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Member postings for Robin Graham

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

Thread: Spectacles and solder.
02/08/2020 23:09:58

My specs broke a few weeks ago:


Because of lockdown I couldn't get an immediate appointment with with my optician, so I soft soldered the join. For reasons too tedious to explain, when I did get to see him he advised me to wait six months before buying new specs and live with the bodged ones until then. "You're obviously very good at repairing things" he said, but I'm not - the soldered join has (predictably) failed.

To get to the point - I'm now thinking about silver soldering, but I seem to remember reading somewhere that it's impossible to silver solder a join which has previously been soft soldered. Is this true?


Thread: Turning a riser for VMC Z Axis
29/07/2020 00:57:13

Dave - I'm in the East Midlands (Derbyshire, about 4 miles south of Matlock). If that's within striking distance, I'd be happy to help.


Thread: Death of a PSU
28/07/2020 02:39:24
Posted by Joseph Noci 1 on 27/07/2020 12:19:31:

Don't know - ask Robin?

Well, my answer to John if he were to ask me would be move on, don't read, that's up to you as an individual.

For me personally this has been a very interesting discussion - for the first time in my life I think I am on the brink of the threshold of understanding an electronic circuit. I could have just bought a replacement PSU - it wouldn't have left me starving. But I wanted to understand what had happened and if I can repair it it would give me a buzz, of the life-enhancing rather than lethal type I would hope!




Edited By Robin Graham on 28/07/2020 02:59:04

Edited By Robin Graham on 28/07/2020 03:00:48

Edited By Robin Graham on 28/07/2020 03:01:28

Thread: A novel 'non-cuttable' material.
28/07/2020 01:23:13

Apologies if this has already been mentioned, but I stumbled across this article in Nature in which the authors report a novel material which is highly resistant to 'attack' by angle grinder discs or drills. The material consists of ceramic balls embedded in a matrix of foamed aluminium. The cunning thing (if I have understood the article correctly) is that the 'dynamic hardness' of the material is the result of resonances set up in the cutter when it encounters the hard ceramic suspended in the much more compliant aluminium matrix, rather than the static hardness of the ceramic.

Seems like clever materials science - informed by biological studies.


Thread: Death of a PSU
26/07/2020 23:02:14

Thank you for the warning Robert . There was actually quite a lot hidden under the the conditional 'if' in my last post. Such as (inter alia) 'if ever I feel I understand this well enough to proceed safely" - which, at the moment, I don't, as you have rightly observed. Doesn't mean I can't learn by asking naive questions though!

Stay safe, Robin.

26/07/2020 20:40:31

Joe, it's not easy to see the markings on the component but as far as I can make out there are two lines - top LT 1117 and bottom MBRF2045CT.

Thanks for posting the schematic. If I have a go at repair, what voltage Zener would I want? Presumably the 22V in the schematic is to do with it being a 20V supply? I am

Ta for the suggestions of mounting the PSU externally - the unit I have is the chassis mount (ie not fully enclosed) type, and I was thinking that by the time I'd bought a suitable enclosure and associated gubbins it'd be getting close to the cost of a new unit. But on second thoughts, maybe I could lash something together from stuff I've already got.


Thread: Pinning joints before silver soldering.
25/07/2020 19:22:16

Thanks for further info Michael and Gary - I'll have a go with binding.

I wasn't really doubting the wisdom of the advice, just surprised. Now I know about I can envisage several situations where this technique could be useful.

Thanks again, Robin.

Thread: Death of a PSU
25/07/2020 19:07:39

Thanks for replies. It sounds like the unit is beyond economic repair, as I suspected. Out of interest though, here is the 7-pin chip in more detail:


and the site of explosion:


The unit is rated 5V 7A - the plate on the DRO gives a power rating of 25VA.

I actually have a cheap 5V 10A psu which would do the job but, as Joseph correctly guessed, the problem is the size. The existing unit (TDK-Lambda CS35-5) is 3.9x3.2x1.4 inches - the replacement from RS I'm looking appears to be a direct replacement. As far as I can tell from my researches, the CS35-5 is no longer available having been superseded by LS-35-5.

If anyone can point to a cheaper alternative which would fit, that would of course be welcome!


25/07/2020 00:28:48

I've had a dead SINO DRO unit on my shelf for years. I'm trying to upgrade my mill to glass scales, so thought I'd have another look at the display unit as I'd been told the most common failure with these devices is the PSU. So maybe an easy fix.

