Strange Swarth

[YYCHM]

I'm attempting to turn a 1.4" dia X 0.6" long shoulder onto a piece of 3" dia round stock.

I'm using hot rolled C1018, a new (sharp) carbide tipped tool, taking 0.01" deep cuts, and turning at 1000 RPM.

Note the blue colored swarth.

The swarth coming off is silly hot and discolored, note the blue colored pieces. I actually had some wispy threads burst into flames

I have never experienced this behavior before. What's going on here?

 

[Dabbler]

If you are using oil, that would account for the burning... 1000 RPM is a little hot for 1018 at that diameter... I was turning 1.75" 4330 at 625RPM with a carbide cutter today. With .080 DOC and 12 thou per rev, the chips were straw that turned bright blue after a second. Pretty normal for carbide. I haven't had flames before, though.

I should mention - and this isn't a criticism - that your long stringy chips aren't breaking properly and can become a safety hazard. Thre are a lot of factors to chip breaking, so it is not possible to suggest a way to get shorter chips without examining all the factors.

As a side note, I tend to use minimal or no cutting fluids where possible. I don't like the fumes, and live with replacing cutters more often.

 

[trlvn]

Just curious. Were the chips 'better' at the small diameter? If I've read your description right, your small diameter is just less than half the original diameter. Thus 1,000 RPM at the small diameter results in about half the surface feet per minute. Presumably that would generate far less heat. No?

Craig

 

[YYCHM]

Just curious. Were the chips 'better' at the small diameter?

Craig

Not that I noticed.

Craig

 

[YYCHM]

I should mention - and this isn't a criticism - that your long stringy chips aren't breaking properly and can become a safety hazard.

A hazard in what way? They were a PITA to brush clear of the tool so I that could monitor cut progress that's for sure.

 

[Dabbler]

They can catch on the work or chuck and swing around. People have had very nasty cuts on their hands or face when that happens. I try to keep chip string to less than hand length, so they can't be harmful - and they are easier to shovel out of the chip tray!

 

[Janger]

nothing like a birds nest of sharp swarf hitting you in the face !

 

[PeterT]

This old Tony talks about chip breaking fundamentals around 20:00 mark. But why would you want to skip ANY This Old Tony time LOL.
Chip breaking is one of the things that isn't quite as straightforward to achieve grinding HSS tools. A lot of the lathe inserts we can buy pretty cheap have chip breaking bumps / divets / dots... Sometimes they work well on our hobby machines but sometimes not as much because they are designed around industrial machines feeds & DOC that isn't practical (or safe) for us. Sometimes you just have to stop & clear the way because it can be dangerous. The worst is when swarf pics up a ball of swarf in the tray & now that spins around the chuck... your hands... your face...

 

[Janger]

if you're using the auto feed then just pause it and resume. the chip will break.

 

[kevin.decelles]

nothing like a birds nest of sharp swarf hitting you in the face !

I took a ball like that in the face 10 months ago. Ripped off my safety glasses, my eye glasses and hearing prot. Small cut to bridge of nose.

Happened reaaaaaly fast. Did see if coming , just got the stinging slap




Sent from my iPhone using Tapatalk

 

[Dabbler]

When I was first machining I had long stringy chips all the time. An experienced machinist took one look at my chip tray, and I've changed my ways ever since... It only takes one horror story or near miss, and breaking chips becomes a sort of religion.

 

[YYCHM]

OK, I get the smack in the puss with a ball of razor wire thing now.

As for the hot swarth, I've noticed that a portion of my tool below the carbide tip has been rubbing on the work piece, so friction is most likely the culprit here. I'll relieve that area on the grinder and see if that helps.

Another strange phenomenon I encountered with this piece was a shower of sparks while facing it.
Working along, everything going well and puffft a shower of sparks just like what you get using a bench grinder. Didn't last long and only happened once???

 

[PeterT]

Lets see the cutting tool & how you have it mounted. The black streaks on your work kind of looks like rubbing but photographing metal is always deceiving.
Are you traversing along the bed axis or across?

 

[YYCHM]

Along the bed, from end to shoulder if I understand what you're asking.

The portion of the tool holder that's contacting is rubbing on the shoulder of the work piece.

 

[PeterT]

Hard to tell, but that's not a 60-deg V (potentially threading) tool is it? The tool holder may not be quite right for that cutting action. I bet that.s whats rubbing. You can grind some away but you also lose meat support. Maybe there is a better solution.

Deep shoulders sometimes may require different setups. Using a right hand tool & traversing from right to left would be the normal way, as long as the tool is angled properly for clearance (red arrow) and as long as the tool doesn't have to overhang the block so vibration sets in. Another option is left hand tool and proceed cross bed, but leave yourself allowance to finish the shoulder & face. The main thing is ensure you have cutting tool (and shank) clearance.

 

[Tom Kitta]

If you are taking such small cuts and at high revs with a tool that is a bit dull you set it on fire. You say tool is new but did the carbide maybe chip? Maybe not on center? Maybe something moved? Was it re-sharpened? Try to play around with speed and change cutting tool. Are you sure you are at 1000rpm? The machine may say 1000 but be at 1200. 20% difference. Measure speed with a laser meter. Most of my machines run 10% or 20% faster then number on them as they are made for 50hz not 60hz. Did you start at full speed of 1000 at 3"? Do you known the grade of carbide - it could be for cast iron.

As for long and stringy stuff I got it in the face around half a dozen times - yes remove birds nest. Yes some steels or metals don't break chip well at all. Some always break chip. Many inserts are not designed to break chips or if they do break chip its for certain depth of cut. I have inserts that only will start breaking chip at taking a cut of at least 0.04 per side. Brazed carbide which I rarely use don't have chip brake or I never saw one on them from as new condition.

 

[YYCHM]

Are there any negatives to turning slower than published other than it taking more time to accomplish a cut?

 

[Tom Kitta]

If you decrease speed too much with HSS you may get worse surface finish. Also operation may take much longer. With carbide you may chip it.

Generally a lot of feeds and speed charts are for maximum allowed speed or close to it. In home shop you should generally decrease these speeds a bit. Sometimes you may decrease them a lot to preserve your tool life.

Also these top speeds are for new sharp tool. If your tool is dull you may want to back off quite a bit or you generate too much heat.

 

[Dabbler]

If you reduce speed, you need to make sure you cut/rev is more -- if your lathe can handle it - - The most common problem with stringy, dangerous birds nests is taking too lazy a cut to improve surface finish. That is taking .002 per rev instead of taking .006 per rev, etc. You need to 'load' any cutter to get it to break a chip. I break chips well even with the flat-topped brazed on cutters. Only on the very last pass with minimal DOC can you reduce your cut/rev to get better finish. (And those tiny chips also break well, because they are so tiny!)

You should take the suggestion above and interrupt the cut, breaking the chip. I do it all the time milling, as a drill produces an equally dangerous string if you let it.

Thre perfect loading with a sharp carbide cutter is a slightly yellow chip, that breaks into thumbnail sized chips, turning blue in the chip tray. Not always achievable, but it is beautiful when it happens!

 

[YYCHM]

I switched to an indexable carbide tool. Same stock, same speed.

And got this.....

Got pelted by this stuff. It was thrown a good 4' from the lathe and hotter than blazes. Had to dawn lather gloves to finish the cut as my hands were being bombarded with hot shrapnel. Was picking fragments out of my hair, shirt pocket, still finding fragments here, there, every where.

I'm liking the long stringy stuff better