Here is a list of all the postings Tim Stevens has made in our forums. Click on a thread name to jump to the thread.
|Thread: Some big tools|
Phil says: If it was all about saving energy, why not make their installation compulsory?
I thought that was exactly what the UK Govt have done, (but being the Govt, they are not pressing the point.)
|Thread: Crumbling Monkey Metal|
Andrew - because when plastics fall apart they do not dissolve completely, but remain as tiny particles and shreds. The plastic is made by polymerisation - joining together long strings of molecules. These bonds are not always permanent, and the base molecules remain, cluttering the sea floor and the insides of critters, including you and me.
The main cause of failure for many plastics is ultra-violet radiation, but once the plastic gets into the sea, the radiation does not penetrate, so small un-expired bits are left, and we, eventually, eat them.
Enjoy your lunch ...
If I can add to the 'embrittlement' idea:
This effect is known mainly on high tensile steel, and is caused when electroplating (such as zinc). When the steel is put under tension, hydrogen (from the effect of electrolysis) trapped under the plating percolates along the crystal boundaries of the steel, causing serious weakness. Just like a single drop of water can loosen the cohesion of a sugar lump.
If this effect happens in die-casting alloys in damp conditions, it may be because layers of different metals make tiny cells, generating small currents. This then creates the same sort of conditions as in steel. And the hydrogen comes from the water (even without electrolysis) as the metal - aluminium, zinc etc - reacts with moisture. This corrosion is called oxidation - the metal takes oxygen from water, and this leaves spare hydrogen ready to creep between the minute crystals.
The real problem is that neither the makers of model cars, nor those who made carburettors, or dashboard knobs, had any idea that their products would be treasured one hundred years later.
The same sorts of effects will destroy our favourite plastics, soon enough, don't you worry.
A common problem with old diecast alloys - whether zinc based or aluminium based. From memory, it can be caused by a lack of purity in one or more of the alloying elements.
And you are right - the answer is to start again - fortunately in this case it seems a straightforward part to machine. Or do I mean straight forward, then back again, then sideways, and then endways ...
Edited By Tim Stevens on 20/01/2019 11:51:02
|Thread: First attempt at threading on a bantam - all didn't go well|
Even if all the backlash is removed - including that between the gear teeth, and otherwise in the drive train bushes etc, you cannot rely on a backwards move matching a forwards one. This is because of the elasticity in the parts, each bit of stretch allowing a small discrepancy, but all adding to it in the same direction.
And I recall a mod to the standard tool holder which held the tool in position against a spring. As the tool reached the end of the thread, a catch was released automatically and the tool sprang back a short distance. When it had been wound back to the start, it could be pushed forwards to the stop again, where the catch held it, and then it was adjusted for the next cut. One day I will get round to making one ...
|Thread: High Speed Sensitive Drilling Machine : 1909|
And you still need a small boy running round inside a drum to provide the motive power ...
|Thread: Split die cutting undersize|
You need to check that your centre screw has a decent point to match the notch in the die. I find that the screws in recent, or cheap, or older die holders can be soft, or worn, or quite wrong for the job.
|Thread: Mill head tramming|
And I suggest that you do any checks with the table in the central position. Especially if your table is on the long side.
|Thread: Algebraic paradox|
And as every schoolboy knows, (to end with a political message) there is nothing more indeterminate than unity.
|Thread: Practice facing|
No, Adrian, the shot of the tool on its own, where the text begins 'would this be classed as a knife edge'
The edges I refer to are really the surfaces of the top face and the ground side you can see. For some of the edge there is no reflected light, but this is behind the cutting end, and shows what a sharp edge should look like.
Hope this helps
Adrian - if you look closely at your tool clip you can see a bright line where the edges meet. This is where the light is reflecting off a rounded surface, ie not a sharp edge. Any tool which shows this effect on the business edges could benefit from sharpening.
|Thread: Completed Twin Inline IC Engine|
Mick B1 says: I'm sure I've seen ball and roller mains and bigends in 2- and 4-stroke m/c engines that weren't force-lubricated
Indeed I'm sure you have. The major reason for using roller mains and bid ends is often to avoid the need for an oil pump etc. Especially on two-stroke engines - those which do have oil pumps tend to feed the oil into the inlet stream, and don't have pressure feed (which is difficult in any real sense with a rolling bearing).
