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* Pop Rivets and Underframes

* Modify your Sieg C2A Lathe

* Assembling a low cost CNC Router / Laser Etcher

* OpenSCAD and Sample 3D Print Files

* Extended Guide to 3D Printing

Technical

3D Printing.

This has become quite common and in fact is something that I researched before coming to the conclusion -that with the high price and low number of things I would print with it I didn't need one! Most modern commercial kits are based on "Iteration 3 of the J.PRUSA design" or "i3PRUSA". A group of four of use once seriously contemplated buying one between us that would I feel have given the RepRap a suitable market for its use...

These are ideal for the production of several parts for models and can use either ABS plastic or PLA. The main use for them could be the production of casting masters.

The paragraph above was true when I wrote it some months ago. However the market has "crashed" and it is now possible to buy £350 machines for a little over £100...

The three articles below (updated June 2019) detail the construction and use of an i3Prusa RepRap kit, OpenSCAD which is the "Design Software", and CURA which is the "Production Software".

The production cycle for a RepRap system is:

A RepRap compatible machine, there are SEVERAL designs available. A design program that can produce STL files from the raw design, again there are several programs. There are several sources of both STL and GCODE files on the WWW. Chief amoungst these is the site "Thingiverse". A production program that takes the raw STL file and generates the GCODE file for the RepRap to use dependant on the choice of machine, material and user options...

I have documented the ones that have appealed to me and I have found very easy to build and use.

Now that you have some idea of what is possible -the next problem is what do I do first? The basic text files for OpenSCAD will have given you some primitives to work from. You should be able to assemble a station from them -just as I have. The station as printed is 1.8metres long and 50cm wide. The primitives are taken from LMS stations but given the time period... A short survey of the Art Deco style as mostly used by Southern and the Futurist style as adopted by the LNER will give you the working basics.


The Laser Etcher.

I bought my laser etcher at the end of 2018. It came as a Chinese made kit and with "Chinglish" instructions. Fortunately along with it on a "thumb drive" came the software and a short video on how to put it all together. The machine is rated 450nm at 2.5W -which may not sound a lot but is more than enough to cut through 160g/m2 card or 1mm thick ply at one pass.

The bed of the device is A4 -however the cutting area of the device is A5. This means that there is a lot of waste if only using A4 sheets. My normal use of this device is to make templates. Although it does sterling service cutting gaskets... At the moment I am using it to build a 2-NOL from the Locomotive Designs plans.

The standard software for this device is called Laserweb, (current release is 4), The software will take scans in the format of PNG or you can produce drawing in SVG or DXF format for it to use. The software is easy -but I would caution that it does require some practice before you undertake major operations with it. The system can be programmed to accept scans from scanners -but the default setting for the DPI may not be the correct one required for perfect scaling. In the case of my device the scaling is 577 DPI for a 600DPI PNG image.

The main problem using the software relates to the cutting speeds and the laser intensity. 100% laser power can easily cut and set fire to your work at the same time... 10% to 20% and using multiple passes is probably a better bet. The speed of the cut really defines how much time the laser will be in the same place. It is "about right" for cardboard at 200cm and 300cm for wood.

Focussing the laser is a manual operation and has to be done with the laser glasses removed -however the glare can be quite painful. If you wear the glasses then these should block the laser frequency -but this leaves you with the problem of trying to focus something that is now invisible! I have found that a laser focus of 0.1mm is achievable with a few attempts.

The best results are produced with the laser in RASTER mode. This is similar to the old 625line B+W tv as it produces a point with either an on/off state. The laser is driven via a PWM driver and you can set it to produce 256 shades of grey if required. Mostly you will set it to Black only.

I have tried it with "laser plastic" in the hopes of producing my own builders plate and shed code plates. The main problem is the fact that the plastic cannot really cool down fast enough between passes as you are dealing with fonts in the 5pt to 8pt region. Large "poster" scale size fonts in the range 16pt to 24pt will cut with little difficulty.


Assemble a CNC Router and Laser Etcher.

The following PDF file will show how I constructed a 3018 Pro kit CNC Router and laser etcher. This is a "step up" from the simple laser etcher as detailed above and uses a 5.5W laser and a 24V motor. It is however more a semi industrial machine than a domestic one...


CNC GCODE -the common language of 3D printers, Lasers and Routers.

