Member postings for Kiwi Bloke

Thanks Martin. Well, we're getting somewhere... But questions remain: why do chelators prefer to bind the Fe from the oxide rather than from the lump of metal? Is it because the oxide is far more soluble in the chelator solution than is the elemental iron? Will chelators attack the base metal significantly / at all? Are there more important things I should be doing at this time?

'I only asked if anyone had used it!' Now look what you've started! Where's Michael Gilligan when you want him? Link to enlightenment required!

Edited By Kiwi Bloke 1 on 26/06/2019 07:53:15

No mocking, but lots of sympathy. What a horrible mishap. I'd imagine that a top-slide could be obtained from a wrecked 7. Easy enough to scrape the base to your existing slide. Otherwise, make a new 'cone' as suggested above.

'The Geo. H. Thomas version specifies ball ended screws working in conical recesses. This arrangement tends to push the gib upwards against the face of the slide locking it firmly in place.' I don't think this is correct. As far as I can see, the gib strip could pivot on the screw point or ball end, but is constrained to follow the path of the screw's movement. Please shoot me down in flames If I've misunderstood, because I've thought about this subject a bit (and posted previously) and am surprised that a definitive solution doesn't seem to have been made widely known. OK tapered gibs are the answer...

GHT was a fan of dowelled gib strips, which seem to me to be a good idea - or at least some form of gib movement control is. The screw thrust is parallel to the dowel's axis, so any pushing of the gib strip in any other direction (eg 'upwards' would be prevented - but I think that the strip would, in fact, be pushed downwards by pointed screws in conical pockets. (We may in fact agree, but are using 'upwards' and 'downwards' reversed...)

If a ball is interposed twixt screw (flat-ended) and gib strip (not dimpled), the gib should be pushed normal to its surface, so this is a problem for dowelled gibs*, unless the dowel is aligned to be normal to the gib strip's surface too. My ancient Superior surface grinder has its gib-strip adjusting screws arranged so that they bear at right-angles to the gib strips. It's about the only nice bit of design in the whole machine (but that's another story...).

* assuming the dowel fits closely into a hole - a 'vertical' slot would be OK - just constraining 'horizontal' displacements.

Scraping is most certainly worth doing in a most important third circumstance - the serious re-building (or improvement) of machine tools - not just minor fettling of cheaper machines! It is certainly practicable for the determined amateur (as well as the professional, of course) to bring well-worn, old machines back to as-new, or better, standards of accuracy. And all with simple hand tools (and power scrapers for the very well-heeled).

Edited By Kiwi Bloke 1 on 25/06/2019 11:26:53

Edited By Kiwi Bloke 1 on 25/06/2019 11:33:00

Poor old dead horse - the flogging continues...

The problem with parcipitating in this forum is that it's too interesting, and it becomes difficult to resist being drawn into discussion. It's also fun to be provoked into finding out more about things.

Chelation seems to be commonly (usually?) discussed in applications where its purpose is to sequester metallic ions from (aqueous) solutions. Does the metal have to be ionized, in solution? Why do (some?) chelators act preferentially on iron III oxide, rather than the bulk metal? Is the presence of an acid also necessary to promote dissociation (oxalic acid and citric acid are also chelators)? I don't know the answers - it's decades since I was taught chemistry, only touched on chelation, and poking about the 'net to try to find the answers only confuses me...

However, from Wikipedia's Iron (III) oxide page: ' Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and sulfuric acids. It also dissolves well in solutions of chelating agents such as EDTA and oxalic acid.' [ my italics ] Unfortunately, the whys and wherefores are not provided. Tantalizing.

The point is that molasses and other chelators do not act by indiscriminately making inorganic salts from both the oxide and the metal as acids do. Clearly, it's magic.

Any chemists out there who could enlighten? At least two of us would like to know...

The devil's in the detail, as usual. If contemplating a locking screw bearing on the gib strip (the usual solution), think hard about the screw/gib interface. This should be such that the gib strip is not displaced in the plane of the dovetail as the locking screw is tightened. The ideal is probably to restrict possible displacement to be normal to the plane of the dovetail. A ball 'under' the screw, bearing on the plane back-side of the strip, does this. Pointed screws in dimpled strips, or flat-ended screws bearing on 'pockets' don't, but are often used. Anyway, it's probably a theoretical worry, since gib strip displacement should be near-infinitessimal.

Apologies to disinterested readers to appear to be flogging a dead horse...

Well, I don't know how chelation works at an atomic level, but it does appear to prefer to bind iron from the oxide than from the lump of the element. Probably something to do with the relative strength of inter-atomic bonds at the surface of the different material surfaces, etc., etc.. One thing I'm certain of, however, is that, at each higher level of scientific training, what one learned at a lower level is shown to be a lie. Now, it's all quantum-effects. Uncertainty rules!

