Drill speed for Aluminium... and lubricant?

[Dog Star]

My Son, Peter, has a Proxxon drill press (model TBM220) with three speed options, being 1800, 4700 and 8600 rpm. I have to drill about 100 4mm holes through 3/32" thick Aluminium flat bar. Which speed option ought I to use for Dormer HSS drills?

I have recollections of using white spirit and light oil to lubricate / cool the metal and drill - is this reasonable?

Thank you, regards, Graham

 

[Marc Dobson]

Best coolant/lubricant for machining Aluminium is paraffin or it used to be. There might be a less flammable one out there now.
There is a formula for working out drill speed it's a material constant multiples by the size of the hole. On most metals the rule of thumb is the bigger the hole the slower the rpm on the drill. Aluminium likes to haul the tools and the snap drill etc.
Marc

 

[simond]

Graham,

you don’t give the diameter, but you’ll find something here

https://www.cutwel.co.uk/hole-making-tools/solid-carbide-drills/aluminium-non-ferrous-carbide-drills/uncoated-carbide-stub-alu-drill-for-aluminium-dca40-series-cutwel-pro-dca40

Google AI confirms high speed, and the use of a light oil lubricant, and suggests WD40 which might be convenient.

For drilling aluminum, use
high speeds (200–300 SFM for HSS, up to 400+ SFM for carbide) and moderate-to-high feed rates to prevent gummy material from welding to the bit. Optimal performance usually involves 10,000+ RPM for small bits and 1,000–2,500 RPM for larger ones, paired with lubricant (e.g., WD-40 or kerosene).
Norseman™ Drill & Tool +4

Recommended Drilling Parameters for Aluminum

• Surface Feet per Minute (SFM): 200–300 (HSS), 150-400+ (Carbide)
• Lubrication: Essential (WD-40, Alumicut, or Kerosene) to reduce friction and prevent built-up edge
• Drill Type: 118° or 135° split-point high-speed steel (HSS) or cobalt
  Norseman™ Drill & Tool +4

Speed & Feed Examples

Drill Diameter	RPM	Feed Rate (IPM)	Notes
1/8"	~9,000 - 10,000+	~10 - 14	High speed, fast feed
1/4"	~3,000 - 5,000	~10 - 15	Moderate speed
1/2"	~1,500 - 2,500	~10 - 18	Slower speed, higher torque

Key Considerations

• Peck Drilling: Use a peck cycle (e.g., 0.75mm or 0.03" per peck) to clear chips and prevent jamming, especially for deep holes.
• Preventing "Gummy" Failure: Aluminum tends to stick to the drill bit, causing overheating. Lubricant is critical to prevent this, and high, consistent feed rates ensure the bit shears material rather than rubbing.
• Tooling: Carbide bits allow for higher SFM and cleaner holes compared to HSS.

 

[Rob R]

It also depends on the grade of the aluminium. Sometimes it is really soft and chewy, other times it drills like a dream.
Do a couple of test pieces, you will know when it 'feels right'.

 

[Dog Star]

Simon,

I am grateful to you for observing that I ought to have stated the diameter of the HSS drill to be used - the size is 4mm and the OP has been changed accordingly. Using the information that you have provided I am going to run the drill at 8500 rpm, coolant/lubrication probably WD40.

Rgds, Graham

 

[Chris Veitch]

I've seen a YouTube machinist using isopropyl alcohol as a lubricant for aluminium recently which seemed to work pretty well. Admittedly it was for parting off rod rather than drilling, but the same principles should apply. As an aside his channel is quite entertaining, not least because he often makes the same mistakes as me (but on camera).

 

[simond]

I've seen a YouTube machinist using isopropyl alcohol as a lubricant for aluminium recently which seemed to work pretty well. Admittedly it was for parting off rod rather than drilling, but the same principles should apply. As an aside his channel is quite entertaining, not least because he often makes the same mistakes as me (but on camera).

