Aluminum build-up on drills

[Erik S]

Was chatting with @giovanni about enclosure drilling over on the workbench thread, and I mentioned how I like to drill with a little alcohol in order to try and reduce the heat at the cutting edge, and try and reduce the amount of aluminum the builds up on the cutting edge of the drill.

I just finished drilling 258 holes all with the same step drill then took a look at the cutting edges.

Getting a phone shot through the microscope is tough, but here's one with a little aluminum booger on the edge, and then after I scraped it back off.

If your step bit seems like it's dull, it might just have aluminum built up on the cutting edges. If you can get it off without messing up the edge it should cut like new again.

Regarding the efficacy of the alcohol, I had no build up on the tip of the tool, and really only significant boogers on the steps where I pause to chamfer the common hole sizes. At that point I think the alcohol at the edge has largely evaporated or gone down the hole, so it's less effective at that point. Not totally scientific, but I'm going to keep doing it.

Looking close I realize my before/ after shots may not be the exact same edge, but you get the idea.

 

[pricklyrobot]

I keep a utility or x-acto knife handy when I have a bunch of holes to drill. Those thin steel blades will scrape the aluminum gunk off of your stepped bit pretty easily most of the time.
* Just keep your safety glasses on while you’re doing it. X-acto blades don’t snap that easily, but when they do, they somehow always fly straight at your face

Interesting idea about the alcohol. I always try to drill on as slow a speed as I can manage, but things do still warm up if you’ve got enough holes…
I wonder if acetone might not work even better than alcohol, for some evap cooling action? Or would it disappear too quickly to do any good?

 

[Erik S]

I wonder if acetone might not work even better than alcohol, for some evap cooling action?

I’d rather not be huffing acetone all evening. I have few enough brain cells left as it is.

WD40 works great, but these enclosures are all going to get clear coated, and any little speck of wd40 that doesn’t get stripped off would screw with the paint.

I did my scraping with a chisel, but an exacto sounds like a good option.

Speeds and feeds are like a dark art of machining. I’m not a machinist but I do watch a lot of YouTube videos about it… I think sometimes slow will run cooler, but depending on your feed pressure, you might end up with higher chip load, more heat blah blah blah.

I’ll try and figure out what I was running that step drill at for rpms…

Edit - somewhere around 1500 rpm’s and pretty gentle feed is what felt right to me.

For reference my 2 speed 1/2 inch dewalt drill says it does 1750 on high.

I have a wall chart that says target for cutting aluminum is 200-300 surface feet per minute. For a 1/4 inch hole that would be between 3,055 and 4,583 rpms. Take that with a grain of salt since those are probably based on production manufacturing numbers, but you certainly CAN run very fast in aluminum.

I cranked the mill up to 4400 just to get a feel for it, but it gets loud going that fast. I think I’ll stick with slow and steady.

 

[rwl]

Well, I'll be damned. I thought I had just bought cheap bits and abused them, rather than thinking they'd built up aluminum scraps...


No microscope necessary! It looked like the edge of the steps was "smearing" out (this was after 40 pedals). I assumed because the temperature was causing the bit to melt slightly.

But raking down the channel with the claw of a hammer and voila!


Not that you should trust my judgment on this (clearly!), but just going from drilling dry to dipping the bit in water before each drill made a huge difference for me.

 

[Erik S]

Well, I'll be damned. I thought I had just bought cheap bits and abused them, rather than thinking they'd built up aluminum scraps...

View attachment 83854
No microscope necessary! It looked like the edge of the steps was "smearing" out (this was after 40 pedals). I assumed because the temperature was causing the bit to melt slightly.

But raking down the channel with the claw of a hammer and voila!
View attachment 83855

Not that you should trust my judgment on this (clearly!), but just going from drilling dry to dipping the bit in water before each drill made a huge difference for me.

Wow! Yeah, that should cut much better now!