Scalefour Forum

This is my first post on this (or any) forum, so my apologies in advance if I breach protocol.

Back on page 6 of this thread there was a discussion about chairs not fitting rails. The problem has been mentioned in a couple of other threads as well, but I cannot find any posts that actually suggest a solution, other than using different products.

Over the last three years I have bought 40m of C&L's Hi-Ni rail and 4000 Exactoscale chairs to thread onto it, but now I find that the dratted things don't fit properly: the chairs' jaws are forced apart and the bases adopt a sharply concave curvature, exactly as per Howard's photos. Grrrr!

Any suggestions from someone who has surmounted this problem would be most welcome. I didn't have anything like this problem with the first eleven turnouts I built using the same components, but they were all bought eight or nine years ago.

Regards,

Bob

I've given this its own topic as it seemed out of place in 'Construction of a test track' som long after the previous discussion.
The previous mention can be found here https://www.scalefour.org/forum/viewtopic.php?f=9&t=5241&hilit=test+track&start=125#p56043
Regards

Bob,

I had a similar curvature on a fair number of my exactoscale chairs. I decided to plough ahead and see what happened. In the event I found that the Butanone softened the plastic during the bonding process such that it gripped the ply sleepers fine and took out the bow. see https://www.scalefour.org/forum/viewtopic.php?f=39&t=5148&start=650 To date ... well over 6 months I... I have had good reliable running, so the bow whilst annoying appears not to be a game changer.

Just my own experience, but no real complaints.

Have you taken the difference in the top and bottom of the rails into account? The top of bullhead rail is slightly bigger than the bottom so it would make the chairs harder to get on and they would bow slightly to get around the slightly larger section. It's sometimes hard to work out which is top and which is bottom so I find I can only do this in a good light - usually a bright 'daylight' lamp but sometimes the genuine article.

Jen

This is a problem that the new Exactoscale team should perhaps be looking into (if they're not already).

DT

I believe a particular problem has been with the C&L HiNi Rail, current stock of which has been shown to have a thicker web than previously, which has given rise to problems with the chairs.

I have recently tried many different rails in the Fast Track bases, my standard for the main running lines, and have found a variation, though not at all serious, with the tightness of fit in the chairs. I have a large stock of very old nickel silver rail which fits perfectly, you might almost say a trifle loosely, but rail purchased recently has been a tighter fit. The bases range from original old orange brown ones to more current grey ones. Again, the orange are a slightly tighter fit on the rail than the grey ones. Which says to me that rail,has got a bit thicker, and the bases have got slightly looser!

I have also some stocks of the individual chairs but I shall only be using these cosmetically snipped in half around rivets, not least after the problems outlined on the Forum with differences between inclined rails and vertical ones.

Philip

My Bullhead was fitted the right way up .. I found that depending on the spru some of the exactoscale chairs fitter easily (perhaps even a little loose) and others were quite tight and exhibited a slight bow to the base. As I said I spaced them to the sleepers, set the gauge and then flooded with Buttanone and held firmly in position for a slow count to 100. To date all seems well

This is something disussed on a thread of mine while back.

Despite appearances at the threading stage, the rail and chairs have gone down perfectly well onto plywood sleepers, with no subsequent problems - pretty much what Tim has said.

The tightness was the same for both C&L and Exactoscale S1 3-bolt chairs. It did make it harder not to bend the rail whilst threading the recalcitrant little blighters in to place. The common factor was C&L Hi-Nickel Bullhead rail (and yes, it was the right way up!).

Colin

Colin Parks wrote: The common factor was C&L Hi-Nickel Bullhead rail (and yes, it was the right way up!).

Nah ... mine was steel rail

On attachment to the rail, mine were all bowed but, blissfully unaware that this was not how they were meant to be, I stuck them with Butatone but only with a count of 12! No problems to report thus far in over 3 years. I did mix in some soldered joints too based on the Iain Rice book.

My bullhead rail BTW was nickel mostly bought back in the 70's/80's from the EMGS presumably before any tooling wore out or got changed.

Colin Parks wrote:This is something disussed on a thread of mine while back.

Despite appearances at the threading stage, the rail and chairs have gone down perfectly well onto plywood sleepers, with no subsequent problems - pretty much what Tim has said.

The tightness was the same for both C&L and Exactoscale S1 3-bolt chairs. It did make it harder not to bend* the rail whilst threading the recalcitrant little blighters in to place. The common factor was C&L Hi-Nickel Bullhead rail (and yes, it was the right way up!).

