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Member postings for Kiwi Bloke

Here is a list of all the postings Kiwi Bloke has made in our forums. Click on a thread name to jump to the thread.

Thread: Microns ...
08/07/2019 06:41:36

I stand by what I said: "That non-temperature-controlled apparatus thinks it can resolve 1nm repeatably enough to justify the scale's resolution? Delusional, surely. It reminds me of a friend tickled pink by his small bench-top oriental CNC mill. He discovered that his CAD software could work to microns, and sincerely told me that he could now machine things 'accurate to a few microns'."

I can accept that the piezo gizmo can, in effect, change its length by 1nm, repeatably and accurately, but I'm talking about the apparatus as a whole. I'm not clear whether the piezo gizmo is a positioner or a displacement sensor, and if a positioner, whether it's working 'open loop' or 'closed loop'. In any case, the gizmo seems to be attached to a complex mechanical assembly, with a complex, cantilevered shape, which presumably has built-in clearances, etc., and the whole lot is subject to temperature effects. Is the apparatus to which the gizmo is attached dimensionally stable to within 1nm? The chain can only be as strong/accurate as its weakest link. Hence my comment about the CNC mill.

Edited By Kiwi Bloke on 08/07/2019 06:43:20

Thread: Curious
07/07/2019 10:01:09

If a cask ("What's a keg?" asked the ex-CAMRA member) contained anything other than ale (and "air" , I wouldn't touch it! cheeky

 

(Multiple edits to try to exterminate invasive emojis. Grrr!)

Edited By Kiwi Bloke 1 on 07/07/2019 10:03:11

Edited By Kiwi Bloke 1 on 07/07/2019 10:03:47

Edited By Kiwi Bloke 1 on 07/07/2019 10:04:27

Edited By Kiwi Bloke 1 on 07/07/2019 10:05:46

Thread: Scraping
07/07/2019 09:52:28

One often sees deep crescent 'oil pockets' applied to the upper face of horizontal sliding ways. If these surfaces can be exposed in use, the pockets can accumulate fine, abrasive crud, not just oil. My belief is that the pockets should be a feature of the upper surface only, the lower being smooth, so the way wipers can keep the muck out. The problem is that visible crescents = $$$ of added showroom appeal. This isn't to say that the lower surface shouldn't be scraped, just that one should aim for a relatively smooth surface.

Thread: Microns ...
07/07/2019 09:41:54

That non-temperature-controlled apparatus thinks it can resolve 1nm repeatably enough to justify the scale's resolution? Delusional, surely. It reminds me of a friend tickled pink by his small bench-top oriental CNC mill. He discovered that his CAD software could work to microns, and sincerely told me that he could now machine things 'accurate to a few microns'. Hmm. But then he also thinks that scraping has been made obsolete by modern CNC machinery. Hmm again.

Thread: Phillips vs Pozidrive and portable drills
07/07/2019 09:25:57

I find it hard to believe that the Phillips drive was designed to 'cam out'. The axial component must be very small, given the very small wedge angle of the drive flanks. Whether the driver 'cams out' or not will depend on the axial force applied by the operator (in my case, often a large proportion of my somewhat excessive weight) and the friction between driver and recess. And if it was an intended feature, the idiot designer didn't think about subsequent removal...

Good old-fashioned screwdrivers for slotted screws (remember them?) are, of course, tapered too. Is this a designed-in torque-limiting feature too? Parallel-tipped drivers are much more secure than tapered tips. Interesting that gun-makers of old often used screws with very narrow and deep slots, designed to be driven by the finely-tapered tips of 'turnscrews'. These fancy-named screwdrivers wedged securely in the slot, making slip-out unlikely. Useful when fixing very expensively-engraved actions into stocks, etc.

I thought that GKN patented Posidriv in the mid-'60s, so it was a late-comer, in competition with long-established Phillips, and the yanks adopted a 'not invented here' attitude. I think the popularity of the different patterns has more to do with commerce than engineering.

The Robertson drive is very common here in NZ. Note that its driver is also tapered, so might be expected to 'cam out', if the Phillips theory is correct. I have driven about 100 in the last few days, without any problem.

