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Member postings for SillyOldDuffer

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

Thread: Myford S7 Cutting Barrel Shaped Cylinders
03/06/2020 10:10:53

Posted by Mike Donnerstag on 02/06/2020 18:23:29:

...

Anyway, after many days of investigation and frustration I have given in! ...

Mike

At this stage it's sensible to make an orderly retreat for a think rather than surrender. You've done well so far in a difficult situation, but have been bombarded with information, some of it contradictory. Frustration may be getting in the way. Take a break and let your mind assimilate what you've got quietly. I often find sleeping on a problem is enough, but it sometimes takes a lot longer.

Be good if someone else could look at the lathe with you. (Any Myford savvy locals available?) At work I used to run Fagan Inspections of new software, where the programmer starts by explaining the logic of his program to a group. Amazing how often chaps and ladies spot problems in their code when asked to explain it to someone else. It works with machines too.

From what I'm reading the most likely answer is wear. It explains the barrel effect, why measuring is proving difficult.

I expect milling the lathe would improve it but it's not good compared with a suitable grinding machine. If wear needs fixing, I'd bite the bullet and do it properly. Chinese machines are so much easier - replace! But a Myford with useful life in it is worth restoring.

Dave

Thread: The story behind my forum image
03/06/2020 09:39:51

The brain is a marvellous thing, and although Tony's example is extreme, I think we've probably all experienced it mildly. As when I find myself upstairs wondering what I'm looking for, or discover I'm putting the kettle in the fridge, or drove home from work and arrived unable to remember anything of the journey.

Charles and Vintage both mention stressful situations, and that could be a factor in Tony's case too, Public speaking is terrifying!

Perhaps the most common serious example is pilots losing 'situational awareness';. Distracted by an unusual event, aircrew miss or ignore the bleeding obvious and crash foolishly. Flight 173 is an example, there are others!

Military men train to reduce the effect. Combat is conducted within an Observe, Orient, Decide, Act loop, and defeat follows if the loop breaks at any point. Breaking the oppositions loop is one of the objectives considered in military planning.

Stressed decision making is often bad decision making, and loss of situational awareness is a major cause of Human Error. Despite everyone on this forum being clever, who's never done something stupid due to a temporary confusion.

We mostly recover quickly from these events, laugh and move on. No joke if the effect is long lasting - very unpleasant, and stressful in itself.

Extreme fear has unusual effects too. I was in busy motorway traffic on the Almondsbury interchange at 60mph, just passing the M3 South exit, when a roof-rack plus suitcases came off a car three or four in front of me. The vehicles immediately behind weaved frantically - I was about to be in a motorway pile-up. I remember vividly the shower of sparks coming off the roof-rack as it scraped across the tarmac, 3-lanes of cars swerving wildly in all directions, and a caravan to my left tilted with one wheel off the ground at about bonnet level. Everything happened in slow motion, in total silence, and in black and white - briefly, the whole world drained of colour. Amazingly it sorted itself out, but I reckon several cars en-route to Wales and the North found themselves heading South instead due to evasive action! Another curiosity, rather than being upset that my family had nearly been wiped out in a serious accident, I was as high as a kite, full of the joys of spring! Not normal!

Dave

Thread: Myford MF74A
02/06/2020 18:22:44

Do you know what change gears it has?

For what it's worth 8 tpi and 3.5pitch are the coarsest threads available on my Warco WM280.

Provide it's in good condition, the machine looks a sturdy beast, but it's probably Imperial only. Might be possible to find gears and other spares for it but more likely an adapt and make problem.

Some misplaced guesswork on the usually excellent lathes.co.uk about the machine being a joint commercial venture between Jones & Shipman and Myford. More likely it springs from wartime rationalisation of British industry when government intervened to raise production by forcing firms to concentrate on what they were good at. Myford specialised in small general purpose lathes. I think this is a Jones & Shipman design, outsourced to Myford, not a real Myford at all. Nothing wrong with that. Judging by the look of the lathe, it's a pre-war design likely dropped in 1944 because plenty of more modern machines were available by then. Many American machine tools, including automatics, were imported during WW2.

