Thread: One of those "What the hell?" moments

Sometimes things do go your way!
Not long ago I bought a piece of 150mm dia bright steel for turning and milling.
The old guy doing it for me said it was hard as "billygoat $h!t" (one of his funny old sayings)
He thought I got him some tooling steel, so maybe there is a glut of quality steel at the moment
and the're under classifying it to get rid of it.

Um, that's the sort of finish I always look for when I use CCMT tips, I find it fun to see if the lathe can cope with the tooling! It looks like you're taking a fairly gentle cut; if you go a bit more aggressive you'll probably find the chip breaker works fine. When I get long spirals of swarf like that I just know I'm going to end up wearing them before the end of the cut.....
If your machine can cope try to get a little closer to the ideal tip speeds and feeds. I flood with coolant as well and just accept the mess, a decent chuck guard helps keep mos...some of it in the drip tray....

Sparks are a bit unusual; are you sure the tip isn't rubbing at all? Maybe just a bees' winky more feed and check the tool height. Back to coolant, if you use a decent water soluble oil mix it stops those tiny spot welds you can see on the finished surface of the top piccy.

Still looks pretty but.

Thanks Guys
I posted this because I was surprised at the finish that I was getting off tool - normally I run carbide slightly faster than HSS (say 2 to 3x), but not having looked at the literature for many years didn't think that I should be up around 9 time faster. When I first bought these tips and holders I had a 7x14 lathe, 1/2 HP, so it was never an issue. I didn't have the speeds or power to run them as they should be. This lathe is 3HP so should be able to cope with bigger DOC and feeds. It would be nice to get the chip breaker working as those long chips do worry me.

Strangely, a coolant pump was an OEM option for this lathe and the original buyer didn't go for it. It's one of those things that is on the refit list but I'm undecided on whether to run water soluble to take heat away for this sort of work or cutting oil for threading and parting. As it is everything is working fine dry but the chuck and tooling were certainly warm after this effort.

Michael

With TC tooling used as it can be the heat generated is quite phenominal; if used dry then the workpiece expands enough to throw out your tolerances unless you allow it to cool before doing your finishing cuts. A soluble oil/water mix keeps everything cool (ish) and does improve the surface finish; the downside is the mess because you have to throw A LOT of coolant on your work area and when it runs down to the chuck it'll spray everywhere. Go all HSSE on yourself and fit some big chuck guards that completely enclose the chuck and a fair bit of the workpiece, and also buy a magnetic based chip deflector you can mount on the cross-slide. This will reduce the ridiculous amount of coolant sprayed everywhere down to a minor amount of coolant.... sprayed everywhere.

Hi Michael,

When you see sparks off carbide, it usually means a chipped or blunt cutting edge.. I've seen video's of hard turning and hard milling that produce red hot chips.. I think that's PCD tho..

Regards
Ray

Very interesting Michael.
I'm sure my go to WMNG tips state 120-170m/min om the box, i'll have to check. One thing i always find with carbide is i get a better finish with a bigger DOC. If i try to take .1mm the finish will be no better than of a standard HSS cutter (not a finishing cutter) If i take .5 or even 1mm DOC the finish is like the one you have shown.
Where you using the lathe feed, or just feeding by hand? One thing that scares me with carbide is at the revs required for smaller dia's the feed is really fast, and it doesn't give you much thinking time.....

This turning was done with power feed - but not a high feed rate. To me it looks very close to a ground finish, which is one of the reasons I was impressed with it. I understand what you mean about the power feeds though Ewan - I'm half tempted to try and find an insert that hasn't got such a high surface speed requirement just so I don't have to run so fast.

Ray, I'll check the insert tonight and see but it is the knife tool I rarely use, so I think it would not have been very worn at all. I did notice a couple of small voids in the steel near the surface, so I'm wondering whether the sparks could have been due to inclusions (it was 100mm bar and the finished size is 3 5/8", so still near the surface). The bar itself was not all that flash. The rolling process had left it with a couple of ears a few mm higher than the rest of the bar so anything is possible.

Michael

Checked the insert - While it has the gold coating has worn off in a couple of places, there are no chips or dings etc there. More likely inclusions in the steel?

Originally Posted by Ueee

If i try to take .1mm the finish will be no better than of a standard HSS cutter (not a finishing cutter) If i take .5 or even 1mm DOC the finish is like the one you have shown.\

Ewan,
I recall someone telling me on this forum that, with carbide inserts, the DoC needs to be at least a large as the radius of the the tip.
Chris

You are right Chris, the tips I have are a .25mm radius corner, but the doc on the box says 1-3mm. I was very wrong with the surface speed for them, it is 140-320m/min. The parting tips however say a leisurely 50-120m/min. My lathe simply won't cope with speeds like the tips need, I normally run them at around 100m/min, and still get that nice finish at a decent doc.

Normally aim for 200m/min and 0.25 feed per rev, no coolant, for roughing mild steel.
Heavy roughing you can go up to 0.8 mm/rev on the right machine.
0.1/0.15mm for finishing.
Chips should break into small pieces and the majority of heat generated gets taken away in the swarf.
Sometimes hard to run at that pace on smaller work and some of the older small lathes cant run fast enough for the modern lathe tooling.
Is fun too when a piece of hot swarf goes down your shirt front.

Originally Posted by Michael G

To me it looks very close to a ground finish, which is one of the reasons I was impressed with it.

several months back a mate demonstrated some ceramic inserts to me on some very hard stuff..I was impressed watching all this red hot (and I mean glowing red hot) swarf coming off and the finish it left..as you say it looked polished

I asked him how they performed on ms and he said he didnt know but he tried it...very deep cuts, red hot glowing swarf going all over the lathe and the finish was the same...polished??

my finish too is dull grey on ms, and looks like the swarf has been ripped off also......I must give the ceramics a try as he gave some some tips...and I now have a tool holder for them

Ceramics arent designed to cut mild steel.
Really are for higher hardness steels.
You need higher cutting speeds than carbide for a Ceramic insert to work properly.
Should get a nice shiny finish with just carbide inserts at the right cutting speeds.

Originally Posted by Clubman7

Ceramics arent designed to cut mild steel.
Really are for higher hardness steels.

yes I know that...but that post was for info only