Member postings for Swarf, Mostly!

Hi there,

I agree with Neil about the Jenolite as preparation for painting.

However, are you sure you've totally got rid of all traces of the Nitromors? I think you rinse with white spirit but I'm not sure about that - I expect the instructions on the tin will tell you.

Personally, I'd have a go at the corrosion-stained patches with a fibreglass pencil followed by an abrasive filled rubber. Years ago, one brand was called a 'Rust-Rubber' but more recently I've seen them advertised by Garryson (usual disclaimer).

Best regards,

Swarf, Mostly!

Hi there,

I'd suggest that you visit the Ironbridge Gorge Museum, see http://www.ironbridge.org.uk/ .

I consider it has a claim to be the birthplace of the Industrial Revolution.

When I visited a few years ago (1987), we 'booked-in' at the visitor centre early on a Friday afternoon and spent the rest of that day, all day Saturday and Sunday morning at the various parts of the site. I expect they've added a lot of material since then.

Best regards,

Swarf, Mostly!

Hi there, Martin,

Thank you for your post.

Well, I did say my memory might be a bit 'iffy' !

I haven't googled it lately - did your hits indicate whether the EITB is still operating?

Best regards,

Swarf, Mostly!

Hi there, all,

I may be remembering wrongly (it's a long time ago) but the training board I encountered was the EITB (which, I guess, stood for the 'Electrical Industries Training Board' or it might have been 'Electronics' ).

The situation was that the big firms were doing all the training and the folks who completed that training would then be persuaded to go and work for the smaller firms for more money - those smaller firms could afford to pay more because they had no training burden.

So the EITB was set up with the power to collect a levy from all the companies according to their staff head-count. The funds collected were then paid to those companies that did set up proper training schemes. It worked reasonably well for me in 'continuing professional development' as I got to go on several post-grad courses and technical seminars. We even occasionally got to visit technical exhibitions on the firm's time provided we wrote a visit report and filed it with the company training department.

I don't know what went wrong, that scheme doesn't seem to operate any more. The last time I googled 'EITB', the only hit I got was for their pension scheme!

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 24/03/2013 15:51:56

Hi there, all,

I still haven't located my copy of the TI application note - watch this space.

Billy, thank you for your post. The fact that, in a full-wave choke input filter system, the current flows for the whole half-cycle in each diode (rather than the extremely high but narrow current spike with a capacitor input filter ) is the unsung merit of the choke input filter. I did mention this in my initial post but perhaps I didn't talk it up as much as it deserves.

The choke inductance has to be greater than some critical value for the particular value of the load resistance. This varies as the load current varies, leading to the use of a 'swinging choke' in which a gapped core is used to control the saturation of the core and hence the inductance. I guess designing these is a dying art.

Sort of following on from Ken's post, I seem to remember from my college electro-technology lectures (some fifty-eight years ago) that in a three phase alternator, the lap and lead of the stator windings can be chosen so that harmonics are cancelled, improving the purity of the alternator output waveform. The harmonics arise because the rotor flux spacial distribution only approximates to a sinusoidal shape. Any more than that is lost in the mists of time and my aged neurons!

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 12/03/2013 21:45:06

Hi there, all,

Thank you, Russel, Andrew and Jason for your responses to my post.

Russel, I have to confess that I have been retired from electronics for several years and am not familiar with the technique you mention. Please PM me with some more information on it.

Andrew, your analysis differs from what I remember of the TI application note, my copy of which is buried three house-moves deep in my 'filing system'! I'd like time to disinterr it and compare, and then come back to you. I do agree that my own post neglected to take account of the absence of an input mains transformer - I'm conditioned to relying on the mains transformer to account for the reduced DC output from the choke input filter.

Jason, your point is interesting, are you referring to the 'brick on a string' usually employed to power laptop computers?

Best regards,

Swarf, Mostly!

Hi there, all,

I'm not going to write about phase angle and power factor - instead I'd like to pick up a point from Andrew's post early in this thread.

I make no apologies if the following is too electronic! Just look at the title page of Model Engineer issues from the Percival Marshall days.

