Turning and Surface finishing - fail.

[NeoTech]

Using a DCMT11T3 carbide tip on a right hand turning tool. I get like a fine groove or more like extremly fine thread.
I have tried different materials cast iron rod and aluminium rod - and the result is the same.





These two items are photographed with a macro, and the larger one is about 15mm in diameter and maybe around 20mm in height.
The thread is extremly small you can feel it and see it but not enough that a nail would catch onto the groove.

I guess this must be something wrong with my setup, speed / feed / angle of tool?!
Tried to find some answers by googling this and searching but cannot find out what would make this result.

[tomrux]

carbide is not the best tool when looking for a fine surface finish. But a lower feed at higher chuck speed may work. Not ideal

HSS real sharp will do better for most steels and anything softer.

Tom R

[NeoTech]

Oki, i will have to learn how to sharpen hss tools then.. i was hunting that "mirror finish" on aluminium, didnt really workout i guess. ;)

It seemed, it would be better finish the faster i go with carbide tips. But when doing the math, my lathe wont do 3000rpm so.
It will max out at 920rpm and cast iron at 920rpm will be really hot tools even with flooding.

But gonna try that thing with lower feed speeds - just gonna have to figure out how the hell i gonna get my lathe doing that. =)

[raynerd]

Is it set at the correct height and is there enough clearence at the front? It isn`t marking the surface after it has been cut has it?

For a decent finish on Al the best I can get is with a round nose carbide tipped tool as has been mentioned on these forums many times....unfortunately due to their shape, I find them very limited in what they can be used for!
 
Chris

[andyf]

How big is your lathe? Some say that the lack of rigidity inherent in small lathes can lead to problems with carbide tooling, so well-sharpened HSS is better.  My own experience (which I admit is limited) with my small lathes is better with HSS than carbide.

Andy

[rleete]

Carbide was developed for production shops so that they could take advantage of the greater rigidity and power of modern machinery.  The claim to fame of carbide is the ability to take deeper and faster cuts.  Using it on hobby machines just doesn't make a lot of sense.

Learning to grind your own bits will serve you well.  It's cheaper, you can make custom shaped tools, and you'll never need a special wheel to sharpen bits.  Oh, and you'll probably get a better finish as well.  Here's a link to using a sander to grind bits:  http://www.machinistblog.com/grinding-lathe-tools-on-a-belt-sander/

One last thing.  Search for diamond or tangential tool bits to get a really fins finish cut on almost any metal.  Here's a link to to one:  http://www.machinistblog.com/how-to-grind-and-use-the-contrary-finishing-tool/  They call it the contrary finishing tool, but it's the same concept.

[Fergus OMore]

I am not going to contradict the earlier posters but it is time to add a few words which need to be mentioned.

The first is to mention what we are actually doing with a lathe. We are cutting a thread. Whether we do it under power with a lead or feed screw- we are cutting a thread. If we use a plain lathe i.e. no screws to do the thing, we are still cutting a thread.
If you look at a piece of work- with a decent glass or microscope, you will find that you have cut a thread- no matter what sort of tool is used.
Looking at it carefully, it will have copied the cutting edge of the lathe tool. If you are not happy with the result- and have done all the other adjustments, the faults lie on your tool. If you look at the cutting edge, it will look like a ragged saw and this is what is going to piss you off.
Regrettably, you are going to get someone who is going to tell you an old wives tale about grinding it on a belt sander or a chunk of concrete or what is not much better whirring round on a grinder.
At best, you will be cutting metal better but it will not be mirror finished.  That will only be achieved if you gradually reduce the saw edges from the lathe tool by lapping or honing( call it what you will) with progressively finer grit sizes untill the tool becomes a mirror.

What has not been said is that you are trying with a lathe to do what industry uses 2 tools to do. You cut to say .002" oversize and reduce it to dimension with a cylindrical grinder or other machine.

