Metal casting

[wbks]

Seems quite interesting. Thinking about the whole John Briten story, I googled DIY casting, and basic skills aside it seems pretty simple to make your own parts for bikes that are hard to trace parts for, or just cheaper, or just for the sake of it. Just stuff that doesn't need to be too exact like points covers, levers, stuff like that through sand casting (I think?), anyone had a go at it?

Obviously engine casts would need to be fairly exact and strict in quality control so does anyone know what process goes into that? Is it something that people can do in their shed?

I don't intend to do any, this is just out of interest.

[P38]

Uncle Bill builds Steam Trains in his spare time in his shed.

He made an LPG furnace and casts Aluminium, Bronze and Brass parts using Green Sand.

It's a facinating process which is relativley easy to do, However the hard part is in the pattern making.

The patterns have to be exact or the casting will not be satisfactory.

Getting the moisture content of the Greensand right is an art too.

Too wet and you generate too much steam which results in a porus casting full of holes, or worse still the molten metal will explode on contact.

Too dry and the sand wont hold the shape of the pattern, fine detals will be lost and the mould could collapse when you pour the molten metal in.

There are also several ingredients added to the molten metal which improves the properties of the finished casting. One ingredient he adds to Bronze is glass, usually a broken Beer Bottle.

Temperatures are very Hot 1100c so be very carefull and make sure there is no water that could spill into the molten metal as it will violently explode.

[Macros]

you also need to think about adding impurities to give the grains a more equiaxed structure.

[James Deuce]

There's a whole bunch of different casting techniques that all produce different results and require a good understanding of metallurgy (experience or study is good) and being able to make precision adjustments to tools and dies by hand. I can't. Which is why I never went much beyond operating machines and lots of classroom time. The whole thing is fascinating, but by golly you need to know your stuff to make things that will work under any sort of load, either thermal or kg/m of force.

As P38 said all of them rely on expert pattern makers, die makers, fitters, and toolsetters. There are a few very talented people out there who can do it all, but it isn't as easy as it seems. I've worked in sand casting, die casting, and vacuum casting and the only sure thing I can say is the successful operations all depend on one or two individuals who now the craft well enough to use intuition when required.

I've been burned enough, and seen enough people burned badly to know you don't step into this lightly. Get moisture content wrong in sand and combine it with an alloy not meant for sand casting and it's a mess. Get a die with micron thick high spot and you have molten alloy spraying out of the die casting machine under pressure. Lose a seal in a vacuum machine and you better run. Even plastic vacuum moulding can be dramatic when it goes wrong and you're talking much lower temps.

The planning and preparation for one off parts is immense. It's cheaper to get them machined.

[TLDV8]

Lost Wax ?.

[wbks]

Could an experienced engineer make a mould of an engine part by part and make a complete copy of it that would run good?

[Brian d marge]

been there ...ouch ......

I use rapid prototyping for small stuff ( pattens ) ..but try 700 dollars for a brake lever ...not much cheaper from the states

The actual casting is much cheaper ,,,about 17 dollar/kg cant remember now ...but not far off ( pattern supplied )

compared to 20 bucks for the lever???

Ps........ yes 3d scan mod the STL , and print ,,,still $$$$$$

[Ocean1]

I use rapid prototyping for small stuff ( pattens ) .

You can RP directly in tool steel or titanium now, (Ti medical prosthetics in particular), and they're working on other alloys. No local supplier though.

[Madmax]

I made a cylinder head for a mates Rudge Ulster
using lost wax method
cast the mold in clay fire it wax comes out,
its dry but does not collaps when you pour your metal in like sand
and does not tend to explode in your face
I worked restoring old race engines (any engines including aircraft)!!
We had to make quite a lot of parts as they were missing
and copy rest from borrowed parts,
Try making a sodium cooled valve!!
or a crankshaft from a piece of billet!!.
one thing you have to allow for when casting is shrinkage
it varies from different alloys and metals
Alloy is about 5%
the lost wax method is used buy jewllers for detail
you can copy make just about anything with practice

[wbks]

Sounds interesting. Hey, just out of interest... Can you make small changes to moulds i.e turn a piston mould into a high comp. one?

[speedpro]

I've got friends who have been pissing round with casting things for ages. So far they've managed a pile of hub centre steering bits, a uniflow 2-stroke engine, and a 750cc V3 bike engine, and twin cam twin port cylinder heads for Subaru aero engines.. They are pretty casual about it but if you are just sitting round having a few beers you get a better idea of the million things they had to get right. some was done in the back yard, others were sent off to the foundry. I've made a few moulds and had stuff cast and heat treated and then machined it myself but it was very simple stuff.

[wbks]

A 750 v3 sounds interesting! Did they make it from scratch? Did it go well?

[Madmax]

Sounds interesting. Hey, just out of interest... Can you make small changes to moulds i.e turn a piston mould into a high comp. one?

Thats pretty easy
the hard part is machning them
A piston is not round its slightly oval,
narrower across the pin sides to allow for expansion,
then there is the ring groves
Try cutting one for an L section Dykes ring
with pin holes to let the compression seal them

The V3 750 used rm250 barrels (I think)
and a ZXR 750 gear box

[wbks]

So you could pretty easily (in your words) make replica piston exactly the same as a stock one or an aftermarket one, and make it out of lighter material? Sounds like burt munroe type stuff lol

[jrandom]

Like Jim2 sez, lots of automation out there these days. If you can make a 3D CAD model of it, someone can cut it for you on their CNC mill.

If you don't have the right 3D CAD software, uh, well, let me know. I can probably help you find someone who can help you with that. Learn to use it and you've gained an employable skill, too.

Machining one-offs with computer-controlled gear is far easier, faster and probably (time being money, etc) cheaper than attempting to cast things.

Not to mention that, assuming your design or replication is correct, you get a stronger, higher-quality part.