Rabs Posted January 19, 2014 Share Posted January 19, 2014 Almost finished the design for a GWR small metro. As you can see, I've got quite a lot of rivets and other details left to add, but it's getting there. The loco is 54mm long. Side view of the mechanism. From left to right there is a 6mm nigel lawton motor, a brass flywheel, a 4:1 pulley and a 15:1 worm driving the rear wheels. The DCC decoder is in the rear bunker. I'll make the frames as PCBs with connections routed on them, so all the wiring will be integral in the chassis and no other wires will be necessary. I'll be printing with thin walls and filling all available space with lead shot and tungsten powder. I'll print the body on my B9 and machine the chassis parts on my CNC mill. I thought I'd set myself a challenge by trying the smallest loco that would be seen in the setting of my layout. Link to post Share on other sites More sharing options...
backofanenvelope Posted January 19, 2014 Share Posted January 19, 2014 Nice work Rabs and looking forward to seeing chassis/motor fit on this one. Link to post Share on other sites More sharing options...
mikeharvey22 Posted January 19, 2014 Share Posted January 19, 2014 Great chassis concept Rabs. Getting it installed in the body will be like me wallpapering my hallway through the letterbox. I am trying out a similar layout for motorising an N half cab bus. Mike Link to post Share on other sites More sharing options...
Rods_of_Revolution Posted January 19, 2014 Share Posted January 19, 2014 Very efficient use of the internal space! I wonder if it's possible to use Tungsten rather than Lead to give it a little extra weight? I think Tungsten is about 70% heavier than Lead and it's relatively easy to obtain. Cheers, Jack Link to post Share on other sites More sharing options...
Atso Posted January 20, 2014 Share Posted January 20, 2014 Hi Rabs, I have to say this is looking most impressive. Will be following this one with interest! Cheers Link to post Share on other sites More sharing options...
Rabs Posted January 20, 2014 Author Share Posted January 20, 2014 After the thoroughly un-riveting task of riveting I think that I've now finished all of the detail above the footplate. I'm not sure how much of the detail below the footplate I'll put in the print and how much I'll do by hand in brass so I'm not going to waste time drawing it in CAD until I need to. This is now complete enough for a test print, once I've designed the features to attach it to the chassis. Link to post Share on other sites More sharing options...
Etched Pixels Posted January 20, 2014 Share Posted January 20, 2014 Very efficient use of the internal space! I wonder if it's possible to use Tungsten rather than Lead to give it a little extra weight? I think Tungsten is about 70% heavier than Lead and it's relatively easy to obtain. Cheers, Jack If it'll print in FUD it's probably not hard to do a wax/brass print of it and get weight that way. Link to post Share on other sites More sharing options...
Rabs Posted January 22, 2014 Author Share Posted January 22, 2014 Very efficient use of the internal space! I wonder if it's possible to use Tungsten rather than Lead to give it a little extra weight? I think Tungsten is about 70% heavier than Lead and it's relatively easy to obtain. Cheers, Jack Thanks! You are right, it is higher density but pure tungsten is a pig to machine because it is so hard. Some people use copper tungsten, which has a density somewhere between the two and is easier to work with but it's relatively expensive. I have pure tungsten powder and some tungsten beads which I use for small volumes but any powder or shot will only pack to ~50% of the volume. When a volume is large enough to get a solid lump in then tungsten powder is no better than a chunk of lead and is a lot more expensive. So I think that I will use chunks of lead where ever I can and then tungsten powder everywhere else. If I have running problems after this I'll look at replacing the lead with copper tungsten. If it'll print in FUD it's probably not hard to do a wax/brass print of it and get weight that way. It's an option, although I would need to remove most of the detail I've just added to get Shapeways to accept it! Another alternative I've been playing with is mixing micronised brass powder into the resin in my printer, which would bump up the weight a bit. We'll see - I have plans for some supercaps mounted on the chassis, and the large flywheel might be enough without worrying about the weight too much. I deliberately chose a small prototype for my first scratchbuild because if I can get this to work then I'll be able to do almost any loco. Link to post Share on other sites More sharing options...
Tricky-CRS Posted January 24, 2014 Share Posted January 24, 2014 Interesting where do you get the tungsten from in these forms ie powder, beads and lumps? Link to post Share on other sites More sharing options...
Etched Pixels Posted January 24, 2014 Share Posted January 24, 2014 Tungsten beads are used by fishing types. China prices are about $50/Kg wholesale bulk (+shipping...!). Most of it is tungsten alloys at about 90% tungsten. Fishing people also sometimes use a tungsten putty which is a tungsten powder in polymer and is sort of like very very heavy bluetac - you can pick all of this stuff up on Amazon at a none too bad premium. Alan Link to post Share on other sites More sharing options...