And if you don't want to go all the way( and most will settle for something less) you will probably dump your carbides, dump your HSS and go back to carbon steel tools which take the best edge of all- easier

[NeoTech]

I have choosen carbide tips tools for one main reason, they are easy and cheap to replace (the tips that is), buying one piece of halv inch HSS steel for tooling, in sweden costs around 30 dollars, i buy 10 tips for 30 dollars off ebay including shipping. But i hear you, HSS or Carbon steel tools seems to have an advantage in lifetime and the ability to be reshapen to whatever the type of cut i need to make. It could prob. paying off in the longrun going with the HSS tooling bits.

What kinda lathe do i use, its a Optimum 320x920 D a small metric lathe, http://www.roughedge.se/blogg/wp-content/uploads/2011/12/k%C3%A4llare3.jpg
I dont know how rigid it is it sits on 8 small "shoes" that are supposed to take up alot of the vibrations.

Craynerd, i have been setting the toolheight with the principle of using the dub tip and then taking a surface cut and measuring the knob produced and then adjuster the QCTH until the knob disappears completely. The tool is setup so that the tip of the tool is going 90 degrees with the work i have been wondering if the trailing thread is cut by som material building up on the tool.

And finally Fergus, i get it that there are thread we are cutting always, what seems strange to me is that the "overstep" of the tooltip is so fine that when feed "normally" it will produce a visible thread. I cant run the carriage slower than the chuck on my lathe, so i would make a smaller overstep that way. And i get it that a cutting edge is not smooth, you could probably never get it smooth either with an abrasive method of grinding / sharpening a toolbit or am i wrong here?!
That part about the industry i didnt know about.. So i guess a tool post grinder and a aluminium oxide wheel would probably be the "finishing" touch i'am looking for?!

Thanks all for posting answers, i greatly appreciate all the tips and responses on this forum! 

[Fergus OMore]

One piece of hss can be sharpened and sharpened and sharpened. OK, my friend, I have a drawer full of HSS tooling- and I'm not going to get rid of it!  I do have the ability to sharpen and then hone because I tend to ignore the general run of so called advice. Indeed, I am a crusty old man. I do take the advice of writers in the past who have owned and run very successfully several businesses, have gone on to win medals for their supreme skills at model exhibitions and others who have taught the subject over  a lifetime.

I either use a diamond lap or diamond paste-- and I get results-- and save an awful lot of money on E-bay or wherever.

In my garage is a swedish steel tool. It was made before the last war. What's wrong with good Swedish steel?

Regards

Fergus

[loply]

Did you say you were turning a 15mm part at 920rpm with carbide tooling?

If so, that's way too slow. I would run that part at the max speed on my lathe, around 1800rpm. And probably faster if I could.

At different times I have had surface finish issues identical to yours, usually the cause has been one of the following:

Insufficient rigidity eg compound slide gib not set tightly enough
Insert is worn and needs replaced or turned around
Spindle speed too low, feed too fast or too slow
Depth of cut too deep for rigidity of part

You will be able to fix this issue, my lathe isn't a scratch on yours and I get near perfect finish on all steels one way or another.

Also, I'm not saying you have this issue, but it can be caused by leadscrew problems eg misaligned or bent leadscrew causing a pulsing feed rather than a smooth feed.



Cheers,
Rich

[jiihoo]

Hi Neo,

Were you using the automatic feed on all attempts? What happens if you feed manually? (try both slow and fast feed; for the slowest feed you might even try using the topslide; that should prevent you from feeding too fast  ).

I have an Optimum D180x300 (way smaller than your lathe, mine is 65 kg and yours should be 410 kg) and I use carbide tools. That shouldn't be the problem in your case.

I looked at the Optimum catalog for you, you should be able to get the spindle up to 1800 rpm (or 2500 if you have the vario model) on the 320. I think you should try that.

Is the lathe new or used?

[The Steamer]

Just a quick note on carbide to, There are hundreds and thousands of differant grades of carbide.

Each grade is specific to ONE machining condition on ONE type of material yet almost every single carbide tip listed on ebay states they are for General maching on steel.

