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Member postings for JA

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

Thread: White rock salt
01/10/2020 13:03:27

The MEW of November 2003 gave details of a very nice heater for a lathe, milling machine etc. It ran off the mains and heated the machine by three, in series, 1 ohm 50 watt resistors bolted to the structure. These were fed with 10 to 14 volts and were turned on by a adjustable temperature sensor.

There is nothing clever about it and the parts are cheap. I rather like it but have no real need for it.

Perhaps it is time for a reprint in MEW?

JA

Thread: Coronavirus
26/09/2020 12:45:48

Queues at B&Q? Supermarkets run out of Brasso? What next?

JA

Thread: Covid causing mental health issues.
23/09/2020 15:38:17
Posted by David Noble on 23/09/2020 15:22:49:
Posted by Martin Kyte on 22/09/2020 22:33:27:
Posted by David Noble on 22/09/2020 21:52:23:
Posted by pgk pgk on 22/09/2020 19:15:21:

Posted by martin perman on 22/09/2020 18:52:13


...50% of the population have below average IQ...

pgk

I know this is glaringly obvious but it hadn't dawned on me before. It explains a lot!

David

So if the population is 3 and they have IQ's of 50 100 and 120 the average is 270/3 = 90 which means in this case only 30% of the population is below average IQ. Maybe it's not so glaringly obvious after all.

regards Martin

I always knew there was a reason that I disliked statistics! 😬

David

I love statistics. With care you can prove anything with them. smiley

JA

Thread: Climb Milling any implications
23/09/2020 15:00:08

In the apprentice workshop I was tought never to climb except on materials that work hardened. I have remained faithful to that teaching.

During a previous discussion, on this forum, about climb milling I ask a couple of friends who had worked in tool rooms whether they had climb milled. The reply, in both cases, was never.

I think you would need a large and very rigid machine to climb mill anything.

JA

Thread: Home workshop accuracy & tolerance?
23/09/2020 11:18:25

In middle life I became a sort of designer. We, the company, had a mantra- "Fit, form, function".

If the part had to fit another, you had to give and work to the required tolerances. There are standard tables of fits together with the associated machining opperations which I try to work to. On a lathe I can get +/-0.0002" with a lot of patience. This is just withing the capabilities of my 0-1 micrometer. Below that it is down to polishing but I cannot measure the result. Thankfully the parts we make don't have to be interchangable.

Form was the general shape. At work this was +/- 0.010" but since models have to look good it may be wise to try to work to a smaller tolerance.

Function was the most difficult to pin down. It required a good knowledge of what the part did. As suggested above, don't expect tight tolerances to work on a clock (as I discovered).

Good tools of all types are adventageous!

JA

Thread: Cheap Oil for hardening
23/09/2020 08:17:15

I use Nuto 32 oil from/for the lathe for hardening and blacking. It is cheap (if bought in sensible amounts), clean with very few additives and I have plenty of it.

JA

Edited By JA on 23/09/2020 08:18:24

Thread: Reminiscences
20/09/2020 12:10:18

I could write all day on this but won't.

However I remember, with great jollity, being on a trolley bus in Derby that tried to overtake the trolley bus in front. Also two of us, as kids in London, would wait for two buses travelling together, usually 19s or 38s, board one each and race each other for miles.

TV pictures, just BBC, were just a blizzard of white dots.

JA

Thread: New Covid Rules
12/09/2020 17:14:42
Posted by Rod Renshaw on 12/09/2020 16:49:50:

So they could both be correct?

Rod

Going to court could decide this. But you do not want to go there.

JA

Edited By JA on 12/09/2020 17:15:18

Thread: Scaling back forum activity
11/09/2020 12:56:47

I left this forum and ignored all forums for a couple of years. In many ways this was a blessing, I realised they were often a substitute for life and reality.

I came back so this forum must mean something.

As for moderators, just give them a chance. They need tolerance and wisdom, both of which I lack.

