Feeds and speeds. Some tips for a newbie please!

[Richard]

That looks like the cutter has been rubbing more than it's been cutting.

Speeds and feeds nearly always involve some experimentation to find what works best for your machine.
The key thing is tooth loading. Too much and the cutter will snap/spindle stall, too little and the cutter rubs. The smaller the cutter, the more precise the tooth loading has to be.

For most machines, two flute cutters are better, as it allows slower feed rates for any given spindle RPM (double the number of flutes, and you have to double the feedrate to achieve the same tooth loading).

Speeds and feeds calcs (I personally use FSWizard) generally only give you an estimate. If what they're suggesting isn't working, it can be worthwhile to look up the cutter manufacturer's specifications, and work out the figures manually to give you the recommended ranges. First work out the possible spindle speeds (manufacturer's will give a recommended surface speed range), then once you have the min/max RPMs, calculate the required feedrates at those two speeds for the min/max tooth loading.

Hi m_c, assuming you're looking at my photos, that cutter cut beautifully for the first 5m of the cut (it was a zigzag path 350mm long, moving across 10mm each pass, doing 30 passes in all).

It left a very clean smooth cut then suddenly it seemed to get noisy and the surface finish got worse. I'm assuming this is when the edges went off for some reason....

This was supposed to be carbide, but no idea if it really is, it was a very cheap set, 2mm to 12mm, 8 end mills, for £25! LOL. (Just checked, the carbide bit is almost exactly twice the weight of the HSS one and it much less magnetic, so probably is carbide)

If there was a build up of aluminium on the tips, would that errode the edges like this?