Model Rail - Gem Kit

Nice set of pictures on chassis assembly in this months model rail. But if anyone following that for their first attempt should be warned that theres
not enough emphasis on getting the frames square. Without them correct then its difficult if not impossible to make a good runner. Simple chassis jig like that supplied by comet does help.
Cheers, Simon
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: Nice set of pictures on chassis assembly in this months model rail. But if : anyone following that for their first attempt should be warned that theres : not enough emphasis on getting the frames square. Without them correct then : its difficult if not impossible to make a good runner. Simple chassis jig : like that supplied by comet does help. :
Very true, the most important aspect is to get all the main axle holes in line, this is something that I'm not sure if the Comet jig (LS16 or LS17) does this correctly, the best and easiest method is to use special axle jigs [1] and the locos coupling rods. Alan Gibson (Workshop) used to sell such a set of gigs but I can't see them listed now...
The most important aspect to any chassis is that the axles are in line and the same distance apart, an out of line buffer beam will look crap but it will not prevent the loco running, axles that don't match the coupling rods (and each set of rods match the other side) will mean that there is no way that the chassis will run correctly. Whilst the Comet jig seems to make a good job of aligning the frames and axle boxes it fails to make sure that the assembly matches the coupling rods IYSWIM.
[1] Hope the ASCII art displays OK (fixed font?)
|X|| ||X| ||X| = frames/bearings ] ------------------- [ === FAILS AXLE === < crank-pin dia. ] ------------------- [ |X|| ||X| [ = actual coupling rods
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Suspect this is out of my experience, cos if the axles are correctly aligned at right angles to the frames and correctly positioned am not sure how coupling rods can be incorrect. Is cos am assuming all from same kit that is of siutable quality.
With my latest attempt at GEM chassis had only to open out holes in coupling rods sufficiently to fit comfortably over the crankpins and that was it. CHassis with wheels and coupling rods ran as freely and smoothly as a good RTR wagon.
Cheers, Simon
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: <big snip> : > : Suspect this is out of my experience, cos if the axles are correctly aligned : at right angles to the frames and correctly positioned am not sure how : coupling rods can be incorrect. : Is cos am assuming all from same kit that is of siutable quality.
You're assuming that all chassies match the coupling rod...
I'm not saying that the Comet (or any other) system won't/can't work, just that dummy axles that use the coupling rods to align the driving wheel axles/bearings is fool proof - the only way for it to fail is if each set of coupling rods doesn't match it's opposite, if that is the case then *any* alignment jig/method will fail at the driving wheel quartering stage!
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Seems to me youre looking for a way to correct an error in one component by introducing an error in another. If rods that bad then as Iain Rice would say - send em back. However do admit to inserting crankpins not quite verticle into Alan Gibson wheels to give problem as you describe - if anyone has a foolproof method of doing these would be very interested as I have a second hand kit that has these wheels. I prefer Romfords as they cannot be slightly out of quartering and the crankpins are more likely to be correctly inserted.
Cheers, Simon
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: <snip> : > : Seems to me youre looking for a way to correct an error in one component by : introducing an error in another. If rods that bad then as Iain Rice would : say - send em back.
Whhoooossssshhhhh.... :~((
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Must admit was afraid that would be the case. But how about giving a poor misguided beginner a bit of assistence in understanding so progress can continue. One day I might reach the exalted levels....
CHeers, Simon
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How do you ensure the frames themselves are accurately aligned? To what degree of accuracy?
How do you ensure the bearings are aligned and positioned correctly when you solder them into the chassis?
Some form of alignment jig is essential if you are fitting sliding hornblocks that require you to cut slots in the chassis.
MBQ
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How do you ensure the frames themselves are accurately aligned? To what degree of accuracy?
How do you ensure the bearings are aligned and positioned correctly when you solder them into the chassis?
Some form of alignment jig is essential if you are fitting sliding hornblocks that require you to cut slots in the chassis.
MBQ
Suspect you are over my knowledge/experience too. Havent reached the level of sliding hornblocks.
Cheers, Simon
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<snip> : : > Some form of alignment jig is essential if you are : > fitting sliding hornblocks that require you to cut slots : > in the chassis. : : : Suspect you are over my knowledge/experience too. : Havent reached the level of sliding hornblocks. :
But it's as relevant to 1/8" 'top-hat' bearings and all types of chassis (even the old style castings found with some kits) as it is to sliding horns or the Flexichas system, what this way of aligning the axles does is ensure that they ARE in alignment - by using the one item that can't easily be adjusted, even a few thousandths of an inch discrepancy can cause binding of the coupling rods or more slop that the you know what up a shirt sleeve, but has to be correct - it's all to easy to build a chassis that requires so much metal to be reamed from the coupling rods that not only are they grossly sloppy on the crank pins but their structural integrity is compromised. As I pointed out before, the most critical stage in any build is making sure that both sets of coupling rods have *exactly* the same pin centres [1] and that the main axle bearings match those centres, the rest of the chassis can be quite some way out of true and the loco will still run down the track looking like a mechanical master rather than a duck...
It's actually easier to adjust the fit of the chassis bearings before they are fixed (soldered) to the chassis frames/block that try to adjust the 'fit' of the coupling rods at the wheel quartering stage - many 'wheel quarting problems' are nothing what so ever to do with the wheels but the fact that the axle centres do not match the coupling rod centres!
[1] o=====o-------o CORRECT o=====o-------o
Compared to;
o=====O-------0 WRONG! O=====o-------o
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OK, understand better. When reach a kit that requires such considerations then will re-read the relevant sections of those wonderful books by Iain Rice, consider the purchase of a 200 jig and muddle on. But thus far GEM kits have not required any more than a simple comet jig and blind faith.
However could you explain one thing to me. I see talk of slop in the coupling rods of thousandths of an inch, yet when look at my new Bachmann Jubilee which runs like a dream it seems to have slop in the hundredths of an inch. It is - I must add - a serious question.
Cheers, Simon
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.
No need to spend 200. If you have the tools, you can make your own by turning down a length of 1/8" rod, or buy the same type for a tenner or so.
How many axles did your GEM kits have? Are they etched chassis?

