Carbide end mills in a hobby machine? your experiences please.

[Roderick JenkinsParticipant @roderickjenkins93242]

+1. Almost all my turning is done with ccgt inserts (and cheap ones at that)

Rod

[SillyOldDufferModerator @sillyoldduffer]

Posted by samuel heywood on 09/02/2023 21:42:03:

Thankyou all.

Quite suprised that carbide is the favoured option for hobby use.

Actually I was expecting tales of doom & re-directed towards HSS.

…

Since time immemorial, old men have pinned youngsters into a corner to tell them nothing good comes of change. Everything is the past was better, quality was sky high, everything was cheap, and men were far tougher than today's weedy youth. Everyone wanted to be deafened in factories by noisy machines, and looked forward to being sent home with no sick pay after being mangled in an accident.

The history of engineering shows all innovations were resisted by the old boys of the day! They preferred horses to steam, rushes to candles, candles to gas light, gas light to arc-lights, arc-lights to filament bulbs, filament bulbs to fluorescent tubes, and now plenty of model engineers don't trust LEDs. Electronics, green and anything smart are all evil.

Same with cutting tools. When the compound slide was invented, old turners disparaged it as "Maudsley's Go-cart", claiming it produced low quality work compared with a master-turner armed with hand tools. Rubbish.

For most of the Victorian era, lathe knives were made of tool-steel. Tool steel cuts well but wears quickly, going blunt in a flash if allowed to get hotter than about 180°C. Hence the importance of suds. Despite HSS being tougher and about 5 times more heat resistant than tool-steel, plenty of old-boys stuck loyally to tool-steel, claiming it took a sharper edge and produced a better finish. Likewise, when carbide appeared, the next generation of old-boys brought up on HSS loyally defended it, claiming that carbide broke easily due to mechanical or thermal shocks, was blunt, produced poor finish, and much else that would destroy civilisation. Same thing with Steam and Diesel locomotives.

I think the issue is psychological. As we age evolution has wired our brains to rely more on experience than new learning, which is a mixed blessing. As a small child I learned to speak English in a few years and could read it fairly well by age 5. Now I understand the causes of WW1 but struggle to understand my mum's TV remote! Obviously not my fault; it must be because the modern world is full of unnecessarily complicated cheap tat that doesn't work properly. Ockham's Razor suggests the real reason is that I'm out of touch.

However, conservatives are gradually removed by time. Member opinion when I first found the forum was strongly pro-Imperial and violently anti-metric. Now I'd say it's shifted to mildly pro-metric. Same shift is happening with HSS vs Carbide: the next generation to enter the hobby have different preconceptions and are prepared to try new things. They're finding Carbide works for them.

I use both. Carbide ticks my boxes most of the time, but it's not universal. I've two main reasons for switching to HSS. I find sharp HSS is more tolerant of speed, depth of cut and feed-rate than carbide if a metal doesn't finish well. I notice HSS cuts ordinary mild-steel well, probably because it's a bit sticky and prone to tear. Most important for me is that HSS can be ground to any shape, making it premier choice for form tools and specials.

One thing to watch is generalisations. I've waffled on as if 'HSS' and 'Carbide' are two easily compared unique materials. They're not! Both are families of related materials, each member being optimised for a particular industrial process. Not all types of HSS are equally suited to all types of cut and material, and neither are all types of carbide.

So beware chaps who see differences in terms of 'quality', old vs new, or western vs far eastern : it's just as likely they don't know what sort of HSS they're using! Knowing the specification might suggest the particular HSS they happen to have isn't a good choice for the job in hand.

As a generalisation, Carbide performs best with high-speed deep-cuts, whilst HSS is more pedestrian. Counter-intuitively, the answer to poor finish with HSS is often to slow-down and take lighter cuts, whilst Carbide is likely to do better by speeding up and going deeper. The operator has to learn what works and what doesn't on his machine. Anyone who claims HSS is always best is wrong, as is anyone who insists Carbide is the answer.

Good news! As much hobby engineering is on the simple side and many problems can be overcome with skill, it's rarely necessary to worry about details. If it works use it, if it doesn't try something else. Be guided by advice but be prepared to experiment and practice, especially practice!

Dave

[Ron LadenParticipant @ronladen17547]

Posted by JasonB on 10/02/2023 09:03:56:

KWIL is the first person I can recall advocating **GT inserts for turning steel, he gave talks at the MEX and the first time I met him in person it was not long before he produced a small container of 1thou swarf from his pocket and said it was off a Myford using inserts.

It was you Jason that suggested GT inserts to me and that they are good for certain cuts on steel especially finishing and I now use them all the time. I have also found them good for the final two or three passes when boring to a finished size.

Ron

[Author]

Posts