Here is a list of all the postings mgj has made in our forums. Click on a thread name to jump to the thread.
|Thread: Hss or Carbide Tooling?|
Perhaps you are doing what we all did when we started. Grinding offhand - which is OK in so far as it goes.It works, mostly, but sometimes you get a great finish, sometimes less good and so on.
But I promise you (said he unintentionally pompously) the difference between a hand sharpened tool and a properly Quorned one (or I expect any other jig sharpened one), is chalk and cheese. Also to sharpen up, I can just set my angles, skim a thou or 2 off which is only a couple of passes, plus one more on the fine stone to polish, and away I go sharp all along the whole edge. I don't waste metal or time, and good high grade HSS is not to be wasted these days given its price. (Eclipse, Cleveland or Sandvik, as opposed to the far eastern unspecified monkey metal)
Drills - sorry - no comaprison. Once you have a means of holding drills properly along the flutes (and the ER collets will do just that), then you can (4 facet) sharpen drills that cut so fast you simply cannot keep up with them - and they will cut straight and to dead size, and don't wander on startup -(they have a built in centring action) - nor do they leave a burr on break through like a new one does. And you can back one off for brass, bronze and copper to stop it grabbing, and then resharpen easily. Chalk and cheese.
Not looking for a mirror finish? With respect, that comes naturally when the tool is properly sharp and radiused. There's no need to look for it.
Its a moot point IMHO, whether the first tool you build is Quorn/Kennet or Hemingway equivalent, or the GHT Versatile Dividing head, but both are things I wouldn't be without.
Does one actually need to?
I'd rough to .010 oversize. Measure. Split the difference and cut - measure. So you now have a final cut that will be, to all intents a purposes offering the same conditions as the last measured cut - spring in the material, feed rate etc. If the lathe is halfway reasonable you will hit diameter. In general its only if the last measured cut is significantly different from the final one that diameters go awry. You might just have to polish up a touch with emery and oil just to get all running absolutely smoothly, but if one has a micrometer one is only talking a tenth or so ...
Taking whispers off is, for my money, an easy way to get the tool to rub, or to run the risk of it anyway. Especially if one is turning to a good finish and so one has just broken the tip of the tool with a stone, which is, I understand standard practise. Not least because a very small radius reduces the stress raiser at a shoulder. Which is exactly why these carbide tips have a radius in the first place - its partly about finish and nose strength, but mostly its about that stress raiser or sharp notch which is the great engineering no-no. .
I think too that a lot of these troublesome shaving cuts can be eliminated by avoiding trial and error. For instance in The Engineers Handbook, all the classes of fit are listed. So if one wants a precision running fit, (or whatever) and one actualy applies that data given, thats what one will get, and the odd thenth or two becomes irrelevant. It may seem a counsel of perfection - perhaps it is! But it don't half save a lot of hassle and wasted time.
With aplologies to grannies, and those who use metric. (Your time will come, but it isn't here yet. Mercifully. )
Edited By meyrick griffith-jones on 09/08/2009 13:43:17
It has to be said that grinding HSS is not that easy - to get consistently sharp - and consistent is probably the operative word - without some sort of grinding jig or cutter grinder.
From that point of view, the Eccentric tools holder looks very good, because even with a proper tool and cutter grinder, it does take a few minutes to set up before grinding. That thing looks as if it will work of a plain offhand grinding wheel rest. - and you get easy set up screwcutting tools out of it as well.
I think, for the model engineer, the advantages of carbide are somewhat misrepresented. Everyone goes on about speed of cutting etc. That's not it for me - its the fact that you can have, quickly, conveniently and easily, sharp tools with no hassle (at a price!), which will consistently produce a good to excellent finish. Are they sharp - yes - very. But the radiused tip means that often they are reluctant to do a shaving cut, so hitting a diameter to say +/-.0002" is a matter of good technique.
The only disadvantage perhaps, is the rake. With HSS you can grind in quite a steep rake angle which generates an "inwards" pull. That greatly reduces the load on the feed mechanism (Don't go overboard!). You don't get that with tips. That is quite a help with the smaller ME type of lathe
So you pays your money and takes your choice. I use tips almost entirely, but I do keep a selection of Quorn sharpened HSS for particular tasks. Also with an adaptor for ER25 collets, the Quorn is just brilliant for sharpening drills, slots drills, and spiral cutters like endmills - paid for itself hands down.
