Machining Hard Materials

[woody1Participant @woody1]

Evening all,

Just wondering how well your machine deal with hard material. Through naivety when I first bought my lathe I just thought chuck in a lump of stock and make some swarf. Its only a myford 3'' 1/8'' but if I try turning for example an off cut of axel or an ss bolt with HSS tooling no chance! Luckily, I have had donated a load of stock from a machine shop which cuts like butter.

David.

[woody1Participant @woody1]

[RainbowsParticipant @rainbows]

Not all HSS is equal. SS should be possible though maybe with M42. Other than that try carbide and if that fails too you need a tool post grinder of some sort. Ceramic insert tools don't to my knoledge work well on smalls lathes.

[Anonymous]

Not really a problem. Turning 303 and 316 stainless steel is straightforward; 304 is more problematic, but that's the material not the machine. I've also turned hardened silver steel (>65Rc) with no problem; although the CBN insert came off rather better than the carbide one. I haven't milled that much stainless steel, but what I have done was fine. I've also milled HSS tool blanks without issues when I need to remove significant metal before finish grinding.

Andrew

[woody1Participant @woody1]

What machines do you have fellas? My stainless Is generally marine 316 as mentioned Andrew, still a bit hard to turn though. I think I need to improve my ML's cross slide rigidity and backlash.

David.

[Frances IoMParticipant @francesiom58905]

on my small WM180 lathe I can handle 316 (with some trouble) using carbide or a freshly sharpened hss tool
What I think is 304 (judging from colour code as was a bin end and also that it was somewhat magnetic but certainly doesn’t work like mild steel seems to chip off rather than peel – 316 comes off as very fine wire) – took out one of my small carbide parting off tools when it jammed snapping the brazing and bending the support (the HSS smaller parting tool was also prone to digging in so I gave it up) though I could take very shallow almost polishing cuts with carbide – guess a narrow cutting wheel on an angle grinder is the best tool to cut it

Edited By Frances IoM on 10/09/2015 22:48:10

[John McNamaraParticipant @johnmcnamara74883]

Hi All

"316 comes off as very fine wire" above…. Yep razor sharp wire. sometimes it will wrap itself around the work. Don't even think of going near it while the lathe is turning. Even when stationary I always use pliers to remove it. It is not brittle quite strong in fact. I got bitten a while back by a wisp of it (and yes the machine was stopped), it caught and dragged on my finger…. Ouch!

Regards
John

[Anonymous]

Posted by woody1 on 10/09/2015 22:33:17:

What machines do you have fellas?

Harrison M300 and a Bridgeport with an early (low power) varispeed head and built-in backlash.

Andrew

[Ian S CParticipant @iansc]

Early in my days of lathe work I required a cup like piece of stainless steel 3" long with a blind bore 1.5" dia. The only steel I could get was 316, and the guy at the warehouse where I bought it was a bit sceptical about me being able to do much with it(he had worked in a machine shop for a good many years). I took it home and managed quite well with HSS tools, and miles of razor sharp swarf, I then cut an internal thread in the first 3/8" of the bore to fit it to the other half of the displacer cylinder of my second hot air engine.

Ian S C

[KWILParticipant @kwil]

Super 7 and M300 lathes, stainless not really a problem, but care with the right tooling.

[Neil WyattModerator @neilwyatt]

I turned down some really tough and nasty to turn 5/8" stainless to make a 3/8" post with a flange recently. Using a carbide insert I took 1mm cuts at about 700 rpm on my mini lathe. I had to use an HSS tool to get a half decent finish at rather less rpm as the carbide was uncomfortable taking shallow cuts.

Neil

[David Clark 13Participant @davidclark13]

I used to turn a lot of 316 AM stainless with no problems but 316 J turned red with the heat. Completely different metals.

[FatgadgiParticipant @fatgadgi]

Posted by Andrew Johnston on 10/09/2015 21:59:29:

I've also milled HSS tool blanks without issues when I need to remove significant metal before finish grinding.

Andrew

Hey Andrew – Doh, Guess it's obvious, but I never thought of machining HSS cutting tools before, that's brilliant. Do you use standard carbide cutters or coated / special ones for that (before I make an expensive experiment)

Cheers – Will

[FatgadgiParticipant @fatgadgi]

Posted by Andrew Johnston on 10/09/2015 21:59:29:

I've also milled HSS tool blanks without issues when I need to remove significant metal before finish grinding.

Andrew

Hey Andrew – Doh, Guess it's obvious, but I never thought of machining HSS cutting tools before, that's smart. Do you use standard carbide cutters or coated / special ones for that (before I make an expensive experiment)

Cheers – Will

Oooops – Trigger Happy  

Edited By Will Bells on 11/09/2015 16:41:28

[Ian PParticipant @ianp]

Posted by Andrew Johnston on 10/09/2015 21:59:29:

Not really a problem. Turning 303 and 316 stainless steel is straightforward; 304 is more problematic, but that's the material not the machine. I've also turned hardened silver steel (>65Rc) with no problem; although the CBN insert came off rather better than the carbide one. I haven't milled that much stainless steel, but what I have done was fine. I've also milled HSS tool blanks without issues when I need to remove significant metal before finish grinding.

Andrew

Andrew

I'm curious to find out how you machine HSS, I thought grinding was pretty much the only way.

Obviously the whatever cuts it has to be much harder, did you have to anneal it first?

Ian P

[Anonymous]

Will/Ian: You are correct, traditionally grinding was the only way to 'machine' hardened materials. But with the advent of carbide inserts, and more esoteric materials, turning of hardened materials has become possible. The advantages for industry are no grinder required, and parts can be hardened and then machined, ie, fewer operations. For turning hardened silver steel I used an ordinary CCMT carbide insert and a CBN insert. Both worked and left a pretty good finish. The carbide insert looked a bit sorry for itself afterwards, whereas the CBN insert didn't look like it had been used. The trick is to run fast with high feedrates; the CBN insert is very particular in this respect. This gets the metal in the shear zone red hot, so it is actually quite soft. As far as I could measure the hardness of the workpiece didn't change. The downside of CBN inserts is the cost, I think mine was £25.

As for milling HSS I don't anneal it. I use my oldest 10mm uncoated carbide 3 flute slot drill. The machining doesn't do the slot drill any favours, but it is old so I don't worry about it. Although the HSS toolbit is going to be finish ground afterwards the milling operation actually leaves a fairly good finish. Again the trick is to run fast and hard. The swarf needs to be coming off orange in colour, and the slot drill may well be glowing a dull red.

Andrew

[woody1Participant @woody1]

Excellent, thank you guys.

Knowledge of materials and the type of tool to attack with, along with experience seems to be more important than the machine your operating? As long as the machine is not a wrecked of course. Lots to learn!

David.

[Chris DentonParticipant @chrisdenton53037]

I use CCGT 09 inserts with: stainless 303 & 304, titanium grade 2,5 & 9, mild steel, aluminium. All is fine and give a very good finish from a fine cut.

Only problem I've had is with enlarging a 50mm hole that had been laser cut into stainless 304, think I was making 0.5mm depth of cut every pass. I presume it had been hardened from the laser cutting?

[FatgadgiParticipant @fatgadgi]

Thanks for the detail Andrew – I will try that and I have a couple of dog eared carbide end mills. I made a couple of accurate lathe tools to cut some worms (near to 0.7 mod) recently and rough ground then finished on the quorn. I had to make them spot on. It did the job, but it took a long time to get them accurate on the quorn after my hand approximation. Pre-milling them would have been much better.

Cheers – Will

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