Some Model Wheel Dimensions that Affect Standards and Running

[Andy Reichert]

Since some wheel issues came up seriously off topic on the 00-P topic, I've started this topic to  allow those to be properly reviewed here instead.

 

First I want to give the back-up data I worked through back in 2011, to find out the extent of the problem of using too narrow wheels when passing over a crossing (frog) of a standard that required full width wheels.

 

 

 

This 2011 drawing shows the length of the frog gap that is wider than too narrow wheels (0.088 wide instead of 0.110 wide)  when using the NMRA HO standard of 0.050" flange ways. In this case this closely matches the DOGA 00 Interim standard, when using DOGA Fine wheels instead, so is appropriate for 00 too. In the case of using PECO's wider flange way, the length of the gap will be slightly longer, but not significantly so.  Sorry about some of the my small dimension texts.  But only the results matter.

 

These are for #6 crossing, 0.073" long

These are for #8 crossing, 0.098" long

These are for #12 crossing, 0.144" long

 

Now looking at the effect of the gap on the standard US HO wagon wheels:

 

 

Here we have the larger circles representing the common US HO scale 33" dia (9.5 mm) wagon wheels trying to drop as low as possible into the frog gaps of the three frog sizes drawn above. (from L to R #6, #8 and #12). The mid size circles are the effect for close to minimum practical size 24" dia wheels (e.g. small trams) and the tiny circles are for a imaginary tiny wheel size the same diameter as the gap, which would actually fall in. The sigle LH and the other RH dimensions iare the measure of the maximum drop of the 33" wheel.

 

The respective rounded up max drops are 0.004" for #6, 0.006" for #8 and 0.014" for #12.

 

To put the #6 drop (,0.1 mm) into perspective, 0.003" is the thickness a single sheet of copy paper .

 

The larger size and scale of a 4mm scale wagon wheel, larger coach wheel and much larger steam loco wheel do of course reduce these drops even more. And using a SWAG, probably cancel out the impact of using PECO's larger flange ways, to come up with comparable or less drop numbers.

 

Again I should point out that these show the maximum drop at the mid point of the gap. The actual rate of decent is not instantaneous, but a portion of something close to a sine half wave falling from its peak, that occurs while traversing half the gap length. Then reverses back up in a mirror image of the first half.

 

It's pretty clear that for sharp frog angles (e.g PECO, and other RTR set track points), the drop is insignificant. Most plain rail joints are about as bumpy. But for those using relatively long turnouts, a fix is appropriate.

 

Andy

[martin_wynne]

Hi Andy,

As far as I can see your diagrams make no allowance for the blunt nose on the vee, which makes a significant difference to the width of the gap in the crossing.

 

Compare the width between the wing rails at the intersection point (yellow lines), and the width immediately in front of the actual vee:

 

 

Also if the wheels are too narrow for the standard, you then have to make some allowance for the top corner radius on the rail section, and the chamfer between the face of the wheel and the tread. Providing the wheel is wide enough for the standard, these factors can be ignored.

 

I know you are desperate to prove that UK kit-pattern wheels will run over 50 thou (1.3mm) flangeway crossings without dropping in with a bump. But the fact is that they do, as anyone who has tried it knows full well.

 

regards,

 

Martin.

[Andy Reichert]

I'm not sure which UK RTR Track manufacturers actually go as far as to slope the Vee points to the half inch point?  I of course do, but then I also have many other crossing details and the "88 safe" floor under the flange to hold the maximum drop to 0.003" regardless of the crossing angle or length.

 

For anyone else, the obvious answer would seem to be why go out of your way to file off such a tiny detail and actually introduce running problems? It not as if anyone here has praised  the idea of using  far more obvious accurately scale wheels in regular 00.

 

Anyway to add this possibility consistent with the figure above, I'll use 1/2" in HO or 0.006". The length of that cut back of the vee point would then be 0.006" x the Frog number as below.

 

#6 = 0.036"

#8 = 0.048"

#12 = 0.072"

 

Adding that length to the already given numbers gives pretty much a 50% increase in the maximum over wide gap length.

