End Mills and coatings

Hi All,

I am not happy with the low quality end mills i currently own and will not eat for a week so i can buy some new ones....

There are lots of options out there and a homeshop machinist generally cannot afford to have multiple sets of end mills in different coatings, different number of flutes, different sizes and so on - there are many combinations.....but then again, we are not doing production machining and so speeds and feeds can be sacrificed tremendously. So, question is - how can we minimise to the most useful only...

A set of center cutting 4-flute end mills is the start....but what coating? HSS or Carbide? My thought is that given we are typically machining cast iron, brass, mild steel - perhaps HSS with Aluminum Titanium Nitride (AlTiN) coating is the way forward. What are your thoughts?

I am thinking that uncoated HSS end mills are really best for soft materials and even TiN coated the same... Again, thoughts?

....of course next step would be the same in 2-flutes , ball end etc...

If you want the minimum then try 3-flute, will do slots without much risk of cutting oversize, end cutting so can plunge and still a reasonable number of flutes for side cutting without slowing the feed down too much.

UNcoated HSS will do for all, but if you want coated then TiAIN will do but keep it away from the aluminium. Carbide a bit better but also a bit more delicate so upto you.

Edited By JasonB on 20/04/2021 16:48:08

Greetings Matt, have you not considered some method of resharpening the ones you have?

Although I have never tried it, I am told the Harold Hall tool holder modified, works well, and is straight forward to make.

Just a suggestion.

Regards

Brian

I try to plan ahead and buy what I need when I need it! I have ended up with all sorts and sizes but mainly good quality HSS...

Thanks for the replies so far....

I will check out the Harold Hall sharpener for interest, however i still think i will get myself a decent set of end mills anyway.

Is TiAIN coating cheaper than AlTIN coating or was there another reason for suggesting it? From a quick google, it seems TiAIN is a good coating for high carbon steels whereas i thought AlTIN was better for mild steels/general?

I suppose it does raise the question about if to bother with coatings at all??? I figured uncoating mills were essentially fine for plastics, aluminium etc but not such a good choice for steels. Perhaps this is a good point to consider the pros and cons of each? For example, are uncoated mills actually sharper anyway?

Are you certain 'low-quality' is the problem? Beginners are often afflicted by other issues:

• Uncertain over-delicate cutting, perhaps related to wrong speed, trying to stop chatter, or not lubricating causes rubbing. Rubbing soon takes the edge off HSS and is a good way of rapidly spoiling cutters, even the most expensive ones. The effect is counter-intuitive: surely a gently treated edge lasts longer than one working hard? No, rubbing concentrates heat on the edge, and there's no swarf to carry heat away.
• Failure to remove swarf causes it mince under the edge, again causing rapid blunting.
• Over brutal cutting also causes rapid wear.
• Poor choice of material! Is the metal known to be machinable? Many are horrible, not meant to be machined at all, or requiring skill. For example, many stainless steels work-harden causing extreme wear to the cutting edge unless the operator does everything right. And aluminium welds itself to the edge and blunts it until cleaned off.

Apologies if I'm teaching Granny to suck eggs, but I have a guilty past. Starting out, everything I touched went blunt quickly. Exactly the same tools last much longer now. The difference is me working them hard, bit not too hard, and avoiding random nasty scrap!

Dave

There was a time when all you had was HSS. People seemed to manage quite well too.

Andrew.

Hi Dave.... Whilst i don't technically class myself as a beginner anymore (been home machining for 5 years or so), there is always something to learn from others and going back to basics is often the right way. Therefore your comments are valid - perhaps if anything, i am guilty of the first item more than any others!

So yes....blunt end mills is a concern....hence i might look at the sharpening options.

That said, they were cheap end mills to begin with and i tell myself everytime to not buy cheap tools and then guess what....the "amazing deal" comes up. So i might replace them with something better and hence the questions and then use the old ones to practice sharpening.

Not much in it price wise, infact just had a look at one of the 3 suppliers I tend to use and the TiAIN was a fraction cheaper than the ALTIN so if its going to allow the cutter to cope better with the odd hard spot in an iron casting there is nothing to loose.

Again of the coated HSS and coated Carbide that I have 95% is TiAIN spread over three suppliers with the odd bit of TiN making up the rest

If you are going to sharpen then then coating starts to become irrelevant after first use.

There is also a good argument for avoiding sets and just getting a small selection of individual cutters then add to them as you need a specific one or to replace blunt ones.

Edited By JasonB on 20/04/2021 18:35:14

....Is that because the sets tend to be 'cheap rubbish' and you are better spending the money on decent indivudual ones?

