Little Wonder

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Re: Little Wonder

Post by SimonWood » Thu Sep 15, 2022 2:19 pm

This is really starting to take shape. The boiler cradle frames look superb.

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Re: Little Wonder

Post by Trevor Thompson » Fri Sep 16, 2022 9:36 am

I keep going back to it!

All of the cylinders are now shaped and fitted to the frames. You can see the cutaway around the valve face and the hole in the frame through which it fits on the nearest cylinder:
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All of the cutouts for the bolt heads are made, and the cylinder is secured to the frame by 4 bolts. From above the bolts fit from the inside:
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From the bottom they fit from the outside. I had to make cutouts in the bottom of the cylinders to make room for the nut spinner to reach the bolt head:
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And of course all 4 cylinders are now fitted to the frames.

On to the cylinder end covers, piston and rod next, and then drill all of the holes.

Trevor

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Re: Little Wonder

Post by Trevor Thompson » Fri Sep 16, 2022 12:10 pm

Four front cylinder covers, and 4 rear covers:
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The basic shape turned, then milled and drilled in the rotating table. That ensures that the milled faces are perpendicular and centralised. It also makes it easy to ensure that the mounting holes are all 60 degrees apart (and on the same radius).

And now to work on the cylinders one at a time. The first piston is made and in the foreground of this photo:
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As an aside I am finding that having a digital readout has made my work much more accurate. For example I was able to turn the piston blank to a diameter of 11.95mm and find it was a smooth fit in the bore first time. I then turned the groove for the O ring to 9.15mm diameter and 2.0mm width (for an O ring 12mm diameter and 1.5mm cord diameter), just using the readout - no trial and error. The piston with its O ring just fits first time with a nice smooth movement.

Really satisfying!

Trevor

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Re: Little Wonder

Post by FWLR » Thu Sep 29, 2022 8:30 am

I bet it is satisfying Trevor. Your'e doing an awesome job. :salute:
Digital really does make things easier doesn't it. :thumbright:

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Re: Little Wonder

Post by Trevor Thompson » Sat Oct 01, 2022 10:07 am

FWLR wrote: ↑Thu Sep 29, 2022 8:30 am I bet it is satisfying Trevor. Your'e doing an awesome job. :salute:
Digital really does make things easier doesn't it. :thumbright:
Awesome until I made a mistake!

Drilling lots of 1.4mm holes I broke a drill, leaving 6mm of it in the hole.
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So in the photo the hole in the end of the cylinder - the one that is uppermost has the drill end in it. I couldn't get it out with tweezers or messing with dressmaking pins. So I drilled a hole from the side ( you can see it) to break into the place near the tip of the drill and immersed it into the acid pickling tank. It took 10 days for enough of the steel to corrode away and enable me to tap the hole most of the way to the bottom. There is probably a bit left in it - and a hole in the cylinder side to fill, but the cylinder is recovered and usable.

I have finished drilling all of the holes:
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The fresh looking holes in the top photo are for cylinder drain cocks, and are linked to the ends of the cylinders with 0.9mm holes. In both photos you can see where I have tapped and plugged the ends of the steam ways. There is a plug to make for the exhaust steam way you can see on the face facing the photo in the second photo.

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Re: Little Wonder

Post by Trevor Thompson » Sat Oct 01, 2022 10:17 am

The first cylinder is test assembled, and holding the air line on each valve port makes the piston shoot from one end to the other (as it should):
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I have turned up ptfe rod into seals for the piston rod. 4.5mm OD, reamed 3mm ID, and 2.5mm long. An idea I got from Tony Bird a couple of weeks ago. Worth trying - If it doesn't work for me I can easily go back to ptfe tape wrapped around the shaft.

I am not sure how to tackle the cylinder drain cocks. The automatic ones seem temperamental. The trick seems to minimise the distance the ball has to travel to seal the drain hole - but I'm struggling to get consistent results. They work on Linda but not on K1 (at the moment). Back to that at a later date.

Just 3 more cylinders to finish. I'll be careful with the drill in future.

Trevor

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Re: Little Wonder

Post by FWLR » Sun Oct 02, 2022 11:10 am

Easily done, breaking a bit in something. I have done it when I worked in the toolroom for the company I worked for many times. It is one of those things, no matter how much coolant I had running on it.

Still you have managed to get resolve the problem, well done. It works a treat now that's the important thing and it's onwards and upwards now. :thumbright:

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Re: Little Wonder

Post by Trevor Thompson » Wed Mar 15, 2023 5:56 pm

All four cylinders are now finished, steam passages, pistons, piston rods, drain cocks, and end caps all made and fitted:
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The cylinder drain cocks are not actually finished, but the body of each drain cock is made and they are assembled onto the cylinders, with the passages into the cylinders made.

