Advice needed

[Rdawson28]

Hello there. As a newbie plunging into building my (sort-of) first decent loco kit, a lovely Finney Dean Goods, I’m about to set up the horn blocks but am a bit confused. As I understand it, the purpose of using the coupling rods is to align the spacing between axles, but it seems to me that the Finney design, which uses the etched 6mm slot in the frame as the guide to stop the axle boxes rotating, dictates the spacing. I don’t for a moment doubt the wisdom of the kit designer which is why I’m wondering whether I’ve missed something obvious….(I’m probably being over cautious and am going to be very embarrassed by the obviousness of the answer, but nonetheless await with poised soldering iron…)

[Will L]

Hello there. As a newbie plunging into building my (sort-of) first decent loco kit, a lovely Finney Dean Goods, I’m about to set up the horn blocks but am a bit confused. As I understand it, the purpose of using the coupling rods is to align the spacing between axles, but it seems to me that the Finney design, which uses the etched 6mm slot in the frame as the guide to stop the axle boxes rotating, dictates the spacing. I don’t for a moment doubt the wisdom of the kit designer which is why I’m wondering whether I’ve missed something obvious….(I’m probably being over cautious and am going to be very embarrassed by the obviousness of the answer, but nonetheless await with poised soldering iron…)

When building chassis with suspension using hornblocks there are two potential approaches.

There is the designed to fit approach. The kit is to designed so that the hornguides are integral with the frames and the coupling rods are manufactured to be at Identical centres. This is perfectly possible with an etched kit and I think this is what Mr Finney was up to.

The there is the make to fit approach, this uses separate hornguides attached the chassis frames, using the coupling rods (or a chassis jig set up to match them exactly) to set the spacing between the hornguides. This ensures any small errors in the chassis axle spacing, the coupling rod centres and the concentricity of the axle blocks are compensated for and it all goes together so it works. Scratch builders, those building kits not "designed to fit" as above, or and those intent on modify chassis to go together other then originally intended, will go this way

The naturally suspicious will have noticed that the "design it fit" approach didn't mention anything about compensating for errors in the concetricity of the axle block and you are dependant on the axle blocks being manufactured accurately with the hole in the same place, ideally dead centre. It is worth checking the axle blocks are uniform before assembly. Mount then on a axle and check the all line up perfectly. If the hole isn't actually perfectly central, but they are are all uniform, you are still ok so long as you insure each axle bock is used with the error going the same way.

[Dave Holt]

Looking at the Finney instructions on the Brassmasters web site (I've never built a Finney loco), it would appear that the accurate guidance of the axleboxes is achieved between the machined groove in the axleboxes and the separate horn guides (part 8). I suspect that the slots in the frames are slightly wider than the square parts of the axleboxes, thus the instruction to fit the rear hornguides to the frame plates first - aligned with half etched lines. It is then necessary to use the rods on extended jig axles to accurately space the remaining four horn guides. This is a standard practice, as outlined by Will.
I'm not sure about Finney kits, but earlier etched chassis were made using hand drawn artwork and there was no guarantee that the frame horn slots and rods would have the exact same spacing - hence the procedure given in the instructions. With the advent of CAD artwork, such discrepancies should be eliminated and it might be possible to just assemble the parts as supplied.
Dave.

[Daddyman]

The naturally suspicious will have noticed that the "design it fit" approach didn't mention anything about compensating for errors in the concetricity of the axle block.

Actually, the instructions do mention this, Will:

Remove all the axle holes as described above. Carefully widen the slot in the rear hornblocks (part 8) until the Flexichas bearings are a good fit. I find a significant variation in the bearings and once I have fitted a hornblock to a bearing I mark the bearing and hornblock so that they can be later assembled together. A good fit between hornblock and bearing is essential if the chassis is to run well.

This is the Achilles' heal of the design. If the variation in concentricity is all in the same direction as Will says, then there is no problem. However, the fact that the instruction-writer says "significant" suggests that the hornblocks are all differently concentric, which would make the task of getting a decent running chassis at best miserable, possibly worse, for a first-time builder. Would it be possible to substitute High Level hornblocks, with their more reliable concentricity?

[petermeyer]

This is the Achilles' heal of the design. If the variation in concentricity is all in the same direction as Will says, then there is no problem. However, the fact that the instruction-writer says "significant" suggests that the hornblocks are all differently concentric, which would make the task of getting a decent running chassis at best miserable, possibly worse, for a first-time builder. Would it be possible to substitute High Level hornblocks, with their more reliable concentricity?

