Author Topic: Strictly.... “ Hot Air “  (Read 71620 times)

Online Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #420 on: November 13, 2020, 08:22:25 PM »
Graham,

I've been making the pins today.  Its taken me almost all day to end up with 4 pins.  There were also 2 that I buggered up, one just at the last step prior to parting off.  :censored:  Once I had worked a sequence out I was okay with them.  Just need to sort out slitting saw for the screwdriver slots and champfer the edge of the screws.

Quick question for you. I don't quite understand how the link to the piston should look.  Is the link offset to one side of the brass boss in the piston, as it looks to me in the drawing.  Or should it be central between two lugs on the brass boss.  Also is the pin joining the two screwed similar to the other pins on the linkages.  Could do with seeing a plan view.  Also the link to the top of the cylinder, Is this pinned similarly.

What material is used for the link down to the regenerator piston?

Thanks,

Colin
« Last Edit: November 13, 2020, 08:30:01 PM by Twizseven »

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #421 on: November 13, 2020, 08:29:01 PM »
This is how I interpreted it, yes another pin

Online Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #422 on: November 13, 2020, 08:31:59 PM »
Jason,

Thanks for that.  Its what I would have expected but not quite what the drawing appears to show.

Colin

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #423 on: November 14, 2020, 11:44:19 AM »
Good morning Colin.

I've just been looking at the drawing and yes, there's a few omissions that I could well have related to in the missing write up.

The small end fork is shown with a " ragged " edge telling you that it's a " cutaway " of the complete item made from Hexagonal Brass bar stock.  ( labelled )

The cylinder pivot pin is made the same as the others but not threaded. It is simply retained by a 1/16" split pin and washer.

The displacer piston rod is made from 5/16" Silver Steel ( ground stock/drill rod ) and needs to be as snug a fit as possible through the platform casting. A 3/16" cross drilled and reamed hole attaches it to the Brass links you've already finished.

Now, if a mistake during the boring of the displacer rod hole is made, no need to worry. As 8 mm is only a few thou away from 5/16" you can always upsize.

Cheers Graham.

Online Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #424 on: November 14, 2020, 01:17:29 PM »
Graham,

Many thanks for those answers.  Now you have mentioned it the the raggedy edge shows up like a sore thumb.  I just had not spotted that on the drawing.  :Doh:

Colin

Offline ettingtonliam

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Re: Strictly.... “ Hot Air “
« Reply #425 on: November 15, 2020, 02:12:27 PM »
Ah, brass hex for the piston gudgeon housing. Makes sense. All it says on my drawing is 'Hex bar stk'. How is the gudgeon pin fixed? A split pin either side?

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #426 on: November 15, 2020, 02:21:55 PM »
Hi Richard.

You could do either, make a pin the same as the cylinder top pivot or, as you say pin, washers and split pins.

I think I posted a reference to Gardner's hand sketched parts list on the previous page, you could always make a more elaborate yoke if you wanted to.

Cheers Graham.

Edit.... No, two pages back....

Offline Jo

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Re: Strictly.... “ Hot Air “
« Reply #427 on: November 15, 2020, 02:23:26 PM »
If you ream the gudgeon pin hole in the carrier with a hand reamer and only go part way through you can leave a taper in one side and the pin will press into the taper  :)

Jo
Enjoyment is more important than achievement.

Online Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #428 on: November 18, 2020, 10:31:57 PM »
My flywheel is now machined.  Came out slightly undersize once it was cleaned up as did one of the bosses (by about 4thou).  There is a large boss on one side and a short boss on the other.  Which way round are these intended to be, i.e. which is on the outside.  I am going to attempt fixing flywheel with a gibhead key as per the plans.  As the flywheel needs a tapered slot, I need to be sure which way round to fit it.  Going up from 3/32 key to a 2.5mm key.  Only 4.6thou bigger, but at least have suitable slot mill for the keyway in the crank.  Never done a keyway before and this is a rather tiny one.  Setting the cutter up is a bit delicate to get the 1 in 100 taper.  This is tomorrows task.  But I may try to make the key first to see how I get on.

Graham,
I have your build notes for this engine, with a couple of modes suggested by Nigel McBurney.  Will get copies to you in near future.

Colin

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #429 on: November 19, 2020, 11:27:10 AM »
Good morning Colin.

I received your email this morning, thanks.

The reduced length of boss is butted up to the main bearing pedestal, with running clearance.

I'm puzzled, are you going to " broach " the keyway in the flywheel hub? There's two ways....

Proprietary keyway broach with bush or set up the flywheel with the correct angle under a slotter and cut it that way? The taper is always put into the flywheel hub, the crankshaft carries the corresponding slot in parallel with the shaft.

