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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: Look out, here comes a woodturner
05/01/2021 02:43:16

Hi Calum. As you are interested in wood , metal, reeds and leather as well I wonder if you are after making bagpipes? If so, I'd say not to worry too much about the leatherwork at first - assuming you have a workable bag, concentrate on getting the pipes/reeds right.

The guy I bought my first set of Uilleann pipes from (Brian Howard of Sheffield) did almost all of his turning on a metalworking lathe - he reckoned that that woodworking lathes weren't accurate enough. It was at least as big as a GH1230 - you need the space to get the reamer in.

Reedmaking is a bit of a black art - weirdly, I seem to be able to make (dry) chanter reeds OK, but struggle with the drones which are supposed to be easier.

Good luck!

Robin.

Thread: Gloves and machine tools - my stupidity.
01/01/2021 01:35:29

I've been doing a lot of brass polishing lately. If ever you've tried to get a really shiny scratch-free surface on brass you'll know that it's necessary to be almost obsessively hygienic, even to the point of washing hands between grits. Otherwise you get up to 1200 say, then a speck of 240 which has been lurking beneath a fingernail drops down and makes a scratch which looks like a canyon. It's dispiriting when that happens. So I bought some cotton gloves. Worked well for hand polishing and I still had one on my hand when went to the lathe to polish some 3/16" rod,. I know that you're not meant to wear gloves when machining, but what could go wrong, hand well away from the chuck and I know what I'm doing - not.

mangledglove.jpg

Luckily the glove pulled off my hand. It all happened so quickly! Put the wind up me proper. That could have been my hand with stouter stock.

Don't wear gloves when machining folks!

Robin

Thread: Motor for a gyroscope.
01/01/2021 00:33:04

Thanks for further replies.

MichaelG - somehow I missed your 3rd contribution, and hadn't looked at your link. Mea culpa! I have now had a look - useful info, thanks for that.

Roger - thanks for sharing your your gyro making experiences.The one I want to make is for demonstration purposes - specifically as a teaching aid in talking about angular momentum. I confess that I hadn't given much thought to the profile of the disc, assuming that the greater the moment of inertia about Z (the spinning axis), the better. I now see that it is a bit more complicated than that if the aim is for the gyro to 'stand up'. My plan is to make the disc from 3" dia x 1 inch brass (expensive, but I have a lump in the cutoff bin) with an aluminium frame.

My thanks to other contributors also - the info about air-driven devices etc isn't really germane to my original question, but is very interesting.

Robin.

31/12/2020 00:17:50

Thanks for replies. To clarify, I was looking for for something to spin the gyroscope up rather than for continuous operation. The product I linked to claims a run time of up to 25 minutes starting at 12,000 rpm. I doubt that I can match their machining standards (they say that their discs are ' balanced to an impressive 250th of a gram accuracy', whatever that means) but I'd be happy with 5-10 minutes. To get up to 12,000 rpm with the 5mm shaft I'm planning by using a piece of string would mean (thanks to a fortuitous cancellation of numerical factors!) pulling the string with a final speed of precisely pi metres per second, which would be hard to do I think.

I can test it with a Dremel type tool for sure, but the person who asked me to make it is unlikely to have such a thing. The motor SoD linked to looks like the sort of thing I want - 12,000 rpm @ 6V/1.9A. That would be four AA's in series - but would I get 1.9A from that arrangement? A quick look suggests that the internal resistance of an alkaline AA is about 0.15 ohms, so in theory they should deliver 10A shorted. Really? That surprises me.

John - thanks for your suggestion of an outrunner motor. I'd never heard of such a thing, but have had a look and they seem to offer possibilities. I'll think on't!

Robin.

 

 

 

 

 

 

 

 

 

 

 

 

Edited By Robin Graham on 31/12/2020 00:18:59

28/12/2020 23:33:08

I have been asked to make a gyroscope, better than the 'toy' ones (but perhaps not to aerospace specs!)

I think I can do the machining OK, but I'm wondering about how to spin it up.

I came across a commercial site which offers gyroscopes stared by a motor which is powered by 4xAA batteries and achieves 12,000 rpm, but they don't seem to sell the motor alone, and I've drawn a blank in searching for something similar - probably because I don't know what I'm asking for.

Can anyone help?

Robin.

Thread: Etching brass
19/12/2020 22:41:18

Thanks for replies. Tony Moss's video which David gave a link to is very informative, and has been bookmarked for further ref. At the moment though I don't want to go to such lengths just to put my mark on the job. It seems like getting a photocopy or finding someone with a laser printer might be the way way to go.

