Tip build-up

[VersabossParticipant @versaboss]

OK, so I did a little experiment today. In the scrapbox I found a piece of zinc-plated tube of about 16 mm dia. I first made a cut with a HSS tool, about 14 deg. rake, 250 rpm, dry. Got a nice build-up edge, and a terrible finish!

Then I changed to a DCMT insert (Chinese, from CTC tools, TiN coated). Speed around  1000.rpm. Much better, but not yet perfect I think.

For the last region I used a multicoated (expensive) Sumitomo insert and turned a part of the second cut backwards (o my!), left to right I mean, and about 0.05 mm deep. Now it starts to look decent!

As I am still unable to find out with which of the icons on top of the edit box I can insert a picture directly, you have to dig into my albun(s), sorry.

Greetings, Hansrudolf

[VersabossParticipant @versaboss]

Please allow me to add a special one for mgi.

The carbide in turning inserts and other hard tooling is not iron carbide. If steel contains iron carbide at the grain boundaries I don’t know; I would think rather no. But others may be more qualified to answer this.

The black stuff in cast iron is graphite, not iron carbide. Quite a difference, hardness-wise!

Greetings, Hansrudolf

[Peter G. ShawParticipant @peterg-shaw75338]

mgj,

Glad you liked the grinding (!). Now you understand why I didn’t show it originally! (Is there an emoticon for ‘shame’?)

 

Versaboss,

Thanks for doing the experiment and confirming what I got. I can’t be certain, but I think my tube as well as being welded, was also zinc plated.

 

To all.

I’ve abandoned this idea and placed an order for some EN1A. So I’m now doing something else to while away the time. Seriously though, I’ve learned a heck of a lot from this so thanks to all.

 

Regards,

 

Peter G. Shaw

 

 

[mgjParticipant @mgj]

Why be ashamed Peter – its always worth a try!.

 

I would consider presenting that tool to the Tate Modern – seriously though I think you went the wrong way with the rake. Had you gone to negative rake – mnay don’t because it doesn’t seem to be “sharp” – I think youd have done that job without too much trouble. The lack of coating also didn’t help you. (I claim no sanctity with negative rake – I managed to screw up my parting off for years by raking tools too steeply)

 

Versaboss, the carbide in most tooling is indeed not iron carbide. Mostly it is sintered tungsten carbide and the tips are fomed from a powder and heated and squeezed to form them. That lack of a crystallne structure accounts for the relative brittleness. (tThere are other processes, but that is right in principle)

 

Yes steel does contain iron carbide on the grain boundaries – what else could it be in an alloy of iron and carbon and very little else? the carbon has to go somewhere: it cannot just vanish.

 

The “carbon” in cast being “graphite”. Well only that excess carbon which can’t find a home with the iron atoms. Ie the surplus.Cast iron is only iron with(lots) too mcuh carbon to form a normal steel, so the carbon does funny things at the grain boundaries. Thats why cast is so abrasive – hard carbides. Quite a lot of it is actually very hard – especially if the cooling goes wrong, and you start getting martensitic structures. (the very hard bits in thin sections).

 

 

[Peter G. ShawParticipant @peterg-shaw75338]

mgj,

 

Well, it’s not up to the standard I try to achieve. Or if I don’t achieve, disguise by a bit of paint.

 

Seriously though, a) I was trying to produce Tubal Cains design, hence the rake as shown, and b) I’ve never had to consider negative rake before, and by the time I discovered the tip problem, it was really too late because the tube is now way too thin for what I originally intended doing.

 

But yes, I’m in full agreement with that saying, how does it go? The chap who never tries never achieves anything. There is one thing though: I appear to be blessed with an odd sort of memory in that none of this will be forgotten, and at some point in the future, I will do a similar thing, and this memory will arise and hey presto…

 

Regards,

 

Peter G. Shaw

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, my colledge notes seem to becoming more interesting now than they were back in the seventies, when I was studying.

 

I have to agree with mgj on iron carbide on the grain boundaries. My dictionary defindes a carbide as; A carbon compound consisting of carbon and a more electropositive element. Well the only electropositive element in steel other than carbon is iron.

 

Below is shown part of a phase test in my colledge days.

 

Cementite forms on the grain boundaries, and as can be seen my answer was wrong, the only other answer in the list that could have been correct was number 2. i.e. Is an intrmetallic compound of iron and carbon.

 

Sounds like an iron carbide to me.

 

Regards Nick.

