Speeds and Feeds - Aluminium

[Ben17484]

I use whatever my lathe was last set at. Aluminum isn't picky. You can get an excellent finish from 200 - 2000 rpm. The 'official' speeds are only a guideline, and they are optimized toward production - i.e. "what's the fastest I can go?". Don't be afraid to slow down (unless you're selling your labor...).

GsT

Interesting. I assume you need to adjust the feed rate if you slow down the spindle speed to reach the desired SFM for finishing? Or is that not how it works?


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[Ben17484]

As a hobby machinist, I use 250 for the SFM of aluminum with a HSS cutter. The formula (the easy way) ends up being 1,000 / bit diameter (workpiece if using the lathe) in inches = RPM

For example, 1000 / .5 = 2,000 RPM for a half inch cutter. This always gets me in the ballpark, quickly. I don't use online calculators, nor do I trust the catalogs for SFM.

In your example, I'd run that part much closer to 1,500 RPM. It's conservative, but I'm not a production shop and I'm not trying to make more parts faster.

I also use HSS for aluminum on my lathe. Carbide likes to take big cuts, and HSS is much better when sneaking up on a dimension. Because I've purchased used machines and tool boxes a few times, I have several lifetimes of HSS blanks. Grining them isn't difficult once you get some experience.

Thanks for the reply. I’d seen a similar formula on a YouTube video before, but couldn’t remember which one. I’d guess if I’m using carbide I’d need to almost double the numbers you quoted? Or just use HSS for aluminium. I also have a lifetime supply from buying old machines that came with a bunch of ‘extra stuff’, I’ve just never learned to correctly grind them. I guess I probably should.


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[PNW_Guy]

Thanks for the reply. I’d seen a similar formula on a YouTube video before, but couldn’t remember which one. I’d guess if I’m using carbide I’d need to almost double the numbers you quoted? Or just use HSS for aluminium. I also have a lifetime supply from buying old machines that came with a bunch of ‘extra stuff’, I’ve just never learned to correctly grind them. I guess I probably should.


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There's a ton of YT vids on grinding HSS. It's not difficult once you learn the basics.
For carbide you can bump your RPM 50% at least.