Dave, making the negatives is quite easy as you can see in Blowlamps video, look at boolean subtract or similar terms.

Paul, there are basic sizes in the second image I posted which graham had worked out using a rule and calculator. I imported the image into CAD and scaled it to show the flywheel at 178mm (7" ) then any line I drew on top would give me a measurement.

Eddie Blowlamp, yes quite a few similarities between the two and I'm sure other programs would work in a similar way though, I did add draft to the core so it could be pulled from the box but that's more a practical issue than the CAD. I don't think I would have it set with cm as the unit, have that issue when I occasionally draw in F360 which defaults to cm on the drawing side but strangely mm in CAM unless I changed it at some time in the past?

All the core features will have draft so should come out of the core box OK.

Dave, yes you do need to understand the casting process to know what the core needs to be made like so that it will do what you want.

Basically the pattern will form the cavity in the sand. The core is then place inside this cavity. It is located front and back you the two large projections touching the surface of the cavity and the same at one end. To stop any risk of it moving end to end the two projections on the top of the core that form the round and rectangular opening are longer so that they go into the two registers created by the black core prints on the pattern.

This shows the core inside the pattern and you can see the protruding features come to the faces so iron can't flow into the holes in the base casting

This has the pattern set to transparent so you can see the core in place

And finally a section along the ctr line showing where the metal will and won't flow. We decided to go thicker than scale to ensure a good pour. The top and bottom surface swill be machined back to leave 3mm thickness and if desired the walls can have a tickle with a die grinder to make the edges look thinner.

Almost hot out of the sand. I'll post some better shots once I get my grubby little mitts on it.

My castings turned up today and I'm quite pleased with how they came out particularly as it was my first pattern with a core. External surface finish could have been a little smoother but I think that is one of the problems with airset as they don't seem to sieve any fine sand on first and just ram it up in one thick layer which can leave the sand surface a bit porous so the iron replicates that. These are the bits from my patterns

The bit of writing that was a last minute addition turned out quite well, easily read yet out of sight for most that will view the model.

And here is the rest of the "set" including the scotch yoke which is a brass casting and the spun brass piston which will give it a thin wall and light weight which should help with running. There is also an iron flywheel casting that I forgot to include in the photo

I just need to catch up with Graham now who is posting good progress over on his Facebook Page

Edited By JasonB on 19/05/2022 14:46:36