My word Jason am I right in thinking that is all one mans output. What gorgeous looking models, yes even the black ones. How ever does one person find the time to produce such models to such a consistency? Bet it's because they don't allow themselves to get distracted
Talking of which
no sailing today - absolutely bitter east wind and wet snow - only one place to be then so made a start back on the Etas
Not a lot to report on them however so a little more on the McOnie.
First off though -
Thanks Ramon,
Any more details on the drawing faults will be much appreciated.
Jo
Jo, Just to make it clear, though I have found the odd error which I will point out when relevant I'm at pains to stress this is not nit picking at someones design. Overall this is going together well just that there are, as said, some pitfalls for the unwary.
One of the big 'dimensional' challenges faced on this engine was going to be getting the pivots directly opposite each other and perfectly in line both concentrically and axially as well as ideally perfectly on the centre line of the bore. Several thoughts were mulled over and finally it was decided to potentially crack two nuts together. As all ready stated I'm not keen on gunmetal and didn't particularly want a gunmetal/gunmetal piston and bore set up. The decision was made then to take the bore oversize and slightly reduce the piston diameter and insert a cast iron sleeve. This would allow cross drilling the casting right through, on centre line and in line - the sleeve then sealing the cross holes.
First off was to hold the casting very gently in the vise on the mill and take a very thin skim cut across the port face. A sharp new 6mm FC3 cutter was used stepping over 5mm at a time in order to keep the cutting forces to a minimum - besides keeping those cutting forces low this also produces a much 'flatter' surface than fly cutting and is a method I much prefer over the latter.
With a nice flat face still with plenty to come off the casting was set up on the lathe against an angle plate and then bored using a between centres boring bar.
After the initial clean up cut it was checked for it's relationship with the centres of the pivot bosses and also to check that the oversize bore was not going to break through the side of the cylinder then the bore was taken to size - this was not critical as the sleeve would be made to fit - and eventually, the piston made to fit the sleeve
I have found that by getting the bore in first its much easier to bring the outside surfaces to a bores centre line both dimensionally and in parallel than trying it the other way round. First thing required then is an expanding mandrel....
.... on which the cylinder is mounted to machine the ends square to the bore and to finished length.
At this point it was realised that there would be no need to machine the pivot bores right through so without removing the mandrel the chuck was transferred to the rotary table set up on the mill and the spindle set to the mandrel centre line. The port face was set square to the table then the pivot bores drilled and 'bored' by sizing with a slot drill with one flute backed off as a boring tool. It was then rotated
on the mandrel 180deg, the port face reset square and the op repeated.
An angle plate was set up and the cylinder held to it with 6mm studding. The pivot bores had tight fitting 'dowels' pushed in then supporting them on two parallels the port face was milled to dimension true to the bore C/L
It was then removed to check the accuracy on the surface plate before setting it back up to mill the steam ports
After milling the ports the cylinder could be swivelled the allow the angular drilling of the steam ways....
Spot facing using an FC3 cutter held in the drill chuck to create a level surface for drilling...
and reaming the hole that will be plugged.
Finally for this post the set up to drill the steam passageways through to the port face
I've been doing this in stages tonight - sidetracked by a bit of telly
I see you've posted since I started this Bob, nice to see you here.
As usual I hope some will find this useful.
Regards - Ramon