HSS and Carbide Milling mills

[Alfie PeacockParticipant @alfiepeacock58331]

[Alfie PeacockParticipant @alfiepeacock58331]

I needed to cut a 25mm x 40mm x 12 thick rectangle in aluminium using a new 6mm 3 flute Carbide cutter. The noise it made was a screeching sound that came from the mill, I tried different directions and was only around 3mm depth, also at different speeds.

I then changed the milling cutter to a 6mm HSS 3 flute and it cut with no problem, both mills are sharp as they are new.

Why would a Carbide cut different to HSS on aluminium.

Also the collets and clamps where fixed so no play on the sx2p mill when cutting

[russellParticipant @russell]

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….

[Jon GibbsParticipant @jongibbs59756]

Hi Alfie,

What speed were you running the carbide end-mill compared to the HSS?

Carbide should be run faster (~3x) and worked harder than HSS.

HTH

Jon

[SillyOldDufferModerator @sillyoldduffer]

Posted by Alfie Peacock on 27/07/2017 02:42:43:

…

Why would a Carbide cut different to HSS on aluminium.

…

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

[Neil LickfoldParticipant @neillickfold44316]

Was your carbide cutter made for cutting Aluminium specifically, or is it a general carbide endmill? They are very different cutters and different geometries.

Neil

[Alfie PeacockParticipant @alfiepeacock58331]

Thanks for all these replies, as for the carbide cutter I have no idea what type it is. It seems that for me general use on a hobby mill its best to use HSS.

[I.M. OUTAHEREParticipant @i-m-outahere]

Run it at double speed of,what you would with Hss and use WD-40 as a cutting fluid . Finish wont be great anyway so use the carbide as a rougher and switch to hss a better finish

WD40 is excellent for aluminium – one of its few usefull properties !

These days I only use carbide on cast iron or unknown materials as hss has a keener cutting edge and for home use it is better

Same goes for carbide lathe tools – run it fast and hard .

Bare in mind there are many varieties of aluminium and some are nice to machine some are not , try turning 6061 T6 after welding , it is like chewing gum !

Ian.

[Neil WyattModerator @neilwyatt]

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

[Danny M2ZParticipant @dannym2z]

Why anybody would use carbide cutting tools on aluminium and its alloys in a home workshop with typical hobby equipment often makes me wonder what one is trying to achieve? Is this just convenience or just an easy way out from sharpening tools?

Maybe I am just a luddite, but a well honed HSS (or even carbon steel for a keener edge) tool is well suited to creating a fine finish on Al. work.

Easier to sharpen too!

* Danny M *

[I.M. OUTAHEREParticipant @i-m-outahere]

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 !

[Neil LickfoldParticipant @neillickfold44316]

Yeah, the carbide cutters for Aluminium and plastics , really are something quite new and fantastic. They work very well even at low speeds, and the surface finish is very good as well. They don't have to be run really fast , so can be run similar speeds to HSS with no ill effects. There are even some with fancy coatings that reduce the Al from welding or building up on the carbide edge. On soft steels like free machining MS, these cutters also work very well giving a great surface finish. Some companies that are specialising in this technology are DHF, A local company here in NZ https://www.carbidenz.co.nz/6mm-3-flute-carbide-aluminium-endmill.html have a great range. I like these 3 flute cutters, great as a compromise cutter, so can plunge, face and do sides. These work really well on plastics and copper as well.

Neil

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