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Saturday 16 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part Fin

The cargo body folded canopy was glued into the cargo body and its frame formed from 'skirt' (see part 5d for explanation). Painting and lettering was applied and the final result is shown below alongside a 1p coin.

Not too bad after all. The troubles with 3D print mentioned previously are far less prevalent for larger objects.

To Part 5a (start of series).

Friday 15 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5f

I hate SuperGlue. It's been troublesome getting these small parts to stick. Why does the glue stick skin better than plastic? (By the way this is PLA plastic and does not work with polystyrene glue) I'm finding I have to wait a long time for the Superglue to fully go off and once it has held its a b****r to break apart if a mistake occurred. The petrol tank is a case in point. I placed it in the correct position on the bulkhead, applied pressure to create the bond and set aside. Came back later to find the tank had slipped down the bulkhead and set hard. The only consolation is it is barely visible once the canopy is in situ.

Photo 1: Cargo body and battery boxes assembled and step glued to the chassis.

Photo 2: Rolled canvas doors with integral pillars applied. I painted the wheel sets off the lorry as once they are in place it would be difficult to access their rears. At the same time I painted the canopies,which are a lighter colour than the rest, although not particularly obvious against the darker wheels. I may need to over paint a lighter colour.

The canopy with strapping  is removable, sliding over the cab rear wall. I might design and make a folded canopy as an option.

Photo 3: Rear wheels, drive shaft and exhaust pipe glued in place.

Photo 4: Front wheels glued in place and rear mudguards. The latter are strips of 'brim' curled over a metal rod to form the curve and glued to the underside of the cargo body. Head lights cut from the plastic rod and glued to side of radiator.

All looks a bit rough I know but bear in mind the photograph equates to your eyeball being about three inches from the lorry, whereas the optimum viewing distance for 'N' gauge is about 2 feet.

In the next posting, painting and final assembly.

To Final Part.

To Part 5a.

Thursday 14 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5e

The remaining parts were printed, cleaned up and assembly begun.

Photo 1: The complete kit of parts, including skirt and brim (see part 5d). There should be a window in the rear wall of the cab. I left it out because it is hidden by the canopy on the model.

Photo 2: Two holes were drilled in the cab floor for steering column, gear lever and brake lever (the latter two in one hole). The steering wheel was glued to a length of 'skirt', fed through its locating hole, glued and excess cut off. Similarly with the gear and brake levers. Front and rear wheels were glued to their axles, the front axle being a length of 'skirt'. The petrol tank was glued in position behind the front bulkhead.

Photo 3: Two lamps were cut from the rod and glued to the front bulkhead and the cab glued in place on the chassis. The four cargo body supports were glued on top of the chassis frame. Mudguards fitted to the front wheels. I may treat the rear wheel mudguards differently and will leave these until later.

Photo 4: Lengths of 'skirt' are used for cab canopy strapping and same for the step, which is cut from a 'brim'.

Assembly continues in the next posting.

To Part 5f.

To Part 5a.

Wednesday 13 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5d

This photo shows the set of wheels, petrol tank, steering wheel and rod. What a mess!

Each component was printed with a brim, which helps these very small components stick to the printer bed. The brims will be cut off and part of the long one on the right will be used for the step up to the cab.

Next thing to notice is none of the holes in the wheels formed as the printer could not cope and the conical shape of the wheel hub is just a blob.

They look useless but with a bit of filing and drilling they become useable. You may think this defeats the object of 3D printing but at least the wheels are round!

In the next posting the remaining components will be printed.

To Part 5e.

To Part 5a.

Friday 8 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5c

This is the raw print of the chassis on the print bed of our 3D printer.

A few comments about the environment. Each time the machine is powered up the printer needs to be calibrated to take into account any deviation in levels between the X, Y, Z arms and printer bed. This may be a peculiarity of our printer design and I don't know if other printers have the same need. In theory it is simply done by loading a set up file into the controller but I go a step further and manually set the print head height above the middle of the bed. Too low and the first layer or two will be too thin, too high and the plastic will tend to float free of the bed.

The bed has a glass working area that is covered with kapton tape. This is a high temperature tape that has good adhesion properties for the plastic as it is laid down. The tape looses its effectiveness after a few prints and needs to be replaced, but its life can be prolonged by wiping vinegar over the surface before each print, which acts as a cleaning agent. Some people have cited success printing directly onto the glass.

The chassis component above shows thin plastic whisker deposits and it is a bit blobby. This is a common occurrence, particularly for small objects. I dare say further experimentation with printing parameters may reduce the problem but it is generally the case that some post processing with files, scalpel and drills to remove blemishes is required. Indentations can also occur and if undesirable will need to be filled with plastic padding.

I mentioned in the previous posting that a skirt is formed around the component. It can be seen in the photo above. In this example it is ragged and not suitable for rod and bar components. You'll have to read Part 5b to understand this.

Here is the finished component after the rubbish is removed. A one penny piece is alongside to show how small the chassis is. If you think it looks a bit rough then it pails into insignificance at normal viewing distances.

Sometimes the component printed may be very poor. In this case either the design would need rework, the printer parameters changed or simply print the component rotated through 90 degrees corrects the problem.

The cab canopy was a case in point.

The photo below shows two prints of the same cab canopy. The right hand version suffered badly. When it was printed turned 90 degrees it held its dimensions correctly. (version on the left).