Give it a careful inspection before buying. Lathes made in the UK during WW2 are likely to have been worked hard, maybe thrashed. Shift work and several different operators racing to meet production targets regardless of the lathe. Or it might have ended up in a backwater and still be in excellent condition.

Dave

Thread: Low cost forge blower
02/06/2020 13:58:22
Posted by Nick Clarke 3 on 02/06/2020 13:10:24:

... I think a couple of sparks up the shorts might put me off !

Not been a spark in my shorts since 1997...

sad

Thread: Arduino/Stepper Motor Dividing Head
02/06/2020 13:35:30
Posted by Paul White 3 on 02/06/2020 11:48:29:

Hello all,

Not wishing to be argumentative but- my approach would be to consider the controller as a part of the project.

Other items- stepper, PSU, stepper controller, belts and gears, are by far the greatest part of the project spend thus

the comparative cost of the eelectronics is secondary.

Go for the most complete answer -Joe's all in one solution. I say.

Best wishes,

Paul

I wouldn't argue with that - it's the correct approach.

But cost is more than money. For example, learning how to make a Printed Circuit Board is a painful overhead if you don't have that electronics experience. Likewise, if you know nothing about programming microcontrollers, and struggle with computers generally, finding out how to set up for Arduino is a stiff trial, and Nucleo is another step beyond.

For chaps who already own a Rotary Table and just want to automate it, the Stepper Motor, Motor Driver, Power Supply and Box can all be bought as modules and joined up without needing a deep understanding.

More difficult to install the Arduino IDE, but once done it's straightforward to plug in an Arduino board, and compile and install an existing program to run on it. And because the Arduino has many modules, the hardware side of a project can be kept simple too. Low cost in terms of human effort, allowing users to concentrate on matters important to them rather than learning another skill-set. There's much in favour of simplified electronics and micro-controlling for customers who aren't interested in that side because the learning cost is so high.

For that reason, Joe's offer of expert help is excellent. He can smooth out the entire process. Decoding arcane computer error messages due to simple mistakes is an agonising time-waster when you don't know the ropes. Joe being practised in the black arts might take seconds to solve the problem. I'm happy to help with my version too.

It's easy when you know how. And when someone helps you cheat!

Dave

Thread: Surface Plate & Height Gauge recommendations
02/06/2020 11:51:48
Posted by Neil Lickfold on 02/06/2020 11:11:09:

...

Sometimes you can spend more time getting what you want from inferior gear, and the right gear allows you to have Sunday free to enjoy a nice meal and glass of wine.

If there's enough money left for a nice meal with wine, you haven't spent enough!

A proper Coordinate Measuring Machine is essential, not that old-fashioned Surface Table and Height Gauge rubbish. Golly, it's impossible these days for a Model Engineer to make anything without a Point Cloud.

Not your ordinary Cast-iron and Granite table CMMs mind, they're yesterday's carp. No, decent CMMs are made of Silicon Carbide and Ceramics. Put daughter on the game, sell drugs, mortgage the house and rob a bank. Only the best tools are good enough...

devil

Dave

Thread: Coronavirus
02/06/2020 11:26:13
Posted by Martin Kyte on 01/06/2020 16:47:34:
Posted by SillyOldDuffer on 01/06/2020 16:28:35:
Posted by Martin Kyte on 01/06/2020 15:07:05:

I suspect the root cause in the UK was shortages, particularly ventilators and the staff needed to run them.

Are you making this up as you go along? Can you point me to a documented case where a patient was not put on a ventilator because none were available?

I may as well add that it will probably never be over because obesity is a major risk factor and therefor the Fat Lady may never sing. Quite happy with your post until you got to "Why ?"

regards Martin

This article in the Daily Telegraph lays out the NICE Triage Policy.

I explained in another post the reason the 'why' question has to be answered. Next time it might be one of us who is assessed 'Critical Care Not Considered Appropriate'.

