Marking out steam engine cylinder block

Hi All
With the dark nights upon us, I find it is a good time to get back into workshop for some model engineer. I have been working on a 3” Foden steam wagon on and off for several years and have decided to start the machining of the cylinder block.

Before machining any casting, especially one as complicated as this cylinder block I like to mark it out. This ensures all holes and details can be achieved and machined in the correct place. When marking out it can take me several attempts and several hours until I am totally satisfied that holes will be drilled concentric to bosses and wall thickness will be equally and to get everything in the right place.

This casting requires a saddle to be made so the casting can be positioned square and upright to aid the marking out process. Also the main datum is the centre line of the boiler this datum point is floating in space.

The saddle cradle is made from soft wood and made square. The under side of the cylinder casting which fits to the boiler has a slight flanking angle when cast. This is common as this angle helps to remove the pattern from the sandbox before pouring. To get the cast to sit snuggle but square the saddle radius of the wooden cradle is linished take this angle into account.

Once happy the cylinder block is glued with contact adhesive and left. Two steel plates are screwed to the cradle so the centre line of the boiler can be marked and used as a reference point for all dimensions taken from this datum.

The cored holes for the pistons will have some aluminium blanks machined for either end so these centres can also be marked accurately.

The cradle can then be clamped to a box plate to mark all the required references on rah face for machining.

The photos show the setup ready for marking out.

wooden cradle
Attachment 44083

Cast iron cylinder block
Attachment 44084

Checking fit before glueing
Attachment 44085

Completed ready for attaching to box plate for marking out.

Attachment 44086

Taking the time to mark out any casting is time well spent in my opinion. Not only is it important to get everything to best fit, the mark out lines give great machining reference points.

I hope this will be of interest and thank you for taking the time to read.
I will add more photos as the cylinder block progresses.
The Home Engineer

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The cradle has been drilled so the cradle and casting can be mounted to a box plate. This enables all five sides that require marking out css as n be do without having to setup each individual face and where needed both sides can be marked at the same setting such as the cylinder bore centre lines.

Attachment 44126
M12 bolts and tee nuts holding cradle. The holes are drilled over size so there is alignment wiggle to get the casting square.

Attachment 44127 Attachment 44128
The photos show the box plate set in different orientations to mark the casting. A really great tool is a digital height gauge to mark the casting out.

The marking out has been surprisingly straight forward and everything seems to be in the correct ballpark. The core blanks help to ensure the cylinder bores are in the correct position.
Attachment 44176
Note the shim under the front edge on the wooden cradle. The cradle had to be shimmed to allow the cylinder block saddle to be level, which means the saddle will maintain a constant thickness all the way around.

Attachment 44177
Core plugs used to aid marking out the cylinder bores. This not only indicates how much material has to be removed but also helps in alignment for line boring.
Thank you for viewing
The home engineer