.

The author, Neil Read, has another simple solution. He uses a square piece
of emery cloth (gritty side down)over pilot hole and drilling through the
emery. This apparently starts the drill off without chattering and produces
a perfectly drilled hole. I haven't tried this myself yet but this guy
swears by it!

Hope this helps!

Regards,

Bill Thornley
Sydney, Aus.

>Dwight wrote:

>Hi Shawn
>  The worst of it is that you are more likely to jam or
>break a bit that is vibrating. When drilling, it is
>best to drill most of the hole with the final size,
>good lubrication and the right speed.
>  I used to do the stepping through the sizes thing
>until a machinist friend pointed out my nasty looking
>holes. He showed me the right way. It is still best
>to drill a pilot hole, just don't drill it so large
>that it causes the drill to vibrate. Like most things,
>a little is a good thing but too much is worse( now,
>where is my beer ).


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