Dave

None of that is based on ventilator availability but what is best for the patient. If you are assessed to be frail and dying with no great expectation of recovery in critical carewhich in Covid19 infections means sedation and ventilation you die without the chance to say goodbye to family albeit by electronic means. It's based on when treatment stops being kind and starts to be invasive.

regards Martin

In normal times one would hope so! But these are not normal times: Metro, Vox Political, Daily Mail. Daily Express Guardian. (A mix of Left and Right opinion, I'm not making a political point.) In the USA, where President Trump has assured the nation there is no shortage of ventilators: BuzzFeedNews.

Telling relatives not being ventilated is kinder isn't a lie. But it's not the whole truth either. It also makes the ventilator and staff available for someone who has a better chance. And some of the people taken off ventilators to say goodbye would have survived. Medical shortages always cause difficult decisions to be made.

Another twist, there have been many Covid deaths in Care Homes, where ventilators aren't available. Who decided these people wouldn't be hospitalised? Was the decision kind or informed by practicalities? Both I expect.

Personally I don't have a moral problem with people being triaged in an emergency. It's a fact of life. But I would prefer triage to be unnecessary if possible. Quite happy if the authorities made reasonable efforts to supply PPE and Ventilators and failed due to shortages. Not happy if it turns out an official gave the contract to an incompetent supplier in exchange for a brown envelope. It happens.

Dave

Edited By SillyOldDuffer on 02/06/2020 11:26:35

02/06/2020 10:40:56
Posted by Steve Skelton 1 on 01/06/2020 19:02:37:

Dave,

I disagree. In the early days tests, in the majority of the UK, were only carried out on hospital admissions and therefore those needing medical care. This was due to the inability of the UK to carry out large numbers of tests at the time – I am aware of people who were not tested, although they asked to be, and are very likely to have had the CV (they holidayed in Austria at the time of the outbreak there and were poorly at home with the expected symptoms) .

Other countries in Europe and Asia were testing far more people who were not hospitalised and therefore who were counted as cases but probably much milder who recovered. We were not doing that to any great extent. So it is not a like for like comparison.

Thus, it is not a reflection on the effectiveness of the UK health service. Other countries who were testing at a far higher rate than we were will then obviously have a much better death/cases ratio.

Steve

Hi Steve,

That's true, but surely ability to test is a major part of Health Service effectiveness?

The NHS depends on having sufficient numbers of trained, well-motivated staff. It also depends on those staff having the tools to do the job. Health Service effectiveness drops if there aren't enough bandages, surgeons, nurses, drugs, beds or cleaners. And effectiveness drops when services are overwhelmed by too many patients arriving at the same time. And that's very likely if sufficient tests weren't available when needed to trace and isolate early patients. As you say: 'I am aware of people who were not tested, although they asked to be, and are very likely to have had the CV (they holidayed in Austria at the time of the outbreak there and were poorly at home with the expected symptoms' Exactly!

If other countries were more effective by testing on a large scale, why didn't the UK do the same?

I'm not criticising the NHS as an organisation or it's staff. Both are wonderful. Both occasionally drop the ball, and both are limited by resource availability.

Almost the worst thing that can be done after an event like this is failing to learn from the experience. Recommended reading: 'Better' by Atul Gawande

Dave

Thread: Arduino/Stepper Motor Dividing Head
02/06/2020 09:48:32

Bazyle makes an important point about user interfaces - they have to suit the user! Unfortunately, in addition to liking the controls, users also worry about cost, and, if its a project, how difficult it is to build. Designing good interfaces is difficult - lots of compromises and judgements.

The Liming's solution is a straightforward Arduino build. Cheap, well supported and plenty of modules. Gary's interface is a plug in display module with a 16x2 LCD and 5 push-buttons. This means his software has to deliver everything needed to control a rotary table with just 5 buttons. It's done with a system of nested menus, where pressing buttons navigates a tree of options until the required setting is found. The problem with this type of interface is it's not very intuitive, it's hard to remember, changing settings takes a relatively long time, and, by accidentally pressing the wrong button it's possible to get lost in the menu.