Although the GCODE instructions have been around for several decades -the instruction set is still increasing as new problems need to be addressed in the manufacturing arena. The code is a simple text stream and can be fed into the device by a serial cable (USB or 9pin) or held on a memory store (SD card). The code is very robust and simple to implement. It does however have one serious problem...

If the machine firmware that the code is being "pushed" to, does NOT understand the line of code -IT IGNORES IT. This means that the firmware in your device has to be kept updated. Most machines in the Domestic market use the Arduino chipset. This can be reprogrammed using the Arduino toolkit suite of programs (they are free).

In the case of a RepRap the firmware program is called MARLIN and is updated very rarely, MARLIN can only understand 150 of the GCODES. Current mainstream release of MARLIN is 1.2. Ver 2.0 "may" be available in Q1 2020(?)

In the case of a Router or Laser the firmware is called GRBL (say Gerbil). The current release of GRBL (Jan 2020) is 1.1H. The easiest way to update your GRBL firmware again is to use the Arduino IDE Toolkit.The complete sequence is detailed in the PDF below.


CAD and CAM

Computer Aided Design... I am going to assume that you have some form of mainstream computer in front of you. This can be a MAC, a PC -or a UNIX workstation. There are several OS specific programs for each of the three options that I listed. On the MAC there is TurboCAD. On the PC there are dozens -the market leader is AutoDesk Products, on the UNIX workstation very few are not found with Solidworks.

But instead I am suggesting that you opt for GNU GPL programs that will run on all three systems. This is not to say that they are any better -in some respects they are far worse... But, they all have one overriding plus factor -they are easy to use.

I would recommend LibreCAD as your CAD design system.The current release is 2.0. It is free, but it is a bit of a memory hog! The design menu options are well thought out and the built in library of parts shows its PCB and architecture design origins. The laser cutter shops will accept LibreCAD files in the format DXF rev 2007. This is the default format of LibreCAD.

Computer Aided Manufacture... The manufacture part of it is the difficult one to pin down. The program I recommend is called LaserWeb. Despite its name the machine options that it has include outputs to Mills, Routers, Engravers, Lathes and Lasers. The main problem with using it is that it is a GERMAN program. The words are English but the method of working it is pure DIN standard. When put onto the cutting area the objects automatically set up at 0.0.0 however the position of the object is defined on the cutting screen by its centre. This is perfect for cutting circles -but makes non circular objects a bit of a puzzle. There is an on screen "twiddle box" to edit the positions of each object. Each item on the list maybe cut in any of the various options. The machining list may be grouped and the sum list "rubber stamped" all over the cutting area.


Laser Cutting Plywood

This article by John Branch

Teak coaches at the speed of light.

Nineteenth Century wood panelling reproduced with space-age technology.

Laser cutting is widely used in the manufacture of model railway rolling stock, especially when repeated features are called for. This is the story of my experience in the application of laser cutting techniques to gauge 3 coach-making in a non-commercial context. I hope it will encourage readers to take the plunge and acquire their favourite prototypes in miniature.

Those of you who have suffered my earlier tales of plastic, metal and wood bodgery in the pursuit of creating reasonable semblances of various railway subjects, mostly motive power, will know that I have attempted to make models of some of the electric locomotives of the Metropolitan Railway. For these to have something to pull, the choice is somewhat limited. There were two basic designs of coaching stock in use after the initial 4-wheelers, one is known as “Ashbury” stock and the later, larger type is “Dreadnought” stock. The first appeared around 1898, and the others in the 1920s. The Ashburys had a strange life, being built as loco-hauled (Electric and Steam) coaches, many were soon converted to electric multiple units for the Uxbridge service and back again some decades later to form steam-hauled shuttles for the Chesham to Chalfont and Latimer service until electrification of that line in the 1960s. Four of the survivors were sold to the Bluebell railway for a few quid, and have since been restored to a superb (award-winning, even) condition. There is another in the London Transport Museum in Covent Garden, London. The Dreadnoughts were somewhat longer and heavier, and served the London-Aylesbury line until it was electrified and limited in extent to Amersham. These coaches also survived in large numbers until the ‘60s, some having been adapted to work with “T” stock electric multiple units. In the case of the Dreadnoughts, the Keighley and Worth Valley Railway have a number of them. Both the Ashburys and the Dreadnoughts can sometimes be seen on TV drama series, usually just as ciphers to indicate “Old train”, and rarely, if ever, set in the right time or place. The two types of coach have in common that they are of panelled teak construction, have no corridors, and thus they each have six times as many windows and twice as many doors as compartments. These are factors that loom large when contemplating the building of models of any coaching stock. I have seen many hand-made models of coaches of the late Victorian era, many of which look superb. But where I differ from the builders of those masterpieces is that I have neither the skill nor the patience to create so many repeated features in such a way that they all look the same. So I was looking for a technique to make a specific prototype rather than the reverse, which had been my approach in the past. I wanted to model the Ashbury stock on account of it being a bit smaller than the Dreadnoughts, and it seemed possible that I could run three Ashburys in the space of two of their larger brothers.