I have built a number of Finney kits and have 2 on the work bench now. The hornblocks are square and are designed to fit into the 6mm slots in the chassis which prevents them from rotating. They are retained by flat etches without wings that are supplied on the fret. There is potential for variation in these hornblocks which it is why it is wise to keep them matched with the relevant retaining etch. These should be eased to get a good sliding fit and always put them back in the same way round. I mark the bottom with colour coded pens to do this. Using the rods to set up the chassis is added insurance to ensure alignment as minor discrepancies can cause running problems.

NB: It is not possible to substitute High Level hornblocks because the Finney twin compensation beams are designed to sit atop the bearings, which have to have a flat filed on top to accommodate this. Some of the illustrations that describe how to do this are not always uploaded on the Brassmasters site but are included in the printed instructions with the kits. In addition, the High Level hornblocks, being deeper when assembled, would protrude too far into the chassis for this still to work. The Finney instructions have the beams set around 1mm off the inner face of the chassis frame. It is also probable that the wings on the High Level system would also foul the compensation beams unless you are experienced enough to work around this.

[Jeremy Suter]

The naturally suspicious will have noticed that the "design it fit" approach didn't mention anything about compensating for errors in the concentricity of the axle block and you are dependant on the axle blocks being manufactured accurately with the hole in the same place, ideally dead centre. It is worth checking the axle blocks are uniform before assembly. Mount then on a axle and check the all line up perfectly. If the hole isn't actually perfectly central, but they are are all uniform, you are still ok so long as you insure each axle bock is used with the error going the same way.

In 35 years of building compensated chassis and several hundred done in all scales I have never come across an axle block that is not concentric. I have made a few dodgy ones my self though. When errors occur its by badly made or fitted horn guides or the chassis is not square or too much slop in the axle block to the guide. that said I'm sure others must have

So to the Finney Dean goods which is a very well designed kit. Make sure the chassis has been put together squarely. The horn guide slots are removed correctly. ( Don't go past the half etched line even if the horn block is stiff at this point it can be fettled with a needle file later. ) When the chassis is together slot the horn guides in the slots and offer up an axle or reamer to check its square. The coupling rods in the Finney kit will match the chassis if the above is all done correctly. If you need to check the axle holes with the coupling rods and you haven't got a chassis jig you can use some 1/8 inch tube with a romford crankpins screwed in the end and then slot the coupling rods on to check.

[Tim V]

You may like to refer to the article on John Brighton's method of over coming this problem, in S4N 142 (May 2005 - in the News archive).

I have used this method many times since - it works.

[davebradwell]

This business of concentricity is just a matter of degree. The square bar is held in a collet and machined so they're as good as the collet - I would expect from measuring axleboxes that this is usually between 2 and 6 tenths of a thou' off centre and, crucially, total difference between one side and the other is twice that. Negligible to lot of people and most won't be able to measure it reliably but it's still better if all the errors go the same way than the opposite.

I will emphasise the importance of numbering the axleboxes and hornguides and marking top or bottom of axleboxes.

Build it as the kit intends, you'll learn a lot and decide how you're going to build your next chassis. Remember that after all this effort it should run better than an rtr.

DaveB

[Will L]

... I’m about to set up the horn blocks but am a bit confused...

When building chassis with suspension using hornblocks there are two potential approaches.

There is the designed to fit approach...
The there is the make to fit approach...

My first reply was from a purely theoretical position and I hadn't read the Finny Instruction. Perhaps I should have but it was getting late. I've made up for it since.

Finny kits do have a good reputation for accuracy, but this one still clearly fits under the "make to fit" heading and jigs the axel spacing from the coupling rods.

The technology behind our etched kits is good enough these days to allow assembly on the basis that you can trust that the axles spacing and rod centres do match, I've done a Bill Bedford chassis which archives this quite nicely, but if you are going to have to fettle the slot the axle block runs in and then fit this part to the frame side, there is still opportunity for sufficient errors to creep in to threaten good running, so the "make to fit" approach it is.

Having gone that far, the concentricity of the axle block isn't that key an issue as the jigged assembly should take care of it, but you must ensure that you know the assigned location and orientation of each block. They will not be interchangeable.

[Rdawson28]

Thanks for all the replies, they’ve been really helpful. I’ve decided to plough on, follow the instructions and trust the designer. Hornguides are now fitted (that was a faff!) and all appears to be ok, though it’s tricky to tell as I’m using the LRM tapered jigs and it feels there is the opportunity for discrepancies, but I hope I’m just being paranoid. John Brighton’s article does seem very pertinent. Anyhow, I’ll make up the Ultrascale wheels on their axles and see how it feels before doing anything more to the chassis, so there’s still the opportunity to adjust. I also have the challenge of the inside valve gear ahead, so wish me luck!

