Mickoo's BR modelling

[demu1037]

In other news, CAD work progresses on the tender etches, though it's not full steam ahead yet as I cannot decide on 15 or 18 thou NS as the source material.
I'd like to keep all the art work on one size material, even for the locos and have already decided on laminated main frames, but, it's the combination of two full thickness's or one full and one half etch with exterior detail, both have merits and only one combination is true scale frame thickness, the one using 18 thou NS and that's quite a hard material and thickness to bend easily elsewhere on the model (footplate, tender cantrail etc)

Anyway, Onward!

Mick,

Don't restrict yourself to one thickness, you will end up introducing all sorts of compromises, real stuff isn't all one thickness.

This tender underframe has 0.022 (=+/- 1") frames & heavy bits with 0.010 (=+/- 1/2") dragboxes. The body is 0.018 because of large areas of 1/2 etch, but if that's not the case 0.015 is perfectly adequate (especially if NS, even for this type of tender).






Andy

 

[mickoo]

Andy, cheers I see what your saying and yes frames at 0.022" are better, the A3 real frames scale out at 0.025" and I'd like them that width if possible, I also don't like seeing half etched holes on the insides of frames or guide half etch lines so settled on a laminate frame set up.

This also helps with the rear end which as y'all know on LNER Pacifics, splits. The inner platework will dive inward and form the firebox support frame work, the outer outward to form the Cartazzi extension. In addition on the real loco the Cartazzi extension is a bolted onto the outside of the rear frames, so another overlay is needed there to represent that. In addittion as mentioned here and in Richards A3 thread, there are several visible bolts or round head bolts that need to be modelled, those are best done as half etched and punched look wrong.

As you note certain items are much thinner, steps for example and cab side sheets, those could be half etched but I found on the GP38 cap that large areas of half etch suddenly take on a banana shape as soon as they are released from the etch framework even small parts curled a little.

Maybe I'm just over complicating things but at the moment it's just lines on a screen

Is that tender the one I saw at Kettering, it is very nice

 

[mickoo]

Thanks Mick. That's a really helpful sequence. Did you, perchance, take a photo of the turning in process with the cutting tool doing its stuff? If so, could you post it please.

Cheers

Dave

Dave, I'm afraid not, these are all posed shots 'after' the main event which part of the process did you wish to see, I can then set it up to show the tool tip in place. Because of the inverted jaws I had to get a little 'inventive'....for me anyway.....in getting the tool in and not smacking on the jaws, I did clip it once but all this was done at low RPM, typically 140-320 so it wasn't too much of an issue

I do need too research a better way to form the depressed area, I used a facing off tool but the angle wasn't good, hence the chamfered edge between raised and depressed areas, I do need to take another 0.010" off it as once the outer face of the rim has been turned the boss then impacts the depressed area when the wheel is turned around to do the rear face, in short the sequence has to be rear face first and then front face.

One other surprising thing I noticed is that Slaters wheels are not round, they're slightly oval, the idea of the 45 mm puck was to be able to check the wheel squareness on the shaft and in the process of spinning the wheel to adjust it (brute force bending) I noticed the tread height varied.

None of this was done with a form tool, just ordinary bog standard tool tips and the tread thus far or flange outer face (that which touches the rail head) and foot have not been machined.

 

[Len Cattley]

Hi Mick, I am with you on the frame thickness, but I think you need two thicknesses of etches for different parts. I would like to etch both sides or one side or none depending on what I am etching.

Len

 

[pakpaul]

I do need too research a better way to form the depressed area, I used a facing off tool but the angle wasn't good, hence the chamfered edge between raised and depressed areas, I do need to take another 0.010" off it as once the outer face of the rim has been turned the boss then impacts the depressed area when the wheel is turned around to do the rear face, in short the sequence has to be rear face first and then front face.

Suggest you use a boring tool to create the depressed area, this will avoid the chamfer.

