Cut using as much of the length of the endmill as you can, rather than taking shallow cuts. Lots of shallow cuts wear out the edges on the end/corners of the endmill long before you've removed much metal.

Also, assume that you can remove 1 cubic inch of steel per minute for each horsepower that the motor's got (other unit systems are available ). Adjust your width of cut to take as much of the motor's power as you can, subject to belt slip etc.

Generally a milling attachment on a lathe will be considerably inferior to a mill for several reasons, most seriously lack of rigidity, less travel and often harder to set-up.

If a particular job, like facing, can be done on a lathe, I prefer the lathe to a mill. It's because the lathe cuts with a single point tool which is less stressful on the machine. That said there are many, many jobs for which a milling machine is the better option. Not because a mill munches metal faster but because it's often more convenient. Slots, edges, drilling, and holdling awkward work are all easier on a mill than a lathe even if you have to take things slower.

All things being equal a mill and lathe of the same power will remove metal at the same rate. But things often aren't equal. A milling cutter has long cutting edges on the flutes and the base. The cut isn't concentrated as it is on a lathe with the result that depth-of-cut can't really be compared. Another issue is that milling cutters are more likely to vibrate than a single point tool. The rigidity of the milling machine matters: even if the motor is sufficiently powerful, the mill may not be up to it. Small mills are less rigid than big ones. It's important to reduce the mills tendency to vibrate by making sure the gibs are tight, and – where possible – locked before taking cuts. Also that the cutter is sharp, and the operator isn't too gung-ho.  Make sure swarf is cleared away.

It sounds as if you're taking a heavyish cut on a small mill that might on the loose side. Depth of cut, rpm, and feed-rate all matter. Some rules of thumb:

• Clamp and lock everything down firmly. Work, gibs, and slide-locks.
• Check the tool is sharp. (Gentle rubbing soon ruins milling cutters, even new ones.)
• For HSS rpm=10000 / cutter diameter in mm will be about right. 10000/15 = 670rpm.
• Depth of cut 5 – 20% of cutter diameter. On a small mill, I'd try 10% ie. 1.5mm
• Feed-rate by experiment. On a small mill as fast as you can go without the machine complaining.
• Lubricate HSS, ideally flood cooling the job when a lot of steel is being removed.

Don't be surprised if you need to experiment with rpm, depth of cut and feed-rate. It's not always easy to find the combination a mill likes best.

Dave

Edited By SillyOldDuffer on 05/12/2017 12:13:25

The lathe is very good at this sort of work, is faster than the mill and uses cheaper tools. I often use the lathe in this way. Colin