Two perhaps pointlessly pedantic points: (1) '...the molasses would first have to change the oxide to something else as a chemical reaction i.e not chelation'; chelation is a chemical reaction, not a physical change. Perhaps you didn't mean to imply that. (2) A strong reduction reaction can reduce rust, with no ions in solution being involved - think thermit. But, of course, that's rather different from reactions in solution.

Evaporust info. pages discuss its function via chelation.

There's a vast amount of info available on the 'net (as well as books, of course). Look for YouTube videos - far more useful than words for providing insight into the physical process. The philosophical justification for this tedious (but addictive) process is that one is working the scraped surface to match, as accurately as possible, a highly-accurate, non-wearing, reference surface, such as a surface plate, straight edge, etc. One may also be scraping a part to fit as well as possible, another part. It is even possible to scrape gas-tight joints which need no gasket or sealant. Machining operations are limited in accuracy by the intrinsic accuracy of the machine, which won't be as accurate as a reference standard. By accuracy, in this discussion, I mean as close as possible to the chosen reference standard - flat, straight, cylindrical, a given angle, etc.

The other advantages of scraping are that one can control the quality of the surface finish (oil pockets, etc.) and, given large enough reference standards, one can bring dauntingly awkward things like long slideways to high levels of accuracy with the use of simple hand tools - and a lot of patience. There's quite a few videos showing how cheap machine tools made of butchered chineesium can be made far better than as-bought. The factory 'scraping' that may appear on them is usually shown to be decoration to fool the gullible...

No. Fresh molasses smells like molasses. Not to everyone's tastes, perhaps, but not a stink. If it is kept clean and not contaminated by microbes, a 'working' mixture won't start fermenting, and will stay molasses-smelling for weeks. Once the bugs get in, however, it can grow a disgusting crust and will stink. Presumably, alcohol may be produced by yeasts, and this may then oxidise to acetic acid, etc., and all sorts of other smelly products of microbial metabolism may be produced. Whether these also remove rust I don't know, but it's irrelevant. By the time it's offensive, anyone with any sensitivity would have slung the stinking mess away (and you don't need to worry about disposal methods). The important point is that fresh molasses removes rust, and it is by chelation. This process does not cause the base metal to be etched. The chelator EDTA also removes rust. Evaporust also works well, and is believed to be a chelator. It ain't magic or mystery.

I don't want to flog a dead horse, but I can't think of any reason not to use molasses, except impatience...

I thought I'd replied, but my post seems to have got lost.

Problem solved!

Thanks Thor, you've got it! Clearly FreeCAD is smarter than this operator. I hadn't realised that the chamfer tool produces different results, exactly as you describe, depending on whether a surface or edge (line) is selected. I had indeed selected a surface to be chamfered, so FreeCAD obligingly found every edge and did its thing.

Apologies for stupid, unintended emojis in previous post. This forum's software has its own ideas about things...

Edited By Kiwi Bloke 1 on 24/06/2019 00:10:47

It's great to see a champion of Free software, isn't it? Is part of the enthusiasm for other packages expressed by others a reflection of the amount of money they have forked out? However, I digress...

I've pm'd SOD about this, but don't want him to feel he has to waste time finding the answer. Far better that his excellent tutorial continues.

Here's the problem. When I applied a chamfer to the annular surface at either of the junctions of the two different diameters of the shank of the chuck key model, FreeCAD produced the expected 'external' chamfer, but also an internal 'fillet' (as would be produced by a V-shaped turning tool). I haven't found a way to restrict chamfers (or what FreeCAD calls 'fillets', but what I call 'corner-rounding' to external edges only. Anyone any ideas - without getting deep into python?

There's a lot about de-rusting on this forum, and others. Some is true, some isn't. Some is frankly magical beliefs.

Although vinegar and dilute citric acid have been advocated - both certainly work - some users report etching of the base metal under certain conditions. Phosphoric acid will certainly attack - especially if used in a high enough concentration to please the impatient. My experience is that the phosphate coat is too fragile to be worth the risk. Electrolysis is probably the ideal, although some warn of the risk of hydrogen embrittlement.

Molasses, improbable though it sounds, really works - albeit slowly - with no risk of attacking the base metal - and it tastes good! It acts by chelation, not acid attack. Other chelators work, but can't be easier to obtain than molasses. Tubs of the stuff can be got from country stores servicing the horsey brigade. I presume it goes into the front end of a horse, but what for I don't know (de-rusting?). Evaporust is believed to be a commercial (ie expensive) chelator. That works very well too.

