Member postings for Robin Graham

I have broken the glass on my ancient Coalbrookdale workshop stove. I've sourced replacement glass, but when I removed the four screws which fix the glass-retaining plate to the door:

one (there's always one!) sheared:

The 'screws' (bolts?) are 3/16 x 1/2 inch 32tpi fully threaded hex head, so BSF presumably. Two questions:

• Can anyone recommend a supplier for replacement screws? Searches so far have draw a blank.
• Any suggestions about dealing with the the sheared screw? It's pretty well corroded in place. The door comes off easily so could be mounted on a pillar drill.

Robin

This is an old thread, but I've not needed to mill anything for a while and have only recently been forced to readdress the issue.

After much poking about I eventually discovered that some swarf had somehow found its way into the motor/spindle top housing. It seems that the tachometer disc (mounted on the top of the spindle) was picking up small pieces and flinging them at the unprotected tachometer pickup interface board. I actually saw a flash from the board coincident with the RCD tripping, which was what put me onto it.

A good clean up seems to have fixed things. It was that simple!

Robin.

A set of expanding mandrels would be good for something I'm doing, and looking at Arc Euro's paper catalogue #10 I thought I'd found the ideal things:

However, it seems that Arc no longer do them, and I've drawn a blank looking for the same things from the 'usual suspects'.

Anyone know of a supplier?

Robin.

Well it was one of my better buys perhaps - like many small towns I suppose my own is seeing a decline in traditional high street shops and the emergence of short-lived 'antique' shops. The owner of the the one I bought it from had no idea what it was, and because there was no obvious upcycling potential (you can't make a retro industrial chic table lamp from an extensometer) let it go cheap.

I did see the other Science Museum example, but thanks for the link. I didn't pick up on the dubious Mercer claim.

My own example is Baty for sure:

My guess, based on the faux leather and the Dymo label is that it is 1960's -70's.

Jacques - thanks for your input. I would be interested to see your designs but it seems that back issues of EIM don't go further than September 2016 on the Pocketmags site. Is the magazine archived elsewhere?

Robin.

Edited By Robin Graham on 28/09/2022 00:31:31

Ah, cripes, I've just noticed that my one has a part that the Science Museum one doesn't - a sort of a cone on a spring which when pressed in 'zero's' the gauge. So maybe that's what the indicated part on the Science Museum one does, but I'd be interested to know which was the earlier development.

Robin.

Edited By Robin Graham on 27/09/2022 02:40:15

Edited By Robin Graham on 27/09/2022 02:49:18

Yes, the frequency is inversely proportional to the free length, but it turns out (if - and it's getting to be a bigger and bigger if as I get older!) my calculation is right the the stress/fundamental frequency relationship is independent of the width and thickness of the blade. I get:

sigma = 4 x L^2 x f^2 x rho

where sigma is the stress, L the free length, f the frequency and rho the density of the blade material.

Good point - the result above was based on the Mersenne's law, though I didn't know the name for it. My gut feeling is that the zero tension beam strength of a bandsaw blade is negligible compared to the tensioned strength, but I shall investigate that when next I have a sleepless night and a coincident fit of brightness. Don't hold your breath! I shan't.

After starting this thread I remembered that I had splashed out a fiver or so on something called a Lindley extensometer at a junk shop some years ago. It looked interesting, but has since been gathering dust:

I think that this is functionally equivalent to the device in Gary's article, so I should be able to make measurements myself. However, having a look around I see that the Science Museum has something similar but with an extra part:

Can anyone suggest what that part does? There is no indication of anything missing (eg redundant threaded hole in the casting) in my example.

Robin

PS the second image was downloaded from the Science Museum and has been altered to the extent of adding a red arrow to indicate a particular part.

R.

Edited By Robin Graham on 27/09/2022 02:26:35

I was interested in Gary Wooding's article 'A Bandsaw Blade Tension Meter' in MEW 319, detailing the construction of a device for measuring strain (or 'tension' ) in a bandsaw blade. This is a topic which frequently comes up in woodworking forums because blade tension is one of the many variables involved in the black art of setting up a woodworking saw to cut true.

One of the standard recommendations is to set the tension so that 'twanging' the free part of the blade gives a musical note - but no one gives the frequency!

I set my own woodworking bandsaw 'tension' by intuition, and it works OK, but after reading Gary's article I was moved to make a measurement. A carbon steel blade set at my normal tension has a dominant resonance at about 180Hz over a free length of ~750mm. That translates to a stress of 144MPa or ~ 20,900 psi - towards the top of the range 14500-21750 psi Gary gives for CS blades, but it fits with my intuition that ' if I tighten it any harder something might break'.

I'm actually surprised that my crude measurements have led to a plausible result, and it makes me wonder if the 'twanging' method of setting tension might be set on a firmer footing given that tuning apps are readily available for smartphones. If Gary (or anyone else who can measure strain) can correlate measurements with frequency it might be a good way for people without a shed load of tools or money to set up their saws.

