RP25/88 wheelsets for steam locos

 
  bjviper Chief Commissioner

Location: Brisvegas
G'day All,

For a while now, I've been wanting to adopt the finer profile RP25/88 wheels for my models.  Now this is easily done for rollingstock as there is a ready supply of suitable wheelsets, SEM and NWSL are two that I know of.  Diesel locos can also be converted with NWSL stub axles.

But what about steam locos?  Can it be done, and where do I find such wheelsets?  I've looked at North Yard and Markits catalogues but come up empty handed.

Cheers
Brendan

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  Geekboy Train Controller

Location: Banned
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  Speedbird Train Controller

Hahaha Geekboy!! I just read- "Try ultrascale. Although OO, they may have something close. Excellent quality."  and in my head i could hear that in the comic book guys voice! that was trippy!
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
Lobby the manufacturers for RP88 at OEM, all of them call themselves model manufacturers, time to ditch the toy wheels. I'd use 76 profile if they were easier to get.
  julesmwatson Junior Train Controller

Hi bjviper,

Good on you for wanting more accuracy.

You may consider turning them down yourself (or a mate) on a lathe.

However, this needs to be given some thought with regards to pushing the wheel centres out and reducing their width etc. It would also require the correct RP25 88 tool to be obtained to ensure the correct tire profile.

All that said, it can be done with the correct tools and knowledge.

Julian
  CraigW Assistant Commissioner

Try ultrascale. Although OO, they may have something close. Excellent quality.
"Geekboy"


No. Ultrascale wheels are manufactured to 4mm scale. They supply one profile that is OO/EM and is used for either 16.5 or 18.2mm gauge and they supply a P4 profile wheel for use with 18.83 or 21mm gauge.

Gibson also supply wheels which are close to RP25/88

Gibson wheels have a steel tyre whilst ultrascale are nickel silver

Craig W
  LaidlayM Chief Commissioner

Location: Research
Hi bjviper,

Good on you for wanting more accuracy.

You may consider turning them down yourself (or a mate) on a lathe.

However, this needs to be given some thought with regards to pushing the wheel centres out and reducing their width etc. It would also require the correct RP25 88 tool to be obtained to ensure the correct tire profile.

All that said, it can be done with the correct tools and knowledge.

Julian
"julesmwatson"


Julian,

part of the benefit of narrower wheels is the reduced depth of the entire wheel thus allowing more accurate cylinder centres.  Similarly by having narrower wheels the gauge can be widened (corrected in the case of 5' 3") without having to move the cylinders out (as is done on most SG models).

Do you have any comment on how the depth of the entire wheel can be reduced?  Is one option for BG models to leave the wheel face where it is and just fit new/machined narrower tyres that move the flange closer to the outside wheel face?

Mark
  TheBlacksmith Chief Commissioner

Location: Ankh Morpork
A steam locomotive driving wheel in RP25/88 really needs to be designed for that profile in the first place. Modifying an existing wheel that may be 110 width is asking for trouble.

A steam locomotive wheel is, in most cases, larger than the wheels used on diesels and has the extra complications of rods and cranks. The hub of the wheel is wide enough to accurately support the wheel on the axle, given the use of 1/8" or 3mm diameter axles.

But if you narrow the hub section down, the wheel become less stable and prone to wobble. Granted, you may manage to fit the wheels wobble free, but it may only take one derailment and a bump to the wheel and it will take on a wobble. Metal wheel centres and rim insulation becomes almost essential for narrower width wheels in order to maintain a stable fitting.

But as soon as you try to modify a wheel designed for one width by machining it down on a lathe, you take on a whole new set of problems. Unless you remove the tyre and machine it separately, you compromise its fit to the wheel centre. Remember, the tye was probably made as a separate item and pressed accurately onto the wheel. Machining it in place on the wheel was never intended by the manufacturer and could end up ruining the wheel as a result.

This is particularly true when the wheel centre is made of a material other than metal, plastic for example. If the wheel centre is plastic, during the machining process you run the risk that the metal tyre, a rather small mass, will overheat due to the friction of machining and melt the wheel centre.

If you remove the tyre, do you have an adequate method to hold the tyre accurately in exact alignment on your lathe? I would suggest not, as the tyre would have been produced using a totally different process in a CNC turning centre and parted off from a larger mass as the last process.