I am now making wheels:
IMG_2847.JPG
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Re: Little Wonder

Post by Old Man Aaron » Thu Mar 16, 2023 1:38 am

Marvellous, just marvellous. :salute:
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Re: Little Wonder

Post by FWLR » Thu Mar 16, 2023 8:45 am

Looking good. :thumbright: Nice bit of recovery there with that broken bit. :salute:

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Re: Little Wonder

Post by Trevor Thompson » Sun Mar 19, 2023 11:44 am

So far I have made 6 wheel "blanks". Numbers 7 and 8 in the lathe:
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I have cut that long chunk of steel into shorter lengths to hold securely in the lathe. I like to turn the face, bore (and ream) the axle hole and finish the tread and flange to size in one go so everything is truly concentric. Then turning the blank around do the same on the other end. You can see that the inner end is already machined in the photo.

What I seem incapable of doing is parting off 40mm diameter steel without causing huge chattering. I have followed all of the on line videos - but I still can't do it successfully. So its back to the hack saw:
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When it's cut off I will hold it in the lathe on its tread, using the flange to locate it, and clean up the inside to get the flange thickness right.

Of course these wheel blanks are really partly machined wheels rather than blanks. They will need mounting in the rotary table for drilling the holes for the crank pins, and milling out the gaps between the spokes. At the end I will mount the wheels in a mandrel on the lathe to form the tapers on the flanges.

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Re: Little Wonder

Post by GTB » Mon Mar 20, 2023 1:45 am

Trevor Thompson wrote: ↑Sun Mar 19, 2023 11:44 am What I seem incapable of doing is parting off 40mm diameter steel without causing huge chattering. I have followed all of the on line videos - but I still can't do it successfully. So its back to the hack saw.
I don't think any of the common model engineering lathes are rigid enough, or powerful enough, to part off 40mm BMS......

My 7" x 12" lathe draws the line at about 1/4" in steel and about 1" in brass and then only with a 1mm parting off tool. The 12" swing toolroom lathe I had in my laboratory early in my career would walk through 2" steel bar using a 3mm parting tool without changing note. The modern equivalent of that toolroom lathe is now made in Taiwan, costs about A$7000 locally and weighs about half a tonne. :shock:

My standard rolling stock wheel is turned from a disc of 1.25" BMS. Just after I got my lathe, I was about 20% of the way through the first cut for my first wheel blank using a hacksaw when I said "******* this". I climbed in the car, drove over to Hairy Forbes in Dandenong and came home with a chinese made 6 x 4 metal bandsaw. I was lucky, the anonymous worker who assembled mine knew his stuff and I got one that can cut square within 10 thous. on a 2" cut. It's on it's third blade and still cutting square.

That bandsaw has now cut something north of 300 wheel blanks and considering the cost of commercial wheelsets, both it and the lathe have paid for themselves just making wheels. The cut is square enough that I only need to skim off about half a mm from each face then drill and ream the blank ready for mounting on the mandrel. I can usually face both sides of one disc while the bandsaw is knocking out the next one. It has also saved over a metre of steel bar, as I would have to cut the blanks to 12mm wide if I was using a hacksaw. I'm not that good at cutting straight with a hacksaw. :roll:

From my point of view the bandsaw was well worth it. My health isn't up to cutting wheel blanks with a hacksaw.

Graeme

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Re: Little Wonder

Post by Trevor Thompson » Mon Mar 20, 2023 5:56 pm

Graeme

Thanks for the encouraging response - it was what I hoped I might get as a result of describing hand sawing it off!

I was wondering if the lathe was insufficiently rigid for parting off like this - and you have confirmed that thought for me.

I can part off brass properly with a 2mm wide cutter on it - and it feels controlled and safe.

I had dismissed a mechanical hacksaw as taking too much room - but I will think about a band saw.

Thanks

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Re: Little Wonder

Post by GTB » Mon Mar 20, 2023 10:22 pm

Trevor Thompson wrote: ↑Mon Mar 20, 2023 5:56 pm I had dismissed a mechanical hacksaw as taking too much room - but I will think about a band saw.
Unlike power hacksaws, the 6x4 bandsaws are lighter and have a couple of wheels at the back so can be moved around fairly easily. Mine lives out of the way under the router table when not in use. There is also a lightweight type in the catalog, designed to be clamped on a bench for use, but is light enough to put away in a cupboard. I've not used one, so no idea how well they work.

