Continuous Springy Beams without tears.

The following was first published in Scalefour News 194.

Continuous Springy Beams (CSBs) have, over the last ten years or so, have proved themselves to be an elegant solution to the problem of providing a suspension system for finescale locos. However Foe many people there is a fundamental problem with them in that the placement of the anchor points that hold the spring wire is non-obvious. This has lead to the use of complicated spreadsheets determine these points, which is of putting to many people. I have long held the belief that what was needed was a simple rule of thumb method where the anchor point positions could be calculated with nothing more sophisticated than a calculator. Now after an afternoon of displacement activity, when I should have been working on something else, I have found the answer[1].

Magic Numbers

The problem that CSBs poses mathematically is that there are an infinite number of solutions. While we can discount many of these, for instance where the outer anchors lie outside the frames, there are still many other possible combinations of anchor that will give similar solutions. However there is one special case that gives a ‘magic number’ that will help with a more general solution.

CSB four coupled

If we use the case of a four coupled loco, it is obvious that if the centre anchor is placed midway between the axles and the outer anchors are arranged symmetrically the bottom of the curve that the spring takes up will occur at a point midway between the axles, i.e. at the central anchor point (Fig 1 A). Now if we move the outer anchor points, so that they stay symmetrical, there will be a point where the top points of the springs curve will be above each of the axles (Fig 1 B). From experience this point is about 0.3 of the wheelbase outside the axles. This relationship will remain true for all wheelbases that we are likely to use and it is also true however many axles there are. So 0.3 is are ‘magic number’ which we can use in future calculations.

The Plot Thickens

CSB test graphic

What I did was to take a symmetrical frame, in this case 8′ x 8′ (32 x 32mm), and built a plot using the spreadsheet to produce a range of wheelbases where the centre axle was progressively offset by 6” (2mm), while the outer anchor points were kept constant. This is shown in Fig 2. I occurred to me that, given I had not been too careful about choosing the ‘best’ outcome, that there were two relationships that were worth pursuing. One was that the lefthand inner anchor was a constant distance from the lefthand axle and that there was a relationship between the position of the righthand inner anchor and the offset of the centre axle. I went back to the spreadsheet and proved my conjectures by plugging in the calculated positions. After then testing the calculations on another wheelbase (6′ x 6′), I felt confident enough that the conjectures were correct to spent time finding all the edge cases to produce this:

CSB Matrix

This is a matrix of all the wheelbases where the rule of thumb gives an acceptable result. The shorter wheelbase is plotted on the vertically, while the longer wheelbase is plotted horizontally. A green block represents a wheelbase where the maximum and minimum weights on the axles are within about 2% of each other. The yellow blocks represent wheelbases which lie just outside the 2% limits or where they could be inside or outside the limit depending on how values are rounded. Looking at the matrix I think that most loco classes will well within the green part of the plot [2], but I would be glad to hear of any that are in the yellow blocks or even the uncoloured parts to the top right hand.

The Rule of Thumb

CSB Universal

Answers

Does this mean that I don’t have to use the spreadsheet?

Not really, since the spreadsheet will give you information on the best size of spring wire to use and the position of the centre of gravity which will help to balance the loco. Also there may well be occasions where the calculated positions of the anchors coincide with some part of the structure of the frames, brake hangers in particular, then you will have to resort to the spreadsheet. You will, however, have a set of starting points for the anchors that will take ease finding a correct solution.

[1] Or maybe just one of many answers

[2] I have not counted any early French or Belgian locos in this.

Kits Shipping

I will be shipping the following 4mm kits in the next few days

BWK1102 HR Timber Wagon
BWK1500 LNWR D.1 Single Plank Wagon
BWK1504 LNWR D.39 Small Glass Wagon

Emails were sent out last weekend to people who had ordered these for confirmation of orders and postal addresses. Enough people have not replied to make me think that there has been a problem with the email delivery. If you had ordered one of these kits and have not had and email notification could you please get in touch with me.

Carriage Kits, the final solution.

It may be obvious from earlier blog posts that there has been a certain amount of indecision about the fate of my etch coach kits. In a way that is to be expected, there are a lot of them and they represent some 20 years of work. However the world has moved on, and the market for etched kits has slowly declined. I had hoped that most of these kits could be up graded by providing new printed bogies underframes and roofs, but that course would have entailed a lot of work for, given the nature of the prototypes, not a lot of sales. Then last month Shapeways made an adjustment to their pricing structure which increased the price of the bogies and underframes made them unviable. As a result I have stopped work on any upgrades to the etched bogie coaches. I will be making all the existing bogie coach kits available as etchings. Look out for new web pages in the next few weeks with details of these etches.

