Greengiant Posted January 22, 2015 Share Posted January 22, 2015 How have you encapsulated the magnets in the brass bar? Martin Link to comment Share on other sites More sharing options...
Greengiant Posted January 22, 2015 Share Posted January 22, 2015 When fitting these casting I tin both parts first with 145 solder then use Woods metal to solder the two parts together, the benefit of this is that woods metal melts at 70c so we don't put lots of heat into the model and is easy to move if the position is out. Next the hole is opened out in the smokebox. Simon What is Woods metal? Martin Link to comment Share on other sites More sharing options...
JeffP Posted January 22, 2015 Share Posted January 22, 2015 Same as lowmelt solder: http://en.wikipedia.org/wiki/Wood%27s_metal Link to comment Share on other sites More sharing options...
Marshall5 Posted January 22, 2015 Share Posted January 22, 2015 It's a low melting point alloy also known as "Cerrobend" - I have an idea it contains Bismuth. Quite a high density so useful for weighting rolling stock - even plastic by melting it in hot water and simply pouring it in. You used to be able to buy 'joke' teaspoons made from it which melted when you stirred your tea with it! Ray. Link to comment Share on other sites More sharing options...
hobbyhorse Posted January 22, 2015 Author Share Posted January 22, 2015 You are correct. Its also a lot cheaper than the the branded low melt type. Simon Link to comment Share on other sites More sharing options...
JeffP Posted January 22, 2015 Share Posted January 22, 2015 Yes, I had one of those teaspoons, plus a plastic mould to remould it. Then my dad saw it and went ballistic, said it was poisonous, and confiscated it. It went into the cupboard with my home-made 20,000V shocking coil, my trumping machine, my stink-bomb maker, my darts to fire down a biro tube...all lost. Link to comment Share on other sites More sharing options...
hobbyhorse Posted January 23, 2015 Author Share Posted January 23, 2015 To encapsulate the 3mm x 1.5mm magnets I used some 5mm x 2mm brass flat section. First a 2.5mm hole was drilled completely through the bar then a 3mm hole was drilled into the bar, but this time not completely through. I used slot drills in the mill for both holes as with the 3mm hole you need a square bottom to the hole without breaking through, leaving a minimal amount of metal to hold the magnet To fix the magnets in the bar a drop to thin super glue on the rear face does the job nicely. Simon Link to comment Share on other sites More sharing options...
KCR Posted January 23, 2015 Share Posted January 23, 2015 Where did you get those boiler clamps, I could do with some of those? Martin Jeff, both Martin Finney kits. Martin, Dad picked them up at maritime models in Greenwich some years ago, never found them anywhere else. Simon http://www.touchstonetonewoods.co.uk/products/clamps-supports-37/flexible-strap-clamp-ingenious-design-ideal-for-clamping-finge-1836.aspx A similar design of clamp can be found here for £1.99 as well not going to break the bank. Quality work by the way! enjoying watching the progress. Link to comment Share on other sites More sharing options...
hobbyhorse Posted January 24, 2015 Author Share Posted January 24, 2015 Valve gear. Assembly of the out side valve gear was straight forward, one of the modifications was to make it removable which other than a couple of 14 and 16 BA bolts. One part I wasn't happy with was the return crank, which was a 2 part etch with minimal detail of the fixings to the crank pin. It was easier to make a quick pattern for the engraver and machine the 4 required, plus improve the method of fixing than using the parts supplied. This was machined from .9mm nickel silver sheet with the boss thickness .9, and the eccentric rod end reduced to .6mm. Using the AGH crank pin fixings,these are then reduced in thickness by 15thou to fit into the recess on the back of the return crank boss. With the crank pin fixing screwed in the return crank was soldered on once the angle was set, it was then transferred the the drill so that the bolt holes could be drilled through into the crank pin fixing. Once the dummy bolts are soldered in and as these go through both parts, the chance of them coming apart is removed. The dummy bolts have a head diameter of .9 and a peg diameter of .6 which is the hole sizes already drilled on the crank. Produced on the milling machine and finish on the lathe. Replacement crank before cleaning up bolt heads, and showing the etched ones. The improvement in detail on the valve gear by adding some extra parts didn't take a lot of time but adds a crispness that stands out. Simon Link to comment Share on other sites More sharing options...
