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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: Molasses has etched cast iron?!
29/11/2019 11:11:53

Choochoo_baloo, I've PM'd you.

28/11/2019 05:12:44

I've de-rusted quite a lot of steel components by immersion in molasses, with complete success, producing a bright finish, after the residual crud has been easily rubbed off. However, on some high-carbon steel items (gravers), the resulting finish has been dull grey, rather than the expected bright finish. I'm aware of warnings that air must be excluded from the surface to be treated, otherwise more corrosion occurs. I suppose it's possible that the soaked-tissue method allows oxygen to get to the surface, so perhaps the problem is further corrosion (oxidization), rather than etching (just material removal). However, this doesn't explain the poor finish achieved by immersing high-carbon steel.

I can only assume that the molasses sequesters some iron from the surface, leaving excess carbon, carbide, whatever, on/in the surface, dulling it. Or, perhaps, the grey represents black oxide, from rust conversion, in the 'pores' of the iron, which is consequently difficult to remove. Any chemists / metallurgists out there who know?

Have you tried to recover the cast-iron lustre by wire-brushing or using fine wire wool?

We discussed chelation in a previous thread, and I subsequently tried to find out more,only to discover that it's rather mysterious...

Thread: Record 25 vice handle
14/11/2019 09:30:27

As above. It is surely a good idea to 'design' the handle to fail by bending before the vice is subject to excess force?

Have a look at this **LINK**

...and the follow-up on the DIY construction of a serious vice!

Thread: Two weeks wasted
21/10/2019 01:53:05

Well, Peter, you've just 'won' two weeks! What are you going to do with it? What would any of us do with an extra two weeks? Suggestions please...

Thread: Is Model Engineering in Decline
21/10/2019 01:50:51

I don't know about model engineering being in decline, but this model engineer has been for years...

Thread: Slideways oil
21/10/2019 01:41:37

Apart from not running off slide surfaces too readily, slideway oil is designed to have better 'stick-slip' properties than most other types of oil. It lubricates well when bearing speeds are very low ('boundary lubrication', IIRC) and there is insufficient film thickness to prevent metal-metal contact. Motor oils, etc, are generally used in hydrodynamic bearings, where a decent film thickness is built up by the relative movement of the bearing surfaces. Depending on dimensions and oil properties, this takes much more speed than slideways generally move at. So slideway oil is designed for the job, other oils aren't. Why use anything else?

A practical example: my Boxford shaper's ram judders horribly, because of the stick-slip phenomenon, unless lubricated with slideway oil. This is a hardly-worn machine, with the ram gib adjusted properly. Some molybdenum disulphide helps on some slideways, sometimes.

Edited By Kiwi Bloke on 21/10/2019 01:48:40

Thread: identify
21/10/2019 01:28:05

As above, plus...

Got any strongish acid? And if not, why not? Every self-respecting model engineer should have accumulated stocks of enough 'dangerous' materials to make a health and safety inspector hurriedly put on his bicycle clips...

Mild steel won't heat-harden, but will fizz in acid. Silver steel will heat harden and fizz in acid. Some stainless steels may harden a bit, but shouldn't fizz.

Thread: Lifting A Tom Senior Light Vertical
18/10/2019 11:01:32

Dismantling is good, but a pair of scaffold poles or stout timbers under the stand's tray, orientated fore-and-aft, and lashed together so they are tight against the base make good lifting points for strops and a crane. It would be sensible to take the head off, though. I used this method when I moved an M1 and a Universal, with large table - both heavier than your machine. In fact, two hefty blokes can 'walk' one of these machines around quite easily, using the poles as handles. Four can lift it...

Edited By Kiwi Bloke on 18/10/2019 11:04:08

Thread: nutcracker
18/10/2019 10:47:11

No need to make one - already got the ideal tool. Sandvik Bahco 8224 ratchet-adjustable pliers ('water pump pliers' ). The jaw shape holds the nuts well and its instant adjustment feature means that it can be set so that great force can be applied with minimal risk of movement over-shoot. But just give walnuts a smart rap with the back of a table-spoon. (Not expecting a prize...)

Edited By Kiwi Bloke on 18/10/2019 10:48:17

Thread: Internet searching
17/10/2019 08:38:47

Michael, just be careful with Google - all your searches are stored, linked to your identity, as part of Google's 'big data' initiative. You have been probably been recorded as searching for a male model...

Thread: Nalon Viper
17/10/2019 08:30:32

I need to correct my previous post. 7075 does seem to be a reasonable substitute for the high-strength alloy 'Dural', aka HE15, or 2024 (or 2014?). I had thought that it had inferior fatigue characteristics, but its mechanical properties seem just a little better than those of 2024 and its corrosion resistance is much better. Apologies for any confusion caused.

16/10/2019 02:46:25

Compared to 6061, 6082 is a newer and somewhat superior general-purpose alloy. My understanding is that, for most purposes, they are interchangeable. Here in backward NZ, as in USA, 6061 is the default alloy, and I haven't found a supplier of HE15-equivalent. "Tooling plate' 7075 is available, but I'm not sure why, and it isn't a substitute for 2014 / HE15. Perhaps 6061 (or something with '6061' printed on it, supported by 'certification'  pours out of China, so is cheap... Excuse my cynicism.

(Edited to remove damned stupid winking smiley. Isn't it time this bug were fixed?)

