Milling cutters choice

Apologies if this has already been answered but I’m looking to purchase a set of milling cutters and there seems little cost difference between tin coated and titanium coated. Just wondered the best choice to make and why please.

What metal are you hoping to cut as some is better tackled with uncoated. I would tend to avoid sets as they are usually bottom of the range and you seldom need them all.

As Jason says, the work piece metal is what should guide you. I once made the mistake of thinking I could get away with a coated cutter on aluminium as the job was small and the cutter brand new. The aluminium built up on the cutting edges within minutes.

Martin C

Hi Gents

im cutting my teeth in ME with a Stuart S50 to give you an idea of current needs and purchasing tools and cutters along the way?

So the old S50 throws up the first issue of it being in imperial measurement which somewhat limits the choice of cutters as the majority now are metric. I would tend towards a few general purpose cutters in metric and any specific imperial ones needed for the S50 can be purchased as needed.

A lot of the Tin coated cutters particularly thos esold in sets are a bit "tinny" and not particularly good so would personally avoid that at teh lower price scales.

TiAIN Cutters are quite common and you find this coating on the better value ones though for manual use on a model debatable if the coating gives much of an advantage.

Uncoated will also do the job and that is what has mostly been used in times past, as John mentioned it is better for Aluminium and also works well on the other non ferrous metals such as brass and Bronze.

The next thing to consider is type of cutter, again in the past it was usually a 2-flute "slot drill" or 4-flute "end mill" but now there is far more choice. I would suggest going for 3-flute cutters as they are a good compromise between the two and you don't end up starting out having to buy as many cutters.

As for sizes I see you have a Mini-mill and I suggest sticking to the smaller size cutters which can be run fairly fast so you get the motor running in it's sweet spot. For general use a 3mm, 6mm and 10mm would do to start you off plus the specific imperial ones needed for the stuart.

For the Metrics look at the HSS 3-flute cutters from APT or ARC with the TiAIN coating as you are not going to be cutting aluminium at the moment and the imperials something like the uncoated FC-3 "disposable" cutters from MSC shown on page 271 of their virtual catalogue. You could even get the metric cutters from the same page of the MSC cat particularly when they have them on their regular discount flyers - the uncoated will be fine.

Edited By JasonB on 04/02/2021 19:13:13

I'd agree that sets are a bad idea. The cheaper sets in particular are often very poorly ground and will never give a good finish. I reckon 80% of my vertical/CNC milling is done with 10mm and 6mm cutters. I use 4/3/2/1mm cutters as needed.

For aluminium I use uncoated and polished cutters, which reduce swarf 'welding' to the cutter, like this:

Choice of coatings depend upon your mill. Some smaller mills will not be able to run cutters fast enough, or with big enough DOC and WOC, to make good use of the coatings. A TiN coating will at least add some hardness to the cutting edges. But TiAlN needs to be run hot (over 600°C) for the coating to be effective. The aluminium tends to melt and adds lubricity. So unless you can run the cutter that hard there's no point in paying for the coating.

Andrew

Clay. I've been milling on an SX2P, with mostly carbide cutters in an ER collet on steel for the last five years ( just for background). For what you are doing virtually any type of cutter would do and it will be just a persons preference. As per my first sentence I would use carbide coated cutters, as that is what I have. The cutters I have come from ArcEurotrade in the main as they are near me, but have used Amazon and other UK suppliers and really have had little trouble other than my ham fisted approach sometimes. Mainly I use an 8mm cutter as that I have found sweet for my machine and gives good cutter life, smaller cutters are used as required but still switch back as soon as practical.

Good luck with the Stuart.

For aluminium I've found un-coated solid carbide are best.

The only problem I've come across is I can't run them fast enough in small diameters.

I did adapt a 'trim router' to fit lathe tool post but it's fixed speed (27,000rpm) worked OK even on 1/2" thick steel (A36, structural steel, don't know UK equivalent, probably EN8 or similar?)

Cutter was 2.5mm dia and 'mostly OK' (not overheated or chipped) after about 35" of cutting.

It was actually easiest 'trepanning' I've ever done

Like Andrew, I use a few standard sized cutters. As long as they are smaller than finished size any cutter will suffice except for internal radii and a very few other scenarios. Larger than finished-size can be good for single passes at times but most milling operations can be ‘got around’, even if the ‘wrong’ size is only available.

Many thanks for all your reply’s, very helpful indeed.

Why would anyone tin-coat a cutter? Are you sure it's not TiN (Titanium Nitride .... often just referred to as "Titanium Coated"  ) that you are reading?

Edit ... darned winkies.