I would suggest is is not simply a matter of the correct tools and knowledge, as anyone with the requisite knowledge would advise you to design a new wheel and make it from scratch.
  Geekboy Train Controller

Location: Banned
.
  julesmwatson Junior Train Controller

Hi TheBlackSmith,

Thanks for your thoughts. They're are considered and interesting, as always.

If you read my post, you will note that I made no comment on whether machining a wheel in a lathe is easy or difficult. That distinction is best left to bjviper, as I have no idea about him or his modelling friend’s access to, or ability/confidence with a mini lathe.

I read you post with interest because you imply that machining down a RP25/110 steam locomotive wheel cannot be done. In fact, it can be done and has been done. You speak of ‘problems’ as though they are insurmountable, which is a pity, because they are not. Perhaps on man’s problems are another’s challenge?

In short; I too used to share you scepticism. But having now been involved with the process, it is my opinion that it is easy and relatively quick. Or, as my gay friend, Paul, once said to me; “Don’t knock it ‘til you’ve tried it...” Ahem...quite.

Hi Mark,

You raise a good point. Typically (always?) the tire width must be reduced from the front face (to preserve the flange), while the wheel centre must be reduced from the back face (to preserve the spoke and crank boss detail). Therefore, the wheel centre must be removed from the tire.

Remove Wheel Centre from Tire
A good modelling mate and I have achieved this by turning down a piece of brass rod, which is slightly smaller in diameter than the wheel centre. With the axel removed and tire sitting on a flat, stable edge (such as an open vice jaw or second turned piece of brass tube), the centre is then gently knocked out from the front. It should be noted that if the wheel was fixed in with glue etc, then you may be in some trouble. As TheBlackSmith has suggested, you may run the risk of damaging the wheel components (most likely the weaker wheel centre). Happily, I have not had this trouble.

Machining the Tire
The tire needs to be mounted on another tool, so as to keep it true while being machined. The first attempt was to turn down a piece of brass rod, such that one end had a recess diameter that was equal to the original wheel centre diameter. The tire was then slipped over the top and machining was commenced. While the fit was very snug, the tire began to slip while being machined. Back to the drawing board. The second, and successful option, was to turn down a mandrel to a diameter that is slightly larger than the original wheel centre. The tire is then pushed on, with the ‘spring’ of the mandrel deflecting in and then pushing out against the inside of the tire, holding it firm.

The tire was then reduced to the desired width by use of vernier callipers and a ‘stop’ on the lathe bed. The wheel profile was finished with a lathe tool, cut to the correct specifications (in this case P87). The tool was borrowed from another good modelling mate - thank God for every last one of them.

The wheel centre was pushed back on, using a small jig to ensure that the face was recessed at the correct depth. The protruding wheel centre was then cleaned up from behind using some fine emery paper that was stuck to a flat surface. With the desired wheel back-to-back spacer, the wheels were pushed on to the axel, using Loctite to secure. The resulting driver wheels are very stable – I have exerted significant force on them (far more than the force generated by the mass of the model) and they have stayed true and square.

Unfortunately, I do not have any photos of the driving wheels, as they are still at my mate’s workshop. However, I do have pictures of the finished tender and pony truck wheels.

Compare the machined pony wheels:

http://vrdays.blogspot.com/2011/08/so-long-and-thanks-for-all-fish.html

With the prototype:

http://www.victorianrailways.net/motive%20power/jsteam/jsteam.html

Please note that the wheel face-to-face effectivly stayed 'put', while the flanges were effectively spread (to answer your question).

As previously stated, I think that this is a relatively easy process. While, one could manufacture the wheels from scratch (see the most recent copy of Model Railway Journal for an example), this was not my approach. In fact, I think that the more time consuming aspect will be to modify the frames, connecting rods, and cylinders etc. Again, I see this as a challenge, and can’t wait to get back into it.

I’ve just relocated with my work to Vancouver, Canada. Consequently, all my modelling gear is floating somewhere in the Pacific Ocean. Once it arrives, I will get back into work. The intention is to have two modified VR steam locomotives completed by Christmas. One will remain here, while the other will be shipped back to Victoria and its owner. I’d suggest that these two will be the first of several. I will update my blog as I make progress.

Julian

PS: Anyone considering fooling around with steam loco kits could do worse than get their hands on a copy of Iain Rice's book 'Locomotive kit Chassis Construction in 4mm':

http://www.amazon.co.uk/Locomotive-kit-Chassis-Construction-4mm/dp/1874103100

Ignore the reference to 4mm scale -  the methods described are readily transferable.
  TheBlacksmith Chief Commissioner

Location: Ankh Morpork
No, I am not implying that machining down an RP25/110 wheel is not possible, just inadvisable.

