On 2010-09-26, Karl Townsend wrote:
On Sun, 26 Sep 2010 17:34:44 -0500, Karl Townsend
wrote:

On Sun, 26 Sep 2010 16:41:07 -0500, Ignoramus24898
wrote:

I bought a couple of 3/4" thick aluminum fixture plates.

http://igor.chudov.com/tmp/Fixture-Plate.jpg

It was a local sale.

I would like to drill and tap them with 5/16" drill and 3/8" tap, say
spaced at 1" interval. That makes for about 200 holes to be drilled
and tapped on my CNC mill.

Some questions.

1. What is the best way to drill aluminum with 5/16" drill bit, making
through holes. What RPM and feedrate and how often to peck.

2. Do I need to center drill those holes first? It is not really a big
deal, just some more G codes.

3. For tapping, can I safely use a ER colleted floating tap holder that has a
little bit of vertical internal travel. Like this one:

http://www.maritool.com/p67/ER25-Flo...duct_info.html


By chance I just finished drill and tap to 3/8 on four holes in AL
1.25" deep. I used G81 (no peck) feed 5.1 speed 2100. Got thick chips
that fed out well and broke every two inch or so. Used my coolant
mister at a heavy flow.

Karl

sorry you had two more queries.

I used a solid holder, your floating holder would be nice.

Spot drill if you need to hold +/- .002 location, stub drill maybe +/-
.005, regular drill maybe +/- .010 or worse. So how accurate
determines answer.

Karl


I will use a spot drill indeed. Full diameter holes with spot drill,
perhaps 1/8" deep, to provide guidance for the regular drill.

i