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Member postings for John McNamara

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

Thread: Antikythera Mechanism
23/11/2021 10:24:43

Good find Michael G

From the first Scientific American link you posted.
If this image is from the Antikythera find it appears to show a larger fragment. Maybe it is an assembly of found pieces? However even if it is it may enable a more precise centre point to be derived, Even if just a "feature" arc is used if the holes are not visible. it might improve the accuracy of the calculations for the hole circle. By knowing the radius of a feature arc and then measuring the distance from the feature arc to the hole circle arc, a more accurate radius for the hole circle might be obtained. I firmly believe that the mechanism was accurately made with true concentric circles.

Maybe there is a better copy of this image available?

antikythera l.jpg

Slideshow Link

Regards
John

Thread: 80th birthday
20/11/2021 05:54:06

Hmm

Maybe oysters... But then again, maybe not.

Happy birthday Bill

Cheers
John

Thread: Help in identifying antique milling machine.
17/11/2021 22:17:56

Both Browne & Sharpe and Pratt and Whitney made similar machines.

**LINK**

Many companies made similar machines

An assembled photo might help identify it.
Are the parts numbered?

Vintage machinery.org have free downloadable documents from that era. the best site I know of for old US metalworking machines.

**LINK**

Thread: Antikythera Mechanism
16/11/2021 13:38:56

Hi Drewt

I should have made it clear in the last post I made that all the arcs placed with the three point method were positioned on the end circle centres. The two "feature" arcs were positioned entirely by eye.

The centre of the hole(s) arc was positioned by eye as seen below. I tried to visually pick the visual average centre of all the holes.

The circles around the holes were also positioned by eye, prior to placing the arc. Reviewing the placement used it looks about right, Improving it would not significantly affect the placement of the arcs. and the the all important radius that assists us in calculating the number of holes.

I am surprised how much the the centres of the hole arcs and the two feature arcs deviate in the tests. There is significant error, they should line up better, assuming the creator had a half decent compass. It is clear the device was created by master craftsman. They would have had high quality compasses and tools.

For me that only leaves distortion, the centres should align a lot more accurately. was this distortion physical? The result of unknown forces over time? Or could it be possible that the X-ray scanning methods introduced error. I know the imaging was done in slices, were they truly planar to the mechanism? Could there be some form of spherical distortion of the scanning beam?

I would really like to know more about the scanning method. what was the accuracy and linearity obtained particularly over the entire area of the objects. The fine detail is good but that is not all we need.

See enlarged images below
yellow arc placement.jpg
cyan arc placement.jpg

antikythera test 3.jpg

Edited By John McNamara on 16/11/2021 13:42:14

Edited By John McNamara on 16/11/2021 13:43:29

Thread: Solid Edge - Community Edition
16/11/2021 11:43:30

Hi Nealeb

The link below may possibly interest you?
Gearotic is a suite of tools used to create all sorts of gears standard and exotic!, Clock escapements, Bolts and and other parts.

Developed by Art Art Fenerty and Bob Landry, Who created Mach 3 CNC.
It is not free and costs 120 US dollars. (For a lifetime licence with free updates forever)

**LINK**

I have no connection with the company apart from having bought my copy maybe ten years ago and updating it as new versions come along. What I can say is it works well. a bargain if you have a use for it.

Thread: DIY Epoxy Frame based CNC MILL
15/11/2021 02:15:37

Hi All

When I started this project I had no idea that having got so close to a finish, Life pressures would push it into the background.
I am also astonished that this post has been viewed about 57000 times.

Clearly I have a debt to repay the interest received with a completed project.
My sincere apologies for the delay.

My workshop is now moved to a new temporary brick garage and hopefully soon I will have 3 phase power. I need the lathe to make some of the parts. I want to build a new shed later this year. But at least I can work in the temporary garage.

At the moment I am bench testing the XYZ drive system. Will post a description soon.

It will be interesting to see if there is any change in the alignment of the mill, having travelled on a truck about 60 kilometers crane on, crane off etc. The columns and crossmember are only bolted, as noted in the post they were to be set in epoxy then bolted to final alignment.

Regards
John

Thread: Antikythera Mechanism
13/11/2021 08:20:52

Hi All

Thank you Drewt for the image, I am not exactly sure who to acknowledge regarding its copyright. However I wish to acknowledge that it is.

More testing and again differing results!
I have been using Autocad to work on the image, I did not select any centre points when placing the true circular arcs. I just used the three point arc method. I am confident the method is accurate.

To me the results all point to distortion.

How many holes? So far the tests have suggested a lower number certainly not 365 is the most likely?