JA

Thread: Strength of Beams
11/09/2020 08:16:52
Posted by John MC on 11/09/2020 07:25:30:

For a book that would help with the calculation side of this topic I would heartily recommend "Strength of Materials" by Geoffrey H Ryder. I've had a copy most of my working life. Still using it now.

I've also used Roark's and Shipley's books on the subject.

John

Ryder took me through college and then I sold it. It is one of the few text books I wish I had kept.

JA

Thread: Power Hacksaw
09/09/2020 17:16:17

new band saw.jpg

Arrived early this afternoon.

JA

Thread: Jobs we had as kids
08/09/2020 11:57:59
Posted by Danny M2Z on 08/09/2020 10:14:20:

A lathe was but a dream but I did manage to save enough to purchase a few model aeroplane engines and kits, usually from Henry J. Nicholls shop at 308 Holloway Road,.

That was a great shop. I guess that it closed long ago.

JA

Thread: cateracts.
08/09/2020 11:52:38
Posted by Clive Hartland on 07/09/2020 22:10:18:

I believe it is Atropine that they put in the eyes, widens the pupil and stops the eye moving.

Thats why you need someone with you.

Once a year I have retinopathy test where eye drops, probably Atropine, are used. You are warned not to drive and use sun-glasses .

Two weeks ago I had a visit to my opticians who decided to have a look at the back of the eye using such drops. On leaving, sitting in my car and about to drive home, I had a think about this. I had been told that the effects wear off after four hours. To me it seemed that the problem was not the brightness but the very small depth of focus since the pupils are fully open. Further, the eye muscels are relaxed so it takes time to change focus. I drove the mile and a half home, over two roundabouts, and was mighty glad to make it to my drive.

DON'T drive with such stuff in your eyes.

JA

Thread: New Moderators
31/08/2020 19:55:17

Welcome. I will try to behave myself.

To be controversial, should a moderator post a profile of himself?

JA

Thread: COMPRESSION RATIOS
31/08/2020 18:34:00
Posted by not done it yet on 31/08/2020 18:05:55:

PV^n = constant

That relationship is for adiabatic conditions, not isothermal.

Yes. I have used it frequently since analysing the performance of a petrol engine at tech.

The compression is rapid enough for there to be no major heat loss. For it to be truly adiabatic n would be 1.4 for air.

JA

Edited By JA on 31/08/2020 18:40:34

31/08/2020 17:59:48

Ideally the pressure in the combustion chamber prior to ignition can be found by the relationship

PV^n = constant

so Pressure at top of stroke = Intake pressure x (compression ratio - 1) to the power of n

If there are no losses n = 1.4. However n = 1.3 to 1.35 makes more sense since there will be a small amount of heat and other losses.

In practice lot of other things will influence the pressure such as valve timing, exhaust pipe, resonance etc. However the above gives a good approximation.

Thomas Midgely found that lead prevented knock in engines in the mid 1920s. He then went on to introduce and develop CFCs for refrigerators. He ended the decade by drinking himself to death. Quite a man.

JA

Edited By JA on 31/08/2020 18:02:15

Edited By JA on 31/08/2020 18:03:42

Thread: Power Hacksaw
28/08/2020 14:10:53

I emailed Stakesys and got a very quick reply. Femi saws will be available soon (I am not saying when).

I will wait.

JA

Edited By JA on 28/08/2020 14:12:12

28/08/2020 12:30:21

I have decided to buy a Femi 782XL saw from Stokesy. However they now have no 230v saws in stock.

I really do not want to use Amazon after one of their delivery drivers decided to take a short cut across my garden.

JA

27/08/2020 17:52:38

Paul

What make is it? I am thinking of buying a small Femi saw.

JA

26/08/2020 13:05:22

Just had a look at Femi and Stakesy web sites. They no longer sell hacksaws but Femi make some rather nice small portable band saws.

Food for thought.

JA

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