 

For #6 crossing, 0.073" long increased to 0.109' long -  similar effect to a #8 left alone

For #8 crossing, 0.098" long increased to 0.146" long -  similar effect to a #12 left alone

For #12 crossing, 0.144" long increased to 0.216" long - probably around 0.033" possible drop.

 

So again for RTR #6 and below, there doesn't seem to be much to worry about. For "88 safe crossings" there is nothing to worry about in any circumstances.

[mightbe]

But there isn't rail down there, so why would I opt for a so-called "88 safe" crossing? I would much rather build my own the correct way and include the blunt nose, because keeping it messes up the entire look of the crossing, as the fine tip won't be supported and there aren't any chairs that could possibly work in that formation. It also saves an especially fine angle from being accidentally bent, either in construction, in laying, or in normal running. I can easily imagine a slight mis-track causing irreparable damage to the fine point such that the frog no longer works.

 

EDIT: Not to mention the blunt nose is slightly easier to build as you have a little bit of room for error in soldering the frog together. If it's a TINY bit too long or a slight mismatch at the fine point it can be filed to correct. 

 

Perhaps it's poor technique but I often have to file a millimeter or more off the front to get the frog to line up with the template exactly (though I suspect it's that a slight curve is accidentally introduced on one or both sides that makes the tip finer than the intended angle).

 

Quentin

[Andy Reichert]

But there isn't rail down there, so why would I opt for a so-called "88 safe" crossing? I would much rather build my own the correct way and include the blunt nose, because keeping it messes up the entire look of the crossing, as the fine tip won't be supported and there aren't any chairs that could possibly work in that formation. It also saves an especially fine angle from being accidentally bent, either in construction, in laying, or in normal running. I can easily imagine a slight mis-track causing irreparable damage to the fine point such that the frog no longer works.

 

EDIT: Not to mention the blunt nose is slightly easier to build as you have a little bit of room for error in soldering the frog together. If it's a TINY bit too long or a slight mismatch at the fine point it can be filed to correct. 

 

Perhaps it's poor technique but I often have to file a millimeter or more off the front to get the frog to line up with the template exactly (though I suspect it's that a slight curve is accidentally introduced on one or both sides that makes the tip finer than the intended angle).

 

Quentin

 

I don' want to jump to the wrong conclusion, so some more clarification of your frog/crossing building method would be helpful. But there are some clues in what you mention that suggest to me that you are not doing it the usually recommended way. (As per many posted topics - Grovenor and Hayfield, to name a couple that come to mind)

[martin_wynne]

As per many posted topics - Grovenor and Hayfield, to name a couple that come to mind

 

Andy, you are surely not suggesting that anything in this topic is relevant to UK modellers who handbuild track?

 

I can't recall Keith or John ever discussing methods to bodge Peco turnouts to stop kit wheels falling into the crossings.

 

Contributors such as Keith and John do their best to help beginners build their own track, and then you come along with this nonsense to confuse them. It reminds me of a Railway Modeller article from the 1960s, which suggested pressing wet tissue paper into the crossings and then rolling a wheel through it to make a groove.

 

Martin.

[Arthur]

.....suggest to me that you are not doing it the usually recommended way. (As per many posted topics - Grovenor and Hayfield, to name a couple that come to mind)

And the usually recommended way is?

 

I'm sure that Keith, John and the rest of us would like to know. Seriously.

[davefrk]

Andy, it might be easier for younger people to understand if your diagrams were in mm as the UK has been teaching metric for several decades now.

 

Just a thought.

 

Dave Franks.

[mightbe]

I don' want to jump to the wrong conclusion, so some more clarification of your frog/crossing building method would be helpful. But there are some clues in what you mention that suggest to me that you are not doing it the usually recommended way. (As per many posted topics - Grovenor and Hayfield, to name a couple that come to mind)

 

The only way I've done vees is the Brian Harrap way. Filing two individual pieces of rail to the same angle with the hope of achieving the indented net angle is too much work absolutely zero gain. If you had the jigs it would be no trouble, but those are impractical for my needs, expensive, and limited to society members if you can't buy at a show (alas my grievances about the various societies have no place in this thread). 

