Member postings for Robin Graham

Well the "27W" Sealey unit has arrived and it consumes about 18W over the advertised 12-30V range. Probably bright enough for my needs though.

I made a simple full wave rectifier with a 1000μF capacitor across the output and there is negligible ripple according to my manky old oscilloscope. 34V as expected, but that can be taken down - I remembered that I have some buck convertors left over from a previous project, might be more efficient than a resistor. It's getting a bit complicated for a lathe lamp I know, but I would like to use the lathe's power supply rather than a free-standing mains lamp if I can.

I did wonder if the 34V output would be enough to run one of the nominally 40V Plessey modules which MichaelG tipped us onto a while back albeit with a reduced output (they are eye-blisteringly bright at 40V). Sadly not, they don't turn on until about 38V.

I think the electrics are now sorted and I'm pondering on the mechanics. A gooseneck rather than an articulated design might be good. I was wondering about this item. It's meant for phones/tablets, but some reviewers complain that it's too stiff/strong so maybe OK for this application? Any suggestions welcome!

Robin.

I know where you're coming from Bill, but perhaps the lad or lass on the phone doesn't actually have the power to make a difference. They are given scripts and if they don't recite the company mantra they're on the dole. I know people who do this sort of work and they are not personally lazy or callous. They just need to make ends meet and do what they're told to do. The callousness comes from above and the laziness from suffocation of individual initiative - why bother if no one is listening.

Robin.

Edited By Robin Graham on 25/08/2023 01:14:26

Edited By Robin Graham on 25/08/2023 01:18:05

I'd like to make a picture of something I've made along the lines of the assembly diagrams we see in machine tool manuals. For example, a lathe apron:

My thing is much simpler but my question is: how are these diagrams produced? The above looks like pure draughtmanship to me. But maybe there are computationally assisted ways for the artistically challenged.

Robin.

Your neighbour is not alone Alistair - from the Guardian. It does seem the company is in trouble.

When my late dad's cognitive abilities began to decline he had the foresight and trust to give me Power of Attorney. I took charge of all of his financial affairs for seven years and never heard a whisper of protest from the many organisations I had to deal with. I simply don't believe that OVO are somehow exempt. Challenge them. As others have said,Citizens Advice is a good port of call.

Rob.

Thanks for further comments. In a moment of madness (as it turned out) I pressed 'buy now' on a pair of 12-30V spotlights - the sort of things people mount on their SUV's to dazzle oncoming drivers help with off-road activities - £16 the pair. Taking on board comments about damp environments (I sometimes use suds) the IP68 rating sounded good too. They are advertised as 48W 4800 lm so I was a bit worried they might be a bit too bright. However:

The regulation is actually pretty good in that power consumption is 15-15,3 W from 12 to 30V , but obviously not as advertised. So they'll go back and I'll order the Sealey.

Robin.

Thanks for replies, all read attentively and (more or less) digested.

Thanks Robert, that's exactly what I was hoping for - a 'rule of thumb'. I have the diodes and some 1000uF 50V capacitors in my 'bits box' so I can lash something up and see how it performs.

John Doe 2 - I came across the formula you quoted (or something very similar), plugged in some numbers (guesswork) and came out with 450,000 uF. Obviously ridiculous, but not being sure which piece of 'garbage in' led to this 'garbage out' I gave up and posted.

SoD - yes, 10-30V not 36V. Not sure what happened there! Thank you for your suggestion of using a resistor to drop the peak voltage. I think I have a box of 5W resistors somewhere. I have an oscilloscope so now I have a reasonable value for the smoothing capacitor I can build a simple circuit and see what happens.

Alan Johnson 7 - it's a transformer. Until I started investigating this I hadn't realised that there is 240/24V transformer which is always energised when the lathe is switched on at the mains plug. It seems to run all the switchgear (interlocks etc) as well as the light. It takes only a few Watts when quiescent so has probably only eaten about £50 over the 5+ years the lathe has been left on at the wall 24/7.

