Author Topic: Strictly.... “ Hot Air “  (Read 71691 times)

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #165 on: August 24, 2018, 12:26:51 PM »
Hi Jason.

They used a CO2 gas bonded sand that has very low fume characteristics. They made the two cores from it too.

The difference in finish was caused by " pattern drag " as has been shown very early in the thread the mould cavity is also made up in a kind of core box itself. My patterns are getting a little tired after over 200 runs. The top is formed from the sand that makes up the top box. This is part of the plate which is " dead flat " with just four prints for the water jacket core to register with, the two oval and two round holes.

Cheers Graham.

Offline Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #166 on: August 24, 2018, 12:38:08 PM »
Thanks Graham, that would explain the vertical shape of the "grain" caused by the pattern being withdrawn

Offline Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #167 on: August 27, 2018, 10:24:52 AM »
Question for those with running engines. How full should the piston be with the wire wool?

I have managed to turn mine from solid 303 stainless ending up with a 0.4mm wall thickness and have put eight 3.0mm holes top and bottom. I used some of the long curly swarf to put inside but if held upto the light I can see some daylight at the other end so do I need more. Or should I try with some fine wire wool?

Engine almost runs just not quite enough to sustain running.

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #168 on: August 27, 2018, 11:38:28 AM »
Good morning Jason.

Could be insufficient displacement.

On the last couple of engines I've built I used those cheap Stainless Steel pan scrubbers as filling, tightly packed too.

Hot air engines are akin to clocks however. An old horological friend used to say " tight enough to work, loose enough to run " makes sense doesn't it?

Cheers Graham.

Offline Chipmaster

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Re: Strictly.... “ Hot Air “
« Reply #169 on: August 27, 2018, 11:51:25 AM »
Hi Jason,
Have a look at the pictures I posted on this thread 22/2/18, I put two stainless steel pan scourers in the displacer. They would have been Spontex or Tesco brand. The scourers were unravelled and packed into the displacer to the extent that the tin lid of the displacer had to be held down when it was soldered in place.
I also followed Graham’s advice and put four half inch holes in the top and bottom of the displacer instead of 1/8 or 3mm holes.
Looking forward to getting my replacement platform casting  :whoohoo:

Andy

Offline Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #170 on: August 27, 2018, 01:23:33 PM »
Thanks, I'll give it another go with more packing.

I stuck with the 3mm holes as mine is only 35mm internal dia x 16mm internal depth.

I may also skim a thou or so out of the bottom cap as I think there could be a little friction there when assembled, engine spins freely but not loosely with the cap off.

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #171 on: August 27, 2018, 01:35:26 PM »
Hi Jason.

I forgot to ask, does the engine have the characteristic compression/vacuum feel when cold?

Also how or what are you using as your thermal barrier between the platform and the hot pot?

Cheers Graham.

Offline Jo

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Re: Strictly.... “ Hot Air “
« Reply #172 on: August 27, 2018, 02:20:16 PM »
Hi Graham, while I recover from this cold I have been doing a bit of casting fettling  :-X

I can report that the ends of the legs on the Robinson base were a bit hard and had to be fettled with a belt sander rather than a file. Those new arms are cleaning up ok.

And I decided as it was an easy thing to start I would have a little clean up of the hot pot. I assume it would be best to wait until I have a displacer cylinder so that I can get a nice tight fit on the bore  :thinking: which means I will need to buy a tin of Crabmeat.

Graham I have some rubber o-rings of 3.5mm diameter in my collection but nothing 4.75mm diameter did you say you had any spare?  :mischief:

Jo
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Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #173 on: August 27, 2018, 02:49:51 PM »
Hi Jo.

Looking good!

Yes I have a spare " O " ring, in fact I forgot to put it in with the kit. I sent them as a matter of course as they became more popular.

Now, don't forget that the " Crabmeat " displacer piston is a very loose fit. You're looking for a few Thou between it and the side of the machined casting.

Cheers Graham.

Offline Jo

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Re: Strictly.... “ Hot Air “
« Reply #174 on: August 27, 2018, 03:10:24 PM »
Now, don't forget that the " Crabmeat " displacer piston is a very loose fit. You're looking for a few Thou between it and the side of the machined casting.

I've been looking out a few recipes for disposing of the crabmeat I think a Crab linguine with chilli & parsley with a nice dry white New Zealand Sauvignon Blanc from Marlborough might be the way to go  :LickLips:

The other option I thought of was to empty two Tuna tins out through the bottom so that the tops are kept intact that was they are stronger for turning and drilling. The two tins are then joined around the mid line where they both taper so that you do not have a soldered on top  :noidea:

Jo
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Offline Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #175 on: August 27, 2018, 05:09:36 PM »
Hi Graham

Yes I do have a compression bounce on the engine when cold, more so at the top of the stroke than the bottom, hopefully you can see it here

<a href="https://www.youtube.com/watch?v=LoCLNsTY0Vo" target="_blank">http://www.youtube.com/watch?v=LoCLNsTY0Vo</a>

I've just put a washer between the cap and base on each of the three mountings until I get something more suitable for insulation, may be letting heat out around the edge and adding to the heat in the bed.

Well I changed to some wire wool, skimmed a thou or so out of the hot cap to get a bit more clearance, ran an airline into the bed to cool it and took a small blowtorch to Robbie's bottom and can now add another notch to the workshop doorframe :pinkelephant:

Still needs a bit of tweaking but at least it runs. Sorry the video is a bit jumpy but I had the blowtorch in my right hand and camera in my left.

<a href="https://www.youtube.com/watch?v=XT8Nn3nbPfU" target="_blank">http://www.youtube.com/watch?v=XT8Nn3nbPfU</a>


Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #176 on: August 27, 2018, 06:03:53 PM »
Aye, another notch indeed.

In your first video you could clearly see both the vacuum and or the compression, it depends upon your point of view.

A good thermal barrier is essential on these engines otherwise they just won't run. When I was at the Anson for the 150 years of Gardner exhibition earlier this year Geoff had managed to gather a whole set.

What was really interesting was that up to the number 4 just simple around the top cooling was used. The number 5 had a small tank that also doubled as the crankshaft bearing. The number 6 was fully tank cooled with the cylinder included!

Cheers Graham.

Offline Chipmaster

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Re: Strictly.... “ Hot Air “
« Reply #177 on: August 28, 2018, 06:57:42 PM »
Hi Jason, I didn’t realise your Wee Robbie was so small. However, it is an impressive runner having no knocking.

Andy

Offline Jo

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Re: Strictly.... “ Hot Air “
« Reply #178 on: August 29, 2018, 04:04:47 PM »
JB how does it compare in size with the Bruce Robinson Hot air  :thinking:

My flywheel has a hole  :wallbang: 

Jo
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Offline Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #179 on: August 29, 2018, 08:13:20 PM »
Not sure of the bore of the Bruce one but mine is certainly smaller. ;)

Probably not quite half the size.

Just put the hole in the right place to help counterbalance the weight of the piston :LittleDevil:

 

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