Machining cylinder castings.

[Eric CoxParticipant @ericcox50497]

I've been looking at the drawings for the cylinders of LBSC's Tich and the Northumbrian.

Both give the centre of the cylinder bores as so far down from the top of the casting and so far in from the side but there is no dimension to fix these two datums.

If I just clean up the casting (top and side) and mark out the centre of the cylinder bore it throws the end covers out of position with the cylinder profile.

Do I work backwards ie. fix the bore centre from the profile then measure up and across to machine the top and side of the casting.

[Eric CoxParticipant @ericcox50497]

[Ryan NortonParticipant @ryannorton40317]

Hi Eric

The datum to use would be the core hole in the cylinder as described in the book and ME.

You need to determine the distance from the center of the core hole to the bolting face and port face.

If the distance to the bolting face is more than 7/8 and the distance to the port face is more than 3/8 than you can start operations as per the description as there is enough material for machining.

If the distances of either are less than the dimensions above, it means that the core hole is not true with the block and provision must be made accordingly. LBSC describes a method here for plugging the core hole with wood and using this to find the correct center of the bore.

Let me know if you come right.

Regards,

Ryan

[JasonBModerator @jasonb]

I never like using a cored hole as a datum as cores can move or be smaller than the core print on the pattern so not sit centrally.

I would plug the cored hole with a bit of hardwood and then strike several arcs in from the outer edge to determine the average centre position. This would then be my datum to measure to the flat faces. It also ensures that any circular cylinder covers are sitting concentric to the outer curved cast surface.

[Eric CoxParticipant @ericcox50497]

Thanks to you both for that. The Northumbrian casting doesn't have a core hole so marking out isn't a problem.

If I'm reading it correctly, determine bore centre from outer curved edge then work outwards to get the flat surface

Simples

I can get back to machining the castings

Edited By Eric Cox on 09/07/2015 09:09:03

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