Maybe it's simpler to junk the 24V lamp and go for something mains powered but I wanted to explore possibilities and learn something along the way.

Robin.

I'm looking to replace the 24V AC 50W halogen capsule lamp on my lathe:

It's a horrible lamp. Hard to position, not very bright and the mount attached to the saddle can get in the way for some operations.

Lots of possibilities I know, but there might be an advantage in using the existing 24V AC supply. Something I'm thinking about is using a 27W Sealey LED array . This works from a 12-36V DC supply, so I'd need a rectifier. A couple of questions:

Q1. I have diodes suitable to make a full wave bridge rectifier myself but don't know how to calculate the appropriate value for smoothing capacitance. Any advice?

Q2. Is it nuts to contemplate making something myself? Perhaps there is some off-the-shelf unit which would do what I want? I've looked but so far failed to find, perhaps because I don't know the right search terms.

Comments along  'if I were going there I wouldn't start from here' lines also welcome of course!

Robin.

Edited By Robin Graham on 18/08/2023 22:07:00

Thanks for replies. It's not dust, grease or whatever on calliper jaws, micrometer anvils or gauge block faces - all scrupulously clean. Measurements are repeatable to within 0.001mm using the micrometer and 0.01mm using the callipers.

SoD makes good points about technique - however, even putting insane pressure on the calliper thumbwheel I can't shift the reading more than 0.02 mm.

I didn't know that the gib was adjustable - thanks Nigel. Having adjusted it the discrepancy is down to 0.1 mm, the callipers measuring undersize. Still a lot though. I have a Mitutoyo vernier (ie not digital!) calliper in a drawer somewhere. Not used it in a while (failing eyesight) but I remember it having that sort of silky smooth feel characteristic of quality instruments. I'll dig it out and see what it says.

My reply: Not at all! The reason I posted was that I wondered why both my micrometer and callipers read within spec (+/- 0.002mm for the mic, +/- 0.02mm for the callipers) when measuring parallel faced objects (gauge blocks) but differed when measuring round objects of similar size. Of course the mic is more reliable - measuring a 1/2 inch edge finder (round obviously) with the mic gives 12.698mm, the callipers give 12.58.

I realise that they don't really matter in the great scheme of things, but little problems like this bug me!

Robin

I have cheap (~ £25) digital callipers which I thought pretty much OK. When I bought them I checked them out and even wrote a positive review on Amazon claiming that they were within spec (+/- 0.02mm). I can't remember how exactly I tested, but likely it was on parallel faced objects which I could either measure more accurately by other means or had certified dimensions.

I've just turned some nominally 17 x 8 mm brass discs which I wanted to be +0/-0.01mm on diameter, and according to my Sunday best Mitutoyo mic they were OK - 16.995 to 16.998 mm. But imagine my horror when I idly applied the callipers - 16.78 - 16.84 mm! Way out of spec!

I checked the callipers on the three Jo-blocks I have - 10, 20 and 25mmm so 10, 20, 25, 30, 35, 45, 55mm. The callipers consistently measured 0.01 or 0.02mm over size. Which is fine. The micrometer was at worst 0.002 mm out on the 10, 20, 25mm blocks.

I can only think that the discrepancies are due to the calliper jaws 'racking' when measuring a round object beause the jaws are in point contact with the object. Maybe that's the reason why Mitutoyo callipers are so expensive? More to do with the mechanical engineering than the measuring technology, which seems common to all these devices - even expensive Mitutoyo callipers quote +/- 0.02mm?

I'd be interested to hear opinions, especially from users of high-end callipers. Is it really worth the investment? And if so why?

Robin.

Edited By Robin Graham on 12/08/2023 23:41:54

Edited By Robin Graham on 12/08/2023 23:44:24

Edited By Robin Graham on 12/08/2023 23:45:29

Thanks for replies / discussion - interesting! I think JasonB got where I was coming from in his first reply. I had never heard of Hotley planes but had a look. It seems that for £10,560 you can have this fine jointer:

It's a thing of beauty for sure, but surely no-one is going to pay that sort of money then actually use it? And if they did would it really be the magic bullet they presumably hoped for?