As John Stevenson mentioned he didn't like nested menus, I developed a rotary controller using a 4x4 keypad and a separate 16x2 LCD only module. The 4x4 keypad provides 16 buttons. Now the user can type in numbers 45.55°, and the keypad is conveniently labelled 'A' for Angle etc. The '*' button is go/stop. Most of the nesting is eliminated, the controls are easier to learn and remember, and it's possible to add more functionality, for example my version can be paused if the phone rings, there's a rewind function in case the most recent command moved the table wrongly, and the ability to type numbers allows the user to change to any table ratio, typically 1:40, 1:60, or 1:90. There's no need to label anything, though a laminated reminder list on the back might be handy. Slightly more difficult to build, about the same price as Gary's version, but the user still has to be slightly computer minded!

Joe's controller is the next step. He fixes the nested menu problem with 5 nice push-buttons, a five way switch, a potentiometer and a logical well-labelled front panel. The build cost is relatively high because of the number of components used, plus there's a need for some chassis banging to make the front-panel. Nothing beyond the skills of the chaps reading this forum.

All three approaches work, but I think most people would find Joe's version most intuitive. It's the most difficult and expensive to build, plus a moderate extra software hurdle to jump to get the Nucleo# working. Mine isn't as easy to use as Joe's, but - being simpler - it's cheaper and more straightforward to build. Gary's is easiest to build but the control interface is clunky. Some people can't get on with nested menus at all - they're just too annoying!

My dad came from a world where levers and buttons only did one simple thing and then you talked to a real person. He thought the computer menus I developed in the 1970s were insane. He had a point...

Dave

# Joe got me into Nucleo.  It's similar to the Arduino but considerably faster, much more memory, and extra pins. It can be programmed from the Arduino IDE by installing optional software, but not all the Arduino libraries work.  (Most do.) 

Another issue is it's 3.3V logic, not 5V, and the interface is electrically more delicate - easier to damage if the wiring is cocked up.  Nothing insurmountable, but a bit more to learn and understand.   I tend to use Arduino Nano's for rough simple work, and the Nucleo for anything remotely demanding.   The Arduino family has some high-end Nucleo-like processors, like the M0-Pro, but I've found the Nucleo easier to exploit, more powerful and it's cheaper.   

 

 

Edited By SillyOldDuffer on 02/06/2020 10:00:48

Thread: Oscilloscope kits - any recommendations?
01/06/2020 20:16:43

Thanks Les, very interesting! I didn't know it was possible to buy a logic analyser for that kind of money. I'm going to order one!

I sympathise with your RaspberryPi shock - that little card has 50 years of software complexity in it! Hours of 'fun' ahead!

Your last paragraph opened up some interesting ideas as soon as I followed the clue. For example, motor vibration caused by 'soft foot' , which is when the motor doesn't sit evenly on it's mounting. Detected by putting a DTI on the motor and slackening eacjh bolt in turn; if the DTI registers more than 1 thou of movement the foot should be shimmed. I'd never have thought of that!

Cheers,

Dave

Thread: Arduino/Stepper Motor Dividing Head
01/06/2020 18:06:41

There's a copy of Gary Liming's code in my dropbox folder here.

Also, for those who don't care for nested menus made necessary by the LCD KeyPad Shield, there's my alternative. It uses a 4x4 matrix keyboard allowing numbers to be typed in directly

dsc04384.jpg

A for Angle, B for Bump (aka Jog), C for Continuous, D for Division, # enter/leave number mode, * start/stop, 0 set direction, 1 rewind, 5 Suspend, 9 set ratio to suit different rotary tables. Number mode allows Ratio, Continual, Division Step, Bump or Angle to be changed.

Blurb here, software here. Intended as to be a magazine article but I decided too many similar had been done already. The blurb is a bit ragged, but a few have been built if you prefer the 4x4 approach to nested menus.

Dave

Thread: Experimental Vibration Analysis of a WM280 Lathe
01/06/2020 17:39:56
Posted by Bazyle on 27/05/2020 23:17:58:

Have you allowed for the vibration of the hard disc and fan in the computer?