In the distant days of my youth I tried etching brass by coating the metal with paraffin wax, scraping out my design and immersing in nitric acid, which was freely available at the time. The results were disappointing - very ragged around the edges. I gave up and moved on - probably to making a firework or something. I was only twelve, too many interesting things to investigate! I may revisit this approach in the light of stuff I've since learned.

Thanks again for leads, Robin.

17/12/2020 21:42:02

I would like to put a 'maker's mark' on a project in brass. I haven't got engraving equipment or skills, so I'm thinking about etching.

I've had a look around on t'internet and the tutorials I've seen start with the assumption that the tutee has a laser printer. It seems that laser toner can be transferred to the the work to make the mask. But I haven't got a laser printer - just an inkjet.

Another possibility would be using photo resist, but I'm having a hard time trying to understand what equipment I would need to do this. There are suppliers of photoresist film on eBay, but they don't give info on how to expose/develop (or even if it's positive or negative), so I'm a bit in the dark. Does one need a UV lamp? If so, what sort? Could I get away with burning a few welding sticks? They put out a fair bit of 300-400nm radiation.

If anyone could cast light (of any wavelength!) I'd be grateful.

Robin.

Thread: M42 bandsaw blades
25/11/2020 22:29:17

As Peter says M42 is a molybdenum/ cobalt HSS. M42 bandsaw blades are invariably bimetallic - the M42 is welded to a flexible backing material, then the teeth milled. There is a short video of the process here

I don't think a solid M42 blade would be flexible enough to run on a bandsaw!

Carbide tipped blades cannot (legally!) be classified as M42 - carbide is a different material entirely.

For what it's worth I use M42 blades (from Tuffsaws - no connection etc.) and they really do pay for themselves over time.

Robin

Thread: Mechanical properties of soft solders.
16/10/2020 23:44:25

Thanks for replies.

On the specs front, I am quite pleased with my repair:

specrepair.jpg

as was my optician. He hadn't noticed it when he measured the optical properties of the lenses - he obviously needs better glasses! I suppose I could put a bar across the top, aviator style - seems a bit 70's, but it perhaps the style will come back, as styles do. And I'll be a trend setter.

It turns out that frames of this type are silver soldered, so had I gone along that route for the repair the specs might have fallen apart completely. I wonder what Roy's frames were made from? Aluminium?

Returning to my main question, I made a test join using the Sn/Ag/Cu alloy:

softsoldertest.jpg

You can see the solder line, which would probably be invisible with Ag/Cu, but it's livable with. That's a 3/16" (4.76mm) 'tenon' in a 5mm 'mortice'. So about 0.12mm gap. Maybe it should be tighter. Anyhow, after destructive testing I'm now sure the joins will hold up. I still don't know what the silver does though!

Keith - what book? I'd be interested. If forum rules don't allow you to promote your work here, please PM me.

Robin.

 

 

 

 

Edited By Robin Graham on 17/10/2020 00:05:38

15/10/2020 23:53:33

For reasons too tedious to go into I am trying to keep a pair of wire-framed specs functional for another month or so by soft soldering the fragile join between the bridge and the lens frame. Initially I used standard 60/40, which didn't work well - about 4 days MTBF. Then I found a reel of lead-free (95.5 Sn, 4.0 Ag, 0.5 Cu) in my soldering drawer, tried with that, and it's held up a treat.

It set me wondering if I could use the stuff for a project involving multiple 'mortice and tenon' joints in a pendulum system I'm making in brass. I had been planning to silver solder, but soft soldering would make the whole thing so much easier. Preliminary experiments make me think that the lead free stuff will be more than adequate - perhaps even 60/40 leaded would be OK. But it set me thinking.

I've tried, but failed, to find to find data on the mechanical strength (specifically shear modulus, which is what mainly concerns me) of soft solders. I have found vague statements suggesting that 'the more tin there is the stronger it is' then 'the silver is added to increase the strength'. Hmm. What does that mean? Is a 99.5 Sn/ 0.5 Cu 'stronger' than the one with the silver?

Most of the information I've found about the properties of these alloys is focused on the mass production of electronic components, where mechanical strength isn't a major consideration.

Any light that can be shed into this fog would be most welcome!

Robin

 

Edited By Robin Graham on 15/10/2020 23:57:06

Thread: Fluxes for silver soldering.
09/10/2020 23:11:14

Thanks. From what has been said it seems the only real downside to using T5 for everything is the difficulty of cleaning up afterwards. I have been using a caustic soda solution, which seems to do the job. So I shall stick with it.

Like Brian I use alcohol rather than water for mixing the flux, then let it flame off before applying serious heat.

Robin.

