Member postings for Andrew Johnston

Errr, that's not how the combining cone works. The steam is condensed by the water and the latent heat of evaporation released as the steam condenses goes to heat the water, but it doesn't add to the kinetic energy. The key to understanding the operation of the combining cone is conservation of momentum.

The release of the heat in the steam determines the maximum inlet water temperature at which the injector will work, and is dependent upon the inlet steam pressure.

Andrew

While in theory it is possible to use small cutters at low rpm by reducing feedrate experience says it leads to broken cutters. The problem with manually feeding at a low rate is keeping the feed constant. It's only too easy to go a bit slow or a bit fast over a fraction of a turn. Too slow isn't serious but too fast can easily exceed the chip load for the cutter. Equals ping and a broken cutter. Been there done that.

Andrew

Like this:

It's interesting to note that the tables on my grinders are not constrained, just resting on the ways. So in that sense they're not particularly rigid. Grinding forces are low and accuracy comes from the geometry and linearity of the ways and the runout of the spindle bearings.

I don't think the surface finish on the cones is critical. For the convergent part of the steam cone the shape is unimportant anyway. For the combining cones some turbulence would be good to help mixing. The delivery cone finish isn't too critical as the flow is slowing down.

Back when I was working on racing cars the engine manufacturers spent hours smoothing and polishing the inlet manifolds with die grinders. Then it was discovered that a slightly dimpled surface, that caused some turbulence, was better.

Andrew

I note that a few people don't temper after hardening. That might imply that tempering isn't necessary. But it could also mean that the hardening didn't work properly. In that case tempering will have little or no effect.

Andrew

Nowt to say that's it's gauge plate at all. It might meet BS specs, but who's to say that means British Standards, might be bullsit spec.

Andrew

Try a CCGT insert, cut dry and the secret to machining plastic is slowish speed and high feedrates. In theory you can whizz through plastic, but the big problem is it melts - equals a right mess.

Andrew

You're probably not getting it hard enough in the first place. I heat gauge plate to 800°C before hardening. I've got an electric furnace so i don't need to judge colour. It's recommended to soak for 30 minutes per inch of thickness, so 10 minutes is about right. Quenching in engine oil is a crap shoot, and I suspect it's the crap that is doing the shooting. I quench in brine and to get full hardness, >65Rc, you need to agitate vigorously during quench. Even a small hesitation results in a hardness of 40Rc or so, if you're lucky. I'd temper at 180°C and leave the tool to soak for at least an hour at tempering temperature. After tempering I quench in brine, but you don't need to agiatate as much.

Not quenching properly leads to a significant loss of hardness, as measured by these:

Andrew

Wow, that's quite a bit more than I pay in total per month for electricity. Obviously I'm not using my machine tools enough!

Andrew

I'd add a gentle warning about converting to metric. When I started on my 4" scale traction engine I had ambitions to convert imperial to metric, ie, metric material rather than just converting imperial values to millimetres. But it became clear very quickly that this would incur a huge amount of modelling work to ensure that everything fitted together, especially with items like gears and the valve gear. I then decided to simply change the threads to metric. This didn't work either; somehow M6 just doesn't look like 1/4" BSF. I use metric threads for internal assemblies where commercial SHCS won't be seen. But externally I've stuck with 1/4" BSF and made all my own nuts, bolts and studs to get the right look.

The drawings for my engine are poor, so I am modelling the engine in 3D CAD; main reasons are:

1. To account for metric material; this is mostly for sheet and plate which now seems to be available only in metric
2. To ensure that the assemblies fit together and work as intended - adding up different dimensions on the same drawing gave different answers for the distance between the crankshaft bearings; which one was correct?
3. Modifying the design to make assemblies nearer to prototype, or in an attempt to make them work - for instance the governor could never work as originally designed

Good luck!

Andrew

That's interesting; a look back at several pages of your previous posts shows that you clearly don't fall into the MTM demographic. There's no discernable evidence of modelling or engineering in them.