Colin

Edit : *For 'bend', read 'distort'. The rail had a tendency to bow in the vertical plane, which must have been caused action of sliding the tight-fitting chairs.

Le Corbusier wrote:

Colin Parks wrote: The common factor was C&L Hi-Nickel Bullhead rail (and yes, it was the right way up!).

Nah ... mine was steel rail

Ah yes. Bang goes that theory then!

Colin.

jschybalski wrote:It's sometimes hard to work out which is top and which is bottom so I find I can only do this in a good light - usually a bright 'daylight' lamp but sometimes the genuine article.

Hi Jen,

Try pressing the end of the rail into a bit of Blu-Tack. It is easy to see which is the rail head in the impression made.

cheers,

Martin.

Thank you everyone for your replies; the positive, practical experience reported by Tim, Colin and David is very reassuring.

A while back, Howard Bolton posted some excellent end-on images of Exactoscale chairs on Hi-Ni rail (follow the link in the second post of this thread). Out of curiosity, I printed one of these images and then drew on, to the same scale, the outline of BS95R rail taken from Table 1 of “British Railway Track”, 1956 Edition. The result is shown below.


It won’t win any prizes for technical drawing, but it contains several points of interest:
• the web of Hi-Ni rail is too thick, as expected. By a whopping 50%!
• The overall size of the head and foot is really rather good, but let down by the corner radii. There should be a much gentler radius at the top of the head, whereas the foot should be much squarer at “A” and “D”, particularly the latter. I have seen it suggested that the foot of Hi-Ni rail is too deep, but the picture shows that, if anything, it is a little under-nourished.
• The rail is a very tight fit in the chair at “A”, in contrast to the jaw above it, which does not appear to be touching the rail at all. The slot in the chair can be seen at “B” and seems to be much too shallow to fit the foot of the rail properly. (You can see this better in Howard’s original post.)
• Prototype radius at A and C is a mere 1/16”, less than a thou in 4mm scale. No wonder the rail feels like it could cut flesh when you draw your fingers along it.

The next picture shows four stubs of rail fitted with Exactoscale chairs prepared in different ways. Each rail stub was cut from the same metre-length and each chair was taken from the same location on four sprues from the same pack. A short lead was filed on the far end of each rail to ease threading.


Sample 1 shows the effect of simply threading the chair without any preparation, which is, of course, what we should be able to do. Massive distortion, bordering on fracture of the base.
For Sample 2, I gave the jaws of the chair a dozen strokes with a thin (0.25mm) flat file. Some distortion, but I don’t feel that the chair is about to snap in two. Eminently usable.
For Sample 3, I left the jaws alone and enlarged the slot (B in the first picture) upwards, using a short stub of my thin file ground to a width of 0.85mm. Same result as Sample 2.
For Sample 4 I combined the techniques of Samples 2 and 3. This was the only chair that fitted smoothly and without any distortion.

So it seems that the lack of fit is down to both the tight clearance in the chair and excessive web thickness of the rail. Dealing with either issue reduces distortion to the point where I think it is acceptable, but to avoid distortion altogether one needs to deal with both. I’ll drop an e-mail to C&L and Exactoscale to see if they have any comments or can offer any hope of a solution, but it would probably help if the Society could add its weight to the discussion. Any takers?

Regards,

Bob

Should there not be some inclination in the rail. No. 4 seems straight to my eyes

Hi Peter.

Yes, there should be 1 in 20 inclination and yes, having looked carefully at the sample, it is more vertical than it should be.

But It was never my intention open out both the jaws and the base for a production run - life is too short. My favourite at the moment is method 2, which gives the correct inclination as well as a reasonably flat base. The only shortcoming is that the chairs have to be removed from the sprue before I can wield the file, which means double handling the pesky little blighters.

Regards,
Bob

In the interest of completeness/fairness are you planning to repeat your experiments using Exactoscale/p4 track company steel rail?

Jonathan

Re. the profile of the rail head as in the above pictures:

Now, I am no engineer, but if Hi-nickel rail has a head profile which is incompatible with the profile of P4 wheels (i.e. too square-headed), would that not make a P4 profile wheel ride up on the root radius of its flange when the wheel is running against the rail? If that is so, then there could be situations when the wheel tread would not be in contact with the rail head, such as when a vehicle negotiates a curve or if the track is slightly under-gauge.

As a matter of curiosity, how does the NS rail from S4 stores stack up by comparison? (I have a batch on the way)

Cheers,

David

Colin Parks wrote:Now, I am no engineer, but if Hi-nickel rail has a head profile which is incompatible with the profile of P4 wheels (i.e. too square-headed), would that not make a P4 profile wheel ride up on the root radius of its flange when the wheel is running against the rail?

