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Member postings for Neil Wyatt

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

Thread: My new favourite threads
16/10/2021 19:12:00

Possibly not a coincidence that there are a lot of 26 tpi threads in larger sizes... cycle threads. A very near imperial alternative to 1mm pitch.

Also 32tpi and 40 tpi 'Models Engineer' threads.

Relatively fine constant pitch sizes have practical advantages, especially if cutting a lot using a lathe.

No reason why 0.8 mm and 0.6 mm don't provide practical alternatives for these finer thread forms, if you can get the taps.

Neil

Thread: Accuracy of Hand Drilled holes
16/10/2021 09:22:42
Posted by Nigel Graham 2 on 15/10/2021 19:16:04:

I wonder how advanced the Ancient Greek craftsmen were in maths, compared to the philosophers of the time. The philsosophers with all their Theorems and things tended to believe their knowledge mystical so kept it hermetic.

Perhaps the artisans worked out the practical geometry themselves but the Euclids and Platos stole the glory so 20C school-children could enjoy having to prove some random shape is a Cycling Quadri-thingummybob!

I think it's a mistake to assume a split between philosophers and artisans. Even if an artisan made the Antikythera mechanism, someone with far greater skill in geometry and mathematics than I was involved very closely - playing the role that Excel and CAD play for me when I make a mechanism.

Neil

Thread: Last Night's Astro Image
15/10/2021 10:19:20

I would love to photograph a goblin or sprite. People have caught sprites from the ground.

Neil

Thread: Watch out for scam emails from a forum member
14/10/2021 09:36:03

I had an unusual email from a forum member yesterday asking when I would be next on line.

I thought it was suspicious, so I sent a vague response suggesting they email me again.

The reply gave a cock and bull story about why they needed me to buy a Google Play gift card for their daughter's birthday present.

This is a very well-known scam. The 'daughter' gets sent lots of loaded gift cards and the senders never get paid.

I've emailed the forum member using a second email I have for him.

I won't share their name or the scam email address for obvious reasons, but they will probably work through his address book and may well contact other forum members.

If you get any odd request about when you are next online or unexpected requests for help that involve sending money or gift cards, DO NOT RESPOND TO THEM.

Neil

Thread: t-bar material advice
11/10/2021 09:55:24

Experience says if you think 6mm will do, go up to 8mm.

The increase in stiffness is huge, and the hole will be less likely to bell mouth as well.

Neil

Thread: Accuracy of Hand Drilled holes
10/10/2021 13:06:27

Smart enough for KISS to apply.

The mechanism itself is, in essence, a dividing engine with many ratios built in. The makers would have been well aware of its accuracies and inaccuracies, including knowing that angular errors in the gears would have been trivial and cyclical - only errors due to gear ratio approximations are cumulative.

They needed a circle of 'x' holes to step the mechanism around in 'x' steps per rotation.. Micron accuracy is not required, so there is no reason for them to go chasing it.

To me the obvious solution is scribe a ring, use a marked strip wrapped around a circumference as an index. Scribe or punch each hole, then drill by hand.

Similarly, gears only had to be accurate enough to run and being hand finished could be eased if there were any tight spots.

Thread: Antikythera Mechanism
10/10/2021 12:59:11
Posted by Michael Gilligan on 09/10/2021 21:34:16:
Posted by Ian P on 09/10/2021 21:31:47:

I think that determining the number of holes in this mechanism is unlikely ever to be solved from the currently available (physical) fragment. […]

.

Thank You, Ian yes

That’s what I have been trying to demonstrate !

MichaelG.

I think that's what Mike Edmunds feels, more or less, he's writing a paper suggesting that errors in the manufacture mean we can't be certain of the actual hole count.

That's why he was interested in the possible accuracy with which the holes could have been drilled.

Neil

10/10/2021 12:57:00
Posted by John Haine on 09/10/2021 20:45:48:

Even back when Michael Wright was working on it he was using X-ray tomography for imaging the object in 3D, and I'm sure they are using more sophisticated studd now.

I haven't really been following this, but are people saying that the project written up in HJ which I linked to, one of the authors being Clickspring, which concluded that the device incorporated a lunar calendar, is wrong?

Edited By John Haine on 09/10/2021 20:46:19

It contains a lunar calendar, but if these holes are for the master motion stepping the device around, it makes logical sense for it to fit the calendar year, with each step a solar day, rather than one of the derived motions.

10/10/2021 12:51:53
Posted by Martin Connelly on 09/10/2021 08:32:22:

Neil, is there any reason you didn't include 366 sidereal days in a year? Wouldn't that track the stars through a year?

Martin C

True.

One of the things it does is derive the sidereal movement from the solar day, so it might be redundant.

Neil

08/10/2021 18:35:57

Perhaps I should explain why the number of holes matters.

The whole device had many gears, some of which can be reconstructed accurately, others estimated, as based on text fragments we can know the sorts of cycles it was displaying. The Greeks knew the lengths of these cycles (from days to decades) with surprising accuracy (the longest cycle is about a lifetime) and were able to calculate their ratios accurately.

It's likely the holes would have been used for some sort of indexing - there are fragments of dials which would have read out various cycles - and the obvious contenders for this are:

365 days = 1 year

354 days = 12 lunar months

355 days = 13 sidereal months (the time for the moon to return to the same place in the sky)

360 degrees

But who knows!

