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Discussion in 'Workbenches, including workshop techniques.' started by Tom Mallard, 27 December 2013.
Absolutely ..........., no, wonderful doesn't go far enough
Simply stunning, my gast is flabbered......
Thanks all for taking the trouble. You're very kind!
An excellent article in the MRJ Tom - the B2 is lovely, I cannot see any trace of solder!
That's because it is held together by will power. No, solder is one of those things that people can get hung up on, but I try to keep things relatively clean and tidy as it means that there's hopefully nothing there to spoil the paint finish. Anyhow, using nickel silver means it's harder to spot... The format of the article wasn't my idea, btw, but I always like detailed captions. However, I'm also aware that sometimes this was a little confusing if the text was skimmed through. A lot of information was squashed in, and next time I will maybe have to go in to more detail on a few things.
I must admit Tom, I do like extended captions myself, its good to talk about in detail about the subject of the photo. I thought there must be some solder in that loco somewhere...
It's been a little while... but here's the K3 finished at last.
As usual completion was extremely involved, even once the body work had been very finely finished by Ian Rathbone. But it works smoothly and reliably which I found is equivalent to looking good in the overall scheme of things.
There's been a lot of work to finish this model so if anyone has specific questions then please do ask.
I will get some better pictures of the K3 at some point, but for now these will have to do.
A few things to add.
Work on model building has slowed since recommencing a career in Engineeering Design.
However, I have researched and drawn up an LMS Compound for Scaleseven which is turning out to be very rewarding based on the scale and skillset applied to this project.
I am combining everything I have learnt over the past 10 years or more to produce something fitting, with a miniumum of etching used, most parts are machined or fabricated by hand, and all the rivets are embossed, making very good use of my CAD model to position these details. The frames are to be in 3 sections as per the prototype and have lap joints to provide a useful narrowing toward the front of the engine, which is very slightly exaggerated by using slightly overscale frame material. All the frame parts are cut from 0.8mm nickel silver sheet.
I have tried hard to reproduce the subtle variation in rivet size and type throughout the model, so for example the cab has 4 rivet sizes.
The tender tank has progressed well, though presented some challenges in that although based on Deeley's 3500 gallon tender, its tank is rebuilt from a 4000 gallon bogie tender, and no drawing can be found for this. Cross referencing with various Midland Railway GA's and meticulous observation of photos helped give something that must be very close.
Thoughts are shifting to the frame stretchers and motion, the Richard Hersey produced wheelset having been in hand for some time now so it is about time they were put into use.
The frames and bogie are profile milled with a template also milled and drilled to be used as an embossing pattern. Care must be taken to ensure the correct rivet or bolt head is reproduced for each side and each face of the frame component, and this is particularly so on the areas of lap joint.
I must also add that the K3 although finished for some time now, it had a number of extra pictures taken for its MRJ article though very few of the completed model were used.
Impressively clean and sharp work. The beading on the side of the cab and splashers is it half etched or have you profile milled the overlays? Given the sharpness of the beading I suspect the latter.
They are overlays, but not profile milled. Because of the effort put into my CAD model I am not so constrained to using just profile milling, and chose to etch certain components. I was in two minds about this as I could see how etching might run against the handbuilt ethos, though in the end I came to my senses reasoning that all the work put into this had been my own, including any design aspects. I suspect my contemporaries who haven't used this technique in their own work perhaps just don't have the ability to do this?
I selected 3 material thicknesses 10, 15 and 18 thou which gave the opportunity to define the locations of embossed rivets and in some cases leave a scale thickness edge exactly where required such as the butt straps (10 thou) or cab front edge (half etched 10 thou). As with any etched part, the edge appearance was treated as necessary to remove any undesirable cusps.
So there you go Adrian, not all profile milled like the frames, just the best approach (in my opinion) for the task or detail being modelled.
Progress has been made again, now I've been able to resume model making.
The compound has a spectacular set of wheels made by Richard Hersey from Alan Harris castings, and I've erected frames for the engine and tender for them to live in. Nearly all the parts have been profile milled from 0.55mm or 0.75mm N/S sheet, with relieving holes drilled into the back of the material where each rivet is positioned. The hornguides are machined from bar stock on the main frames.