 Ive seen inserts for nylon listed as stainless grade tips, cast iron as steel tips. Unless you have been tought the carbide companies grading system you are buying grades of carbide that are utter usless to you.

[Fergus OMore]

Hoorah, Mr Steamer!

Whilst HSS can be of varying grades, none are that critical for the little man with a little lathe.

One of the greatest gurus described his grades as Eclipse Grade H5 and VH. The latter stood for Vacuum Hardened but others took it as Very Hard whilst he used stronger descriptions. I have a few grades which are designed to cut whilst red hot. Of course, I always use lard oil as a lubricant and my workshop is opening as a restaurant later this year!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[NeoTech]

Fergus: its nothing wrong with swedish steel.. Just it's overpriced, and hard to comeby outside speciality stores. I have ordered myself a bench grinder today and will try to grind HSS toolbits though. =)

Steamer: I have discovered that.. the ones i have is described as "misc. cutting".. i dont really belive them. ;)

Jiihoo: yes, the machine is completely new.. first thing i had to do was take everything apart clean it, put it together again and tighten exactly everything.. Took about 2 days of measuring (and swearing). I should try that 1800rpm setting. And as you say, feeding manually makes the surface finish more or less mirror like, requires a steady hand though and doing larges parts this way is hard. =D


I got pretty good results today though with a 700rpm setting, and a carriage feed of 0.028mm/revolution.. it took like forever to surface cut a 10cm rod. but it came out not that bad.. So i guess, higher speed is the solution to this tooling thread afterall.

[DaveH]

Neo Tech,

"..........................to surface cut a 10cm rod"

I am not too sure I understand.

 
DaveH

[NeoTech]

DaveH: It's ok, you dont have to.   

[Pete.]

I cut steel and ally at lower speeds using carbide tooling sometimes, but I prefer to use HSS mostly. Grind a couple of bits up and pay close attention to the cutting edge. When I first started grinding HSS I would get the shape right but often found that I neglected the very tip that was doing the cutting, and ended-up with negative rake or a rounded tip or something. Now I finish them off with a stone or EZ-lap diamond hone and the difference is astounding.

I was right pleased to find 10 pieces of Stellite 100 last week and only £4 a pop. If you can get hold of this stuff - grab it with both hands.

[Pete49]

I seem to be repeating what the others have said but I have to agree. when I bought my first metal lathe I went with carbide tools as I had no idea how to sharpen hss and like you was not happy with the finish. Then a friend, a machinist, gave me some hss tools to try and showed me how to sharpen & shape them and hardly ever use carbide tooling now even in my mill/drill. They have their place but as Fergus and others point out mainly in industry. I even went as far as buying a diamond tool holder and have found it to be an asset(http://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=2&Itemid=17)  Unfortunately most sellers of hobby lathes suggest carbide tools but very few sellers have an engineering background so perpetuate the myth about carbide tools being the best. Another problem with some of the cheaper carbide tooling is it can be brittle as well and when I started I had some chipping on me but that could have been inexperience as well.
Saying that I admit to having a set of brazed tip carbide tools that I use for roughing out on unknown (rusty) steel as it saves my good tools 
Hope this helps
Pete

[Fergus OMore]

I was right pleased to find 10 pieces of Stellite 100 last week and only £4 a pop. If you can get hold of this stuff - grab it with both hands.

Stellite is certainly remarkable stuff and will cut at red hot temperatures.

One of the great- well, he helped to make the Atom bomb, made ball bearings on a riickety lathe( sorry a Drummong) and designed the Quorn used----------------------------------------old worn out files for some jobs.
Clearly, we don't need to buy fancy steels and mine are mainly collected from deceased club members. I'm not sure whether that reads OK but who cares?
I have a set of carbides from buying a little titchy lathe-- but I don't tell people about my inner secrets. Maybe I threw them at the neighbours cats?