I suspected that the pricey saw in my first post might be the same sort of thing, but reading replies maybe not.

JasonB, thanks for the suggestion of using the mill, but the box has to be about A3 size (though shallow) so edges too long. I think I'll probably go for the saw and chisel solution. I'll foul up at first but will learn!

Robin.

This is tangentially related to metalwork in that I want to make a nice wooden presentation box for  some brass work. I have to learn how to make box (finger) joints and it seems that I need a fret saw to do them by hand. Prices vary from about £7.99 to:

for £235.

I'd like to know if (and why) paying so much for what seems essentially a simple tool would be worth it even for a professional woodworker. Seriously - I may be missing something, wouldn't be the first time.

I also wonder what feature of the tool qualifies it for a patent. The design and mechanisms shown in the picture  are surely 'prior art' ?

Robin.

Edited By Robin Graham on 02/08/2023 00:51:47

Edited By Robin Graham on 02/08/2023 01:05:42

A couple of months or so ago my pension provider sent me a letter saying that there had had been a data breach at Capita, who they had unwisely trusted to manage their (my) data. Private Eye calls them Crapita with good reason. All my personal details are now out in the wild in a collated form it seems.

As some sort of recompense I was given a subscription to Experian's premium service which tracks requests, eg for opening a new bank account or more generally enabling new financial activity.

It's surprising and a bit scary. I get emails from Experian detailing requests from companies I've never dealt with or even heard of. I suppose it's the selling of data - I do buy a lot of stuff over the internet.

I post on this forum under my real name. Maybe that's unwise. If so, that's sad.

Rabbie Graeme.

Michael, a review I wrote on Amazon for kitchen foil may be of some interest. I said:

"In the 'questions and answers' about this product there have been enquiries about the actual thickness of the foil in microns - no number is given in the product description or on the box. Being somewhat obsessive-compulsive about this sort of thing I have measured with a micrometer which I know to be good to +/- 1.5 microns, and get 24 +/-1.2 microns on average. Cutting off a strip, measuring, then weighing on a precision balance gave me 23.7 +/- 1.0 microns. So I think it's fairly safe to say it's 24 micron foil."

I can't remember the details exactly but I made many measurements and used standard mathematical methods to calculate the errors. The point is that the best I could do was about one part in 25 or 4% on dimension - if I had been working the other way (ie to determine the density of the foil) the error would be of the same order.

I once worked as an analyst in the laboratory of a non-ferrous metal foundry. XRF was used as a quick and easy method to ensure the alloys were within spec but could be trusted to only ~ +/- 0.1 %. I'm sure things have moved on but I'd be be surprised if a scrap merchant's gun would be able to achieve even that! And on a tiny piece of wire? I reckon you have to trust the seller and see how it works out for your project.

Robin.

Thanks for replies. I'm confident about tailstock alignment. I think the method is wrong - the tailstock / chuck / slot drill assembly just isn't rigid enough to prevent the tail wagging the dog.

NDIY - thanks for the reminder about the knurling trick. I always forget about that! Unfortunately it wont work here because the 6mm shaft has to pass through a bearing during assembly.

I don't have a boring bar small enough, but the 'cheap and nasty' method Malcolm recommends sounds good - I think JasonB suggested essentially the same method as well. I'll give that a go.

Thanks to all for suggestions, Robin.

I fouled up (yet again) today. I wanted to make a 5.5 mm deep 6mm diameter blind hole in the centre of a 17mm diameter by 7.5mm thick brass disc to accept a 6mm axle. Plan was to glue the axle in place with retainer.

I put the disc in the lathe and had at it with a 6mm slot drill held in the tailstock chuck. In retrospect a disaster in the making. The hole turned out true to centre, flat bottomed, but about 6.7mm in diameter. I'm going to have to try again - any advice would be welcome.

