Model wheel proportions

Model wheel proportions

Postby ConducTTor » Mon Dec 28, 2009 1:19 am

This may be a dumb question but why are model wheels out of proportion? Surely the flanges can be of a lesser diameter even if they are not exact to prototype without derailing. And the width of the wheels? Is that for better traction on locomotives?
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Re: Model wheel proportions

Postby Marquette » Mon Dec 28, 2009 2:25 am

Well, I can't answer the history portion of your question as to why they're the way they are.

What I can say is that (much) finer wheels *are* possible, witness Proto:87, and even Proto:120 is theoretically possible, though would take a big investment that, after spending considerable time investigating, I decided was not worth it (for now), when the P:87 wheels are an immense improvement over existing TT wheels, and are proven and available - NWSL has HO narrow gauge wheels that translate exactly to 33" and 36" wheels, as well as others suitable for diesel drivers. So, I figured that the P:87 wheels are an acceptable compromise for my needs.

The only thing I can guess as to why wheels are as coarse as they are is that the finer wheels require much tighter tolerances in the trackwork - meaning that readymade switches etc would cost greatly more than to the looser tolerances needed for the coarser wheels.
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Re: Model wheel proportions

Postby CSD » Mon Dec 28, 2009 2:57 am

NEM standards are much looser than NMRA standards, therefore; European manufacturers have a lot fewer restrictions in designing their track work. This leads to a wide range of tolerances from different producers. To combat this, wheel standards include the big treads and pizza cutters to overcome the problem.
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Re: Model wheel proportions

Postby scaro » Mon Dec 28, 2009 8:54 am

I measured a few wheels;I have a side interest in Aussie 5'3" broad gauge and it'd be nice to build a bit of track in TT as a test project. It would involve 13.5mm track - one of the gauges supported by the 3mm Society, so track gauges are made.

Generally, European wheels are not as fine as US ones, in either Z, N, TT or larger scales.

The TT wheels I'm most impressed by are the stub axled 7 - 7.1mm ones Elmer (Possum Valley Models) uses in his kits and they are in a lot of other trucks too. I think they are either HP, or copies of HP wheels. I suppose they represent 33' diameter wheels. They have a 1.37mm tread.

For Australian prototype, we followed the UK in using wheels slightly over 3' diameter, either 3' 0 1/4", 3' 0 5/8", 3' 1" or even 3' 2 1/4", which is a hefty 8mm in TT.

3' wheels in finescale present a problem. Tillig do a 7.5mm dia, 1.75mm tread wheel with an 18.55 axle. There's at least one another Euro manufacturer too, based on a few sets of NEM 7mm, 7.5, 7.7 and 8.0mm wheels I bought on ebay. While nice, all these Euro wheels are made of incredibly hard steel. It is not easy to turn down the tread or flange to a finer standard, quite aside from regauging them! Further, as they have axle points, I wonder how they would sit in PVM or Coastal Engineering trucks which are designed for stub axle wheels.

When I ordered my Coastal Engineering trucks, they came with an unusual plastic 7.5mm dia, 1.55mm tread wheel with a brass axle. I don't know who makes these. The wheel itself and the axle point are a one piece moulding- the axle comes out about 1mm from the face of the wheel before coning to a point, perhaps so they can be used in trucks designed for stub axles? These technically can be regauged but as the plastic wheel/axle end is all one moulding, it's not simply a case of sliding the wheel along the axle a bit - they'd need a longer brass axle and their axles, including plastic points, are already quite long, 19.8mm. HP wheels by contrast, have an 18.6mm axle.

Further, 3' wheels may not look good in the cast 'Bettendorf' style freight trucks I've seen in TT, as both the PVM and Coastal Engineering trucks are about 5' 4" wheelbase and 3' wheels in Australia were typically used in 5'9" wheelbase trucks. 5'4" seems small for a US cast freight truck but I believe the real thing varied in wheelbase from 5'6" - 5'9". (By contrast, Elmer's PVM roller bearing trucks are 5'11" wheelbase.)

I think these issues make finescale or Proto:120 TT a problem. Whatever you do entails a compromise that negates the point of going down the path in the first place.

One thing that would help TT is a one piece cast delrin truck that can become the scale standard, like MTs in N. Not to disparage any existing products, but a 'RTR' cast freight truck of 5'6" - 5'9" wheel base, able to take either 33" or 36" metal wheels is perhaps one small step that would take TT to a new level. I think one thing that derails (pun intended) small scales is not having a consistently available, reliable truck. Building wagon or coach bodies is one thing, but the tolerances that apply to running gear in a small scale are very fine, and even very good scratchbuilders will walk away if they have to assemble their own trucks, or if they can't reliably get them.

What I have not taken into account here is the trucks made by Gold Coast Railway which do appear to be one piece cast delrin. (edit:since found that they are also three part snap-together trucks.) From their site, they appear to take Tillig 7.5mm wheels. But, nice as they look, I've never been able to successfully contact the proprietor to order some.

Ben
Last edited by scaro on Mon Dec 28, 2009 1:29 pm, edited 1 time in total.
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Re: Model wheel proportions

Postby areibel » Mon Dec 28, 2009 9:27 am

Hi Ben,
The Coastal Engineering axles were part of their truck, they came with the brass axles and plastic wheels. Jim O'Brian had the mold made out of his own pocket to offer with his cars, they were the first "modern" TT trucks available.

