Bailey's 1881 Bee

[Jo]

Back in 2001 my friend Anthony Mount brought along to the Guildford show a rather nice Vertical Concentric Hot Air Engine Bailey's Bee:

Tony wrote up his build of his model later that year in Model Engineer and if anyone is interested his short write up starts in ME No 4155 page 270. The model was designed from the engraving in this advert:

I purchased these castings from Polly Models for under £300 the set including P&P but be aware they will have them made to order so will ask for a deposit and the castings will arrive a couple of months later 


As I wait for the paint to dry on the base of one of my other models prior to the hand over  We have commenced casting fondling:

Unlike another of the Stirling models casting sets I have previously purchased from Polly's this one did not come with the stainless tube necessary for the displacer or the cylinder  With these ordered from Fleabay I can start looking at the challenge of the bottom stand:

Yes the legs curve/taper in every direction  And if they are not all the same length the model will be lopsided  As I do not own a CNC jig maker I am using the next best thing my cheap as chips printer to make a couple of wedges of the right shape to hold the casting:

This could take a while 

Jo

[propforward]

It's a nice looking engine. I'm most curious about what you have contrived to hold the legs - those are challenging parts for sure.

[Alyn Foundry]

Hi Jo.

Another hot air engine eh?

Whilst familiar with most castings I’m intrigued by the colour, what material are they done in?

Cheers Graham.

[Dave Otto]

Looks like a fun one, I will be following along for sure!

Dave

[Jo]

Yes another Hot air engine... While I wait for my magic tablets to start working again (they have been fiddling with the dose)  I need nice easy builds   

Whilst familiar with most castings I’m intrigued by the colour, what material are they done in?

Other than the Flywheel which is Cast Iron, the Castings are all bronze. I think Polly's prefer to use the Bronze foundry as the foundry man delivers to the factory for them.

Jo

[Jasonb]

They look nice crisp castings Jo, lets hope they are a good firm bronze and not too much at the soft gun metal end of the scale, looks like they have been sand blasted hence the uniform colour.

I'll have to dig out the old mags to see if Anthony soldered or screwed the legs into place and whether the legs cut a curve cut into them of thebase three flats .

[Jo]

Tony's drawings give both metric and imperial measurements and to quote Tony from the model engineer article : " I feel it is high time we stopped using imperial measurements". Drawings with two sets of measurements that are not interchangeable can be confusing    So we need to make some decisions and update the drawings to suit:


I will use BA threads where ever possible (as I have the taps/dies), these threads do not (always) use either full fraction imperial or whole metric diameters.

I shall use decimal metric measurements to the nearest 0.1mm (as that is what I was taught and my workshop is not sufficiently temperature controlled to go to 0.01mm measurements).

I am going to bias the build towards the materials/tooling to hand: But what does that mean? I have lots of 9.5mm diameter stainless (drive bars out of old printers  ) so I will probably use these instead of 9.53mm (3/8"). I will not use 5mm diameters as I want to use BA threads which matches the 3/16" or 4.76mm  diameter bar I have. I will also use an imperial reamers if I don't have a suitable metric reamer and will adjust both the hole and the mating part to suit as I go along. Etc.


The 3D printer has nearly finished 

Jo

[Jo]

I forgot yesterday to provide an example of these "dual measurement drawings"  Sorry.



Attached is the flywheel drawing. As you can see it is 6" / 152mm diameter - the diameter does not matter. The width is either 0.5" or 13mm - the width does not matter. The bore is another matter: The two measurements for the bore are 0.375" (yes lovely decimal inches  not confusing fractions) or 9.5mm. The difference is 0.03mm. Not a lot? but enough to have a wobbly/loose flywheel.

If you recall I said I am working to 0.1mm as my workshop is not sufficiently temperature stable for greater accuracy of measurement. Whilst 0.1mm is more than acceptable for most bits, on items like flywheels they need to be machined to that much tighter fit. If you read the article you will see that Tony machined the Flywheel as the first item, I will be leaving it to one of the last and it will be done along with the crankshaft so I can achieve that nice fit  .


I can report that the two 3D printed wedges look like they will do the required job but I feel a bit of the brown stuff needs to be butchered shaped to make the final part of the support jig for the engine legs as the printing took ages 

Jo

[Laurentic]

"If you recall I said I am working to 0.1mm as my workshop is not sufficiently temperature stable". 