The flash point of IPA is a bit on the low side… I really would not recommend using it in this context, it can form a flammable mixture at room temperature, and using it asca machining lubricant presumably spreads it far and wide!
Whilst it’s really unlikely that a spark could be struck from aluminium, it would not be difficult to imagine another source of ignition.

Flash point	Open cup: 11.7 °C (53.1 °F; 284.8 K) Closed cup: 13 °C (55 °F)
Autoignition temperature	399 °C (750 °F; 672 K)
Explosive limits	2–12.7%

 

[JimG]

Whilst it’s really unlikely that a spark could be struck from aluminium, it would not be difficult to imagine another source of ignition.

Simon,

From many years ago, I remember, when sending film camera crews down coal mines, that the main safety consideration was the alloy bodies of cameras causing sparks if knocked against steel props or rails.

Jim.

 

[simond]

Simon,

From many years ago, I remember, when sending film camera crews down coal mines, that the main safety consideration was the alloy bodies of cameras causing sparks if knocked against steel props or rails.

Jim.

Jim,

I'm surprised by that, but it adds weight to the argument that alcohol is not a first-choice cutting lubricant!

I don’t even have a good idea of how to find out if it could be a real risk. I did a bit of Googling and found the bit below on Wikipedia. It suggests that striking the flint causes tiny particles of the steel to be removed with enough energy to be hot enough to burn, and thus ignite the tinder or vapour mixture. I don’t think that aluminium (alloys) could ever be hard enough to break steel, so I doubt that the camera cases could strike sparks from the steelwork. Surely the steel wheels, on steel rails, would be more likely to do so. I could imagine steel striking particles out of aluminium, but I think they’d oxidise instantly, and I can’t imagine them burning. And it wouldn’t do much for the cameras either.

best
Simon

Flint and steel​

The cold remnants of steel sparks struck by Robert Hooke using a flint. These were collected on paper, studied using his early microscope and drawn by hand.
Robert Hooke studied the sparks created by striking a piece of flint and steeltogether. He found that the sparks were usually particles of the steel that had become red hot and so melted into globules.[8] These sparks can be used to ignite tinder and so start a fire.[9]

In colonial America, flint and steel were used to light fires when easier methods failed. Scorched linen was commonly used as tinder to catch the spark and start the fire, but producing a good spark could take much time. A spinning steel wheel provided a good stream of sparks when it engaged the flint, and a tinderbox designed to do this was known as a mill.[10]

In a modern lighter or firesteel, iron is mixed with cerium and other rare earths to form the alloy ferrocerium. This readily produces sparks when scraped and burns hotter than steel would. This higher temperature is needed to ignite the vapour of the lighter fluid.[11]

 

[Tycho14]

The issue with aluminium in coal mines is in relation to it striking rusty steel - high intensity sparks can be created - thermite reaction. It's been banned in UK mines following an explosion in 1958.

 

[simond]

The issue with aluminium in coal mines is in relation to it striking rusty steel - high intensity sparks can be created - thermite reaction. It's been banned in UK mines following an explosion in 1958.

Thanks, that’s interesting.

I remember the thermite reaction from school chemistry. A couple of lads “from the back of the class” mixed rather more reactants than Sir had instructed, placed a Bunsen underneath, and retreated to a safe distance. That was interesting.

as usual, Wikipedia provides a wealth of info, Thermite - Wikipedia, but suggests that ignition is at least not simple to achieve. It also suggests that having mixtures of metal filings & dust in an area where grinding wheels are used is probably a bad idea. I’ll mention that to the production manager this morning.

 

[James Spooner]

I remember watching rails on Britannia Bridge in Porthmadog being laid and then connected to each other by thermic welding. Quite an impressive sight.

Nigel

 

[Bob Essex]

Getting back to the original question because aluminium is generally a soft material I have always used slower speeds with no lubrication and for aspects such as drilling holes etc. used lower feed rates to avoid the drill jamming and especially for deep holes where lubricants can mean a grinding paste type scenario can arise. Not an issue for 3/32” with a large dia drill though.

Bob