Here is a list of all the postings Cabeng has made in our forums. Click on a thread name to jump to the thread.
|Thread: Parting Off MEW225|
Can I offer a somewhat different view of the parting off situation, arrived at after many years of expensive research - a.k.a. playing about and writing off parting tool tips? But first, some caveats:
1) I haven’t read the MEW article (I don’t buy the comics)
2) the following comments are based on the S7 & Connoisseur lathes, which I've used for umpty-one years, you'll have to make up your own minds re their applicability to your machine, if different.
3) This will take some time and space, I can't upload it as a single posting, and chopping it up, adding diagrams, etc. is a pain in the parting tool with this system.
4) I fully accept that I risk being accused of heresy by disciples of GHT, and hence being condemned to eternal damnation – after being burnt at the stake, of course!
But first, a response to Blowlamp's last posting - compliance isn't the solution, it's the problem! Think about a beefy CNC machine chewing metal off at high rates, parting like a knife going through butter - works perfectly, but it's very rigid, no compliance.
Kiwi Bloke1 wrote:
“The late, lamented George Thomas wrote pretty much all anyone could ever need to know about parting off (and many other topics) in his many comprehensive Model Engineer articles and his books.”
He did indeed write a lot of good stuff, but I certainly wouldn’t extend that accolade to his analysis of the front versus back tool post argument! As far as I know, he never actually claimed that his explanation was rock solid, e.g. in Model Engineer’s Workshop, p61 he writes:
“…I imagine (my underlining) that the main reason is that a tool subjected to a downward pressure tends to lean forwards and so dig in whereas upward pressure will cause the tool to move back and out of cut.”
That on its own is sufficient to get rid of the 'down & in' versus 'up and out' argument, but additionally GHT's choice of pivot points for the tool posts is entirely arbitrary, and bears no relation to reality! Unfortunately, if one starts from an incorrect assumption, one ends up with at worst an incorrect answer, and at best a misunderstanding of the problem – so given the above errors in the ‘explanation’ it is indeed unfortunate that GHT’s efforts have resulted in the imprinting of the ‘down and in’ versus ‘up and out’ argument into the genetic code of countless model engineers.
“We love taking simplistic views of problems. When we talk about the tool "springing", we are actually referring to the movement of the point of the tool relative to the point on the work piece where it acts. In between them is a whole series of slides, screws, bodies, joints etc - as well as the workpiece itself. The whole system is a combination of linear (sprung) and non-linear (backlash etc) elements, often with quite different characteristics in different directions”.
Absolutely right Muzzer, particularly the bit I’ve underlined, which hits the parting nail (and indeed any machining exercise on lathe or mill) smack on the head. What matters is the ability of the complete system to support the tool tip in a stable position relative to the workpiece, when the tip is subjected to the forces resulting from the metal cutting operation. So let’s look at that, having removed our GHT-coloured blinkers!
But first, can we agree that the problem of parting off can be parted off into two problems (sorry about that!), viz. chatter, and jamming?
Better stop there for this posting, or it's going to tell me it's too long!
|Thread: S7 Newall DRO v Taper Turning attachment|
I see that I made an invalid assumption that it was the Ainley design to which you were referring - Wrong again! So my apologies for disagreeing with you Andrew!
I would agree 100% with Andrew re the re-positioned saddle clamp, not vey good, and inconveniently located - it always seems to hide under the cross slide every time I want to use it!
