Small Boiler

[editor@glue-it.com]

The old flat smokebox door really annoyed me. So, after making a tool to machine a radius of 71.4mm I turned a domed door.



I then annealed and pressed the brass plaques to shape, I used a sheet of rubber and two blocks of wood in the vice to do this.



It's only a small change, but I think it looks much better.



The engine with radiused smokebox door sat on my A4 notebook.

Merry Christmas and Happy New Year to everybody who has supported me over the last year, Nigel

[editor@glue-it.com]

I've now got the door hinge made and the brass plaques bolted to the door. Moving forward again after deciding the flat smokebox door wasn't good enough.

[editor@glue-it.com]

I've now made the Burrell door handles and the locking system, this now all works at 1/20th scale.


This hopefully shows the basic locking system.

The Burrell door lock is a T-head bolt with flat sides on the threaded section. This bolt goes through the door from the back, a handle with a slot then goes on allowing the bolt to be rotated. A second handle with a threaded not then allows the bolt to be pulled up tight.

In the smokebox a beam goes across the diameter of the opening and has a slot in it to allow the bolt head to go through. Then the bolt is rotated and hence the T-head gets a purchase on the beam.


The handles were made as one part based on them being so small and then I split them into two parts later.


Still lots to do

[editor@glue-it.com]

I’ve been thinking about the Burrell gearing for some time. Calculating the overall ratio, estimating the maximum torque and speed of the traction engine.

I think 1000rpm is a good top speed for this small double acting engine. The rear wheels are 97mm OD and the gearing gives me around 10:1

My simple calculation says that this will give me 1.1mph or ~0.5m/s which feels reasonable for an engine that might run on my dining table.

This is very similar speed to a Mamod Wagon with 2000rpm, 16:1 and 75mm OD wheels

[editor@glue-it.com]

12mm bore at 60psi is ~45N on the conrod

14mm stroke means ~0.32Nm of torque at the flywheel

hence 3.2Nm at the wheel

the drive wheels are 97mm OD and so hence 32N of tractive effort and the engine will be around 1.8 to 2kg

Also, I'm likely to run at a pressure of 45psi mostly and so I think around ~24N

That should be fine

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Just been working out how to get to 10:1 as an overall ratio and where the layshaft can go.



then some calculations of the options (using excel)



and I think I have a sensible result



Next step is cutting some gears

[editor@glue-it.com]

the first prototype differential for the Burrell, some way to go yet, but hopefully you can see what I'm trying to achieve

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a still image of the gears here

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I have to firstly say a huge thanks to JG for sorting out the angles and cutting of these bevels. I thought I knew how to cut them and they would be easy....how wrong I was

I spent a happy hour (no drinking) setting out a 9.5° angle on the milling table and then aligning the rotary table to it.





Now I have to go and cut those gears. Must admit that the cost and effort required in fitting the DRO has been paid back several times over...and it isn't the simplest thing to fit

[editor@glue-it.com]

The differential has not started again, but there is a different angle on the Burrell.

I have to say a big thanks to JG for contacting me and offering to calculate the correct angle for the bevels. As you probably saw in the above youtube they don't run that well. JG's calculations showed that the angle needs to be close to 9.5° rather than 20°, hence last post on setting out the 9.5° on the table.



Since then I have managed to re-cut the crown wheels. Perhaps I should not have re-cut them, but there was enough material in them still.



plus, this has thinned down the whole assembly. Although, note that the next image isn't using the correct pinion wheels - they are to be made from scratch again as 10T and 9.5°



Thanks and remember the whole story of this design and build is in minute detail here: Miniature Traction Engine