The price for printed carriage roofs actually went down so I will be adding these to my Shapeways page shortly.

In the mean time I still believe there is a market for pre-grouping coaches, but with the way the hobby has been changing I think that something a lot simpler and less time consuming is call for. With this in mind I have recently completed the CADs for a new series of coaches, the first two of which should be ready by March next year. These will all resin, with only the commode handles and buffers metal.

The prototypes chosen are the GNR 45′ Howlden, brake third diagram 277 and composite diagram 129. If these sell well enough then the brake composite diagram 189 will follow.

These are the CADs for the diagram 277:

BRK0441 GNR D277 BT CAD Flat

BRK0441 GNR D277 BT-2 CAD Flat

…and the fret of small parts:

GNR 45' Underframe Fret

Wagon Update

The pattern for the following wagons have recently been sent for casting. The finished models should be ready in late January

BWK1102 HR Timber Wagon

BWK1102 HR Timber Wagon

BWK1504 LNWR D39 Small Glass Wagon

BWK1504 LNWR D39 Small Glass Wagon

BWK1500 LNWR Single Plank Wagon

BWK1500 LNWR Single Plank Wagon

Carriage Update

For those of you who worry that I’ve not been producinging anything, here is a list of recent etched coaches and npcs that have been updated and made available on the website.

BCK0260/4 NER D. 60 PBV
BCK0454/4 CLC D. 59 Cl
BCK0519/4 GCR D.1z5 milk van
BCK0532/4 GCR D. 5Q3 FK
BCK0534/4 GCR D. 5H1 BCK
BCK0580/4 CLC D. 15 T
BCK0790/4 M&GNR Large Stock Brake Van
BCK1036/4 LMS D.1879/1952/1956 HorseBox
BCK1766/4 MR D. 399 HorseBox
BCK1769/4 MR D. 529 Clayton 25′ PBV
BCK1788/4 MR D.429 Hound Van
BCK1798/4 MR D.403 CCT
BCK6820/4 B&CDR 5 Comp. Third Oldbury
BCK6821/4 B&CDR 6 Comp. Third Oldbury
BCK6822/4 B&CDR Brake Third Oldbury

Mailing lists

Due to a technical fault, by yours truly, none of the mousa mailing lists, i.e. E4um, S7list and the Mousa Models Announce List, are working. It is very unlikely that I will be able to recover the necessary information to get them running again.

So it’s an end of an era.

Older and maybe wiser…

Almost all the advances I had hoped for and wrote about in the last pasting have proved in one way or another a disappointment. Much of the reason for this lies with my growing understanding of the limitations of 3D printing and the present generation of materials used. So this summer has seen much wear on the path back to the drawing board.

Out of the fog of despondency some progress has bee made. I will be upgrading the main website in the next few weeks and add a number of coach etching that have existing production tools. To cut down confusion these will only be available with etched underframes. The long term intension is still to convert many of these to resin kits, and with so many available, and on my wish list, there is much development time to be spent refining my ideas and turning out patterns for models. As a basic principle I want to concentrate on those coaches that have a family affinity so that a single underframe moulding can be used for a number of different carriages.

The guinea-pig for this development work is the MET Dreadnought third. Some of you may have seen a body of this coach done as a one piece 3D print. However having spent a long time playing with it during the summer I reluctantly came to the conclusion that it was impossible to clean the stepping from the lower panels without compromising the beading. I have therefore decided to take a step back and make the patterns for the body by building up the thickness from brass etches. The design allows me to incorporate flanges at both the top and bottom of the sides. Etching drawings for the side and end components are finished and ready for printing.

Met Dreadnought T-etch

I’ll be posting photos and graphic of this and other major components at various stages of their development to keep you informed of the progress.

Where we are now

It seem a very long time since I last posted to the blog, so maybe it’s time to run through what I have been doing since the beginning of the year.

Locos

There are three loco kits in preparation, the S&D Scottie and two unannounced Midland Railway Johnsons. All are well advanced with most of the design work finished on the Scottie and one of the others. There is one major test still to do and if this is successful I expect the Scottie to be available by Railwells this year and one, if not two, of the MR locos by Scalefourum.

