Need Help!- Milling 4130 Steel

[JWB_Machining]

I Just tried to mill this with a 1/2" Coated Carbide with the RPM at 400 and a Feed of 10 IPM with a depth of cut of 0.25" Instantly my Cutter Broke. This was with a SFM of 520 and IPT of .0025

The Machinery handbook tells me Run this at 100 SFM with .010 IPT which translates to RPM of 764 and a Feed of 15 IPM. Is this Right? I Only have one Endmill left and i've kinda gotta get this done today.

[Geof]

400 rpm x 0.0025" per tooth x 2 teeth = 2IPM

If it was a four flute cutter it would be 4IPM

How did you get the figure of 10IPM?

Incidentally I think the Machinery's Handbook figure of 0.01" per tooth is a bit optimistic at least for a 1/2" dia cutter.

[JWB_Machining]

Sorry I Meant 4000 RPM. What's a Proper SFM and IPT when Milling Steel with a Carbide? Also how deep can my depth of Cut go before It Becomes a problem?

[Geof]

For 4340 I would probably go with not more than 300 feet per minute, quite possibly less.

Feed per tooth on four flute or more, something like 1% of the cuttere diameter for cutters 5/8" and above and 0.5% for smaller than 5/8". Two flute cutters are not as strong.

Depth of cut around 1/4 of the cutter diameter, bit less for cutters smaller than 5/8", bit more for larger.

A point to remember is that SFM and feed figures given by cutter manufacturers and the handbook are sometimes predicated on a short(ish) tool life in favor of removing material fast; it is always a play-off between the cost of the tool and the cost of the time. For one-offs I tend to halve whatever is recommended because the extra time is normally a small proportion of the total job time. For production very often time is money and it is more economical overall to burn tools out faster.