Little Wonder

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philipy
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Re: Little Wonder

Post by philipy » Thu Apr 06, 2023 7:42 pm

By heck Trevor that is an amazing bit of drawing, let alone actually making it all.

The wheelsets look fantastic, btw.
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Re: Little Wonder

Post by ge_rik » Fri Apr 07, 2023 7:48 am

I am totally envious of your skills and equipment. Those wheels look amazing.

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Re: Little Wonder

Post by FWLR » Sat Apr 08, 2023 9:12 am

Brilliant..... :salute:

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Re: Little Wonder

Post by Trevor Thompson » Sun Apr 09, 2023 2:25 pm

I am fitting the first bogie with its axle boxes. Since I am going to spring the axles (not that the springs will bear the locos weight, but merely keep the wheels on the rail when the loco passes a dip in the track) I want to make the surface they run against a bit wider than the steel chassis. So the exlebox:
Screenshot 2023-04-06 at 19.04.39.png
Screenshot 2023-04-06 at 19.04.39.png (45.5 KiB) Viewed 5537 times
and the horn guide:
Screenshot 2023-04-06 at 19.02.43.png
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The first 4 axleboxes and horn guides have been milled, and 2 of them fitted:
IMG_2898.JPG
IMG_2898.JPG (2.2 MiB) Viewed 5537 times
I had intended to hold the guides with screws, but it seemed like a good idea to soft solder them on. The finished wheel sets will be removable and held in place by "keeper plates" screwed up into the horn guides:
IMG_2897.JPG
IMG_2897.JPG (2.1 MiB) Viewed 5536 times
Trevor

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Re: Little Wonder

Post by -steves- » Mon Apr 10, 2023 11:55 am

16mm model engineering at it's best, a big well done so far for everything. All well outside of my humble capabilities, but it's awesome to see it all happening.

:woo

Re the wheel blanks. I followed some help from an old loco build I found once in a magazine, which I found online, these were for the Kerr Stuart Brazil, but all the same principles apply.

It's written by Keith Bucklitch and they can be found in the steammodelloco16mm.groups.io under their files section. Not sure if it's ok to post them here as I think you need to be in the group to read it, they are PDF documents. Don't get me wrong, clearly you don't need this Trevor, but if someone is reading and wants to give it a go, then it may be of help.

P.S. A lay down metal bandsaw has saved my arms and shoulders, many, many many times over and I would be lost without it. :dontknow:
The buck stops here .......

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Re: Little Wonder

Post by Keith S » Tue Apr 11, 2023 1:43 am

I really like how you've a set of rails on part of your workbench. It looks like a real erecting shop!

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Re: Little Wonder

Post by Trevor Thompson » Tue Apr 11, 2023 9:31 am

Keith S wrote: โ†‘Tue Apr 11, 2023 1:43 am I really like how you've a set of rails on part of your workbench. It looks like a real erecting shop!
Yes it can be really useful. It was intended as a place to test live steam locos before taking them up to the railway. It incorporates a number of curves set to the minimum radius on the railway.

However I do seem to start so many projects that it ends up with all the unfinished things cluttering it up.

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Re: Little Wonder

Post by Trevor Thompson » Wed Apr 12, 2023 5:36 pm

After a concerted effort to get all of the suspension made and assembled I have a rolling chassis:
IMG_2899.JPG
IMG_2899.JPG (2.12 MiB) Viewed 5478 times
The next stage is to make the eccentrics and fit them to the axles. Before I can do that though I need to be sure about how the valve gear is going to work out. So some planning. The valve gear is a variation on Stephenson's Valve Gear where the expansion link is held still and the gear selected by moving the radius arm up and down instead. The Stephenson gear I used on Linda does get close to digging into the ballast, and just misses the boiler cladding, depending which gear it is in. Holding the expansion link still will avoid this.