But I must disagree 100% with his comments on this one:
I've lived with this for nearly 20 years (I didn't make it, it came fitted to the lathe) and have found it to be very effective and very convenient - a nice solution to a tricky problem, and I can recomend it without hesitation. Here's the original design by Don Ainley, from ME:
I'm currently making one for my Connoisseur, alongside a friend making one for his PCF S7B - unfortunately we've found that the few dimensions given aren't quite right for a PCF machine, the position of the indicator stud seems to have been shifted slightly on green and blue machines compared to grey ones. I should have the right dimensions before too long, but this is a relatively slow process as it's being used as a teaching exercise for my friend, who's new to model engineering, and progress only happens one afternoon a week. And for some reason has completely stopped over the last couple of weeks!
|Thread: Units of thermal conductivity|
Carl: yes, ok, send me a PM. But that's with some reluctance as a) I really am rusty these days, b) my experience of heat transfer calcs is in a rather narrow speciality, and c) forget the Btu, I'll have to talk in Watts etc.
I doubt I'll be of any assistance, so don't get too hopeful!
Neil: see my response above, thermal conductance is the reciprocal of thermal resistance.
Time isn't missing, Neil, what's wrong is that the equation is for thermal conductance, not conductivity.
Thermal conductance is the heat transfer per unit time, per unit area, per unit temperature, per unit thickness . If you see what I mean!
A.k.a. how much heat (Btu) flows in one hour through one square inch (cross section) of material, one inch thick, with one degree F of temperature difference across it.
IN SI units, Joules/sq.m./degC/m/sec. I think.
Thermal conductivity is a property of the material itself, independant of the structure of the object through which the heat is passing.
Thermal conductance depends on thermal conductivity of the material, but in conjunction with the dimensions of the object through which the heat is passing..
Thermal conductance is the reciprocal of thermal resistance.
Caveat - I'm rusty, having given up heat transfer calculations 3 years ago when I retired, and although I'm bilingual (well, more than that, but I'm not sure that quadlingual is a word - I can (or could) work in fps, cgs, mks, and SI) in most units, I haven't used imperial units for heat transfer in over 40 years! So any errors in the above are down to atrophy of the relevant brain cells!
|Thread: Myford lathe paint code.|
BS 16 E 53.
|Thread: Earth fault on lathe|
Dampness could have something to do with it. If you have an electric fan heater you could use it to warm everything up and drive out any dampness, see if that makes a difference.
My myford 254 has just started tripping the house RCD as soon as I plug it in, I've traced the fault to the 110v control system but that's the limit of my electronics knowledge.
It is possible that the problem lies elsewhere, rather than on the 254. A 30mA RCD will trip when the TOTAL earth leakage current hits 30mA - and there are lots of sources of leakage current. Switched mode power supplies in computers, TV, wall warts, flourescent and CFL lights, wiring, workshop equipment (VFD's can be problematic) .... everything contributes a bit, there's always some of it around. Eventually something adds another piece of straw to the camel's back, and it trips. So something else could have caused an increase, brought the RCD near the limit, then when you plug the 254 in with its 'natural' leakage, the RCD decides to go home to mummy.
Of course, it might be a real problem with the 254, but it might be on some other piece of equipment around the house/workshop. Easy enough to check - disconnect everything else by removing ALL fuses except the one to the workshop, then unplug anything and everything left on that circuit, house & workshop. Including lighting!
Then plug the 254 in - if the RCD trips, you have a problem on the 254. If it doesn't, then you have the 'last straw' situation. Which could be more difficult to resolve!
I'll send you a PM later.
|Thread: 08 shunter quartering|
Do you have a lathe available, with something like 3.5" centre height? If so, it's very easy to do, and I'll post some words and photos describing the method.
|Thread: Polymer bearings|
Yes Jonathan, I've had 12mm Glacier DU bearings in the axleboxes of a 5" gauge 0-6-0 diesel outline loco for, I think, 4 years now, and have in the last few months had to take a wheel off an axle, so I had the opportunity to inspect two of the bearings.
Perfect condition, no detectable wear on the axles, other than the chemically blackened finish of the axle being worn off in the bearing area. The DU was nicely run in, exactly as expected from the DU literature.
The other two axles were removed, but not dismantled. The axleboxes felt in good condition.
All axleboxes and DU bearings were re-installed to the loco, so we'll see how they go from now on!
