Strictly.... “ Hot Air “

[Alyn Foundry]

Good morning Richard.

My sincerest apologies, the last couple of weeks have  been very busy due to school holidays and my full time carer duties. I'll contact you today via email.

I visited Andy ( Chipmaster ) yesterday and was shown his collection of Alyn Foundry engines, amongst others. His craftsmanship is of a very high quality and his recently completed Robinson hot air engine ran almost silently!

Andy is helping me coordinate with the foundry that's going to, hopefully, produce a small batch of castings for us from the patterns pictured above.

Cheers Graham.

[ettingtonliam]

Graham
What do you use these days for the jointing/insulating material between the lower displacement cylinder and the tripod base. Its shown as asbestos string on the drawing.

Hope you are getting over your chest infection

Regards

Richard

[Alyn Foundry]

Hello Richard.

We're quietly getting better, thanks.

Regarding the insulation, on the last 4 we haven't used anything but you could probably use the " sealing rope " that's made for " wood burning " stoves.

Cheers Graham.

[ettingtonliam]

Graham
What clearance do you use between the displacer piston and the displacer cylinder bore? The can I am using for the piston gives an OD of around 3.280", and the cylinder bore will probably clean up to around 3.300". The drawing shows a bore of 3.400.

Richard

[Alyn Foundry]

Good morning Richard.

The bore diameter isn't too critical. The bigger the clearance the less air travels through the regenerator piston and the quicker the engine will run.

I'd aim for the smallest clearance that ensures the displacer piston doesn't rub against the cylinder walls.

For those of the readership here interested, I had a phone call from the foundry. They are about to cast a platform in the next day or so. They have successfully cast some of the other parts like the flywheels and bases but these are child's play by comparison, I'm keeping my fingers crossed for a positive outcome.

Cheers Graham.

[Jasonb]

Thanks for the update Graham, hope those cored parts come out OK

I got a few more "castings" from my foundry too

[ettingtonliam]

Thanks Graham.
I think I'll go for a bore of 3.300" giving 10 thou clearance all round If it isn't enough, then its easy to bore out a little more later.

Richard

[Jasonb]

For those of the readership here interested, I had a phone call from the foundry. They are about to cast a platform in the next day or so. They have successfully cast some of the other parts like the flywheels and bases but these are child's play by comparison, I'm keeping my fingers crossed for a positive outcome.

Any news yet on how the platforms came out or any other bits of interest?

J

[Alyn Foundry]

Hi Jason.

Sadly no, it seems a bereavement may well have put things on hold for this week.

The tally is mounting I'm expecting the total weight to exceed 100Kg by the time they have completed my order.

Cheers Graham.

[Alyn Foundry]

Hello All.

Some minor setbacks, see attached.

First picture is how the cores are laid out in the mould before closing and pouring.

Cheers Graham.

[Jasonb]

Bit hard to see from the photos but has the iron not flowed down to the cylinder end of the casting?

[Alyn Foundry]

Hi Jason.

Yes and by the looks of it trapped core gas was the prime culprit.

The guys at Rhuddlan used a little trick called a " run off " they ran a channel off from the opposite end of the " in gate " . This channel carried both metal and gas away whilst the core " fumed " and fresher metal replaced the gassy stuff.

Cheers Graham.

[ettingtonliam]

Graham
My drawing shows the flange of the displacer cylinder as 4 5/8" dia. The studs fastening the main casting (the one the foundry is having trouble with at present) to the tripod base pass outside this flange, and presumably help to centralise the displacer cylinder. The drawing shows them as 1/4" dia, on a 4 27/32 PCD. Should this be 4 29/32 PCD, otherwise they foul the flange?

Regards

Richard Wilson

[Alyn Foundry]

Good morning Richard.

I've built many of these engines over the years, the drawing was made from the first. One modification was the practice of making the " O " ring groves one eighth the thickness of the ring in both the platform and the " hot pot " . This both accurately registered the 2 components and ensured a good thermal barrier.

I've recently discovered several inaccuracies that strangely were never reported, you've reported another!

Ideally you would like to see the nuts flat on the platform flange and not overhanging the edge. By using the registering method above you could always reduce the " hot pot " flange diameter a little.

Cheers Graham.

[ettingtonliam]

The hot air engine progresses but slowly. I've machined the tripod base and the displacer cylinder, now progressing to the platform.
I've got a Denford Synchro 280 lathe which swings 11 1/2" over the bed, so its not small by home workshop standards. I had the devil of a job setting the platform in the 4 jaw to machine the underside. When the cored out cylinder was running true (as near true as a sand casting can be), the outer corners of the platform clouted the back Vee on the bed, and the pivot shaft for the chuck guard. The chuck guard pivot was no problem, I don't use it anyway, so off it came.
I had to radius the corners of the platform (big file!) to get clearance for the bed, but thats OK now, only just skimmed the edges of the end letters of 'Robinsons Patent'.

Thinking about it now, maybe I'd have been better off setting it up on the mill and using the boring head.
The other solution would be to grind off that back Vee, it doesn't do anything near the chuck as the tailstock is the only thing that runs on it. If I thought I could do it neatly, so it looked almost as if it was made that way, I think I would, I'm just afraid of ending up with it looking like a butchered job.
Now to start machining it. Theres a few surface blow holes, so I'm hoping they don't open up as I get below the surface.

Richard