Edited By Peter Greene on 04/02/2021 22:27:04

Hi Peter

RDG in there milling cutter set section show Titanium coated and Tin coated HSS.

Clay, its in the fine details. RDG's site being all in capital letters make it hard to tell but Titanium Nitride coating is abreviated as TiN not Tin or tin. Though by some of the comments on these and similar sets they may well be tin

Ah thanks Jason.

make it hard to tell

In instances/sites like that, it is best to assume the lower quality as the best common denominator. That way, you won’t be disappointed with the lower quality item.🙂. Buyer beware (or buyer be aware).

If you mean by that, assume it's "tin" (i.e. Sn) .... again, why would anyone coat a cutter with tin (Sn) in the first place? It isn't a question of coating quality but of coating appropriateness. What would tin (Sn) do for the cutter? (Other than probably get removed in the first cutting pass).

(I can see that very loose/un-knowledgeable references to "tin" might occur but I wouldn't assume that it actually meant a "tin" (Sn) coated cutter.)

Edited By Peter Greene on 07/02/2021 17:24:02

What I meant was that if the website is at all possibly ‘devious/doubtful/ambiguous/misleading/etc’, look elsewhere.

Exactly the same as sites which sell air compressors air by ‘air displacement’ rather than delivery. Same as sites which only quote motor power in kW without any reference to efficiency or whether the power is ‘output’.

That is ignoring the items which may be bought, thinking they are something they are not, without checking exactly what you are buying.

Plenty of good sites where openness is plentiful.

Maybe tin coated is truth in advertising.

Quick review of coatings.

Any hardenable steel can be used to cut machinable metals. Ordinary tool-steel works well unless it overheats, unfortunately rather easy to do. The Victorian's did well enough with tool-steel cutters, but they cut slowly with much flood cooling.

HSS revolutionised cutting because HSS alloys resist heat far better than Carbon steel. A plain carbon steel loses hardness below 200°C, whereas some HSS are still hard at red heat, about 550°C. Later versions of HSS are also tougher than plain steel, thus HSS can remove metal 5 or 6 times faster, and stay sharp for longer. Good though it is, HSS isn't the best possible cutting material.

Carbides are harder and even more heat resistant than HSS. They can remove metal about 5 or 6 times faster than HSS. High metal removal rates are a major advantage in manufacturing, less so in a home workshop. We don't get the full benefit of carbide and for many purposes HSS is fine, and it can be ground to special shapes.

The cutting performance of both HSS and Carbide can be improved by coating them in something harder and smoother.

Titanium Nitride (TiN) is the original gold coloured coating. Under the same conditions TiN coated HSS should last about 3 times longer than plain HSS.

Titanium Aluminium Nitride (TiAlN) is smoother and harder than TiN, plus it can withstand higher temperatures, and it age hardens.

Titanium Aluminium Silicon Nitride (TiAlSiN) is super-hard.

Coatings are extremely thin and don't alter the tool dimension. They're not particularly useful on tools reground by the user. Coatings aren't magic because cutting performance always depends on the underlying tool. A well-made coated cutter will last longer than the same cutter left plain, but a badly made cutter coated in TiN is still a badly made cutter. Nothing to stop dodgy manufacturers spraying cheap nasty poorly ground Carbon Steel twist drills with TiN. Beware very cheap tools!

Although I don't go out of my way to buy coated tools, I don't avoid them either. I mainly buy mid-range cost from reputable suppliers without worrying about whether or not they have coatings. Most of my twist drills are uncoated (from Tracy Tools), and for my purposes they appear to work as well as a TiN coated expensive brand.

Self taught, poor technique turned out to be my main problem. My teacher was an ignoramus. Took me a while to develop a practical feel for what's right and wrong across a range of materials. Often a narrow gap between a tool cutting nicely and the same tool struggling and going blunt. Letting cutting tools rub quickly ruins them, coated or not. So does over enthusiasm, failing to clear swarf, over-heating, wrong rpm, and failure to lubricate appropriately. Brass prefers a sharp new drill, and using drills on steel spoils them for brass. Experience matters!

I feel learning how to cut is more important than throwing money at expensive tooling. A set of drills I thought were rubbish as a beginner are actually quite good - apart from the half-dozen I wrote-off...

Dave

SoD - Thanks for taking the time to put this 'guide' together, clarified many points I was confused about! One query though - "Brass prefers a sharp new drill " I was always taught that you should take a tiny amount off the edge of new drills for brass to stop any risk of them grabbing. The drill equiivalent of zero top rake on lathe cutting tools. Its something thats been discussed a number of times before in the forum, but there seems as many opinions as contributers? So I remain confused (as usual!)

Regards Mike

Edited By Mike Hurley on 08/02/2021 11:56:25