Oh and the one tipped tool that is just the must have - can't be without, won't jam - is a proper parting tool. I have a Glanze sliding blade type with a 2mm wide tip. And one from Greenwood which uses the Sandvik 2.5mm tip. The Kit Q cut from Greenwood is the more expensive, and cuts much more freely and to a better finish, even though it is broader. Probably the tip geometry. The Greenwood is, for my money not only superior, but can also be fitted with a greater variety of tips.
Edited By meyrick griffith-jones on 09/08/2009 09:45:01
Edited By meyrick griffith-jones on 09/08/2009 09:46:26
Edited By meyrick griffith-jones on 09/08/2009 09:55:08
|Thread: collet thread|
Might be wise to start on a blank, - get it cut to size, and set so it fits. Then munch the real thing.
Start getting into multi - start coarse helices (worms) and its easy to find it gets very interesting. So interesting that its probably worth buying the worm from the specialists. But a common or garden thread - and its dead simple.
Its like all these things - once you have done it once, you wondered where the problem was.
All the best - M>
|Thread: Choosing a lthe|
Well I was the one who had more money than sense .... and bought a brand new Myford (some 25 years ago). It is, whatever anyone says, and I have two Chinese machines, a very good lathe. Like any other machine, one shouldn't abuse it, but it is absolutely dead accurate. You can turn to .0002" on diameter routinely with sharp tools, and as she is set, se is turning to 0 taper over 12". (Something is going to move!). She has the advantage over those on metal cabinets of being set up on a proper marine ply base, so the damping, and hence finish is improved.
Having said that, I like the Chinaman too. That too is very accurate (I can turn to .0002" on diameter, and she's shimmed up to .0005" per foot over a metre on taper). While it is not a Harrison, and doesn't have the feel so I'm told (though I have insered needle rollers in the handles so they run like silk!) its not worn like an old production machine. Nor have I had to spend however long or however £ getting from 1 to 3 phase. Can be achieved, at a cost, but there can be torque problems at low speed with certain set ups. Equally the recent Chinamen (however inferior) are hadly likely to be worn out by the average model engineer.
And having said all that, you do get, from a a Chinaman, an awful lot of capability for your money. And if htye are set up and shimmed up, from my limited experience, will turn very straight.
|Thread: collet thread|
Well if its brass gas, its a plain whitworth 26 tpi form.. Set that up on changewheels or the gearbox and you'll have it cut or cleaned up in no time. On an 8 tpi lead screw you can engage on any 2 opposite marks on hte TDI. Use topslide movement along the bed to position the tool for first engagement (so the helices overlap truly) and away you go.
There is a choice - have faith and learn to screwcut (I learnned myself! from Allan Bradleys book and if I can do it anyone can). Or pay the money and get the taps and dies from Tracy Tools.
If I could just make two points:
1. It ain't that difficult.
2. You are going to have to learn sometime - so now is as good a time as any!
|Thread: Piston rings-cast iron|
|Model Engineer a couple of issues back!|
|Thread: lathe tool cutting oils|
I must admit, I use Morrisons soluble cutting oil for everything. - comes in 5l cans - dilute to 20:1 so its dirt cheap, doesn't smell, and greatly improves surface finish. Use it for cutting cast iron to keep the dust down, ali, brass (to stop the chips flying) everything!.
I like the oily surface it leaves behind .
I have a little pump supplied by Axminster but for a jet, I use a 2mm hypodermic needle. They come from vets and are the perfect delivery spout. You get full flood on the job and a very accurate jet into parting off slots, inot hte back of drilled boring tools etc, without soaking everything!
|Thread: BA Threads or Metric Threads?|
Well one thing is for sure - metric is far more freely available and a great deal cheaper. I go down to my local fastener people and come back with all the nuts setcrews etc, and I have extreme difficulty spending more than a couple of quid for 20 of this and 20 of that. and I can get them easily in stainless, button head socket caps (pretending to be rivets) etc etc.
So for me, the only time I'd deviate from using metric would be for something specific - putting a nut onto a shaft of specific imperial size, something like that. If I need particulary fine threads, then the metric fine series seems to do.I have a complete set of BA taps dies spanners and sockets, but they are rarely used nowadays.
