1802 Bell Crank Engine

[Jo]

I've started work on the covers: As normal I start by turning a register on the top cover casting. This can then be used to hold the casting whilst the underside is turned. Not forgetting to also drill and ream the hole for the piston rod so everything is square



Then holding it by the 25.4mm boss it is possible to turn the top and using a D bit for the hole in the centre of the valve gland. (I took this before I turned the under cut on the top of the cover )



Because both the top and bottom covers need the same nick cut out of them I next mounted up the bottom cover/stand and turned the top of that:



I first tried mounting the cover in a 5C collet to mill the part out the side but it proved to be too large a diameter so had to mount the cover in the vice, centre it up then use a milling cutter to cut the piece that goes around the valve surface:



Then I could do the same for the bottom cover having made sure that the legs were square and holding behind the cover and not on the legs to prevent the gunmetal bending as it does



This was when I found that milling the top of the cylinder had caused burrs in the location holes  It took a while to get rid of them I did consider mounting the cylinder up and boring the burrs out but using engineers blue I scraped them out



The fit seems ok around the valve chest:



There is a slight misalignment between the milled outside edge of the cylinder and the covers that is going to touched up with a file.

Jo

[Jasonb]

Its comming along.

Looking at the burrs being thrown up in that picture of you milling the notch in the top cover I think you could do with some sharper cutters, I know GM is soft but a sharp cutter will create a lot less of a burr than that.

J

[Jo]

Looking at the burrs being thrown up in that picture of you milling the notch in the top cover I think you could do with some sharper cutters,

That was a brand new cutter I was using  . No the problem was using that nice and wide carbide tipped tool to cut the face in a single cut. Its great on steel, not so great on GM  .

Jo

[Jo]

The top cover has been drilled and the cylinder tapped for it (for now)



Now the challenge 



With a casting that is 50.1mm across the outside of the feet, you cannot put two mounting screws on a PCD of 25.4mm

Jo

[Stuart]

It would seem that the casting to small syndrome is alive and well

Is there enough meat to shrink the PDC down a smidge ?

Nice work with the documentation Jo

stuart

[Jasonb]

You could use bolts from above or a stud and nut above, both easily drilled and tapped from above.

Should the width across the legs not be 1.875" ( 47.63mm ) anyway

[Jo]

Hi Stuart: no the bolt holes are just on the outside of the legs, it would nearly be down the bore on the inside   

Should the width across the legs not be 1.875" ( 47.63mm ) anyway

The width across the legs should match that of the cistern = 50.1mm

I noticed one of the other finished engines the builder resorted to letting the legs only sit on the inside of the cistern but that looses a lot of strength  I might have a plan

Jo

[kvom]

On the few engines I've made to date, I've been drilling and reaming the piston rod hole with the cover mounted to the cylinder and with the mill spindle centered on the bore.  Have you found that drilling the hole on the lathe presents any issues with it being concentric when later mounted on the cylinder?

[Jasonb]

I know its a later engine but looking at the one in the science museum there is no way a nut or bolt head would fit on that, unless it were a tee headed bolt. So must be a stud & nut or bolt into tapped hole



Also you mentioned the other day about the shape of the piston gland, the science museum one is oval but looking at the etching of the 1802 that is round. See your first post.



Kvom, like Jo I have always done mine in the lathe, provided you do the hole at the same setting as the short spigot that locates in the cylinder then they will both be concentric

[Jo]

Jason, I do not understand what you are trying to say about the bolts.

Also you mentioned the other day about the shape of the piston gland, the science museum one is oval but looking at the etching of the 1802 that is round. See your first post.

A bit late  as you have seen I have already drilled and tapped it to be an oval gland.

Kvon: If you machine the bottom of he cover and the register at the same time as boring for the piston rod on the lathe everything has to be in line. The only way it can get out of line is if the bore of the cylinder is different to the register on the cover  .

Jo

[Jo]

The cylinder base continues

The legs were taken to the correct height:



Then the sides, the flange under the cover and the step that goes into the cistern:



At least it now fits into the Cistern:



But it is still not there. In every casting set there is one piece that is a challenge and clearly for this engine this is it 

Jo

[Jasonb]

And don't think you can sneak in that last photo without a comment on whats in the background

[Jo]

  Yes I must repair that apple picker.

Jo

[Jo]

We are over the peak and heading down hill for this part 

You can see that the bolting down holes on the two sides come through on the side of the foot 



Which meant that I had to use a Tee slot cutter to give some clearance for the nut to hold the cylinder down 



Clean up the bottom and make sure everything looks square:



And finally check that a square bolt will fit and a nut (once I make the square ones  )



Now to try and sort out that top cover   

Jo

[kellswaterri]

Hi Jo, have not been doing a lot this past few days,tore shoulder...black ice    working on Coombes ,end in sight, took a few detours on the way...your latest build would seem quite a challenge in machining,it would appear to be a common problem with castings which do not  fit the drawing,the square bolt is a great save, 50 yrs. of working on mechanical devices i have rarely seen it used for this purpose...
                        John