On 3/24/2010 Guy Molinari wrote:
> Hi all,
> I don't know why this is so hard. I'm trying to drill out
> some hole on some 3/8" steel plates that I'm going to have
> galvanized. I bought a 13/32" drill bit and it worked great for
> about 10 holes or so. The problem is that I have about 140 more to
> go. Any recommendations on a good quality drill bit?
Hey Guy,
OK, some questions, and a quick tutorial on drill bits
What are you using to drive your drill bit? What kind of speed, and what kind
of pressure? It's going to be REAL hard to get sufficient pressure on a 13/32
drill bit with a hand drill. What kind of cutting fluid are you using?
OK - Now let's back up, and go into a bit of theory
Look at the pointed end of a drill bit, end on. You will notice that there are
2 cutting edges, and a center area that has a straight line across it joining
the two edges (flutes). The BIGGER the drill, the BIGGER and thicker this
center point. The big issue is that the point does NOT cut!
You are going to want to drill a "pilot hole" just slightly larger than the
diameter of the point on your 11/32 drill - this will make life a LOT easier
Now, look at the business end of a drill bit from the side - the angle made by
the 2 cutting edges on MOST drill bits will be 118 degs. 118 is a nice,
generally 'comfortable' angle, but it's a compromise. Wood really wants a
pointer bit, where steel really wants a point angle of around 135 degs.
There are some other tricks - back to looking end on - if you don't have to
worry about the bit "walking" when starting the hole (your using a drill press,
or there is a pilot hole already) there is a way to make what is called a
"split point" drill, which is where the area in back of the flutes is extended
to the middle by grinding - this makes the drill cut much easier, but DOES make
the edge a tad more fragile to shock/impact
As for cutting speed - unfortunately my machinery handbook is downstairs, but
many (most?) people run their drill bits WAY too fast on large bits - they need
to turn slowly, and turn out those nice "curly chips" - if the chips are blue,
your running way too fast
Cutting fluid/oil - for a bit that size, you really need to run with some sort
of cutting oil, an no, motor oil is NOT cutting oil. The stuff they sell at HD
for threading pipe will work nicely for drilling holes that size in steel
plate. Yes, it'll smoke and smell, but that's the oil taking heat away from
the edge of the bit
Of course, the joke is that depending on how thick the plate is, there is a
real good chance a commercial fab shop would just PUNCH the holes (I've punched
holes a LOT bigger than that through the flanges of BIG I-beams). You MIGHT be
able to find a shop that does moderate duty steel work, and have the plates
punched for not a heck of a lot of money
--
73 de KG2V
"But when a long train of abuses and usurpations,
pursuing invariably the same Object evinces
a design to reduce them under absolute Despotism,
it is their right, it is their duty, to throw off such Government,
and to provide new Guards for their future security."
My Website: http://www.thegallos.com
My Blog: http://kg2v.blogspot.com
Hi, my name is Annie Key. Please don't hit me!
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