I have a quite intimate knowledge of the chassis you are working on, and it was not designed with the modifications you are planning in mind. In the UK, many chassis kits are designed to allow construction in different gauges and to different standards, this kit was definitely not.

If I was tackling such a job, I would not be using any of the existing structure, but would design a new chassis from scratch, along with the wheels. That is the difference in our approach.
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
Nice job on the flanges, but I don't understand going to all that trouble and keeping the 110 width.
  GreatSouthern Junior Train Controller

Nice job on the flanges, but I don't understand going to all that trouble and keeping the 110 width.
"Aaron"

Reading the post from Julian Watson above, he mentions that the front face of the tyre is machined first to reduce the overall width, so there's no question of a fine flange attached to a wide tread.  So far as it goes all this discussion has piqued my interest and I had a close look at the wheels on the SEM J and the X.  The stainless steel tyres actually measure 2.5mm averall, so they are already about halfway between RP25-110 and RP25-88 in width.  It's therefore not necessary to remove a lot of metal to get down to RP25-88, which is 2.24mm wide.  One problem with the driving wheels though is that the tyres have been counterbored, so that there is a lip at the front face of the tyre that hangs over the front of the centre.  Presumably this was done to retain more material in the rim of the wheel centre moulding, while still giving the appearance of a fine rim.  The problem is that this lip is only about 0.3mm thick by the look of it, so it's not possible to remove much metal from the outside face of the tyre without it disappearing, which would look a bit odd, to say the least.  To get to RP25-88 it might be possible to machine, say, 0.08mm from the back of the flange, a wee bit from the tip of the flange and 0.18mm from the face of the tyre.  That will still leave a lip in front of the centre, but of reduced thickness.  It will also be necessary to round off the tip of the flange again, but a bit of judicious use of a small file should achieve an cceptable result.  P87 will pose more of a problem, however, because the overall width of the tyre will be only 1.7mm or so.  That means 0.8mm will need to be taken off the width of the SEM tyres.  If any flange at all is to be preserved then that lip will disappear from the front face completely.  Looks like new driving wheel tyres would need to be made from scratch for both the J and the X if you want to go the P87 route.  Fortunately the leading truck wheels and the tender wheels have plain tyres, so they can be processed as described by Julian.  Best of luck.
  julesmwatson Junior Train Controller

Hi TheBackSmith,

Fair enough. We’ll just have to agree to disagree on the subject of machining down wheels then.

We too considered fabricating our own drivers. However, the SCOA-P wheels made us reconsider. Hence, the method described above, which has resulted in sturdy wheel sets. Nonetheless, I think that hand making them (fretting blanks or machining down moulds etc) would be a fantastic way to do it. I’d be keen to see the HO scale SCOA-P wheels that you have made (if you have a photo) with this approach.

I agree that the chassis wasn’t designed to be modified to correct prototypical width or have compensation, in so much as neither ‘options’ are provided by David Foulks (with good reason). However, I still see no reason why the modifications cannot be made. Apart form the frames spacers which are too narrow, I’d be interested to know why would you also discard the chassis side frames? What would you replace them with instead, and how would they be better than those provided in the kit? I too have considered fabricating my own, but couldn’t convince myself that is necessary.  So I’d be interested to hear your thoughts.

Hi Aaron,

The face to face distance of RP25/110 wheel sets is very close (we’re talking around 0.01mm or thereabouts) to the face-to-face distance of 18.37mm gauge, P87 wheel sets. Obviously, the distance of the flanges increases significantly for the latter, and P87 has a more prototypical profile overall.

Hi GreatSouthern,

The P87 lathe tool enabled the correct tire face width to be achieved, while a small jig was used to ensure that the wheel centres is recessed, as per the prototype.

Julian
  GreatSouthern Junior Train Controller


Hi GreatSouthern,

The P87 lathe tool enabled the correct tire face width to be achieved, while a small jig was used to ensure that the wheel centres are is recessed, as per the prototype.

Julian
"julesmwatson"

Jules,
I can see that technique will work for the lead truck and the tender wheels, but given that the new P87 flange has to be contained within the profile of the existing flange, you need to machine about 0.5mm at least off the outer face of each wheel tyre.  From what I can see this means that you'll expose the counterbore in each driving wheel tyre, which will spoil the appearance of the finished wheel.  For that reason I think you'll need to make new tyres from scratch if you want P87 profile on your J driving wheels.
  julesmwatson Junior Train Controller

Hi GreatSouthern,

I had a similar discussion with David Foulks. However, I can assure you that they compare very favourably with the prototype.

