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Member postings for Farmboy

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

Thread: Antikythera Mechanism
19/10/2021 11:55:53

Having now downloaded and started to read the BHI paper it seems my trial-and-error findings are worth even less than I thought blush The apparently intact section between breaks is only around half of what I assumed so distortion probably accounts for most of the difference. There are in effect several centres, each relating to only a part of the segment.

But I enjoyed the exercise nerd

19/10/2021 10:34:20

I still agree with MichaelG that it is almost impossible to acurately reverse engineer the full disc from this small segment but I had to try, within my limits, to explore things further, purely for my own satisfaction.

Since I have very little understanding of statistical analysis or trigonomotry I resorted to basic geometry as originally suggested by Neil. I loaded the photo into TurboCad and drew a cross-hair over the apparent centre of every tenth hole from 2 to 72. I then drew a series of overlapping chords spanning sets of 20 holes (2-22, 12-32, etc.) and drew radius lines. Next I drew arcs centred on the intersections of various pairs of radii. The arc which apeared, to my eye, to most closely follow the holes has its centre a little below the one originally marked on the photo. Using this new centre I then measured the angular displacement between 2 and 72, which was 71.36 degrees. I believe this gives an angle per step of a little over 1.0194, suggesting a full circle of just over 353 holes.

I'm certainly not qualified to challenge the experts but I would suggest that the marked centre on the photo is at least open to question. Given the range of possible results found by different experts perhaps this is not surprising.



Thread: Accuracy of Hand Drilled holes
16/10/2021 13:45:33

Lacking even an O-level in maths I have played around with the photo in TurboCad, measuring angles by visually centreing the cross-hairs on the holes ( the harder I try, the harder it seems to get ) and using the centre of arc marked on the photo since I didn't feel capable of re-calculating it. Most of my somewhat cruder findings are at least in the same 'ball park' as MichaelG's results. However, by selecting different groups of 20 holes I found it just possible to get the hole count up to 354. The variation in apparent hole size and placement is a limiting factor.

My thoughts, for what they're worth, pretty much agree with MichaelG. There are just too many variables to allow accurate extrapolation from the sector to the full circle. For that to happen we need to know that there is no image distortion at any of the stages between the original x-ray and the viewing device we are using, and that the actual mechanism was not distorted by physical damage or corrosion. We also need to be sure that the hole spacing was actually intended to be regular in the first place, although it is hard to imagine why it wouldn't be.

As for making the original, I think it would be fair to assume that there were many simpler earlier mechanisms on which they developed their skills. By the time of the Antikythera machine there were possibly many skilled craftsmen capable of achieving the required accuracy. I would imagine they had also developed some fairly sophisticated measuring devices, even if they were not widely available. A couple of thousand years earlier, the Egyptians were obviously capable of some pretty accurate design and marking out, albeit on a larger scale!


Thread: Nails ?????
02/10/2021 16:13:52

Good old BBC sad


Surely there can't be many people who think these are nails . . . apart from journalists, obviously.

Sadly it is probably irrelevant to most people today crying 2

Thread: I need to cut chamfers into x64 pieces of mild steel - any advice?
04/09/2021 14:48:48
Posted by JasonB on 04/09/2021 13:37:42:

... He was not able to cut bits of metal to 8 x 16 or put the holes in them after long threads on the subjects and has ended up getting them laser cut ...

Looking back to the original posting, I would suggest the laser cutters didn't make such a great job either. They don't look like 8 x 16 to me dont know

Thread: Dewpoint
20/07/2021 10:28:44

I had an unusual experience travelling home yesterday evening. It was still quite warm so I had the aircon on in the car, but the windscreen was slowly misting up. I increased the fan speed which only made it worse . . . until I realised the misting was on the outside, caused by a combination of the high air temperature and humidity and the chilling of the 'screen by the air conditioning. A burst of warm air from the heater dispersed it quickly, but it's something I have never before experienced in 50 years of driving. Maybe I never had such an efficient air conditioning unit before dont know

Not really model engineering but perhaps a good illustration of the 'dewpoint' effect which causes rust on machines and has been discussed on the forum many times.

Thread: Stone moving machine
04/07/2021 11:41:47

There's scope for a lot of serious time-wasting, trying to work out how (and, indeed, why) ancient people shifted so much masonry over great distances. Not to mention how they managed to erect somewhat irregular sized massive stone pillars so that the tops were almost perfectly aligned, then fit stone lintels on top with mortice and tenon joints!

Once you've worked all that out you can move on to Baalbek and work out how they quarried and moved stone blocks weighing 800 tons or more.

Believe me, I've tried . . . most avenues of research end up with giants, aliens or magic disgust

Thread: Thread on front forks on a Raleigh bike
31/05/2021 11:13:33
Posted by James Alford on 31/05/2021 09:21:00:

How well does it handle? I had a two litre Vitesse and the handling was scary until I fitted a swinging rear leaf spring from the very last models. It lowered the rear end somewhat, but utterly transformed the handling.


The 2-Litre Vitesse Mk1 rear suspension taught me to brake before the bend and accelerate through it. Really wish I'd kept my convertible, such a great little car to drive.

Thread: Any info on this?
22/05/2021 13:11:02

Just a thought, as I've never seen anything like it: If used in the conventional way, held in the left hand and cranked with the right, the chain comes out at the top so the device would rise with whatever it was lifting; the opposite to any conventional winch I've seen. Could it have been used to pull something down?

Thread: Laptop with a SD card slot
12/04/2021 12:46:24

Might be worth checking out PCSpecialist. It's a couple of years since I used them but they still seem to have a good assortment to choose from. If you 'customize' to your requirements they build to order so might be a few weeks delivery time.