Regards
John

antikythera test 3 excel.jpg

antikythera test 3.jpg

Thread: A very close call with a scammer
13/11/2021 00:17:16

Firstly I never repost but this is an important lesson. apologies.

Just because it looks all right? You better look very very very carefully.

We recently bought a new house. An exciting time. The usual thing we paid a nominal deposit on the day pending payment of the full amount a couple of days later. Having looked at a number of properties with the same estate agent we knew several of the sales staff and the name of the sales office accountant who had properly handled the initial deposit.

All good so far.

A couple of days later we received an email telling us the bank account details for the rest of the deposit, The email used the logo and office details of the agency together with the names of the sales agent and the details of the amount owing. However, there was one difference. the bank account details had changed to a new account number. Apart from that it looked like the initial deposit email.

Luckily this triggered an alarm in our minds. It was then that we also noticed a difference in the web address, so we phoned the agency to check the validity of the email. They were shocked! They knew nothing of the infiltration of their computer. And yes! it was a scam.

I later found out that this bank account number was indeed a genuine Australian bank account number. The Police told me that this is the norm. However, any money paid into that account would have been whisked out of the country in seconds.

What had happened is that the estate agent’s office computer system had been hacked. The hackers had gained access to the records of current sales taking place at the time and were able to construct bogus documents to use against current transactions. With all the correct names and logos in place.

We were lucky, the small discrepancies triggered that essential check phone call. Had we not done that we would have suffered a substantial loss. As I understand it another client did not notice. and was snared by the scammers net. I don't know if they were compensated. I suspect not.

As a consequence, the estate agent shut their offices for several weeks while a new system was put in place.

We made the payment in person at the estate agents bank after checking the credentials of the account with the bank manager.

In Australia Property is now settled by computer, not like in the past where the conveyancing Layers for the parties concerned sat around a table. and exchanged documents.

Our lawyer who conducted the final settlement told us that many lawyers and other businesses that handle cash had also been hacked in a similar way. She told me that in spite of automation they always telephone other parties verbally and only use account numbers obtained verbally having confirmed that there is no possibility that the party on the other end of the phone is a scammer.

While the settlement is normally done by a layer in Australia the deposit is usually just done personally, typically about 10%, a substantial amount of cash to loose.

The event also triggered a long investigation by our two banks not because we were affected but because they were trying to set up defences to counter this sort of activity, however in my discussions with them I gleaned that as soon as the cash is out of the country it is almost impossible to recover it.

Naturally we had put a stop on all our bank accounts immediately, We did not know what sort of information the scammers had.

Just because it looks all right? You better look very very very carefully.

Thread: Antikythera Mechanism
13/11/2021 00:08:25

Hi All

Using the second set of observations I made shown in green I calculated 355,83deg. This used the larger fragment with no visible cracking. I guess this larger fragment offers the best approximation accuracy available.

The method used was to visually place small circles over the “points” then apply an arc over the circles using eyeball best fit analysis.

Can we assume the points were holes? If they are holes I would be very interested to know if the “silt” mentioned previously by Drewt contained iron, particularly at the bottom of the holes? Maybe this would suggest pins protruding that might suggest a pin gear.

Getting back to the method. I would like to try it on the best available known image. If available online I would appreciate a link. I will repeat my test using this image.

I am somewhat confused by the apparent inaccuracy of some of the points, I firmly believe that a person capable of constructing this mechanism will have been capable of better hole placement.

Maybe we should ignore certain outliers from the calculations. Local corrosion might possibly have moved the apparent hole in the substrate.

Additionally, there is the possibility of larger (not visible) cracks deforming the substrate.

I look forward to a retest on a better image if found.

Edited By John McNamara on 13/11/2021 00:09:54

Thread: So what design software will you use in 2022?
12/11/2021 08:43:20

Gee there is a lot out there....

Best free CAM software search

11/11/2021 21:31:11

So what design software will you use in 2022?

A serious contender Is Siemens Solid edge, Free to hobby users, not web based it runs on your computer you do not have to be connected to the internet. This has to be a bargain. It is competitive with Solidworks some say better. There is no CAM included with the hobby version. But apart from that it is all there. They clearly state that it can be used indefinitely for hobby use.

Surprisingly the Siemens developed Parasolid engine it uses is also licenced to many other commercial CAD packages. From memory even Fusion 360. And Solidworks?

I made a small solid model in Solid Edge and exported it to Fusion 360 as a Step file and it worked perfectly. As you would expect from Siemens developed software. The interface takes a little getting used to but not that hard. Solid edge can Export and import many, formats, very useful. Again, a feature removed from the Hobby version of Fusion 360.