I'm aware that I don't use my broaches correctly, I push them to the last cutting tooth before pulling back and then re push with the shim in place. The proper way is to use a tapered slot bush and push the broach right through.

The propriety bushes are useless for this job as they're far too short, only supporting the broach half way. I made longer ones years ago.

Cheers Graham.

Offline ettingtonliam

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Re: Strictly.... “ Hot Air “
« Reply #430 on: November 19, 2020, 12:47:35 PM »
Graham
I'm sure you've covered this before, but my drawing suggests that the governor valve and the bore the the end of the cylinder are both 1" dia. Instinct suggests that the valve is slightly smaller, say 15/16", so that when it activates its sucked into the bore, but with a 30 thou annulus all round to choke the engine and slow it down. Otherwise, slightly larger, say 1 1/16" but with a few 1/8" air hole drilled in it.

Even though I've done most of the engine, if you do get hold of a copy of your build notes, I'd appreciate a copy, if only to see where I did it wrong!

Do these hot air engines run either way round? I presume they are not self starting, but need a good pull to get them going.

Online Jasonb

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Re: Strictly.... “ Hot Air “
« Reply #431 on: November 19, 2020, 01:10:45 PM »
A couple of small holes in the governor will stop it plugging the cylinder hole

http://www.modelenginemaker.com/index.php/topic,7561.msg167581.html#msg167581

Should just need a gentle flick to start it off, they almost start moving by themselves as they get upto temp, one way only.

<a href="https://www.youtube.com/watch?v=oWf9DnTIIJI" target="_blank">http://www.youtube.com/watch?v=oWf9DnTIIJI</a>

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #432 on: November 19, 2020, 01:33:38 PM »
Graham
I'm sure you've covered this before, but my drawing suggests that the governor valve and the bore the the end of the cylinder are both 1" dia. Instinct suggests that the valve is slightly smaller, say 15/16", so that when it activates its sucked into the bore, but with a 30 thou annulus all round to choke the engine and slow it down. Otherwise, slightly larger, say 1 1/16" but with a few 1/8" air hole drilled in it.

Even though I've done most of the engine, if you do get hold of a copy of your build notes, I'd appreciate a copy, if only to see where I did it wrong!

Do these hot air engines run either way round? I presume they are not self starting, but need a good pull to get them going.

Hello Richard.

Actually the governor disc should be slightly larger in diameter than the hole through into the cylinder. This creates a firm seal. But.... The problem is that when it operates is stops the engine dead. To soften the governor Gardner placed a couple of 1/4" diameter holes ( at full scale ) through the disc, so as Jason suggests a couple of 1/8" holes drilled will work just fine.

They run in one direction only, pull the flywheel away from the cylinder opening.

Please PM me your email address, definitely got it somewhere but just remind me. I'll send on the PDFs to you.

Cheers Graham.

Online Twizseven

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Re: Strictly.... “ Hot Air “
« Reply #433 on: November 19, 2020, 03:04:09 PM »
Graham, Following my chat to Nigel McBurney who has made a number of these engines he has made a couple of mods to them to help with running. One is a change to the pins on the linkage rods. They are fully reamed both sides and a sleeve type nut put on from the back. His other mod is to the governor valve assembly. He has fitted an adjustable brass sleeve in the casting and the governor rod slides in this bushing. The sleeve is then used to control the distance between the governor valve and the face of the casting in which it runs. I sent the copy of the schematic for this to you with other stuff this morning. He had these mods described in Model Engineer Vol. 179, No.4050, 12-25 Sept 1997.

Thanks for reply re flywheel boss.  I intend (hope) to machine the key way in the flywheel on the lathe. I have ground a suitable cutter and have just ground some gauge plate down to a fraction under 2.5mm. Now going to shape the gib head key and try it in crankshaft prior to cutting jetway in flywheel. Will use the carriage on the lathe with cross-slide set to give 1:100 taper. That’s the plan. Whether it works or not I have no clue.

My mate Tom has a spotter for his XYZ (Bridgeport clone), so this is a possible last resort. Unfortunately I do not have enough space to swing the head 180 degrees so that I could fit it to mine.

Colin
« Last Edit: November 19, 2020, 03:07:48 PM by Twizseven »

Offline Alyn Foundry

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Re: Strictly.... “ Hot Air “
« Reply #434 on: November 19, 2020, 03:41:28 PM »
Hi Colin.

Yes, I saw the mods but, if you're making a " true " replica of the Robinson then the modifications are non original.

For the link motion assembly an old clockmaker adage comes to mind...

      " Tight enough to work, free enough to run "

I've never done a keyway on the lathe so I'll be interested to know how it turns out for you, lots of patience will be the " key " to success !!  ;)

Cheers Graham.

 

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