Tip build-up

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Tip build-up

This topic has 45 replies, 17 voices, and was last updated 11 October 2012 at 21:13 by Peter G. Shaw.

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31 January 2011 at 15:49 #63344
Peter G. Shaw
Participant
@peterg-shaw75338
Hi folks,

Come across something, well er, different – different to me that is, and I could do with some ideas as to what’s happening. Suspect I know, but am not sure.

I’m attempting to turn down some tube, provenance unknown. It responds to magnetic strip so would seem to be ferrite based. But I’m having a lot of trouble getting a smooth finish. I ground up a new HSS tool – that didn’t work properly so suspecting an odd (peculiar) bit of HSS I went back to a known HSS tool. And discovered a build-up on the tip, bit like aluminium only the tube is some sort of steel. Actually, the original HSS did work and did cut, but wouldn’t produce a smooth surface. FWIW, it had a steepish back rake, but no side rake wheras the known tool has no back rake to speak of, but does have side rake..

Photos below.

This is the tube and as you can see, it’s hardly what I would call smooth.

This is the known good HSS tool.

A closeup to show the actual shape of the tip. Note the slight flat on the front to get a smooth finish.

And finally a closeup of the build-up on the tip. Colours are’nt correct as it’s actually shiny steel, but at least you can see the buildup.

So, any ideas as to what’s happening? Or should I simply scrap it. I have tried TCT as well, but no difference.

Regards & MTIA,

Peter G. Shaw

Edited By Peter G. Shaw on 31/01/2011 15:51:19
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31 January 2011 at 15:49 #29429
Peter G. Shaw
Participant
@peterg-shaw75338
31 January 2011 at 16:28 #63346
Keith Long
Participant
@keithlong89920
Hi Peter

From my own experience and other’s that I’ve read about on here as well as elsewhere, tube, especially stuff originally intended as water pipe can be a right pain to machine and get a good finish. My only suggestion would be to get the tool as sharp as possible, hone it and get as good a finish on the tool tip as you can. If you’ve tried with suds or cutting oil then, might as well try without as well – and vice versa – covers all bases! If all else fails, get as near size as you can and them resort to emery cloth.

I don’t know what it is about tube that causes the problem but I do know that the manufacture of solid drawn tube is a pretty brutal process, so I’m not surprised at any stresses locked up in the metal, and I doubt if it gets heat treated after forming unless it’s by special order at a special price.

Keith
31 January 2011 at 16:50 #63347
Peter G. Shaw
Participant
@peterg-shaw75338
Hi Keith,

As far as I was aware, not having had any training in this, I had the tool as sharp as possible, and had honed it using diamond hones down to extra fine. Yes, I have been using Warco’s Neatcut on it – sorry, forgot to say. Size is, within reason, immaterial as all I’m trying to do is make a couple of circular squares as per “Bogstandard” elesewhere. I haven’t tried cutting dry for the tool, but I may as well have a go as the tube’s now approaching too thin really for it’s purpose so I may as well now experiment.

If all else fails, then I’ll go back to using freecutting ms – which of course I’ll have to buy. (And as a Yorkshireman, that hurts!!!)

Regards,

Peter G. Shaw
31 January 2011 at 17:05 #63348
Terryd
Participant
@terryd72465
Hi Peter,

Steels will produce a built up edge to a lesser or greater degree as well as aluminium, and this will cause the tearing of the surface as obviously when the material builds up on the tip of the tool it is no longer sharp. I won’t go into detail about the way in which material is removed while turning except to say that it is a shearing process, not like the cutting process we commonly think of. The sharper the tool, and the better the rake angle, the smaller the shear plane will be and the better the finish.

The surface finish is related also to the shear properties of the material. The softer and more tenacious the material (like annealed copper) the more likely is a poor finish. You can improve your finish by having a sharp tool with a rake angle at the higher end of the range for steels, or even a bit greater.

The built up edge will quickly make the tool effectively blunt, increasing the length of the shear plane and tears the material more than it should hence the poor finish, and any build up must be removed frequently, (ideally before it forms). You can hone it with a diamond file. Help to prevent the built up edge by using copious amounts of cutting fluid to keep the tip lubricated which will delay the formation of the build up. Small cuts, slow feed for the finishing will help but you’ll never get a mirror finish as with free cutting steel but it can be made quite presentable with care.