What I needed was a way of making the various characteristic features of the stock such as windows, panels and the fillets where panel joined panel in a simple and repeatable way. My first attempts involved thin ply, Bristol Board, a computer printer and several scalpels. Plywood of 0.8mm (1/32”) thickness is a good material for coach construction, as it is strong, easy to cut, bends well and smoothly and looks like wood. Bristol Board can be printed on with a simple inkjet printer, and cuts smoothly with a sharp knife, with strips only 1mm wide quite possible. It seemed that it might well have been possible to devise a system of construction involving ply for the bodies and board for the panelling. After several attempts, I found that, although it was possible to turn out a fair job, it was going to result in a huge expenditure of time, much scrappage and a general decrease in enjoyment and hence low motivation to complete the project.

Reading the advertisements in this magazine for wooden rolling stock kits, I noticed that many stated that the components had been “Laser-Cut”. I wondered if that process was applicable to manufacturing on a “one-off” basis, or if I would have to commit to a longer production run than I needed. I browsed the web; I spoke to experts, I grilled company’s staff (possibly the company proprietors); I came to realise that those involved in this new industry had many ways of making a living. Some were at the industrial end-making decorative steelwork for buildings, and had fairly massive machines, others could cut thin gauge metal sheet, or specialised in plastics and wood for architectural and other models. In these conversations I discovered that several companies were used to dealing with enthusiasts like me, and I allowed them to lead me gently into this new world.

The usual way that design information is transmitted from customer to cutter is by a .dxf file. This is supported by most CAD packages. My software is called Autosketch, and, although bought by me when Windows 3.11 was the general operating system (in 1994), it runs very well in Windows XP. I blew up a 4mm drawing that is in the LT plans book (Ian Allen) to G3 standards. This was not easy, as scanners do not seem to apply the same magnification in all directions, so I then re-drew the whole thing, applying some judicious simplification in measurement, so as to eliminate all fractions of millimetres except 0.5. I then created a folder of separate files, each one being a discrete component of one or more of the coaches. When saved as .dxf files, each one is only a few kB and so a couple of dozen can be easily emailed at a time.

Both sides of each of the coach types are identical, and all types of coach are of the same length, width and height. Thus the cross sectional form is common to all, and that means that compartment partitions and coach ends all have the same basic outline. As I stuck to 3rd class stock, all the compartment widths are the same, thus the panelling between compartments follows identical repeats. The doors are all the same, as are the vents above them. The differences are in the number of windows in the sides due to the purpose of the vehicle (Compartments only, Brake Ends, Motor coaches etc), and in the ends, where some are blind and some have windows. A straightforward 3rd class trailer has seven compartments, and the number of separate components I had to have laser cut to make the body was 68. I divided up the panelling of a coach side into discrete and repeated sections that could be superglued onto the side panel that already had the window holes laser-cut into it. So a seven compartment side would have six panel sections (frets) that run from mid-door to mid door, two sections that end the panel run at each coach extremity, seven over-door vents, seven droplight frames and seven door panels. Additionally, there are two ends plus two end panel frets and six partitions to cut from 3mm plywood (ends and partitions) and 0.8mm plywood, (everything else). I used pre cut strips of spruce to reinforce the structure, and five 5mmsq and two 2x10mm longitudinal strips run the length of the coach in notches cut (by laser, natch) into the partitions and ends. Additionally, the floor (5mm ply), and some 42 pieces of transparent Plastikard for the windows were cut by hand. Each door has a safety bar to stop small boys from leaning out whilst the train was in motion (it did not work), each door also has a “Tee” handle, and a grab handle. Buffer beams and stepboards were made from spruce strip, and the under-floor details, such as brake cylinders, battery boxes, dynamos and trusses were built up on a rectangle of 3mm MDF which was then screwed to the floor. At various stages in their (prototypical) lives, some coaches were fitted with semi-permanent link couplings with no buffers instead of the original screw couplings and conventional buffing gear. The “outer” ends, which coupled to locomotives or to other multiple units were always conventionally fitted.

