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Scratchbuilding a Sharp Stewart Cambrian 440


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I have started scratch building a Sharp Stewart Cambrian 440 which will be in EM gauge and hopefully powered by a portescap motor on a split chassis. The choice of material is nickel silver (NS103-half-hard) as I believe this is superior to brass when it comes to scratch building. Tufnol rod will be used to make top hat bearings to isolate the driving axle from the motor and pcb board for the split chassis. 3D printing technology will play a part in the construction of the loco and will be employed in areas that will benefit from it. As I progress with the loco I will post photos of the parts I have made with details of materials, construction methods and tools used. I expect there will be a few errors made along the way and the involvement of some experimentation which I will be happy to share with my readers.

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In the attached image A, C, and D were cut out on the pantograph machine and B was cut out on the cnc machine. The rivet holes on D were done by hand and the ones on B were machined on the cnc machine. The rivets will consist of scale rivets from ScaleHardware of America that have a .5mm head and .35mm shank. I am waiting for .35mm large shank drill bits to arrive from America so that I can adapt them to my cnc machine. I have decided not to fabricate the cab but to make it one piece with the sides being folded over. The fold lines will be engraved on the machine to almost the depth of the material so when the sides are folded over the edged will be sharp.

Cab

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Having purchased a pantograph machine over a year ago I was eager to put it to good use on my Cambrian project. I decided to have the master laser cut in acrylic sheet at a ratio of 4:1. I could have cut out the shape by hand using another material but why make work for yourself when you can easily draw the artwork on the computer. When the artwork is finished it is simply sent to the laser cutter for cutting. The image I have posted shows three tender chassis sides machined using two different machines. 1 & 2 were machined on the pantograph and 3 was cnc machined on my Roland Camm-2 pnc 2300. The first two were done in 1.6mm NS before I purchased the cnc machine. Having done the artwork for the laser cutter I simply reduced the artwork to 4mm scale and sent it to my cnc machine for comparison. The first two frames are probably too thick for job I am doing and although I would have a nice rigid chassis the thickness on them would spoil the look of the chassis and soldering might be a problem. The last one is .57mm NS with a fold up tab to aid fixing to the tender floor. The chassis was cut out using a 2mm cutter and on the fold line I used a 45 degree angle engraving cutter. Unfortunately the fold line isn't deep enough so I will have machine the side again taking a deeper cut with the engraving tool. I will probably use my pantograph machine for the heavier cuts and the cnc machine were thin material is sufficient.

Tender Chassis

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As I mentioned in my introduction regarding 3D printing, I decided to produce my own axle boxes as there were none available that resembled the Cambrian one. I was fortunately able to obtain some good photos of the loco and a works drawing which helped me design the axle box. After creating a 3D model it was then saved out as a stl file for 3D printing. I am awaiting delivery from Shapeways where I have sent my stl file for printing using their frosted extreme detail material. The axle boxes will be printed at 16 microns which is .01mm layer thickness. If the prints are satisfactory Dragon Models has asked if they can have a set to cast from. Depending on the quality of the castings I may either use the castings or 3D prints on the loco.

Axle Box

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Having received my springs minus their axle boxes from Shapeways I decided the sprue needed more supports. I also beefed up the model and although probably over scale in places it should now stand up to the rigours of being printed and cast. Shapeways were kind enough to offer a full refund or store credit.

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Visited Scaleforum last Sunday and really enjoyed the show. Alan Buttler of Modelu was there and he kindly gave me some new test prints of my axle boxes. They are much better than the previous prints and what I was looking for in terms of sharp edges. I have cancelled my order with Shapeways as I don't see how they can improve on the ones Modelu have printed. The unit cost on these will be 50p based on a minimum order of £15. So is it worth having a casting done as you will lose some of the detail when they are cast?

Cambrian 440 Axle Boxes

 

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Hi Peter

 

Originally I was hoping to use a portescap motor in the loco. The portescap has a metal gear chassis that comes with brass tophat bearings the axle sits on. If I am able to use the motor I will have to isolate the chassis from the axle by turning one or two tufnol bearings depending on where I split my axle. The axle bushes for the frames will stay brass.

Tufnol Tophat Bearing

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Now that's a hansom looking loco and I think it going to be a great build. I'll follow this with interest. Steve

I hope you live long enough to see its completion. It's my first attempt at scratchbuilding a loco so there will be no doubt lots of trials and tribulations along the way which I will share with my readers.