Some other parts have been made as shown in the accompanying image.
As requested, Richard made the axlebox bearings insulated so pickup is off the top of each one. It interferes a little with my compensation beams for the driving wheels, but won't affect performance.
Next will be some work towards populating the space between the frames with valvegear parts.
Not got onto the motion yet, as I wanted to get more of the bogie done. There are numerous fabricated and machined parts to the compensation/spring arrangement some of which in future might be better served being cast items. I wasn't prepared to accept any lead time on this, so made them all myself.
The beams are formed in a small improvised press tool, which although time consuming to make in the first place allowed all of these to be formed in a few minutes! I am learning that having confidence in taking the time to make jigs or think things through saves more time in the long run.
Although I enjoy the use of CAD tools to design my models I do have to use numerous old fashioned processes to make them. One of the most dated and quite traditional machining processes is to use a pantograph milling machine, in my case to make a number of blanks. Some of you have invested in CNC desktop and/or laser cutting devices, which look quite appealing every time I undertake these tasks...
Some of the details of this quite laborious yet still time saving technique are outlined a bit.
I print paper templates out at a predetermined scale of either 3:1 or 5:1, then stick them to plastikard sheet (1.5mm thick and upwards) using solvent. These are then fretted out and filed or smoothed to shape. the templates or profiles are stuck to a backing sheet of plastic and then taken down to the pantograph mill.
The sheet metal stock is stuck down with double sided tape onto another sheet of plastikard, leaving a clearance border.
Clamps secure the material to the work tables of the machine and if necessary all the rivet or hole centres are spotted with a centre drill. The cutters I use are disposable 1.5mm 3 flute for most work. Rarely I employ 1mm cutters but these are for small slots such as those in expansion links, or for areas where a tighter radius inside corner is desirable.
I have tried hard to select free machining grades of both brass (CZ121) and nickel silver (NS101 or NS103) where possible as they really do make life easier. Beware trying to use etching grades of these materials, particularly of nickel silver, as these snag and grab at the cutter very easily and leave a poor finish. For thicker n/s I often employ a cutting oil brushed on, and this obviously prolongs tool life and improves cutting finish at the expense of everything being covered in clag.
duplicates are made as required advancing the work table in nice round numbers. Completed parts removed with a modified artists pallete knife (just sharpened the edges a bit to slide under parts more easily)
Once into a routine, the rhythm of making parts makes the time pass quickly!
removing sections of double-sided tape is often required, as is removing cutting fluid residue.
The cylinder covers are the first time I have jigged a part up on my pantograph machine to counterbore a profile, and it turned out I need not have worried. In most cases it just working out how to hold the workpiece. I soldered the blanks, two of which are shown as these are for the front of the cylinders, onto piece of scrap brass bar.
The bogie is up on its wheels, and the compensated axleboxes articulate nicely.
Though I use lots of manual machining methods and skills, and it might seem a bit of a shame to a 'purist' like me, I am actively investigating the new digital additive manufacturing 3D printing techniques and CNC profiling, now that I am satisfied that these processes have reached a sufficient quality to cost ratio...
Some of the metal confetti has ended up in the slide bar assemblies. The slide bars are from machined lengths of nickel silver, sawn from 1.6mm sheet. Lots of cosmetic bolt heads are used, as none of these parts of the motion used rivets on the prototype.
I have machined the bodies of each cross head from solid blanks as I think it simpler than trying to put numerous components together at the right spacing and not interfering with subsequent soldering activities for the details. I have set the rearmost face of the low pressure cross heads outwards by 3 tenths of a mm and thinned their backs to give additional clearance in the bogie splasher. It all adds up!
There have been numerous challenges to overcome in making this lot, mostly stemming from the slide bars and pistons functioning on 3 different planes... I am fortunate that a lot of this can be worked through or checked on my CAD model and this reduced guesswork. Even with a lot of photos of preserved Midland Compound '1000' to go off I still had some head scratching to do when it came to the back of the inside cylinder and valve chest. There were several variants of this arrangement between batches as they progressed from Midland to LMS manufacture and right hand drive to left hand drive engines, and in all likelihood there is some cladding to bear in mind as there certainly is on the preserved example.
