Work on a Hornby J15
Entry posted by Fen End Pit
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When Hornby announced that they were producing a J15 I was very happy. A favourite locomotive read-to-run and an excuse to get a second to go along side my kit build model Alan Gibson.
Edit 16/8/19 - Work on the J15 EasiChas has now made progress see later blog entry here https://www.rmweb.co.uk/community/index.php?/blogs/entry/22523-j15-chassis-kit-design/
Initial inspection gave the impression of a nicely made model but the more I looked at it the more I felt disappointed. What on earth made them get the handrails so wrong! Instead of the handrail knobs sticking out of the boiler at the perpendicular they were horizontal. For no apparent reason someone had decided in the design process to add completely erroneous little mounting points on the boiler and then make the handrail knobs stick out of them horizontally. I can't even see a manufacturing reason for making this design choice, why would the boiler be easier/cheaper to make with the holes horizontal? It doesn't seem to be a mistake which has occurred on other similar models in the Hornby range.
I just couldn't satisfy myself that 'it looked alright' and so the locomotive has sat in the drawer for over a year while I wondered what to do about it. The problem was how to re-drill the holes for the knobs in the right place and at the right angle in Mazak, which is horrible material to drill. I clearly needed some kind of jig, but it would have to be a complicated shape to hold a drill at the right angle. Using a combination of measurements from the works drawing which I had from the Gibson kit and measurements from the Hornby model I came up with a shape which could be bolted over the footplate which holds a brass tube at the correct angle. The opposite side of the jig is also angled so, when you put it on the bench the hole to drill is vertical.
The two parts are held together by a pair of M4 bolts and the 3D printed material is strong yet soft enough not to damage the foot plate when clamped together.
The original handrail was removed carefully and it was clear that it was a very nicely made unit. The knobs are pretty much scale and it can be reused as is. It took a little effort to pull it out from the boiler but a little bit of card to protect the boiler followed by using a scalpel blade as lever go it off without damaging either the rail or the boiler. Filing off the support 'bumps' was harder as several of them are quite near detail such as the washout plugs which you want to retain.
The positioning along the boiler was done with a set of vernier calipers, measuring the distance from the front of the cab to the handrail hole and the subtracting half the width of the jig.
Drilling was horrible. The Mazak is a very hard material and I only had some nasty cheap .5mm drill bits. After several hours (and several broken bits!) I swapped to a decent Carbon Steel .45 drill bit from Eileen's Emporium and things became much easier. The hole which I'd 3D printed in the jig for the drill was sleeved with a short length of 1mm external - .5mm internal tube. Once I'd drill the initial pilot hole the piece of brass tube was removed and the holes enlarged to .75mm to take the handrail knobs. A little bit of filling was required on the original holes.
With the handrail back in place I've just brush painted a little black on to cover up the work, the finish is better than the photo makes it look but I'll get the airbrush out to tone things down and blend the finishes together a bit more once the chassis has been rewheeled. To my eyes the handrail just looks so much better and I'm very pleased that it is still horizontal and in the right position vertically. (it lines up with the one on the cab side) and the boiler looks better without the extra mounting points which never existed on the prototype.
I've purchased a conversion set from Alan Gibson to rewheel to Scalefour, There is a good guide to this on the Alan Gibson site at http://www.alangibsonworkshop.com/Hornby%20J15%20Conversion.pdf I'm not sure at the moment whether I can bush out the crankpin holes or if I would be better of drawing up and etching a new set of rods.
Don't expect any rapid progress, but at least now I have the handrails sorted I can feel it is worthwhile.
David
Footnote - I apologise to all of you who have Hornby J15s and have been trying to convince yourselves that the handrails are ok
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