Cutting Speed and RPM on the Lathe and Mill

[TomG]

Proper rpm on the lathe and mill increases tool life and productivity. This lesson discusses how to determine the proper cutting speed for various metals and how to convert that cutting speed to the correct rpm for the tool or part.

Tom

[b4dyc]

Neat! I will have to give this a go :) I use the ``that`ll do speed`` D`Oh!

[Mayhem]

Thanks Tom - Ken just walked me through this last week and this has just reinforced what he said.

One question (that I didn't think of last week) is what do you do if your machine cannot reach the calculated speed? For example, there is no way I could spin a 1/8" endmill at the 9600 rpm needed for brass. Or what if your mill couldn't go slow enough for the 6" slitting saw you have there?

[TomG]

Andy, the "That'll do speed" will get you broken burned or broken end mills. You'll be surprised how long they last when run at the proper rpm.

Darren, If you can't reach a high enough rpm, just run it at max and reduce the feed accordingly. Not getting slow enough is a different story because even light cuts may still generate enough heat to trash a cutter or tool bit. Getting slow enough shouldn't be a problem for your lathe.

Tom

[Mayhem]

(10-01-2013, 08:01 AM)TomG Wrote: ...Not getting slow enough is a different story because even light cuts may still generate enough heat to trash a cutter or tool bit. Getting slow enough shouldn't be a problem for your lathe.

Tom

Smart arse

Actually a ø 12" chunk of cast iron would push it past it's lowest speed of 25 rpm

I was thinking more of my mill, which has a range of 70 - 2500 rpm

[b4dyc]

Just a thought Does this work with metric endmills? or do we need to use another formula
I agree, i do need to use this as i have had mixed results with my end mills before, although i think thats down to the quality rather than any thing else

[PixMan]

In the formula Tom has given as "4 x cutting speed / cutter diameter" is for converting inch cutter diameter into feet. The constant derived by:

(Cutter diameter x pi)/12 (12 inches per foot)

It actually generates a constant of 3.819718634, so many people round up to 4. I use 3.82.

For metric cutting speeds and cutters, the cutters are usually given in millimeters and the cutting speeds given in meters per minute.

I wish I had time to figure out the simple formula for metric, but I'm sure it's out there.

[Mayhem]

I'd just convert the metric to inch to make it easier, otherwise you would need to know the surface meters per minute for each material. So if you are running a 10mm endmill in 1018 the calculation would be:

4 x 100
0.394 (10mm) = 1015 rpm

note: 1mm = .0394"

[dallen]

nice video

[TomG]

Thanks David.

Ken, I never know how much detail to include in the videos. It's nice to know the background behind some of these common formulae, but at some point eyes start to glaze over.

Andy, I agree with Darren, the easiest way to apply this formula to metric end mills is to just convert their diameters to inches.

Tom