Also some experience of the Igus bearings, in one of Dave Noble's wagon kits, carrying a load of 28kg. Been running for one season now, and again recently inspected. They look good so far!
Oh, and I know of a chap who fitted very small DUs in the Walscheart valve gear of a 5" gauge Black 5, which has been running for some years. Not seen him for quite a while though, so I can't say how well they've performed since the last time we met up.
|Thread: Poly V belt modification to Super 7 lathe|
Yes, I've done the modification.
The bushes are an interference fit in the pulley bore, pressed in. There's a gap between the bushes, into which you can get a drift to knock them out, not difficult.
BUT.... a) use a brass drift, not a steel one, and b) for knocking out the first one file the end of the drift at an angle that provides a square seating against the end of the bush that's being driven out.
The problem I discovered is that the drift must inevitably be at an angle to the end of the bush being knocked out first as a result of it being pushed out of line by the bush that's not being knocked out ( if you get my drift - deliberate pun!! ), so a flat ended drift then bears on the inside circumference of the bush, and even a brass drift will cause some small deformations around the rim - sufficient to stop it going back onto the spindle and necessitating some fiddling about with a scraper. Chamfering the end of the drift should at least reduce the damage, and hopefully eliminate it.
For re-fitting to the new pulley, I bored the pulley an interference fit for the bushes, and pressed them in. Started them in the lathe (pulley in the chuck, bushes pushed by the tailstock via a shouldered mandrel) to get them aligned, then finished them off in the bench vice.
Oh, at this stage, the pulley steps had been left 0.005" over diameter and the grooves had not been cut. The o.d.'s and the grooves were finished and cut with the pulley mounted on another mandrel to ensure that they were concentric with the bush bores, and, of course, the spindle.
|Thread: Indexable tool holders|
Mmmm - the cutting speeds on the boxes are puzzling - have a look at the link I posted, which takes you to a Korloy data sheet for the tips. The cutting speeds thereon are 10 x what's on your boxes, up to 1500 m/min!
Re. height gauges for setting tools accurately to centre height.
I made a setting gauge for the S7B, which sufficed until I added the Connoisseur two years ago - which unfortunately has a different centre height to the S7B. I didn't fancy making another gauge, so I bought a 150mm Baty digital height gauge at Harrogate in 2011.
Having determined the centre height of each machine from bed and topslide (sometimes one is more convenient to use than the other ) and stuck the numbers to the wall behind each machine, there's no need to make any other form of gauge.
Has the advantage that as well as setting tools, I can actually do a quick measurement of the height of each tool as it gets fitted to the Dickson, as a check. Or use it to check the height if something isn't going to plan.
Oh, and it can also be used as a height gauge!
Perhaps Cabeng could discuss more re tip geometry. It seems many users are not quite aware of the various top rake angles available with carbide inserts.
I'm not sure what you're after here, are you refering to positive and negative rake inserts, or rake angles for specific positive rake tips? Could you clarify please?
Andrew: having tried to get some information on your inserts, I am in some confusion, because I can’t get any consistent information! JTS have the –AK chipbreaker down as medium and heavy cuts:
• Feed Rate = 0.004 – 0.020 ipr
whilst their link to ‘Triumph Chip Control’ gives:
• Feed Rate = 0.001 – 0.020 ipr
which happens to be the same as on the Toolmex site, where it’s classed as ‘light to medium’! But according to the Korloy website at:
it sits nicely between the two (for both 0.4 and 0.8mm tip radius) at:
• Feed Rate = 0.002 – 0.010 ipr
Whilst on another page of the same Korloy data sheet it says max feed 0.020” and max depth 0.160”. So which is it? G.O.K.!
