This post is slightly out of order as I did the main and pump slideways first. These were simple milling jobs, I made a small video of machining the slots in the air-pump one…
But, now we made a second trial assembly of the principal engine castings, to get a feel for how we were progressing – the engine is really growing now, and I can just lift it, but could not go far – I would guess it at about 80-100lbs.. and there is no crank, auxiliaries or valve gear yet!
Well, we have reached a bit of a milestone I think – I have managed to erect the main castings (cylinder block, rear columns, base).
In the end I changed the order described in the manual, and mounted the rear columns first. Fitted the lower cylinder covers to the block (to ensure accurate positioning of the bolts, and then mounted the lower covers on the rear columns with a single bolt (as suggested) then remounted the block, spotting through the other mounting holes on to the column tops.
I came to this approach for two reasons:
1 -I did not manage the machining the “spare bits” off the HP & LP covers accurately enough so there was about a 15thou gap between them. This meant that their angular position in the bores was not “totally” fixed.
2 – when I ran I trial erection, I discovered that very small lateral changes in the location of the block (displacing it along the line of the crank) produced very significant angular displacements of the covers – I am sure the geometry would show this to be the case. So I concluded that it was better to settle the position of the covers (and their bolt holes) and manage the final alignment of the crank/slideways/cylinders by control of the crank end-float.
Time will tell if I am right!
Next step is the front columns (a Boxing day job)! I am looking forward to this, although I have considerable concerns that the off-set turning jig to produce the offset footings will not result in a column that correctly matches the base and cylinder bolt holes without considerable “fettling”!
I tripped over a couple of problems –
1 – LP steamchest cover mounting bolts. It may be that my Technical Drawing A-level from the ’70s was to a different standard but only 8 of the 12 holes for the valve chest cover mounting holes should be drilled through. The 8 down each side do carry through to the block, but the 4 at the top and the bottom, should be blind – as the “clash” with the port pockets.
2 – The bottom (and top) cover mounting bolts. The location of these is not well defined on the drawings, and care needs to be taken to ensure that they miss the ports in the cylinders (I wound up needing to redrill two on the LP side, as it became clear this was to be a problem.
3 – The bottom cylinder cover-to-column mounting holes. Again the location of these are not well defined on the drawings, and in the end I wound up re-drilling these to ensure their correct location.
I have added a section to this site to log all the drawing errors I and others have noted… You are welcome to contribute too! Please see here.
I took most of the half term week off and with the weekends before and since real progress is being made.
I am also learning how to make sense of the notes from Mr. Leak, and decided to buy an up-to-date set of plans from Camden… this is all leading towards making progress…
Firstly to return to the columns – as noted earlier I machined these individually on the milling machine, but eventually concluded that they were not “perfect”. The two columns were about 8-thou different in hight, the tops were not completely orthogonal (about 4thou front to back) and the milling cutter was not completely true, so there were ridges. (here was this intial set up)
First attempt at finishing the columns
I spend a day “getting things true” – resetting the vertical head on the mill to within about 2thou over a 6 inch distance (front to back) and to a similar accuracy over a 10 inch distance left to right. I spent half a day trying to resharpen the flutes on the milling cutters on the Quorn to the desired degree of accuracy, and failed (marked down roller-bearing or air-bearing tool holder as a future necessity – just too much stiction/slop in the current arrangement to do good work). (I will re-create this set up and take a picture later!).
easily done on the shaper – at the limit of the Ram’s throw!
The backs of the columns (air pump slideways etc.) were also finished on the shaper – right at the capacity limit of the wartime, American, lend-lease machine – but as always it produces a really nice finish with simple tools and is quite relaxing to watch too!
finishing the rest of the rear surfaces of the columns
In the end the columns were returned to the miller to have the rest of the “rear” surfaces finished with a flycytter and long-series end mills…
In the spirit of “getting it right” I purchased a new angle plate at the Midlands model engineering show, and then learnt and practised the craft of hand scraping with engineer’s blue to get it flat etc.
Then fitted this angle plate to the side of the shaper (to make a “lower table”) and managed to get the two columns fitted (side by side) onto that with the slideways clamped to the side of the table, and then was able to re-finish the tops of the column. A much more satisfactory finish – no discernible difference in height between the two (phew!)
the column erection jig in place
trying the rear columns agains the erection jig
You can see them “tested” against the erection jig (adjusted for the over-width main bearings here…
Then I started on the cylinder bases. A nice return to lathe work! A simple job, first facing off the inside faces, and drilling/boring/reaming the 3/4″ hole for the piston rod, then clamp it face down on the milling table and face the mounting face, and bore for the gland/stuffing box.
drilling the pilot hole for piston rod in LP cylinder bottom cover fly-cutting the mounting flange on the HP cover
fly-cutting the mounting flange on the HP cover
Soon a pair of nicely finished covers emerged – now the fun begins…. getting to grip with the cylinders…
I have read and reread the discussion on how to address these components, with no clear picture emerging of the approach the author intended.
So my approach was as follows – we will discover if it’s a good one. Clearly, perhaps the biggest issue is that the top and bottom faces of the columns are true to one another and properly perpendicular to the crosshead slideways.
So, looking at the castings I concluded that the most solid foundation to support during most of the machining IS the slideway facings – so we will start there, and then turn it over bolt it down and try to do the rest.
Sadly, the Adcock & Shipley cum Bridgeport Mill I created does not have a very big table or much movement in the Y direction (6 inches), so one can’t do them as a pair.
So as this picture shows, I supported the two ends of the casting and fiddled till the face of the slideways was horizontal in two planes – then clamped it down and set to with the flycutter…
Here’s a mobile-phone movie… sorry about Bob Harris in the backgound!
SY Befur 