Interpreting Cutting Speed Tables

[john_reese]

I suspect the letter designations refer to the material being cut. Kook at the right side of this chart: http://www.iscar.com/Ecat/EN/iscar_grade_chart.pdf

 

[Bob Gibson]

My table is
Left vertical column =Material (inc items such as Aluminium, Cast Iron etc) so this cant be the cutter column
Across the top the horizontal column headers contain the items I listed in my previous post.So the horizontal column must be cutter material because no body would make a cutting tool out of aluminium !!!
I guess I just answered my own question

 

[Wizard69]

What do you normally machine? Aluminum, steel, cast-iron, stainless?

What if you were handed a very high-dollar piece of Inconel, K-Monel, or Titanium, and you needed to make first-time quality cuts? Would it be worth your time to look up the recommended tooling & feed rates?

If I got handed such a nice piece of material I might trade it for better tools.

I really understand his point though, this isnt industry, you goal isn’t maximum speed/production so calculations to reach those values don’t make sense. This especially in the common materials found in the home shop. Even when the uncommon ends up in the shop an experienced machinist can adjust on the fly to material conditions. In fact I had to do this with a bit of heat treat 4340 recently.

Frankly I kinda doubt any calculations would have help on a flimsy hobby machine. On the flip side if I had a rigid machine with all the proper tooling and hardware it would be a bit foolish not to start with th suggested machining parameters for what is about to be machined. This is even more so if we are talking CNC machining.

I like to think about this relative to a drill press. Yes the ideal RPM would be great but reality is you only have a few course settings (assuming belt driven here) beyond that feed rate is all by feel. Yet we can get perfectly good results from a drill press. If any attempt at all is made to adjust the drill press it is likly done off the cuff.

 

[john_reese]

Bob,
You are overthinking the whole surface speed thing. The tables given by the major manufacturers are based on industrial machinery in good condition and are probably somewhat optimistic. Manufacturers need to optimize their machining operations. Hobbyists do not. The speeds and feeds given in the Little Machine Shop tables are probably the most useful for hobby sized machines. Whether or not you can achieve the surface speeds listed depends a lot on the rigidity of your machine. For gear head or step pulley machines you probably will not be able to match the recommended speeds exactly. Just use the nearest machine speed. There is no penalty for exceeding the suggested speeds except for tool life. Experiment and find out what works best for you.

 

[Hopper]

A much simpler formula taught when I was an apprentice:
For HSS tooling, on mild steel:

400 divided by job diameter (in inches) = RPM.

For carbide tooling, double the RPM found by the above formula.
For brass or aluminium, double the RPM.
For cast iron or alloy tool steel etc, halve the RPM.

Thus, for HSS tool, cutting mild steel,
RPM for 1" diam. = 400 divided by 1 = 400rpm.
RPM for 4" diam. = 400 divided by 4 = 100rpm
RPM for 1/2" diameter = 400 divided by 0.5 = 800rpm.

Simples.

(There is a simple number like this for metric too, but it's too modern for me to figure out. )