 

I believe both Grovenor and Hayfield have used the Brian Harrap method on at least an experimental basis.

 

It's interesting that you should say there is a "usually recommended way" as every person you ask does it a little differently.

 

EDIT: When I say slight curve, I mean from the filing process itself, as it's difficult to get a truly flat angle, and sometimes when filing in a vice I think that it's nearly dead flat but I remove it only to see that the vee has bowed slightly downwards and I have to turn it over and try again. Eventually I get to the necessary angle but it takes some rinse-repeat and frequent checking.

 

Quentin

[Grovenor]

 

The only way I've done vees is the Brian Harrap way. Filing two individual pieces of rail to the same angle with the hope of achieving the indented net angle is too much work absolutely zero gain.

Somewhat off topic, but the conventional way to file rail for a vee, doing each rail to the vee angle then soldering together as point and splice rails as the prototype usually did involves the minimum of filing and soldering them in a simple jig to set the angle takes care of any slight errors in filing such as the curve you mention. If you file rails at half the vee angle ot bring both rails to a common point you have to file each rail for twice the length with more room for error.

But whatever works best for you, stick with it, Brian's method is fine if you like it, but not a reason to disparage other methods that you have not tried.

Regards

Keith

[mightbe]

Off topic:

 

Well I have tried to file other ways (unsuccessfully, so I don't 'count' that really--I made something, but calling it a working vee is a step far  ), but one of them seemed to work very well. Slight errors in filing led to unsatisfactory matching at first, but once I had a pair that fit together well I attempted to solder in a simple jig (like the one on your website) but kept bumping the rails ever-so-slightly out of place in spite of the Blu Tack. After a couple rounds of soldering and unsoldering I gave up and eventually found Brian's way. 

 

The nice thing about it is that it guarantees a perfect fit and lets you get the rails into the proper shapes to make it look 99% identical to a two-piece vee (though not everyone who uses the general method tries to copy the more prototypical construction)

 

 

(Only clear picture I could find, and sadly it's from the wrong direction)

 

Quentin

[martin_wynne]

Well I have tried to file other ways (unsuccessfully,

 

Hi Quentin,

 

For bullhead rail you can do most of the filing after assembling the vee. This way you can get solid metal at the tip, and any slight mismatch and stray solder is cleaned up. The assembled vee can be held in a vice for filing, or clamped to a bit of wood for a disc sander.

 

I've posted this below a few times but here it is again.

 

The rail is shown in horizontal cross-section, yellow is the rail head and orange is the web of the rail. The crossing angle is exaggerated for clarity.

 

A is the start rail, simply bend the end at the crossing angle, or maybe slightly less.

 

B the rail is then filed back as shown, down to the rail web. This makes the splice rail. The filing is not critical.

 

The point rail at D is the same as A but of the opposite hand, notched with a file to receive the splice rail at C.

 

Print a template and glue it to a block of wood. Clamp the rails down onto it as shown. Make sure they are all the right way up. A penny washer and screw is a good clamp, or if none available you could drill a hole in an old coin. The bottom of bullhead rail is slightly rounded -- to keep the rail vertical it may help to tap in a few veneer pins each side of the rail. Pull them out first (or snip the heads off)* so that the vee can be removed.

 

Solder the rails together. If disc sanding, it's better to use high-temperature solder because the rail gets hot while sanding. If necessary stop and dip it in a jar of cold water. Using high-temp solder also reduces the risk of it coming apart later if you are using soldered track construction.

 

E is a scrap of rail or metal strip temporarily soldered across the vee rail ends to improve stability while filing or sanding. It can be left in place until you are actually building the track, and then the surplus vee rail ends are trimmed back as required.

 

V is the result after making two cuts on the sander as shown. The bulk of the metal can be quickly removed with a coarse file or metal shears before finishing on the sander.