A diagram to illustrate:
Screenshot 2023-04-12 at 16.41.36.png
Screenshot 2023-04-12 at 16.41.36.png (34.66 KiB) Viewed 5478 times
The axle with its eccentrics is on the left, with the eccentric followers and their shafts joining to the expansion link in the centre. I have drawn the expansion link as a straight link, rather than it following the radius of the radius arm. On the right is the front axle, with a bent radius arm reaching over the top of the front axle. I have drawn the radius arm twice, once in ahead and once in reverse, so I can be sure that it is sufficiently "bent" to always clear the front axle. The valve rod would be on the extreme left if I had included it in the drawing.

As with redesigning the valve gear for K1 I have referred to Don Ashton's book on designing valve gear - and of course the experience of designing Linda's Stephenson's valve gear.

I have learnt that the positioning of the suspension of the expansion link is critical. The length of the suspension link, and the position where it is suspended from are important. The book describes calculating these or or alternatively drawing it out to scale. I couldn't work out where that was leading so I made the electronic equivalent of a scale drawing in Sketchup. I just experimented with lengthening and shortening the suspension link to see what happened, and manually moving all of the links to see what changed. A couplings of evenings later I had this sketch:
Screenshot 2023-04-12 at 17.38.53.png
Screenshot 2023-04-12 at 17.38.53.png (38.7 KiB) Viewed 5475 times
Honestly it's not as bad as it looks at first sight. Just look at the top row for now. On the left is the valve sitting on top of the ports. On the right is a "Y" shaped "thing" which represents the offset of the eccentrics and the crank pin. The crank pin is sitting horezontaly to the right and the two eccentric centres are one over the other offset to the left of the axle centre. That offset is related to the "lap" . It just offsets the valve opening to make the valve open at top dead centre. In the middle is the expansion link as a skeleton and a rectangular box representing the suspension link. In this gear the suspension link is attached to the expansion link at the bottom. The radius arm is shown attached so far down from the top of the expansion link, and for the other gear the same amount from the bottom.

The top two diagrams show the linkage at top and bottom dead centre - the point is to make sure that the valve is just about to open - but that it hasn't already opened which would make it go backwards. I have drawn a radius arm in both forward and reverse positions and in these top two pictures you can see that the two valves are near enough one on top of the other.

The bottom two diagrams are to show that the valve opens the same amount in forward and reverse, and the same amount at when the crankpin is at the top and bottom of its travel. Again two radius arms and two valves, but the valves are overlapping in these diagrams. A bit less obvious but if you compare the valve in one of the top diagrams perhaps you can see that the valve is opening the same amount in ahead as in reverse - that is the important bit.

Having changed the length of the suspension arm, and moved where it pivots I think that the diagram now shows it "as good as I am going to get it". So I can measure the length of the suspension link and measure where it has to be suspended from - so that I can add extra holes into the chassis for a suspension rod. The suspension point needs to be 10.4mm above the line between the axle centres, and 40.4mm from the inner axle.

I think I can make the eccentrics next. However its time to give this a rest and work on other projects for a while.

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Re: Little Wonder

Post by Trevor Thompson » Mon Jul 31, 2023 3:31 pm

A couple of spare hours and I have the first part of the valve gear created. This is what I am making:
Screenshot 2023-07-31 at 15.15.22.png
Screenshot 2023-07-31 at 15.15.22.png (101.53 KiB) Viewed 5137 times
It shows the 4 eccentrics which drive the valve gear. There is a carrier and 2 "cams" or eccentrics mounted on that carrier, in turn mounted on the axle. There are of course 2 of these side by side one for each cylinder. I have made the carrier with a boss to take a grub screw which will secure it to the axle so that it can be adjusted. Two eccentrics fit onto each carrier, and will be silver soldered into the correct orientation. I hope I can silver solder them without getting solder where I don't want it. I will have to make a jig to set the eccentrics at the correct angle to each other before soldering.

So here are the components made:
IMG_3160.jpeg
IMG_3160.jpeg (1.25 MiB) Viewed 5137 times
So the next job will be to drill and tap M2 for the grub screws, make the jig, and fit and solder them together.