Regards

Terry
31 January 2011 at 17:06 #63349
Keith Long
Participant
@keithlong89920
Hi Peter

I wasn’t doubting what you’d done only listing the things I could think of.

As I said, from what I’ve read the stuff can be a real pig to machine and some of the comments have come from much better engineers and machinist than I will ever claim to be.

Interestingly John Stevenson has commented in another thread that he’s found black bar, certainly in the larger sizes machines OK, but the smaller stuff was more problematic. I wonder if the same sort of process is going on here in that once the section is reduced by hot rolling or forming (think of tube as collection of small section bars located around a hole) then the metal cools faster and doesn’t stress relieve itself to the same extent as a piece of relatively chunky solid bar? You might find that a bit of black bar can be got for less than the freecutting variety.

Keith
31 January 2011 at 17:13 #63350
Terryd
Participant
@terryd72465
Hi Peter,

By the way, I forgot to add that it helps to reduce build up of the tip of the tool by keeping the top surface as polished as possible. I have been known to use the finest wet and dry I had, used wet (1200 grit) on a flat plate glass surface and then final polish on a polishing buffer using a fine crocus compound or similar.

I would expect to be able to cut paper using the tool like a Stanley knife.

Regards

Terry

Edited By Terryd on 31/01/2011 17:15:49
31 January 2011 at 17:36 #63352
Ramon Wilson
Participant
@ramonwilson3
Hullo Peter

I don’t think the problem lies with your tool so much – though I do agree it could have a bit more side and back rake but with the tube material itself. Is it welded or drawn?

Are you getting any chatter or ringing as a matter of interest – that won’t help the finish either.

Most ‘tube’ is notoriously ‘awkward’ to machine – it tends to be rather ductile and very ‘claggy’ (local term) to machine – a bit similar to machining sheet steel. I’d say that’s the cause of the build up.

If that is the case then theres not a lot of options, you could spend a lot of time trying to achieve a finish on it even with all the suggestions – personally I would bite the bullet and use some better material.

Sorry to be so negative but never found a real solution to this problem other than has already been suggested – messing around with rakes, speeds and feeds and cutting fluids. Quite time consuming and not always successful.

Regards – Ramon
31 January 2011 at 17:52 #63354
Richard Parsons
Participant
@richardparsons61721
TerryD Try using Autobrite Chrome polish on hard leather instead of Crocus
31 January 2011 at 21:47 #63366
Terryd
Participant
@terryd72465
Hi Peter,

I see that you are using Neatcut which is a good lubricant but how are you applying it. The flow should be directed at the tool tip, not at the workpiece which is a common fault. It is the tool you need to lubricate not the work.

It’s worth persevering if only for the experience, after all anyone can achieve good work given the wherewithal.

Hi Richard,

I never tried Autobrite or Autosol but I have used similar pumice based compounds. I will try that next time, once my workshop is back up and running I’m told that toothpaste gives a good final polish but I never tried it myself, have you?

Regards

Terry

Edited By Terryd on 31/01/2011 21:50:01
1 February 2011 at 01:19 #63377
Martin W
Participant
@martinw
Terryd

I don’t know whether modern toothpastes will give the desired results as I expect they are very different from the older versions which contained ‘diatomaceous earth’ which is basically a very fine silica based powder, shells of microscopic diatoms. Modern stuff probably has something else in it that is less abrasive!

Just a thought mind you it may give a finer polish!

Cheers

Martin
1 February 2011 at 10:54 #63387
Ian S C
Participant
@iansc
I suspect that the hollow tube flexes as the tool passes over it, as I mentioned in another thread, if its water pipe, its a right pain, yet given another bit of pipe and it cuts like a dream. The biggest trouble i’v had was boring a bit of two inch water pipe, cut out the weld bead and started into the pipe propper, and “pop”the pipe opened up 1/4” as the weld let go. Took it out of the lathe, squeezed it up and ran a weld down the outside with good penitration, put it back in the lathe and finished boring, then I lapped it, and it became one of my better hot air engines. The weld’s still there, looks pretty good compared with my normal welds.