Andrew

Well, that's an "interesting" first post by Fred. All guns blazing, pity he seems to have shot himself in the foot. That's slapstick comedy for you, or it's his Chinese/Scottish ancestry.

Andrew

Edited By Andrew Johnston on 10/06/2019 10:57:40

A good few years back we designed a battery pack for a hybrid that utilised a lead acid battery with carbon in the cathode (I think) which essentially created a part battery part supercapacitor. See this research paper, the electronics and battery I designed are on the right in Figure 5:

**LINK**

Separate supercapacitors are currently very good at accepting and delivering charge but the problem is limited voltage. Stacking them in series quickly reduces the capacitance.

I've just thrown in my job so I'll be back down to less than 6000 miles a year driving. I cycle to work in the summer (5 miles each way). Over the years it's changed from a pleasant ride in the country to busy roads and now just plain bl**dy dangerous. Due to road "improvements" there are now long queues of cars in the other direction to me. Cars coming my way can't be bothered to wait so squeeze through leaving a few inches between them and me.

Can't say I've been very successful growing vegetables but I do grow a significant amount of fruit. Economically it's daft to grow, say, carrots when I can buy a large bag for less than a pound. But have you seen the price of rhubarb? Not to mention blueberries and raspberries! I'd rather grow my own along with gooseberries and currants whcih you never see in the shops.

Andrew

That's appropriate.

Welcome to the forum. I'd be interested in more details of the micro-milling setup. Currently I've got a 24000 rpm spindle, but it's mounted on a conventional CNC mill. I've used it with 0.8mm cutters but haven't had the nerve to go smaller.

Andrew

Been there, done that.

Back in the early 1990s a company I was with worked with PG&E and CARB on the idea of using electric vehicles on charge at home or work to meet daytime peak requirements and then charge back up at night. One of the issues with US power distribution is that it tends to be radial rather than a true grid, so power limitations of a specific feeder are important.

We also used our vehicle inverter as a power factor corrector, with the batteries replaced with capacitors, as the current recirculates rather than needing to charge. In the UK larger companies pay the price for poor power factor. I thought this would catch on quicker than pure electric vehicles, but sadly it didn't.

Andrew

PG&E - Pacific Gas & Electric

CARB - California Air Resources Board

It seems a lot of work for possibly not much gain. I'd be inclined to do the maths to work out the saving before committing to metal. It might be better, and easier, to remove excess material from the original cylinder block. At least the cast iron cylinder removes potential problems due to differential expansion. The coefficient for aluminium is more than twice that of steel.

Andrew

Therein lies part of the problem. When drawing in CAD the method of manufacture of the part should be uppermost in the mind. There are three ways to create a crankshaft:

1. Create a single part making cylinders and webs in sequence until the crankshaft exists as a single part
2. Create individual parts such as cylinders and webs and then put them together in an assembly
3. Start with an oversize block and subtract to create the crankshaft

Method 1 would be used if the crankshaft was to be machined from solid, so it is one part and a 2D drawing can be created for the part. Method 2 would be used if the crankshaft is to be built up; 2D drawings of each part can be simply made. Method 3 is similar to 1, but seems a rather odd way to do it.

Andrew

Drill Service sell ordinary twist drills with thru hole coolant down to 1mm diameter. I understand that thru coolant tooling needs high pressure to be really effective, hundreds or thousands of psi.

Andrew

Hi Chris, welcome to the forum. As a professional draughtsman you'll be able to give us chapter and verse on the 2D versus 3D "discussions" that arise on a regular basis.

Andrew

Ooopsie, my mistake. I'll modify my previous post in the light of the stated conventional machines and not pushing them. You don't need coolant as nothing will be getting hot enough to need it.

Information on coolants and lubrication is out there, but you'll need to be reading professional literature. Start with Machinery's Handbook.

Andrew

How deep is the slot? A slitting saw with 140 teeth is very fine and not suited to deep slots as there's nowhere for the swarf to go.

Andrew