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2 mm Finescale loco chassis

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The HR Society's list of drawings is online here but it doesn't appear to have GA drawings for the Small Ben. The drawings in Peter Tatlow's Book are good though, and detailed enough to build a loco in 2mm scale.

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I can't remember whether the 38:1 worm-wheel is beyond the production sizes at our Polish manufacturer, possibly when the next round of stock is required the shop or product officer could enquire.

I recall that a metric 38:1 set was available when we started stocking the Polish gears, but to get a reasonable price we would have had to order twenty years worth of sales (or something like that, I think Jerry was the only person buying them ;) ). You could source them direct, but as a guide I paid 13 euros for a very tiny worm gear set and a handful of 1mm bore axle muffs recently.

 

One of the other reasons for the Association biting the metric bullet has already been mentioned; the Ultrascale product are good quality, but their supply timescales were way beyond erratic.

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My favoured gearing for passenger locos is the Ultrascale 100DP 38:1 gear set, for smaller wheeled locos I like a 30:1 reduction followed by 14:28 secondary gears, also 100DP which gives 60:1 overall. I tend to order half a dozen or so at a time from Ultrascale and although they quote up to six months delivery I've never had to wait that long. It varies between a couple of weeks and about three months depending where they are in their production cycle.

 

The above is purely preference largely based on John Greenwood's methods as he taught pretty much everything I know about building locos. That said I've built numerous Kits by the likes of Chris Higgs and Bob Jones which usually have a combination of gears which end up at around the 40:1 mark and all have proved to be good, controllable runners.

 

I think we can get a bit over influenced by the tables of motor speeds that are published and complex formulas to calculate required gearing based on no load speed, wheel size etc. As Nigel said above if you can get a gear reduction somewhere between around 40:1 and 60:1, a good motor and a descent controller it will be fine.

 

Jerry

 

Jerry

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I have the Model Railway Constructor magazine for March 1980 and the HR Small Ben 4-4-0 loco is described in quite some detail, together with very good [almost] 4 mm scale drawings, and these are virtually identical to those in Peter Tatlow's excellent book.

The coupling rods are quite a prominent feature on this loco, they are slightly tapered towards the huge bosses.

I think that I will draw the loco probably 8x 2 mm scale size and instead of trying to envisage / guess the motor and gears as I've already done, I will cut out some discs to represent the various gears / motors and shuffle them around  - until they fit inside the firebox etc.

Thank you for all the information and especially your encouragement.

Keith 

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Can anyone recommend a reasonably priced simple controller suitable for my proposed non-digital 2 mm scale loco please, which will run on a single line end to end layout ? 

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Can anyone recommend a reasonably priced simple controller suitable for my proposed non-digital 2 mm scale loco please, which will run on a single line end to end layout ? 

 

Firstly I have to say I have never built a 2mm scale loco or layout, but in other scales I've always found the standard Gaugemaster (non-feedback) controllers to be excellent with all motor types.

 

Cheers, Dave.

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Thanks Dave, presumably the Gaugemaster 100 panel mounted controller would do the job ?

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Can anyone recommend a reasonably priced simple controller suitable for my proposed non-digital 2 mm scale loco please, which will run on a single line end to end layout ? 

 

The small MedVend unit which the 2mm shop sells.   Its really superb - far better than a Gaugemaster in my view - and only about £30.   

That's a battery device, takes a PP3 9v battery, and has a socket for external DC power. 

Optionally add a 12v (or if wanting really fast trains 15v)  DC power supply - less than £15 at many electrical sources if you don't have one kicking around from a long dead device. 

 

If going with Gaugemaster you must use the non-feedback types.

 

- Nigel

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Can anyone recommend a reasonably priced simple controller suitable for my proposed non-digital 2 mm scale loco please, which will run on a single line end to end layout ?

 

I went DCC a few years ago and have never regretted it. When I was analogue the Pentroller was far and away the best with a range of 2mm motors but they can now only be picked up second hand, often at silly prices. The Pictroller which was initially promoted as its successor was not happy with the small (8mm and below) coreless motors I use. As for other options I have little experience so can't really comment.

 

Jerry

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The small MedVend unit which the 2mm shop sells.   Its really superb - far better than a Gaugemaster in my view - and only about £30.   

That's a battery device, takes a PP3 9v battery, and has a socket for external DC power. 

Optionally add a 12v (or if wanting really fast trains 15v)  DC power supply - less than £15 at many electrical sources if you don't have one kicking around from a long dead device. 

