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Member postings for Bob Mc

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

Thread: Potty overcrank
29/03/2019 18:02:29

And this one.

The very first engine I attempted, gave me a good idea of how to build an engine... not got round to prettying up yet.... but it goes like a mad thing.


Thread: Scrollsaw for the occasional user
12/03/2019 11:52:22

Hi Ian S C ...

Are you saying you have an engine driving that saw! does look as if there is a boiler and a flywheel in the picture.

If that's the case its great if you have actually made and engine to do some serious work, would definitely like to see that running...!


11/03/2019 16:40:59

Hi Ian T...writes...

"Please don't take this as criticism Bob Mc - but I break a lot less blades when I use the saw vertically and just let it drop into the work on the down stroke (e.g. let the saw do the work) etc."

No I certainly won't take it as criticism and I am only glad to hear how others tackle these problems... I will give your method a try out and see if it does the job any better, my only concern is that you say you use this method for brass which is a lot softer than mild steel...nevertheless thanks for your post ... if it works I will give due credit.


11/03/2019 12:17:41

I am with Roy Entwistle on this one, re posting :11.03.2019.

"If you are wanting to cut thin metal occasionally then whats wrong with a piercing saw? If you want to cut thin wood then either a coping saw or a fret saw"


I will say however that the blades are inclined to break very easily because 'hand' control is not steady, but I found a simple way to help save the blades and I have cut 8mm mild steel for at least an half inch length before the blade had had enough.

It doesn't sound much but the alternatives are either drilling bashing and filing or going in for something expensive which could cause the 'Marital' arts to become the 'Martial' arts and the blades come in packs of about 10 and are quite cheap.

The saws do have a tendency to wander which doesn't help in keeping the blade in piece.

Picture shows piercing saw cutting two sandwiched pieces of 4mm mild steel for Mogens Kildes Double Diagonal Engine, the saw frame top rests on an engineers clamp which is inclined to give a guided cut in the right direction.


piercing saw.jpg

Thread: Atlas Sphere Lathe
04/03/2019 12:06:03

Hi Phil...

just seen a very similar lathe on ebay with what looks like a full set of gears... I can make out about 16 in all,

it is listed as an ATLAS 618 LATHE.

I've got one myself but made an electronic gearbox for it.

Hope its of some help....Bob.

Thread: print-offable and laminatable chart
05/02/2019 15:13:54

Micrometer...? dont know

Thread: Last Night's Astro Image
29/01/2019 17:19:11

Mick B1.... you beat me to it.... I don't know that one either..., but due praise to Neil, great pictures taken with a small scope.

Thread: What is this machine?
22/12/2018 09:44:46

John Reese says.....

" There must be quite a few seniors on this forum. I know what a comptometer is but I can't recall actually seeing one and I am 81."

Yes... in my first job at the Equitable and Cooperative Society in 1965... ie The Co-op...I had the pleasure of using one for a full week but not like the one shown in the picture, the one I used had a handle , when you put in the amount to be added you then pulled the handle towards you and this was added to the last total..

As there were quite a few other comptometer operators in the room, mainly young ladies,, wink there was a lot of noise from the little machines, it was difficult to keep your mind on the job .....due to the noise... honest...! I got sacked shortly afterwards....


Thread: How does solder stick ?
08/12/2018 19:58:00

Hi Neil...

you beat me to it...!

Oh goes...!

Yes an accelerating object such as a rocket has thrust from its engines, the occupants are thrust back in their seats which is opposite the acceleration direction... similarly an object on the earths surface is pushed down by gravity and the reaction force of the ground keeps it in place.

For those who may not know of the argument of dispelling centrifugal force, it seems to have arisen as far as I am aware because of the famous (late) Eric Laithwaite lecture in which he stated that the academics will not even say the word 'centrifugal' because they say 'it doesn't exist'...the televised lecture was 'expunged'....

My argument is that there must be two forces in place in order to keep an orbiting object at its distance from the centre of rotation just as the Earth's (centrifugal/centripetal) force due to rotation is kept in orbit because of the Suns gravitational pull.

In fact 'Centripetal' actually means the force directed towards the centre of rotation, so if we have the Earth with the Suns pull + this 'Centripetal' pull we will soon be toast.. and if you look up Centripetal in Wikipedia as far as I can make out this is exactly stated in Wikipedia.. ie that there are two pulls in the same direction....correct me if I am wrong.

So I stand by my original post, that there must be two forces equal and opposite on an object in orbit, whether it be a gravitational force or the force of mechanical restraint...this force must be towards the centre of rotation, whereas a 'Centrifugal' force would be away from the centre and is the reaction to the centripetal force.