Now I don’t have much experience of aluminium inserts, so I’m a bit out of my comfort zone here, but I think it’s a good guess to say that they will be designed to produce short curly or comma chips, so as to provide easy clearance from automatic machines. Long continuous spirals would not be popular as the machine would have to be stopped to rake it all out, and tangled stringy swarf would be as welcome as a f**t in a lift. Bearing that in mind, together with the Sandvik diagram of chip formation, your recent tests show that everything is going according to plan, and perhaps provides some clues as to why it’s the wrong plan!
You’ve been working at the left hand edge of the envelope shown on the first page of the Korloy data sheet, perhaps even a bit left of it – marginal conditions for long spirals, so that it only takes a bit of a hiccup at the tool tip to throw it further left and get into stringy mode. Perhaps just build up of aluminium on the surfaces across which the chips must travel, as in this photograph of the Sandvik tip I mentioned earlier – used tip at the top, unused at the bottom:
Moving rightwards on the diagram by increasing the feed might serve to get it away from marginal conditions, hence the good spirals at 0.012” feed. That, together with your doc of 0.010” puts the conditions more or less in the middle of the Korloy diagram, so I would have expected it to be forming non-continuous chips – so why is it not doing that?
I don’t know the answer, but suspect a clue might lie on the left axis of Korloy’s diagram – cutting speed might be too low to smash the chips hard and fast enough against the breaker bits of the tip to actually break up the spiral. You’re down at 25% of the recommended cutting speed, so I’d have a go at higher cutting speed.
Of course, if you’re happy with continuous spirals at doc 0.050” and feed 0.012”, then you’ve found your solution. But if not, here’s something else you can try to find, in a logical manner, what would suit you:
Say you’re happy with doc 0.010” or steps thereof. Turn a bar down in 1” long steps with doc .010” for each step. Whilst doing this, try different feeds for each step until you find a satisfactory chip formation. Set this as your feed. Then turn the whole length parallel at that feed, so doc increases in 0.010” steps as you proceed along the bar. With a bit of luck you’ll hit gold. The following photographs show this process for a Sumitomo tip cutting steel at feed 0.004”:
Top left – doc 0.005”
Top right – doc 0.015”
Bottom left – doc 0.025”
Bottom right – doc 0.120” feed 0.002”
These piccies also show exactly how the Sumitomo breaks the chips. In the first one the thin spiral is formed by the primary cutting edges, but the spiral runs away from the tip without further contact and remains as a spiral.
For the second two, look at how the chip breaker grooves are working – the thicker spiral from the primary cutting edges first contacts the chipbeaker formations, which deflect it downwards so that the spiral now contacts the leading edge of the chip, where it gets broken into bits.
In the last one, the same thing happens, but the spiral is now strong enough to resist fracture.
After returning late from a long weekend away, I did a reply to postings that had come in during my absence, only to have this bloody system loose it! Too late to re-do it now at 02:50 hrs, I'll get back to you tomorrow. Or later today!
Who or what put those ~@^&^^%$ smileys in after I'd posted that message? Not me! I deleted them, and somthing or other has put them back.
Would it be possible for Caneng to suggest a few suffixes that we should look out for that would be suitable on hobby lathes
Blunt answer - no! Each manufacturer has his own designations, new ones are forever appearing, and some are for very specific cutting operations in specific materials.
I can, however, give some guidance based on experience. But before I start, I do not work for, and never have worked for, Sumitomo! I came across their tips umpty-one years ago, and the recommendation to try them out has been so succesful that I've never had any urge to use anything different for most of my work. They've cut steel, hardened steel, HSS, cast iron, stainless steel, copper, phosphor bronze, Tufnol, Floursint, even wood - just about everything except aluminium. All sorts of diameters and shapes, hexagon bar, square bar, rough and hard castings. So they do provide a good basis for identifying what a model engineer might want to write down as a purchasing specification for his tips. Here's the Sumitomo diagram that identifies the cutting region for the NSC geometry:
From that we get that the NSC geometry is intended to operate with depth of cuts in the range 0.5 - 2mm (0.020" - 0.080" ) and feed rates of 0.1 - 0.3mm/rev (0.004" - 0.012" ). Within those ranges they will cut and CHIP FORM exactly as their designer intended. However, they will work outside those ranges, albeit without 'correct' chip forming - but acceptable in a model engineering, non-production environment. I've used them down to 0.002"/rev feed (slow feed tumbler gear on the S7) with depth of cut from say half a thou up to 0.125" - that photograph of the swarf was 3mm d.o.c., can't remember the feed, probably 0.004"/rev., but definitely not chip forming correctly!
