Be gentle with me.

Hi all,

I have joined other model engineering forums (forii?) recently, so if you have read a post from me somewhere else, you've heard it all before.

I am hoping to build a working scale model of a 1930 Austin Seven engine. I have two good full size drawings and a real engine I can strip down and measure. I am teaching myself to use 3D cad programmes, I seem to have settled on FreeCAD even though I also have Fusion 360 and Solidworks. I am now looking to buy a 3D printer so I can see what the model will look like and figure out how to make the moulds for the castings. I would prefer to use cast iron for the block, head and crankshaft, but I might have to settle on aluminium for the first two and steel for the crank. I have seen other A7 engines and now realise what a task I have set myself. I can't wait for the day I fire the engine up!

Lee. (Illogan, Cornwall)

That's a pretty ambitious project, Lee. I wish you the best of luck. I know there are Austin Seven owners on the forum who might be able to help you out with any queries. I owned a 1934 Austin 7 Ruby in my youth and was, at one time a member of the 750MC. I have a copy of their "Design for competition" book on my bookshelf, which may contain a few gems.

I have a vague recollection of seeing the germ of a build thread of an A7 engine, on another forum, somewhere. It was a couple of years ago but it could have been on HMEM or Model Engine Maker.

Jason Bellamy will probably be able to give you chapter and verse.

I'll be interested to follow your progress.

Oh, and welcome to the forum!

John

I knew I'd seen it! Have a look Here

Edited By John Hinkley on 17/10/2019 10:11:02

Hello Lee and welcome to the forum. That sounds like a very interesting project, speaking as a former A7 owner.

What scale are you thinking of working to?

Brian

Welcome Lee. Please publish photos as you make progress. That's quite a project. As a beginner I'd tackle the easy bits first. More experienced builders seem to prefer doing the hard parts first.

I use FreeCAD and Fusion360 and like them both. FreeCAD is fine for modelling single parts but it doesn't do Assemblies yet. F360 is much more advanced when it comes to modelling the joints needed to create assemblies.

Assemblies are particularly useful when designing a new object or recreating the actions of an old one when you don't have a plan and can't take a real one apart. For example, developing a piston, FreeCAD requires all the parts be modelled separately : head, rings, gudgeon pin, and con-rod with bearings. Each part can then be made and, provided the designer got the critical dimensions correct, there's a very good chance the parts will fit together in the real world, hurrah.

Fusion 360 goes a useful step further - it allows all the parts to be assembled realistically in the computer model, including the rotary joint between conrod and gudgeon pin. More! Multiple assemblies can further assembled making it possible to model an entire engine and check all the parts move correctly without colliding when the flywheel is turned.

With full access to a real engine, FreeCAD is 'good enough'. An example where F360 would be better is one of those old steam loco designs notoriously riddled with drawing errors. It would be worth modelling one of these in Fusion to flush out the bugs before attempting a real-world build!

Never used Solidworks myself. Fusion 360 is being developed as a competitor and still has some catching up to do. F360 takes a different approach to modelling joints than Solidworks and other similar tools. AutoCAD claim that Fusion's 'Joints' are more intuitive than everyone else's 'Mates and Limits'. I think they have a strong case, which is good for attracting newcomers, but I doubt anyone who has already mastered mates would rush to switch.

Apologies to Lee if he knows all this already!!!

Dave

Edited By SillyOldDuffer on 17/10/2019 11:08:23

Welcome to the forum, Lee.

Sounds a great project. Don't make my mistake and model a full size engine too small.

Neil

Hi Lee,

All I can say is that "You are a better man than me ,Gunga DIN" !

Thanks to all for the replies. I had originally thought I would make the model 1/4 scale, but that looked awfully small when I started to draw it. I then decided that 1/2 scale would be easier for me, this is my first attempt at model engineering. OH! I can hear the groans already! Start small, make something easy. I know I should, but there's something broken inside me that says, you can do it. I then dallied with 1/3 scale before listening to reason(?) and I have settled on 1/2 scale with 1/3 on the back burner. I know I have taken on a large task, but I built my first full size A7 in a garage 7 miles from home with no electricity. I love a challange! The only challange I don't feel up to is making cast iron parts. I will have to make most of the engine in aluminium and then paint it to look like a display engine, I don't mind that.

