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1/3 Scale Robinson Hot Air Engine

deverett

Registered
I have recently started building a 1/3rd scale of a No.4 Robinson Patent Hot Air engine; castings from Polly Models in England
http://www.pollymodelengineering.co.uk/sections/stationary-engines/index.asp
It is not a true scale model, but I am hoping to put a few touches to it to make it a bit closer to the real thing. To give you an idea of size, the platform will be about 8" long.
I'll just put up a few machining pics so you can get an idea of how I progress.

The stand was cleaned up top and bottom and then the cut outs for the legs were done with a hacksaw and abrafile.

Next job was to clean up the legs and this was done with an endmill and round noser in the corners.


Dave
The Emerald Isle
 

Owen Bosma

Subscriber
Age
78
Last Subscription Date
02/07/2018
Re: 1/3 scale Robinson Hot Air Engine

Hi ............ I build a Robinson engine several years ago from scratch and not to any scale. I liked the layout and the use of a half walking beam. The engine is a nice runner.
The first picture shows it on its test stand, after that i build a wood stove. The open water cooler keeps it running nicely for several hours.

Owen ........... http://home.cogeco.ca/~obosma
 

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deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Interesting engine you have there, Owen.

I have heard that one of the problems with the Robinson type of engine is that they are prone to overheating quite quickly.

Dave
The Emerald Isle

---------- Post added at 10:20 PM ---------- Previous post was at 10:13 PM ----------

Next part to be machined is the platform. The casting for the platform has a laser cut steel sheet to close off the chamber which is held in place by 7 small screws.





Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

This is how the underside of the platform looks with the steel sheet screwed to the casting.



Next job was to machine the displacer cylinder. This went well but there are a few blowholes in the casting, on the outside and in the bore.





I will fill these with a mixture of JB Weld and cast iron dust. I don't consider it necessary to return the casting for a replacement for these small blemishes.

I rested the displacer cylinder in the platform to make sure that the top of the cylinder touches the underside of the platform. It does!



Next, the two need to be screwed together, screws going through the top of the platform into the top of the cylinder.

Dave
The Emerald Isle
 

Culy

Registered
Last Subscription Date
08/27/2010
Re: 1/3 scale Robinson Hot Air Engine

Keep up the good work Dave and keep the pictures coming. I really enjoy watching builds step by step. Looking forward to seeing the completed model.
Brian
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Now to finish off the platform by drilling the transfer passage.

Careful alignment is required for the hole as there is not much spare metal.





Dead centre! The hole is 7/32" diameter and just short of 3" long.

Now to join the displacer to the stand.



The two parts were held together with clamps and the holes were drilled through both parts.

Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

A bit more progress. The stand, displacer cylinder and platform are now joined together. It is starting to be recognisable as a Robinson engine now.



I will tackle the displacer next.

Dave
The Emerald Isle
 

lazylathe

Registered
Re: 1/3 scale Robinson Hot Air Engine

Excellent work so far Dave!:D

This is going to be an interesting build to follow!
Keep the pictures coming!

Andrew
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

The displacer piston is supplied as a brass spinning with wall thickness of about 1/16”. A piece of brass plate is supplied to silver solde to the top as a cover for the piston but the drawings show a fabricated plug.

I chose to go with the drawing version and machined up a top for the piston from some brass bar I had after reducing the wall thickness of the spinning to about 20 thou, leaving just a small area below the top ridge at the full thickness. This to reduce the weight and also to try and reduce the heat transfer through the brass.



The two parts will be joined together by JB Weld after I have made up the displacer rod.

Dave
The Emerald Isle
 

benz1890

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Last Subscription Date
Mike White
Re: 1/3 scale Robinson Hot Air Engine

My Robinson has a match stick where the snifter valve should be! Do you have drawings for the snifter valve?
Mike.
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Mike

Is your engine a model or full size? Also, do you have a power takeoff pulley on the flywheel? If so, any chance you would let me have a picture of it and tell me how it is secured to the crankshaft. Thanks in anticipation.

