The most difficult project?

[Tony MartyrParticipant @tonymartyr14488]

The double Tangye

In my life I’ve completed several ‘big’ model projects including the Mastiff, the Reeves triple expansion engine, a 3.5” William locomotive, a Beam engine and finally the Reeves Double Tangye engine. All but the Tangye have been given away. I found the machining of that double Mill engine the most challenging of all my projects. It was obviously a company that liked big complicated castings!

Added to the expected difficulties was the fact that the thin end parts of the two trunk standard castings were chilled and required localised grinding with a Drexel set up on the tool post.

The 7 equally spaced cylinder and head bolts are an interesting exercise when complete interchangeable is desired and machining the connecting rods out of rectangular bar is quite challenging.

When I was an apprentice one of our tests was to machine, then hand scrape the white metal bearings of an in-line shaft with three bearings; this engine has four bearings in line the outer two being in housings set at an angle to the horizontal.

I’ve ran it once on steam, but to avoid corrosion it now occasionally runs only on compressed air, the speed governor has too much stiction to operate subtly but it’s smooth and powerful. It sits on my bedroom window ledge and is a source o, until now, private pride because it was the most difficult of all to get absolutely right.

[JasonBModerator @jasonb]

I’ve never been convinced that the 4 bearing shaft is right. It’s a bit like the Clarkson Compound, cobbled together from two models of singles but the surplus two bearings were never removed. Tangye had it right with just the two angled ones

 

[Chris GunnParticipant @chrisgunn36534]

Tony, I recently bought a set of castings from a guy who had started it, but not done a lot, maybe now I know why, I was getting ready to make a start soon.

He has ground the base and deeply centred all the holes for the 2 trunk standard castings, maybe not a good idea, i would be inclined to make them first and spot the holes through when construction was further advanced, what do you think?

Chris Gunn

[Chris GunnParticipant @chrisgunn36534]

Jason our posts crossed, have you made one?

Chris Gunn

[JasonBModerator @jasonb]

No but if I did I would be thinking seriously about cutting a section out of the bed casting or starting from scratch so that the inner bearings could be done away with.

I’d also do the two part flywheel as I have made one of those before.

As for machining I’d get the two frames either onto the base or a machining plate and set up on the cross slide. Between ctrs bar to do the two trunk guides parallel and horizontal then swing the plate 90 degrees to do the bearing housings.

[Tony MartyrParticipant @tonymartyr14488]

Chris, I used a dividing table to drill the 7 holes in the two cylinder heads the used them as drilling jigs to drill the holes in the standards. I used the lathe as a horizontal borer to machine the standards but it is a tricky intermittent cut and I had to use the Drexel grinder to get a decent finish in the cross head bore due to patches of chilled hard surface.

[Tony MartyrParticipant @tonymartyr14488]

Jason, What supports your opinion is the fact that the halving joints of the inner bearings are horizontal while the outer are angled, I don’t think that is a sensible design and certainly makes work difficult. I got all four bearings taking load by using a straight alignment bar and shimming up the inner bearing stands which were made 10thou too short. It is a heavy flywheel but it all runs very smoothly.

[JasonBModerator @jasonb]

Agreed, the different angles just don’t look right.

Sounds like it may be worth giving your castings a roasting Chris, there is a Clarkson in there somewhere.

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