Hi Colin,

I don't think that is very likely at normal vehicle weights and speeds, unless the rail corner is extremely sharp (in which case it would be likely to wear down a fraction with use).

What it does mean however is that the effective track gauge is reduced, and the effective flange thickness is increased. It would be a good idea to set back-to-backs at the lower end of the tolerance, otherwise check rails will not be fully effective. Alternatively, it would be worthwhile filing the rail edge to a more rounded profile on wing rails and vee nose. The correct corner radius is 1/2" scale = 0.17mm (say 6 thou).

Martin.

Given the postings in various threads on this forum pointing out the deficiencies of chairs and rail available for P4, it is a wonder that any P4 modeller has ever managed to achieve decent running standards. If I was a newcomer thinking of adopting P4 and read these posts, I think that my my next step would be to join the EMGS. If there is indeed a problem with Exactoscale chairs, and if that problem does truly have an adverse effect on performance, is anything being done about it (I'm assuming that there are people on this forum who are part of the new Exactoscale team)?

DT

David Thorpe wrote:Given the postings in various threads on this forum pointing out the deficiencies of chairs and rail available for P4, it is a wonder that any P4 modeller has ever managed to achieve decent running standards. If I was a newcomer thinking of adopting P4 and read these posts, I think that my my next step would be to join the EMGS. If there is indeed a problem with Exactoscale chairs, and if that problem does truly have an adverse effect on performance, is anything being done about it (I'm assuming that there are people on this forum who are part of the new Exactoscale team)?

DT

But the problem is in the rail, not the chairs, is it not? See the post further up where it states that C&Ls own chairs have the same issue on the Hi-Ni rail.

Yes it's a poor advert for P4; but would things be any better in EM?

I presume that our society's own brand of rail doesn't cause this problem. Can anybody confirm this?

Concerning the profile of the rail at the point of contact, I think it would have two effects. First, a smaller contact-patch causes faster wear; but the wear rate will be tiny in any case. Secondly, anything that reduces friction at the contact point will encourage flange climbing. The coefficient of friction
shouldn't vary with the size of the contact patch but who really knows what goes on in there?

buckie5507 wrote:In the interest of completeness/fairness are you planning to repeat your experiments using Exactoscale/p4 track company steel rail?

'Fraid not Jonathan. Apart from any other reason, all my stock of steel and plain n/s rail is at least eight years old and may not be representative of recent production runs. Any conclusions I reach could be seriously misleading. Maybe some other members could step forward here. As for fairness, the chairs and rail which are giving me grief were supplied by the same company over a short time period, so it seems perfectly fair to expect them to be compatible, the way they used to be.

Colin Parks wrote:Re. the profile of the rail head as in the above pictures:

The subject of rail head profile was discussed at some length in On my workbench>Paul Townsend>Rail head profile - new die required. (Please can someone point me to the guidance for adding proper links to a post?) I think I'm with Colin on this one: a scale radius of 0.17mm doesn't sound like much, but it's half the flange depth, so I would expect it to have a significant effect on the quality of running.

Regards,
Bob

bobwallison wrote:Please can someone point me to the guidance for adding proper links to a post?

Regards,
Bob

I thought instructions for doing this would appear in the board's FAQ, but if they do then I can't find them. So this lashed up sequence may assist:

I was a bit surprised by Guy Rixon's comment that anything that reduces friction at the contact point will encourage flange climbing. I'm not saying this is wrong, but find it counter-intuitive. At the microscopic level, surely pressing one rough metal surface against another does nothing other than hold the two surfaces more firmly in the same position relative to each other? If so, doesn't that suggest that some force other than friction would need to be at work to cause the one surface's position to be displaced relative to the other, whether upwards (flange climbing) or otherwise?

In reply to David Thorpe's post on chair deficiencies, I have not found any such thing! It is the particular make of bullhead rail that causes the 'curved base' effect. For me, both C&L and Exactoscale chairs have proven to be reliable products and they are not, not ,not the problem!

In practice, the chairs sit flat on the sleepers once a suitable solvent has been applied (such as EMA Plastic Weld). I suspect that the solvent softens the webs that hold the two parts of the chair moulding together, allowing the chair webs to stretch enough to accomodate the wider-than-designed-for rail section.

I shall now read Paul Townsend's topic on bullhead rail head section/new die. I must have missed it in 2016. Meanwhile, new Society members/P4 modellers would not know of the topic and must be experiencing tight-chair syndrome. Many could be discouraged by the diffculty of threading chairs onto rails.