Agnes.... 1/16 Scale Pollit & Wigzell Tandem Compound Condensing Engine.

[pgp001]

Yes that's the plan.
The visible holding down studs and nuts will actually be dummies on the model, the whole engine is bolted to another sub base from below where you cannot see it.

Phil

[Steamer5]

Hi Phil,
 That is a little beauty! Like Pete said, it's a lot smaller than first thought.

Cheers Kerrin

[yogi]

Fantastic work Phil! 
Thanks for the update. 

[pgp001]

My neighbour is a cabinet maker, this morning he delivered me some wood for making the floor boards for my engine base, it is a bit of nice walnut that he has kindly cut and planed into suitable scale size planks for me.



I also finished the flywheel for the barring engine.









Phil

[pgp001]

Do you remember me asking for advice on how to make these helical shaped parts.



Well I figured it out. Having a toolmakers milling machine allowed me to set up a gear train to my universal dividing head, and then produce the helix using the slotting head.
The feed was manually applied by turning the handle on the dividing head, at this point the dividing plate turns with the handle and the gearing train. the indexing for each of the three helixes was done using the dividing plate in the normal manner in between each cut. The photo's will show what I mean.





Here are the two blanks turned to shape using Phosphor Bronze material.



And shown in the collet of the dividing head ready to start cutting.



First cut finished.



First part finished with all three cuts.



Both parts machined but will they mesh together ?



YES 



Here they are in position on the barring engine. I just need to finally attach the gear onto the sliding one.



Phil

[10KPete]

That is soooo cool! Keep it coming, this is great!

Pete

[Ramon Wilson]

Lovely work as usual Phil and a superb result. 

As one of my old bosses would say with a job well done - "Excellen-tay"

Regards - Ramon

[pgp001]

Next part to be made is the cylinder and its column, this is the full size one.



I had a gunmetal casting for this but it turned to be unsuitable for various reasons so I elected to fabricate it from two machined parts. My initial thoughts were to use gunmetal or phosphor bronze and then silver solder them together.
However in reality this engine is intended to be run on compressed air and will probably never need to run on steam, so I have decided to make the parts from cast iron and bond them together with loctite 601 instead, this has the advantage that areas of bare metal will be the correct colour as per the prototype.

Most of the operations are fairly straight forward turning and milling and the photo's should be fairly self explanatory.
The basic shape of the column was turned and bored for the crosshead.



A mandrel was then made and loctited into this bore so the part could be reversed and held in a collet for machining the cylinder bore and sleeve diameter for the steam chest to fit over.
This mandrel was also used to hold the part on the jig borer for milling the 1mm wide slots for the valve ports to transmit steam/air to either end of the cylinder.





The four mounting holes were added using the PCD function on the jig borer DRO, I had to make an extended centre drill to reach the flange.



For reasons which will become apparent I had other things on my mind and completely forgot to take photo's at this stage, so you will have to use a bit of imagination.

Moving onto the bigger milling machine I mounted the part in the dividing head to remove the material from either side of the column. I had designed this with an angle of 50° either side of the centreline, so I had to work out how many turns and holes were needed to achieve this.
I counted 80 teeth on the wormwheel, so ended up with the calculation (50/360) x 80 = 11.11 turns of the dividing head handle, which equals 11 turns and 2 holes on the 18 hole circle.

Being cautious and not wanting to scrap this part I decided to test my maths and see if it looked right in practice prior to cutting any metal. A good job I did because it moved way too far, in fact it seemed to go twice as far as it should 
I checked my maths again and got the same result which was very puzzling, it was a little while before the penny dropped and I discovered the dividing head has a two start worm and is in fact 40:1 ration and not the 80 that I had counted earlier 

So back to the maths and we now have (50/360) x 40 = 5.5555, or 5 turns and 10 holes on the 18 hole circle. Back to the machine to test the maths again and all is now OK. At this point the day is over and I went indoors 

So the following day I resume work and start making cuts, the first cut went perfectly, so I indexed to the next position and proceeded with the cut, something did not look just right and I started to doubt that I had counted correctly with the dividing.
The third cut seemed to go a lot better, but the last cut was an absolute disaster, there was a massive gouge where too much meat had been removed. It was now clear that this part was going in the scrap bin 



You are probably wondering why this happened as I was. Well it was a case of me thinking I must have tightened the dividing head collet the night before, but not actually doing it.
So the part was only finger tight and was revolving in the collet and being pulled into the cutter........What an idiot 

The only option now was to start all over again and make another one but remembering to tighten the collet this time.



The last operation I did was to drill and tap the 10BA holes for the piston rod gland.



And here it is in position on the engine, all it needs now are the webs up each side making and fitting.



The steam chest part of this assembly will follow in due course.

Phil

[Dave Otto]

Bummer on the column Phil 
The second one sure turned out nice!


Dave

[Jo]

Made it in the end 

Does this mean that you are back working on Agnes for the fall 

Jo

[Jasonb]

Must be those magazine articles that have got him inspired

I had not thought about cutting the passages into the outside of the cylinder, have done it on the concave inner face of the part that forms the valve face before and both are easier than drilling angled holes.

[pgp001]

Jo

I have never not been working on Agnes, this is my normal speed throughout the whole year.

Jason

I came up with this method of porting during my model compound traction engine build many years ago, you have to be quite inventive at using special liners etc when starting from a solid casting.

One thing you might be able to help me with though.
I seem to remember seeing a good method of machining piston and valve rod glands, but cannot remember where it is.
I am undecided whether to use my normal shape of four radii and four flats joining them, or to go for four blended radii, I am leaning towards the latter at the moment.

Did I see a table of gland proportions somewhere on here ? and perhaps a fixture for turning the large radii ?

Phil

[Gas_mantle]

Looking great Phil, it's a complex build just making the barring engine let alone the main engine.

You going to make another smaller engine to bar the barring engine into position ?   

[Jasonb]

The boring head does a reasonable job, a jig in the 4-jaw (as sketch) produces similar results for the more rounded ones.

Prepare your gland


Mount on your valve chest if you need to produce a matching spigot on that and with head set for external turning reduce to the major axis


Adjust head to your large radius and cut one side


Then the other


File the ends with teh aid of buttons and jobs done

[crueby]

Jason, great tutorial on milling the curved sides of the gland! Another one for the file...