And so it turned out - the display works fine with an external 5V supply.

My question (to which I think I might know the answer, but have to ask) is whether it is worth trying to repair the PSU. This is what it looks like:


The fuse under the connector block is open circuit and something's clearly gone wrong with the component marked Z1 to the left of the capacitor at the bottom of the pic. From the underside:


I can get a slot-in replacement unit for 20 quid, so that's what I'll probably do - but I'd be interested in any info from the electronics bods on this forum about the possibility of repair and the probable reason for failure.



Edited By Robin Graham on 25/07/2020 00:33:22

Thread: Pinning joints before silver soldering.
24/07/2020 23:00:03

Thanks for suggestions - a few things to try. A couple of further questions about about the binding wire approach though.

First, what gauge of wire would be appropriate? The discs are 1.5" dia x 3/8" thick,the 'struts' are 3/8 x 3/16" to give an idea of scale. I see Cookson do 0.69mm binding wire, presumably for this kind of thing.

Second, why doesn't the wire stick to the work? I use Silver-flo 55 with Tenacity 5 flux which works well for steel parts as well as brass - is there something different about soft iron?

Georg49 - thanks for your input. It's likely that the design will change - my drawing was really meant to illustrate a general problem which I think I need to solve as I strive to tart up my work. It look's like you're a new member - if so, welcome.


23/07/2020 22:52:39

I'm OK with silver soldering in that I can make a sound joint between two pieces, but I now have a project which is more complicated - I want to make something like this:



It's two discs of CZ121 brass joined by horizontal CZ121 struts with a curvy bit of CZ108 between.

I don't think I can just assemble this on the brazing hearth and have away at it - something will move. So I wondered about pinning (or perhaps riveting would be a better word) in the locations shown.

Do you reckon this would work? I've no experience of riveting, but I'm thinking if I drilled countersunk holes and bashed soft copper rod in, it might hold it together for soldering.

Or any other strategies?




Edited By Robin Graham on 23/07/2020 23:03:53

Thread: Cognitive ability.
21/07/2020 00:58:36

I read a recent thread about clamping forces on this forum, and thought I could sort it easy-peasy - I earned my crust doing that sort of thing. But I kept on going round in circles*. I must be going senile I thought. Well, that's a real possibility so I had a go at the Montreal Cognitive Assessment:


I aced it! I'm clearly a stable genius. How would you do?

Apologies for potentially political content - just seems funny. And a bit tragic.


*Im hoping the reason that I went round in circles is that the problem wasn't properly specified - too many unknown constraints!.

Edited By Robin Graham on 21/07/2020 01:00:23

Edited By Robin Graham on 21/07/2020 01:04:20

Edited By Robin Graham on 21/07/2020 01:10:07

Edited By Robin Graham on 21/07/2020 01:14:26

Thread: Cigarette Papers
14/07/2020 21:06:56

I obviously have too much time on my hands - a while back I also asked myself about thickness of fag papers, and made measurements of stacks of 1,2,3,4 and 5 papers, taking five measurements at 'random' locations for each stack. Results for Rizla green (X number of papers, Y thickness in microns):


Linear regression gives a slope of 24.56 +/- 0.18 microns, with 95% confidence interval 24.20 - 24.92 microns. So I think we can say a thou! No doubt, in time, metric papers will be available.





Edited By Robin Graham on 14/07/2020 21:08:50

Thread: LED GLS bulbs
07/07/2020 00:47:52

Thanks for further replies.

Steve - I appreciate your advice concerning using the existing wiring to run a low voltage DC system. After mooting the idea I I had a look for the DC current rating of standard light switches - it seems that MK will not give even a derating figure for their switches, and don't supply any alternative switches certified for DC. This info comes primarily from a thread on BuildHub where the topic is discussed in some detail. You are right - getting it signed off would be a nightmare.

In the light (sorry!) of Steve's comment about the possibility of arcing in the switches, SoD's rat smelling, MichaelG's experiences and my own observation that my stairwell light which burns continuously has lasted a year and still going strong, the switches seem the most likely culprit. That might add up - the house had a 'makeover' a couple of years before we bought it, and I suspect that every expense was spared. The light switches certainly feel 'spongy' compared to the to the industrial-standard jobs I specified for my workshop.

Thanks again for comments - I'm slowly 'doing up' the house so replacement switches will go on the list.


