Here is a list of all the postings Swarf, Mostly! has made in our forums. Click on a thread name to jump to the thread.
|Thread: Small cast iron bar supplier?|
Hi there, all,
As has been said on other threads, scrap metal dealers nowadays seem reluctant to let us 'browse' through their yards.
Slightly off-topic: Some years ago, my next door neighbours inherited a player piano but couldn't find anyone to take their old upright piano (to play). So I volunteered to 'constructively dismantle' it. It had a cast iron frame on a wooden sub-frame. The cast iron machines beautifully and I still have a few pieces in-stock. (Its cross section would lend itself to being made into an engineer's level.) The board with the tuning pegs was beech and now forms the front apron on my carpentry bench and the front jaw of the carpentry vice. The wooden sub-frame was 4" x 3" white pine with not a knot anywhere; I managed to keep that out of the rain for 30-odd years (and three house moves) but recently gave it away to an acquaintance who makes guitars.
Now for a question - I have a substantial block of cast iron (60 mm x 60 mm x 90 mm) that I need to reduce and 'rough-out' before I start to machine it. The only bandsaw to which I have access is an old Burgess. What do members here think of my chances that the Burgess will cope with such a job and what sort of blade should I be looking for?
Edited By Swarf, Mostly! on 20/04/2013 15:50:54
|Thread: Propane mixer|
Hi there, Mark,
Get out your Yellow Pages and look up BOC or BOG or whatever British Oxygen are calling themselves this week.
('Saffire' is, or used to be, a BOC brand/model name.)
Hopefully you'll find they have a depot on an industrial estate near you!
When I lived in Essex, I used to use the one at Basildon.
|Thread: Myford tread cutting|
Hi there, Norm,
Did you mean 'idler' or did you mean 'tumbler'?
|Thread: An Alternator for the Stuart S9|
Hi there, Ian,
Did you remove the shading coils or did you leave them in-situ?
|Thread: What did you do today? (2013)|
Hi there, Kwil,
I wonder if your oil gun is the same as mine because mine certainly doesn't seal properly.
The front end works fairly well, the problem is with the filler cap. As I posted in a recent thread, I have the same problem with both the old style and the new style guns.
The design of the gun expects/requires the disk of leather/plastic in the filler cap to seal on the thickness of the 20 SWG wall of the oil gun body.
It has about as much chance of doing that successfully as I have of winning the Lottery (even if I bought a ticket!)
I've been toying with a scheme to modify the filler cap to use an O-ring but I don't have a convincing scheme worked-out yet.
|Thread: painting over rust staining.|
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).
|Thread: Visiting UK from Aus|
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.
|Thread: Maybe there is still hope|
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?
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!
Edited By Swarf, Mostly! on 24/03/2013 15:51:56
|Thread: Reactive power loading|
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!
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?
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.
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
|Thread: Worn Bearings|
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.
|Thread: Teflon glide bearings|
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.
Edited By Swarf, Mostly! on 06/03/2013 22:26:26
|Thread: Leveling a Lathe|
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!
|Thread: Arc Eurotrade delivery performance|
That looks like Leylandii, that well-known weed!
Well done Geoff, that stuff's an abomination!
|Thread: Metric Screwcutting on Super 7B with 127 Tooth gear|
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.
|Thread: Taper Attachment Advise / Help|
Hi there, Rick and Brian,
Brian, you wrote 'saddle' but I think you meant 'cross-slide'.
|Thread: cellar to workshop - benches|
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.
|Thread: Source of "Soft" Iron?|
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!
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