Thread: Accuracy of Hand Drilled holes
08/10/2021 10:08:59
Posted by Bill Pudney on 08/10/2021 09:52:00:

During my apprenticeship we had to make loft plates, typically 1/8" al.alloy, with an accurate photographic "picture" of what was required, printed on the sheet. They were usually developments of folded/pressed structural members, some were small 6" x 6", some were long and with a complex shape, the biggest I saw was about 72" x 12". The outline had lines from memory 0.006" or 0.010" wide, holes were indicated by crossed lines, with a circle appropriately sized for the drill bush destined for that hole, usually either 3/32" or 1/8" bore, with an outside diameter of something like 5/16" or 3/8". The bushes were very accurate, I think that they were sintered. The outline had to be filed to (ideally) half the line thickness, and the drill bush ideally would show half the line thickness all the way round. This is a long winded way of saying that, in my yoof I regularly achieved +/-0.003" or +/-0.005".

cheers

Bill

And so is this, from another Bill, thanks.

08/10/2021 10:08:30
Posted by Bill Davies 2 on 06/10/2021 12:21:05:

I make no claim for my ability to achieve such accuracy, but my instructor taught us to mark out perpendicular lines, pick up intersections and lightly mark with a sharp prick punch (60° centre punch), then using an eyeglass, 'nudging' the position until properly located, then apply a heavier tap. We used a small centre drill and opened up and reamed in the usual way. He claimed, with care, 0.005".

I think Chapman's first volume of Workshop Technology also claims five thou. I've put my copies somewhere safe, and can't find them. There is a set of all three on Ebay for £27.99.

Machine Tool Operation ( [US textbooks] Burghardt, etc., 1953, vol 1) claims it is possible to set external calipers 'easily' to within 0.002-3" against an engineer's rules. In those days, they were accurately ruled and deeply etched.

By my time, vernier height gauges were universally used, and we had mills and jig boring machines for accurate work.

Bill

That's particularly useful, thanks Bill.

Thread: Workshop lighting / energy costs
07/10/2021 19:04:31

I've gone for five 43W LED battens.

If I get fed up in the workshop, I will be able to take my shirt of, lie back and develop a tan.

Neil

Thread: gr 8.8 ht bolt steel which carbide tip
07/10/2021 11:23:39

Please, can everyone play nicely.

That includes not to slipping in snide insults under the guise of fair comment, or broadsides of comment intended to prompt a heated exchange of views - that's trolling.

Being inflammatory may not make the information in a thread less valuable, but it devalues the whole forum, as most of those who come here do so in the hope of good-humoured, polite discussion.

I'm going to lock this thread as the useful content is being outweighed by the confrontational comments.

I think we can all do better than this.

Neil

Thread: Accuracy of Hand Drilled holes
06/10/2021 10:37:26
Posted by Dave Halford on 06/10/2021 10:06:58:

That's an eye sight dependant / age question.

My daughter at 18 could be spot on easily, at 40 she could not as glass lenses had not been invented, or had they?

Edited By Dave Halford on 06/10/2021 10:09:07

I'm assuming a skilled worker with no physical impediments.

So what is 'spot on'?

Neil.

06/10/2021 09:51:12

Another thread has wandered from this question, for unsurprising reasons.

Can I ask more specifically, if you were marking out a circle out small (about 0.4mm) holes and then drilling them by hand, how accurately could you place them?

0.2mm? 0.1mm?

Thanks

Neil

Thread: Antikythera Mechanism
06/10/2021 09:43:53
Posted by John Haine on 05/10/2021 16:20:13:

Neil, I'm registered with Academia.edu, I just emailed you a copy to your mytimemedia address.

Thankj John,

Neil

06/10/2021 09:43:35
Posted by Dave Halford on 05/10/2021 20:28:43:
Posted by Michael Gilligan on 05/10/2021 18:03:53:
Posted by Michael Gilligan on 05/10/2021 15:08:59:

.

Thanks, Neil … it also answers the question posed in my P.S.

.

But, unfortunately, I am not entirely convinced by their Least Squares Fit

… see the substantial deviation from the circle within my green Region of Interest :

.

8af343aa-48e9-4043-985c-f079f541996b.jpeg

.

MichaelG.

.

If we are trying to decide how many holes there must be in the full circle, then we need a good estimate of its radius.

That also looks like an area of damage, I suspect that without all the corrosion it would no longer be attached to the rest.

The paper mentions the fracture.

On the plus side, i measured the distances from hole 1 to 41 and 41 to 81 as being the same.

(They shouldl have numbered the holes 0-80 IMHO).

Neil

05/10/2021 15:51:10
Posted by Michael Gilligan on 05/10/2021 15:01:31:
Posted by Neil Wyatt on 05/10/2021 14:14:32:

Much as I find this discussion fascinating, has anyone got any estimates for the accuracy of setting out and hand drilling small holes?

[ … ]

.

Not an estimate, Neil but possibly relevant … Have a look at the section about John Bird : **LINK**

https://www.academia.edu/5340304/Dividing_to_Rule_Precision_Mathematical_Instruments_in_mid-18th_Century_England

MichaelG.

Unfortunately that site will only let me in if I allow it to download my contacts!

05/10/2021 14:16:40

Next thought... Prof Edmunds pointed out some of the measurements would have had large cyclical errors, e.g. it would have predicted lunar months accurately well into the future, but moon phases could have been many days out.

He suggested it may have been a teaching aid, rather than a calculator per se. as they had the capability to calculate astronomical events manually to far greater precision.

Neil

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