0-6-0 Chassis coupling rods

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Winander
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0-6-0 Chassis coupling rods

Postby Winander » Tue Sep 14, 2021 7:50 pm

I am building an 0-6-0 chassis and using couplings rods that have been etched to the correct wheelbase. I eventually intend to put a proper joint in the coupling rods adjacent to the centre axle, but is it OK to use the coupling rods intact to test the chassis?

My thoughts are to test the chassis before complicating matters by jointing the rods - which itself could cause a problem if done badly.
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davebradwell
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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Tue Sep 14, 2021 8:00 pm

It all depends on how you add the joint but it seems a backwards and dangerous way of doing it. Have you thought of coming up with a way of setting the hornblocks in the frames to the correct dimension, too......without using the rods? This works very much better than jigging which I abandoned years ago.

DaveB

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Winander
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Re: 0-6-0 Chassis coupling rods

Postby Winander » Tue Sep 14, 2021 9:21 pm

davebradwell wrote:It all depends on how you add the joint but it seems a backwards and dangerous way of doing it.

OK, that answers my question, thanks.


davebradwell wrote:Have you thought of coming up with a way of setting the hornblocks in the frames to the correct dimension, too......without using the rods? This works very much better than jigging which I abandoned years ago.

I was going to use a jig something like the Avonside one and set the axles using the etched coupling rods. Are you suggesting I shouldn't use the rods? Why wouldn't an accurate jig be useful?
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steamraiser
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Re: 0-6-0 Chassis coupling rods

Postby steamraiser » Tue Sep 14, 2021 10:02 pm

I use the Avonside chassis jig.
I first set up the jig using the etched coupling rod which are the correct wheelbase on the short pins.
Then I assemble the forked rods on the jig.

Gordon A

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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Tue Sep 14, 2021 10:35 pm

These chassis alignment jigs enable better results to be achieved than with the original jig axles which caused me to abandon the method but, if you have appropriate equipment, nothing will beat setting the hornblocks to the correct dimension then measuring them after fitting to check this is the case.

I think a fundamental problem with jigging is the clearance between axle and axlebox (quite small) and the clearance between axlebox and hornguide (more significant). By holding the axles in the correct place these leave a significant uncertainty in hornguide position. Moral is to take great care to reduce clearances during construction and remove all burrs and sharp edges.

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Winander
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Re: 0-6-0 Chassis coupling rods

Postby Winander » Tue Sep 14, 2021 11:42 pm

Dave,

I have to ask because it is unclear to me and you have referred to hornblocks and hornguides. What exactly are they because if we don't use the same/correct terminology, we will be confused? Can I ask that you once again remind us?
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Re: 0-6-0 Chassis coupling rods

Postby petermeyer » Wed Sep 15, 2021 6:20 am

nothing will beat setting the hornblocks to the correct dimension


Surely it's more fundamental to have the hornblocks match the coupling rods rather than being set to the "correct dimension"?

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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Wed Sep 15, 2021 8:08 am

Back to the start - the hornguides or hornblock is fixed to the frames and the axlebox slides in it and has a hole for the axle. We should all be using these prototypical names.

I am suggesting - given suitable equipment or technique - that the hornblocks are set to dimension because the first post said the coupling rods have been etched to the correct wheelbase. They can be expected to match very well in that case. In fact as all recent kits are done on cad systems I would expect all coupling rods to be "correct wheelbase" these days. A number has to be entered and it should be the right one. Only uncertainty is with odd inches - has 0.3mm or 0.33mm been entered, that's a thou' difference.

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Re: 0-6-0 Chassis coupling rods

Postby petermeyer » Wed Sep 15, 2021 11:34 am

The OP seems to suggest that the rods are in one piece which kind of implies it is not a modern CAD produced kit unless I am wrong. Not all of us are building recent kits and I have had experience over the past few years of modern kits where the rods did not match the frame cutouts. Either one of the two was out but I have zero faith in my ability to measure dimensions that accurately. I think I adjusted the frames which to me was easier than the rods.

I now have a Hobby Holidays jig but have successfully produced running chassis using Perseverance and LRM axle jigs in the past.

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Re: 0-6-0 Chassis coupling rods

Postby Winander » Wed Sep 15, 2021 12:22 pm

petermeyer wrote:The OP seems to suggest that the rods are in one piece which kind of implies it is not a modern CAD produced kit unless I am wrong.


Peter,
The rods were purchased separately from the kit from Lanarkshire Models, so may be considered accurate. They can be jointed but one piece is complete. The loco kit was bought part built second hand.