Thread: I honestly canít think of an suitable title
17/12/2020 11:32:58

I don't object to advertising, I just choose to avoid it wherever I can, but I do object to people covertly harvesting information about my browsing and shopping habits, and even more strongly object to people harvesting information from my contact list, etc. angry 2

I try to keep things as secure as possible but privacy doesn't really exist any more in the 'digital age'.

Thread: Windows 10 latest offering
18/11/2020 22:27:14

Just a word of warning to anyone thinking of buying one of the cheap mini-laptops available for around £150. Some of these have only a 32Gb SSD as the primary drive and 4Gb of RAM. Many people, including my partner, have found that Windows cannot install the mandatory updates due to insufficient space on these machines, even though I moved all the installed apps/programs to the secondary SD card drive so that the primary drive only holds the operating system. The only way to update these would seem to be to download the latest ISO file and do a clean install.


Thread: The Raspberry Pi gets domesticated
02/11/2020 12:56:57

Reliability issues aside, the ZX81 was more than adequate for controlling something like a central heating system, with just 1k of memory and machine code I could understand. I was in the process of adapting one for an automated cattle feeder just before I gave up keeping cattle a few years ago, and the program used nowhere near 1k of memory.

The Pi sounds rather like a sledgehammer to crack a nut in such circumstances. It has as much RAM as around two million ZX81s and the processor runs about a thousand times faster disgust

But, if there was enough free time in my life, I would love to play around with a Raspberry Pi . . .

Thread: For the latest in PC fashion! (Anyone here with a Master's Degree?)
28/10/2020 08:33:19

Don't think they had degrees, but many of my ancestors were Master Primary Carpenters sarcastic

Thread: Bleeding hydraulics
07/10/2020 22:08:17

The workshop manual for my mini-digger says you should fully extend and retract all the rams several times to expel air after working on the hydraulic circuits. In a lifetime of working with farm machinery that always seems to work for me. I guess the seals are oil-tight but not air-tight.


Thread: Mystery Object ... This one has me beat
14/09/2020 08:34:03

Having followed this thread with interest, I just had a thought to throw into the mix: the flat shape of the 'anchor' suggests it might have been designed to build into brickwork, i.e. set in the mortar between courses. Probably way off the mark but the best I can come up with so far . . .


Thread: Hydraulic ram machining
20/08/2020 10:57:00

I seem to recall our local (U.K.) ag. engineers replacing a bent ram rod with plain steel as an emergency repair many years ago. No idea what grade of steel, and of course it needed regular greasing to prevent rust, but it lasted many years. Might be a cheaper alternative if funds are tight?

I had a similar shock recently when it came to replacing the tipping ram on a 30+ year old trailer, just about the same price as the trailer originally cost! But I was pleasantly surprised to find an exact (imperial) match for the original, and I have a usable trailer again.


Thread: Old School Drawing Exercises and 2D CAD
26/07/2020 13:07:03

Thanks for your answer, Dave. I genuinely wondered if it was a trick question and I had missed something.

I should obviously have included a rule and possibly a set-square with my T-square and compasses! For quickness I used the digital version (TurboCAD) to produce my 'approximation' of the drawing based on the assumption about the second circle, but I didn't use any of its other functions. Point D may be determined by the intersection between a parallel line 100mm below A-B and a 91mm arc centred on E. Point B is where this arc meets the line A-B. All other arcs were similarly centred as shown on my drawing. Incidentally, my coordinates for point D seem to agree with those mentioned in answer to Michael Gilligan's earlier question.

While none of this really matters here, it might have serious consequences in a real-life situation to make assumptions about missing dimensions on a drawing. No doubt someone will now point out some grave error in my work, on which I have now spent far too much time


25/07/2020 17:10:32
Posted by Gary Wooding on 21/07/2020 10:24:29:

Here's another challenge for you. All transitions are tangents, and the top line is horizontal.

cad drawing test2.jpg

Going back a bit to the 'simple' exercise, is it safe to assume that both circles are in the same position on the Y-axis? Although they appear to be, the dimension line does not pass through the right-hand one. I am genuinely interested to know if there is any way of calculating its position from the dimensions given, except that it is 24mm from the left-hand one on the X-axis. If you centre both circles on the same horizontal the exercise seems very simple using just T-square and compasses.

Thread: Box-Shifters and Quality Assurance
12/05/2020 10:06:55

Surely it's purely economics? If you want quality assured 'out of the box' someone has to pay for all the checking, setting up and testing throughout the whole production process. If you are on a tight budget you have to accept that you might need to do a lot of that yourself. We all have the opportunity to take the first option if we can afford it, but for many the choice is between the second option or nothing at all. At least there is usually the third option of returning the faulty item for refund or replacement.

If there were no 'box shifters' many of us would not be able to afford so many toys important pieces of equipment. Without Clive Sinclair, whatever you think of some of his products, we might have waited a lot longer before computers became so widely available. In the absence of cheap imports from the far east, second-hand machine tools would probably be even more expensive due to supply and demand.

In my early teens I developed a huge interest in all things mechanical and steadily built up a tool kit of my own. At that time there were a lot of cheaper hand tools coming from Spain, some of which I bought with my pocket money and still have to this day. Maybe I was lucky, but I would have waited a long time before I could afford the same items from the likes of King Dick.


P.S. I do have plenty of better things to do really, but I picked some rhubarb yesterday and I'm waiting for the rhubarb crumble to finish cooking . . . and by the smell coming from the oven I think it is done smiley

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