The Gold Coast trucks are three piece similar to the CE and PVM, but they are made to snap together without glueing them. It's an interesting design, I've always wondered if a different sideframe could be made out of resin to use the existing bolster (if they could be purchased separately). Or have a more modern sideframe done as a mold, but then it's raising the cost quite a bit. Felix (Gold Coast) is notoriously hard to get in touch with, but he travels quite a lot. Yopu can sometinmes catch him through his eBay sales, look for the seller "gabbysuz". He offers his freight car kits pretty often, try sending him a message through the Ebay "ask seller" link.

And the wheels offered in the PVM trucks are HP wheels, or identical. It's amazing, the wheelsets they offered in kits 60 years ago are finer than most today. But unfortunatly a lot of that came from the slow growth in TT, in my opinion. The old tubular track wouldn't take a fine flange, just like the Lionel 3 rail stuff today. And the big flanges carried over when stick rail became common, many manufacturers still think you need a big flange for good operation. Good trackwork and properly weighted cars are the key. I wish one of the big TT makers would realize it and offer closer wheelsets- even if they were an option, like in S scale now. Any of the newer S scale locos or rolling stock can be ordered with scale or High Rail (tinplate style) wheels, with little difference in the price.
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Re: Model wheel proportions

Postby AstroGoat760 » Mon Dec 28, 2009 10:02 am

Part of the thing with the oversized flanges is to help with the sometimes poor nature of model train tracks. I have a few finescale HO locos that have a hard time with Bachmann's EZ-track. (the rails are sometimes not as long as the roadbed, and relies on railjoiners to make up for the lack of length).

Also with the profile of track such as Rokal, deep flanges were needed to hold cars onto curves.

I have never had a problem with getting in touch with Felix of Gold Coast. I think the longest that I have had to wait between sending him an e-mail and getting a reply was about a week, most e-mails were returned within a day.

I like the Goad Coast truck, but the origin listed on the case my GC boxcar came in (China) makes me prefer to use the PVM truck. I am trying to minimize the amount of stuff from China in my collection -in all scales. I know, that limits me big time....
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Re: Model wheel proportions

Postby scaro » Mon Dec 28, 2009 11:22 am

Thanks Al and AngrySailor

I did not know the GC trucks were three piece so thank you. If I get hold of Felix I'll buy a couple of pairs of the trucks to play with. No problem with China here. Empires come and empires go, which reminds me, two copies of TT Empire from Mike to read today . . . ;)

Cheers

Ben
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Re: Model wheel proportions

Postby ConducTTor » Mon Dec 28, 2009 11:55 am

Slightly off topic but

scaro wrote:two copies of TT Empire from Mike to read today . . . ;)


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Re: Model wheel proportions

Postby Marquette » Mon Dec 28, 2009 1:20 pm

scaro wrote:3' wheels in finescale present a problem.

Further, 3' wheels may not look good in the cast 'Bettendorf' style freight trucks I've seen in TT, as both the PVM and Coastal Engineering trucks are about 5' 4" wheelbase and 3' wheels in Australia were typically used in 5'9" wheelbase trucks. 5'4" seems small for a US cast freight truck but I believe the real thing varied in wheelbase from 5'6" - 5'9". (By contrast, Elmer's PVM roller bearing trucks are 5'11" wheelbase.)

I think these issues make finescale or Proto:120 TT a problem. Whatever you do entails a compromise that negates the point of going down the path in the first place.


Well, as I've mentioned before, either here or elsewhere, North West Short Line make wheels for HO narrow gauge to Proto:87 standards that translate *exactly* to 33" and 36" wheels in TT scale, so I don't see any problem for a TT:Superfine standard. I think any effort at developing such a superfine standard should be centred on using Proto:87 standards for wheels and trackwork, as it is both very fine and (relatively) widely supported, with a broad array of wheels available. In addition to the 33" and 36" wheels, they have others that work very well for TT - I re-equipped my Lionel/PVM GP9 with NWSL P:87 wheels that are only abou 1 scale inch off the diameter of the prototype. For North American modellers, 33" wheels are the bread and butter for freight cars, I would say pretty much ALL freight equipment ran on 33" wheels. So, for a finescale TT, I don't see a problem as far as wheelsets go.

For Proto:120 I don't see a problem either, as ALL wheels would have to be custom made, since nothing exists to that standard. And if they're being custom made, then the wheel diameter can be anything. So again, I don't see where the problem is.
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Re: Model wheel proportions

Postby areibel » Mon Dec 28, 2009 1:56 pm

TTQuebec wrote: For North American modellers, 33" wheels are the bread and butter for freight cars, I would say pretty much ALL freight equipment ran on 33" wheels. So, for a finescale TT, I don't see a problem as far as wheelsets go..

For older equipment this might be true, but starting in the 1950's 36" wheels became more common as truck weight capacity increased. 50 ton trucks and some 70 tonners came with 33", but later 70 ton and heavier would be bigger wheels.

TTQuebec wrote:For Proto:120 I don't see a problem either, as ALL wheels would have to be custom made, since nothing exists to that standard. And if they're being custom made, then the wheel diameter can be anything. So again, I don't see where the problem is.

Except the cost!
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