Yes in most cases and in the ones where the cutters are decent you may get sizes you won't ever use.

I suspect that coated endmills are unnecessary on hobby sized machines. They don't have enough horsepower to benefit from a coating. When a coating is applied it blunts the cutting edge, I think uncoated HSS tools with a sharp cutting edge are best in light machines. I have a 3h Bridgeport and most of the endmills I have are uncoated HSS. I do have a couple of carbide insert face mills

There are coatings for some quite specific materials, so new coating for Al, other coatings for Stainless, others for Ti and others for steel. Then there is the coatings for cutting very hard materials as well.

I’m with John Reese on this one. Dad ancd Grandad did nog have this multitude of coatings to deal with and they got by OK.

IMO, most coatings are there to befuddle the hobbyist - get them buying more cutters than they probably actually need. I go for the material. HSS and carbide do all I need done. Different cutting edges/angles, yes, but that is about my limit.

Edited By not done it yet on 24/04/2021 07:53:31

What,s that old saying about the workman blaming his tools--------------------?

I have no coated end mills of any kind and I machine mostly BMS. Dont have any real problems with them and they are cheap enough to replace. Any time I did/do have a cock-up, it,s my doing, not the cutter.

My view is coatings are a 'good thing', unless the tool is used inappropriately, most likely on Aluminium.

The coating is extremely thin - on cutting tools about 0.7µm - and I doubt it reduces sharpness. Even if it does, uncoated HSS wears faster than coated HSS, so an uncoated tool will soon end up blunter than a coated one. (A microscope would reveal the difference._

Coated vs uncoated performance is tested in an industrial setting, where it's shown TiN multiplies tool life by a factor of 4x, and TlAiN by a factor of 10x. The comparative test is done at maximum metal removal rates typical of manufacturing, not the more complicated usage patterns found in home workshops, where we work slower (which extends tool life), but unscientifically (which reduces tool life, especially in unskilled hands), and apply many different processes. Industry is very different from what goes on in my lightly loaded workshop: they measure tool-life in minutes, whereas mine might last years unless I do something stupid.

Amateur measures of tool life can't be accurate because the way we use them is so random, and industrial measures of tool life may not be meaningful to us for the same reason.

Plain Carbon tool steel cuts as well as HSS provided it's not overheated and regularly resharpened. In comparison HSS is tough stuff, wears far more slowly, and is much more heat-proof. Coating HSS improves performance further by protecting the 'soft' HSS with a thin hard layer. The layer resists corrosion and reduces friction, hence heat, because it's slippier than steel.

Coated HSS leaves uncoated HSS in the dust, but only if the cutter is used optimally. That means matching the tool to the material, clearing swarf and lubricating correctly, setting optimum depth of cut, feed-rate, and rpm, and having a machine with considerable rigidity and power repeatedly doing the same operation. Though I avoid mismatching, I can't meet all the requirements needed to get the absolute best out of cutters,

So I don't care much and buy coated or uncoated as it suits me. I prefer coated because in theory they last longer, but I certainly don't avoid uncoated. On similar individual cuts, I doubt it's possible to tell the difference between coated and uncoated HSS. The advantage of coated cutters is simply they last longer than uncoated, but that's almost impossible to prove in a home workshop. Industry have proved it, but they don't work as we do.

Best advice I can offer is give both a try. I doubt the difference is worth fretting over in most home workshops.

Dave

There was a time when all you had was hand chipped flint, people seemed to manage quite well too!

HSS was adopted by Model Engineers when it was literally Cutting Edge in industry, the desire to stop time and manage with what Great Grandad had when he was actually using the best available technology at the time is quite funny!

How many urban myths have been generated by an excess of "Disposable" income? Sorry, I'm of the old f*rt brigade when tools for the lathe were either carbon or HSS and a "Wimmet" tipped tool was held in holy reverence even in industry where the machinery had the b***s to cope with strong cuts. Then accountants drove the "Faster cheaper" economy and I remember our toolroom foreman virtually breaking down into tears when the SKF rep told us to use the "New" three flute weldons once and chuck them away. as opposed to machining the tool steel blanks to make the punches for my avatars components by co-ordinate milling on Sir Johns nemesis, a Bridgey. using a "Rougher", then a "Smoother" and finally a "Fine finisher". All this was emphasised with a "Film" showing the embryonic "Computer Numerically Controlled" ( no acronyms at that time) milling machines cleaving gert lumps of Aluminium for the aerospace industry.

Save thi brass Matt and learn the relaxed version of hobby machining.

Regards Ian.