Delage GP engine 4

When building the 1/3rd Scale ‘Blower’ Bentley engine, there were problems building the gearbox because it had such a complicated shape and how to hold and machine the component. Mike’s stepson Paul, as a birthday present, made the odd shaped gear box by 3D printing, so Mike could handle the part and work out how he was going to machine it. There was the advantage that there was already a 3D computer image which allowed the 3D printed part to be made. The 3D print is quite rough and the finish is abysmal, but it is reasonably accurate in shape and dimensions. The other advantages of the 3D model were that Mike could work out how to orientate the component, and to make sure the cutters didn’t interfere with the area that needed to be machined next. Gearbox and blue 3d model shown below.

Pictures showing progress on the Delage engine shown next.

It was realized that 3D printing would be an advantage here as well. The Delage presents similar challenges to those of the ‘Blower’ Bentley. The 3D computer images that Paul drew up, were based on photographs and sketches of the original cylinder block measured up at the Brooklands Museum. As can be seen below, it is an awkward component to machine out of blocks of cast iron.

Why not obtain a 3D print of the cylinder block to help visualize the approach? How difficult can that be?

Well, it wasn’t as easy as first thought.

Paul’s colleague had set himself up with a comprehensive home 3D printing setup, and offered to do this work for him.

There were a couple of problems:

Problem 1. The component was too large for domestic level printers and would have to be printed in two sections.

Problem 2. The material cost alone was going to be £100 and time to print would be 1 week.

Going to a commercial outfit would have been very expensive.

Being in possession of the 3D computer images, which could be loaded into a 3D printing programme in two sections, it could be seen what the machine could produce.

First though, it will be expedient to describe the three main methods of 3D printing.

3D Printing Methods

•FDM or Fused Deposition Modelling where a melted filament is deposited layer by layer. Not particularly accurate and slow to print. Poor finish.
•SLA or StereoLithogrAphy, using laser light cured photo polymer liquid resin. This gives high dimensional accuracy and a fine finish. It is a three-part process.
•SLS or Selective Laser Sintering. This uses laser fused powder and can produce engineering quality usable components depending on the powder used. Very expensive.

Comparison of the FDM and SLA methods for 3D printing the Delage block.

The FDM Process

These are the first views of the digital image of the rear half of the cylinder block, as it would be printed using the FDM process:

The basic outline of the block can be seen, but there is supporting structure to keep the 3D model in shape while it’s still warm and flexible. This is all calculated by the 3D printing programme. The programme decides what support is required, and where. It is quite complex, and the supporting structure has to be removed.

Due to the size and time constraints, it was decided to produce the centre cylinders only, by the FDM process, as it was going to take so long to produce them all. As can be seen below there are a number of supporting structures on the cylinder, all of which have to be removed.

Two views of the actual FDM print of a centre cylinder with all the supporting structure still intact:

The SLA Process

The front and rear cylinders were produced by the SLA process, because of the slightly quicker printing time, and more accurate definition. Below is the digital computer model of the front cylinder, in what was thought to be the attitude in which it would be printed using the SLA process.

This is the digital model of the same front cylinder produced by the SLA process. The 3D printing programme has decided the best orientation and the degree of “scaffolding support” required.

It was decided that the SLA 3D printing method was the most appropriate for the Delage cylinder block sections.

The photo shows the front cylinder being printed. Note that it is printed hanging from the platen.

When immersed in the vat of resin below, the guided laser light cures the relevant areas and produces the shape.

The completed print with its support structure still attached:

After removing the support structure, the print is then washed in isopropyl alcohol to get rid of excess resin, and then dried.

It is then exposed to UV light in a curing cabinet to complete the process.

Front and rear cylinder 3D prints completed.

These photos show the front and rear 3D printed cylinders mounted in position on the crankcase. With a sectional drawing, the component can only be seen in one plane. Each cylinder is the same, but with the 3D prints, the shape of the cylinders on the engine can really be appreciated.

The engine can be ‘seen into’ more, and there is a better feel for what needs to be machined.

Part one here. Part two here. Part three here. Part four here. Part five

Bentley series starts here.