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Member postings for John Olsen

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

Thread: A question about traction.
29/10/2021 00:29:48

I'm not too convinced about that. Locos with small wheels will often have a higher tractive effort, but that is because the effective gearing is lower, like being in first gear in a car. Like the car, they also can't go as fast.

The actual grip between the wheels and track depends mostly on the coefficient of friction and the weight on the wheel. The civil engineering department gets upset if you increase the weight on any one axle too much, so to get more tractive effort you need to add more axles. Eventually the civil engineers will start to complain about the length of your fixed wheel base spreading the track on curves. so to keep the wheel base reasonable you make the wheels smaller, which will tend to limit the top speed. So hence express locos with fewer but larger wheels, and goods locos with many smaller wheels.


Thread: Is it possible to machine a lathe more accurate than the one you machine it on? If so, how?
29/10/2021 00:17:57

Maybe worth mentioning a couple of techniques.

Accurate flats and straight edges can be made by making three at a time. if you hand scrape a single flat, you need another to compare it to. (using engineers blue.) If you scrape two, they end up matching but not necessarily flat. If you do three, and keep comparing A to B, B to C, and A to C, then eventually they all end up flat. This also applies to straight edges, so you can make an accurate straight bed with enough patience.

Then we will want a leadscrew. One technique is to draw some wire through a diamond die, which can give you a nice long length of wire of a consistent diameter. This is then wound around a mandrel which you have turned parallel. As implied by others above, this can be done by hand turning between centres. Then wind the wire around the long mandrel, and now you have a leadscrew. Coat it with some graphite and cast a lead nut around this, then use it to make a master leadscrew quick before you wear it out. As mentioned above, you can also correct errors in a leadscrew if you have the means to determine what they are.

If you can get hold of the Gingery books, they give quite a lot of information about how you can make a set of machine tools without having access to other machine tools. The problem with using other machine tools to make the new ones is of course that usually the new machine will be smaller than the one you have, when the usual problem we have is that we want a bigger one.

The other useful thing to look at is the Handmaiden series in ME by Tubal Cain, where he built a stationary steam engine using nothing but hand tools.



Thread: gas burners
20/10/2021 21:08:08

Wikipedia has a table of US number drill sizes and gives 0.032 for #67. Wikipedia link

I believe that US wire gauge sizes differ slightly from British Standard, I'm not sure if that applies to drill gauge sizes or not.

I've never quite seen the point of assigning arbitrary numbers to designate sizes that can be perfectly well specified with a linear dimension. Maybe it is a deliberate attempt to make things more arcane and complicated?



Thread: Oxy propane welding kit
20/10/2021 03:41:56

The end product from making acetylene with calcium carbide is calcium hydroxide. This is pretty harmless stuff and occurs naturally anyway. It is used in food preparation (E526)


Thread: mamod
11/10/2021 09:20:54

Mamod boilers are brass and dezincification does not seem to be a problem.

How bad is the dent? Is it worth worrying about? They run at a pretty low pressure, and provided they are used with the standard burner are pretty much inherently safe, eg if the safety valve was blocked off the burner would be unable to build up enough pressure to burst the boiler. Also the burner would be unable to heat the boiler up to a temperature that would soften the joints or damage the material even if bone dry. They are below the size where there is any legal requirements in most countries.


Thread: Hello from Brisbane, Australia
11/10/2021 06:04:48

Most of the Weir pumps had Monel metal piston rods. I have about four inches cut from one that had been quite badly seized. I also have a copy of their catalogue somewhere, I wonder where that is?


Thread: SKY abandoning their satellite customers
11/10/2021 05:52:24

I don't know how they are installing fibre in the UK, but here in NZ it only required two small holes on my property, one right by the house where the fibre comes out of the ground, and one in the lawn area where they were making a turn. Both about a foot square. The fibre was put into the ground using a machine to thrust from one end, and one of the guys used a detector device so that he could tell where it was going and correct the angle from the thruster machine. So no real disturbance to any of the garden, not that ours is especially fancy, but there are trees and shrubs. It would be 30 or 40 metres from the front fence to where the fibre enters the house.

Satellite was good for getting connected (Internationally) back in the day, but has some limitations. There are only so many spots in the geostationary orbit, and the delay is long enough that you don't want a double hop. The bandwidth is limited by the range of frequencies that pass through the atmosphere easily. The delay is not so much of a problem for TV, but can be for Internet connections. So hence lots of long distance optical fibres have been and are being laid, since you can get plenty of bandwidth, and increasing the number of fibres in a cable does not greatly add to the cost of the installation. This is also why there is interest in constellations of low orbit satellites, since it pretty much eliminates the delay, at the cost of requiring handover between satellites at frequent intervals.