Paul

 

[mickoo]

Len, no doubt about that, but the parts I may need a thinner size will require a new photo tool and probably not fill a sheet, the problem I had with the 08 doors was that I ended up with four sets, at no extra cost mind, but two useless extra sets, I'll probably get away with doing one A4 sheet for the tender body and getting probably four sheets for the thinner detail work, it all amounts to cost and often as not, wasted space on the main etch.

It'd be far better to pick a material that whilst not prefect for every application can be used across the board, where you need fine detail you half etch it, where you need thicker, you double up. You can then fill a sheet with all the details and not waste space and thus save costs. I also dislike thick material, anything above 0.022" just leaves an enormous cusp to file off, often as not ending up making things a sloppy fit.

The whole of the EMD GP38 cab was one thickness, in hind sight 0.010" was too thin for cab walls, even in NS, 0.012" would of been better, but the advantage of 0.010" was superb detail in the grab handles and walkway anti slip detail. Fortunately, most steam engines don't have that sort of minuscule detail, not etched anyway or not in such large visible areas.

 

[mickoo]

Suggest you use a boring tool to create the depressed area, this will avoid the chamfer.

Paul

Much obliged I did think that, but my 'basic' understanding is that the boring tool is used for the inside face of a tube, not for running across the face? and if running across the face, do you run from the outside inward like a conventional tool or from the inside outward.

I'll set one up and try right now

 

[pakpaul]

As you already have the axle hole which can take the point of the boring tool, it will be easier to run from the inside outward.

Paul

 

[mickoo]

As you already have the axle hole which can take the point of the boring tool, it will be easier to run from the inside outward.

Paul

Paul, I just found that out



Much better

Next step, face off the boss and crank pin hub






I've a grub screw that has been partially taken off as a depth guide for each wheel, a fresh wheel will have a raised boss higher than the small step in the grub screw, hope that makes sense? This wheel has already been finished and re countersunk so the 'special' grub screw sits a little low, but overall I take about 0.003-4" off.

 

[daifly]

Dave, I'm afraid not, these are all posed shots 'after' the main event - which part of the process did you wish to see, I can then set it up to show the tool tip in place.

Mick, I'd be interested in all stages of the machining of both the puck and the wheel, tools used etc (suggested use of a boring tool for the recess as suggested above is noted!)
Thanks
Dave

edit: our postings crossed! Thanks for the extra photos.

 

[mickoo]

Mick, I'd be interested in all stages of the machining of both the puck and the wheel, tools used etc (suggested use of a boring tool for the recess as suggested above is noted!)
Thanks
Dave

edit: our postings crossed! Thanks for the extra photos.

Dave, Ok I'll run up a set of photos and text over the weekend for you and post up, but basically it was all done with just a standard tool...except the recent boring tool work....I did have to use a RH tool to get in between the reverse chuck jaws to skim off the larger diameter to make it look nice, but other than that just a case of moving the tool around and adjusting the tool post to get the best angle.

I did find that the bar supplied wasn't round, I think it may be extruded, it's round enough for general purposes but not round enough for my use, again another reason to clean off all the exterior surfaces and make sure they are true....as true as you can get on a SIEG lathe

The bar I bought off Ebay and they offered a cutting service, but you do loose 5 mm with every cut, my order was for a 50 mm length but I asked for 18 mm pucks, so I lost 10 mm in the cuts and by rights am still owed a 4 mm slice somewhere LOL, but being as it came in at 18.5 mm each, and saved me the hassle of hand cutting it, I'm not bothered. The cost of the material was £9.50 or so and I opted for 1st class postage so all up around £16 or so. I've a lot of 6'9" wheels to do, at least 36 for current models so 45 mm bar is perfect, but as noted, you can turn it around and make it smaller to suit other wheels, so two pucks will give four basic wheel size supports, each side is good for about 6" of wheel dia change I reckon.