Fergus

[jiihoo]

. I should try that 1800rpm setting. And as you say, feeding manually makes the surface finish more or less mirror like, requires a steady hand though and doing larges parts this way is hard. =D

I got pretty good results today though with a 700rpm setting, and a carriage feed of 0.028mm/revolution.. it took like forever to surface cut a 10cm rod. but it came out not that bad.. So i guess, higher speed is the solution to this tooling thread afterall.

Hi Neo,

There I think you have it. I'd say your feeds have been too high. The radius of the tool tip is quite narrow (0.1-0.8 mm or so; this is one of the things that you can change either by buying carbide tips with different tip radius or when grinding your HSS tools). Thus your feeds should generally be in the same area; higher when roughing and lower when finishing. As a very general rule use 0.2-0.4 mm / rev feed for roughing and 0.05-0.1 mm / rev for finishing. And do turn up the spindle speed when using carbide and turning small diameter work; if you double the spindle speed you will also double your speed of working and the "low" feeds won't bother you.

Look up the correct speeds from the tables or use a surface speed calculator like Gwizard machinist's calculator; you can go lower than the suggested speeds but you should not go too low... Eventually your ears will tell you if you are doing it right    .

The above should give you a good starting point for further experimenting. They are based on my (limited) experiences and work well on my smaller lathe with carbide tools.

Then just enjoy and experiment with feeds, speeds, depth of cut, HSS tools, a few different kinds of carbide tips etc. (The carbide tips that you have are reasonably "general purpose" and should do you fine until you decide to experiment further.)

Until you get the "mirror finish" by turning, you can always improve the surface finish with a little filing in the lathe (just beware the turning chuck!).

Cheers,


Jari

[Fergus OMore]

At this point, our poster is armed with more than enough articles on tooling to keep him going and to make a simple tool grinder which fits onto a fairly cheap 'foreign' double ended grinder. What's it like? Pretty old but the forerunner of lots of slightly improved grinders which- cost a lot.

If he wants to do 'magical things', I also  put in drawings for two tool and cutter grinders which do not require anything more than ordinary bits of mild steel.

But let us look at 'alternatives' to going into a good tool shop or E-vil Bay. An old friend, long gone- but he gave lectures on what he used.
He used Allen keys, he used high tensile bolts, he used old files, he used broken drills, he used reground taps and broken ball race cages and even bicycle spokes. His work was of the highest exhibition standard as many would testify.

Points taken? I hope so

[udimet]

NeoTech,
                   What nose radius are you using? you mention DCMT 11T3 [11 is the edge length and T3 is the insert thickness is you nose radius either 02, 04, or 08? looking at the picture I would hazard a guess and say it is either of the 2 smaller sizes 02,or 04 if that is the case then, try using the insert with a 08 radius you should see a far better finish. Also if you are using auto feed then choose the slowest you have  [ Carbide gives a super finish at high feed rates but home machines are not really suited to them]
Also if you really want to stick with carbide then try the positive inserts used for non ferrous metals [they can be used on mild and stainless steel for finishing, but at very small depth of cut and ONLY for your finishing cuts.
                                                                                                     Regards,
                                                                                                      Udimet.

[Pete.]

Material looks torn in the pictures. If the tip is in good condition and right on center height it could be too much slack in the system or too much tool overhang. I would try another cut but with the tool pulled back in as close to the holder as possible.

[BillTodd]

looks like a chipped tip to me

[NeoTech]

Udimet, the radius is 04 according to the box it came in. I would guess that means like i should lower my carriage feed ,to a step lower than the radius of the as jiiho mentioned?

Pete, BillTodd, yes the surface is chipped/chattered, a bit rough but grooved. I could possibly had a micro crack in the tool maybe?! Cause looking at it with a magnifier dont really showing something visible that could be a problem.

I have tried a bit of diferent speeds now, maxing out the machine at 1800+ rpm with a 0.028mm/revolution overstep the surface finish is really much better, but i need to take very light cuts. I will have a go with the HSS tools as soon as my bench grinder arrives. =)

And btw,