JeffP Posted January 24, 2015 Share Posted January 24, 2015 Engraving machine? Pantograph? Link to comment Share on other sites More sharing options...
Pete Harvey Posted January 24, 2015 Share Posted January 24, 2015 Simon How are you controlling the play on the rods when the eccentric arm is screwed in? Link to comment Share on other sites More sharing options...
hobbyhorse Posted January 25, 2015 Author Share Posted January 25, 2015 Jeff, Yes the machining of the crank is done on a Taylor Hobson pantograph engraver. Pete, I control the side play on the rods by adding a 15thou washer over the con rod once the centres have been set with all the rods on, the crank pin is then reduced down in length to this washer, which is removed before the return crank is set. One of the problems with a lot of kits is that most motion work isn't thick enough, this is so with this kit so from the base of the crank pin we have the side rod followed by packing washer which brings the con rod out to the centre line of the piston, followed by the con rod and the return crank. So overall the play within the pin is 15thou in total, this is with using the Harris type crank pin. Hope this explains the setup. Simon Link to comment Share on other sites More sharing options...
Guest Isambarduk Posted January 26, 2015 Share Posted January 26, 2015 "... one of the modifications was to make it removable which other than a couple of 14 and 16 BA bolts."Come on, Simon, we look to mentors such as you who produce such super work: they are not bolts but screws! David Link to comment Share on other sites More sharing options...
hobbyhorse Posted January 28, 2015 Author Share Posted January 28, 2015 I've mentioned using various screw fixings on the build, those that are visible are replaced when the final assembly happens with Hex headed bolts, and just as David posted about the screws I was machining up the said bits. Your quite correct David, I've told the workshop Forman its his last chance! To ensure that the chassis runs smoothly firstly the side rods are fitted, and then run on the rolling road for a day. If all is well one con rod and piston rod is fitted and then put back on the rolling road again, this carries on for the other con rod and the two valve gear assemblies. This process ensures that any tight spots can quickly be identified. One problem I did encounter was with the crank axle on the wheels that the customer supplied. The bearings on the crank are captive and one was a bit tight, this seized up when on the rolling road. To free the bearing a small amount paraffin was applied to bearing and put aside overnight, then washed out the following morning with more paraffin and re oiled and then rotated for a while whilst watching the box. After a couple of hours rotating all look to be OK. With the chassis whizzing away on the test bed I've been getting on with detailing the loco bodies. It's one of those jobs that takes a long time, 2 days spent so far with probably another couple to go. While doing this instead of listening to the radio I've down loaded some podcasts from "model rail radio" and it very interesting stuff. With the detailing the only part I want to mention is the smoke deflectors as these are removable to help painting. The base fixes to the running plate by adding some 2x4 brass strip which is tapped 12ba, with holes through the running plate. The u section on the top slides over the handrails. Looking more like a Nelson now. Simon Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 2, 2015 Author Share Posted February 2, 2015 Before the final detailing of the chassis can be completed the rods and valve gear for the inside cylinders need to be fitted. What looks complicated when broken down into small sub assemblies is no more complicated than the outside motion, the drawing with the coloured areas gives the idea. As with the outside motion making these parts removable is a must, and this time 14 and 16ba screws are used. The importance of fitting the parts to allow free movement without any tightness is probably more so with these parts as access is very time consuming if things go wrong. The slidebars and valve guides had previously been fitted to the sub frame so it’s just a case of fitting these with their associated rods, starting with the expansion links and straps. The expansion links are fixed to the hangers with some 14ba screws which are tapped into the links them self, the thickness of the nickel silver is just thick enough to allow this. The eccentric straps needed thinning as these run in rebates in the eccentrics which are slightly to narrow to accept the four layers of etches, this was achieved by rubbing the outer faces of the straps on some emery paper. The design of the straps is good as its in two parts, one part has the straps and arms with the other a cover plate which folds over the first part with small fold over tongues to secure both parts onto the eccentric. Unfortunately the thinning process removed the tongues which isn’t to much of a problem as a small dab of solder will suffice, also a couple of tabs joining the folded section together also came away on a couple, needing a more robust joint with a section of strip soldered in. Photo shows the strip soldered in on the bottom. When I made the eccentrics for the crank axle an extra one was also made and not parted off the bar, and this is used to test fit each strap before fitting to the crank axle itself. Last two photos show the access hole in the sub frame and progress so far. Simon Link to comment Share on other sites More sharing options...