Rabs Posted January 24, 2014 Author Share Posted January 24, 2014 Tungsten powder is a bit tricky to get. I happened to come across someone selling a largish bottle from an old school science lab but you can get small quantities here: http://www.ebay.co.uk/itm/TUNGSTEN-metal-99-87-WOLFRAM-COARSE-POWDER-GRANULES-x-100g-/330819796817?pt=UK_Collectables_RocksFossils_Minerals_EH&hash=item4d06657f51 Alternatively there is this brand for golfers which seems to be available from several shops: http://www.gamolagolf.co.uk/acatalog/Tungsten_Powder.html As EP says, beads are easy to come by on amazon or ebay: http://www.ebay.co.uk/itm/TASKA-BASELINE-TUNGSTEN-RIG-HOOK-STOPS-SMALL-QTY-25-CARP-FISHING-BEADS-TACKLE-/111228309653?pt=UK_SportingGoods_FishingAcces_RL&hash=item19e5b95095 I'm not convinced by the tungsten putty myself because once the metal powder is mixed with the putty it isn't actually much denser than lead. Link to post Share on other sites More sharing options...
Etched Pixels Posted January 24, 2014 Share Posted January 24, 2014 Depends on the product - basic stuff is usually about 10g/cm³ so a shade under lead. Decent tungsten rubber is nearer 18g/cm³ Link to post Share on other sites More sharing options...
Rabs Posted January 25, 2014 Author Share Posted January 25, 2014 Depends on the product - basic stuff is usually about 10g/cm³ so a shade under lead. Decent tungsten rubber is nearer 18g/cm³ Oh, interesting. I've not seen that available. Do you have a link? Link to post Share on other sites More sharing options...
Etched Pixels Posted January 25, 2014 Share Posted January 25, 2014 Not to hand, golfers use it though. Link to post Share on other sites More sharing options...
Rabs Posted March 26, 2014 Author Share Posted March 26, 2014 First test print finished yesterday evening. I'm pretty happy with the outcome but there are some areas for improvement. Mainly I need to try printing it at a different angle to remove the banding on the top surface (not visible in this picture). Then I need to add some snap features to hold it onto the chassis. Otherwise it'd pretty close. Link to post Share on other sites More sharing options...
Karhedron Posted March 26, 2014 Share Posted March 26, 2014 Looking very impressive. Once you have got it finished, is there any chance of your offering it in kit form? I would love to have a crack at building that. Link to post Share on other sites More sharing options...
Rabs Posted March 26, 2014 Author Share Posted March 26, 2014 I'm not sure. To be honest I get so little time for my own modelling that I'm not desperate to give up a chunk of it to make kits. Also, I suspect that I'd have to make them pretty expensive for it to make any commercial sense. I'm not saying never but it's not going to be soon I'm afraid. I'm happy to put the design for the shell up on shapeways (although you won't get the rivet detail with them), but that still leaves the chassis, drive train and wheels for the builder to work out. I guess that would be too much of a stretch for many who might buy a complete kit. Link to post Share on other sites More sharing options...
Etched Pixels Posted March 26, 2014 Share Posted March 26, 2014 Oh we'll have a go ! - and quite a few of the folks who build 3D printed shells seem to be building to 2fs to judge from my emails. Alan Link to post Share on other sites More sharing options...
Atso Posted March 27, 2014 Share Posted March 27, 2014 That Metro tank is looking very nice Rabs, a real credit to your CAD and printing skills! Link to post Share on other sites More sharing options...
Rabs Posted April 28, 2014 Author Share Posted April 28, 2014 Thanks - It's been fun so far. After a long interruption from work I've finally had time to work on this project again. This evening I milled out some of the chassis components in 0.4mm copper-clad: It's always a bit of a shock going from the CAD, where it looks huge, to reality, where you realise quite how small the bits of this loco are! I've got some more bits to machine and then I'm going to try assembling the chassis. Then it will be onto the wheels. Link to post Share on other sites More sharing options...
Rabs Posted April 30, 2014 Author Share Posted April 30, 2014 Some more pictures showing a little bit of progress. This chassis was a rough test to check the dimensions and fit. There are a couple of modifications I need to make. Here is how the motor fits in the body Link to post Share on other sites More sharing options...
bluemattersoda Posted June 27, 2014 Share Posted June 27, 2014 Very well done! interesting work on the cnc milled chassis too! Will you be milling the wheels as well or purchasing them with the gearings too? Link to post Share on other sites More sharing options...
Rabs Posted June 27, 2014 Author Share Posted June 27, 2014 I've been experimenting with 3d printed wheels with turned tyres and wheels cnc machined from solid. Not got very far with either yet though! Link to post Share on other sites More sharing options...
bluemattersoda Posted June 29, 2014 Share Posted June 29, 2014 I've been experimenting with 3d printed wheels with turned tyres and wheels cnc machined from solid. Not got very far with either yet though! I've been experimenting with 3D printing the wheels myself as well, though I've discovered that that stepping effect you get with 3D printers means that the wheels encounter too much resistance to roll. I look forward to seeing how the CNC milled wheels work out! Link to post Share on other sites More sharing options...
Rabs Posted June 29, 2014 Author Share Posted June 29, 2014 Have you been printing the rims of the wheels!? I can imagine the trouble that they would have going round! I use turned metal tyres with just the spokes and the hub being 3d printed. Link to post Share on other sites More sharing options...
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