PS - one of my favourites is "How many social workers does it take to change a lightbulb?" "None - they convene a working group on 'living with darkness' ". I guess there must be (equally unfair) ones out there about engineers!


Edited By Robin Graham on 07/07/2020 00:58:53

06/07/2020 00:20:07

Thanks for replies. Reading MichaelG's and other respondents' suggestions that it may be the the switch that's the problem I remembered that I have a 4W LED bulb lighting the stairwell down to my cellar workshop. It's been burning 24/7 for over a year - I've become so used to it that I forget it's there. I installed it as a 'temporary' replacement for a PIR LED lamp which failed within 6 months, So maybe it is to do with switching - though obviously the switching in a PIR must be rather different from a normal light switch, presumably solid state. Hmm. The specs for the bulbs I've had claim 100,000 switching cycles, so I'd assumed that switching wasn't an issue.

Sam - thanks for the link to Big Clive - I'll have a wade.

George - I take your point, but in my (admittedly small) sample I haven't yet had a bulb to the right hand side of the mean.

Since my original post I have discovered that 12V (presumably DC) LED bulbs are available in GLS form. Is there any reason why I shouldn't disconnect the 240V house lighting circuit from the MCB and run the house lighting from a 12V power supply though existing wiring? The upstairs and downstairs have independent circuits wired with 1.5mm cable, which is good for 10A I believe.So 120W for each floor, which might be liveable with given LED efficiency.



Edited By Robin Graham on 06/07/2020 00:28:29

Edited By Robin Graham on 06/07/2020 00:29:11

04/07/2020 23:45:28

Has anyone found a brand of LED GLS bulbs which last anything like the the 25 - 30,000 hours burn time which is commonly advertised? I think my record is about 9 months, so I must burn them for over 100 hours a day.

I've bought cheapo Wilko bulbs, mid range from Screwfix, pricier Phillips and Osram but they all fail well before the advertised MTBF. The only advantage I've noticed with the 'big name' brands is that they seem brighter than the cheapos with the same advertised lumens / colour temperature. In all the brands I've tried there is quite a big spread (in the same brand/model) between lamps which fail very early and those which last longer.

I'm not really complaining - still saving money, but I'd like to know more. Does anyone know how these lamps typically fail? The LEDs themselves, or the drivers?


Edited By Robin Graham on 04/07/2020 23:46:15

Thread: clarke cl500 improvements
04/07/2020 02:40:02

Nice work John - shows what can be done. I too have a Far Eastern lathe, the screws don't have the silky smoothness of of a Raglan, but I can turn to a couple of tenths if I need to.

Three tenths with a three jaw is indeed pretty good!


Thread: EN42J heat treatment
01/07/2020 23:54:34

Thanks for replies, and apologies for not following up on this sooner. I was struck down by some sort of bug - not Covid the Dr says - which jellified what remains of my brain.Seems to be recrystallising a bit now though.

I've made some blades from O1, and they are OK, but quite brittle - fine for plane irons which are supported close to the edge, but not so good for kitchen knives. The reason I was thinking about spring steel is that I'd seen stuff about people in '3rd world' countries making functional knives from Landrover springs etc, and thought I'd like to try something like that. But I haven't got a Landrover to take the springs from.

Especial thanks to David George for offering some 420 stainless for me to work with - I couldn't make use of it because it was round bar, but the offer was much appreciated.


Thread: Voltage feeding DRO "usb" digital scales?
01/07/2020 22:58:32
Posted by Les Jones 1 on 01/07/2020 20:28:00:

Hi Robin,
I have some digital calipers that use CR2032 cells but the data output is still 1.5 volts. I think they have a built in regulator to drop the 3 volts down to 1.5 volts.


Hi Les. This is interesting! Well, to me as someone with little knowledge of electronics anyway. The ARC readout unit can be powered from the mains via a 6V output 'wall wart', or from two internal AAA cells in series, so about 3V. But it puts out 1.7V, so there must be a regulator in the unit which can drop either 6 or 3V to 1.7. Then it presents the 1.7V to the scale, which anyway must have a built in regulator to drop 3V to 1.5. It all seems a bit over-complicated! Can you explain why it's done like this?

Norman - apologies for hijacking your thread, but I'm trying to get to grips with the same stuff myself - glad your question has been answered,


01/07/2020 13:05:54

Les, the ARC scales in question use CR2032 (3V) cells - I think the OP wanted to know if the remote unit just replaced that voltage or supplied 1.5(ish)V direct. The latter seems to be the case.


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