Andrew referred to the conversion of incoming single-phase AC to DC using rectifier diodes feeding a (reservoir) capacitor. With such a circuit configuration, current only flows through each diode when/while the instantaneous input voltage exceeds the voltage on the capacitor (apologies for expressing that in non-rigorous language). The result of this is that the current drawn from the AC supply consists of two brief but large pulses per cycle (assuming full-wave rectification). Not only does this give the electricity generator a bad time, it also requires rectifier diodes with a very high forward current capability (which is used for only a small percentage of the time!). The reservoir capacitor is also required to have a high 'ripple current' rating

An alternative configuration, the 'choke input filter', follows the rectifier diodes NOT with a reservoir capacitor but with a suitably valued inductor (aka 'choke' ) which is, in turn, followed by a filter capacitor (and a 'bleeder' resistor to set the minimum output current). With a properly designed choke input filter each rectifier diode conducts continously for its complete half-cycle but at a much much reduced current. Rectifier diodes with lower forward current capability can be used and the filter capacitor can be rated at a lower ripple current and hence reduced physical size. This promises reduced component stress and hence better reliablity for the electronics and a much better input current waveform to the benefit of the electricity supplier. It might also reduce the filtering burden that seems to cause nuisance tripping of RCCBs.

The differences between capacitor input and choke input rectifier schemes are very well explained and illustrated in a Texas Instruments Application Note on power supply design which may, just may, be available on-line.

The cost of these benefits is the inclusion of the choke or inductor, a wound component of non-trivial but non-outrageous cost. However, during my career as an electronics engineer, it was notable that many of my contemporaries were uneasy with inductors!

I've no idea whether or not the designers of workshop inverters employ choke input filters - I do suggest that if they don't then they should have a good think about it.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 10/03/2013 21:07:22

Edited By Swarf, Mostly! on 10/03/2013 21:08:35

Edited By Swarf, Mostly! on 10/03/2013 21:09:38

Edited By Swarf, Mostly! on 10/03/2013 21:10:05

Edited By Swarf, Mostly! on 10/03/2013 21:10:54

Hi there,

Belt tension isn't the only force on the lathe mandrel. The reaction to the tool cutting force also tends to displace the mandrel in a direction depending on the headstock geometry.

Best regards,

Swarf, Mostly!

Hi there, Bob & Andrew,

What Andrew writes is true of pure PTFE (aka 'Teflon'  ) but I seem to remember mention of a material which is PTFE with some sort of a filler.

It still has almost as low a coefficient of friction as PTFE but the filler gives it (more) dimensional stability.

I don't have a name for it and it might be difficult to procure in hobbyist quantities but other forum members may be able to throw more light on the subject.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 06/03/2013 22:26:26

Hi there, all,

I'd like to pour a little oil (Nuto 32? ) on these troubled waters.

My Concise Oxford English Dictionary includes the following for 'Level':

"8. vt make level, even or uniform." (My emphasis) This would seem to me to legitimise use of the term 'levelling' for adusting a lathe bed to be free of twist.

'Level' has a lot of other meanings, many to do with being horizontal, but they don't invalidate those I've emboldened above. Context is everything!

Best regards,

Swarf, Mostly!

That looks like Leylandii, that well-known weed!

Well done Geoff, that stuff's an abomination!

Best regards,

Swarf, Mostly!

Hi there,

When my ML7 was new (to me) and I was all super keen, one of the goodies I bought was a 127 tooth change wheel. I have to confess that I've never used it.

I haven't checked the tables but I seem to remember that there was an alternative method that used 2-off 21 tooth wheels.

Best regards,

Swarf, Mostly!

Hi there, Rick and Brian,

Brian, you wrote 'saddle' but I think you meant 'cross-slide'.

Best regards,

Swarf, Mostly!

Hi there, all,

I have a (microscope) bench comprising a length of 1" kitchen worktop resting on two kitchen cabinets. The gap between the two cabinets is not quite four feet. Over about five years the top has sagged and taken a permanent set.

If I were starting again, I'd glue a sheet of melamine (e.g. Formica) on the UNDERSIDE (the side that's in tension). Or maybe screw a couple of flat metal bars to the underside, angle would be better but the vertical web is hard on the knees!

My workshop bench is 3/4" blockboard on an old steel kitchen double-drainer sink unit carcase - that's really solid but the base supports the top in at least four places. I haven't seen blockboard for sale in timber merchants' for decades.

Shuttering ply is good but my own choice would be at least two thicknesses of 3/4" glued together and trimmed along the front edge with a hardwood strip.

Best regards,

Swarf, Mostly!

Hi there, Dean,

Yes, the 3000 pattern relay was extensively used in telephone exchange equipment of the generation developed when the GPO (aka 'General Post Office' was responsible for telephones as well as the Royal Mail. They were available with a wide range of contacts and coil resistances. There was also a smaller type, the pattern 600.

