Complex casting

[matt-jaysey]

Hi, im new to this site so i'd like to say hello all!
I've wanted to make engine models for years now, and finally im gonna give it a go. However, I want to make modern engine models not old school ones. Nothing against then I just like the new stuff. I'm starting out with a Subaru 2.5 liter STI 4 cylinder boxer. I've collected hundreds of pictures and constructed a basic model on the computer. What i wanted to bring to peoples attention is how im planning to get the scaled model off the computer to here in the real world.

Unfortunately I can't afford a CNC milling machine. I had to come up with a simpler amd less costly method. At work one day a was using our Epilog CO2 laser and it hit me. Searching around at work I found some card that was exactly 0.5mm thick and was heading for the bin. I collected this card, and when i finished my shift, i cut out a simple gasket shape to see how it performed. It came out fantastic.

After a few weeks I sliced my 3d model into 0.5mm thick sections and set about with the card and laser. I produced several sheets with acurrately cut out sections. Im going to have to take and upload some photos this evening if i can on my progress, hope this is of some intrest to some of you.

matt+

 

[90LX_Notch]

What's your machining and metal working background? I'm not saying it can't be done; but, that's a lofty goal unless you've done this before. This is a hobby that isn't as easy as it looks. You really have to understand fits and tolerances, especially for an internal combustion engine. Anyhow, best of luck with it and keep us posted. Make sure to post your progress; it will be a neat model.

 

[matt-jaysey]

Hi notch

Im 26 years old and from England, I have worked for various machining companies, I used to work for a company that make surgical instruments for the British army. No this is my first model engine project but I have about 15 years engine experiance. But im here to learn as much as i can as i only cut my first piece on the lathe 5 years ago and I know thats not long at all. Cheers for the reply

matt+

 

[90LX_Notch]

Matt,

Well that's good to hear. If you are serious about this, take this advice: build some simple engines first. You'll be amazed at what you'll learn.

Bob

 

[Lakc]

Congrats, .5mm cardstock should work fine, thats basically how the first rapid prototype machines worked. Having a good pattern is a great start to parts coming out of the sand correctly.

 

[matt-jaysey]

When you mean simple whjat exactly do you mean? Surely an engine from a casting is an engine from a casting if its shape is complex or not. I have seen what alot of people have done on this sight. Machining entire crankcases from a billet block. Thats amazing and well above my ability. But I only want to cast a block and then drill and ream some holes.

Ah one thing i didnt mention before is that this engine isn't going to run. I know that seems abit crazy. I just want to make a model replica. After hopefully completing this one and possibly afew more I want to give a running one a stab. but for now just a scale replica.

matt+

 

[matt-jaysey]

I must appologise i sound rude but im just telling you what my ideas are. This is probably gonna end up tits up but i love just jumping in and having a stab at it.

matt+

 

[matt-jaysey]

Hi all,

Ive got some pictures i justy hope they load

This is the crank built up before slicing.

This is the head before splitting. This took me about 6 hours to construct. (Im not the fastest modeler in the world)

This is the head split into 71 0.5mm sections the scale of the head and engine is 1 to 4.

I then cut the card with the epilog laser and ended up with sets of card. Theee were then stuck together to form a solid 3 dimentional object. More pictures coming soon

matt+

 

[90LX_Notch]

Matt,

You have to realize that the engines on this site actually run. That's why I was trying to convey that it is not as easy as it looks. A static model is a whole different story. Good luck with it. Keep us posted.

 

[Tin Falcon]

Matt first of all welcome to the forum.
Bob was just trying to offer some friendly advice. the consensus here if for most folks to start out with a simple air powered single cylinder wobbler or the like .

it may be benificial to read these threads :
Getting started in Model engineering :
http://www.homemodelenginemachinist.com/index.php?topic=9413.0

selecting a first engine to build.
http://www.homemodelenginemachinist.com/index.php?topic=16003.0

Jump in where you feel comfortable.