[davebradwell]

It's good to be paranoid with chassis. A sound approach is to do your best with the jigs and if there's a problem with the result then turn to John Brighton.

DaveB

[Tim V]

John Brighton (and sub contractors) was building locos professionally at the time, if it's good enough for a professional it's good enough for the rest of us.

A professional wants to build quickly, once and right. They can't afford to spend time fettling components. They don't want to see it come back for warranty repairs.

[zebedeesknees]

if it's good enough for a professional it's good enough for the rest of us.

Hmmmm, perhaps I am the only one who feels that this attitude is totally at odds with the objectives of The Society and 'getting it ALL right'?

Ted.

[Horsetan]

....NB: It is not possible to substitute High Level hornblocks because the Finney twin compensation beams are designed to sit atop the bearings....

I'd suggest it is possible to use HL hornblocks and bearings if you're getting rid of the twin beams and substituting CSB suspension. However, you will need to be just as careful in setting up because the HL hornblocks have a narrower width (5mm, I think) than the Finney standard. Also, spacers may need modifying to allow the CSB wires to pass through unhindered.

if it's good enough for a professional it's good enough for the rest of us.

Hmmmm, perhaps I am the only one who feels that this attitude is totally at odds with the objectives of The Society and 'getting it ALL right'?

That really depends on whether you want to use EMF profile wheels on P4 track.....

[Tim V]

That really depends on whether you want to use EMF profile wheels on P4 track.....

Where did I say that?

Both of you have ignored my second paragraph
"A professional wants to build quickly, once and right. They can't afford to spend time fettling components. They don't want to see it come back for warranty repairs".

It is that attitude that gets good running first time.

[jon price]

"A professional wants to build quickly, once and right. They can't afford to spend time fettling components. They don't want to see it come back for warranty repairs".

It is that attitude that gets good running first time.

Agree entirely. In my (olden) archaeology days I set up a grid on a particular site in a couple of minutes using string and a 3:4:5 triangle. Then some bright spark claimed it wasn't likely to be very accurate. they then spent all day setting up a theodelite and relaying the grid. They ended up with a grid exactly the same as mine, except it was a few inches to the side and therefore not aligned on the existing older grid point which meant everything had to be constantly corrected to match the existing plans.

[Will L]

I wonder how many of us have taken the time to (re)read the Snooze 42 article about John B's methods. Despite the way the early section reads on the accuracy of the chassis cuts out this is a classic "make to fit" method. In the hands of a fine craftsman like John, who knows exactly what he's doing, it will work reliably (most of the time) but may give the less skilled the heebie-jeebies. Overall it a lesson in understand where all the variables are and how best to deal with them. In practice this method is robust enough to producing a fully satisfactory running chassis even if the axles are not entirely parallel. I have the proof to hand. The prohibition on not driving the outermost axle is, I thing, a big bow in the direction of the needs of the professional builder not to see his creations back for further work.

At one time, when enforced retirement loomed, I did think about building for others but I am far to slow and pernickety to make that a practical proposition. I did wonder how much the returns rate could be influenced by the fact that a for a fare percentage of the time you may be building shelf ware. I can see why a professional would want to favour rigid chassis.

[Will L]

... In my (olden) archaeology days I set up a grid on a particular site in a couple of minutes using string and a 3:4:5 triangle. Then some bright spark claimed it wasn't likely to be very accurate. ...

Interesting, before I finally got a real job in the computer industry, I spent the long summer holidays being paid for digging round assorted pottery kilns, castles, priories and other things of a medieval nature. In a similar vein to the above, your response should have been, I think, only if your competent with that fancy equipment and don't forget the Egyptians got on very well with bits of string.

I did wonder about doing archaeology professionally too, but being a dyslexic doing a degree is computer science I wasn't sure that being competent with a trowel was going to be sufficient qualification to get me a permanent job.

[Philip Hall]

I agree entirely with Tim. That is my own attitude, although I do often spend more time than I would like getting the running that satisfies me. Because I'm fussy I like to think my customers appreciate the sentiment. It is true that I would rather not have models coming back to me, and I guess I must have succeeded because it is rare that they do. What am I saying?!!

I would also say that the choice of gauge or standards, or reliability and quality of work, has nothing whatever to do with 'getting it all right', which I seem to remember was a slogan from earlier Scalefour publications. An engine I have built or converted has to work, smoothly, reliably and be relatively robust. I have no idea of the environment in which models will run or the care that will be given to them. And that quality of running can be given to a 00 chassis built with Markits wheels and no suspension just as much as it can be given to a P4 chassis with every possible set of bells and whistles. It is, however, commensurately more difficult and time consuming to do the latter.

Philip