Big Boys CAD shootout for SOD

Now that Dave (SOD) has unravelled how to draw his cotton reel here is one to think about while digesting all those Easter eggs. DC-1 may also be interested as he mentioned wanting to do some pattern making.

Over the last week or so I've swapped a few e-mails and FB messages wit Graham Corry of Alyn Foundry fame as he had found details of Nikolaus Otto's flame sucker of 1873 and fallen in love with it. Some useful input also from Wayne Grennings and Linda Boots

I got another e-mail from him about 4.00pm yesterday asking if I could do a pattern and corebox for the base. together with this image and a note to say he has 7" flywheels that can be used so that will be what the drawing needs to be scaled to.

Well it sounded more of a challenge than cotton reels so I fired up alibre and in an hour or so had the basic pattern and core worked out.

Pattern

Core half

I've played about with it a bit more today and now have the core box halves to mould the sand core in

And this is the pattern with the core "removed" and the surfaces that had a machining allowance taken back to finished size. Still some small tweaks to do but just modelling the basic components to check geometry first.

So Dave is this something the Freebie CAD is upto

Whilst FreeCAD is more than capable of producing these parts, I wouldn't want to use it in case (in case?) it crashed. FreeCAD can annoy and amaze in equal measures (leaning to annoy just a tad).

This may be my nemesis! So far so good, though the way FreeCAD colours faces has me in me a tizzy:

Hmmm, the need to think about negatives and positives for castings has stopped play. I shall have to sleep on it!

Dave

Are there a few basic dimensions that we can use ?

Not too bad to do in MoI.

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?

Ta, Jason. Blowlamp's video is helpful, and I'm impressed with by MOI's user interface. Although the software is functionally similar, FreeCAD often uses dialogue boxes, which are a bit clunky for controlling CAD.

Likewise, FreeCAD's pad/extrude tool doesn't support tapers yet, and I find their Draft Tool to be more of an intelligence test than I'm comfy with! So I mostly do tapers by lofting them, easy enough but needs a few extra steps compared with slicker packages.

It wasn't making negatives in CAD that had me confused. It's the thought process required to work out the shape of the mould needed by a sand core. Even though I have high confidence Jason knows his stuff, I'm still not convinced this is correct:

Anyway, back from delivering Easter Eggs, I was ready to FreeCAD the mould except I've gone all blurry due to Hay Fever. And it was snowing a few days ago...

Dave

Despite not being able to see properly:

Less than half an hour - had to stop and feed the cat!

All done by eye, but I could go back and dimension it properly.

Dave

It may have to be a multi-piece corebox in order to get the core out without breaking off something.

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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.

Well to avoid my screen turning red with collision warnings in F360's simulator I has to set quite a bit of tool stick out, 115mm to be exact particularly as it was only a 4mm dia ball nose cutter.

Pattern looks to have come out OK though and all tools intact

Core boxes next on the list but only about 50mm deep needed.

Very nice pattern work !

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I prefer Jason's picture to Andy Warhol, who made a lot of money from this tin can:

Cream of Mushroom used to be my favourite, until they cheapend the recipe and ruined it.

One half of the core box having been machined, last op was drilling two 6mm holes for dowels, HSS Lip & Spur drill

And bot halves complete with the base pattern and the small item at the bottom is a pattern for the pair of bearing caps. Should be off to the foundry tomorrow.

I don't think I have ever seen anyone put the lettering in the core, and not by CNC either.

Saves having a two-piece pattern.

Reversed lettering I guess.

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Edited By PatJ on 28/04/2022 20:33:14

No the lettering is the right way round, it will be in reverse when you look at the core produced from the box and that will then leave the cast impression the right way round.

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

Nicely done !

The 3D world opens up a lot of potential for recreating the old engines.

I will be glad when I get caught up with work, and can get back in the game again.

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