Member postings for Nigel Graham 2

I'm a bit puzzled by the small holes in the side of the cylinder in the sketch. They make the device look more like a simple pressure-regulator.

I can understand a piston-type gauge working by graduations on the rod protruding from the top though.

However, it is normal practice to give the gauge or sensor some protection from the hot steam by a U-bend in the tube from boiler to gauge. Often called a "syphon" though it is not really a syphon, it becomes partly filled with water so the gauge feels only air at the boiler pressure.

You could fit a filter in the line, or better for appearance, make it to screw into the tank bush so the gauze is inside the tank. The latter having the advantages of being hidden and taking no space around the loco, while still reasonably accessible for cleaning.

If the tank is of brass, the usual for smaller scale locomotives, it does not need internal paint; and as Baz found with his, it can create more trouble than it solves.

Jason -

I had no great problem making the cavity in the slice like in your picture; maybe not in the most efficient way but it did work.

What I was unable to do, was stick the two slices together.

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Just looked, Dave -

Yes I see the sketch and model mirror types' difference.

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I think I see what you mean, Nick.

I'd envisaged that making the cavity on the complete block would have to done rather like sinking a blind screw-hole, from an outline circle on the face to be "drilled". I can do that as it is a nice simple cylinder, but this shape would not have worked like that. Or might but horrendously awkwardly.

I did not know you can Extrude Cut the middle of a solid. I had only known it as digging in from an external surface, like the drilled screw-hole.

Though also I don't know how to place an auxiliary plane within a figure, then using it. I tried that first step, experimenting with an existing model, but without success.

"dodgy thinking" ? Aye, it's called ignorance, inexperience and confusion. Plus being very slow to learn anything (that's always been so).

Not as much as I should have done!

Mowed the hay-meadow (allegedly a lawn).

A little work on the steam-wagon, then moved it off the outside bench it has occupied for some three weeks, back into the workshop. Accidentally knocked the water-tank filler on the door-frame, distorting it.

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Good deed for the day:

My washing-line post cleat is a short length of half-inch steel tube pressed flat in the centre section and bent to a sort of shallow U-shape, and pop-rivetted to the steel pole.

I noticed this morning a solitary bee building a nest in the down-pointing section. She would fly away somewhere and return with a fragment of freshly-cut leaf to carry up into the tube and secure by however they do that.

The top of the tube was open too, and despite the near-closure of the mid-section, rain-water would run down into the nest. Can't have that!

Ferreting around the kitchen and bathroom soon produced a plastic bottle-top that clipped neatly onto the tube top.

I like my garden's bees - and many other invertebrates. Well, perhaps not the snails devouring my bean plants. I chuck them over the wall into the overgrown garden of the empty house next door.

The bees though, and the butterflies, the spiders, wasps and woodlice, a different matter. So I hope my leaf-cutter bee approves of the new roof!

How "good"?

Like any other human construction; it's as good as it is designed and made to be, so may be brilliant for its intended use... but then you've to consider the 'oomans using it.

That's not buried. It says the same thing but in more technical language

Aha! Very likely the root of the problem!

He's probably letting the die hit the shoulder with enough force to at least distort the thread there, enough to start stripping the thread on the way back. Especially as Martin suggests, the die then has to fight its way along a thread choked with chips.

Using a die or tap under power needs great care in setting, slow speed and switching off well before the tool hits the limit. It is much safer to isolate the machine, disconnect or slacken the belt if possible (to make the next bit easier) and rotate the lathe by hand. By the spindle if the chuck is screwed on.

I do reverse the tool from a lengthy thread under power, but at low speed, and after brushing all the swarf off. Unless using a slotted die-holder in the tailstock I also gently help the tailstock back by hand so the new thread is not doing that all alone.

Quite often I do use a conventional die-holder but use the tailstock chuck or a bit of rod held in that, as a gentle pressure-pad to keep the die square to the work.

So to sum up from all:

Verify the work diameter and roundness, and faced with a small chamfer or step to help the die onto the bar.

Set the die correctly in an appropriate holder, with the grub-screw into the split and the others just engaging their dimples.

Ensure the die meets the work squarely

Take the cut slowly and gently, rotating the spindle by hand. Back off at intervals to brush off the chips.

Do not let hit the die ram the shoulder. Just ease it gently to the stop point.

Brush the work clean before running the die back off.

Cut brass dry but for other materials, use an appropriate lubricant.

Ahem! Coughs politely. Now then, gentlemen...

I do like that worm-drive tool - gives accuracy and good looks!

If a lever-action ball-turner produces eggs and acorns when not centred accurately, might that be an advantage in some work, by appropriate setting?

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(There is, by the way, a method for milling ball-ends, using a boring-head or fly-cutter and rotating the work on a rotary-table or dividing-head with its axis suitably inclined on a plane parallel to the machine table; but I don't know the necessary geometry for the required diameter and angular extent.)