That was 'fun'.
Most of the fitting and assembly of the slide bars to the motion brackets went to plan, but so far I think that it might be the most demanding part of the model to get through. Probably the inside slide bars and motion bracket could have been developed from a 3D printed pattern or something, but it is very satisfying to build these things up by hand, plus I have control over any part of it right up until it is finished. Surface appearances don't rely on post casting finishing, plus I suspect that the strength of the nickel sliver sheet and bar is higher than the equivalent lost wax cast section. This sort of thing depends on a few conditions such as who is doing the casting and what grade of brass they choose. I have experienced very wide variation in the stiffness of cast parts and by and large I wouldn't expect them to be stiffer than the grades of metal I have used in these assemblies.
I made a lot of cosmetic nuts and bolts again, and it's quite nice to find these are becoming less onerous to make after the first few dozen.
The inside motion bracket and slide bar assembly now clearly show the 3 separate planes mentioned in a previous post.
I think ultimately I will contrive a way to screw the slide bars to frames to prevent drift, particularly downwards, but also to keep the outside ones close to the frames. I am sure I have seen this on Tony Reynalds' GWR King models and doubtless he does this to other models he has made.
I have a Chowbent Compound with Laurie Griffin inside valve gear to do sometime. This thread will help me no end as I got a little confused with all the different planes when I had a brief look at it.
Cheers Richard. When you get to it, if it helps, I'll let you have a look at my working drawings which separate it all out.
Thanks Tom, that's most generous.
A small assembly to add this time, which introduced another technique which has been passed down to me - using a pantograph milling machine to machine a component in two planes giving useful relief for the arms attached to the reversing shaft. I try to avoid name dropping unnecessarily but in this case it's polite as this came from Martin Finney who knows a thing or two about pattern making... Maybe I would have come up with this myself in the end, but it is all to easy to get consumed by one approach or another when someone else has already done the lateral thinking to save a bit of effort.
The second images shows a few part blanks which were to be built up from turnings and profile milled sheet, but which I now plan to use this new approach for. Including the bosses on these parts (which are drop links for the reversing arms and attach to the expansion links) seems like a nice way of putting this detail in.
Finally the motion work is nearing completion. It has been mentioned that maybe I could use all of this as patterns for making castings, but I have reservations about this as I cannot have complete faith in the casting process to keep things in tolerance, let alone things like shrinkage, drilling of holes, machining and surface finish. I completely agree that it could be a time saver and that this would be very welcome, though for this work that wasn't the priority...
The expansion links are of built up construction quite a lot like the prototype with the cantilever brackets for the bearings being pinned to the link itself. The piston rod fork is pinned through a block that can slide up or down in the link instead of having it fixed in forward or reverse gear. I think it will help installation and proper articulation of the parts if this is free to move up or down until the drop links are pinned to the reversing arms.
The valve rod blanks are just the forks and sliding surface the runs through the motion bracket. The low pressure motion has off centre handed piston rods. The eccentric rods were an exercise in perseverance as each rod is unique. A shame the engineers of the LMS couldn't manage to standardise on such things. A jig was cut from some paxolin sheet to position the strap, separate boss for the rod and the rod itself pinned at the correct distance from the faces of the strap before soldering up with 221 degree solder using an RSU. All the little fixing bolts and oil nipples are from small machined components added at the end.
Finally a couple of images showing the collection of parts ready to install with just the fluting on the outside rods to do. The fluting is undertaken after the rod has most of the flute removed with an end mill. A small improvised cutter was built up from a piece of 6mm steel bar cross drilled to accept a stub of tool steel with a cutting tip ground into it. A screw set into the end keeps this in position. I projected a pair of lines through the part to describe hole centres that would allow the mounted part to articulate the right amount to allow the machining to follow the taper of the connecting rod.
Onwards and upwards