Nice work btw Gary - I may have to make one!

Robin.

Edited By Robin Graham on 25/09/2022 02:17:08

Edited By Robin Graham on 25/09/2022 02:18:14

Edited By Robin Graham on 25/09/2022 02:24:54

Well, I should have listened to/ acted on advice given above - the £39.73 was for 0.4 hrs labour + parts to replace two fuses. Think I could have managed that myself .

They still haven't done the blower - now awaiting a quote for that, but apparently it can be accessed by removing the glove box. So I'll have a go at doing that myself - seems simple enough (in principle!).

Thanks again for discussion, Robin.

Thanks for your suggestions John Doe 2. Sound advice I'm sure, but I don't have anywhere to work on the car any anyway even 'simple' instructions such as 'remove the instrument cluster' baffle me.

Saga so far - the car went back to the garage this morning and they rang this evening to say it was all fixed at a cost (according to my wife who took the call) of £39.73. I can't believe that - I think she must have misheard - but we'll see tomorrow when we pick the car up.

Robin.

Link not live for me - for a horrible moment I thought that you had succumbed to the lure of some ghastly plastic imitation (Salter aren't what they were) but a moment with Grace's guide reassured me. I have the No 1 and have never had any problem with fatigue grinding enough for a cafetière. About 30g for a 350ml cafetière in my case, but I like it strong!

Robin

Edit - posted before your ref to Grace's appeared! R,

Edited By Robin Graham on 20/09/2022 23:08:32

Thanks Nick - that does help. It looks like my suspicions of skullduggery on the part of the garage were unfounded.

It's going back there tomorrow - arm and a leg I fear, but probably cheaper than buying an new old car.

If the Director of the People's Bank of China comes through though, I don't need to worry. He's sent me a charming letter saying that Hubert Graham (no doubt an uncle I'd forgotten about) had a fatal accident whilst in China and, as I'm the only living relative, he would like to transfer Hubert's assets (amounting to 1 million USD) to my bank account if I will give him full details. Bit of luck eh? I'll be able to buy a Tesla.

Robin.

Edited By Robin Graham on 20/09/2022 01:28:44

The Spong machine (whilst not compact perhaps) does have lugs which allow it to be attached to the wall, if you have space.

I think they can still be had on eBay &c at reasonable prices. Mine, although ancient, certainly produces a finer and more consistent grind than I've been able to achieve with spinning blade coffee grinders.

For grinding spices (because I don't want to pollute the Spong) I have have the blade grinder attachment for my Bamix stick blender. For an extra £15 (!) you can buy the 'powder disc' which is just a piece of plastic which sits above the blades:

I was sceptical but it does work - even tough stuff like coriander seed is reduced to a powder rather than just bouncing off the blades, So maybe that's an engineering answer to improving the performance of blade grinders - constrain the 'free volume' in which the seeds/beans have to move about. I suppose that's why burr grinders work better - they can't escape.

Robin.

Thanks for further discussion.

In the light of what's been said I have to retreat somewhat from my original position which was that they had obviously mucked something up and were hoping to charge me for their mistakes. It's an aged car for sure, and it's quite possible that it has what the doctors call multiple morbidities. I've always bought cars second hand and run them into the ground - invariably they have gone along fine, then the trickle of faults becomes a cataract and they go to the knacker's yard when maintaining becomes more costly than replacing. Maybe that's where I am with this one. It's been so good that I suppose some part of me hoped it would outlive me!

I'll ask the boss to explain when he gets back - he's a reasonable chap.

MichaelG - thanks for the link to the DVSA complaints procedure. I wonder how many people complain that they have been given a pass when the car should have failed! About the same as the number of A level students who write indignantly to OFSTED complaining that they have been awarded an A* I suspect.

Robin.

Edited By Robin Graham on 16/09/2022 00:31:19

Edited By Robin Graham on 16/09/2022 00:56:15

Thanks for further replies.

Raymond - thanks for further info about your Celestron. That model (suffixed with -C) is still available, albeit at ~£70, which is probably reasonable compared to the £47 you paid in 2012 given that the cost of tools imported from the Far East seems to be rising more rapidly than the general rate of inflation.

Robert G8RPI - thanks for your comment re the Amscope offering.

A couple more questions though. First is that the Celestron has a 2 megapixel camera, the Amscope 0.3 megapixels. What difference would that make, assuming (hypothetically) that the optics are the same?

Second is that the Amscope description says explicitly that device adheres to the UVC standard, so should be usable with my Linux machines, but the Celestron says that only Windows and Mac OS operating systems are supported. It may be that Celestron are referring only to ancillary image processing software supplied with the device - I don't need that, provided I can capture an image in a format the GIMP recognises. Is it just that everything is UVC these days, so no need to mention it?

