Here is a list of all the postings JA has made in our forums. Click on a thread name to jump to the thread.
Queues at B&Q? Supermarkets run out of Brasso? What next?
|Thread: Covid causing mental health issues.|
I love statistics. With care you can prove anything with them.
|Thread: Climb Milling any implications|
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.
|Thread: Home workshop accuracy & tolerance?|
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!
|Thread: Cheap Oil for hardening|
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.
Edited By JA on 23/09/2020 08:18:24
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.
|Thread: New Covid Rules|
Going to court could decide this. But you do not want to go there.
Edited By JA on 12/09/2020 17:15:18
|Thread: Scaling back forum activity|
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.
|Thread: Strength of Beams|
Ryder took me through college and then I sold it. It is one of the few text books I wish I had kept.
|Thread: Power Hacksaw|
Arrived early this afternoon.
|Thread: Jobs we had as kids|
That was a great shop. I guess that it closed long ago.
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.
|Thread: New Moderators|
Welcome. I will try to behave myself.
To be controversial, should a moderator post a profile of himself?
|Thread: COMPRESSION RATIOS|
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.
Edited By JA on 31/08/2020 18:40:34
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.
Edited By JA on 31/08/2020 18:02:15
Edited By JA on 31/08/2020 18:03:42
|Thread: Power Hacksaw|
I emailed Stakesys and got a very quick reply. Femi saws will be available soon (I am not saying when).
I will wait.
Edited By JA on 28/08/2020 14:12:12
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.
What make is it? I am thinking of buying a small Femi saw.
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.
I think that is what I vaguely remembered.
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