Toothpaste is getting fine enough to polish samples for microscopic examination / photography, I think it maybe finer than rouge. Ian S C
1 February 2011 at 11:08 #63388
Gordon W
Participant
@gordonw
I have to make most of my stuff from “scrap”. My feeling is that a lot of steel, especially general purpose stuff, and black bar, is contaminated in some way. It is not unusual to actually see inclusions, of what I don’t know. Also I’ve had plate which delaminated when cut. Seems some of it is just rolled scrap, and not remelted at all. This is steel from all sorts of different sources and ages. These are just my observations, and may well be not common.
1 February 2011 at 12:03 #63393
Nicholas Farr
Participant
@nicholasfarr14254
Hi, from my experence of screw cutting general purpose pipe either by hand dies or the various machines available, I find that unless you have decent sharp dies and suitable cutting fluid, you will get tearing.

I don’t think it is much suited for machining. As has being said, very hit and miss on the finish when turning the stuff.

Regards Nick.
1 February 2011 at 12:15 #63394
David Clark 13
Participant
@davidclark13
Hi Gordon

Laminated material is not that unusual.

It happens even in good quality steel.

I once pressed out several hundred bottom motorcycle engine mounting brackets.

The steel looked fine.

Once they started to weld them up the steel split where it had been laminated .

Result several hundred pieces of scrap.

Another problem that used to occur in ministry issued steel bar was that there would be ball bearings included in it that had not remelted.

Completely wiped out the cutter, just wore it away by rubbing. This was rather annoying when you had spent two hours carefully grinding a side and face cutter to cut one side of a dovetail.

regards david
1 February 2011 at 12:43 #63396
Nicholas Farr
Participant
@nicholasfarr14254
Hi,

laminated steel plate has always been available, even when it was mostly of British manufacture. It hates being flame cut, sparks all over the place and makes the cutting nozzles bark, and makes your job look amerturise, not to mention time cleaning the edge up with the angle grinder before welding, and then more problems with that.

Regards Nick.
1 February 2011 at 13:01 #63397
Peter G. Shaw
Participant
@peterg-shaw75338
Hi folks,

Thanks for all the comments. Here are some replies.

Terryd.

I wasn’t aware that other materials can cause tool build up like that but it isn’t surprising, my lack of knowledge that is. However, this may explain why my homemade tool appeared to have tiny edges appearing where there shouldn’t have been but I can’t really say that they weren’t there when I started although I do deliberately try to ensure that all corners are sharp and clean.

I do use DMT diamond hones. I have the full set of double sided diafolds, and for small items, the full set of minihones. This is how I have been sharpening the TCT tools and honing the HSS tools. I’ve no 1200 grit paper or crocus powder – never needed them before.

As you correctly guessed, the Neatcut is applied by brush onto the work, usually lots of it all round the circumference before I start turning.

Ramon.

The tube is welded.

I have had both chatter and ringing, cured by reducing speed to 250 rpm which according to Tubal Cain is about right for finish turning on BDMS or black steel of 35mm dia. From what I’ve now picked up, I suspect I may be better going down to 178rpm which T.C. seems suggest is better for harder/tougher steels.

Keith.

Of course I understood you were suggesting whatever you could think of. And I’m grateful for that. Interestingly, Tubal Cain somewhere has said that he always used black steel in preference to BMS because the black steel hadn’t been stressed as much as the BMS in the manufacturing process. (My words, not necessarily technically correct, but should give the idea.) In addition, despite my reservations re cutting dry with HSS, I also note that T.C. cuts dry when ‘levelling’ his lathe(s). And that he recommends when milling to either cut dry, or to flood the work, his reasoning being that damp fluid simply creates a ‘mush’ which then gets under the cutter and hey presto, bad cutting, whereas the other two don’t do that.

Gordon W.