I believe your point about the ability to measure accurately is valid, and would add the accuracy of the tool used. I suspect many use the rods in a jig because they believe that will ensure the 'measuring' is accurate and many successful models have been made that way.

I think Dave's point is that it is easy to add cumulative errors in a jig and care needs to be taken fitting components together.
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Re: 0-6-0 Chassis coupling rods

Postby Winander » Wed Sep 15, 2021 12:25 pm

davebradwell wrote:Back to the start - the hornguides or hornblock is fixed to the frames and the axlebox slides in it and has a hole for the axle. We should all be using these prototypical names.


Thank you Dave, I agree consistency in terminology is essential for understanding and as I have been confused about the difference between horblock and hornguides, I asked the question.
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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Wed Sep 15, 2021 3:25 pm

It is very difficult measuring hole centres accurately and the most useful I've seen was described by the much missed Don Rowlands. He would have put dowels through the holes in a pair of coupling rods and measured over and between them with a vernier, taking the average. Spacing the rods and measuring in the gap would likely be best but this is where you'll be glad you splashed out on a +/- 1 thou' vernier and not the woodworkers +/- 2 thou" as with 2 readings the potential measuring error is doubled.

This technique is very good on limping chassis as it takes out the clearance in each direction and gives the wheelbase as built. A valuable first stage in correcting these things.

I use separate pieces for the front and rears of the hornblocks so strictly they are hornguides. With stuff I etch for myself, including most kits, the fronts are just bent up out of the frame - very carefully so as not to influence the bend position - and it's remarkable how accurate this is. I usually measure them in my mill using a lever type dial indicator as the probe and reading off the calibrated leadscrew dial and don't expect to be able to see any error. Incidentally, a mill or co-ordinate table is the best way I've found of getting frames square - it's just an extension of the measuring exercise.

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Will L
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Re: 0-6-0 Chassis coupling rods

Postby Will L » Wed Sep 15, 2021 9:09 pm

davebradwell wrote:It is very difficult measuring hole centres accurately and the most useful I've seen was described by the much missed Don Rowlands. He would have put dowels through the holes in a pair of coupling rods and measured over and between them with a vernier, taking the average. Spacing the rods and measuring in the gap would likely be best but this is where you'll be glad you splashed out on a +/- 1 thou' vernier and not the woodworkers +/- 2 thou" as with 2 readings the potential measuring error is doubled.

This technique is very good on limping chassis as it takes out the clearance in each direction and gives the wheelbase as built. A valuable first stage in correcting these things.

I use separate pieces for the front and rears of the hornblocks so strictly they are hornguides. With stuff I etch for myself, including most kits, the fronts are just bent up out of the frame - very carefully so as not to influence the bend position - and it's remarkable how accurate this is. I usually measure them in my mill using a lever type dial indicator as the probe and reading off the calibrated leadscrew dial and don't expect to be able to see any error. Incidentally, a mill or co-ordinate table is the best way I've found of getting frames square - it's just an extension of the measuring exercise.

This is all very well Dave, but to achieve your results by accurate measurement, you've used lots of stuff many of us aren't going to find on our workbenches. While good engineering practice I'm sure, as a hobby the techniques a-la-Sharman which enable us to build things which suit the size things they actually are may be of more value. If the going gets difficult I do use Don's measuring method to track down problems, but in the end what is most important to me is that axle and rod hole on the same centres rather than a paticular distance apart. Therefore, learning to use available the jigging methods reliably must be more important to many of us.

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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Thu Sep 16, 2021 12:09 pm

I'll repeat that I only made these suggestions because the first post said he had accurate coupling rods and I believe that will be the case for nearly all kits produced in the past 15-20 years. The only method of setting horns to dimension I have described is aimed at the increasing number of folk who etch their own models, otherwise it's just precautions when using a jig. Yes, I described how I measure hornblock spacing but that's just part of the clarification - if someone wrote they measured an awkward item I would automatically ask how.

On the other hand there's a significant number of folk with mills, or access to one and they may have found something useful above. I am not aware of any bans on referring to machine tools in posts and a mill is the number 1 bit of kit for getting hornguides at the correct spacing - my Finney V2 chassis came out very well. Great for just assembling chassis squarely, too. Will add the precaution that I only mill frame plates when they're securely clamped to the table and before assembly.

You don't necessarily need much equipment for accurate work. I've used gauge bars (bits of silver steel filed to length) to push a bit of plate along a fence under a pillar drill to achieve accurate coupling rod centres before I had the mill.