Edited By Nicholas Farr on 06/02/2011 23:42:32

[TerrydParticipant @terryd72465]

Hi Nick,

 

You’re not the only one who’s college notes are more meaningful now than they were then. Except mine were more from the ’60s and I am now finding my work on steam entropy diagrams of great interest, what is the world coming to!

 

Regards

 

Terry

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I looked up the meaning of Cementite in my dictionary today (don’t know why I didn’t yesterday) it defines it as ; A hard britle iron carbide Fe2C formed in steel with more than 0.85% carbon.

 

Terry, I first started my college days in ’68, it was only a day/evening release, but continued untill ’74. These notes are from a half day/evening Welding Institute Technicians course that I was invited back to in ’77/78 period. The matallurgy lectures were much more indepth than the previous, along with the maths and science. Practical lectures weren’t really covererd much, but fabrication design was.

 

Sorry for stealing your post a little bit here Peter.

 

Regards Nick.

[Peter G. ShawParticipant @peterg-shaw75338]

Hey Nick,

 

No apologies are needed. It’s fascinating to see just where my OP has gone. Keep going, I’m enjoying reading, and hopefully learning at the same time.

 

Regards,

 

Peter G. Shaw

[mgjParticipant @mgj]

Im just glad my rather decaying memory (I think young Farr and I were at our studies at much the same time) is holding up.

 

I am not, and never was a metallurgist, except in passing, because I got deeply involved in welding of rolled homogenous armour plate with stainless rods – the alloys get quite complex, and the results uncertain if you don’t get the controls right.

 

My initial training was all structural engineering and mainly automotive systems on tanks and to a lesser degree tank gunnery. Later I got into guided weapons, and if you are going to attack armour, either kinetically or explosively, then one ought, so Her Majesty decided, to know how the stuff behaved. But the MSc was actually in guided weapons, not tin bashing. However, aircraft structures (even if designed for a one way trip) and aerodynamics do help you build racing cars – and one could always pester the auto department.

 

My machining wasn’t trained as such – I just used to go to the evening classes run by the then DQA apprentice instructors at Woolwich Arsenal. They gave of their time to help the apprentices to improve, and I was able to tag along. Enormous value and a great debt owed to them.

 

Amazing where you can end up.

Edited By mgj on 07/02/2011 18:07:17

[mgjParticipant @mgj]

To go back to the original point – why did this pick up in the first place.

 

Probably inadequate cooling, resulting in sliding friction, heat on the tip and then a weld build up. For sort of work, cooling volume is a good thing, and dilute oil is often a better bet than the neat cutting stuff. We don’t by and large put the stuff under industrial loading where the neat comes ot the fore, and nor do we use or neat in industrial volumes.

 

I would also suspect the quality of the tool, as well. (the smart professional looking one. There is a lot of monkey metal posing as tool steel, and its ok in so far as it goes, but it does abrade very quickly, and then you are in trouble.

 

Its been a while since I bought tool steel, (I mostly use carbide or tangential tooling which is v economical on bits) but you can get Far Eastern stuff for a quid or so for a 1/4 sq bit. You can also pay over £20 for the “same” item.- if it has a name likeEclipse or Cleveland or Hydra on it. For my money the cheapest tool stel is always the £20 per bit stuff. Because it works. The other stuff I find always has a lot of trouble cutting from the trash can- because that is where it ends up.

 

I’ve tried these job lot type packs of tools and never had a lot of success. The tool steel ones are mostly NBG, the carbide ones have brittle tips, and I have never had much luck with them. What I have had a lot of luck with is high grade indexable carbide, or good grade tool steel properly ground on a Quorn, to known and repeateable angles.

 

Perhaps a Quorn is a bit OTT (until you see the preQuorn tooling toolholder for the quorn – chickens and eggs – ) but some kind of decent jig is very very useful.

 

Perhaps it depends on what one is looking for, but I have Eclipse parting blades which I bought with the Myford 30 years ago, and are still giving good service. – thats why I don’t like the look of that tool Peter. Im sure that is where the problem started, but I’m very willing to be corrected

[Richard ParsonsParticipant @richardparsons61721]

Ah Mr Versaboss of course! Zinc Plated water pipe! There is the answer. Plated materials often give problems with machining and Zinc is one of the worst. Hot plated zinc can penetrate well over 0.040” into the mother metal in defuse quantities. It ‘monkeys about’ with the structure of the metal somehow. Lead solder is another. In order to repair something which had previously been soft soldered I had to remove over 0.025” before the ‘silver solder’ would take.

There are also cautionary tales about using zinc plated sheets under stress as they give way at a far lower yield point than the equivalent thickness of non-plated steel. Some put it down to the metal used in plated sheet being of inferior quality.