The smaller side on this puck I'll probably turn later to suit 6'2" as I've a Britannia to do and planning some other locos with wheels in that size region.

The current recess needs opening out a little so that a tender 4'3" wheel sits in there flat, I skim the boss back to the same as the rims on these wheels to give more clearance between the tender frames, so the wheel can sit flat both ways around and no need for an additional smaller depression in the depressed area

 

[Dikitriki]

This is really useful Mick. You have made it look easy, and given me the confidence to have a go sometime.

Thanks for posting

Richard

 

[mickoo]

Richard, it is relatively simple, though I should warn that the only traction you have to the piece is through the axle and spokes so you need very light cuts when doing the steel rim work.

I also run at a low speed, no more than 340rpm but usually around 120-140 on the steel rim during the larger cuts and then the faster speed for the last very light polishing cut. After that I use a Vellorbe cut 4 lightly hand held needle file to take any burrs off and add a final polish with some worn abrasive paper. The 4 mm axle clamping bolt is not wound down really tight, hopefully it'll slip there if the tool does dig in and not snap the spokes, but neither has happened yet.

The more complex and robust method using clamping pieces and a rotating tailstock will take more punishment as will the method using clamps that clamp the work to the puck with straps and retaining screws through the spokes. The problem I can see....not having used either first hand...is that you cannot do the rim and the hub at the same time in one facing pass, without removing some form of the clamping.

But each to their own, this works for me and until I got up to larger spoked wheels, simply used to just put the axle in the jaws and make sure the rim was hard against the chuck jaws, that works fine for small wheels, spoked included, but relies on your jaw faces being flat and faced off, knowing my Chinese SEIG that's probably not a good assumption

I have to confess, the slim wheels do look much better, what started out as a needs must, rear Cartazzi wheels thinning due to scale clearances, has moved on to all wheels for improved clearances and visuals. I may have taken too much off the flange on the intermediate drivers, I need to check the S7 book of words, but being intermediates, shouldn't present too much of an issue on a rigid frame toward smooth running.

Once all the drivers are faced and thinned I'll probably reset the tool slide to the correct conning angle and take a bit off the tread, mainly to make them round, at the moment some look like they're up to 0.003" off centre, not a problem for fully sprung, but might be for a rigid chassis with S7 flanges.

 

[JimG]

Much obliged I did think that, but my 'basic' understanding is that the boring tool is used for the inside face of a tube, not for running across the face? and if running across the face, do you run from the outside inward like a conventional tool or from the inside outward.

I'll set one up and try right now

Mick,

Another tool I use for those type of jobs is a trepanning tool, which is basically a stubby tool which is normally fed into the face of a piece of material to form a circular slot, and is a cross between a boring tool and a parting tool in shape. This message in a machinists' forum gives some idea of the use.

http://www.practicalmachinist.com/vb/general/parting-tool-tricks-161145/#post925595

It's a handier tool than a boring tool if you can't get a decent sized hole in the centre to get the boring tool started.

Jim.

 

[mickoo]

Mick,

Another tool I use for those type of jobs is a trepanning tool, which is basically a stubby tool which is normally fed into the face of a piece of material to form a circular slot, and is a cross between a boring tool and a parting tool in shape. This message in a machinists' forum gives some idea of the use.

http://www.practicalmachinist.com/vb/general/parting-tool-tricks-161145/#post925595

It's a handier tool than a boring tool if you can't get a decent sized hole in the centre to get the boring tool started.

Jim.

Jim, that's interesting, never heard or seen one of those tools LOL.

What I did find with my boring tool was that it will not give a good parallel bore into the material, it faces off quite well but when it gets to the side wall will always produce a bevel, the tool tip seems to be flexing into the middle of the work, everything appears tight and the tool is set as close to the tool post to reduce flex and is a little low off centre, but I would of though even so, it should still give a parallel cut into the work?.