So a tip that will do d.o.c. 0.5 - 2 mm at feed 0.1 - 0.3mm/rev would be a good starting point. These tips would not be suitable:
ap is the d.o.c., fn is the feed range, Vc is the cutting speed. Don't worry about cutting speed, not significant for model engineers, and they'll all work outside those ranges. The speed ranges are for 15 minute tool life - cut faster and they'll wear out quicker, cut slower and they'll last longer. We're not worried about optimising tool life, and they'll all go faster than we would need anyway!
The coloured letters are the material classifications for which the tip is designed: P is virtually all 'normal' steels - unalloyed, low alloy, high alloy, cast steels. M are the stainless steels, K are the cast irons, plus aluminium alloys. The others are not relevant to model engineering activities. Well, maybe if you're building gas turbines...
The presence of cutting data for P and M materials shows that the tool is suited to cutting steels and stainless steels. But it would probably cut K as well, perfectly satisfactorily for our purposes, but not optimised for high performance on cast iron in industry.
Carbide grade - not something to get hung up on in any detail, we're not in need of optimising everything for production, so we can use less than optimum materials. I would suggest going for titanium carbides (cermets) or coated carbide grades, as these are good for minimising (but unfortunately not eliminating) BUE problems. The gold clour on tips is titanium nitride, so it's obvious that they're coated. But be aware that some coatings (e.g. Al2O3) are not gold, so not being gold coloured doesn't necessarily mean that it's not coated.
Coatings are also present to reduce things like flank wear on the tips, it's not all about BUE
Tip radius 0.2mm. Not as strong as 0.4mm, but a lot less trouble on a small machine.
But one thing you should NOT do is to buy el cheapo tips from a second hand tool dealer at an exhibition. And NEVER buy tips that are just piled up in a box where you rummage about for something that looks right Only buy tips in original boxes, and only in sealed boxes at that - if the seal is broken, don't touch 'em. I did that once, having dropped on a full box of Sumis at a good price - they wouldn't cut properly, and a trip to the microscope showed that every one was worn! Fortunately they were from a decent source and I got my money back. But I've never bought from them since that experience. Plenty of industrial grade suppliers around, better to stick to them as the source for your tips.
That's about the best I can do on advice, but for recommendations:
Sumitomo tips in T1200A titanium carbide, NSC chip breaker for turning and facing. For Martin's tool holders, CCGT060202-NSC/T1200A.
Sumitomo T1200A again for boring tools, but with the W chip breaker, it's brilliant. Beware - the W chip former is assymetrical, you will need the L (left) version for normal going right-to-left boring operations.
Parting - only ever used Iscar tips and blades. Tried several variants of carbide, coating, chip former, never found much difference between them. Problem with parting tools is that blades and tips are manufacturer specific - an Iscar blade will only take Iscar tips, you can't mix manufacturers.
Hope that helps!
Edited By Cabeng on 12/09/2013 15:03:18
Edited By JasonB on 12/09/2013 15:59:24
Andrew, re turning aluminium...
I've not done much with Al, only recently done the first serious job, turning and facing an 8" disc of the stuff using Sandvik inserts from Greenwood Tools, and did have a similar problem initially.
Examination of the tip revealed the presence dreaded BUE phenomena. When this builds up, it has several bad effects, listed in no particular order:
1) If it stays in place, it changes the geometry of the cutting edge and the chip forming surfaces of the tip. Chips don't form properly, or in the right direction, or both. Bits of metal stick to the turned surface, giving poor finish.
