7mm Pencarrow - Cornish BR(S)

[simond]

I'm betting a pound to a penny that Bill's frames are spot on.

That aside, the compensation question: I can see no reason not to use double beams between centre & rear axleboxes, this will certainly allow the motor to sit upright in the firebox, but I did have challenges with the crosshead clearance to the front crankpins on mine (POWSides for those not familiar with Chris' thread over there) and I had to counterbore the rods and make ultra-short, recessed crankpins nuts to get enough space. Not sure where you are regarding slide-bar centre lines, so you might have enough room to accommodate the rocking front axle, but it might be tricky. Forewarned, as they say...

Best
Simon

 

[Scale7JB]

A recessed crank pin nut might help in this situation perhaps..?

JB.

 

[Pencarrow]

So I think the next step is to screw the two frames next to each other (without spacers) and do some drilling and cutting as follows:

Two slightly inclined cuts top front to slot in the new scratch built cylinder assembly and another for the motion brackets.

Drill New fixing points for the central spacer and open up the existing ones into ovals to show the ash pan.

And the bit I'm dreading...openings for the hornblocks.

 

[Overseer]

Before you cut the openings for the hornblocks make up the coupling rods and check the centres match. There is nothing to dread about cutting the openings for the hornblocks. You have a straight top to the frames so it is easy to mark the location of the sides of the openings using a small engineer's square and scriber. The top of the opening is marked as an offset from either the top or bottom of the frame and is not critical. Choose one axle to be the datum and cut that accurately to the width required using a jewellers saw and finish with a large second cut file, then cut the other slots with a bit of extra clearance to allow some adjustment when soldering the hornblocks in place with the jig axles and coupling rods providing the spacing.

I would also add a hole for the twin beam pivots to your drilling list.

 

[Pencarrow]

I knew there was a hole missing from the list!

How much vertical travel to folk advise I place the hornblocks to allow? The plan is to do the centre axle first and work off that.

New track for me again!

 

[Scale7JB]

2-3mm on the middle axle above the outside axles would be plenty..

JB.

 

[Overseer]

I don't think there are definite standard dimensions for travel. Unless you are planning a matchstick climbing challenge, you probably only need +/- 0.5 mm but I usually set them up so the axlebox is about midway in the hornguide. This allows far more movement than needed but other factors such as brake blocks and tolerances in the coupling rods will restrict the movement.

I forgot to add, scribe the axle height centre line on the outside of both frames before cutting the slots so you have a visual guide of where the axles should be when setting up the chassis.

 

[simond]

Chris,

Not sure whose hornblocks etc you're planning to use (sorry if I missed it), but the horn guide itself should provide sufficient for you to hack the frames to fit. I have used Fourtrack ones on many of my locos as I didn't like folding & soldering sheet metal, and then trying to solder it to the frames, particularly big thick heavy frames... Seemed better to me to start with a casting. I'm sure other suppliers have similar products

www.meteormodels.com

Interestingly, the instructions talk about a "standard" cut out.

Certainly using dummy axles, located by the coupling rods, and with a suitable spring between the hornblocks, thus pressing the horn guides onto the frames in the right location, makes the soldering easier.

Hth
Simon

 

[Pencarrow]

Thanks for the comments folks, very useful.

Simon, the hornblocks I'm going to use are those on the photo below from Finney7:



Etched units but look straight forward (famous last words).

 

[Dikitriki]

Hi Chris,

I'm just wondering whether you have considered (and dismissed) springing as an alternative. I think it's easier to set up.

Same hornblocks and guides, but attach a bracket with a 12BA nut centre top of each hornguide. Using a 12BA bolt, interpose a spring between the bottom of the bracket and the top of the hornblock. If I'm doing this, I wind down the bolt until it rests on the top of the hornblocks on the first and third axles only and adjust the bolts as necessary until the chassis is dead flat and standing square. On the centre axle I allow 1mm upward movement - you really don't need any more than that.

In practice, this means that the loco is running on the first and third axles which can only drop, and the middle axle can rise and fall. If the trackwork is decent, it won't come off. It can be adjusted whenever - I often find some slight adjustment is needed when the body is attached, and you can lock the bolts in place with solder or (eg) Loctite thread lock. You can change springs to something heavier or lighter to suit the body weight, as the centre springing does not want to be too light.

Richard

 

[Dikitriki]

OK, I see you are using Finney7 hornblocks. That makes springing easy as you already have a top 'shelf' - drill a clearance hole through and solder the 12BA nut on top.

Richard

 

[SimonT]

If you prefer cast hornblocks and axleboxes, there are sprung GWR standard small engine horns and axleboxes in Laurie Griffin's range. For experience I would try the F7 ones first. If they work, job's a good'un. If not try something else.
Simon

 

[Overseer]

The Finney hornblocks work very well and are my first choice of 7mm hornblocks. I have used quite a few over the years and never had a problem with them coming apart while being soldered to the frames. When soldering them on, heat the frames with the soldering iron rather than the hornblock and it should be fine. They are probably also close to correct for the 1366 class.