 

If going with Gaugemaster you must use the non-feedback types.

 

- Nigel

Ah I'd forgotten these. I have one that lives in my tool box and is used for testing at the club and when doing demos - excellent.

 

Jerry

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Can some kind person please help me with gear ratios for this Small Ben loco ?

It has been explained to me and I've looked on the 'net, but I've tried to work them out and seem to get different answers.

 

I might be able to get a 30:1 worm and wheel but I believe that there will only be space in the firebox vicinity for a 21:1 worm and wheel, on a 6 mm x 10mm long can motor.

The can motor apparently has a speed of 30,000 rpm

 

On the same shaft as the 21 wheel [ or the 30 wheel perhaps ], there's a 14 t spur gear and this drives an 18 t spur gear on a lay shaft. The 18 t spur gear then drives a 37 t spur gear on the driving wheel axle.

I suspect that the 18 t spur gear is of no value except for spreading out the gear train and that if it was possible, it would be easier [ to construct ] to just run the 37 t gear off the 14 t spur gear.

 

If I use a lay shaft gear, what diameter steel rod should I use with a gear muff please, assuming Imperial gears ?

 

It would seem to be highly desirable to use the 30:1 worm and wheel to reduce the motor speed "at source" if at all possible and not have to reduce it through reduction gears. Back to the drawing board ! 

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From what I read it seems you understand correctly. 37/14*21/1 = 55. 55:1 sounds good. Don't worry about the speed unnecessarily.

 

 

One thing that does concern me is that the 37 tooth gear may be larger than the driving wheel. I'm not familiar with the prototype but I have made this mistake myself. The outside diameter must be smaller than the driving wheel unless you're going for a rack railway!

 

The gear muffs are designed for the axle steel that the association sells and this is 1.5mm) diameter.

Edited by richbrummitt

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That's brilliant - thank you.

 

The driving wheels are 6' 0" diameter at 9' 0" centres.

 

One thing that I find I could do with in addition to the outside diameter dimension, is the "meshing" diameter of each spur gear. I presume that I could probably work it out using the meshing centres for pairs of gears, deducting this dimension from the combined outside diameters of both gears, then dividing that by two - and deducting that from the outside diameter  There must be an easier way, or a table of these dimensions somewhere !

 

Is it possible to make a basic chassis out of say 0.010" nickel silver and then attach [ glue / solder ] an overlay of the correct frame outline on each side of say 0.005" brass, to hide the ends of the gear shafts, which would be a couple of thou shorter than the width over the basic chassis ? Just a thought !

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Diameter and meshing tables for all 2mmSA gears, both metric and imperial, along with running clearance recommendations, are on pages 26/27 of the current 2017 yearbook which has recently been sent to members.

 

The general axle diameter for loco wheels/layshafts is 1.5mm onto which all the various sized muffs are a tight push/interference fit.

 

I hope you can get something worked out to your satisfaction. Forgive me, and I might be wrong, but I would be wary of whether the small 6x10 motor has sufficient power for the job required of it. The Farish 4F is a nice looking loco with a 7x16 motor, runs nicely, but lacks the adhesive weight to pull anything much. The latter factor is probably the most important one in this scale, much more so than in others, and why the general advice is to power a well weighted body from a tender mounted motor both for traction and good electrical connection between wheels and rail.

 

Overlaying the chassis sounds good, but means the gears/layshafts can't be removed at any stage for adjustment. I often have to fiddle about with mine to get sweet running - lack of skill probably!

 

Izzy

Edited by Izzy

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I think Richard was having a bit of a mental block moment this morning, the axle steel sold by the Association shop is 1.5mm diameter.

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This is true. I've edited my previous post. 1/8" is, of course, what the outside diameter was before we went metric.

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This is true. I've edited my previous post. 1/8" is, of course, what the outside diameter was before we went metric.

Was it? That doesn't seem right. If all that changed was going to the nearest metric size and the sized we ended up with is 1.5mm, are you sure it didn't start at 1/16"? 1/8" is over 3mm and that seems like a major change.

 

Sorry for the threadjacking :nono:

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This is true. I've edited my previous post. 1/8" is, of course, what the outside diameter was before we went metric.

1/8" = 3.2mm, which was OD of imperial muffs, and thus bore of imperial spur gears.

 

I can't remember a time when axle steel wasn't nominal 1.5mm dia, and I've been a member since the early 1980's.

