The Bucket Foundry

[Flettner]

if you were making enough to make it worthwhile, you'd press the piston in two halves from sheet. Then TIG weld and finish machine.

But dies are time consuming to make - unless someone can 3D print a master to use to cast them.

The CNC can make the steel dies.ok. Another thought..
Can you get 4140 in sheet?

[husaberg]

T

The CNC can make the steel dies.ok. Another thought..
Can you get 4140 in sheet?

Apparently yes well close enough.
https://www.apparts.co.nz/product/4130-steel-sheets/

[Flettner]

Apparently yes well close enough.
https://www.apparts.co.nz/product/4130-steel-sheets/

4130, Ive got a sheet of that at 0.065"
Make some of my gyrocopter bits from it.

I want 4140 so it will nitide.

I might be better to machine it out of three parts then weld together. Two sides and a crown.
Maybe press the sides and machine the crown?
Can you nitride 4130 I wonder?
Or better still machine the main part of the piston from both ends then weld a machined crown on. Stronger and only one weld needed.
Working with steel means you have different options to play with.

[husaberg]

4130, Ive got a sheet of that at 0.065"
Make some of my gyrocopter bits from it.

I want 4140 so it will nitide.

I might be better to machine it out of three parts then weld together. Two sides and a crown.
Maybe press the sides and machine the crown?
Can you nitride 4130 I wonder?

Google says yes

Materials that can be nitrided include low carbon steels, which will develop file hardness, alloy steels such as 4130, 4140, 4340 and Nitralloy 135M which are the most common nitriding steels.

https://blog.metlabheattreat.com/pos...shock%20steels

[Frits Overmars]

Ive been thinking about how to make the exhaust piston for this engine. Id like to make it from 4140 steel but the machining is going to be quite complex and not really what I want.... Thought came to me, make it in two halves, tig weld it together, finish machine the outside. That way I can machine the inside of the piston quite thin and easily. Just a 3D die cut on the CNC, or better machine a carbon eletrode and spark erode, get very fine detail that way. Keep the weight acceptable....
I might be better to machine it out of three parts then weld together. Two sides and a crown.
Maybe press the sides and machine the crown?... Or better still machine the main part of the piston from both ends then weld a machined crown on. Stronger and only one weld needed.

Neil, the piston design shown below was intended to be produced without access to CNC or spark erosion. You can make the skirt as thin as you want, zero welds needed.
The only place that is not easy to reach with conventional milling is right above the gudgeon pin bores, but you need support between the pin bores and the crown anyway. And since most of the mass of any piston is concentrated above the pin bores, placing the pin high in the piston is advisable if you want a light piston.
This design, intended for a short gudgeon pin, shows a through pin bore, intersected by the recesses milled from below, but of course it can also be made with a blind pin bore. It also shows short, straight load support paths and heat paths between the crown, the pin bores and the skirt.

[Flettner]

A bit like this,

[Frits Overmars]

A bit like this

If you're going to screw caps into a piston, it'd better not be an aluminium one. Steel will definitely provide stronger threads. Or you could consider titanium: lower mass and better high-temperature strength (and terrible detonation-inviting heat properties, but steel won't be so much better in this respect).
I know you're only going to use it for the exhaust piston of your uniflow engine; still...

[F5 Dave]

Said with the disdain of an 80s boss paying wages "heres your weeks worth, even if you'll only spend it on beer and hookers"

[Flettner]

If you're going to screw caps into a piston, it'd better not be an aluminium one. Steel will definitely provide stronger threads. Or you could consider titanium: lower mass and better high-temperature strength (and terrible detonation-inviting heat properties, but steel won't be so much better in this respect).
I know you're only going to use it for the exhaust piston of your uniflow engine; still...

Hypereutectic aluminium heat trasfer properties aren't wonderful either.
I have a plan Frits, as you might imagine.

[Flettner]

A wee press tool to make some dimple holes to aid airflow from the radiator.

[F5 Dave]

That should prove quite sturdy. I was looking out for you at Bermbuster this weekend on the off chance.

[Flettner]

That should prove quite sturdy. I was looking out for you at Bermbuster this weekend on the off chance.

One day soon I hope. I havent wreaked the engine on the dyno, just yet. Did some runs Saturday with Wayne Blackwood, its running a lot better but still needs work. One issue is this extra fuel needed as the engine gets hot, E85 an oxygenating fuel apparently. I need to keep the engine temp constant while we tune it. At the moment we have a few minutes window then temp climbs away.
Im setting up a centrifugal fan that I will attach diret to the
radiator.
Once this is initial tuning is done I can work on the temp related extra fuel variation.

[ken seeber]

Well, been getting distracted from working out how to test (various dyno designs) the wonderful & huge power increasing benefits of the DCI system, been doing more casting stuff.

So, following on from my last post in Foundry of #4881 (nearly a year ago) and some to-ing and fro-ing, have been casting qty of inlet runners. These are for an Infiniti V8 engine that has been fitted to a Nissan 300ZX. The runners fix to the heads and, with a rubber boot, connect to a series (4 left & 4 right) of Hayabusa throttle bodies.

Been using a mix of Plaster of Paris and fine sand. Still they can crack up. So added a small mix of chopped fiberglass to give it some reinforcement. Doesn’t stop catastrophic failures, but contains this to very fine surface cracks. Made a small fixture to hold the castings for machining the flange face.

Just can't help to add that the smoke and carcinogenic fumes when burning out the 3D print are not less than really impressive.

In hindsight, it would probably have been easier to two patterns and corebox and mould in sand. However, it was a bit of an exercise in lost 3D casting. The Polycast printed ok and could be vapour polished using Isopropyl alcohol, but it was really annoying that the last 25% of the roll of filament was bonded together and unable to unroll. Not cheap stuff. Will stick to PLA for any future exercises.

[Flettner]

Almost too ashamed to show this.

[F5 Dave]

I'm not surprised. The photography is dreadful. What am I looking at?

Although I'm reading this on a phone in a cafe over heating in too much riding gear.