You will find plenty of differences of opinion as to whether compensation or one of the forms of springing are best and lots of different methods will work, so you will probably want to experiment over time and find what suits you. My preference for small 0-6-0 locos is twin beam and rocking axle exactly as you are planning, so I recommend continuing with it. I find it easy to set up, the beam heights can be easily worked out by overlaying them on the drawing and once set up stay that way. I often end up with odd shaped beams to clear obstructions and frame cut outs so you don't have to just think in straight lines. With no fixed axles you don't get any clunking over bad track work or baseboard joints.

 

[Pencarrow]

Being a relative newcomer to kit building I did initially find the often contrasting advice from seasoned kit builders quite confusing. I have found however in just about every case there is no single best way to do things and the opinions offered are based on personal experience and preferences.

Couplings, gauge, motors, gearboxes, soldering, fluxes...the list goes on. As time goes by I'm developing my own preferences.

How to compensate a loco is certainly one of those areas!

At the start of the 1366 build on RMweb I knew nothing about compensation. There was a general agreement on the thread that compensation of some sort should give smoother running. At the time the weight of advice was behind beam compensation.

That's what the kit sort of allowed and what I went for. The Agenoria beams were poor and had a point of failure built in. These were replaced by my own stronger efforts. I'm now taking advantage of the new chassis to install proper three-point beam compensation to see how that works.

I've not tried sprung compensation yet, other than a Slaters wagon. That will be on the cards at some point, but not just yet with a loco.

Please continue with the advice - I'm still learning (and making mistakes)!

 

[Steph Dale]

Chris,

I'm not going to offer any further 'advice' - you've got loads of it and it's all good. But, I will say that you're taking the right approach in evaluating the solutions offered. It's true that there's elements of thinking about the chassis as it's built and here's a good example from frequent discussions I have with Brian Clapperton (ABC gears).

All other things being equal, Brian tends to go to ball-race bearings and wiper pick ups whereas I tend to use split axles and therefore plain bearings. Both of us have come to our separate conclusions after a lot of trial and each are a valid solution. It's the crossover conditions which are a problem, well one specifically (ball races and split axles). So you've either got to evaluate, as you are, or pick one complete solution set and try it for yourself. Blindly mixing and matching solutions can lead you to avoidable problems.

And the springing/rigid/compensated argument need not be definitive even with one person: I mix and match all three according to what's easiest or likely to be most effective!

Steph

 

[Pencarrow]

I remembered earlier that I have previously considered springing a chassis and even git as far as buying these:


I don't remember why I didn't use them. One for a later project?

 

[oldravendale]

Hi Chris.

The problem with the Slaters sprung hornblocks is that there's no adjustment built in to the design. If you don't get them set up perfectly at the first time of trying there's a good deal of fiddling involved. I've used the insulated version but substituted the peg for a screw by drilling in to the hornblock from the top and dispensing entirely with the peg. Sadly the earlier version had this system of adjustment built in to them! Despite discussions with David White Slaters remain convinced that this is the way to go.

As a result I now use the SDMP hornblocks. Some would advise that I would say that, wouldn't I, as Steph is my son and I'm also one of the partners in Finney7 from whom this hornblock can be obtained. However, whatever route you choose I believe that some form of adjustment is essential - after all, no engineer would design a component without recognising the need for tolerances, and the current Slaters offering provides none.

Brian

 

[Pencarrow]

Thanks Brian. I'm a Chartered Civil Engineer by trade so probably spend too much time when modelling thinking about how things will go together, what to make them from and what are the likely pitfalls in the options on offer.

I dropped in at a fellow modeller's house this evening on the way home with the 1366 and the mass of chassis parts (thanks Mark) and I think that I've sorted out in my head where the various parts need to go. The Finney7 hornblocks are definitely part of the mix - just got to pluck up the courage to start.

One question to all - whilst at Mark's he showed me an article by Julian Robert's in the latest Scalefour News (he does that P4 thing). This advocates not having the pivot point for the compensation beams in the center but moving it towards the outer set of wheels in a 1/3 - 2/3 split.



What do folk think - worth doing??

 

[mickoo]

Interesting, your shifting the weight balance to give the middle axle less pressure, or more correctly, more weight on the outer axles and thus hopefully better tracking capabilities.

You can do a similar sort of thing with CSB suspension, rather than have all axles set to 33% you aim for 35 - 25 - 35% or more aggressive 40 - 20 - 40% which allows the middle axle more float and also stops the nodding donkey effect.

MD

 

[Pencarrow]

Mick, I can certainly see the logic behind the idea.

I suppose it also means that you need twice as much travel on the center hornblocks.