RTR locos are mass produced and they cannot individually fettle each loco like you would with a kit. To get down to thousandths of an inch, they would need to tighten the tolerances on the whole production process, and that would push up costs. Some RTR locos are geared to drive every axle and the conn rods just come along for the ride.
You can run a kit built loco with considerable slop but if you take pride in it, it will not be as satisfactory, even if it's only you who knows.
MBQ
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wrote in message

Not set up for turning, so interested in where can buy one if you have info ?

This is a 4-4-0 George Vth. But have done a 0-6-0 Cauliflower (but not as well as soldering technique very poor at that time).
Am having problems with weight distribution as its front heavy, and trying to understand how to get the bogie arm right so bogie chassis doesnt foul main chassis - theres isnt much clearence on the prototype.

I want a loco thats not available in RTR (or a variation) so will kit build. If its a good runner thats a bit sloppy from an engineering point of view then will live with that. Its all about compromise with attempting to improve skills whilst having a life with other interests within modelling.
Do think some people are put off trying as they arent experts with great experience right from the start. I'm a hacker in a rush with poor dexterity and struggle with understanding engineering. Yet can assemble, paint and line a GEM kit to give a model that am happy see running on my layout.
On sunday we're going to GCR at loughborogh, his nibs will see Thomas and I will see a hundred year old hunslett (unless its ex Coventry pit loco).
Cheers, Simon
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To be honest I can't remember and I'm not at home at the moment. It probably came from Mainly Trains, but I moved to N gauge now and rarely look there.
Looking at the Comet ones, there are actually two different issues. They sell frame assembly jigs. With most etched kits these days, its relatively easy to build a square chassis.
The type of jigs I'm thinking of are to ensure accuracy and alignment of the axles within the chassis. They are 1/8" dia and come with springs that go between the chassis to hold the hornbock guides and top hat bushes in place. The ends are turned down to fit the holes in the con rods. Thus, the holes in the con rods determine the axle spacing (and using the jig this way ensures they are the same). It does depend on the con rods being a matching pair either side!

There are ways to transfer the weight around but I would suggest you read Iain Rice's books or Mike Sharman's Flexichas rather rthan try to explain it here. It's not too difficult.


