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an aluminum bar with a crater like 'splash'

I need to make a couple of 3mm holes in this 0.75" 6063-T52 Aluminum Square Bar. I grabbed a 3mm drill bit, and consulted this chart. My drill press only goes up to 3200, so I set it to that and tried to make a hole. The above was the result.

I've never worked with metal before, let alone aluminum, so I'm sure I did something stupid. Did I have the wrong kind of bit? I'm not sure if it was a 135° or 118° bit. I'm extra confused because I had previously managed to make an even smaller hole at an even lower RPM, could I have had it too high?

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  • RPM looks very high: I am not a machinist but have drilled a lot of holes . I usually start at low speed and increase speed if cutting goes well ( variable speed hand drill).
    – blacksmith37
    Commented Nov 23, 2021 at 15:26
  • Aluminium is very easy to drill (with a sharp bit). Are you talking about the 'crater' next to the hole? If so, are you sure you didn't use a masonry bit (or a very blunt HSS bit)?
    – NMF
    Commented Nov 23, 2021 at 20:06
  • When machining a hole, what is the order of operations? - When drilling metal, should I start with a smaller bit before using a larger bit?
    – Mazura
    Commented Nov 23, 2021 at 22:57
  • "I had previously managed to make an even smaller hole" .... Next Q: now the larger bit binds in the hole? Run it backwards for a second then try again, using less pressure, to try to bite the burr off. Use a screw gun so you can wobble it around a little so that it either jumps over the burr or chips it out.
    – Mazura
    Commented Nov 23, 2021 at 22:57

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The high speed/rpm was correct, but try with less pressure to aid the chip evacuation for a cleaner finish and less deformation at the mouth of the hole.

Use low enough pressure to the point that you do not feel the need to "peck" (repeatedly insert and recede the drill).

Lubricants are messy but if you can't get low enough pressure for the finish you desire, you may have to try with a lubricant.

For more:

https://www.ctemag.com/news/articles/aluminum-can-be-hard-drill-despite-its-easy-rep

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  • Thanks! I was pushing pretty hard, I'll bet I heated it up and deformed it. That article seems to recommend a pointed bit, do you happen to know of any bits I should get at a home improvement store? or is a 118 degree bit alright?
    – Sam Borick
    Commented Nov 23, 2021 at 15:58
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    @SamBorick the tip really matters for steel and large holes, but if bit life and production speed (seconds per hole) are not a concern to you (i'd think they are not) then pressure control alone can suffice.
    – P2000
    Commented Nov 23, 2021 at 17:13

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