I use scrap steel because I have it! Some of it doesn’t seem too bad depending on it’s ultimate purpose, but I’ve come to the conclusion that for my purposes, I am going to have to use freecutting stuff if I want any sort of precision. It does go against the grain having to buy new when I may have something which might do, but I’ve always got at the back of my mind a comment from somewhere along the lines of ‘if it’s a bit of good stuff from Jones the scrap, then you could be better off getting a piece of known specification.’ Interestingly, my grandson used a bit of scrap and produced a perfectly turned section. Which just goes to show that not all scrap is bad. Experimentation is the name of the game.

General comments.

When I first started this thread, I was interested in the tool tip build-up which I had not come across before, except for aluminium. As I have said before, I do not have any engineering training, hence this is all learning by experimentation for me. And so Terryd’s explanation was very helpful.

In respect of the present project, I had the tube doing nothing; I had seen BogStandards article elsewhere on making the squares from tube; so I thought ‘why not’, I’ve nothing to lose and everything to gain. And when I started, the thread on different steels hadn’t started otherwise I might well have thought again. As it is, I’ve learnt quite a lot, and apart from a bit of time, I’ve not lost anything. So what I’m going to do is to order up a length of EN1A, or whatever it is and start again. In the meantime, I will experiment further to see if I can improve my tool sharpening, and try a lower speed.

So, many thanks to one and all.

Regards,

Peter G. Shaw

ps to Ramon. By ‘eck lad, I haven’t heard ‘claggy’ for heck of a long time! But it’s a good word to use in these circumstances and makes a lot of sense to me.
1 February 2011 at 14:15 #63399
Ramon Wilson
Participant
@ramonwilson3
And there I was thinking that was a Suffolk term!

It’s good to see the ‘forum’ living up to it’s usual justfication Peter, what would we do without it.

Keep on machining – it’s a great hobby.

Ramon
1 February 2011 at 17:59 #63405
Speedy Builder5
Participant
@speedybuilder5
When I was an aircraft apprentice, when we had to turn some thin wall tube, it was filled with ‘rosin’ (stuff violinists use on their bows). This was melted, poured into the tube and allowed to cool (Also used when bending thin walled stainless tubes of more than 1″ Dia) I guess as already stated, it probably stopped the tube ‘ringing’
2 February 2011 at 11:24 #63411
PekkaNF
Participant
@pekkanf
My first instinct would be to try coated (any coating for iron metals) carbide bit and run the heck out of it. Least 3*rpm you are using now. I probably would try pretty deep cut as well even on the expence of feed.

My reasoning is that more ofthen than not I have got rid of build-up by increasing the speed.

Another thing: Some HSS/work material combinations seem to more prone to “welding” due to HSS composition I guess….different tool material might help when geometry/speed/feed trinity does not manifest any appreciable improvement.

PekkaNF
2 February 2011 at 11:40 #63412
Versaboss
Participant
@versaboss
Pekka, I’m with you here. 178 rpm is way too slow, especially for carbide. And this ‘good’ HSS tool has not enough side rake. I guess that is not more than about 6-8 deg. Grind this tool down about double the distance we see on the picture, and the picture will change so to speak. But I admit that you (Peter I mean) has a piece of terrible material which adds to the trouble.

Greetings, Hansrudolf
2 February 2011 at 13:09 #63414
PekkaNF
Participant
@pekkanf
Someone really should biachslap me again! Carbide bit – cry out loud! I mean carbide insert, not carbide tipped tool lookin object, which only has ecological niche on taking skin off from mystery metal or cast iron.

Carbide insert please. Those shiny candy or blingy lookkin metal cutting objects!

If this mystery metal has carbide inclusions or other type of minor crap in it, HSS can’t take it.

PekkaNF
2 February 2011 at 14:05 #63415
Peter G. Shaw
Participant
@peterg-shaw75338
Hi PekkaNF & Versaboss,

I did initially use a TCT tool, but not very good. I do suspect I wasn’t cutting deep enough anyway, but I was conscious that I didn’t have that much thickness to play with. Agree about using higher speeds, which I did try – I seem to think about 710 rpm.

178rpm is only as advised by Tubal Cain using HSS on tougher steels. If using TCT, he does recommend using 50% to 75% faster.