I don't mind the bevel, so long as it's clear of the 4'3" wheels, which it is, it's more a case of knowing why it's doing it and possibly how to fix it.

Addendum, just spun round in my seat, my lathe is behind me but higher than my desk, and spotted why the boring tool will not make a parallel cut, I don't have enough side relief on the tool to clear the diameter of the bored hole, thus the base of the tool is catching on the work and pushing it into the depression , which means I need to increase the side relief angle and I'm not back at work until Weds where we have tool grinding equipment, but at least I know why now, and having the tool tool low of the centre line isn't helping either.

 

[JimG]

and having the tool tool low of the centre line isn't helping either.

Mick,

I've sometimes cheated with boring tools when clearance is tight and set the tool above centre and just went easy on the cuts to allow for the negative rake.

Jim.

 

[Overseer]

Mick,
I would be surprised if the Slaters wheels were all not round, some could be a bit eccentric due to movement in the glass filled nylon centre but the tyres should be round. Is the apparent eccentricity due to the holding screw in your puck pushing the axle slightly off centre? You also haven't explained how you set up the puck to ensure the centre is in the centre when mounted in the chuck which probably doesn't close in the same position each time. The puck idea is fine for facing off the front and back of the wheels but using a collet instead of the chuck when turning the tyre will ensure it is as concentric as possible.

 

[mickoo]

Mick,
I would be surprised if the Slaters wheels were all not round, some could be a bit eccentric due to movement in the glass filled nylon centre but the tyres should be round. Is the apparent eccentricity due to the holding screw in your puck pushing the axle slightly off centre? You also haven't explained how you set up the puck to ensure the centre is in the centre when mounted in the chuck which probably doesn't close in the same position each time. The puck idea is fine for facing off the front and back of the wheels but using a collet instead of the chuck when turning the tyre will ensure it is as concentric as possible.

Possibly but the bored hole is 3/16" and a 'tight' fit........or so I thought!

The chuck is centre punched and the fixing screw lines up with this, thus the puck always goes into the chuck in the same place, once in I DTI the face and external circumference and they are pretty good, usually less than 0.05 mm





These are posed so y'all just have to trust me the puck is 'true'

However, I checked the axle and lo and behold it's out , the original hole was 3/16" (4.76 mm) and a little tight so I reamed it, but on reflection used the wrong reamer, I used the 4.8 mm but not all the way through, so the bore is over size. Worse yet the run out on the axle when the screw is tightened can be as much as 0.1 mm (0.004").

So it looks like I'm at home to Captain cock up and his merry band of fellows!

One solution will be to drill two further retaining screws each at 120° from the first, then it should be possible to adjust them to centre the axle better, the only issue with that is that the retaining screws are at the back, and it's the bore at the front face that's critical, the axle may still move when being turned in the free end of the bore at the front.
I suppose I could get some 3/16" ID tube, measure the OD and re-bore the puck to accept that as a tight fit, a bit of lock tight will make sure it does not move, then drill the tube for the retaining screw and go from there.
Another other option is to discard this puck and make another, or just live with any discrepancies in the rolling concentricity, accept the error in my axle and not turn any treads, just the flange and facing off....I can live with the run out on the flange easily enough, I've remeasured a couple of wheels and the flange run out is averaging 0.05 mm.

I do have an ugly feeling that my bed maybe warped, if I insert a long bar (I know it's straight as it's machine steel and if the tail stock chuck is rotated it stays centred) into the tail stock chuck from more than half way along the bed, it centres pretty close to the jaws of the lathe chuck, yet up close it kicks away from the tool post a fraction. Having said that once the puck was bored to 3/16" it was still a very tight fit on the axle, too tight to push in with fingers, hence the light reaming, in hindsight I should of reamed from the rear face.