If you bust a tap, you can get a new (cheap) metric one from Halfords or Screwfix - even on a Sunday if need be. BA are a little less convenient!
|Thread: Measuring tool accuracy|
Thanks for that about bore gauges. Glad I'm not alone.
Fitting--well its all very well scraping away, but if I want a precision running fit or whatever, I look up the fits in the Model Engineers Handbook and machine to that (or whatever the process is and appropriate clearances are) - voila, it fits and does what it's supposed to first time (mostly) every time. If I'm planning on a bit of scraping, then I'll machine to an allowance.
That's fitting, innit?
Spent enough time munching metal big time on this traction engine, without spending another year or two scraping.
Well - only a comment or personal opinion.
Rulers and calipers are all for rough and ready measurements anyway? Though accuracy of transfer on sheet metal has been improved enormously by using an optical centre punch. (About the most useful had tool there is IMO)
Calipers - electronic - I can never get a good reading out of. If someone can tell me how I would be most grateful.
Which leaves me with a set of electronic digital micrometers by Mr Mitutoyo. Since they are so accurate, and agree with both the Myfords dials and my cheap but large Chinaman too, I use my old calipers as bore gauges and measure across the hooks with a micrometer. Electronic calipers I use for a quick reading only, but micrometers I could not be without. The micrometers come out spot on when used on the reference bar, to many places of decimals, and any difference is usually resolved by wiping hte anvils, because a layer of grime does affect them.
As a matter of interest, has anyone had any great success with accurate repeatable measurements with ordinary telescopic bore gauges in the smaller sizes.
I recently fitted a 6" scale on the downfeed of the mill (awaiting saving for the 2 axis DRO) and that is spot on, and agrees with the mitutoyos perfectly. But the mills imperial dials are clearly out by .002 over 1/8 inch. That scale reads to 1/2 thou (or metric at the touch of a button of course).
Edited By meyrick griffith-jones on 01/07/2009 22:02:52
Edited By meyrick griffith-jones on 01/07/2009 22:06:56
|Thread: Outrageous Set-ups!|
Well lets just say that many model engineers do many things to extend the capabilities of their machines, and provided speeds and feeds are kept sane, they do it fine well. (and always knew they would)
In most cases all one risks is the machine, or even just the job, rather than the operator.
Which proves that in most cases, a little common sense is a lot more useful than a whole passel of elfins.
(Perhaps we might also remember that rules are for the guidance of the wise, and the blind obedience of fools.)
If its any consolation to either of the injured parties, I'd have cheerfully done that job at a low speed - but I have 2 fixed steadies, and I would have used both, the additional one being nearer the cut, to prevent the job from vibrating or kicking.
Is it more stupid than the individual who wanted to surface grind a chunk of austenitic stainless and so secured it to the machine table with a magnetic chuck....... now that really is an outrageous set up!
Frankly I put up with enough half baked nonsense from unthinking elfins at work, who seem to assume that statistics as remote as the chances of Mars colliding with Earth represent commonplace reality, and back them up with the pseudo science of risk assessment figures for the feeble minded - I thank the Good Lord that they have no jurisdiction over me while I play. Its probably entirely appropriate that 2 Jags was given responsibility for H&S, in between other diversions?
Oh and if anyone wants a temporary but quite effective fixed steady- make up a bookend shaped bit of wood out of sane sized ply. Clamp to lathe bed and drill an appropriate sized hole in it, and then place as required. Adjust for line with a DTI on hte job. Anyone who has made a Dore Westbury quill on a Myford will have met that cheap, cheerful and very effective approach! I don't suppose it is as good a proper fixed steady, but its a lot better than none. Proceed with sanity and caution, because I for one have no patience with the determinedly stupid!!!!!!!.
Edited By meyrick griffith-jones on 30/06/2009 23:37:10
Edited By meyrick griffith-jones on 30/06/2009 23:50:01
|Thread: good beginner book - timing diagrams, etc|
Oh if its that sort of stuff you need, the RAC motor sports association has a very good book on tuning 2 strokes. Tuned exhausts, exhaust theory, inlet and exhaust overlap, the effects of overlap on ignition timingtop speed and idle, momentum and movement of air in inlet tracts, organ pipe theory in both inlet and exhaust. Open Loop and Schnuerle scavenge and the effects of head design. And the formulas and figures to allow you to work your own bits out.