I have now! I've switched to a RaspberryPi3B, which is vibration free - no disc or fan!

dsc06263.jpg

The breadboarded device at right is an MPU6050 6-axis Accelerometer and Gyroscope Module. It connects to the Raspberry's GPIO pins. Quite easy to use. There are two outputs,

  • binary frames sent serial at 115200 baud which can be converted to USB with an adaptor or connected directly to the RX pin on an Arduino or Raspberry UART. This data is integrated on the module by a digital motion processor, ie the two sensors are corrected relative to each other by black magic.
  • The module also allows raw sensor data to be read directly over I2C.

The module's DMP continuously sends acceleration, spin rate and attitude data, all in x,y & z dimensions. And temperature. Conceptually the module's accelerometer can detect lathe vibration in three planes, to answer:

  1. Is lathe vibration cause for concern, and in which planes is it vibrating?
  2. At what frequencies is the lathe vibrating?

No problem getting the Arduino to work, but I got into trouble by writing Python3 on the Raspberry to decode the binary stream. After several tantrums and false clues, the answer turned out to be easy. Python's integers aren't directly compatible with signed 16 bit shorts. Fortunately Python's ctypes module supports the binary sent by the MPU6050.

That sorted out, I did a few trial recordings expecting great results. Nope! Either my lathe doesn't vibrate, or more likely it's not vibrating enough for the module to detect it. Another cause for concern is the relatively low sample rate. More research needed, but looks like I've bought the wrong accelerometer.

There is a Plan B. Anticipating trouble I ordered a Keyes 801S Vibration Sensor at the same time. Although much simpler than the MPU6050, I'm hoping it will be more sensitive. Not betting the farm on it though - I couldn't find a detailed specification.

The advantage of hosting on a RaspberryPi is they run headless, on a battery if necessary, can store large logfiles, could be used to do the number crunching, and the logs (or graphics) can be accessed over wifi from Apple, Windows or Linux.

In the prototype the unboxed Raspberry and sensor are powered up resting on the lathe's headstock and then the Python program is started from a remote terminal. Logging to file is started and stopped at the lathe by grounding the green wire. Each start opens a new logfile, so many recordings can be done per session. If the sensor can be made to produce meaningful data, the computer and sensor would be boxed up and provided with push-button controls.

Dave

Thread: Coronavirus
01/06/2020 16:28:35
Posted by Martin Kyte on 01/06/2020 15:07:05:

I suspect the root cause in the UK was shortages, particularly ventilators and the staff needed to run them.

Are you making this up as you go along? Can you point me to a documented case where a patient was not put on a ventilator because none were available?

I may as well add that it will probably never be over because obesity is a major risk factor and therefor the Fat Lady may never sing. Quite happy with your post until you got to "Why ?"

regards Martin

This article in the Daily Telegraph lays out the NICE Triage Policy.

I explained in another post the reason the 'why' question has to be answered. Next time it might be one of us who is assessed 'Critical Care Not Considered Appropriate'.

Dave

01/06/2020 16:17:32
Posted by Steve Skelton 1 on 01/06/2020 15:25:37:

SOD how on earth can you justify the deaths per case column. The UK has no idea (as is probably the case with most nations) how many cases there have been or are occurring each day so this is totally irrelevant.

Steve

Steve, I thought I'd explained.

  • The number of cases is determined by a Covid test. It's not an estimate of the number of infections in the community, its the count of confirmed infections, ie people ill enough to be tested.
  • The number of deaths is counted off Death Certificates

On the face of it, the ratio indicates the effectiveness of the health service, ie the likelihood of an unsuccessful outcome after a patient tested positive.

I suggested shortage of ventilators as a cause; not having enough of them means patients who would have survived don't. Likewise, shortage of staff to manage patients on ventilators would have the same effect. It's not a criticism of the Health Service; no matter how caring people are, they can't deliver an effective service unless all the essential resources are available. Another possibility is genetic make-up of the victims, or maybe difficulties in Care Homes allowing the virus to spread rapidly inside vulnerable communities. Possibly it's a statistical artefact caused by different reporting systems. I don't know.

My point is the cause of this disparity between countries has to be explained whatever it is. Not about blame, unless stupidity or corruption was involved. If another country did something clever, we should copy them. If we made a mistake, it should be fixed. The idea is to do better next time, and it can't be done if embarrassments are swept under the carpet.