There are none of the Fusion 360 restrictions on number of parts open etc. I also opened a commercially developed machine model that contained several hundred parts no problem. I have an early I7, it struggled a bit, took about a30 seconds to open it, but no problem. The model contained sheet metal, castings and small components. This was a great test.

Unlike Fusion 360 fully functional FEA, Generative design, collaboration Etc is all there.

My guess is that Autodesk will continue to trim Fusion down, and sooner or later they will start charging and charging big.

So the search is on for a CAM replacement, as of Now FreeCad (Open Source) is a contender. You can also use FreeCad stand alone although it will take a long time to catch up with professional level design software. The Cam feature is useable.

So for me it will be Solid edge for modelling parts.
Fusion 360 for as long as it lasts and we are cut of at the knees, For CAM
And in the mean time I am learning to work with FreeCad For CAM

I guess this all looks like a Fusion 360 rant, roast. OK It is! They sucked in a huge Fusion 360 user base with the “honey pot” trick. Only to rip them off a bit later.

The same applies to other Autodesk products. The Perpetual Autodesk design suite licence I paid the price of a compact car for, followed by many years of annual update fees was stopped dead last year. Yes, I can use the 2021 version, the last maintenance fee paid for version for as long as their licence server works. (Read one day it won’t when there is a major Windows update, They will claim product lifetime expiry)

Oh, and the current price tor that suite now available on annual subscription only (with 3DMax removed you now pay for that separately), has gone up from an about $1700 AUD optional annual maintenance fee to a just under $5000 AUD subscription fee, you are forced, if you don’t pay, they turn the software off. No I did not fall for that.

So what is your plan for 2022?



Thread: Telephone / Internet Scams
11/11/2021 13:13:26

Just because it looks all right? You better look very very very carefully.

We recently bought a new house. An exciting time. The usual thing we paid a nominal deposit on the day pending payment of the full amount a couple of days later. Having looked at a number of properties with the same estate agent we knew several of the sales staff and the name of the sales office accountant who had properly handled the initial deposit.

All good so far.

A couple of days later we received an email telling us the bank account details for the rest of the deposit, The email used the logo and office details of the agency together with the names of the sales agent and the details of the amount owing. However, there was one difference. the bank account details had changed to a new account number. Apart from that it looked like the initial deposit email.

Luckily this triggered an alarm in our minds. It was then that we also noticed a difference in the web address, so we phoned the agency to check the validity of the email. They were shocked! They knew nothing of the infiltration of their computer. And yes! it was a scam.

I later found out that this bank account number was indeed a genuine Australian bank account number. The Police told me that this is the norm. However, any money paid into that account would have been whisked out of the country in seconds.

 

What had happened is that the estate agent’s office computer system had been hacked. The hackers had gained access to the records of current sales taking place at the time and were able to construct bogus documents to use against current transactions. With all the correct names and logos in place.

We were lucky, the small discrepancies triggered that essential check phone call. Had we not done that we would have suffered a substantial loss. As I understand it another client did not notice. and was snared by the scammers net. I don't know if they were compensated. I suspect not.

As a consequence, the estate agent shut their offices for several weeks while a new system was put in place.

We made the payment in person at the estate agents bank after checking the credentials of the account with the bank manager.

In Australia Property is now settled by computer, not like in the past where the conveyancing Layers for the parties concerned sat around a table. and exchanged documents.

Our lawyer who conducted the final settlement told us that many lawyers and other businesses that handle cash had also been hacked in a similar way. She told me that in spite of automation they always telephone other parties verbally and only use account numbers obtained verbally having confirmed that there is no possibility that the party on the other end of the phone is a scammer.

While the settlement is normally done by a layer in Australia the deposit is usually just done personally, typically about 10%, a substantial amount of cash to loose.

The event also triggered a long investigation by our two banks not because we were affected but because they were trying to set up defenses to counter this sort of activity, however in my discussions with them I gleaned that as soon as the cash is out of the country it is almost impossible to recover it.

Naturally we had put a stop on all our bank accounts immediately, We did not know what sort of information the scammers had.

Just because it looks all right? You better look very very very carefully.

Edited By John McNamara on 11/11/2021 13:16:44

Edited By John McNamara on 11/11/2021 13:18:06

Thread: Antikythera Mechanism
10/11/2021 03:58:49

Hi All

I tried another approach just measuring the sections between the visible cracks

Regards
John

antikythera 2.jpg

antikythera 2 cad.jpg

09/11/2021 14:58:02

Hi All

Yes I am still around double Vaxed and healthy! I must however admit I will be happy to see the end of 2021.

