Good day all..It's been a while since my last update, I've been doing a little more work over recent weeks and now seem to have found my way again....anyway here's were I am now, I have stripped down the frames and busy working out where the middle cylinder sits....here's the latest update....
I have a fair number of photo's to show today although in physical terms not a lot of progress has been made but it's an important step that i'm working on and so will try to show how I'm dealing with it. I am of course referring to the positioning of the middle cylinder, I'm not there in machining terms yet but have hopefully covered most of the ground work ready for fitting. There is very little info given in Don's words, in fact unless I've missed it all he says is to drill the holes, either for bolts with nuts on the back to secure or to be tapped 6BA, I'm going for the tapped option,purely as I don't fancy in any future maintenance having to fiddle around with nuts in hidden places. There is very little on the drawings either but the one measurement that is given is to be honest all that's required, it took me a few looks to find it so would have been nice if Don had mentioned it in his words, after all, the positioning of the middle cylinder is fairly critical to a smooth running 2:1 gear.
I have included a picture of the drawing as a visual aid to describe what I'm on about. The top left drawing you will note the measurement from the center flange to the most forward of the mounting holes, that being 1 37/64, probably not that best of things to measure from, that being a rough casting but that's what the man says and who am I to argue, I guess the position isn't as critical as i had assumed?
The next thing to check is the height of the cylinder, the known hole gives me both axis required as the top edge of the cylinder flange runs parallel with the frames so it's just a matter of pivoting the front upper right-hand corner (looking from the right hand side) to get it's position, basically that one hole and the angle of the top edge is my datum. This picture shows the underside, it's all pretty tight here, the bar that I've pushed through is the main cross shaft for the drain-cock apparatus, there are in fact two crosshafts, but these details are for another day. Note that the hole for the shaft is just below the line of the bottom row of mounting holes for the middle cylinder, as i said, very tight, clearly a section of the cylinder middle flange will need removing when it comes to fitting the pulley for the bowden cable to operate, I'll need to remember that before final fitting of the cylinder.
The final thing to check here was the position of the steam chest in relation to the 2:1 gear stay and the outside cylinder steam chests as they all need to be at the same height and parallel, this check is the last to show that the cylinder is at it's correct height and things begin to become clearer in ones mind, or should I say i breathed a little easier. Anyway, the picture shows the cylinder in position with a length of BMS bar pushed through the as of yet un-machined steam chest as a visual check on how things are looking, I also checked with one of the outside cylinder flanges in place and a cylinder casting held by hand to see if anything looked amiss, all looks good, needless to say i couldn't take a picture with all of this for obvious reasons..
One thing that has become very obvious is that I still have a fair bit of material to machine off the top edge of the cylinder flange I tend to leave such things oversize anyway to play safe, especially when there are no overall sizes given for the flanges in the drawings, i hadn't realised though that it would be as much as it actually is, more of that later. first job though is a little more machining of the saddle. I hadn't finished machining the bottom flange edge yet nor had I drilled the holes for the steam inlet/exhaust pipes, I had left all of these until I was sure of the middle cylinder's position. with the cylinder's final position known I could line up the saddle on the frames and plot exactly where I needed to drill the two holes. Before starting these I machined the lower edge of the side flanges and back edge too , IIRC this is about 5/16 from the lip that sits on top of the frames, with this done I could now work out how much needed to come off of the cylinder flanges, hope you guys are keeping up, I'm getting lost just writing it... Picture was taken as I made a start on the exhaust passage from cylinder to blast nozzle. Now the drawing states that this hole is 2 1/2 inches (REF) back from the exhaust hole from the outside cylinders, those who have been following me from the beginning may recall that I have positioned the saddle 1/8" back from that shown on the drawing, this is to keep it closer to the prototype ref photo's that i have and IIRC to match Don's GA. I did go into this in more detail some time ago but basically I think the error, if you can call it that, comes in due to the re-positioning of the front bogie from when it changed from swing-link to side-control types, the bogie yoke is actually moved 1/8" due to this change and perhaps why it looked wrong?
Here I have machined down the flange to 5/16 from the lip as mentioned and also finished the two steam holes, the exhaust in the centre and the steam inlet to one side, the drawing states to drill the inlet to 13/16, I haven't done that, I'll wait until I know the exact size of the pipework that connects here, the smaller the hole the easier to seal for a vacuum is my way of thinking. I will most probably make up some stainless baffle plates to go around the pipes ho help with this, Don just states to fill with asbestos or today's safe variant but I like the idea of fitting baffles, final decision on this will be when I know how much room I have to play around with inside the smokebox to be able to get to the fixing screws for the planned baffles, that's another on of those jobs on the back burner... Note that I have also cleaned up the inner edge of the flanges and reduced both the bottom area around the exhaust hole and taken out a section of the rear flange for the exhaust passageway to fit. Not very pretty but it's all going to be buried and out of sight so not a concern, well not to me, I have plenty of bits to do that will be seen..
With a little trial and error I got the saddle machined enough for the cylinder to sit on, now I have more to do here but will leave it until I have finished machining the cylinder flange down to size in a hope of keeping the fit between them as good as possible. The pen marks are from earlier when I was trying to get some idea of how much metal needed removing , it's not as much as it looks here and yes I know that the line isn't running parallel to the blue dots, it was just a rough guide, clearly the cylinder had moved during marking.
Here you can see how much does need to be removed form the cylinder side flanges, I'll need to re-jig the casting for this, that's a job for Thursday..
A view from above, the rectangle shape in the casting around the rear exhaust hole is roughly what needs to be removed for the saddle to sit down lower onto the cylinder..
Another to show that the steam inlet lines up...
Final picture for tonight is just me double checking that things are as should be, with the middle cylinder in place and parallel to the top of the frames i wanted to see if the main bore was still sitting at the required 7 degree incline. For this I pushed a length of 1/2" BMS into the piston gland opening, calibrated the gauge to be zero on the top of the frames and placed it onto the BMS bar.. ok you can wiggle it + or - 0.1 degree due to the play in the gland and length of bar but it's where it needs to be which is nice too know...
So, I know what I'm going to be doing this week after completing my grandfather duties, first will be to machine down the top edge of the cylinder side flanges, that drill/tap all of the 6BA holes, the forward of which are shared with the outside cylinder flanges, I tell you things are certainly close fitting on this design.... With all of that done I will re-check the frames for required holes (still need to do the bowden cable clip holes, will make a jig for those) and then I may be able to take a look at a good clean up and getting some paint on the frames, now that I am looking forward too....
thanks for looking in guys..
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Edited by greenglade, 30 April 2018 - 21:14 .