Your also right on the source of wobble (if any at all now), it won't be the machined tyre, it'll be the hub or plastic moving in the moulding process, and, a 3/16" collet holding the axle would be perfect, except that means I need to take the whole chuck off the lathe and fit an adapter for the collet chuck and make sure that's centred and once done, put the 3 jaw back and centre that as well, this is a SIEG we're talking about, highly unlikely the chuck will go back on true

Anyway, it's something to ponder, thanks for the reality check LOL.

 

[mickoo]

Okay, moving onward, are we all sitting comfortable, good, here's another episode from the fun filled fiction factory!

Some wag passed comment at the last Sudbury meet that all I'd done was add a few bits to the footplate, visually that's probably true, so on reflection I decided to add something more tangible.

I'm soon coming to the point where the bit that makes it go needs to be added, I already know the smokebox saddle is junk and needs a whole new one so I figured that rather than dive headlong into more scratch building I'd start at the other end with some bits from the kit, I.E. the cab

The cab basically consists of five parts, two sides, a front, a roof and the floor, how hard can it be!

First off they are all in separate parts, the instructions note the sides should be turned in at the rear so that the gap between then when constructed is 49.6 mm (7'1" on the real deal) so some quick math knowing the full width and the final turn in results in a turn in each side of 3.8 mm. This actually went quite well, the first time annealing has worked and the final curves turned out satisfactorily, well chuffed

The next step is to add the sides to the front and make square, okay, hmmm, that's not as easy as it sounds, the front and sides are separate parts and that needs a butt joint along the front edge, albeit with a recessed half etch to help. The problem here is that the recess is in the front face, which means you then trim the excess on the outside faces...right next to some nice half etched rivets.
The recess should be in the cab sides, so that any excess protrudes forward past the front, and can be trimmed back flush with the cab front.....which has no raised detail.

I kind of empathise with this approach, there are two types of cab side, early and later, the rear turn in varies in height, so to save material your supplied with one front and a choice of sides. Having said that, the jig that holds the valances for fitting to the footplate is a throw away item, worse yet all the space in the middle isn't used for any other components.
If you just shifted 30% of the parts off the cab sheet onto the valance support jig, you could then offer both types of cab as one piece items with a half etch fold line for the front corner.

None the less, it is what it is and there will be designed tabs in the kit to align all these individual parts to make a nice square cab, yeah right!

The first photo


All the component parts laid out, tape holds the sides to the front, note two tabs for the front, but zero tabs for the sides, the two side slots in the footplate are for other items.

Adding the assembly to the footplate



I figured the floor would hold the sides the correct width and square



Err no! The cab floor is under size by a good 2 mm, worse yet it's too short length wise and way too narrow at the turn in, rechecking everything to make sure the turn in gap is still 49.6 mm it turns out the cab floor behind the cab is too narrow, basically it looks wrong. Additional information below.

There is no facility to aid construction in getting all sides square, just ridiculous, and it gets better, note the cab roof behind the engine, what an earth is that supposed to represent? This?


Not even close by a country mile, so not only a new cab floor at the rear end to match the turn in's but a new cab roof as well.

One could put forward that information was scarce when the kit was published (2001), here's a crop from Yeadons book on the A3, published 1990.


The cab floor and turn in is clearly illustrated as is the cab roof, if any one can find a photo of any loco of any period with a roof that matches the kit, please let me know, I've not found one yet.

So in a valiant attempt to show progress and move forward, I've actually gone backward, still, it won't be the first time, nor the last LOL.

Onward!

 

[mickoo]

Addendum,

New research shows that the cab floor under the fall plate, was constructed to the full width of the cab opening between the turn in's, as seen in the photo above.
In later years the overwhelming proof is that the corners were cut back, to give a narrower footplate under the fall plate, matching the kit. The fall plate looks to remain a constant width through out.

The pictorial evidence so far, tends toward full width pre war and cut back BR era, that's as narrow a time frame as I've accomplished so far.

Apologies to the kit proprietor and anyone else misled by my previous comments on this aspect, further research continues.