A friend of mine in our village is building a Connoisseur G5 as his first loco kit and I am helping him by sharing advice and making a few components along the way.
Last week we were discussing we were discussing what Jim describes as blower valve castings in his kit which I suggested would be much better in brass than the whitemetal casting supplies.
These are the offending items taken as snips from photos that I have taken of preserved locos at the NRM.
This one is from BR Built J72 Joem
This is from the D17 at Shildon. Note that the fitting is further back on the smokebox on the D17 and it seem N9 tank engines which have a similar arrangement with a front extension to the hand rail.
Some time ago Ian Middleditch (@Ian@StEnochs) and I were discussing making globe lubricators and I had made a form tool to turn them when Ian suggested that I use brass ball bearings drilled through instead. So I ordered some in a couple of sizes from China for about £3 or so for 50. At the time I drilled a couple of the smaller ones out, made a pair of lubricators and put the rest away in a drawer. So I thought I would dig them out to see if I could make some blower valves.
First I dug out a few lengths of tube to see if I had any suitable to hold the brass balls for drilling. I had a vague idea that last time I had used a length of copper tube and it seems that my memory served because the only length of copper tube that I had was perfect.
So I popped it in the lathe and used a countersink bit to falr the end slightly before cutting a slit with a piercing saw to allow the chuck jaws to tighten and hold the ball for drilling.
Jig for drilling first hole
Next I did the same at the other end but this time I used a slitting disk to widen the slot that it would accept a 0.9mm rod in the slot (my friend had pre drilled his hole in the smokebox 0.9mm.
Jig for drilling 2nd Hole
Then I drilled the first hole 10 1.2mm deep
Brass ball mounted for drilling first holeDrilling holes in the brass spheres to 1.2mm
Next I soldered in a length of 0.9mm nickel rod
Blower valve with locating stem drilled
Then it went back in the lathe to cross drill at right angles
Valve mounted for drilling 2nd hole at right anglesBlower valve with 2nd hole drilled
Finally some nuts with a hole in one end for the end of the handrail and a setm on the other to go into the brass ball were added to complete the fitting. The photos do show an oval base but this was left off initially to see how it fit height wise with the handrail. a base could be files up from thin shim stock if there is room.
Blower Valves for Stock
As you can see I made one for my friend and a few more for stock while I was set up. last night I had a quiet count up of the ex NER engines in the queue that require them and I think I need another half a dozen. So I will do those this morning while it’s all fresh in my mind.
As a consequence of the need for miniature studs for the return cranks on the 8F I decided how hard could they be to make.
I started as I would make miniature bolts by turning down the end of a piece of 1.2mm nickel rod to 0.8mm at either end (to make two at a time from each piece of stock). Then I removed them from the lathe and popped them in a hex headed pin vice to file the hex flats on. If I did a production run which I may at some point I would have set up the spin indexer to make them all consistent. As it is they are okay but not perfect.
Then I came to put them back in the lathe to turn the short length of dummy thread which protrudes beyond the nut. This is where I started to struggle a little. Even though I had sharpened the cutting tool I was still getting a bit of deflection of the stock.
Then I remembered that just after Christmas in a Warco Sale leaflet I had bought a live centre with multiple interchangeable points.
This got me wondering if I could make another tip with a 0.8mm hole in it to support the tail of the stud while I turned the other end down to size before parting off.
This is what it looks like in the live centre. The taper isn’t a perfect fit but it’s under so little load that it isn’t an issue
Mini Stud Tail Support
For those struggling to visualise what I am talking about, I did a simple sketch
Well, I would be lying if I said that getting the chassis running with all the motion fitted was anything but a trial. Much of it my own doing. I am not sure how but I had scaled the drawing wrong so my many attempts were all destined to failure I just didn’t know it yet. It was mention of the scale size of one of the rods that Ian Allen @lancastrian) posted on the Guild forum that made me double check and find the error. A trial assembly of the final version of the return cranks confirmed that they were indeed almost a millimetre too long between centres.
I confess, that this almost did me in and I nearly consigned the 8F to its box for another decade. Saner heads prevailed and I recalled the drawing, redrew the return crank in Fusion 360 and created an updated working drawing. From there I made a ninth set of return cranks and again I made an error in so much as I predrilled the cranks and the small bosses that I added to clear the ends of the studs protruding above the face of the crank. When I then soldered them together, I hadn’t noticed that the holes were slightly out of line until I tapped them the tapped them and the tap went in at angle. So, I started again and this time I made four return cranks with the view that I could pick the best two.
This was taken part way through making them. – I did trim down the boss on the deeper pair after testing.
Having taken great care in the shape of them I also only drilled a pilot hole in the bosses. Then I clamped the cranks to my Metalsmith drilling plate in the mill vice and drilled right through to ensure that all the holes were aligned.
Next, I used a small engineers clamp to clamp the cranks to my tapping jig to ensure that the tap was aligned to the hole and then they were tapped 12 BA
I also used my homemade tap spinner to reduce the risk of breaking the tap.
Finally, I had two pairs of cranks fitted with miniature studs
A test fit had me heaving a sigh of relief as they fit and the motion turned over under power but there were a few clicks where the bits were catching. I knew that clearance was always going to be tight so I patiently worked my way through the various parts easing them.
They included but were not limited to, filing two etched bolt heads off of the insides of the expansion links; filing the bottom front corner of the new valve blocks to allow a minute amount of extra forward travel; turning the head of the 14ba steel screws that retain the combination lever to the valve block down to the thread thickness while retaining the slot, to allow them to be easily removed. Again, to allow a minute amount of further forward travel; easing the faces of the connecting rods to allow the expansion link to pass without catching. – Incidentally I measured the thickness kit provided connecting rods at 1.7mm and the Premier ones at 1.5mm so had I used the kit rods that problem would have been exacerbated.
I also replaced a couple of 14ba brass screws (which retain the expansion links) with some homemade nickel silver replacements with the view that they would be slightly more hardwearing than the brass ones. In fairness given how little mileage my locos actually do. this may have been overkill on my part.
After all that I had a smooth-running chassis. The tinging noise that you can hear is because I haven’t permanently fitted the retaining pins that hold the radius rod and the combination lever together yet so there is a bit of slop in them.
