3' Narrow Gauge on 3-1/2" gauge?

[Curtis_F]

Gentlemen,

As I'm progressing on the 3/4" consolidation, and with the quickly approaching "Small Scales Meet" at Golden Gate Live Steamers next month, I keep thinking about possible future projects for 3-1/2" gauge.

It’s no secret that there’s a special place in my heart for 3’ Narrow Gauge equipment.

Below is a link to some thoughts about modeling 3’ gauge on 3-½” gauge I've committed to “paper” and am interested in hearing your thoughts on the subject.

Any and all criticism is welcome.


Thank you for your time,

Curtis F.


*EDIT*

Revised the wheel standards based on data from the Baldwin Locomotive Works standard practices books.

Proposed Standards for 30mm Scale

18 July 2010

*EDIT*

[Harlock]

Definitely a good way to go regarding the back to back dimension. You'll just have to get past the unwillingness to go from English to Metric, and not having a wide availability of metric bar stock which might lead to more machining in some parts and pieces. For those with DROs, it's a bit easier because it's just a button push when machining. For those who live where metric is the standard, well, fabulous for you!

I haven't seen too many narrow gauge engines in 3.5" gauge - that would be a fun and enjoyable scale / gauge combination. You'd get as much power as 1" scale engines in some cases, and still have the small track / turning radius, which is easier for small backyards.

Also, you have a typo on page 3, "Mush"...

--Mike

[alanstepney]

Over this side of the "pond" there are a few narrow gauge locos on 3.5" tracks.

Makes for a BIG engine and on that gauge, they look bigger than they are.

[gcarsen]

Curtis,
Thank you very much for this proposal and idea! you have put plenty of time and thought into it. i love the scale equivilants to all the stock and fastener sizes. very well done!
Grant

[SteveM]

My dad's tank engine is 1" scale, 3.5" gauge.

It was a freelance design modeled after British tank engines used on narrow gauge railways in India. The engine was named the "Major Grey" after dad's favorite brand of chutney.

Steve

[Benjamin Maggi]

Another typo in the first sentence of page three... "molders gauge."

If a 30mm engine went off a high-line track, it could be a much more disasterous wreck. If it is a ground level track, then it wouldn't be much of a problem.

[Pennsy fan]

Hey C man,
I am waiting, wheressss the prints, choo choo.
d.

[Curtis_F]

OK, the PDF file has been updated to correct the typos and to fix some bad math.

Thank you all for the feed-back!

-----------------------------------

Mike,

I know what you mean, but the main principle for the proposed standard is to round the materials to the nearest Metric or Imperial material size to reduce the amount of needed machining and design compromise.

Getting Metric material here in the states can be a bit more of a buggar, but in this age of the internet it's a lot easier than it was when the IBLS was formed.

If I get around to designing some 30mm equipment it'll probably be a mix of Metric and Imperial material. The drawings would also have both Metric and Imperial dimensions.

-----------------------------------

Grant,

Apparently I didn't spend enough time thinking about it. I re-read by own document this evening and found I had put some wrong numbers into the Wheel Standards section.

-----------------------------------

Benjamin,

Larger scale models of smaller engines on the same track.

I would think that a 3/4" scale USRA 2-8-2 would impact the ground about the same as a 30mm K-36, and cause the same amount of tears/cursing.

Like Alan said, "...they look bigger than they are."


-----------------------------------

David L.,

I spent part of evening tweaking the core design for your project. :p

[sncf141r]

Curtis;

Go for it. A friend here has a "Conway" narrow gauge "slate" locomotive for 3-1/2" gauge; have seen a Don Young Lucky7 (2 ft gauge) on 3-1/2".

Don't worry about the metric; I work in metric, I picked up that good habit when living in Europe; I don't seem to have much of a problem machining in metric now that I'm back here in Canada, even though as stated, much of the materials we get are still in that old-school-hard-to-understand inch measurements. (ok, ok, inches are fine!)

JohnS.

[10 Wheeler Rob]

I am curious as to why the additional taper SG is on the outside of the tire? The IBLS Standard dose not have it.

Also why would you not keep all the same demensions as the IBLS for 3.5 gage.

Also keep in mind tire widths in the IBLS are minimum, and the wider the better form an operating point of view. Specially if running on older club tracks with wear and tear. If you want a nice display engine, then keep them thin, but if you want run it and let the trottle out, then add some width.

[Curtis_F]

I am curious as to why the additional taper SG is on the outside of the tire? The IBLS Standard dose not have it.

One thing to keep in mind is that the IBLS Wheel Standards were designed to be made in on a simple manual lathe. Fullsize wheels actually don't have a 10deg taper, they're a series of reverse and compounding curves. Part of the fullsize profile is a second taper extending approximately 1-1/4" in from the outside of the tread.

This second taper helps guide the wheels over switches and crossovers where rails are joined together at angles. It also comes into play on tracks that are wider than gauge. On normal track the second taper never touches the rail.

It was probably left out of the IBLS specs as it requires one more machining operation on the wheels.

Also why would you not keep all the same demensions as the IBLS for 3.5 gage.

To use the full 3/4" scale wheel profile would give the engines thinner wheels than scale, and even if the wheels were made to scale width they would be pushed apart. That creates a series of compromises in the design process that one must be careful of.

Like on 1-1/2" scale on 7-1/2" gauge. They're models of 4' 8-1/2" gauge equipment on 5' gauge track. That's almost 1/2" that needs to be accounted for in the width of the frame, width over the wheels, the width between the cylinder & valve chamber center lines, the valve gear needs to double checked for interferences, distance between the sidereal and crosshead, etc.

Scaling an engine based on the back-to-back minimizes the need for special design work as the inside and outside dimensions of the wheels is to the same scale as the rest of the equipment.

Using the 1" scale flanges gives an almost scale Back-to-Back measurement for 3' gauge in 30mm scale.

The taller flanges do also allow for a little bit more safety,

And the under-scale flanges just looks funny too.

Also keep in mind tire widths in the IBLS are minimum, and the wider the better form an operating point of view. Specially if running on older club tracks with wear and tear. If you want a nice display engine, then keep them thin, but if you want run it and let the trottle out, then add some width.

Good point!


Cheers,

Curtis F.