The compartment interiors were represented by a basic ply seat, covered with a printed representation of the seat upholstery, together with a route map diagram, an advert for new houses in Metroland, and a picture of cottages in Long Crendon. All of these were scanned from reprints of the originals and are readable with a very good glass.

Even before the roof was added, the resulting “open box” resulting from this early stage of the build, was immensely strong and resisted any attempts to twist or bend it (within reasonable limits, of course). The roof was made by gluing 10mmx2mm stripwood longitudinally to the top of the ends and partitions, filling the gaps with plastic wood and then sanding it smooth. I treated the wood to a few coats of sanding sealer, then applied a couple of coats of high-gloss domestic white paint. Torpedo vents were added along the centre line at two per compartment, and narrow strips of thin card were stuck to the roofs to represent the rainstrips. In total there were 235 separate parts to assemble just for one basic body above the stepboards.

My first order of parts included enough components to build two 3rd class trailers. In fact, I built one trailer and one control trailer, but there is virtually no difference between them apart from at one end. For the second batch of coaches, a brake end and a driving motor-car, I tried a different technique and a different supplier.

After building the first two coaches, and having gained some confidence both in my ability to define the design, and in the laser technique to produce a useable product, I decided to take a risk for the second batch. This entailed the manufacture of the complete panelling fret for a coach side in one burn. This meant that around 15 formerly separate frets would be produced as one long (very fragile) fret, to be stuck on the coach side which had all the window apertures also laser cut as before. With the former method, any slight inaccuracies could be dealt with by judicious adjustment of the individual small frets. With one long fret, any adjustment would involve an altogether more nervous builder. My earlier experience taught me that if the drawing said two millimetres, two millimetres is what you would get. Thus, with some care, it is perfectly possible to get an overlay that sits as well around the first window in the side as it does on all the others.

The total parts count for each body using this method dropped to 189. I also changed the adhesive for sticking the frets to the sides from super-glue (Cyano-acrylate) to PVA wood glue. This was necessary due to the unforgiving nature of super-glue as it cures. The downside was that each fret had to be left for a day or so before releasing the spring-loaded clamps that held the assembly together. With some attention to detail, it should be possible to reduce the parts count for the body to around 150, with maybe another 50 odd to take care of the underframe, running and buffing gear.

Each bogie’s components (two side frames, two ends and one stretcher) were laser cut from 2mm mild steel, with the axle hole centres positioned accurately in the frames. I opened up the holes to suit the top-hat bearings supplied with the GRS (Slater’s) wheels, and one side was brazed (Silver soldered) to a stretcher. The other frame had a smaller piece of steel brazed to it in a position such that it sat below the stretcher for just under half its length. The two ends were also brazed to the second bogie side. To assemble the bogie, the axle journals were inserted into the brass bearings in the bogie sides, the wheel assemblies inserted, then the main stretcher was bolted to the shorter stub-stretcher underneath it, and the free ends were soft-soldered to the first side. Thus the assembly would be capable of disassembly without recourse to a saw or naked flame. I reckon this is a wise move, as it is quite possible that at some time in the future I would want to add working electric pickups, either from the wheels (conventional 2-rail) or actually use the third and fourth rails for power or signalling. This would require a complete rebuilding of the bogies. The bogie details, springs, axleboxes, etc., were modelled by using cut-down white metal castings (Brandbright) designed for wagons, to which were added some small Plastikard details. This method made it easy to fit pick-up beams, as the beams, when superglued to a bracket glued to the underside of the axlebox casting hung at the right distance from the bogie frame for a pick-up to sit over the conductor rail.