....Now my brain hurts...!

08/12/2018 19:20:39

Hi Tim...

It seems that the topic changed from 'How does solder stick' to the physics of gravitational and rotational forces with Dave's (SOD) and others with myself included musings, you are right to bring the thread back to its original theme and I think you are correct in what you say about the 'wetting' idea.

Perhaps my last post should have started another thread but it was in answer to pgk pgk's post...for those who may not know of the argument that only centripetal forces exist I should point out that this is the accepted formal view of physics which I believe was challenged originally by the late Eric Laithwaite who's theories were later discounted by the academics and his televised lecture was 'expunged'.. I think the word was.

I am not going to elaborate on this further as it starts to get quite involved and is not what the topic intended.


08/12/2018 17:04:24

pgk pgk says...

One can then illogically extrapolate that the failure to find a subatomic particle to call the graviton (one of the hopes for the higgs boson/field) is that there is no such thing - there is no gravity any more than there is a centrifugal force (it's centripedal).

I'm only a simple engineer and will stand corrected, but it seems to me that in order for an object to stay in the same place on a rotating plane there must be two forces at work, centripetal and a restraining force , as Mr Newton said that for every force there is an equal and opposite force... What do we call this restraining force..?


Thread: Tool and Cutter Grinder
03/12/2018 19:33:15

I use one of those diamond grinding wheels on my cutter grinder (pic below) but don't use it for sharpening hss cutters .. they are only intended for carbide.

it clogs up and the wheel can't be dressed again...unless someone knows differently..!



Thread: Arduino DRO
28/11/2018 19:43:54

Hi Peter...

I have been thinking about making a wire draw DRO for the y axis on my lathe, as you say commercial units are available but are rather expensive... the rotary encoders on ebay would be suitable if a wire draw mechanism was available with it .

Using the Arduino for the control and readout is the easy part..and after much deliberation as to how to fit some sort of wire draw retractable mechanism it occurred to me that something like a tape measure or retractable dog lead might be the answer but they are not exactly what is required.

I came across a possible solution when I saw for sale a retractable key ring, this is fairly small and has a reasonably good retracting pull, the torque needed for the rotary encoder is very light and the only consideration would be to fit the mechanism to the encoder and to the machine...and it is very cheap.

I haven't got round to doing the job yet...but pictures below show the parts; for my lathe I only need a readout for the cross slide I have bought a normal dro from Chester Machine tools for this which sits in line with the bed and is just where the line of sight with the work is.... anyway see pics below...hope this might be of use...


The x axis readout below.


Rotary encoder.

rotary encoder.jpg

Retractable keyring .

retractable keyring.jpg

Thread: Hi from Australia, Pick a subject for next post
21/11/2018 15:07:41


should have added .... Welcome to forum Kevin..


21/11/2018 13:24:07

Hope this fits in with this thread...

John McNamara says... Greetings from Melbourne OZ

An old mill to a tool grinder. That would be interesting.

I made this tool/cutter grinder using an old flatbed lathe and some other bits I had, the spindle head is from a discarded contact lens making machine and can be moved vertically with the very coarse threaded pillar...similar to the Quorn setup.

The toolpost can be swiveled in x & y axis and rotated about a vertical axis, the whole toolpost assembly is carried on the bed topslide. There is a DTI on the bed to set the amount of grinding so that equal amounts are taken taken off the cutter or drill.

The cutter holder is based on Harold Halls design in his Cutter grinding book and is easily set up for four facet grinding.





Thread: What did you do Today 2018
26/10/2018 19:26:08

Been messing about with Mogens Kildes Double diagonal engine...

Have made most of it in perspex as I hope to use it as a template for cutting the steel frames & cylinders, also trying my idea of wedge shaped cross head guides which saves quite an amount of metal and fixing and the cylinders are fed compressed air through the frames instead of external pipes...hopefully.


18/10/2018 14:34:14

Thanks Neil...

You are making me think now...!


18/10/2018 13:15:45

During a tidy up session I found the jars of brass turnings I had saved over a number of years...and I have quite a lot of brass bits & bobs & offcuts ... was hoping to melt them down and cast something but it seems to me quite a dangerous and involved process... do the scrappers take brass turnings...?


Thread: MEW 273 Bonus Content
10/10/2018 16:57:31

Thanks Emgee...Thanks Neil..

10/10/2018 10:17:17

How do I get to the 'Introducing the Arduino' article as mentioned in MEW 273 ?

Thanks ...Bob.

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