The third (in my 'baker's couple'  of questions is about ndiy's explanation of the quoted magnification being the square of the 'actual' magnification. Is that just because they are talking about area magnification rather than linear, or is there some more subtle optical thing going on?

Thanks for your patience in answering my naive questions,

Robin.

Edited to get rid of an unintended 'wink'.

Edited By Robin Graham on 15/09/2022 23:39:57

Thanks for replies, which have all been helpful. I'm now thinking that I should probably just get a cheap USB device as a way of dipping my toe into what is evidently deep water.

Raymond - thanks for the pics. Can you tell me which model of Celestron camera you used? They seem to have quite a range.

Michael - thanks for the link to the Micrographia illustrations. I have ordered a pack of greeting cards - if the recipients don't like them, well that's their problem.

Robin.

Thanks for replies which, on balance, seem to support my suspicion that they mucked something up and aren't giving me the full story. The garage (the only 'serious' garage in my small town) has served me well over the last 20 years or so, but when I asked the receptionist when they could look at it again she said they had only two mechanics working due to hols &c so the best she could offer was 10 days hence. I suspect that these two guys have been under some pressure to get jobs done quickly and I didn't recognise either - quite youthful so not long-timers.

I'll just bite the bullet and pay up to get it fixed I suppose. With luck the boss (who is a reasonable chap) will be back by then. Could threaten to tell the tale on local Facebook, but I don't like confrontation (or social media).

The car is a 2010 Vauxhall Astra which I bought in 2013. It's basic but has been extremely reliable - apart from tyres, wiper blades, brake pads and the odd bulb or two it has sailed through MOT's hitherto. Maybe it's getting to the age when it should be replaced though.

Dave (SoD) - if you have managed to keep a BX alive for this long I can only gasp in wonder. I had three (in succession, not at the same time!) and loved them but was defeated by the cost of keeping the microbore hydraulics going. Went on to C5s, again lovely but ruinously expensive to run/maintain. Hence the Astra after I retired - basic but cheap to run.

Robin.

Edited By Robin Graham on 14/09/2022 23:00:16

Thanks Michael - not yet read, but encouraged by the title of the article because when trying to think about it all I realised that I didn't know what magnification meant and began to think that resolution was a much more useful concept. So I might be on the right track!

Robin.

Wife took our car in for an MOT last Thursday and also asked them to fix failed heater blower motor. They called back to say the car needed two new tyres, but they wanted to keep it in overnight awaiting parts. They also said that the ABS warning light was coming on intermittently.

Picked it up on the Friday, two new tyres, MOT pass with advisory 'Intermittent ABS fault'.

Problem is that when I took it out on Saturday the speedometer and the computer screen were dead. And the ABS warning light was on constantly.

Went back on Monday, lass on reception 'had a word' with the chap who had done the MOT and he said that the speedo/computer failure was because of the ABS fault. I scratched my head and went away. But surely:

• If ABS was faulty when the car was taken in, why were the speedo and computer still working - which they certainly were- if the explanation is correct?
• If the explanation is correct the ABS fault must have developed while they had the car.

Well, we've got the car back with a valid MOT despite it having two major fails - non-functioning speedo and malfunctioning ABS which weren't there when wife took it in.

I don't know anything about car mechanics - does this make sense to anyone who understands these things?

Robin.

I know next to nothing about microscopes or cameras etc, so I'm in that confused state of not even knowing what questions to ask, still less how to frame them.

So I'll start with what I would like to do and why, then go on to research so far.

On another (woodworking) forum I saw some pics of plane irons sharpened by different methods which he had taken with one of those cheap ($19 in his case) USB 'microscopes'. I thought I would like to do something similar as I sometimes make knives and my sharpening process is a bit hit-and-miss. I also wondered if having something like that might help with diagnosis of polishing problems - I do a lot of polishing.

I had a look on Amazon and there are many offerings. Most advertise 'magnifications' up to 1000x, which seems crazy to me for a device like this. On eBay there are claims of 1600x, which seems even madder. Amazon reviews are patchy - some, who seem to know what they're talking about, say that these things are no better than a 10x loupe.

I looked at an offering from AmScope which claims 10x - 200x and even gives the sensor size - 0.3Mpx - so they're perhaps being more realistic and honest. Only £35, so maybe worth a punt.

Further research makes me wonder if these things are more akin to macro cameras than microscopes, but I don't really know what I'm talking about.

I'd be OK going up to maybe £200 for a trad microscope, and worry about getting an eyepiece camera later. Would that be better for what I want to do? Can it be done on that sort of budget?

Apologies for nebulous nature of this question, but I have to start somewhere!

Robin.

Edited By Robin Graham on 13/09/2022 23:05:06

Thanks for clarification Dave - now you say it I see the perspective in the images to which I had been strangely blind.

Robin.