Edited By Robin Graham on 09/10/2020 23:12:03

08/10/2020 23:14:57

I've been using Tenacity 5 with SF55 to join both steel/steel and brass/brass joints. It seems to work, and I like it because when it it melts and flows I know that the parts are close to temperature.

However, planning an emergency dash to my local ME supplier tomorrow for supplies of SF55 I looked at their catalogue and noticed they they list Easy-Flo flux as suitable for SF55, Tenacity 4A without any qualification, and Tenacity 5 for joining stainless steel.

Question is - apart from the slightly higher cost of T5, is there a downside to using the stuff as 'one flux fits all' with SF55?

Robin.

Thread: Ball bearings and friction.
07/10/2020 10:44:15

Thanks for further comments which have been read and are in the process of digestion. All the bearings in my bearings drawer (marked 'bearings' confusingly - it doesn't usually work as literally as that) are of the double metal shielded type with (AFAIK) steel cages. I'll unpick one and investigate further. I can certainly do away with at least one shield and wash out as Ketan suggested.

Following Neil's suggestion of ceramic bearings I had a look around and came across this video on YouTube

The guy is concerned mainly with frictional losses in bicycle wheel bearings, but it's in the same area. His conclusion seems to be that ceramic bearings aren't all they're cracked up to be, for bikes at least.

I think the main thing I have taken from this discussion is that there isn't an easy answer and I need to experiment to see what works best for my application. Which I can now do with a better sense of direction than I had before raising the issue - thanks.

The videos showing 'Swinging Sticks(R)' linked to in Vic's reply are interesting from both mechanical and psychological perspectives. The tabletop devices there run very slowly compared to my version - they are described as 'creating the illusion of perpetual motion'. Well, maybe. I guess that illusion arises because the mind focuses on the motion of the main beam and can't immediately grasp the way energy is being transferred to-and- fro between the two pendulums.

I first made one of these devices as an illustration in the course of of a discussion about the solution of differential equations which I had with an unusually able A-level student. That was a while ago- I don't know where it took him, but it left me with with an abiding interest in the chaotic evolution of systems governed by simple laws . Which might 'explain' many things. But I risk verging on the political, so shall cease and desist.

Robin

 

Edited By Robin Graham on 07/10/2020 10:45:36

Edited By Robin Graham on 07/10/2020 10:47:23

05/10/2020 23:34:38

JohnH/NielL - thanks for your contributions.

John - Swensen's article was very interesting. He has answered my principal question I think, as well as some subsidiary questions about bearing lubrication which were lurking in the back of my mind. I had made some experiments and found that, irrespective of size, my bearings ran for longer after lubrication by light oil (sewing machine oil was the thinnest I had to hand) than they did dry. This appears contrary to accepted wisdom. Further work (by me) is needed!

Neil - thanks for the report of your experiments. While 'unscientific', your results are clearly significant. A 50% increase in spinning time is impressive. I have 1um polish and would like to try this, but I can't see how to take a deep groove bearing apart and reassemble it without damaging something. Can you tell me how you did that?

Robin.

03/10/2020 02:06:22

Thanks for replies.I'm not sure if my question has been answered though, probably because I didn't frame it clearly enough. My bad. After further thought I'm pretty sure that all other things being equal a large diameter bearing will dissipate more energy through friction than a smaller one. That's assuming that bearings can be characterised by a single (velocity independent) coefficient of friction, as with sliding surfaces - which surprised me at first, but I think I now understand.

MichaelG - thanks for the links. It may take me a while to get my head around that stuff . The Unipivot designers claim that their arrangement is 'extremely damped' which may not be what I want.

This is a rough sketch of what I'm proposing:

doublependulum.jpg

Yeah, I'm no good at technical drawing, it's just an aide-mémoire . The whole thing pivots about the central disc, and the secondary pendulum about the disc on the right arm. Something I have found when making prototypes is that the bearings need to be 'tight' in the sense of keeping all the moving parts coplanar. Any wobble and parasitic vibrations set in which sap the energy surprisingly quickly. I guess there is a trade-off between that and friction. I imagine people making Stirling engines must face the same sort of challenge.

Robin.

 

 

 

 

Edited By Robin Graham on 03/10/2020 02:07:02

Edited By Robin Graham on 03/10/2020 02:16:06

02/10/2020 00:25:02

Some time ago I made a double, or chaotic, pendulum for my own satisfaction. My wife showed a video of the thing to a friend of hers, and now I'm instructed to make another one.

I didn't worry myself too much about the bearings first time round- the device ran for about 30 seconds from an initial shove, which was long enough to display chaotic behaviour. But I'd like to make the MKII run longer if I can.