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What kind of pantograph machine have you got? I've got an ancient one, that's a bit of a family heirloom, that is assembled in my workshop, but I haven't got it working yet. I was thinking about converting it just to do light milling on, as I'm not sure if it's suitable for model making, although if it is I may be able to cut masters on my Silhouette Portrait cutter.

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Hi John

I have a GH Alexander pantograph machine which I purchases about two years ago. I get my masters cut out of acrylic sheet on a laser cutter. I usually have them cut to a ratio of 4:1 or 6:1 depending on the final size of the piece I'm cutting. I use either a 2 flute or 4 flute 2mm milling cutter. I could use a smaller cutter but I would run the risk of breaking it if I was too heavy on the cut. I think your idea of using a silhouette cutter would not work as they only cut very thin material and you would have problems fixing the master to the pantograph bed. You need something quite ridged to cut around. If the shape is not too complicated you could cut it out yourself using a suitable material. The photo shows my pantograph with a Midland Railway 060 chassis master cut out of acrylic.

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John

 

GH Alexander ceased production quite a few years ago but you can still pick them up quite cheaply on ebay and other places. I bought mine at more or less scrap value. It took a while to get the calibration right before I got it to produce what I wanted. If the silhouette idea doesn't work out let me know. A friend of mine has a laser cutter and would welcome some work thrown in his direction. I would be interested to see a photo of your pantograph.

 

Tom

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It's a Taylor-Hobson, made I think in the 1930s, but seems to have been in production until the late 1950s from what I can remember. It came from Huntley & Palmers in Reading, where my big brother used it during his apprenticeship, and acquired it when the factory closed. I swapped a pillar drill I inherited from my Dad for it, that my brother has used a lot, but I've never used this, yet! I need to find a round drive belt before I can try it, but I think everything else is there. I think the motor has been replaced, and that it's been adapted to take standard milling cutters, but haven't checked this yet. It's had a coat of Hammerite though, and was originally green!

 

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My large shank micro drill bits arrived the other day so I was able to make my .35mm drill attachment for the cnc engraving machine. I decided to attach the 10 thou nickel silver to the engraving bed with strong carpet tape instead of clamping it down. The problem with using clamps is that they can interfere with the cutting tools as they travel across the bed. I used a 2mm two flute milling cutter for the windows and cab profile, a 90 degree engraving tool for the fold lines and my .35 mm drill attachment for the rivet holes.

Front Cab Rivets

 

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  • 3 months later...

Hi, what an interesting approach you have adopted to produce your "Sharpie".  I applaud your approach of best material for purpose and it is great to see 3D printing being used where it works best.  I have made models commercially for thirty years or so.  When it comes to pattern making and one or two offs the Alexander pantograph is still the best, most flexible aid you can use.  It is still a mainstay on my commission work.  I do not know what cutters you use.  For a long time I used engraving cutters, then I discovered mini mills, but for the last six years I have used solid carbide slot drills from Drill Service (Horsham)  ( usually 3/32 or 1/16 stub slot drills)  The 3/32 cutter (I puchased five at the time) is still in use, razor sharp after six years work on and off at 18,000 rpm! Very helpful and knowledgeable company who will also make specials( at a price) They might also be a source of microdrills for you since I know they do a lot for the printed circuit makers. (I only endorse the company as a very happy customer!)  They cut very fast in non-ferrours and give an edge finish of better quality than laser cut. 

I do not want to teach my granny......., but I think from the point of view of making your loco in a realistic time frame I would not use separate rivets, especially if you can etch what would be behind the rivets eg angles in the cab or doubling plates for riveted tender side plating.  Spot them on the CNC or panto and emboss them with a punch and die set.  Again easy to make in a whole range of sizes and head shapes - use small size allan key bits in the head of the male die for bolt heads. Make the deap throated frame of the rivetter from 3/4 thick steel .Drill the die and anvil hole for 3/16, hacksaw out the throat. The size of the anvil head determines the pitch of the rivets etc.  The die is male made first. Harden and temper to straw and this can be used to form the anvil depression by using it to finish a drill hole.  Hardern and temper the die to blue.Emboss the rivets using an adjustable centre punch. By sweating pre- etched riveted strips to the rear you have no emboss holes from the rear that detract from so many nice models and avoid the tedium of fixing many 100s of separate rivets.  All the best will follow this thread with interest.

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