Up to the 1930s, many (four-stroke) cars had no pressure feed to the big ends, they relied on a dipper in a trough of oil. The last time I looked, some mowers still did ...
|Thread: Measurements from the past|
The Babylonians were keen on fractional methods, as much of their maths was involved in dividing inheritances, and carving up areas of land. For them, the idea of sixty bits making a whole was very sensible, as it could be shared out equally among 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 30, and sixty.
PS when I was an apprentice, one of the older workers used expressions such as 'Two and a half and three of them little uns.'
For Bazyle: to the caveman, the calendar was important as soon as hunting and gathering ceased to be the sole method of survival. What was needed by then, the earliest of the Neolithic, was a way to renew the gene-pool of the family, its animals and its crops. Those who did not do this died out, sooner or later, because of in-breeding. So, how do you do this? By meeting up with other groups and exchanging DNA. So, there was a need to meet at a place others would know of, at a date others would know of - and this is a seriously complex business. It relies on recognised landmarks, and a common calendar of some sort, known to everyone who might be needing to renew their DNA too - ie most folk.
This idea can explain details which have puzzled archaeologists (and me) - but just think. What is special about the neolithic landscape? One thing stands out - It is dotted around with clearly recognisable landmarks, and most of them seem to be kitted out with astronomical clocks of some sort. With them it was possible to be at the right place at the right time, otherwise, well, how else could you do it?
See you at the Ring of Brodgar the day after the next vernal equinox, OK?
Edited By Tim Stevens on 01/01/2019 16:15:15
Edited By Tim Stevens on 01/01/2019 16:16:06
Mille was the Roman term for one thousand - hence the M in their letters for numbers system. I expect they got the term from the Greeks or the Etruscans. It survives in English as the basis for words like Millipede and Millenium, and in almost its Roman form in several languages (Italian, Spanish, Romanian, Welsh, etc) and as a multiple in the Metric System.
Mille. Thanks, Michael. Oh dear, another term from Europe ...
|Thread: Mill tooling runouts|
All materials bend when subject to a load. All gaps in the structure also allow movement in the same conditions.
If we assume that you were putting no load on the table of the machine when applying your light finger pressure there could be movement in the attachment of the column, the gibs on which the head slides, the attachment of the back half of the head to the front, the bearings locating the spindle assembly, and the quill inside the assembly. Take up all these potential gaps and much of your flex will disappear, but you won't be able to do anything useful with your mill. As Michael Gilligan says, you can have stiff or you can have cheap ...
|Thread: Measurements from the past|
I have been reading a 1909 book (in English English) about dynamos which has a long discussion about the thickness of the insulation of the windings, silk, cotton, linseed oil, varnish, asphalt, mica, etc - from a period when plastics were unknown. My question is 'What was a mil?' It looks rather as if it meant the same as a thousandth of an inch, but nowhere does it allow me to be sure.
If it was what we now call a 'thou' - ie 0.001 inches - is/was the same term used in our ex-colonies, I wonder ? And why was the older term abandoned? It would seem to be a better option than thou as it avoids confusion with thou as in the ten commandments.
As an aside, the Anglo-Saxons had a way to avoid the confusion, by having different letters for th in the and th in thing. But we lost the distinction due to influences from Europe ...
A traditional way to even out the heat was to use a tray of sand. However you do it, the trick is to avoid any chance of overheating the thin, sharpened edge compared with the rest of the blade.
|Thread: Setting lathe top slide angle accurately.|
A brief caution regarding printing a drawing: Check that the printer actually produces the same scale in both directions. Most are near, but not all are bang on. And do not rely on paper or card being really stable in moist or dry conditions. They can shrink or stretch more one way than the other.
Not really a problem unless you are after accuracy - but sometimes, we all are.
Seasonable Yuletide wossnames
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.