As a final thought why not combine your jig with some measurements? Don't forget the hole won't be exactly in the centre of the axlebox, though, and that's something else to consider. The jigs compensate for this, but only if you don't turn axleboxes round or mix them up.

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Re: 0-6-0 Chassis coupling rods

Postby Daddyman » Thu Sep 16, 2021 12:35 pm

davebradwell wrote: I've used gauge bars (bits of silver steel filed to length)


So glad that you mention this, Dave. I thought I was being utterly heretical and didn't dare mention it in response to Will's post! As it is, these "gauges" have helped me get one chassis set up and working beautifully with 0.05 clearance on the crankpin bush, and I have a second chassis built using the same method on the way.

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Re: 0-6-0 Chassis coupling rods

Postby Will L » Thu Sep 16, 2021 5:37 pm

Winander wrote:I am building an 0-6-0 chassis and using couplings rods that have been etched to the correct wheelbase. I eventually intend to put a proper joint in the coupling rods adjacent to the centre axle, but is it OK to use the coupling rods intact to test the chassis?

My thoughts are to test the chassis before complicating matters by jointing the rods - which itself could cause a problem if done badly.

While that ought to be Ok, I'm not sure what happens if the rods stop working once jointed, so I would joint first and build the chassis to match them.

I have documented producing jointed rids here if that helps. This applies to a set of Gibson universal rods, but should be made applicable to a set of simple etched rods if need be. The key element being the provision of the third layer.

Also there can be a issues setting the Avonside jig up to match the rods exactly but this post shows you what to watch out for.

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Re: 0-6-0 Chassis coupling rods

Postby Jeremy Suter » Thu Sep 16, 2021 9:31 pm

Will L wrote:
Winander wrote:I am building an 0-6-0 chassis and using couplings rods that have been etched to the correct wheelbase. I eventually intend to put a proper joint in the coupling rods adjacent to the centre axle, but is it OK to use the coupling rods intact to test the chassis?

My thoughts are to test the chassis before complicating matters by jointing the rods - which itself could cause a problem if done badly.

While that ought to be Ok, I'm not sure what happens if the rods stop working once jointed, so I would joint first and build the chassis to match them.

I have documented producing jointed rids here if that helps. This applies to a set of Gibson universal rods, but should be made applicable to a set of simple etched rods if need be. The key element being the provision of the third layer.

Also there can be a issues setting the Avonside jig up to match the rods exactly but this post shows you what to watch out for.


Hi Richard
lots of ideas here but the short answer is NO get the chassis horn blocks fitted first to fit the rigid coupling rods, once you joint the coupling rod the way you want to you are introducing a point of error. You are pivoting them between the crank pins not on the crank pin.

I assume they are for your LNWR DX that you are working on.

The coupling rods need to match the wheel centres and the wheel Centres need to match the footplate. You are building a kit and we assume the designer has done the measuring for us although you say the coupling rods are not from the kit I assume you bought the rods to the correct wheelbase.

Some one else had already cut the axle holes out for the horn guides to be added. Hoping that the person who cut them out cut in the right place or the new horn guides fit the gaps. I Suspect there will be some play. You need to loose any side play. So start some where either one end and work along or in the centre and work out. Personally I would start at one end, the front. You showed us the Jig you made to set the horn guides and blocks so work along fitting them the rigidity in the coupling rod will help with keeping the three holes inline. I assume as you have a lathe you can or have made a set of long axles with either a hole in the end that you could screw the coupling rod to or turn the ends down to fit the coupling rods.

Then cut the coupling rods if they don't work there is something wrong with the way you have jointed them. Short or long coupling rods go tight at the quarter to or quarter past positions.
Last edited by Jeremy Suter on Fri Sep 17, 2021 5:07 pm, edited 1 time in total.
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Re: 0-6-0 Chassis coupling rods

Postby petermeyer » Fri Sep 17, 2021 5:56 am

With the LNWR Special DX, being such a small loco, there is a chance that the front hornblocks will foul on the front spacer as there is very little room here. Don't ask how I know!

There is also the issue of clearance within the splashers if using a kit designed for OO. And then the crankpins can foul on the valance: I built the LRM kit and this is already acknowledged in the instructions. One solution suggested is to shave down the Gibson wheels (before fitting crankpins)

A Coal Engine is an easier 0-6-0 to build with the smaller wheels and share the same wheelbase (as do most GWR 0-6-0's and tankies). Peter

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Winander
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Re: 0-6-0 Chassis coupling rods

Postby Winander » Fri Sep 17, 2021 3:43 pm

Thank you all for your contributions.

