HEAVY METAL Gallimaufry

Brian McKenzie

Western Thunderer
IMG_72959a Headstock Channels .jpg
.........................................9" x 3-1/2" Channel...........................................................................Brass stock...................................8" x 3-1/2".....


First modelling work for 2018, was converting strips of brass into lengths of channel section - to represent scale 9" x 3-1/2" steel channel, plus a couple of lengths made as 8" x 3-1/2".

Wagons, of my 1/48 scale New Zealand Railways prototype, have very distinctive headstocks of steel channel - where the exposed ends show prominently.

The channels were cut by 'flick milling' - a term used by some to describe using a shaped tool in the manner of a fly cutter - most commonly performed using a milling machine's horizontal arbour.

Channel.jpg

Brass sheet was first sliced into strips to the finished width of the channels.
Slicing brass bar_68243a.jpg

A pair of steel bars was prepared to support the sides and base of the brass material by cutting a groove along the uppermost edge. Pins were inserted at each end as alignment dowels.
IMG_72933a.jpg

Much effort was expended on grinding the end of short lengths of 5/16" square H.S.S. (lathe turning tool material) for cutting out the internal contour of the channels to show the tapering section of the flanges. This task was made more difficult by endeavouring to additionally trim the flange height at the same time and provide some rounding to the inner edges.
IMG_72924a.jpg

The cutting tool was secured in a small diameter arbour (machining time is usefully speeded up by arranging the tool to have the smallest diameter cutting circle), and carefully centered over the brass bar visually by taking a trial shallow cut.

When all is well, cuts are made at full depth in a single pass - to avoid any collapsing of the thin channel section.

-Brian McKenzie
 
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AndyB

Western Thunderer
Hi Brian,
That's dedication to fidelity! I considered milling channel for gauge 3, which would leave a serious pile of chips for each!
A couple of questions, if I may.... The video says that you use a single point tool for the slicing off. Is this shaped like a lathe parting tool? Why use that rather than a slitting saw? And do you use a clamp or anything to hold the loose end once you get >3/4 of the way along, to prevent it from sagging or flapping?

Andy
 

Brian McKenzie

Western Thunderer
I considered milling channel for gauge 3, which would leave a serious pile of chips for each!

Andy, yes - even in my much smaller scale, there was a pile on the floor. :)

The video says that you use a single point tool for the slicing off. Is this shaped like a lathe parting tool? Why use that rather than a slitting saw?

Slitting saws of a size or thickness (thinness ;) ) appropriate to my scale, are notorious for wandering off line and taking a path of their own, thus spoiling the precision and the finish desired. Yes, the cutting tool used is just like a lathe parting tool. It is mounted to cut in the smallest diameter circle, so that the spindle speed can be increased to take more cuts per minute of feed.
Slitting tool+swarf.jpg

. . . do you use a clamp or anything to hold the loose end . . . . to prevent it from sagging or flapping?

Yes, you're on to it! :thumbs: And when the slicing cut is just about to finish, a finger was placed on top of the start end, to tip the newly cut strip upwards away from the spinning cutter (it pivoting at the clamp in a see-saw action).
Slitting_68239a.jpg

Cheers, Brian McK
 

AndyB

Western Thunderer
Thanks Brian - more things to put on my 'to-do' list now!
May I also ask what sort of mill you're using? - it looks similar in size to a Tom Senior, but with a wider table.
And that ?Colchester Student? in the background looks a big lathe for 1/48 work!

Andy
 

Brian McKenzie

Western Thunderer
Andy,

The machine is an Elliott Omnimill with both vertical and horizontal spindles. You guessed right about the lathe, but there is also a smaller (green) lathe creeping into one of the pics.

Years ago, I made some underframe channel in a larger scale. Brass sheet was glued firmly (Ados F2) to MDF board clamped flat on the table. A side-and-face cutter was paired with a slightly larger diameter slitting saw, with a thin spacer in between, on the horizontal spindle. The channel was hewn out and parted off simultaneously in a single cut.

Would you use brass or steel for Gauge 3? A (contoured) two-flute slot drill might make life easier for a vertical mill in your scale. Good chip evacuation would seem desirable. Keen to see how you might get on . . . .

-Brian McK.
 

Overseer

Western Thunderer
Hi Brian

Very impressive. I presume you are building L-6 open wagons with the reversed headstocks. Victorian Railways had one group of wagons with the same detail due to a NZ connection. They were iron coal hoppers designed by Allison Dalrymple Smith in 1886. AD Smith was ex New Zealand Railways and brought some ideas with him. Only the first 50 of these hoppers had the reversed channel headstocks 9" x 3" x 3/8", the remainder had 10" x 4" x 7/16" channel headstocks mounted the conventional way round. All of them had 9" x 3" x 3/8" solebars. The reason for this rambling diversion is to ask if you would consider an order for a few lengths of the 9 inch channel as they are on my list of things to build in 1:48 and I don't have a large enough mill to make them (tempting as one is).

Part of the GA for the 1886 batch-
O 1886 crop.jpg
The hoppers looked like this, although this is one of the later ones with conventional headstocks.
O 166 c.jpg
 

Brian McKenzie

Western Thunderer
Hi Fraser,
The easiest and quickest way of obtaining 9" x 3" channel in 1/48 scale is to slit K&S 3/16" square brass tube longitudinally. I do this for wagon solebars - and reserve the labour and time intensive milled channel for the headstocks - where the profile is more visually exposed. Alas, I didn't expect to machine any more underframe channel and recycled some of the setup for making other items. :oops:

I was very impressed with the great job David Foulkes of Steam Era Models made of your split-spoke wagon wheels Scale Wagon Wheels - A Saga, and his neat methodical tooling work in general for kits, when visiting once. Some years earlier, I was encouraged by the late Graham Selman (originator of North Yard Models) to make my own split-spoke wheels in 1/48 scale. These six-spoke 30inch diameter wheels have injection moulded centres of glass filled acetal, with stainless steel tyres. Moulding acetal successfully as a hobbyist proved quite a challenge compared to less demanding plastics.