JeffP Posted February 2, 2015 Share Posted February 2, 2015 That's not modelling...it's model engineering! Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 2, 2015 Author Share Posted February 2, 2015 Yep that's what I like do. Simon Link to comment Share on other sites More sharing options...
Horsetan Posted February 2, 2015 Share Posted February 2, 2015 There should be more of this in 4mm scale Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 5, 2015 Author Share Posted February 5, 2015 With the last valve gear bits cut out, the the Inside motion is ready for assembly. The remaining motion work is added to the sub frames, which went together without any problems other than having to adjust the eccentric rods to match the eccentric centres. Although the sub frame makes working on the motion easier, the final assembly is still vary time consuming, with a few tight spots on one of the sets most of a day was spent doing this. Its good that these are now fitted With the inside valve completed and tested on the rolling road, the weight shaft for the inside motion needed fitting, again this is removable by threading the ends of some 1.25 nickel silver bars 12ba. 4 12ba nuts were run onto a screw to enable these to be turned round to give a better representation of the fixing collars. The photo shows one fitted. Simon Link to comment Share on other sites More sharing options...
david.hill64 Posted February 5, 2015 Share Posted February 5, 2015 Wonderful work! Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 5, 2015 Author Share Posted February 5, 2015 Thanks David Simon Link to comment Share on other sites More sharing options...
JeffP Posted February 5, 2015 Share Posted February 5, 2015 I always click on any updates to this thread quite eagerly...and I'm never disappointed! But I AM jealous........I wish I had your skill with machine tools. Link to comment Share on other sites More sharing options...
scot6p Posted February 5, 2015 Share Posted February 5, 2015 Fantastic work Simon, you make me feel envious Len Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 5, 2015 Author Share Posted February 5, 2015 One thing I've found with the RM web is the fantastic depth of information and support that is offered. I was going to do this build on another forum but this is the place for me, and whatever your skills or gauge I'm always picking up new ways of doing things. With this build not far off completion, I've started another thread which will show my other passion which is scratch building, although not in 7mm but a bit bigger in 16mm. Simon Link to comment Share on other sites More sharing options...
hobbyhorse Posted February 18, 2015 Author Share Posted February 18, 2015 Not a lot of progress lately as I’ve got 3 MOK Merchant Navy’s that need fitting with sound chips and a few repairs. But several people have PM me about the cylinder cleading, wanting to know if I was have any problems with them and why leave them off so late in the build. Both PM's had also said they'd encountered problems forming them. Leaving them off until now helps when setting up the various rods with the valve gear. I think we all find different approaches to forming and bending sheet metal, mine is based on not softening the metal but using it in its rolled state, yes it’s vey spring but with a bit of care can be worked very easily with the benefit of not being damaged easily, and no chance of distorting the plate work with heat. The following photos show the various stages of forming the bends, starting by using the cylinders to start the initial bends, and following with bars that are just under the diameter of the curve held in the vice. Taking your time is the key, with the end result just needing light pressure to seat the cleading ready to solder. Yes I've spotted the cylinder cover needs filling. And finally soldered on. Simon Link to comment Share on other sites More sharing options...
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