 

The end result is an accurately aligned vee comprised of solid rail at the nose.

 

The final tasks are to blunt off the nose, to a scale width of 3/4" (bullhead) or 5/8" (flat-bottom), and to re-instate the rail-head corner radius on the filed areas. A few strokes with a fine file and a final polish with abrasive paper will do that.

It's also a good idea to take a few thou off the top of the vee nose so that it dips down slightly below the wing rails. This allows for the coning angle on the wheels as they run off the wing rail onto the nose, producing smoother running.

 

* Wear eye protection. If disc sanding the dust will be toxic from the solder, wear a mask.

 

Hope this helps.

 

regards,

 

Martin.

[Arthur]

 

I have used the method outlined by Martin in the half dozen turnouts I have, so far, built. Took a little while to get my head around 'so I bend this bit this way, this the bit the other' etc. but once clear in your mind, it's a method which works very well.

[Andy Reichert]

The only way I've done vees is the Brian Harrap way. Filing two individual pieces of rail to the same angle with the hope of achieving the indented net angle is too much work absolutely zero gain. If you had the jigs it would be no trouble, but those are impractical for my needs, expensive, and limited to society members if you can't buy at a show (alas my grievances about the various societies have no place in this thread). 

 

I believe both Grovenor and Hayfield have used the Brian Harrap method on at least an experimental basis.

 

It's interesting that you should say there is a "usually recommended way" as every person you ask does it a little differently.

 

EDIT: When I say slight curve, I mean from the filing process itself, as it's difficult to get a truly flat angle, and sometimes when filing in a vice I think that it's nearly dead flat but I remove it only to see that the vee has bowed slightly downwards and I have to turn it over and try again. Eventually I get to the necessary angle but it takes some rinse-repeat and frequent checking.

 

Quentin

 

Thanks for the reply. I wanted to wait for that before adding anything else.

 

My only worry in making my earlier comment was your mention of a weak, unsupported from underneath, sharp vee point. To me that sounded possibly like the "Duck Beak" shape that will occur if you file rail to a point without bending it,  to make sure the rail web runs all the way to the end of the point as well.

 

Just about every experienced write up on crossing building I have seen here and elsewhere relies on bending the rail end to bring the web into the centre of the vee end to avoid any "duck beaks", and that's echoed by the other postings that answered you here earlier. And that's all I wanted to ask about.

 

The prototype has a far worse weak vee point problem, due to the massive weights of the various vehicles. So of course they use the bent end to have a centered web form of construction too. Or solid castings in special circumstances.

 

Andy

[Andy Reichert]

SNIP

 

I know you are desperate to prove that UK kit-pattern wheels will run over 50 thou (1.3mm) flangeway crossings without dropping in with a bump. But the fact is that they do, as anyone who has tried it knows full well.

 

regards,

 

Martin.

 

Just to keep the record from being altered and misrepresented .

 

Anyone who has read any or all of my past posts, here, on other lists and in many letters to the NMRA and magazines over the past 15 years should be aware that I have written continuously informing all that code 88 wheels have no place in the NMRA HO standards. Nor do I ever recommend or suggest they form a sound engineering and proper running solution for 0.050" flangeways, without some other form of wheel support.

 

Andy

[Andy Reichert]

Andy, it might be easier for younger people to understand if your diagrams were in mm as the UK has been teaching metric for several decades now.

 

Just a thought.

 

Dave Franks.

 

I'll try and use/add double dimensions where I can. The problem with the "Code" sizesfor both rail and wheels, is that they are based on old Imperial 0.001" units.

[davefrk]

I'll try and use/add double dimensions where I can. The problem with the "Code" sizesfor both rail and wheels, is that they are based on old Imperial 0.001" units.

 

That's okay Andy, rail is still sold in 'code' sizes in the UK  so everyone will understand that bit  but, AFAIK all wheel spec is quoted in metric, i.e. gauge, B2B, flangeways etc. 

 

Hope that helps,

 

Dave Franks.