There was an apocryphal story that the evening before the telephone activities split from the GPO to become British Telecomm, it still hadn't been decided how the Royal Mail were going to pay their phone bills or how British Telecomm were going to stamp their letters! Probably not true but it makes a good story!

Regarding loudspeakers, keep a lookout for the really old fashined 'wound field' types where the field winding provided the magnetic bias for the loudspeaker (instead of a permanent magnet) and also acted as the smoothing choke (aka 'inductor' for the high tension supply. I remember that some of those had a serious lump of soft iron.

Do be careful though, iron (& steel) components of that era, both loudspeakers and relays, were often cadmium-plated. Cad plate was the default anti-rust treatment in the electronics industry. (A typical plating shop cad-plating bath would have an anode consisting of a metal basket containing lumps of metallic cadmium that started out the size of tennis balls.) If cad-plated components are stored in humid conditions, they can develop a surface coating of a white powdery cadmium compound that is dangerous if ingested - now wash your hands, please!

Best regards,

Swarf, Mostly!

Hi there, Dean,

I suggest that you cultivate your local Amateur Radio club and see if any of their members have any P.O. 3000 relays in their 'might come in handy' box. The bobbin core and yoke are made of soft iron.

This source won't fulfil your 200 mm requirement - that seems a bit long, did you mis-type?

P.O. 3000 relays (try a Google) aren't used as much since telephone exchanges went digital though I guess the less exotic versions are still used in some control & switching applications. My Google search before writing this post threw up several hits from firms who are still manufacturing them though, for cannibalisation, eBay is probably a more cost-effective source.

Best regards,

Swarf, Mostly!

Hi there, all,

Just a comment about the 'Machinery' handbook. It's good to have a copy but for me, the earlier editions are more useful than the very latest.

The explanation for that is that my workshop has been built up over some 40 years, largely from surplus sources such as K.R Whiston ('Have you seen my Cat?), A.E.King of Sidcup, Brown's Garage in Loughton etc., etc. I bought my lathe (ML7) in 1970.

The data tables in the older editions of Machinery's match the tools in my armoury whereas the modern editions have dropped a lot of such information because, as far as Industry is concerned, they're obsolete. Having some of these older tools (e.g. taps & dies) enables me to get to grips with 'stuff' that dates from the era when repairability was appreciated.

(For completeness' sake, let me state that I do have metric tooling as well, but the data to support that is commonly available.)

Best regards,

Swarf, Mostly!

Hi there, all,

I have both the original and the 'improved' Myford-supplied oil guns. My experience is that some oil goes into the oil nipple but some (probably more) goes round the outside of the nipple, it's a bit messy.

However, what I find even more messy is that even more oil exits the oil gun via the filler cap into the palm of the hand. Despite the great volume of adverse comment about the ML7 oil gun, I've never seen any reference to this defect on any of the forums - does this not happen to other ML7 users?

The disk of cork or whatever in the oil gun filler cap only has the thickness (about 10 thou) of the oil gun body to seal against, it owes more to superstition and blind optimism than to reasoned design!

Just my two penneth.

Best regards,

Swarf, Mostly!

Hi there, all,

I hope the following won't be judged 'off-topic'; it amused me.

Some time ago I was the 'contact man' for a South Bend lathe purchase. The deal was done and the buyer, another friend and I set off in a hired Luton with tail-lift.

The lathe came complete with full industrial stand and the deal included a bench drill, a large cast iron surface plate and several boxes of useful but weighty raw material. It took the three of us and the seller several hours to get it all aboard the Luton, by which time we were all a bit fatigued!

Partway home one of us (not the driver!) phoned the buyer's home to tell them our ETA. We were told that several young men were on-site, visiting the younger daughter of the house - 'Keep them there until we arrive' was the reply.

The Luton was backed up to the garage door and the rear door of the van raised. The said young men, all eager to impress the said daughter of the house, had all that heavy gear off-loaded in about fifteen minutes!

Why do Model Engineers power their engines with steam when testosterone is obviously so much more powerful?!?!

Best regards,

Swarf, Mostly!

Hi there, all,

I hope that my question won't be ruled as outside the scope (no pun intended!) of this site - I know that at least one member will have the answer.

On that well-known auction site there are often listings for engineer's (maybe it would be better to say 'surveyors' ) levels, the tripod-mounted telescope with a bubble and a cross-hair reticle.

They are often described as 'Dumpy' levels but I thought that was a trade name, not a generic one. Am I mistaken?

They are also sometimes (often!) described as 'theodolites' which used to annoy me but nowadays I just shrug and move on.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 17/10/2012 15:15:03