Scrape crud off first, and de-grease with a strong detergent wash, then into the molasses (all sorts of dilutions are suggested; I use about 1 molasses : 2 water - or not - it's not critical. Leave, fully submerged, for a few days (longer if thick rust) and gently scrub off the grey residual coating. Rinse and repeat, if needed. When all done, oil immediately.

It's all been said before, but the message clearly hasn't got out...

It's sometimes difficult to remember individual steps made when blundering around in the semi-dark... I think I selected the surface to receive the chamfer, expecting the chamfer to be applied to its external arris. Lo and behold, a chamfer was produced, but simultaneously also a fillet in the internal 'corner' at the junction of the larger and smaller diameter of the body of the key. Impressive and pretty, but was that what was intended...?

Just got my latest subscription copy of ME. Glad to see old friend DAGB is still going strong. I thought I might add a little to his article.

In the late '90s (?) I bought a couple of goose-neck 12V halogen machine lights from Warco. Similar ones were quite common around then, and probably since. Good light, but unpleasantly hot, so a mixed blessing when working close to the lamp, as in when using a Unimat with magnification.

Last week, I finally got around to the mod I'd been intending to do for years. It took about 10 minutes (isn't it always the way?). The bulb, reflector and bulb-holder were removed, and a MR16 LED down-light 'bulb' was installed. I used a pukka ceramic MR16 socket, which came with fitted flying leads and cost next to nothing, but a couple of terminals separated from a small 'chocolate block' can also be used. More details of the mod would be superfluous - its obvious once you start, and dead easy. Lamp transformed!

Hopefully, this mod is common knowledge, and I've wasted your time reading this, but if it isn't common knowledge, it should be!

Wow! Fantastic! Thank you Dave for taking the time to put such a clear guide together. Over the last year or so, I've installed FreeCad - and removed it in disgust - a number of times, having got nowhere. Today, I followed your guide to the end, with success! But what a tortuous process. I suppose that with practice (how much) and a comprehensive background knowledge of the application, its use becomes second-nature - but, until then...?

Locating the hole for the T-handle took a bit of guesswork. However, a guide such as this should not spoon-feed us with every minute step, should it?

The chamfer tool seems also to add fillets to the selected surface. How do you remove them, or have I done something stupid?

I haven't been able to install freecad-doc: it seems to be incompatible with the latest (Linux) version of the freecad package. This seems to mean that off-line help isn't possible. Again, have I been stupid?

SOD - Brilliant! Thank you! Now you've shown where the front door is, I'd better be brave and venture in to FreeCAD. Ever thought of writing a bit more on the subject for MEW?

FreeCAD appeals to me because this is a Linux-only household, but the fact that it's free (and runs on any platform) should surely appeal to many of our colleagues, some of whom appear to be as tight as myself...

You say FreeCAD is a few years behind some commercial products; is this a bad thing, is it significantly handicapped? Most of us use manual machines, conceptually designed, or even dating from, the turn of the last century. We are used to old-fashioned stuff - ourselves, partners and friends included...

There's clearly a lot of fear, verging on hysteria, about the hazards that surround us. A lot of it is amplified by the bureaucrats who seem to want to think for us and/or instruct us how to think. Keep the public anxious, in ignorance and submissive. Create the illusion that the masters are lovingly looking after the people, wrapping them snugly in cotton-wool and keeping the nasty, scary things away. When you're lying on the floor, paralysed with fear about all this, it's worth finding out what the greatest dangers to life and limb are - and what the government isn't doing about them...

Elemental Hg (and Pb - also hysterically demonized) really aren't that risky: it is unusual to be in a situation where significant absorption is likely. Anyone should know that inhaling fumes of more-or-less anything (including tobacco and other combustion products, of course) is to be avoided. Some heavy metal compounds - some salts and, particularly, some organic compounds are, however, horribly toxic. That includes some compounds of gold. Some gold compounds were (still are?) used to treat inflammatory arthritides. IIRC, the safe dose range was very narrow. Gold is a toxic metal! OK, again, elemental gold is 'safe', although it's, surprisingly, a recognised allergen. Perhaps our 'protectors' should ban gold, just to be on the safe side...

On a less cynical note, one metal that really is an 'everyday' danger to model engineers is copper. If you ever suspect that you have a penetrating eye injury (and this can be surprisingly painless, at the time) due to copper, or copper-alloy swarf, for goodness' sake please panic: get to A&E pronto (and make sure they understand the possibility of Cu in your eye). Copper destroys eyes, very quickly!

'I suspect the toxic smell was evaporated residue from the carpet cleaning products.' - or, perhaps, panic-induced soiled underwear...