Dave

01/06/2020 14:47:40

This website tracks 215 countries, plus a few cruise ships, where Corana Virus is reported.

The top 13 yesterday (31 May) were:

covidstatsmay31.jpg

I've added a column on the right showing Total Deaths as a percentage of Total Cases. It compares the number of deaths with a Certificate identifying Covid-19 as cause with the number positively tested for Covid-19, ie Total Cases. Both numbers imply medical supervision, probably hospitals. I don't think the figure has any relationship to population density or other external factors, it indicates the effectiveness of the Health Care system.

Worst performer is France(15.25%), then Italy(14.34%), and the UK(14.01%)

Comparable countries include: Spain(9.47%), Canada(8.02%), USA (5.78%), and Germany (4.69%) On the face of it a positive Covid-19 test is about 3 times more likely to be fatal to a Brit than a German.

Why?

Too early to tell, years of analysis and argument ahead! I suspect the root cause in the UK was shortages, particularly ventilators and the staff needed to run them. Just a guess because history suggests the UK is good at theory but very disinclined to spend money preparing for emergencies that might never happen. After all we are caught with our pants down every time it snows!

Another comment, only a small number of countries have so far reported more than 100,000 cases. There are plenty of countries nowhere near this number, therefore their statistics are unreliable. For example Australia has only had 7195 positive tests, which sounds like good news and maybe is. But we don't know yet if countries like Australia have successfully weathered the storm, or if the virus will run amok there in due course. Brazil, Mexico and Chile all reported similarly low numbers until recently, now they're showing Corona Virus is spreading rapidly.

It's not over until the fat lady sings!

Dave

Thread: Machines and equipment sourcing chronology...
01/06/2020 11:37:00
Posted by Ronald Morrison on 01/06/2020 10:42:40:

i put off buying a bandsaw for years, using the hacksaw for all my small cutting and oxy-acetalene or plasma for the bigger cuts. What a mistake! Now that I have a bandsaw I will carry parts 100 meters to the bandsaw instead of picking up the hacksaw that is 1 meter away. The accuracy of the cuts is better than I ever managed with the hacksaw and I can clamp the stock in, start the bandsaw and walk away to do other things, knowing that the bandsaw will just shut itself off when the cut is done.

+1 in favour of the bandsaw! Not sexy but my goodness they save time and effort. Doubly appreciated because hand-sawing must be the most boring, tiring and least rewarding of all workshop activities.

In order:

  • Hand tools, Taps & Dies, Digital Caliper, bench, vice
  • Pillar drill & Grinder
  • Mini-lathe
  • DTI, Stand and Micrometer
  • Bandsaw
  • Insulating Bricks, Seivert Torch
  • Engine Crane
  • Milling Machine with Drill and ER32
  • Parallels, Boring Head, Rotary Table, improved vice
  • X,Y DRO for mill
  • Angle gauges, Wixey and Angle plate
  • Replace mini-lathe with big lathe
  • Ball cutter, knurling tool, rear toolpost, Reamers, centre set & other accessories to fit big lathe
  • Planisher
  • Improved lighting
  • Air Compressor

Dubious purchases: 3-in-1, Height Gauge, Scribe Block, milling vice for Mini-lathe, Flood Coolant system, Clamp Set, Press, Engineering Blue

Made Redundant by Milling Machine: Pillar Drill (mostly), Tap Stand.

Completely Daft: cross-vice.

Dave

Thread: Surface Plate & Height Gauge recommendations
01/06/2020 11:02:38
Posted by Andrew Johnston on 31/05/2020 17:33:50:
Posted by SillyOldDuffer on 31/05/2020 17:27:34:...

If there's a need for repeatable accuracy......................