Cheers, Brian McK.
 

Overseer

Western Thunderer
No problem Brian. The square brass tube is an option but has radiused outer corners instead of the sharp arris the real channel has. I will probably revert to my usual folded brass solebars (which I punch the rivets in before folding) with fabricated headstocks to achieve the sharp corners where they can be seen.

Yes, David Foulkes is a brilliant toolmaker with his pantograph mill. His earliest kits were good but the recent HO kits lift the art form to a new level, I should post some more examples of them here. Acetal is strange stuff, I was surprised a while ago at how low the temperature needs to be for it to deform. I had some rolling stock in storage in less than ideal conditions and one piece bogies distorted, a combination of heat and some pressure. They were saved with a dunk in boiled water and twisting.
 
Riveting experience - 'gangnam style'

Brian McKenzie

Western Thunderer
Something I've wanted to try is to equip a CNC milling machine for embossing rivet heads.

The first version was a spring-loaded tool fitted directly into the machine spindle, but the spring used was far too feeble to make any impression. Being mindful of applying shock loads to the spindle bearings, a more complex arrangement of turnings was assembled to transmit the minor impacts straight into the machine body, avoiding the spindle. This unit is held in position by the air-operated fingers that grip the 'pull-stud' that is screwed into the upper end of regular tool holders or chucks.
IMG_87011_Rivet punch.jpg


Bogie Sideframe.jpg

Although a die plate was made for the bogie sideframe example in the video below, the concept works sufficiently well to be worth devising a single fixed female die - and using the CNC motion to feed the sheet metal over it - thus obtaining rivet patterns quickly off any digital plan.
 
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Brian McKenzie

Western Thunderer
More embossing of rivet heads, this time at 0.9mm diameter in 0.015" nickel-silver. The pre-drilled steel die plate was a piece of soft mild steel - as only two work pieces were required. Despite 'riveting' several more parts ( just in case :thumbs: ), no deterioration to the edges of the holes in the die plate was noticed.

Alas, the rivet pattern in the prototype is very 'uncoordinated' and the inherent accuracy of the machine is only made use of to replicate the mess!


Seasons Greetings everyone, from the South Pacific (first to reach Xmas Day :) )

Brian McK.
 
Joggling brass angle

Brian McKenzie

Western Thunderer
Currently scratchbuilding a few wagons originally of British design for New Zealand Railways. 9mm scale is used for O gauge track, which scales neatly for 3' 6" gauge.

Machining all the many different size angles used by the prototype became tedious. But interest perked up by tinkering with a tool to see if a joggled end could be formed in angle with a wall thickness of 12 thou (0.3mm). Photo shows the first piece made and installed.

IMG_9481+ joggled angle_1.jpg

Then when I inserted the prototype pic above, noticed the end treatment of an angle along the top edge was not the same as for the wagon's other less tidy end - which I had copied.

IMG_8462a Joggled angle.jpg


IMG_9450a Joggle die block.jpg


IMG_9434a Joggle tool for 1.5mm angle.jpg
 
Boring wheels for 2mm dia axles

Brian McKenzie

Western Thunderer
This unusual method was used to finish bore axles holes in a recent batch of tiny drivers for industrial locos.
It's more model engineering based than model-making, but may be of interest to some.

For larger diameter wheels, it has been practical to secure them with screws into the end of a bar in the lathe - and 'clock' them up with a dial indicator to run true. This time the small size precluded that, so an alternative method was devised to hold them. This is basically a long oversized collar arranged to clamp the wheel from the outer front face of the tyre, against the end of a mandrel.

Boring arrgt for 2mm axles.jpg

An important requirement is that it is necessary that the OD of all wheel flanges is identical, and that this diameter can be reproduced successfully in the two aluminium items used to mount the wheels.
Boring 2mm dia axle holes.jpg

The clamp component is made first, bored very carefully full length, that can accept the wheels over the flange diameter with no axial play.
It is easier to bore this right through to achieve the diameter required, then insert a stubby bush in the opening to retain the wheel.

A mandrel is then turned to be a very neat fit inside the large collar. The length of these components can be judged from the photos.
The collar is made long enough to have several saw cuts across the end nearest the chuck, and a hose clamp is used to tighten this to the mandrel. Some sideways pressure applied by hand when tightening the hose clamp is quite sufficient to drive for the drilling and boring operations.

-Brian McK.
 

Brian McKenzie

Western Thunderer
Some screen shots ex a video I'd overlooked - of the 'boring' process described above:

Initial drilling 1.6mm dia.jpg
Axle bore started with a 1/16" drill


Boring tool ground from a 3mm drill blank.jpg
The boring tool for finishing to size was ground from a 3mm dia. drill blank*.


Boring for 2mm dia underway.jpg
Boring underway expelling swarf. A second spring pass brought the hole spot-on to size.


Checking for size with a gauge pin.jpg
Checking 2mm hole diameter with a gauge pin.​

A comment about drill blanks* for anyone not aware of them. In a sense, these are HSS drills before the flutes are formed - but I'm not sure that is entirely true. They are hardened and ground full length, whereas drills commonly have softer shanks. Being of High Speed tool Steel (HSS) they can be ground to make all kinds of shaped tools for a variety of machining processes. Another advantage is the availability of a vast range of diameters from specialist suppliers like Drill Services at Horley, most useful when some odd diameter is required in a ground shaft, that standard silver steel sizes can't cater for.
 
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