I'll post some photos on my blog as soon as they arrive so that you can make up your own mind.

On another note, I had dinner last night with some fine scale modellers located here in Vancouver. The host, Rene Gourley, has had (amongst other things) P87 steam locomotive wheels printed in 3D by a small crowd in New York, called Shape Ways:

http://www.shapeways.com.

Printed steam loco wheels:

http://www.flickr.com/photos/renegourley/5820569164/in/photostream/

Printed Canadian Pacific Railway passenger coach:

http://www.flickr.com/photos/renegourley/4705641436/

Of course the only 'rub' is that one has to provide the Auto-CAD design (which is no different to etching etc).

See more information about Rene's experiences with 3D printing at:

http://www.proto87.org/d/?q=blog&page=2

Julian
  NSWGR1855 Deputy Commissioner





Hi Aaron,

The face to face distance of RP25/110 wheel sets is very close (we’re talking around 0.01mm or thereabouts) to the face-to-face distance of 18.37mm gauge, P87 wheel sets. Obviously, the distance of the flanges increases significantly for the latter, and P87 has a more prototypical profile overall.

Julian
"julesmwatson"


Julian,

My calculations indicate 6" 1/2" prototype wide wheels set for H0 RTR track using RP25-110  flanges works out that you need 2.5mm wide wheels. 0.110"= 2.794mm. About a scale inch to wide each side. Many locomotives had only  6" width tyres. I suspect you were thinking of H0 RTR fine scale wheels like RR25-88's at around 2.23mm wide.

I would argue the P87 profile is no more or less prototypical than many coarser flanges, there just closer to scale, hence the improved appearance.
  GreatSouthern Junior Train Controller





Hi Aaron,

The face to face distance of RP25/110 wheel sets is very close (we’re talking around 0.01mm or thereabouts) to the face-to-face distance of 18.37mm gauge, P87 wheel sets. Obviously, the distance of the flanges increases significantly for the latter, and P87 has a more prototypical profile overall.

Julian
"julesmwatson"


Julian,

My calculations indicate 6" 1/2" prototype wide wheels set for H0 RTR track using RP25-110  flanges works out that you need 2.5mm wide wheels. 0.110"= 2.794mm. About a scale inch to wide each side. Many locomotives had only  6" width tyres. I suspect you were thinking of H0 RTR fine scale wheels like RR25-88's at around 2.23mm wide.

I would argue the P87 profile is no more or less prototypical than many coarser flanges, there just closer to scale, hence the improved appearance.
"NSWGR1855"

Um, there seems to be some confusion here.  At least I'm confused by these posts. Confused
I've just measured a randomly selected SEM wheelset with -110 tyres and it measures 20.09mm over the faces of the wheels.  That seems reasonable with a 14.5mm back to back and tyres that are 2.79mm wide.  Meanwhile a VR general arrangement drawing for Heavy Harry quotes a back to back of 5' 0" and the tyres were 5 1/2" wide.  That produces an overall width for driving wheels of 5' 11", measured over the faces of the tyres.  That scales out to 20.71mm in HO, which is a fair bit more than the 20.09 of the standard gauge wheelset with -110 tyres.  I admit to having no experience with P87 wheels, but I am assuming that they're at least very close to dead scale if not an exact reproduction.  Seems to me a P87 wheelset made for 18.37mm gauge will be more than 0.01mm wider than a 16.5mm gauge wheelset with -110 tyres.  How does around 0.6mm wider sound?   What dimension did you arrive at with the pony truck and tender wheelsets, Julian?
  julesmwatson Junior Train Controller

Hi GreatSouthern,

You are correct – my apologies for the confusion. While I actually meant 0.1mm (typo), I would still have been wrong. The back to back (~17.4) and tyres (2*~1.63) result in a face to face of ~20.66mm

So P87 18.37mm gauge is around 0.285mm wider for each wheel than your measurement of RP25/110 (ie not very much). Nonetheless, my point remains unchanged; this face-to-face is very close to that of RP25/110 wheel sets, and is why P87 18.37mm wheel sets from NWSL slot in and run with SEM bogies.

Hi Terry,

I've never said that P87 was exactly prototypical, as it is not (unlike HOpur etc). I agree with you; it's closer to prototype than RP25/110 wheels.

Julian

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