Little Wonder

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Trevor Thompson
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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:
IMG_2855.JPG
IMG_2855.JPG (1.92 MiB) Viewed 4205 times
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:
IMG_2858.JPG
IMG_2858.JPG (2.32 MiB) Viewed 4205 times
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:
IMG_2869.JPG
IMG_2869.JPG (2.32 MiB) Viewed 3762 times
And the finished wheel:
IMG_2870.JPG
IMG_2870.JPG (1.82 MiB) Viewed 3762 times
Eventually there were 8 wheels:
IMG_2871.JPG
IMG_2871.JPG (2.35 MiB) Viewed 3762 times
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:
IMG_2878.JPG
IMG_2878.JPG (2.06 MiB) Viewed 3681 times
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:
IMG_2884.JPG
IMG_2884.JPG (2.04 MiB) Viewed 3681 times
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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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
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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 5538 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 5537 times
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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: 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 5479 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
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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 5476 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.

Trevor

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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 5138 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 5138 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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