My first build attempt was from castings in retrospect a different choice would have been better.
Tin

 

[matt-jaysey]

Thanks fellas for all the input. I have done alot of casting in the past and its what im comfortable with but i here what you say. However I've read through alot of peoples post and many people seem to ignore what engine builders have done for years. Many of the engines posted on this site have tiny crankpins. Bears are made from brass without oil feed holes and not much attention is focuses on hardening steel parts. I maybe young but I ahve been doing this type of work since i can remember. Im not a novice and i appreciate that there are many people that have started project with bright ideas and not finished them. Only time will tell of course. One question that I do have is does anyone use core drills to great effect and what dimentions do they undersize to? cheers

matt+

 

[Mosey]

Matt, Welcome.
Keep rocking the boat! I love it. Who knows what you can accomplish?
Mosey

 

[idahoan]

Matt

I'm not completely clear how you plan to use the laser cutouts; will they somehow be used as a casting pattern or just glued up for a full scale mock up?

About your comment on the crank pins, brass bearings and lubrication; keep in mind that a lot of these small models are not a scale models of any particular full size machines; but in many cases they are scale models and they did have bronze or Babbitt bearings and used drip lubrication or grease cups. Primitive I know but that is the way stationary engines were made back in the day.

Please keep posting pictures of your progress.

Best regards,

Dave

 

[gbritnell]

Matt,
Good luck on your future projects.
gbritnell

 

[matt-jaysey]

Just thought I'd add some more pictures of how things are going. Yes im stacking the layers of card together to make a 3D 'plug' to mould from

This is some of the sections for the left side cylinder head cut out. The white tape is to keep then in order before gluing.

Here is the cylinder head glued together and sprayed with primer to give you and idea and better look at how the layers build up. It took me 2 hours to glue and isn't perfect, but im going to sand it back slightly and fill in the steps between the layers. The Aluminium casting is going to shrink slightly. Therefore im going to use high build primer to build up the model. I'll use a dial caliper to measure how much i've put on roughly. Im looking for about 2% increase in dimensions.

The holes havent been cut as they will be drilled and tapped when the casting is complete. The model will be painted and polished before apply the RTC silicone. This will aid in removing it from the silicone casting.

Below are some more pictures to give you an idea......

You can see the protrusions sticking out where the valve seats are to go. This is for the core prints needed when casting the metal. I'll show them when ive finished them all.

This is the back end. The not so round sections will get the treatment from the filler then cut back into shape.

The con-rod half finished although this was a dummy run just to give you an idea. the actual rods wont have the holes incorporated into the casting, they will be drilled and reamed. I'm gonna make up a jig for the hole alignment.

Hope you enjoy! Any ideas, questions or criticisms please fell free to comment.

matt+

 

[matt-jaysey]

Sorry i've kinda missed the point of what im trying to achieve. Im building up scale replicas of each part from models that i've done in 3d on the computer. Ive then built these from card and im going to pour RTV silicone in 2 or more planes, like sand casting. Im then going to pour paraffin wax into the silicone impression to give me a wax model of the head and other components. This will have the cores already incorporated into the silicone before pouring. Im then going to submerge the wax in green sand and turn the sand box upside down and melt the wax away in the oven. Once this is done i'll have a void in the shape of the head. Then in goes the aluminium and bam! i'll have a perfect copy of the head in aluminium.

 

[stevehuckss396]

Can't wait to see the outcome. Keep the pictures coming!

 

[IronHorse]

Fantastic idea! I'm going to be following this for sure ;D

IronHorse

 

[Jasonb]

So if you are using that laminated card as your casting pattern how will you pull it from the sand, you will also need loose pieces, cores, core prints etc and have you allowed for shrinkage. What have you added for a machining allowance on all the machined surfaces, I can't see much if any allowance.

I would have cut it out of something that can be melted away then you can use a lost wax/foam type process.

J

 

[matt-jaysey]

Sorry i've kinda missed the point of what im trying to achieve. Im building up scale replicas of each part from models that i've done in 3d on the computer. Ive then built these from card and im going to pour RTC silicone in 2 or more planes, like sand casting. Im then going to pour paraffin wax into the silicone impression to give me a wax model of the head and other components. This will have the cores already incorporated into the silicone before pouring. Im then going to submerge the wax in green sand and turn the sand box upside down and melt the wax away in the oven. Once this is done i'll have a void in the shape of the head. Then in goes the aluminium and bam! i'll have a perfect copy of the head in aluminium.

1mm was added to the valve cover surface and 1mm (2 sections of card) was added to the head surface. shrinkage is added by layers of U-POL high build primer number 5.

matt+