Marking out steam engine cylinder block

[thehomeengineer]

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


Cast iron cylinder block


Checking fit before glueing


Completed ready for attaching to box plate for marking out.



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