is 'sharp' on HSS the same as 'sharp' on carbide? the load on the mill may be different.

I'd expect they have different co-efficient of friction, so the noise may well have been the swarf sliding (or not) over the clearance surfaces.

or not….

I asked a related question recently about avoiding swarf ribbons. Andrew Johnston put me right by highlighting the importance of feed-rate. I'd twigged that carbide works best cutting 3 to 5 times faster than HSS, and that deep rather than shallow cuts are needed, but not that the rate of cut should be aggressive as well.

When you get carbide right, hot chips fly off. Reduce rpm, depth or cutting rate and you get ribbons. If you are too gentle, carbide rubs and chatters, which I think matches Alfie's description.

Alfie asked 'Why would a Carbide cut different to HSS on aluminium?'. I did some digging after Andrew's advice and found that the way metal is removed varies with speed.

• Carbon tool steel cutters lose hardness at about 220C, which temperature is easily reached in a power tool. For that reason the maximum rate the Victorians were able to cut mild steel was about 35 feet per minute. At these very slow speeds, the tool's cutting action is that of a knife through wood, and the tool must be kept sharp.
• Although HSS is mildly inferior to carbon steel in terms of edge and hardness, it stays hard up to about 650C. As such, HSS cutting rate is up to eight times better than carbon tool steel. At very high speed and deep cuts, a new cutting mechanism appears. Rather than the edge shearing at the point of contact, the tool acts as a wedge with the metal tearing just in front of the edge. This mode is said to need less energy than a cut, and it also means that more heat stays with the chip rather than overheating the tool. Unfortunately HSS isn't sufficiently heat resistant to cut in this way for long.
• Carbide is much harder and temperature resistant than HSS. On the downside, it is comparatively brittle and it doesn't take a good edge. But, run hard and fast (3 to 5 times harder than HSS) it cuts using the wedging mechanism, where a blunt tool is an advantage, and this saves much time and energy, most important in a production environment.

So, Carbon Tool Steel, HSS, and Carbide aren't one-for-one replacements. They each have advantages and disadvantages. HSS is popular because it's a good compromise. It's sharp enough to get a good finish at slow speeds, and man enough to do serious work. Carbide has many advantages, but you have to use it right. Gently turning a small diameter on a slow lathe with a small motor isn't a sensible way to use carbide. Hacking into a large diameter spinning fast on a big motor, definitely is. There's room for experiment, for example, the sharp carbide inserts designed for Aluminium seem to work quite well on mild steel at slow speed.

I have Chinese tools. One advantage they have over older kit is high spindle speed. As a result a lot of the work I do sits on the border between 'HSS is best' and 'Carbide Today!' After much messing about I still find it hard to choose between them; this I think, is mostly down to inexperience. If forced to choose only one, I'd go for HSS. As it is I use Carbide more than half the time. That suits me, but proves nothing. So much depends on what you're doing.

Dave

Edited By SillyOldDuffer on 27/07/2017 11:04:03

I'll differ a bit, I have some 10mm carbide mills with very sharp edges designed for aluminium. Run at 1600 rpm they send swarf everywhere and leave a decent finish.

Neil

Neil ,

I suspect you are talking about high helix cutters that some will not be aware of or experienced with – Now there is an article for MEW to discuss in the magazine in there somewhere !