Repeatability and accuracy are not the same thing. Generally the former is easier to achieve than the latter. smile

Andrew

Quite right! I hope it's correct, but this diagram shows how I remember the difference between accuracy, precision and resolution. Using a bulls-eye target to illustrate accuracy and precision came from Neil Wyatt I think. I've added resolution. Apologies for the colours; red's fairly obvious but blue isn't good on my screen.

accprecres.jpg

Resolution is how finely a particular instrument can read. It's not the same as the graduations, which are often over optimistic. However, assuming the operator has a good touch, successfully avoids parallax, and corrects for temperature, the resolution of a 0.001mm micrometer is limited by the state of its threads and anvils. The instruments ability to measure down to 0.001mm is compromised as it wears. Not possible to repair worn threads and anvils in a home workshop, and the professionals rarely bother either. It's cheaper to replace. Serious measurement requires ruthless reduction of all sources of error, and having a good looking but untrustworthy instrument laying around is asking for trouble. Calibration rejects are one source of ebay bargains.

The diagram represents the actual dimension with cross-hairs. Ideally measurements would hit the bulls-eye every time but it's impossible. Minimising measurement errors gets progressively more difficult and expensive. Consequently engineers should be mindful that good enough is good enough. Time and money is wasted on a grand scale when quality is pursued without justification.

The picture has three examples.

On the left bulls-eye, the instrument gets close repeatable results but is persistently off target. It's precise, but not accurate. Not bad news though, because the error might be due to incorrect zeroing, and in any case precise measurements can be corrected by calibrating the instrument. I wonder how many forum members working to better than a thou bother to correct their micrometer readings, or even need to? But calibration and subsequent correction of readings is certainly necessary for serious measuring!

The centre bulls-eye shows an instrument scattering measurements around the target. On average the instrument is correct but its individual readings are all untrustworthy. This is typical of practical measuring, and it doesn't matter provided the scatter isn't too big for the purpose. The instrument is accurate but not precise. Again, the scatter matters for serious work, but how many of us take the trouble in our workshops to average several readings before proceeding?

The bulls-eye on the right is measurement heaven. The instrument reads accurately and precisely. But note that none of the measurements is spot-on. Magnifying this chart shows it has the same character as the central diagram, but the instrument is better because it measures with less scatter. Unfortunately this kind of performance is expensive to buy, tricky to apply, and expensive to maintain. Screw micrometers inevitably lose precision and accuracy because they wear slightly every single time they're used. For that reason serious micrometers are checked periodically against standards and dumped as soon as they exceed specified tolerances. The gauges used to check micrometers also wear, making it necessary for them to be regularly checked against even better standards and replaced too. At the top of the tree is the standard metre, defined from the average of several high-end atomic clocks. There's an enormous gap between the standard metre and my £30 micrometer! Fortunately for me, a £30 0.01mm micrometer is 'good enough' for my purposes, and I don't need to apply any of the disciplined methods made necessary by working to close tolerances.

When buying tools I feel it's important to separate utility from desirability. Understand your reasons. On the down-side, a £30 micrometer looks and feels cheap. There's no pride of ownership in it and having to use it carefully wastes time! My workshop meets my needs but it wouldn't suit a time-is-money professional or the type who enjoys 'quality' tools.

But please don't tell beginners struggling to start on limited money that only the best will do, especially if the best is second-hand, condition unknown, and is over the top. There's a great deal of fun and education to had from imperfect equipment, and one can always upgrade later.

Dave

Edited By SillyOldDuffer on 01/06/2020 11:05:31

31/05/2020 17:27:34
Posted by Lee Jones 6 on 31/05/2020 14:29:29:
Posted by Barrie Lever on 31/05/2020 13:39:10:

Lee

I would add that decent second hand 0.001mm digital micrometers can be had for S/H £25.00 they can easily be calibrated against a 1" standard. Why not buy good gear at this price.

Surface plates are not so easy that is why granite is good, it does not move much !!

I have just bought an unbelievably good micrometer (£1000.00 new) for £40.00 and it makes the digital 0.001mm jobs look like a blunt instrument, like I said earlier if you dont open the door you don't know what is on the otherside, you might think you do but who knows?

Obviously this is exactly what I'm after.

...

Yes, but beware!!!

If there's a need for repeatable accuracy better than 0.01mm you can't just buy second-hand and hope for the best. Checking against a 1" standard is a good first move, but have you got a 1" standard? With a certificate? Do you know how to use standards properly in the 0.001mm region?

