Mint gauge for sharp curves

[jc2001]

I’m seeking the opinion of fellow S7 track builders about whether the S7 mint gauge* will correctly set the gauge widening for fairly sharp curves, e.g. down to 4ft or will I have to add a bit more. If so how much? I should note this long curve is on hidden track and I built it using my own crude gauges and although my 2-6-2 chassis (body not built yet) runs over it very reliably my Heljan Warship Class 42 derails - I think because the gauge is too wide in places. It’s PCB track with only every 2nd/3rd sleepers soldered so it should be easy to resolder with a tighter gauge - hence the question: do I use the mint gauge and simply resolder the rails in a position where it fits snuggly?

*my mint gauge is a milled brass version bought from S7 stores some years back.

Thanks
John

 

[daifly]

John

Not sure if it fully answers your question but there was an article in the S7 Newsletter 136 (May 2024) by David Nicholson on the use of mint gauges. If you've mislaid your copy, it's available to download from the S7 website members area.

BTW the same issue has an article by David Rayner on printing your own mint gauges. The code is also available for download by members.

Dave

 

[jc2001]

Thanks Dave. In the article David says the gauge provides automatic gauge widening down to the recommended ruling radius of 7ft - my curve is closer to 4ft. A bit of googling (actually DuckDuckGoing these days) cites the Permanent Way Institute which says curves below 5 1/2 chains should have 3/4ins widening - i.e. 0.4375mm in 7mm scale. I think I’m going to make sure I have no more than 0.5mm widening and see how it goes.

John

 

[SimonT]

John,
Aberbeeg went down to 76" min radius and I used 0.55 gauge widening. I have two of the original sprung track gauges which can be dismantled. The Slaters S7 spacer washers make very good packers . There may be a table that says maximum gauge widening of such and such but I prefer to see what works. The Peak went around 76" at pace!
Simon

 

[jc2001]

Thanks Simon. That's very helpful.

John

 

[Paul Stokes]

technically the shorter the length of the mint gauge the tighter radius

 

[simond]

technically the shorter the length of the mint gauge the tighter radius

does that not depend on whether you're measuring or making?

If you're assembling track, the longer the gauge, the greater the gauge widening for any given radius

If you're measuring/checking existing track, the gauge will only fit if the gauge widening for the actual radius is more than the gauge requires, which means that the shorter the gauge, the less widening is required at any radius.

Simon
(who uses 0-MF / 31.5)

 

[Bob Essex]

I believe that the common triangular 3-point gauge is based upon an equilateral triangle with equal angles i.e. 45/90/45. These seem to provide a measure of gauge widening that as well as being relative to the tighness of the radius used also matches pretty well the amounts used on the full size railway. This is of course with the single leg on the inside. In experiments to see how far gauge widening can be 'pushed' in model track I have increased it until it was just shy of a wheelset dropping between the rails. It can be handy in such as hidden track etc, where the tight nature of the looks isn't an issue. The term 'Mint Gauge' to descibe the block gauge alternative is not one I have encountered before

 

[simond]

Hi Bob,

Not equilateral (= “equal sides” and all angles =60 degrees) but all the ones I have seen are isosceles (equal legs - could be 90 & two 45)

It’s possible to choose the angles to give gauge widening, though I’d have to sit down with a spreadsheet to work out the optimum

 

[Bob Essex]

Yes, thanks for the correction Simon, I often get muddled between what I mean and what gets written down!

Bob

 

[simond]

Happens to us all!

 

[Stephen Freeman]

I must be struggling to grasp something or else 2 different things are being confusingly discussed.

A mint gauge is usually rectangular with parallel slots to set the gauge etc as per the S7 article. As such it is only suitable for use on track where the radius is straight, if you try to use it on curved track you can't because there is no way it would fit on a curved rail of any sort. I suppose you could have a mint curved gauge but I have never seen such a thing nor do I expect to, it must be of little use.

On the other hand, a 3 point triangular gauge can be used to widen or narrow the gauge, the closer together the 2 pegs/slots are then the lower the widening can be, the side with the two pegs/slots needs to on the outside rail. Of course if the outer rail is very sharp, there must come a point when the widening is too much. The third peg slot/peg needs to be equidistant from the other two.

 

[Tim Humphreys ex Mudhen]

The mint gauge does not have grooves. It is machined to provide two thin strips the length of the gauge which are 33mm to their outside edges. These fit between the rails to set the gauge. It will also fit curves. The radius of the minimum curve radius will depend upon its length.

Tim

 

[daifly]

This is a S7 mint gauge:


Ignore the machining marks. As Tim says, no grooves; just the two strips, the length of the gauge, that fit between the rails.

Dave

 

[Eastsidepilot]

Yes, thanks for the correction Simon, I often get muddled between what I mean and what gets written down!

Bob

...also happens with speech Just for a laugh post #1,199

 

[daifly]

And with reference to comments above, the angles do not have to be 45/90/45.
This is a S7 3-point track gauge.

Dave

 

[Eastsidepilot]

......and although my 2-6-2 chassis (body not built yet) runs over it very reliably my Heljan Warship Class 42 derails - I think because the gauge is too wide in places. ....

Thanks
John

....or maybe the bogies don't have enough tolerance to turn on 4'-0" curves, that's very tight for mainline loco's ? . Although 4 wheeled bogies or chassis' shouldn't have any problems on tight curves it maybe that the wheelbase dimension is too long for the radius regardless of gauge widening ?
Dock tanks on tight radius curves didn't have short wheelbases for no reason.
Col.

 

[Bob Essex]

And with reference to comments above, the angles do not have to be 45/90/45.
This is a S7 3-point track gauge.
View attachment 239990
Dave

Yes, that was the point I was attempting to make, and rather badly as it turned out! That the relationship between the two outer legs determines the amount of gauge widening. This S7 mint gauge in reality seems no different in principal to a simple block gauge, just a thick rectangular block the width of the gauge and deeper than the rail section used which sits between the rails the overall length determining as with the 3-point the level of widening produced when building curved track.

Bob

 

[jc2001]

Thanks for all the feedback everyone. I’ve just spent a couple of hours adjusting the hidden PCB track with the mint gauge so it can be run smoothly along without any slop - which there was quite a lot of in places - and then ran a slow test run of the Warship. It traversed the PCB track perfectly, however it then derailed on the return trip on some pointwork in chaired track which the mint gauge showed was a tight spot. It is clearly a bit fussy about the quality of the track so another trackwork adjustment session is due. My prairie chassis (which I run weighted until the body is built) has run reliably many times over all of this track.

John

 

[Eastsidepilot]

S7 has much more exact tolerances than Oh! gauge and track building has to have more attention paid to it. Another often overlooked aspect is back to back dimensions on rolling stock wheel sets which can be critical. Often the track is seen as the culprit when it's the wheel sets to blame.

Col.