Here are a couple of scans of the Alyn Foundry 1/2 scale drawings of the governor. Thanks to Orrin for these. Speaking to Graham Corry of Alyn foundry, he says that in model size they don't make any difference and are just another source of potential air leaks. In full size, the disc has 2 x 1/4" holes in it, diametrically opposed.





Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Work on the Robinson progresses somewhat slowly. The power cylinder casting needed a fair bit of work on it because the outside was oval. I cleaned it up on the linisher as far as I could. Before boring, the outside was turned as far as the link anchor.



Before honing the cylinder, I will use a mandrel to mount it on the dividing head to clean up the outside.

The model design uses a flat plate where the governor should be. I chose to make up a governor as per the diagram in my previous post, although I do not anticipate that it will make work in this size engine.




Dave
The Emerald Isle
 

stirlingmaier

Registered
Re: 1/3 scale Robinson Hot Air Engine

My Robinson has a match stick where the snifter valve should be! Do you have drawings for the snifter valve?
Mike.
I have a set of full-size original drawings of all Robinson hot-air engines and could send you a scan showing this detail if you contact me directly via email
Regards
Gerd
 

benz1890

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Last Subscription Date
Mike White
Re: 1/3 scale Robinson Hot Air Engine

Hi Dave and Gerd,
Thanks for the info and possible copy of the drawings.
My engine is a well made full size copy made in 1985 possibly by Ed Bolton. There isn't any pulley fitted but I need to make one.
Mike.
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Mike

If you look at the thread 'More help for #5 Robinson' towards the bottom of page 1, and go to Dave Allen's reply, you will see thumbnails of drawings. If he is able to scan the drawings, maybe he could get a better scan of the pulley - for both of us!

I tried contacting him, but never got a reply. See if you have more success.

Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

The outside of the cylinder has now been cleaned up as well as can be done. To get a decent surface for painting, I will fill in the hollows with JB Weld. The piston has been lapped into the cylinder and is a good fit.

The crank disc on the model is just a 1-3/8" slice of steel. However, the full size is a casting with the counterweight incorporated, so I have tried to copy it. The crankpin boss was silver soldered in place.

Dave
The Emerald Isle
 

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deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

It is ages since I updated my progress on this little engine due to various reasons for absence from my workshop.

A few small bits have been done, but the latest setback is that when I started to machine the flywheel, a serious flaw came to light which ran from the side up to the face of the rim. Even machining way under the correct diameter could not get rid of it, so the casting has been returned and I am waiting for a replacement from the supplier. Unlike the other flawed castings, the flywheel rim will not be painted so the defect cannot be hidden.

The castings were not as good as I originally thought. The metal may have been OK to machine (no hard spots), but the outside of the cylinder and bearing block were oval instead of round. I have been doctoring them to make them presentable. You'll see the results later.

Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

The crankshaft bearing has been machined. I had a couple of miniature roller bearings and these were incorporated instead of the original brass bushings. Anything to reduce friction in these low power models.

The casting was oval, so a bit of car body filler was applied and rubbed down to get a cylindrical shape using the two buttons inserted in the bore to guide the file and emery cloth. One roller bearing is also seen. It is shown here after being painted with etching primer and red oxide primer as a second coat. The ends of rubber ear plugs were cut off and used as masking bungs in the ends.



The crank disc was painted before pressing it onto the crankshaft. Now waiting for the replacement flywheel casting.



Dave
The Emerald Isle
 

deverett

Registered
Re: 1/3 scale Robinson Hot Air Engine

Well, it's only taken 6-1/2 years to get this model Robinson Patent hot air engine finished.
Tested it yesterday and am quite pleased with the way it runs. It is now bolted to a base and now doesn't bounce around.



Dave
The Emerald Isle
 
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