Robin.

Thanks - my Google-fu is indeed failing it seems. If only they called them Atwater calories I'd have got there! I did know about the factor of 1000 between nutritional and 'physics' calories though. Anyhow, you have answered my question.

The question arose from idle pondering rather than any personal dietary concerns, but reading other responses I do wonder how useful these measures are. I suppose it's just a matter of averages and perhaps extremes. Personally my weight has been pretty stable over the last 50 years without any need to diet or feed up - I just eat what I want when I want. Doesn't work for everyone obviously - metabolism is complicated!

Robin.

It's perhaps a daft question but it's been bugging me and I haven't so far found an answer.

If you wanted to measure the 'calorific value' of, say, a portion of bacon you'd bung it in a bomb calorimeter, fill it with compressed oxygen and measure the energy released by complete combustion.

Would that be the same as the 'calories per portion' listed on the packet? Obviously what we excrete can be burned and release more energy. Do the numbers on the packets refer to total energy (referred to the baseline of completely oxidised bacon) or to energy released by metabolism? Someone must know!

Robin

Thanks for you reply Michael. The clone lenses are, according to the seller's description, 'prismatic' as are the Donegan lenses. I was surprised that it was easier to focus using them in the Donegan headset than in the clone headset which places the lenses about 2cm further from the eyes. I can understand that if the 'wedginess' is less well done than with the Donegans there might be an advantage in placing the lenses further away because you wouldn't have to go boss-eyed as much to focus - but why do they work better in the Donegan headset? Maybe it's my old eyes, which are hardly reliable test instruments.

Can you suggest any way of making simple objective measurements which would distinguish between the characteristics of the lenses? I have a laser pointer and a makeshift optical bench...

Robin.

To pick this up again I bought the Donegan with the #5 (x2.5) lens plate and it is certainly a leap up from the cheapos I've had in the past - optical quality rather than comfort of wearing, which doesn't concern me too much. When I decided that would like an additional lens plate or two (~£45 each) I thought it was worth buying a clone (£20 inc. 4 lens plates) from Amazon just for the lenses - I could always send back if no good. I went for this.

Comparing the 2.5x clone lenses with the Donegans in the Donegan headset I could detect little difference - perhaps a tad longer for my eyes to adapt to form an image uninterrupted by a central bar with the clone lenses. Using the clone headset I couldn't form an uninterrupted image with either the Donegan or clone lens plates. The clone lenses all performed well in the Donegan headset but less well in the clone headset. The difference between the headsets:

The (genuine) Optivisor positions the lens plate about 2cm closer to the eyes than the clone. That seems to be the only material difference.

Upshot is that I shall be keeping the clone set if only for the lenses and it seems straightforward to modify the clone headset. I don't understand why, given that the the magnifier is an obvious copy of the original Optivisor, they have deviated in this detail.

Robin.

Edited By Robin Graham on 08/07/2023 23:21:24

Thanks to all for all responses. To flesh out my original post a bit my last NHS review was in 2021, back in the days of facemasks and general reluctance to stress the NHS. I saw a Scrivens 'audiologist' (outsourced) and to be brutally honest he seemed a bit dim. He equipped me new aids (the new thin tube/dome things) but was unable to explain why these might be preferable (or even equivalent) to the wide tube/earmould system I'd been using. They seemed OK at the time (Ie in the room with him), but were subjectively much worse than the old ones in real life. When I went back for a follow-up consultation he said that maybe I needed different hearing aids, but as they could only supply once per three years I'd have to wait or go back to my GP for a referral and start from square one. Gosh! so I went back to my previous ones, all well until on a routine clean when I mistook the acetone bottle for iso-propanol. One melted. Still nine months until I can go back to the NHS, hence the exploration of private provision. In the meantime, I seem to have lost the Scrivens aids. To be brutally honest I can be a bit dim.

Anyhow, your replies have been very helpful. I can pay (~£250) for replacement NHS aids which will likely be as good as the private offerings.

Robin.