Indeed and that's where magazine articles can do a lot of good. But using no jig or using one of the very expensive ones doesn't really help the average modeller. Perhaps there's scope for an article about how the different types of jigs work and can be used.
MBQ
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wrote:

Thanks, used brain and made sure ends of bogie arm remained flat and couldnt tilt. Then set height correctly. Obvious now !

Yep, thats why started this thread. With GEM chassis and comet jig a beginner can put together a good chassis from the included instructions, from Model Rail article would struggle. Although I acknowledge the type of jig you and Jerry suggestion will be useful in a wider context.
Thanks, Simon
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On 13/02/2009 22:39, simon said,

...and that's why people can be put off kit-building. The feeling is that if they can't even build a kit the way Model Rail (a beginner's magazine) tell you to, then it isn't for them. That's so wrong - when shown the right way, anyone can build a kit. Iain Rice's books have been mentioned - it was through his books and his style of writing that I realised that I can do this. Now, I don't necessarily do things his way, but the important thing was that by starting off his way I've gained the confidence to go off and do things my way. People have been kind enough to comment favourably on the models on my website, but I too started off not being able to get an 0-4-0 to run!
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Hi Simon,
- your loco needs it's axles in line. (ie parallel to the rails) - your loco needs it's axles parallel to each other. (across the loco. - bearings need to be the right size for the axles. - coupling rod bearings need to be at the same spacing as the axles. - wheels need to be concentric. - crank pins need to be parallel with the axle. - crank throw needs to be consistant between wheels. - quartering needs to be consistant. - wheels need to be at rightangles to the axle.
Romfords cover the last 5 points, but didn't a long time back.
I try to drill connecting rods and chassis sides in one go and then open out the axleboxes. Using a milling machine gets them in line and parallel, but I've done them with a Black and Decker in a cheap B&D drill stand using a clamped on wall (bit of brass and cheap G clamps) to get them parallel. Before I discovered reamers I used good quality drill bits and didn't have any problems. The stepped axles sound like a good idea for setting up a chassis - been meaning to turn some up for the last 20 years! Never had a jig - I just use some parallel bars (ok, some brass bars) placed on a heavy mirror (as close as I get to a surface plate) I use some 1/8" drill rod through the axle holes and sitting on the bars on the mirror. That gets them at the right height and in line. Use some graph paper on the mirror to make sure the chassis frames are 90 degrees. (ie axles are at right angles to the track)
I don't believe I can do any better or that I need to do any better. It wrks for me from 2-4-0s to 2-12-0s.
Greg.P.
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wrote:

Was thinking about that this afternoon after Jerry's explanations. Got to cut out frames anyway so obvious now to use connecting rods to determine axle centres. May be an idea to start holes through connecting rods ? May use computer to get a drawing of frames with axle holes to ensure they are centred. have concentric circles at axle holes as guide to reaming - need all help can get.

That is where the comet jig is useful. put big round bits fair distance apart with a romford screwdriver through the axle that is nearest the spacer currently being soldered in place. Move screwdriver to next axle and solder.

Thanks. Simon
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Well, I start with the connecting rod hole spacing (scale measurement) and then try to arrange frames and rod blanks in a stack and drill them all at once. Then I open out the frame holes to axle or bearing size. (Ok, I'm getting awfully pedantic) :-) The "trick" is always to think ahead lots about the following requirements so that the bodging bits are made accurate by what went before. (things like having to solder inside the tender body after you've sealed it up :-) My best one was designing cylinders that screwed on through the inside of the frame where the solid combined frame spacer/ smoke box saddle was screwed in from the outside. The cylinders covered the screw heads on the outside of the frame. (Duhh!)

I think you're just about understanding what it's all about.

That's where I use the drill rod!

Greg.P.
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wrote:

Daft - you want to talk about daft things - heres a least embarrassing ... I used to think about fixing body to chassis as the last task when every thing else complete. Got caught out when cut screw for bogie too short. Spent lot of time working out how to use shortened screw or replace it without damaging paintwork (yep really was last thing). Then after all the delicate handling the chimney fell off - oh thats a usefull hole just revealed.
Cheers, Simon
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