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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.

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