For local connections, fibre has a lot of advantages, not least bandwidth but also being less prone to getting stolen and less problem with corrosion.


Thread: Antikythera Mechanism
08/10/2021 06:18:58

Well, I find the study of this sort of thing fascinating, even if we may never know the full details of this device. It does give us a glimpse of the sort of things that the ancients were actually capable of. The existence of this one device obviously implies the existence of a workshop capable of making it, and although one does not expect them to have been mass produced, there were quite likely more than one made, as well as possibly simpler variants when the ideas were being developed. The problem of course is that metals does not always survive well, both due to corrosion and also due to the fact that it is very recycleable.

As well as this, we know about Hero's simple steam turbine. I wonder what else they might have been playing with?


Thread: Motorcycle General Discussion
08/10/2021 06:04:26

A gyroscope will move at right angles to the force applied. They don't really resist movement, they just try to move at right angles to the force applied. So if you have a gyroscope with a vertical axis and you push the top away from you, it will actually move to the right or left. Which way will depend on the way the gyroscope is turning. So now if you have two gyroscopes of the same mass and rotational speed on the same axis, one turning clockwise and the other turning anticlockwise, when you push away, one will want to move right and the other will want to move left, both with the same force, so they will cancel. The only remaining resistance to movement will now come from the total inertia of the system.

You do generally move the bars to initiate the lean, but it is only by a very small amount. If you think about the fact that you might only want to move the track of the wheels across by a foot or so, and you might be traveling at fifty feet per second or so, you can see that a very small angle on the handlebars would shift the track of the wheels sideways by a large distance quite quickly. (It is not too hard to exceed fifty feet per second on a bicycle, let alone on a motorcycle.)

Getting a motorbike or bicycle to lean by shifting weight is one of those things where the tyre contact forces come into play. Shifting your weight to one side makes the tyre contact area with the road change, which introduces forces into the steering. You will I think notice that the control available in this way is very limited compared to what can be achieved with the bars.


08/10/2021 00:34:19

Gyroscopic forces have got very little to do with it all. Bikes have been built with counter rotating flywheels beside each wheel, which can be used to completely cancel any gyroscopic effects. It is still very easy to ride such a bike.

The main factor in balance on a bike is like balancing a broomstick on your hand, except you only have one plane to worry about with the bike. When you are going straight, you move the steering as required to keep the centre of support under the centre of gravity. When you want to turn, you steer to move the centre of support out to one side, then steer so that all the forces balance. So you actually push slightly the "wrong' way to start the turn, then steer slightly with the turn, Then to come out, you steer a little tighter into the turn to get the bike upright again. It doesn't pay to think to hard about this while you do it!

Centrifugal force only exists if you have a rotating frame of reference, what is actually happening is that as you turn you have a centripetal acceleration, which to the rider in his rotating frame of reference appears as if there is a force away from the centre. This is not a real force, it is just things trying to continue in a straight line.

Forces from the tyres also make a difference, that and castor and trail on the front are why a bike can continue for a while with no input from the rider, although it will usually tend to drop into a curve.


Thread: Beginer builds missing articles...
02/10/2021 02:59:50

I have that issue. I will send you a personal message.



Thread: Old gear
18/09/2021 22:22:38

Try it with a magnet first. Obviously if it really is bronze or brass there won't be any suck, however this looks a bit like a couple of gears I have in a drawer. They were spare primary drive gears for some sort of two stroke motorcycle engine that I picked up at a surplus shop. Mine are steel, but as is sometimes done they had been copper plated. This is done selectively to allow nitriding only the surfaces that need to be hard. So the teeth would not have been plated, and would get the hardlayer, while the rest of the material would remain in its normal state. Which is still likely to be fairly tough. The plating typically seems to end up going black, but apparently is enough to stop the nitrogen reaching the steel underneath.

I've seen connecting rods treated the same way, so the eye where the rollers ran on the crankshaft would be hardened while the body of the rod would not.


18/09/2021 11:49:04

DC31K has said exactly what I thought when I saw the pictures. Cutting keyways in shafts was once an important function for shapers, and if you look you will find that some power shapers are built so that you can if necessary feed a shaft right through the machine. One of mine has a forked end on the connection to the ram to permit this, so you could if necessary cut a keyway in the middle of a shaft of any arbitrary length. (You drill a hole at each end to permit the tool to start and finish the cut.) The setup on the shaper pictured above would also permit that.


Thread: How do you make this
18/09/2021 04:36:13

OK, this is not a Stuart. Not that that matters for the questions, and it looks like a nice design.