[MikeParticipant @mike89748]

May an absolute amateur contribute to this learned discussion? I took gas welding lessons back in the early 1970s, and my instructor told me that any structure made of zinc-plated steel should be brazed rather than welded, because at welding temperatures – in his words – “a very hard and brittle zinc-iron alloy would be formed in the joint.”

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Mike, he was probaly correct, fusion welding zinc plating will certainly produce a poor weak joint, not to mention the nasty fumes you get. If zinc plated steel has to be fusion welded this can be done by sanding off the plating both sides of the plate, down to the bear steel, to about 15 to 20mm each side of the joint. The weld and surronding area can then be spray painted with a zinc paint designed for zinc/galvanized repair.

 

Regards Nick.

Edited By Nicholas Farr on 09/02/2011 11:43:06

[Ian S CParticipant @iansc]

I find its a good idea to grind the zinc from the area to be welded on galv water pipe, on the machines that we build we also use a large amount of Duragal steel (I think its electroplated zinc), and it gets welded as is. Ian S C

[The Merry MillerParticipant @themerrymiller]

Slightly OT,

 

Zinc plating introduces Hydrogen embrittlement. this is why zinc plated fasteners are subject to a De-embrittlement procedure as a part of the finishing process.

[Richard ParsonsParticipant @richardparsons61721]

The real problem here is the penetration onto the ‘mother metal’ by the Zinc. Welding etc has problems, but here Peter is machining into the metal which has been subject to this treatment. That is that it has been penetrated by the zinc and this is causing what I call ‘scabbing’. That is small chunks of the mother metal are ripped out of the main structure of the metal along the lines of weakness caused by the penetration of zinc. The melting point of Zinc is about 420°C and it is this which may be causing the build up on the tool tip. How you deal with it I do not know. Peter does not tell us how much he had skimmed off. May be if he went deep enough he could get through the problem, but water pipes are normally plated on both sides (inside and out). I think the only answer is not machine zinc plated pipes unless you have to or do not care about the ‘finish’.

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

A question for our more knowledgeable readers, Do you get the same problems with Zinc plating (an electro deposit) as you appear to do with Galvanised (hot dip zinc coating) ?

chriStephens

[Peter G. ShawParticipant @peterg-shaw75338]

Richard,

 

O.D. about 34mm. Original wall thickness about 3.2 to 3.4mm. After much machining, down to 2mm at one side. Tube is quite rusty on inside, noticeably so in one or two places. Tube is quite old – 20/30/40 years? More? Suspect possible came from Dad’s so don’t really know it’s source or provenance other than it does appear greyish black (or blackish grey ?) on outside – not paint. Definitely welded as can see seam in places, took a lot of turning to get down below the rusted weld, and there is a very thin narrow longitudinal line appearing.

 

Original idea was to create a pair of circular squares as per BogStandards instructions. Although parallel, not as smooth as I want, and getting concerned about remaining wall thickness standing up to clamping pressure. Hence idea abandoned in favour of a solid device as per Harold Hall’s book.

 

Regards,

 

Peter G. Shaw

[TerrydParticipant @terryd72465]

Hi Peter, if you are still around.

I thought that I would share these following comments in this thread, which I rediscovered quite by accident.  Since my workshop is now getting back into some kind of order, I have made a pair of Bogs' 'Round Squares' and thought that you might like to see the results. See the pictures below, also here and here for larger versions, I don't know why they aren't clickable on the forum. If you look at the latter picture, on Photobucket you can see the remains of years of limewash on the tube.

These too were made from some scrap, galvanised welded tube but they came out ok using HSS tools despite the materials. The tubing actually came out of the milking parlour of my property in France. Also the carriage was hand fed as I was awaiting a couple of shear pins which had failed for the gearbox. The result is not too bad as you can see.

As for built up debris on the tip of a tool, it needs to be stoned off regularly while machining if it occurs as yours has as it appears from the pictures in your first posting..

 

 

 

Best regards

Terry

Edited By Terryd on 11/10/2012 15:54:31

[Peter G. ShawParticipant @peterg-shaw75338]

Thanks Terry.

By 'eck, it's along time since I started this thread, lot of water under the bridge etc.

I made a pair from solid EN1A/230M07 and they came out very well indeed. I used them on the milling machine to machine up a pair of ali 3-way squares, only to find that the milling machine table was well and truly bowed and the squares aren't! The table has been reground, and is awaiting new gibs & fitting. Trouble is that other things have a nasty habit of getting in the way, so everything engineering wise is very slow.

Still, it's interesting to see what can be done.

Regards,

Peter

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