He might have been unlucky and bought under-par dies, but I suggest he measures the stock metal in several places and in more than one plane.

The alloy might be fine for the work, but slightly over-size or irregular, forcing the die to work as a stripping-tool rather than thread-cutter.

Skim the surface to a couple or thou or so under-size, to relieve the load on the die and remove any serious out-of-roundness. The tiny reduction in thread flank area, and flattened crest, will not affect its performance.

I assume he using the die opened for the first cut (it might not need a closed repeat); but it may also need more regular reversals to break and clear the swarf.

Sometimes I turn a little spigot on the end, of root diameter and a pitch or two long, using a slightly chamfered or radiused tool, to help the die start.

(I have occasionally seen this in full-size practice, neatly rounded off, projecting above the nut; but it does depend on the designed purpose and appearance.)

I didn't realise you can mirror a 3D Part, but I did use that for the initial 2D sketch.

If I had made it as a single block I could not have formed its internal cavity, with its odd shape and centring problem.

(It resembles closely the 4MT locomotive cross-heads in photo 189 of Doug Hewson's latest LNER B1 episode, in ME. My source castings may have been for a similar loco.)

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I made the ledges as you describe, though my first attempt left thin walls along the outside edge. I had to delete them and make new rectangles extended to reference-lines a set distance from the face of the block.

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No Rectangle menu. Not here! Just Rectangle. I've just opened Alibre and one sketch to see.

No arrow, no drop-down menu.

Resting the cursor on "Rectangle", it says only that it creates a rectangle by opposite corners and dimensions. Right-clicking on it says only "Minimise the ribbon" - a strange thing to do.

I drew a little rectangle away from the main sketch and examined that. I found hovering and left-clicking on it is for editing it. Right-clicking opens a menu partly copying the main tool-bar but saying nothing about placing the figure except by direct co-ordinates.

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I had tried to use the Flip tool. I could not make it work! The whole Constraints tool seemed to lock itself into just one way of working.

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Do we even have the same editions of Alibre? Is yours a more advanced version, with more comprehensive tools and menus? (Mine is 'Atom'.)

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"... worth answering" ? I am very grateful for everyone's help but perhaps I cannot learn advanced techniques such as Assemblies, beyond say, a plain cylindrical bearing-bush in a simple wheel.

If so I can use Alibre only for individual, simple Parts that can be created in one piece with no difficult internal features.

Edited By Nigel Graham 2 on 09/08/2023 09:38:32

Just finished trying to draw that blasted cross-head again.

This time starting as a half-thickness slice with the end cut-outs. The really awkward bit, taking several goes, was making the halves of the guide-bar channels. I doubt I used the most efficient methods but the two copies - front and back - came out as I wanted, complete with the front one's rebate and four screw holes for the cover.

I placed these four little circles on the corners of a temporary rectangle set by dimensions: I still can't see any other way to make polygons concentric with each other. Maybe there isn't.

The basic shape was not centred on that default grid on the screen so I had to set vertical and horizontal reference-lines. They obligingly gave themselves a node just a little way up the vertical one, and very close to the screen node, making placing the big central circle on their intersection a bit tricky.

So far so good, only I could not foresee that when I collected the rear slice Part for Assembling to the front, it would appear inside out and backwards.

Somehow, I turned the back half so its cavity faced the anchored front half as it should, but it was still wrong. Taking the fixed front half as open towards the imaginary crankshaft, the back half pointed to the cylinder so needed rotating 180º around the gudgeon-pin axis, called ' Z ' on the screen.

I tried everything likely I could find, and on all three axes. Nothing worked.

I returned to its Part sketch - even less help there.

Closed Alibre with its four new files: the basic 'X'-shaped half-thickness slice with its guide-bar channel halves, the right front half, the wrong-way-round-both-ways rear half, and the useless Assembly.

Hopeless......

The EC has admitted that, but it says something for the skill of the attackers that their actions were so well hidden.

Is this not both drifting far from the original topic and drifting far too close to the rocks of p*l*t*cs?

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(No name given after 'Thanks' .

Jason -

That is as I was trying to draw the cross-head, cutting the cavity to mid-depth on the half. I was going to add the piston-rod connection after assembling the two parts.

I think the bigger problem I had was not appreciating how the sketch would develop, so not planning how to draw the whole thing.

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Nick -

I have often read this about people whose manual draughting experience makes it harder to learn CAD. I doubt it is true generally, but it could well be true of some. I'd have thought it gives the advantage of knowing engineering drawing as such, but there is the point that most manual drawing is orthographic. You might make a rough freehand, pictorial sketch of the item to start with, but draw it formally in 2D.

Perhaps trying to transfer from one make of CAD to another would be harder.

Having visited it I think I can answer that.

The LaRance turbines are in a row along the bottom of a quite short dam, and consequently almost all of the river flows through them at every low tide. So the reservoir is being flushed at every use.