 

- Nigel

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Is it possible to make a basic chassis out of say 0.010" nickel silver and then attach [ glue / solder ] an overlay of the correct frame outline on each side of say 0.005" brass, to hide the ends of the gear shafts, which would be a couple of thou shorter than the width over the basic chassis ? Just a thought !

I've used this sort of arrangement, but with the overlays attached to a spacer bolted to the frame spacer at the front and with lugs on the overlays which rest on top of the frames at the back.  the brake gear is attached to these so that it is possible to remove the brake gear if there is need to service the chassis.

 

Also, I wouldn't get too hung up about gear ratios or the power of small motors.  As has already been said, adhesive weight is the biggest limiting factor in a 2MM loco.  In my experience the loco will lose traction and slip long before the motor stalls.

 

Jim 

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A week or so ago, I received a copy of the 2016 Yearbook, so I'm looking forward to receiving the 2017 version sometime. I presume that the Tables referred to are the same as those in the 2016 one.

 

It would be so useful to duffers like me to know the "meshing diameter" of individual gears, so that I can fiddle around with enlarged discs of each spur gear to see what I can get in the space available.

It would also be useful to know if it is possible to reduce the length of the worm gear - I appreciate that it is probably 9.5 mm long to allow the worm gear to clear the motor casing.

 

This is all very interesting, even having tender drive as well - the same size motor sitting above the centre axle and driving the front and rear pair of wheels !

At this stage, I'll consider anything, including electrical pick-up from the bogie wheels.

 

Thank you everyone.

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This might be useful, for metric gears anyway. Put the Module and Number of teeth in the first set of boxes and it will calculate the pitch circle diameter. You can get the meshing centres for two gears in the set of boxes at the bottom.

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A week or so ago, I received a copy of the 2016 Yearbook, so I'm looking forward to receiving the 2017 version sometime. I presume that the Tables referred to are the same as those in the 2016 one.

 

It would be so useful to duffers like me to know the "meshing diameter" of individual gears, so that I can fiddle around with enlarged discs of each spur gear to see what I can get in the space available.

It would also be useful to know if it is possible to reduce the length of the worm gear - I appreciate that it is probably 9.5 mm long to allow the worm gear to clear the motor casing.

 

 

Gear tables, won't have changed between issues.    

 

If you want a gear-centre calculator, there is one on the 2mm website (link from the "products" page), covers all the Association's spur gears  

 

Alternatively, there are two extremely thorough articles on gear theory in a backnumber of the 2mm magazines, one of the 1990's issues, articles by Denys Brownlee and Henk Oversloot in the same issue.  Those will tell you how to calculate the outside diameter and the mesh centres of any gear.  

I think we no longer have "corrected" gears in the shop; with some very small tooth counts one can "correct" a gear so it is smoother running than the theory, the result is that its diameter isn't standard, though it still engages.  Some of the smaller 100DP gears used to be this way.     

 

The standard Worm is plastic, fairly easy to cut with a sharp knife, the idea is that you cut it to the required length.  

 

Also note the recently added "information" file on the 2mm shops pages about de-burring gears before use. 

 

 

- Nigel

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Keith,

Something that may cut across the gear centring problem is a device called a "depthing tool". This is available from the Association shop No 3, reference 3-271 Gear meshing and marking tool, price £12.50. This piece of kit allows a any two gears to be set on axles and the mesh finely adjusted to run smoothly. Then the axles centres can be scribed onto the chassis frames and axle holes drilled (alternatively, centres can be marked out on paper to review design options).

Generally, to summarise:

Adhesion weight is vitally important

A total gear reduction ratio of 40:1 to 50:1 is adequate

Chassis frames should be at least 0.010 (10 thou), preferably with frame bushes

Finally, if possible, keep it simple!

Best wishes,

John

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I  would like to  thank everyone for their interest, most helpful information and encouragement, which is really appreciated and will certainly be made use of.

 

I hope that everyone including RM Web, has a peaceful and enjoyable Christmas and I wish everyone good health, happiness and especially good modelling in 2017.

 

Keith

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[snip]

One thing that does concern me is that the 37 tooth gear may be larger than the driving wheel. I'm not familiar with the prototype but I have made this mistake myself. The outside diameter must be smaller than the driving wheel unless you're going for a rack railway!

[snip]

 

'Thread drift'

 

Actually the driving gear on most types of rack locos has a smaller OD than the minimum wear diameter of the driving wheels so as to clear the rail head at points, which makes life much easier.

/Thread drift.

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