Edited By Kiwi Bloke on 16/10/2019 02:47:59

Thread: Heat insulation
16/10/2019 02:20:15

To correct some misinformation in a previous post...

The original MAPP (sic) gas - a mixture of methylacetylene and propadiene - is no longer available. MAPP substitutes seem to be propylene. Both burn in air with a higher flame temperature than propane, which burns hotter than propane/butane mixtures, which burn considerably hotter than butane. As a self-contained, hand-held torch, a 'MAPP' torch makes a butane torch look rather silly.

In your application, you probably need to concentrate on heat output, rather than temperature, so propane feeding a larger burner will almost certainly be better than a self-contained 'MAPP' torch. Large bottles of Propylene are available (in USA, at least), but I don't know about in UK; pity us in backward NZ, where, apart from MAPP-substitute hand-held torches, the best we can get (easily) is a propane/butane mix (of no standardised proportions). It's not too bad with Sievert burners, but, for small jobs, I still go to my MAPP-subs. torch.

Thread: diameter calculation
13/10/2019 06:05:02

SOD. ' In practice, dividing a circle isn't an accurate operation, in fact the best way to do it is to calculate the tangent to as many places of decimals as needed, and then to lay out the angle over a large baseline. Dividing Y by X is the tangent of the angle, and tangents can be calculated to as many places of decimals as reqiired.'

I don't agree that tan calculation is a good way to divide, because as X tends to zero, the calculation becomes difficult to handle in practice, as the tan tends towards infinity.

I think the key is 'in practice', especially when engineering, rather than theoretical maths is concerned. In practice, we would use whatever hardware we have at our disposal to do the job. Polar to Cartesian translation makes sense if our machines can only cope with rectilinear movements, but when a rotary table is available, or something like a BCA or Boley UFR milling machine can be used, it would probably be sensible to use polar co-ordinates, if that's how the job has been specified. The accuracy we can achieve in practice is far less than the calculation accuracy achievable by cheap scientific calculators, so in practice, translating between co-ordinate systems isn't going to damage accuracy. Theory is another matter...

13/10/2019 05:48:00

'My goodness what a waste of time. The OP just wanted to know a shop grade calculation (and got one early on) .'

So the thread served its original purpose, and quickly. Now it's moved on to an intellectual discussion about other, but still related things. What's wrong with that? Whose time is being wasted? If a few old codgers wish to spend time in a virtual pub, close to a virtual fireplace, bouncing ideas around, should anyone complain? If this forum confined itself to answering questions, it would be a dull place indeed. I have posted to ask questions, to inform, to challenge, to entertain and to get people to think. I don't intend to stop. Naturally, not all of my posts will have been appreciated by all watchers. That probably goes for all other posters too. Too bad. I hope the thought police aren't welcome here.

12/10/2019 01:18:44

Blowlamp: 'I would far rather make a division plate using a DRO on a milling machine than use a rotary table or dividing head if I wanted the best accuracy.'

I wouldn't, because the problem is effectively specified in polar co-ordinates, so errors are introduced by converting to cartesian. Plus, it's far more likely to suffer from operator error (well, at least in my case...).

Thread: Resistance Soldering question
12/10/2019 01:10:32

Patrice, just how restrictive is your house insurance? I can understand acetylene being frowned upon, perhaps also big bottles of propane, etc., but are you allowed a gas cooker, barbeque, gas cigarette lighter (and is it size-limited?), paraffin (kerosene) blowlamp, spirit blowlamp, jeweller's spirit lamp (or candle) and blow-pipe? Just trying to think of other sources of pre-heat...

I have done naughty things in the past with welding transformers. You might be able to get the job done by making very good electrical contact with the small and large part (thus avoiding local over-heating), so the current flows across the joint area. Electrical resistance here will be high, relative to other areas, so will heat up. It might be quite spectacular, because you're less than one step away from an improvised spot-welder (which is another avenue to explore...), so current-control would be a necessary addition. A 12V car battery may also work. I think you may be approaching suggestion-overload... Apologies for adding to this, but it's an interesting problem, and it's making people think!

Thread: diameter calculation
12/10/2019 00:45:39

Duncan: 'But if you work out the diameter for 3 holes on a pitch circle I suspect you get an irrational number whichever way, it's most unlikely to be an exact number'

Most unlikely, yes, but there's a couple of solutions that spring to mind that are rational. I'll leave it as a teaser, for others to find...

12/10/2019 00:29:10

This has got complicated and no doubt I'm out of my depth...

It seems to me that, if the problem is specified in Cartesian co-ordinates, such as could be the case for absolute hole positions, then Cartesian co-ordinate geometry is the way to go, even for problems involving positions on a circle. It's all done without Pi or trancendental functions poking their awkward noses in. However, if relative positions are specified, in terms of lengths and angles, then polar co-ordinate geometry is appropriate. Perhaps that's what Michael and Andrew are saying... For practical workshop applications, especially with simple co-ordinate tables and DROs, Cartesian rules, doesn't it?

11/10/2019 11:50:41

Michael: 'I think it's useful to remember that this is an example in polar geometry'. You mean 'R - theta' geometry? Not really, although I agree a bit of construction is required to get to this, 'sine-formula'-like answer. Co-ordinate geometry is good, if only because it's easy to transfer that approach to machining co-ordinates.

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