So to my question - how do the sizes of the bearings affect frictional loss? I had a look round and found, to my surprise, that bearing types are characterised by a single scalar  coefficient of friction - about 0.01 for deep groove rollers. If I take as true that bearings behave like that , the frictional loss should scale with the diameter of of the bearing - the frictional torque should be the load times the coefficient of friction times the distance of the race from the centre of the torque? And the energy loss (torque times angular velocity) should be directly proportional to that? If so I guess I should be going for infinitesimally small bearings. Or take up knitting - knit one, purl one must be easier than this!

Robin

 

Edited By Robin Graham on 02/10/2020 00:37:32

Edited By Robin Graham on 02/10/2020 01:13:37

Thread: Covid causing mental health issues.
26/09/2020 21:39:03
Posted by Trevor Crossman 1 on 26/09/2020 19:12:55:

...

From what I read and hear many of these are suffering and are quite likely to continue to do so long after our well heeled rulers have allowed people to return to normal human existence.

...

Trevor

Trevor, I agree with a lot of what you said, but think it may be worth saying that it's really not our rulers (whatever you think of them and their motives) preventing us from returning to normal existence, it's the blasted virus. The death count in the UK currently stands at at about 40,000 and rising - that's comparable with the number of UK civilians killed in the seven months between Sept 1940 and May 1941 by bombing. But the virus doesn't whistle and bang, so the perception of threat is less immediate. I imagine Londoners in WWII were by and large happy to live with  the inconvenience of the blackout regulations decreed by their well-heeled rulers in order to preserve their lives.

Apologies if I have misconstrued your point - I wish you well.

Robin.

Edited By Robin Graham on 26/09/2020 21:44:46

22/09/2020 22:34:12
Posted by Neil Wyatt on 22/09/2020 19:36:37:

I think the best answer is to say be grateful and count your blessings, and don't be sceptical of the toll 2020 is having on many people.

Neil

+1. What is important at this time is to support each other even when we can't relate directly through shared experience in our 'bubbles' of age, income, politics, culture, mental health or whatever.

Robin.

Edited By Robin Graham on 22/09/2020 22:34:57

Thread: Electrical contact cleaners.
21/09/2020 01:07:28

My wife has managed to dunk her iPhone in the lavatory - a 'back pocket incident' I believe it's called.

I took it apart, dried it out and replaced the battery - it's an old phone (SE) and wanted a new battery anyway. It now boots up OK, but the touch screen is completely unresponsive. I noticed that pins on one of the connectors between the screen and the motherboard looked dirty (on the female motherboard side). That might (or might not) be the problem. I tried cleaning with a cotton bud and isopropanol, but it didn't make any difference - the contacts didn't come up shiny.

I'm wondering about about contact cleaner sprays, some of which claim to deal with corrosion, but I have never used these preparations - can anyone advise?

Obviously I realise that it might be a lost cause, but I'm not giving up without a fight. Certainly not going to pay Apple 276.44 to fix it.

Robin.

Thread: Reminiscences
19/09/2020 23:22:51

I'm a spring chicken (b. 1956) compared with some on here, but remember well the discovery of a chemist's shop - JN Hogg on the Parade in Birmingham - at age 12. My passion at the time was Chemistry, and you could buy pretty much anything from the amiable Mr Hogg. Fuming nitric and sulphuric acids, phosphorus red and white, ether, chloroform, thionyl chloride, carbon disulphide - no problem for a 12 year old to procure. I even bought half a kilo of picric acid for a purpose I don't recall, but nothing to do with explosions! Things have certainly changed in that respect over the last 50 years.

Another striking change is the way children get to school. At age eight I was bunged on a Corporation bus (as they were then called) to make the two mile journey, and told to get on with it. Maybe I was somewhat deaf even at that age because I listened to what other children said when they proffered their fare, and when my turn came asked for a "penny-ha'penny Charles". When you're eight everything's a bit weird - it could have been! "Child's" I eventually realised. On the back of the ticket was some text urging me to buy a Sumlock Comptometer. Ever a sucker for advertising hype I wanted one but my parents wouldn't oblige.I'm still suffering from that.

I would walk back home rain, hail or snow to save the penny ha'penny for sweets. I don't think that happens nowadays - I would certainly worry if I had an eight year old who might take anything up to 2 hours to tramp home. I don't know if the world's a more dangerous place now, or if it's to do with the perception of risk.

I should say that I was by no means a 'latchkey kid' - it was just a different world.

Robin

 

Edited By Robin Graham on 19/09/2020 23:23:28

Edited By Robin Graham on 19/09/2020 23:30:47

Edited By Robin Graham on 19/09/2020 23:32:53

Edited By Robin Graham on 19/09/2020 23:34:01

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