Note the indentation on the left hand version. This could be filled with plastic padding but it is not necessary here. The canopy on the prototype is in fact canvas pulled over a frame and exhibits depressions between the frame bars. This I recreated with a file for the finished component shown below.

More component printing in the next posting.

To Part 5d.

To Part 5a.

Thursday 7 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5b

There is logic behind deciding on how to disassemble the lorry into individual components. The main consideration is the printing process itself because the extruded plastic is initially soft and any parts of a component that overhang or have an air gap beneath are likely to droop due to gravity. Supports can be built in to overcome this but it just means more work to cut and file them off the finished component. Looking at the complete lorry I found a workable split line between the chassis and body that avoids overhangs.

Another consideration is the scale of the object. How much detail is practical to print in 'N' gauge? Not a lot I wager and that which is barely seen and has complex curves in the prototype can be designed as a rectilinear block, if at all.

These images below show all the parts designed in CAD for the lorry and explanation is given below.

1. The chassis

This has most detail. I designed it upside down as that is how it will be printed. The image below shows some of the lorry parts included in the design. Note the block design of the leaf springs - not like the prototype but do give a resemblance of springs and are fit for purpose in the model. The strut with the hole does not have the curvature of the prototype but it serves its purpose to give rigidity to the frame and facilitate passage of the drive shaft through it.

2. Wheels, steering wheel and petrol tank

These were presented in Part 5a of this series.

3. Radiator, engine housing and cab

As shown.

4. Canopies

On the left is the opened cab canopy, deliberately oriented this way for print to avoid overhanging parts. There is a cavity in the back for the canopy to slide over the rear wall of the cab. The other part is a folded canvas for covering the cargo body. This will be stored in the open cargo body.

5. Cargo body, supports and battery boxes

I decided to model this without a cover in place thinking that the lorry may have been delivered to the customer like that. I have seen photos as such, which also show the cab canopy folded up vertically on its frame.

The supports stand the body off the chassis frame and the battery boxes hang beneath the body.

6. Lamps and rolled canvas doors.

This is just a rod that will be cut with a scalpel into slices and fixed to the model to represent the four front lamps and rolled cab doors.

7. Rear Axle

As Shown.

8. Left and right mud guards

The tabs on these are glued to the backs of the wheels.

9. Various tubes and bars

This is not a CAD design. It is the redundant skirt created during the print process. What happens is a string of plastic is laid around the perimeter of the piece to get the plastic flowing before it prints the actual component. This is a very fine thread of plastic that is ideal for use as 'N' gauge struts, drive shaft, axle, gear stick etc..

In the next posting I start the print.

To Part 5c

To Part 5a.

Tuesday 5 May 2015

'N' Thornycroft J Class Lorry - 3D Print. Part 5a

In this series of postings I shall be making this:

as a kit of parts to a scale of 1:148. Now that is small and will stretch the limits of our printer capability, as you will see.

First thing we need is a dimensional drawing. A chassis dimensioned drawing is on display at Milestones Museum Basingstoke. With regard to the bodywork I shall use the specified wheelbase dimension to scale the above photo.

Now I need a Computer Aided Design Application, one that can create 3D models and has an export facility for Stereolithography files. This is a data file that defines 3D products built up one layer of material at a time, being what 3D printers do. I reviewed popular open source CAD Applications and choose FreeCad, which seemed to have good tutorials. Help is also available from YouTube videos. Even so, CAD can be quite complicated and the method I used from the plethora of options available in the Application may not be the best or even most effective means. I used a facility called 'Part'. The drawn model is created by adding and subtracting geometric shapes rather than starting with a 2D line drawing. It sounds a simple method and it is, although I have not yet needed to create convoluted shapes.

These photos demonstrate the principal as applied to the front wheel of the lorry:

1. A blank cylinder 5.94mm diameter and 1mm thick.
2. Another cylinder is superimposed (height arbitrary but, more than the first cylinder) that is embedded 0.5mm into the first cylinder.
3. The second cylinder is 'cut' from the first, which leaves the impression it made in the first cylinder.
4. A cone is added, representing the hub of the wheel.
5. 9 more cylinders superimposed and embedded the full depth of the part.
6. the 9 cylinders are cut from the wheel leaving an axle location hole and 8 vents.

I decided to create a group of objects in the same drawing for quickness although it is quite acceptable to have separate drawings for each object.

On the left are the four wheels, a steering wheel and petrol tank. The steering wheel is solid as it is not practical to print the spokes for something this small. Each rear wheel is a set of two in tandem with the rear one being a solid disc. The right hand image shows how the wedge shaped petrol tank was made from two rectangular boxes. The angled box is cut from the other to form the wedge.

Having exported a steriolithography file it needs to be converted to a G code file that is specific to the printer in use. It sets parameters that heat the plastic, moves the printing nozzle in x-y-z planes (within the bounds of the available printing bed) and extrudes a string of plastic the length of which is set for each segment of the printed object (the object is created by laying down strings of plastic in rows and layers).

The conversion utility is Slic3r. The utility needs to be configured and a configuration file compatible with our printer was supplied by the printer manufacturer. All we need to do is adjust parameters when necessary for optimum printing of specific objects.

The next posting will present all the remaining drawn parts for the kit.

To Part 5b

To Part 1 (About the printer)

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