2) It can break off cleanly, the tip returns to normal functionallity.
3) It can break off and take some of the carbide with it - the tip is wrecked!
In my case, and possibly yours, it was 1) above. I tried the usual paraffin lubricant, but the fumes were most unpleasant, so that experiment didn't last long. The answer that I eventually found was to run very fast - 2500 rpm (the VFD is set to 60Hz) at a high feed rate (the machine has power cross feed, thank God!) whilst standing well back and allowing it to shut the feed off of it's own accord! Excellent finish.
If it happens again, I suggest that you take the tip out and put it under a lens. If you see something like this:
then BUE is the problem. The photographs are actually steel on a Sumitomo titanium carbide tip, NSC geometry, which identifies the complex forms of the chip forming bits on tip.
Andrew, re pedantry... feel free! I use the 'correct' equations when calculating things with Mathcad, which tracks units and ensures consistency. But I think the crude 'torque x RPM' version gives a better sense of things to many people who might not be quite so familiar with mathematical rigour. As long as they don't try and do any sums with it, of course!
Russell: the height tolerances are for turning, facing is not so critical, but they're manufacturers recommendations, not mine! Obviously, you're right, as diameter reduces, the tool angles change if not exactly on centre height - rake, as well as clearance.
As diameter reduces it does, theoretically at least, become more important to get closer to centre height, but in my experience it doesn't seem to matter very much, and I can turn very small diameters without difficulty, without getting over-fussy about centre height. As long as it's not above centre height, of course.
However, you need the right tip to do it - have a look at the edges of the Sumitomo NSC tip above, you'll see that, by carbide tip standards, they're quite sharp. Some (many?) tips have rounded edges, which limit their minimum depth of cut and minimum diameter.
Oh yes, whilst looking at that tip - set the tip of the tip to centre height, keep the gauge well away from the chipbreaker parts - the Sumitomo NSC shapes are significantly HIGHER than the very tip of the insert, so sitting the gauge thereon would result in setting the tip far too low.
Ah, could that be Martin's problem with that spirit level height gauge that he uses?
Very good advice for someone coming from a 'big' machine shop where inserts rule the roost.
Who would that be, then? Certainly not me! Strictly amateur at metal cutting, albeit in the original sense of the word amateur, meaning 'lover of'!
But I've been involved with the metal manufacturing trades for 40+ years, as someone who designs bits and pieces and then gets someone else to manufacture them. As my technical education and training included all the metal working processes, my designs could usually be made straight from the paper, but of course they could always be improved for manufacture, so the manufacturer was always welcome to help me refine things. That led to very good relationships with the machine shops, with lots of knock-on benefits for Home Office jobs!
One was helping me to sort out my parting problems and introduced me to carbide parting tools some 25 years ago. They introduced me to a local tool supplier, who in turn introduced me to a manufacturer's technical department, and it all developed from there. Whenever I had a problem, they not only helped me to sort it out, but also contributed significantly to my education in these matters. Provided tips for me to try out, and lots of technical information and back up, even to the extent of visiting a few times. Well over and above what the call of duty required. Sandvik even provided a copy of their book 'Modern Metal Cutting', even though it was officially out of print and unavailable!
Add to that a willingness to turn perfectly good bars of steel into nothing just to find out how things worked out, to photograph it all, then inspect tips under a microscope to look at their wear and failure characteristics to identify what was going wrong, and it all added up to something useful.
Thanks for the favourable comments, very much appreciated, But as far as articles are concerned, well... they were written some years ago, and offered to ME towards the end of David Carpenter's reign. I won't go into the saga here, but let's just say that after some considerable time things did not progress to publication. It wasn't a satisfactory experience, and I don't want to repeat it. Sorry!
Separate postings for replies to other comments/questions.
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