‘Good’ tool versus ‘bad’ tool are purely descriptive. The ‘good’ tool is one that was bought ready formed and whilst it has been re-ground, as far as I can tell, the angles are more or less as bought. The ‘bad’ tool is an attempt to make a tool as per Tubal Cain’s sketch ‘E’ on page 5.5 of his Model Engineer’s Handbook Third Edition. (Different page nos in earlier editions.) These photos show what I ended up with. It’s a piece of HSS brazed onto a MS shank. Sorry about the slight fuzziness of the photos. As you will see, it’s hardly a text book piece of grinding, and yes, a tool & cutter grinder is on the ‘want’ list. However, despite the ugliness of parts of it, I did hone the relevant parts that do the actual cutting and swarf removal.

Strangely, it does actually work, and there wasn’t that much difference between the two tools, except that the good tool developed the tip build-up. Which perhaps suggests that more rake would have been better.

Regards,

Peter G. Shaw
2 February 2011 at 14:27 #63416
mgj
Participant
@mgj
I’m always interested in htis comment that carbide likes going fast. Because of the geometry and heat/wear resistance it will certainly take going fast – feed most tipped tools don’t like much compared with high raked ground HSS. I just chomp away at ordinary HSS speeds and feed simply because that is the speed I’m most comfortable working at.nor am I under production pressure, nor do I have a desire to beat the c++p out of my lathes.

Somehow my carbide tips work extremely well, give a (very) good finsh and last a long time.

Carbides in there. Doesn’t all steel contain iron carbide at the grain boundaries – well all non stainless anyway, and even stainless does so long as it is not in its normal austenitic condition? Yes? Isn’t that what steel is?

HSS seems to cope pretty well with cast, and there is a LOT of iron carbide in that. Thats what all the black stuff is. – yes?.(Not the cheapo tool steel around lately, but proper stuff with a real brand name and price on it)

Some materials do not shear well, particulary these bendable ductile metals – for very obvious reasons. It isn’t a matter of quality usually, if supplied by a reputable dealer to a spec, its just the property of the material.

Be careful of large rake angles in stuff like ERW and CDS and other pipe type .

steels, because they are very prone to grab.

What does cut them pretty well are negative rake (tipped ) tools, again for very obvious reasons. You are not getting a tendency to dig in and increase the depth of cut within the backlash of the feed screw, because they generate an outward vector. A suitable tip would be one of the W series. Tipped toolholders suitable for small lathes are hard to come by, so you could grind up a negative rake tool (and use it later for brass bronze copper, like we all should but never do!). Polish – if you are grinding on a tool and cutter grinder with say 100grit, you would be pushed to beat such a surface, and you’ll be there awhile. And its very difficult when polishing to hold angles correctly – so I might skip that approach.

Because of that outwards vector, on a smaller lathe a travelling steady would be good to stop push off.- low speed, lots of coolant, negative rake tavelling steady and you should get an acceptable result which can even be quite good with the application of a bit of emery afterwards.

If you get a bit of singing – a collar along the length usually will alter Fn of the bar adequately, but a better answer is usually, given a sharp tool, to increase cut or feed, or the pressure of the travelling steady. Singing is usually a high frequency/small movement phenomen, so if you can do something to alter either the frequency or the small movement bit, it often goes away.

The best thing of all is to understand why it’s tearing – usually (but not always of course) a soft material and something allowing mini “dig ins”. Rake angles and a touch of slack in the mechanism. Do the opposite and mostly the problem goes away. But unfortunately not always. Sometimes the material just doesn’t want to help.

Edited By mgj on 02/02/2011 14:28:36
2 February 2011 at 21:28 #63438
mgj
Participant
@mgj
Our posts crossed. Wonderful piece of grinding Peter. Possibly unrepeatable, and good to hear it did the job.

For info this is a carbide insert specifically for that sort of task – note the rounded nose, and the negative rake. The cutting angle is just the thin rim round the edge, the rest is the chipbreaker which is not essential of course A flat surface in HSS at that angle would be fine of course, but the chipbreaker is handy with some materials.

Perfect for the bronzes/brasses, because it won’t grab or tear.

Edited By mgj on 02/02/2011 21:29:15
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