If the two eccentrics are being made in one piece, then the angle between them would matter, however if as is more usual they are made as two parts, then the angle only matters when you set them up on the shaft, one being set for each direction. Since your eccentrics are supposed to have a groove, there is nothing to stop you having a small grub screw set down inside the groove to bear on the shaft, so each eccentric can be set separately

The hole in the bottom of the strap is for a small screw with a spigot on the end. The thread only goes as far as the thickness of the strap, and the spigot protrudes into the groove on the eccentric strap. This stops the strap working sideways on the eccentric. Some designs make the strap with a groove and the eccentric with a ridge around it, which is more like full size practice and would provide more surface in contact. But that is more tricky to machine, especially in small sizes.


Thread: Unimat Millenium Model.
17/09/2021 06:56:39

I just measured the centre from my early eighties original Unimat 3. It measures as 10.37mm on a metric mike, or .405 on my Moore and Wright. It is parallel, a ground surface, and is an easy slide fit into the headstock or tailstock bore. I would guess that it was originally chosen to be the largest that would fit inside the spindle thread while leaving enough meat for the chucks etc to screw on.

I've never had anything try to jam in either bore. I would have preferred a proper taper, except I would guess that such would reduce the size that can go through the headstock. I guess you can't have everything on such a small lathe, and it has done some good work over the years. I've done between centres turning and also between centres milling for a Stuart double ten crankshaft and it has always done the job.



Thread: Empty Drill Boxes
02/09/2021 12:18:18

Meanwhile I have several empty or mostly empty drill boxes here in NZ. It turns out to be uneconomical to buy the drills to fill them, you can buy a full set in another box cheaper than buying loose drills of the same quality.


Thread: What are the potential hazards of using E10 fuel on classic car seals
02/09/2021 12:15:23

Not long after the 70's fuel crisis we had a talk at uni by a guy who had been researching the possible effects of adding ethanol to petrol. One concern was the effect of the ethanol on the plastic floats in some carburettors. He said that one thing they had found was that the material in a Jaguar carb float was in fact not even suitable for use with ordinary petrol........


Thread: Mounting stuff to a Faceplate
31/08/2021 06:43:57

Figuring out how to hold things can sometimes be a quite major part of the art of machining. Quite often the thinking and planning part takes longer than actually mounting the part, which then takes longer than the actual machining.

I've used sacrificial layers added onto the faceplate quite often. These can be plywood, or if you want a more accurate thickness, a piece of aluminium, which I prefer. They can be held on in various ways, depending on whether or not your faceplate has T slots or through slots. Whatever holds the extra piece on has to either be clear of where the job needs to sit, or flush with the surface, eg using countersunk fasteners. With an aluminium plate, you can tap holes into it to hold the job to it. You do need enough thickness to allow this.

The beauty of mounting things on the faceplate is that it allows jobs that are much closer to the theoretical limits of the machine than chucks do. This is useful for those of us with smaller machines than we would like, which is probably most of us. I was able to bore a three inch bore HP cylinder on my Myford, the furthest out part of the casting was clearing the bed by about an eighth of an inch.



Thread: Tig welder controls not working correctly
29/08/2021 12:09:23

From my long experience of electronics I would say that the magic smoke has escaped from one or more devices inside. I suspect that unless you are very experienced with power electronics you are not going to be able to fix it yourself, so checking with the manufacturer is probably your best bet. The problem with fixing this sort of stuff is that a low level fault can easily destroy a power device, so you come along, spot the obviously blown up power device, and promptly destroy another one because the original fault is still there. Fuses don't operate fast enough to save the devices either.


Thread: Dipping a toe in TIG - what do I need (apart from skill)?
10/08/2021 00:55:01

I'd agree with the bit about having to unlearn reflexes. I still have a tendency to want to pull the electrode away when I finish, when of course the correct thing is to release the button and wait until the gas cuts off.

With DC only you will not be able to do aluminium. The scratch start will be a bit of a limitation too, but I guess better to have a try with what you have rather than spending a lot on new equipment. If anyone is thinking of buying TIG equipment as a learner, I'd suggest that you go for something more than the bare minimum. The features I would suggest you want to have would be HF start, which makes it a lot easier starting the weld, and AC (as well as DC) which means that you can do aluminium. Being able to do aluminium turns out to be a very useful bonus feature that I hadn't really thought about when I got mine. I had been thinking mainly in terms of stainless steel tanks for the boat, which it does really well.

If it doesn't have a gas solenoid you should be able to add one externally. I've seen a video on Youtube where a guy added one to one of those very cheap very small DC welders that you see advertised. Thus turning a DC MMA welder into a simple TIG machine.



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