That is an interesting comment, one to which I have not given any previous thought.  0.1mm is nigh on 0.004" - I am of an age when we all worked to thousands of an inch and I do still - and 4 thou seems a lot. 

How temperature stable has a workshop to be to be able to work to better than 0.1mm?  I ask out of interest as I have no real idea.  My workshop is reasonably temperature stable in any given season of the year - it gets cold in winter but when I am working in there I heat it up to around 60-ish deg.F in real money, 15-17deg.C in new fangled foreign units, but it soon cools down back to ambient after - but it is not temperature stable to a constant throughout the year, I wonder how much affect that would have on parts made.

Chris

PS - I was also wondering what the light coloured material was until you clarified that Jo - at first I thought that looks like a varient of that brown stuff, then thought, no way, that would be so out of character for Jo............

[Jo]

If you want to do a temperature test then think about your freezer and normal summer temperature. I often put things in the freezer to shrink them and they grow when they warm up. Same goes for summer and winter machining in a workshop: If you pick up a cold micrometre and hold it in your hand it warms up to body temperature you can have a variation in measurement from the cold to the warm micrometre.

A bit of clarification: When I state measurements on drawings I am going to one decimal place... I am machining to normally 2 decimal places accepting that the accuracy on the second digit is subject to temperature variations both on the item and on the measuring device that has not been calibrated against a standard. I normally machine bits to fit i.e. I use the same uncalibrated measuring device to check the measurements between pieces and am not surprised if I change measuring device and measure again to find the last digit varies. The measurement between devices still holds to one decimal place. 

Jo

[Jasonb]

Yes, I think working to 0.1 is more than adequate at the design/drawing stage. In fact most of the time you can work to whole millimeters with the odd 0.5 on smaller items or when something that is a multiple of 5 overall needs a half measurement eg radius of a 35mm dia arc. 0.1mm increments only really come into it of very small items or when giving tapping sizes.

What you actually work to will be different to what's on a drawing, some parts you may be able to work to +/-0.25, others may require a tighter tollerence of say +/-0.01, others you just make one part using the other mating part as a gauge and who knows what the final dimension is provided it has the right "fit"

As to the flywheel bore then it would really have been better shown as 0.375" or 10mm so that easily available stock sizes could be used (though 9.5mm silver steel is a stock metric size) as no one really wants to turn down 10mm mild steel to 9.5mm over any length.. You would only really end up with a wobbly flywheel if you made parts mixing the two dimensions as to get a wobble you would have to make the flywheel to the imperial 0.375" and the crankshaft to the metric 9.5mm and that is something that should not be done. Also if Anthony was consistant and dimensioned the crankshaft as 0.375" or 9.5mm then so long as you used the same system for all parts the fit will be fine The other way round does give a nice press fit though

[Laurentic]

I think you hit the nail on the head with your statement Jo saying you machine parts to fit.  I think that is what the vast majority of home model machinists do, they are not producing parts that have to be shipped to a customer far away that just HAS to fit on arrival, it just has to fit the part they themselves made.

The DRO on my mill amuses me, it reads out to five decimal places of an inch.  Yes I know it is a function of the reading actually being metric and the DRO converting it, but it always amusing me, the thought that I might work to five decimal places, like in my dreams maybe but never in a milion years in real life!

I do know all about parts growing a tad just by being held in the hand for a quarter of an hour or whatever, just wondered what constituted, or was considered to be, a temperature stable workshop, how close would those limits have to be.  An interesting thought!

Chris

[Jo]

The third part of the jig still needs to be made. First draw round the inside of the casting:



Stick the pattern on some brown stuff 



Shape to suit and check with casting:



Use three part jig to hold the casting while machining the underside of the leg flat, the top face and the edge:



Sitting the three together it is clear they each came from different patterns as the tops are all over the place 



Before I do the tops I need the piece that joins them together. This is a ring of bronze with tapers on inside and outside that needs to be turned parallel:



Once I turn it round and hold it on the inside I will use old bit of coke can as packing to protect the Bronze 

Jo

[Roger B]

Looks to be a fun build with all the usual casting challenges 

[bent]

Yes, different patterns apparently.  There seems to be a lean/angular offset in two of them, wonder if it was intentional?