The 6x4 bandsaws also come with a rudimentary table attachment and while it's awkward, they can be used vertically. I use mine in the vertical position to rough blanks out of steel sheet when starting new loco frames.

Parting off is a series of trade-offs, the deeper the cut, the further the blade has to stick out of the holder, the more the forces try to deflect the top slide. To keep the blade rigid for deeper cuts it has to be wider, which means even more power is needed and it all spirals down on a small lathe until something gives...... I use a 1mm parting off blade in a tee holder for steel, which is mostly when making shouldered screws. I can use a 1.5mm blade in brass, but usually use the 1mm blade up to 1/2" bar and only use the 1.5mm blade when parting off something big like a dome.

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Re: Little Wonder

Post by Old Man Aaron » Tue Mar 21, 2023 11:59 am

I too prefer the hacksaw to parting off. Good to know it's not just my lack of machining skills to blame - my lathe's only 2" X 12". :lol:
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Re: Little Wonder

Post by Trevor Thompson » Wed Mar 22, 2023 1:30 pm

Old Man Aaron wrote: ↑Tue Mar 21, 2023 11:59 am I too prefer the hacksaw to parting off. Good to know it's not just my lack of machining skills to blame - my lathe's only 2" X 12". :lol:
Yes I also feel reassured that it isn't my lack of skill!

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Re: Little Wonder

Post by FWLR » Mon Mar 27, 2023 6:46 am

Oh to have room for a toolroom... :cry:
You are doing a brilliant job and you will have a feeling of tremendous joy that isn't matched when you finish the loco and getting it running. :salute:

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Re: Little Wonder

Post by Trevor Thompson » Tue Apr 04, 2023 9:50 am

I have been milling out the spokes on the wheels. It takes a bit of thinking about as how to set out the work and avoid errors. The digital readout was very useful - particularly as I am using coolant while cutting the steel (you cant always see what you are cutting). Each spoke was cut out by setting the angle on the rotating table, and cutting at 45 degree intervals. Having zeroed the axes on the centre of the wheel I was able to offset the X axis by 3mm each way (including an allowance for the 4mm diameter cutter) and mill between a radius of 7.5 and 22.8mm until the tool cleared the underside of the wheel. So that leaves 2mm wide spokes. When the milling was complete I set the table to 337.5 degrees, the X axis to 0 and the Y axis to 8.5mm to drill the hole for the crank pin in the centre of one of the two solid areas. Drilling the crank pin hole on the first wheel:
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And the finished wheel:
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Eventually there were 8 wheels:
IMG_2871.JPG
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I only made one error - and that was to partly cut through one of the counterbalance areas on one wheel. I got a bit bored with the repetition and my mind wandered! I will fill that with Milliput in due course, it is after all only a cosmetic error. It can be one of those outer end wheels which is largely hidden by the motion.

I have to finish the flange profile and then on to axles.

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Re: Little Wonder

Post by Old Man Aaron » Tue Apr 04, 2023 12:38 pm

Those are beautiful. The in-depth explanation of how you go about it is also appreciated, if slightly over my head. :lol:
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Re: Little Wonder

Post by Trevor Thompson » Thu Apr 06, 2023 7:23 pm

Making axles.

I have made the 4 axles from 6mm diameter stainless bar. For 32mm gauge, the back to back measurement is 28mm, and I can make sure that is accurate by turning down the axles to fit into the 4mm hole in the wheel for 6mm (the thickness of each wheel).

I usually use turning tools with replaceable tips, but I find they are not very good for delicate small components. Perhaps its a bit of a bodge, but I have a separate tool steel insert for my parting off tool holder which I have ground to a tool tip which seems to work. It's basically a miniature turning tool:
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Having turned each axle to 40mm length (28 + 6 +6 mm) I can make each shoulder 6mm deep and be fairly certain that the finished dimensions will give the correct back to back measurement. I found that turning the shoulder down to 3.96mm consistently provided a fairly smooth fit in the wheels.Wheels and axles temporarily assembled:
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That leads me on to making the axle boxes and being able to place the wheels into the chassis. In deciding how to make the axleboxes I was able to work forward in Sketchup, and try different valve gear arrangements, to see if they would fit into the available space. I have concluded that it is little extra effort to use the "Gooch stationary link" valve gear that the original locomotive was fitted with. More of that in due course but for now a view to show how the axle boxes, horn blocks, and eccentrics fit into the 28mm length of the axle:
Screenshot 2023-04-06 at 19.00.55.png
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Trevor

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