The late Colin Campbells book- The Sports Car (I think it was), but it may be "The Racing Engine" does the same for 4 strokes - very practical and down to earth. Google it on Amazon, they have a remarkably good out of print section. Well written, easy to understand, and well worth having. A litle dated now in these days of electronically mapped multi sensor engine control units, but the basic theory remains the same. All the maps do is apply optimum conditions over a broad range.
Again the 750 motor Club had a range of publications on the subject and very good they were too.
|Thread: crankshaft bearing material|
Unwise to ignore the BS recommendation for use.
Still it isn't going to wear that quickly, so you could finish the machine, get it into steam and have some fun and then order the 660 bronze. I've done the same on my 3" LS and that's my plan, and I'm not planning on a new crank! (Nor do I have the slightest intention of calculating the loads, nor of case hardening)
A lot depends on the load in the bearings and the highest load will be imposed by the water feed pump probably, if you are simply doing a bit of light steaming to run it in. Use the injector, shove a bit of proper teflon based grease in there, keep them clean and and keep an eye on them?
I'll let you know when mine pack up!
If you are really worried get crank and shaft nitrided?
|Thread: acid pickle|
We can get citric easily enough at a proper chemist.Thats what I use, and it seems very effective.
I have 5l of sulphuric, but of the two, I find citric better.
Best of all in that line is to get the metal really clean, and to solder when it isn't too hot.,and use a lot of flux. That way water is pretty good and leaves nothing behind. You just don't get any of that burned on black glass - its all a soft paste which washes off in a couple of seconds. probalby wouldn't work on a big job, but on small stuff I rarely need the pickle.
Ordinary chemists also stock caustic which also works well.
|I asked in our lab about dry acid salts. Sulphuric and the inorganic acids don't exist as a salt or crystal, I'm told. Organic acids like citric, do.|
Well try the bike shops anyway - yellow page one or two. I've been able to buy it as recently as a month ago, so its about.
Incidentally most welding shops do a pickle paste - wouldn't do for a copper boiler or some such, but quite handy for small jobs.
Have you looked in the yellow pages under chemical factors?
Also water treatment people. They add caustic and sulphuric to adjust the ph of things (Not at the same time I wouldn't imagine!), so they have gallons of the stuff.
Still the B&Q option seems pretty good.
Quick point, but I have always done better at motorcycle shops. For some reason the smaller batteries are often the maintenanceful acid filled types stored dry charged.
Which would also mean that a bigger garden machinery place that sold and serviced ride on mowers would possibly be worth a phone call too.
|Thread: First Project|
Trouble is, to make a model you do need tools- or they help.
Some kind of simple indexing arrangement, perhaps a fairly simple jig for grinding lathe tools, a depth stop is very handy, a handy lock lever for the saddle, perhaps a samll boring and facing head, or at hte least a small flycutter holder. Oh an accurate tee bar for squaring up up vertical slides quickly without having to change to a faceplate. A little holder for small milling cutters, and a drawbar for a small milling chuck.
Keep anyone a bit busy. My list included a GH Thomas Versatile dividing head, which, apart form the dividing/indexing, is one of the mose useful toolholders for slotting (before you make a little slotter) and of course for milling because anything round up to 3/4" is automatically at centre height. Thats a great timesaver....Where do you stop?
If one is honest, even the most complex bit is only a combination of several single operations. The suggestion would be to think each operation through, whats to be used as a datum, and above all, how it is to be held for each operation.
But there is always a problem if you cannot viualise the object in your mind....so it might be worth looking at a small toolmaking project which will ease life in the future, but which comes with an isometric drawing -thats like a 3d drawing/pic rather than the old style single plane first or 3rd angle projections. An isometric drawing is a lot more user friendly and you know what the finished lump should look like. You should avoid end making a left hand version of a right hand bit!
Hemingway supply that sort of thing, and a good set of instructions (usual disclaimer) and I imagine there are others too ... oh and get Tubal Cain's book, Workholding in the Lathe. (absolute Godsend, along with everything else he wrote!)
|Thread: Lathe Bedway Regrind|
Google lathe bed regrinds. There are some 10 pages of contacts (various -some refer to articles).
KMZ near Exeter look as if they might be worth a ring.
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