The comments made by SOD about F360 are one of the reasons I stopped using it. I felt that exploring the creation of joints would take me away from learning to design the engine. I now see the point behind watching a working model in action on screen. I have all my cad programmes on a second computer (second hand but very well specced) which is very rarely connected to the WWW. Fusion is supposed to run without internet connection, but it refuses to on mine. Both Solidworks and FreeCAD are happy, for the moment, to not be online.

My next purchase will be a 3D printer so I can print the parts I have drawn, the block and the head, and figure out how to make the moulds. I had considered the lost pla way of casting parts, which is why I will probably buy that type of printer rather than the type that prints at a much higher resolution with resin. I would like to make moulde I can re-use. When I have the parts printed I will post them online.

Neil, do you mean that a scale model sometimes doesn't look like the real thing scalled down? A friend used to build scale model locos and said once that some of the dimensions were "out" to make the model look more like the real thing. It's a shame he doesn't live in Cornwall anymore because he was also an A7 owner.

Lee

You could always carve it from a solid block of cast iron in much the same way as one linked to above was carved from a block of aluminium. Or have it cast in iron from your patterns though there would be a lot of work with cores and loose pieces as lost PLA is unlikely to replicate all the internal passages even if you tried to investment cast it.

Grey cast iron would not be strong enough for your crankshaft, you could machine from SG Iron bar if you don't want to use steel

Which shows why it is so important to have a clear search engine friendly title on threads.

Or Just a good memory for where the thread is, I gave Lee a link to the engine yesterday when he was asking on MEM.

It is interesting to know that a half size engine will end up being 1/8 of the capacity, so a 750cc engine will be 94cc.

The main thing I don't like about Fusion is it's a Cloud product. Although designs are stored locally - 'cached' - for performance reasons, they're also copied to a central repository on the web. The web copy is the master, most useful when a team is working on different parts of a large project.

Fusion does work off-line, but only within limits:

1. Installing the product requires creation of an online Account and downloading an installer that does further downloads as the package is built. This stage requires an Internet connection.
2. In order to start Fusion the first time it is necessary to login with a password. This is validated against the central account and requires an internet connection.
3. Not having an internet connection later means the product isn't kept up to date. As it is still being developed, Fusion is frequently upgraded with bug fixes and new features, sometimes every day .
4. Not tested it but this is what I think happens. Once a user has logged in, Fusion remains active for about a month. During this time it's possible to work off-line but Fusion eventually Signs-Out automatically. Then the user can only reactivate Fusion by logging in with an internet connection. Once reconnected, her project is uploaded to the cloud and any backlog of upgrades downloaded and installed.
5. If a user signs-out manually at any point, an internet connection is needed to log back in again.

The purpose of the arrangement is to allow Fusion to carry on working during temporary network outages and to allowing work to continue on a mobile computer over a short holiday. It doesn't support unrestricted off-line working like Solidworks or FreeCAD.

I re-connected my cad computer to the internet yesterday to allow F360 to update its licence. All my old drawings were gone from the left hand panel, can't remember what it's called, but I still had a copy of the drawings on my HD. I started to use it and soon remembered another reason why I stopped using it. I don't like the dimensioning tool, in fact I don't like most of the tools and the method of selecting them in F360. I suppose I am more used to FreeCAD and Solidworks to bother with Fusion. I am not sure if I will ever need to see my design 'working'. But my main dislike of F360 was the internet connection. I had it installed for many months before I tried it without the internet on my back-up computer, it fell over and refused to work. One of the reasons I never upgraded Sketchup 2017 is because the later version is cloud based.

94cc! Thats almost two mopeds!

3D printer now on order for delivery Monday. If my designs print out OK I will post pictures.

Lee.