I have had an interesting time jiggling hornblocks. My original intention was to manufacture axles for the jig with a 1.5mm spigot each end for the rods but my skills were insufficient (although the spigots are OK). I adapted some London road Models axle jigs to fit. These have tapered ends which I don't like. I fitted the rods to the jig by eye and then measured the distance over the axles and compared it to the wheelbase plus 3.175mm. My caliper is adequate, its certificate states a 0.01mm error over the measured range.

My conclusion is that it is difficult but possible to get the axles perfectly aligned. I ran out of patience with the tapered rods but managed perfectly with the spigots. The recommendation to measure the spacing is valid but only if your measuring stick is up to the task. I rather like the idea of gauge bars as they will be consistent, but you still have to measure to make them.

To answer some of the specific point raised above:
The chassis is for a London Road Models LNWR DX, it was bought second hand and the chassis was built. It did run but had plastic hornblocks, plunger pickups, rods jointed on the centre crankpin and the springing didn't work.
I purchased the additional coupling rods mainly because I wanted an accurate measure. I cannot reuse the ones that came with the model unless I bush the crankpin holes as they are a bigger than 1.5mm. My time would be better spent altering the new ones to the delicate profile of the prototype.
I haven't read the instructions much past the chassis stage but became aware of the frame spacer fouling the hornblocks and realised I might want to work on the splashers' positioning. Thanks for the heads up regarding the valance but it is too deep anyway, as are the frames. These photos show how much fresh air is below and around the frames and the small valance
https://lnwrs.zenfolio.com/p1027016558/h4b9a383d
https://lnwrs.zenfolio.com/p1027016558/h4b9a361d
Thanks for the links Will, I possibly know your build threads as well as you do.

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Re: 0-6-0 Chassis coupling rods

Postby ArthurK » Fri Sep 17, 2021 4:54 pm

The easiest way is to make up the rods (rigid or hinged). Cut out the frames to take the hornblocks for the first and third axles. Then using whatever jig you have position the hornblocks using the centre axle and rods as a guide. Once these are in place cut out the frame for the centre hornblocks. Put everything back in your jig with the centre hornblocks in position then with the rods in place solder the centre hornblocks in place.

Of course this assumes the the frames come with holes for the axles, not with frame cut-outs.

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Re: 0-6-0 Chassis coupling rods

Postby FCA » Sat Sep 18, 2021 3:06 pm

Given that most of us use the rods to align the axleboxes, I think it essential that the pair of rods are identical. As this can't be guaranteed with etched rods, especially after they're fettled, I now bush the rod bearings on a jig.

The jig is a thick brass sheet or bar with tapered steel pins set at the required centres. The bushes (phosphor-bronze for preference), are a tight fit over the pins and are soldered into enlarged holes in the rods. Obviously rod joints need to be made before fitting the bearings. Once prised from the jig you have two rods with precisely aligned centres.

One advantage of this method is that, suitably marked up, the jig can be kept and used for rebushing at a later date in the confident knowledge that they will match the chassis.

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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Sat Sep 18, 2021 3:46 pm

There's plenty of good stuff in your post, Richard, but I am wondering what leads you to believe that etched rods will not end up with correct centres. Certainly in the days of drawn artworks they would be different but photoplotters are pretty accurate things - or used to be - and as long as the holes are etched close to correct size I've always expected that they would come out right. I've never tried measuring any directly as it's not easy to get sufficiently accurate results but they've always matched axles placed at the correct measured centres.

The original jig axles, if the correct length, would actually adjust the wheelbase to match slightly different coupling rods. That is unless scuppered by too much clearance, of course and those springs that prevent hornblocks floating to preferred position.

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Re: 0-6-0 Chassis coupling rods

Postby FCA » Sun Sep 19, 2021 3:36 pm

I suppose it dates back to the early days when etches weren't necessarily that reliable. Plus a desire to be able to replicate the rods in the (unlikely) event that they wore out or somesuch.

Richard

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Re: 0-6-0 Chassis coupling rods

Postby davebradwell » Sun Sep 19, 2021 4:42 pm

Must say I like your phos bronze bushes, presumably on steel crankpins and the care you take. Nickel silver on brass has never struck me as a wonderful bearing combination but with regular application of moly grease it seems to survive. I have the advantage that I can just etch myself some extra rods if needed, though. Must check the centres next time.

DaveB


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