I will update the web site to reflect this when I have more information on pricing and availability.

Coaches

The supply of the nylon coach underframes has been a nightmare this year. Shapeways, who manufacture these, changed their way of checking the uploaded drawings which resulted in models that had printed in the past being rejected, and because only the first fault was reported, I soon found myself in a seeming endless cycle of error correction and rejection. In the end I gave up and withdrew all these underframes from the website. Recently I have found a local resin caster who is willing to experiment with some my ideas, so the plan is to remodels all the underframes and bogies in a resilient resin. This will improve the surface finish and maybe lower the price.

I have the first prints of the MET Dreadnoughts bodies, so it is likely that these will be used as guinea pigs for a wider range of bogies and underframes. I would expect these coaches to be available certainly by Scalefourum this year.

The long term plan is to convert those kits that have been produce in the past as etchings to either all or part resin kits. The problem with this approach is that as the patterns and moulds for the resin are relatively expensive, I will have to be careful about which coaches get this treatment. My gut feeling is to go for specialist stock, such as push & pull units and restaurant cars, but I am always open to suggestions.

In the mean time all the etchings listed in the old lists are still available at the quoted prices.

Wagons

With so many new wagons listed, I determined that what was needed was a much quicker way of generating 3D models than painstakingly drawing them in CAD. So a start was made on writing a script that could generate the required 3D information. I made a good start and managed to get the headstocks, solebars and w-irons working, but them ‘other stuff’ intervened and now I have to go back to the scripts and try and work out why it did it all that way…
However I have patterns for three NSR wagons ready to go for casting in the next couple of weeks and two more close to being finished.

Wheels

The wheels have been on a back burner for a while, mainly because I have had increasing doubts about the material that I have been using. By it’s nature it is somewhat brittle, and because it is a photopolymer it will tend to age and become more brittle over time. Ideally the wheels should be made in a tougher material than the one used at present. It it is likely that this will be possible with a resin and work will start soon to find a way of producing suitable moulds.

It has been one of my long term aims to be able to to produce ready to run locos in P4 and EM as well as OO, so being able to make prototypical wheels is a fundamental part of that ambition.

All in all the first part of 2013 has been disappointing and frustrating. Let’s hope that the change in the weather will see more of the pile of part finish projects brought to fruition.

A little closer

Prompted by a mega thread on RMweb (and an enthusiastic customer) I’ve completed the drawings for a set of loco frames that, it’s hoped, will make like much easier for those who want rarer locos but who don’t enjoy assembling etched brass kits.

The renderings represent a MR 1F 0-6-0T which is part of a batch of MR and S&D Johnson kits that will be put into production in the first half of next year. The main part of the frames is cast in brass and the keeper is sintered nylon. Etched phosphor-bronze strips are attached to the keeper to for the pickups. This particular set of frames is a test piece to test the fit of the keeper, it is intended that the frames that are included in kits will have the footplate and splashers included in the cast. With luck this set will be ready before Christmas and then work can start on the production frames.

Constructive comment welcome.

MR 1F 0-6-0T cast frames.

Components of cast frames for a MR 1F 0-6-0T

Loco Bodies

There has been a discussion of 3d printed loco bodies in this thread with interesting contributions from Atso and Atlantic 3279. Experience with the O4/5 body has shown that, not only will a raw 3d print be expensive and need a lot of finishing, but that the machines which these prints are made on are not always consistent in what they produce. I have come to the realisation to the best way to produce loco bodies is to cast them in resin from 3d printed patterns. This will give major advantages e.g.

Lower prices and/or better margins.
‘Ready to paint’ finish.

However there are some disadvantages.

Longer lead times.
Batch sizes will be larger.
The holes for fixing handrails have to be drilled by the modeller.
Some parts e.g. backheads, cab fittings and possibly smokebox fronts will have to be made separately.

In view of the need to order resin castings in batches I am going to need some, maybe 12-15, pre-orders before they are put into production.

However this is all in the future, as most of my design time of the next few months will be directed towards producing drawings of frames for the loco and loco frame kits that have already been announced, together with some others that have been promised but not announced on the website. In all I am aiming to have about a dozen done by Christmas. Renderings of these drawings and forthcoming wagon and coach kits will be posted on my Newsletter as they are finished.

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