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Re: Little Wonder

Post by ge_rik » Sun Aug 13, 2023 8:15 am

Strewth! 6 decimal places of millimetre precision!? Even with my 3D prints I'm happy with a 0.5mm tolerance..... :lol:

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Re: Little Wonder

Post by Trevor Thompson » Sun Aug 13, 2023 5:45 pm

Just laziness - I could (and and perhaps should) alter the number of decimal places displayed!

I am happy with 0.2mm precision on something like this which is a tight fit into the available space.That is of course only attemptable because of the digital readout.

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Re: Little Wonder

Post by Old Man Aaron » Tue Aug 15, 2023 12:00 pm

Beautiful work as always. I machined a pair of bronze eccentrics for an Accy Ruby some years back. Simple one-piece objects - you're braver than I to jig up and solder yours! I'm sure they'll come up to your usual standard.
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Re: Little Wonder

Post by Trevor Thompson » Thu Dec 28, 2023 6:03 pm

I have finally got back to this after a couple of months absence doing other things.

So I have set the eccentrics on to their carriers:
IMG_3617.jpeg
IMG_3617.jpeg (2.57 MiB) Viewed 3072 times
The carrier is 15mm diameter and the eccentrics are 16mm diameter. They were assembled using bearing lock and quickly pressed against a block of brass. By holding the carrier flat on the bench while pressing the three components against the brass, the eccentrics were locked in a position which will mean that the valve opens just after the piston has reached the end of its travel - in both ahead and reverse. When the motion is made and all connected each pair of eccentrics can be adjusted so that the valve timing is the same in both directions.

I thought I was going to silver solder the eccentrics, but the lock tight method seemed easier. Rather than rely on lock tight alone I have bored through all three components and fitted a clockmakers taper pin. I fixed that with bearing lock as well. So one set pinned, and the other pinned and filed up:
IMG_3619.jpeg
IMG_3619.jpeg (2.01 MiB) Viewed 3072 times
The eccentrics mounted on the axle, and all fitted to the frames:
IMG_3618.jpeg
IMG_3618.jpeg (2.25 MiB) Viewed 3072 times
Both bogies are in the same state - both have the eccentrics and axles in place. These two inboard wheels on each bogie are fixed to their axles with bearing lock, and quartered by eye. When the lock tight has cured I will drill and pin these wheels in place. The other axle can't have its wheels mounted permanently until the coupling rods are fitted.

So the eccentric straps are next, and I am working towards assembled valves and valve gear.

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Re: Little Wonder

Post by Old Man Aaron » Fri Dec 29, 2023 12:53 pm

Suitably fiddly. :lol:
They're really packed in there, between those axleboxes.
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Re: Little Wonder

Post by philipy » Fri Dec 29, 2023 4:17 pm

Old Man Aaron wrote: โ†‘Fri Dec 29, 2023 12:53 pm Suitably fiddly. :lol:
They're really packed in there, between those axleboxes.
Watchmaking comes to mind! :lol:
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Re: Little Wonder

Post by Trevor Thompson » Tue Jan 09, 2024 7:18 pm

While I was waiting for the materials to make the valve gear from I started working on the valves:
IMG_3620.jpeg
IMG_3620.jpeg (2.22 MiB) Viewed 2396 times
Milling the slots into one of the 4 valves. A 2 mm wide slot to take a 2mm diameter valve rod, and one at 90 degrees to take the threaded strip which moves the valve.

4 valve operating rods with their fittings to take the valve gear:

IMG_3622.jpeg
IMG_3622.jpeg (1.88 MiB) Viewed 2396 times
I have yet to make the strip which actually drives the valve. The fitting, locknut, and rod are tapped M2 (right hand thread). The valve end of the rod , and its strip are tapped M2 ( Left hand thread). The idea is that the adjustment of the valve can be done mainly turning the end fitting around, and then connecting it to the valve gear. The fine adjustment can then be done by slackening the locknut and turning the valve rod. With the opposing handed threads turning the rod will move the valve in and out.

and finally test fitting the first valve:
IMG_3621.jpeg
IMG_3621.jpeg (1.96 MiB) Viewed 2396 times
Well it all seems to fit, so on to actually assembling the pistons, cylinders and valves with gaskets before going back to the valve gear. It will be satisfying to see compressed air move the pistons in and out as the valves are moved.

