It's been a little while since the last update, but things have been busy. A new loco in the shed (5" gauge Speedy) with a few problems in the chassis to sort out, a new axlebox was required amongst a string of other jobs.
Here we see a bit of progress on a 3-1/2" gauge Princess Marina (LBSC design) and I have been handed a bunch of parts to build the engine with. The boiler has been constructed by me earlier, and I thought the rest of the loco was a rolling chassis!
Going through the drawings, I thought to assess the axle boxes and horn castings, what we have is bigger than the cutouts in the laser cut frames. This revealed a few other questions, and I thought to lay out the frames in CAD to see what the running height of the loco was to be. This is a critical dimenison for those who are not aware, as the loco cylinders are laid out off this.
The drawings and "words and music" are a great help to get going, but sometimes a few things get overlooked...something I can understand in the rush to spit out a design for a magazine going to press. Not to be critical by any means. But I found the running height using the dimensions as supplied meant the axlebox was almost at the top of the horns and some funny business with the dimensions of the motion bracket and placement of the cylinder.
Long story short I have been developing some views and dimensioned parts which differ slightly to the drawings but definitely lay out a working arrangement on CAD. I have moved the axle 5/32" up in the axlebox, and it looks much better. The lubricator drive was a mystery, and have since found buried in the writings to include another eccentric on the front axle...just in case the builders were up that far using the drawings and wondered how they were going to drive it!
I'm in the throws (see what I did there...) of driving the lubricator off a long rod on the axle pump gudgeon pin. The running boards are not shown in plan view and a few long hard looks at photos reveals the cylinder protrudes a ways past the running boards, as also the swing of the expansion link fouls the running board valance and must be relived to clear this...an odd practice, looks like something the Victorian Railways did on the K classes!
Several cross sections have been done on the motion brackets and cylinders & crossheads to make sure it all lines up. Have found some oddities & unhappy clearances with side rods and knuckle pins, can be a pest trying to find room in the bushes if there's not enough to prevent the knuckle pin dragging over the crank boss or hitting a 10 thou protruding axle. By the end of this little exercise I hope to have a set of working dimensions to check this loco off against in it's construction, plus a good sized laser cutting order to speed it all up immensely.
The supplied driving wheels have been machined to size, but the spokes un-fettled. I bluntened two files having a go, and resorted to a 1.5mm carbide cnc router bit in the dremel to get the hard bits off. They look nice now.
Below are some screenshots of the CAD work on this engine, a couple of days going through drawings and reshashing things. Almost ready to make a start....
Happy steaming!
Nigel
Here we see a bit of progress on a 3-1/2" gauge Princess Marina (LBSC design) and I have been handed a bunch of parts to build the engine with. The boiler has been constructed by me earlier, and I thought the rest of the loco was a rolling chassis!
Going through the drawings, I thought to assess the axle boxes and horn castings, what we have is bigger than the cutouts in the laser cut frames. This revealed a few other questions, and I thought to lay out the frames in CAD to see what the running height of the loco was to be. This is a critical dimenison for those who are not aware, as the loco cylinders are laid out off this.
The drawings and "words and music" are a great help to get going, but sometimes a few things get overlooked...something I can understand in the rush to spit out a design for a magazine going to press. Not to be critical by any means. But I found the running height using the dimensions as supplied meant the axlebox was almost at the top of the horns and some funny business with the dimensions of the motion bracket and placement of the cylinder.
Long story short I have been developing some views and dimensioned parts which differ slightly to the drawings but definitely lay out a working arrangement on CAD. I have moved the axle 5/32" up in the axlebox, and it looks much better. The lubricator drive was a mystery, and have since found buried in the writings to include another eccentric on the front axle...just in case the builders were up that far using the drawings and wondered how they were going to drive it!
I'm in the throws (see what I did there...) of driving the lubricator off a long rod on the axle pump gudgeon pin. The running boards are not shown in plan view and a few long hard looks at photos reveals the cylinder protrudes a ways past the running boards, as also the swing of the expansion link fouls the running board valance and must be relived to clear this...an odd practice, looks like something the Victorian Railways did on the K classes!
Several cross sections have been done on the motion brackets and cylinders & crossheads to make sure it all lines up. Have found some oddities & unhappy clearances with side rods and knuckle pins, can be a pest trying to find room in the bushes if there's not enough to prevent the knuckle pin dragging over the crank boss or hitting a 10 thou protruding axle. By the end of this little exercise I hope to have a set of working dimensions to check this loco off against in it's construction, plus a good sized laser cutting order to speed it all up immensely.
The supplied driving wheels have been machined to size, but the spokes un-fettled. I bluntened two files having a go, and resorted to a 1.5mm carbide cnc router bit in the dremel to get the hard bits off. They look nice now.
Below are some screenshots of the CAD work on this engine, a couple of days going through drawings and reshashing things. Almost ready to make a start....
Happy steaming!
Nigel
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