Also there might not be much sediment in the R. Rance, and the barrage is very close to the sea. So the mud is going into the sea as it would normally, and not washed back and forth by the tides as it is in the Severn Estuary a long way inland.

Regarding the environmental considerations, I don't know when that scheme was built but whether it could be now, for environmental reasons, is another question. You'd have to ask the French Embassy, or EDF!

Thankyou.

Yes, my cross-head is much the same shape as that.

I was trying not to do anything I'd not done before, but could not see how to create the internal cavity except as a hollow in the surface of each of two identical parts. It is not a nice easy shape but has two sides that converge inwards to be tangents on a curved end wall.

Even making that bit was not easy. I could not work out whether you pick the Tangent Constraint then drag the line from the corner to the circle, or the other way round, or what; so when it did work after numerous attempts I had no clear idea what I had done right.

I thought there should be a "Symmetrical Constraint", or something like it, but failed to find one that offered what I wanted: a single line placed centrally across an axis. So I had to resort to very roundabout ways. The little instruction on the command labelled "Symmetric Constraint" is about two separate objects. The nearest alternative, Midline, didn't seem the right choice either.

Then putting the halves together was a nightmare. I had to delete both Parts and re-draw them from scratch to make it work.

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I'm not sure how you meant an assembly of four parts to that stage. It was two parts. I had four drawings, but the first was to generate the two halves, drawings 2 and 3 were the two halves, then drawing 4 was the Assembly of Parts 2 & 3. My comment about four repeats was of the construction to make the corner cut-outs.

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Ady -

I know there is only one basic route, as with any software. I am not trying to "explore" short-cuts that probably don't exist anyway, but trying to use it correctly - or at least as seems to work. Sometimes it takes me so many attempts that I don't know what I did that was finally right.

I doubt I'll ever be able to make more than very simple arrangements of a few simple parts with fine details omitted. Never a 3D CAD GA of an entire machine.

There is another problem with stored hot-water systems: Legionella.

The bacterium for this respiratory disease seems to be able to withstand normal water-treatment enough for individual to find their way from Nature to stored water, where they multiply quite happily at about 40ºC.

Heating the water to 55ºC or above will kill it. Instant, or on-demand, systems that raise the incoming mains water to well above that, kills any stray bacteria, even if we then mix the hot water with more cold: the number of bacteria in the cold water is too low to be a problem.

We become infected not by drinking the germs but by breathing them in with the fine spray and low-temperature vapour from, e.g. showers.

In theory it is possible to contract Legionella disease from waterfall spray but I don't know if this is ever known. There may be too few of the little blighters in the water to attack us.

Tried again over the last few evenings but this time slightly more ambitiously - one of my engine's cross-heads.

It's a locomotive type with the small end in a cavity, so I assumed draw it as two halves then stick them together.

The first attempt went all to rats. One half was facing all the wrong ways and I could not flip it over or align it with the other properly.

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I decided where I might have gone wrong, and the second go succeeded that far.

One face has a large hole, opening into the arcuate end of the internal cavity, and on the drawing it was visibly not quite concentric with the arc, but we can't have everything. Much of the time most of the figures were indicating "position not defined" , as well.

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Then I tried to cut away the ends to form the profile, a sort of portly 'X' shape. That went all to rats too.

I traced the cut-outs on frames of reference-lines, one plotted at each end and made symmetrical about the centre-line by dimensions (must be an easier way).

Then the two halves of the assembly stayed as separate entities so the Extrude Cut tool would work only on one and I could not make it work on the other.

Surely it's not necessary to plot completely the same geometry four times, twice on each half, either.

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By now I had four drawings.

They were the basic rectangular block with the rectangular guide-bar channels and a rebate for the central plug that holds the gudgeon-pin. That was fine. I think. From that base drawing, the two hollowed-out halves; possibly on the correct planes (the first attempt was all over the shop). Finally, the failed assembly.

I might have had the order of creating the drawing all totally wrong: e.g. should have made the 'X' shape on the basic block. The piston-rod spigot was to have been the last operation. Didn't get that far.

Obviously far too difficult !

Gave up.

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Though of a real thing, I did not need draw it except as just a CAD "exercise" .

An expert would draw it in twenty minutes, then easily incorporate it, twice, in a 3D GA of the whole engine, all parts correctly placed and aligned.

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Besides, I have already made the two real cross-heads, from their raw casting pair bought from M.J.Engineering at a model-engineering show. I'd spotted them in the waifs-and-strays tray, and a quick measure at the sales-stand showed they'd do! They look as if intended for a 7-1/4" g. locomotive. I machined them from a directly-orthographic drawing in TurboCAD.

NASA does love to entangle the language, but I must admit "periodic reset" suggests a normal, regular adjustment to correct any drift.

Whatever actually needs doing, the whole thing is a superb achievement.