All four coaches were built in a similar, but not identical, manner as I do like to improvise and improve whilst working on the job. One vehicle, however, the Driving Motor car, had special features not possessed by the others, namely the traction motor/power bogie, the battery, receiver and electronic speed controller plus the best part of 100 louvres to provide ventilation to the switch-gear in the front compartment. I made the louvres from 2mm styrene quadrant. Each length has the ends shaved to simulate the domed end of the original metal components. Painting the white styrene to match the teak sides was fun. I used acrylic paint, brown, ochre and yellow, daubing roughly until a semblance of grain resulted. It is OK, but I could do better if I knew how. Another strange visual effect here- under natural light the plastic louvres match the varnished real wood pretty well. Under artificial light, the louvres can appear yellower or browner than the wood. The prototypes had either screw couplings and round buffers, or a close-coupled arrangement using a rigid central link. I used this latter method for the joints between the “Inner ends” to join the cars in “Sets”. I have equipped all the cars with screw couplings on their outer ends, with their other ends having rigid links. Thus I can run two 2-car trains (B/E+Trailer+loco, and DM+ CT), or as a four car EMU rake, with the BE as the third vehicle. Even these short trains take up a lot of track.

The motor bogie is built around a Como motor/gearbox as found on sale in many model shops for around £20, this has a ratio of around 11:1. I used a Meccano helical gear-pair which gave another 1.2:1 reduction to get the drive to the first axle. A pair of Technobots timing pulleys and a toothed-belt take the drive to the other axle of the bogie. I needed a new radio transmitter, receiver and voltage controller for this project, and it turns out that technology has advanced since my previous purchases. I ended up with a Planet 2.4GHz system which has 4 digital proportional channels. The transmitter has two joysticks each able to control two channels (up/down and left/right). It also has a 5th channel which can cause a servo to travel over its full range slowly, but does not offer proportional control. The system is primarily designed for flying models at ranges of up to 100 metres. It is said to a bit more sensitive to terrain, weather and obstacles than 35 and 27 MHz systems, but I have had no problems yet. There are no crystals with this kind of system; instead, receivers are “Bound” to the transmitter, and then cannot be controlled by any other transmitter until the “Binding” process is repeated with another transmitter.

The originals were very solidly built of inch-thick teak planks, with many coats of hand-applied varnish. The livery changed several times over the life of the coaches, involving white top and waist panel in-fills, yellow or gilt edging to the panels, white and blue shading to the lettering, and slapped -on brown paint when times were hard. I contacted the website manager of the Bluebell Railway, Mr Richard Salmon and asked him for some digital photographs of the lettering on the Bluebell-restored coaches’ sides. He was very generous and sent me a selection of examples that he took especially for me, including “Guard”, “3”, “Luggage”, “Metropolitan “ etc. I imported these into Word, adjusted them to the right size, and then printed them onto white-backed transfer paper. On the examples at the Bluebell, none of the rebuilt coaches now represents a driving motor-coach, thus there is no “Driver” signage. Luckily, the letters D, R, I, E and R are in the other words, and the central section of M is close to the letter “V”. Never has the technique of cut and paste been so intensively used. To finish the wooden parts of the coaches, I treated the plywood sides and ends to two coats of a pale brown sanding sealer followed by three or four coats of antique pine varnish. I tried teak varnish, but it was too dark-this is a very subjective area, but I think there is something like a scale factor that comes into play when a large object, normally viewed at a fair distance, is reproduced in miniature and viewed very closely. It seems to shift the shade very slightly. Also, looking at photographs of the prototypes, the shade on any given coach can vary from a dark brown to a bright yellow depending on the age of the wood from which that particular panel was made, and the time since it was varnished. I added cast brass “T” door handles, wire grab rails, white metal torpedo vents and various other small details to build up the atmosphere. Fortunately, almost every published photograph of the stock shows a slightly different arrangement of pipes, connectors, lights, brackets and handrails. I reckon that I can justify the presence or absence of any number of these details with a straight face and a clean conscience.

The total cost of all the laser cut parts was a shade light of £520. The cost of the cutting service decreases with increasing numbers of individual parts ordered, so if you have confidence in your design, and know that you will build a lot of vehicles using common parts, then you can take advantage of the economies of scale. Additionally, I spent around £250 on other bits, the most expensive being wheels and cast components. A total outlay of less than £200 each for the coaches was the final cash cost, plus a total of around 400 man-hours.

Main Suppliers were

Wheels and cast components: GRS and Brandbright

Strip wood, ply etc.: Hobby’s. Transfer paper: Crafty Computers

Laser cutting services: York Modelmakers and Cut-Tec

Gears, motor and pulleys: Meccano, MFA-Como and Technobots.


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Page last modified on April 11, 2021, at 12:06 PM