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Re: Little Wonder

Post by -steves- » Wed Jan 10, 2024 12:12 pm

Great work as always Trevor, still loving the "live" photos :thumbup:
The buck stops here .......

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Re: Little Wonder

Post by Trevor Thompson » Fri Jan 12, 2024 4:51 pm

The first bogie now has its valves fitted permanently (hopefully!). Each cylinder has its end covers fitted using a lock tight gasket fluid. The cylinders are also fixed to the frame using the same sealant. The valve stems are in roughly the correct setting, and it is all assembled:
IMG_3629.jpeg
IMG_3629.jpeg (2.31 MiB) Viewed 2163 times
The cover has been fitted with a paper gasket, and the holes drilled out for fixing it in place.

The steam intake is a third fitting which is just visible below the valve guides in both photos. The exhaust will be made from 3mm copper pipe and will exit the cylinders at the top between the frames before being joined together. The details of how that will work will be clearer (to me) once the boiler is made. So the front end assembled and steam tight:
IMG_3634.jpeg
IMG_3634.jpeg (2.3 MiB) Viewed 2161 times
I have tried it out on 25 psi with the air line, and I can confirm that each piston shoots in and out as the appropriate valve is moved.It is reassuring to see that the valve stems clear the front axle! So, apart from having lost a couple of half made automatic valves, I can repeat all of this on the second bogie.

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Re: Little Wonder

Post by Trevor Thompson » Tue Jan 16, 2024 6:46 pm

Today I started to make the expansion links. I am making them out of 3mm thick mild steel, so that involved coolant oil, and one of my rotary tables. This one has a flat bed which I can fix metal strips onto. The metal was held down so that the centre of the strip was 42.5mm from the centre of the table. That gives the expansion link the correct radius.

The drawing:
Screenshot 2024-01-16 at 10.16.18.png
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Having set up the table so that the centre of the milling head was lined up with the centre of the rotary table, I just had to move the X axis the 42.5mm to set the radius. All the milling and drilling can then be controlled by rotating the table. Milling the slot:
IMG_3640.jpeg
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The finished slot and the holes to take the eccentric rods. I then milled out the outline of the link.

IMG_3642 2.jpeg
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I have diverged slightly from the drawing - in that the slot is 3mm wide not 2mm wide - I think that will make it easier to make the block which slides up and down in the slot.

The first expansion link finished:
IMG_3643.jpeg
IMG_3643.jpeg (1.86 MiB) Viewed 1849 times
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Re: Little Wonder

Post by Trevor Thompson » Tue Jan 23, 2024 7:42 pm

I now have 4 completed expansion links:
IMG_3649.jpeg
IMG_3649.jpeg (2.27 MiB) Viewed 1631 times
and I have started on the eccentric straps. This is what I am trying to create:
Screenshot 2024-01-23 at 18.51.49.png
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and a detail:
Screenshot 2024-01-23 at 18.48.13.png
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I started off hacksawing out 8 off 25mm square blanks, and drilling an 8mm diameter hole into each of them. That enabled me to mount two of them at a time in one of the mandrills I use for making wheels:
IMG_3650.jpeg
IMG_3650.jpeg (2.32 MiB) Viewed 1631 times
The next task is to turn the outside diameter down to 24mm diameter. I hope to then be able to mill out the slots and drill and tap the holes (10BA) which will hold the two halves of the eccentric strap together. Then I plan to saw the two halves apart, clean up the sawcut and bolt the halves together. Hopefully I can then hold each strap in the chuck while I turn the inside diameter to size.We will see if it works! Then I have to repeat it 7 more times.

Turning the outside diameter to size:
IMG_3651.jpeg
IMG_3651.jpeg (2.26 MiB) Viewed 1631 times
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