Thought I would have a think on the problem and try to resolve it with CAD.
These are my findings, also in my Album.

Somewhere between 360 and 366 segments
Maybe this could be refined a little but with a distorted part it would still be a guess.

I hope I got the calculations correct.

calculations.jpg

antikythera.jpg

Thread: Plans for updating the archaic forum?
16/02/2021 08:26:12

Hi All

If the current discussion was about the interface with the users, for example improving the methods used to upload images; Some platforms support "drag and drop", that would be a worthwhile improvement. Making the program easier to use is a worthwhile objective.

However the current font size and the grey background is easy to read. Please don't muck about with it without very careful testing with users.

This is a commercial website as well as a great (and free) forum. The advertisements are an important part of the websites continuing success, advertisements occupy the right hand side of the screen OK to me. On the left the poster name and stats, so far so good.

What concerns me is as shown in some of the examples shown in this thread the width of the left or right columns can dominate the available space, squeezing the hard to read small and pale text of the actual posts into a small space.

If there is going to be changes a clearly defined need for each change must be documented taking the end users point of view and the commercial imperative into account.

So who will get the job to "Fix" the program ?
Management will often pass the design to the web programmers. This can be a big mistake! Savvy computer users are not typical users, what appears simple to a power user can be quite daunting to a less experienced user. Testing and retesting with typical users is essential.

Regards
John

Edited By John McNamara on 16/02/2021 08:28:33

Thread: Facing parallel between centres.
13/09/2020 06:56:28

One way to face two sides perfectly that has worked for me in the past is to:

First face the work piece both sides in the three or 4 jaw it does not mater. then drill and centre one side of the workpiece.

When you take the workpiece out of the lathe chances are that it will be a little out of parallel even if you set it up with a dial indicator, it will probably be a few tenth's out.

The next step is to place a piece of scrap in the lathe and then face the outer edge say 10mm then turn a recess in the centre say 10 thou deep. leave this piece in the lathe. It will be perfectly true.
ithin the limits of the spindle bearings If you want to be technically correct.

Then hold the non centred side of the workpiece and centre it up with the tailstock centre pressed firmly against it and locked. This process works better with a ball bearing centre. Another possibility would be to bolt it through the spindle to keep it pressed against the fresh turned surface.

The last step is using a fine light feed face the centred side, you will leave a small unfinished section in the centre, this can be removed with a file if need be. You should not need a dog if the workpiece is a reasonable diameter. friction will hold it

The method also gives limited access to the back and all the side of the disk. Probably enough to do a riser in one sitting. if you plan it well.

Regards
John

Thread: Mystery Object ... This one has me beat
12/09/2020 07:32:31

Yes I know this is a segway... assuming the part is a survey mark

It's Been a while since I posted on this forum. The past couple of years have been very hectic.
Next Wednesday we pick up the keys to a new house. After 38 years in one house we are moving to the hills about a 45 minute drive from Melbourne.

I wish to build a new shed and in order to do so the council requires survey, I was on site when this was done in order to discuss the location. And yes the EPOXY CNC mill post on this forum will continue when the shed to house it is built.

A Land survey starts not at your property but at the known reference points in the area. One of those points was in a council field nearby, about a foot below the grass! Using the very accurate GPS station that surveyors use he had no problem locating it. The surveyor told me that there are many of these hidden reference marks around the city. The importance of the mark determines how it is founded, the more important ones may sit on hidden but massive concrete foundations.

Thread: Mechanisms in modern engineering design Artobolevsky
14/01/2020 12:50:44

Hi David George.

If the mill was running I would have shown it here.
My posts re the mill are up to date.
Alas it has had to just sit there reminding me. Hopefully I can get back on it soon.

Regards
John

14/01/2020 05:40:39

Hi All
Yes I know I have not been around here much.
2019 was a pretty tough year, a high workload and a fair smattering of other issues.

Anyway back to the topic. There was a time when elaborate mechanisms were time consuming to build and therefore costly. Creating complex shaped parts has now become a very much automated process. From CNC laser and plasma cutting, CNC punch pressing, CNC metal machining machining to microns if necessary, all created with CAD CAM Design.

There is a shortage of contemporary published books on Mechanisms. And those that are published tend to feature reprints of older authors.

Those old books may be more relevant to today's engineering needs than you think.

Regards
John

Edited By John McNamara on 14/01/2020 05:41:00

Thread: MSMEE Exhibition Melbourne Video
07/10/2019 07:28:53

Hi All
Link to a well prepared video of the Expedition Prepared By Arron Powter.

**LINK**

Regards
John

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