Unfortunately, checking high-precision instruments at only one point on their scale isn't good enough either - they have to be calibrated across the entire range. Whilst a micrometer thread might be in excellent condition at the 1" end, it could be badly adrift towards zero where most of the action is.

Instruments in this class can't be trusted until their accuracy is confirmed. Best not to be led astray by a quality brand with fine graduations and a good feel. Sod the fantasy, get it calibrated! If it's good, hurrah, otherwise no tears please. In the bin with it.

Comes back to what the tool is for. At best I suspect most Imperial model engineers work to ±0.001", and most Metric model engineers about the same at ±0.02mm. Working to 0.01mm is comparatively unusual and a home workshop cutting to ±0.001mm must be a rare beast indeed. Don't get sucked into miserably chasing accuracy that can't be had outside a properly equipped tool-room.

Dave

Thread: Coronavirus
31/05/2020 15:42:15
Posted by J Hancock on 31/05/2020 12:42:49:

We are all, two or three generations on, survivors of the ' Spanish Flu'.

No lockdowns then, so what happened ?

...

For sure, the next few weeks will show whether all this 'sacrifice' has been worthwhile, or a complete waste.

The 1918 pandemic killed more than the First World War. About 150,000,000 people died of Flu.

UK policy is based on a prediction that unconstrained Covid-19 would kill about 300,000 Brits. There's no doubt lock-down is effective. As of yesterday we're only up to 38,768 deaths. However that number is too high in that the UK death rate is significantly worse than all comparable countries. Catching Covid-19 in the UK is much more dangerous than catching the same bug in Germany. Something is wrong here.

Thee largest number of Covid-19 deaths so far have occurred in the USA, over 105,000 as of yesterday. The most likely reason is relatively weak lock-down in the US. We've yet to see what Corana does to a country with poor health services and no lock-down. It may be out-of-control in Brazil. As many countries haven't really kicked off yet, the grand-total could still get nasty.

Certainly can be argued the sacrifice is a complete economic waste. Cheaper to let the virus bump off the old folk, but all the old folk I know are nice people.

Dave

Thread: Surface Plate & Height Gauge recommendations
31/05/2020 12:30:08
Posted by Lee Jones 6 on 31/05/2020 11:18:55:

I really need to stop SWAGing/eyeing things up!

The time has come to take this to the next level. laugh

....

Is there anything I need to be cautious of ...

 

Main thing to be cautious of is wasting money on tools you don't need! My 'surface plate' is a sheet of plate glass on ordinary kitchen worktop. Worktop is flat and strong enough to support it, and the glass is very flat because it's made with a float process. In practice I don't need a precision lump of granite or cast-iron. Full of enthusiasm I lashed out on a height gauge only to find I don't use it much.

Two reasons, I rarely take measurements off existing items to copy or repair them, and a milling machine with DRO can often be positioned accurately enough to eliminate the need for a height gauge. The mill's table substitutes for the surface plate, and the cutter can be positioned relative to edges or other reference points without messing with a height gauge.

As always much depends on on the type of work being done. Getting started I expected to spend ages blueing, marking up and centre-punching etc. It didn't turn out that way for me. A height gauge is jolly useful when needed, but here that's once in a Blue Moon. My home-made surface plate is rarely deployed, and my scribing block mostly gathers dust. They might be more useful if I worked with castings, but my stuff is fabricated.

In the duffer workshop, I've decided to not bother with a certificated 0.001mm micrometer, slip gauges and surface table. They're just not needed. Instead, spring calipers, steel rules, digital caliper, 0.01mm micrometer, DTI, try-square, parallels, angle gauges and V blocks do most of the work.

In a hobby it's perfectly OK to buy tools for pride of ownership or to enjoy learning them. But if money is short, better to prioritise utilitarian items! What's it for, and how often is it needed? Can the money be spent more fruitfully on anything else?

Though I always ask myself the question, I'm not strict about discouraging answers. Quite happy to waste the kids inheritance on pensioner fun!

Dave

Edited By SillyOldDuffer on 31/05/2020 12:31:17

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