Thread: EMCO Compact 5
29/06/2019 03:01:48

Posting after I should have gone to bed after a bibulous evening was a mistake. Thanks Barrie for reminding me about Emcoshop re spares availability: I should have checked before posting. A bit of detective work, cross-checking numbers and availability between ProMachine Tools (www.emcomachinetools.co.uk) and Emcoshop reveals the following:

A5A 020 011 Saddle (A5A 050 020 appears to be the cross-slide)

A5A 021 010 Cross slide feedscrew bearing / mounting plate

A5A 000 091 Longitudinal leadscrew nut (adjustable)

Above available from Emcoshop

A5A 020 060 Cross-slide nut (adjustable)

Above apparently not available from Emcoshop, but is available from ProMachine Tools, who can also provide A5A 000 091

Also needed would be A5A 020 050, the adjuster / retaining nut for the cross-slide nut, not listed by either supplier, but could be made easily enough. As expected, the prices are depressing. Hope this helps.

Thread: Metal de-coroder
28/06/2019 11:13:49

My experience is that months of immersion in molasses doesn't cause the base metal to be etched - but the rust goes.

It does rather seem that 'chelation' is a term that gets used without being strictly defined. Oxalic and citric acids get called chelators. Both remove rust. Both are acids and, as far as I know, form iron citrate and iron oxalate. Is this chelation? Are these relatively simple metal salts of organic acids chelates? I'm not getting much further in this particular quest for knowledge...

Thread: EMCO Compact 5
28/06/2019 11:04:02

Same problem here. My early-model, second-hand Compact 5 arrived with an excessively free-running cross-slide feedscrew. The cross-slide feedscrew bearing in the alloy plate is also worn. The lathe shows no other evidence of significant wear or abuse. The nett result is that the un-balanced handwheel will rotate because of machine vibration, and the cross-slide will withdraw, unless the gib is adjusted more tightly than I like. The screw-nut backlash is not excessive. I have not used the machine for milling, but would expect to have to lock the slide after each feed adjustment. The worn feedscrew bearing makes it impossible to get a smooth rotation without allowing additional backlash at this bearing.

The idea of making a machine with no provision for replacement or adjustment of the feedscrew nut is ridiculous, and leads me to suspect that Emco never really expected the machine to be taken as seriously as it has been. The later modification - to provide for adjustable and replaceable cross-slide feedscrew nuts - is an admission that the original design is defective. But that's no help to owners of earlier machines. As far as I know, new saddles, and all the other bits which would be needed to revamp old-spec machines (except the nuts) are unobtainable new. Pity, although, knowing Emco prices, they would make an upgrade very expensive. One day, I might get around to re-engineering the thing. Until then, it remains in storage - a reminder that it's not only the Orient that can produce disappointing machines.

Thread: Scraping
26/06/2019 12:23:53

Machines are still rebuilt by scraping, presumably because of a combination of the accuracy achievable and the ease with which long dovetails, etc. can be attacked. No need to hoist heavy machines into awkward set-ups for machining or grinding. Slideway grinders are thin on the ground, and you'd still want to scrape. It's quite possible to scrape several thou off slideways, to remove the effects of wear, and then bring the surface to a few tenths all over, and to a similar level of accuracy of alignment to another surface. And all with hand tools...

It's hard and tedious work, although fascinating. I scraped all the sliding surfaces of a late model Senior Universal. It took ages, and much metal was shifted. It was hardly worn, but alignment was all over the place. Perhaps it was a Friday job, but it made a bit of a joke of the frequent advice to buy British if you want quality. For the next rebuild, I'll buy a Biax power scraper - to hell with the cost, I'm not getting any younger, damnit!

There are videos around showing Swiss commercial rebuilders of Schaublin (etc.) lathes, scraping away. At the other end of the scale, there are videos showing how bad slideways may be, when roughly hewn out of chineesium, and how readily they may be corrected by hand-scraping. There's actually a lot of it about...

Thread: Metal de-coroder
26/06/2019 12:03:17

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?

26/06/2019 07:49:59

'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! cheeky

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

Thread: Myford Super 7 Top Slide Base - Alternatives?
26/06/2019 07:44:54

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.

Thread: Cross Slide Lock
26/06/2019 07:40:29

'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.

Thread: Scraping
25/06/2019 11:25:29

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

Thread: Metal de-coroder
25/06/2019 11:15:45

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...

Thread: Cross Slide Lock
25/06/2019 03:01:41

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.

Thread: Metal de-coroder
25/06/2019 02:50:25

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.

Thread: Scraping
25/06/2019 02:29:27

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...

Thread: Metal de-coroder
24/06/2019 06:40:43

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.

24/06/2019 00:15:32

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

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