Coupling Rods, how to fabricate?

[melmerby]

Hi all

I have 80% built my M&L 850 saddle tank kit and I am in the process of making up the chassis.

Unlike the 633 chassis which went together well the 850 is not so accurately fabricated. (even the body is a bit iffy)

e.g. The rods do not match the wheel base!

See below:

 

The dimension is 7' 4" + 6' 4" but the chassis seems to be 7' 3" + 6' 3" (29mm + 25mm) so the rods supplied, which seem to be correctly dimensioned, cannot be used

 

I can make some new ones from brass strip but how do I get the centres accurate enough?

I need some way of transcribing the axle centres to the brass strip.

I suppose I could just try basic measuring?

Any suggestions?

Edited April 6, 2019 by melmerby
Wrong word!

[OFFTHE RAILS]

They are not connecting rods. They are coupling rods.

[DCB]

Coupling rods connect the wheels and connecting rods couple the pistons to the cranks.  Its done to confuse newcomers.

Bit like freemasons handshakes and regimental traditions.

Back to the plot, it's always best to start with the rods and drill the chassis to suit them.  It should be possible to carefully hammer the rods to lengthen them by 0.3mm but its a skilled job.  Rods can be fabricated by soldering but all the ones I have seen have failed in service.

There is not enough meat to open up the holes in the rod eccentrically  and fit bushes  and It will run like a 3 legged crab if you just open the holes up. 

Making new rods to better than 0.2mm is no mean task, way beyond my skill set..

 Maybe you could return the rods and request some correct ones but I reckon most people open up the holes and then stick the loco in a display cabinet because it runs so badly.

 

Edited April 5, 2019 by DavidCBroad

[MarkC]

If you're sure that the axles are running square and true in the frames, you could make up a set using an Alan Gibson Universal Coupling Rod kit.

[chris p bacon]

I have once in the past used the frames as a jig to mark and drill some new rods but you have to be careful not to damage the bearings in the frames. I used some BH rail, and don't forget to sweat your rods together if you drill new ones so they're identical.

[N15class]

If the rods are right why change them? The best and easiest way to get over the problem is to elongated the front and rear axle holes until they match the coupling rods. Use the rods and dummy axles to make sure they are both the same. 

[polybear]

It'll be worth making sure that both coupling rods match each other before going further.  I believe this problem is often caused when rods and frames are not etched on the same fret.

HTH

[Jeff Smith]

What you really need for accurate axle and coupling hole matching/checking is a set (3) of these.  I wouldn't know where to get them as I've had them for years.

[Paul Cram]

I believe London Road Models sell them

[doilum]

I would prefer the new frames option, but to make new rods start with a template. This can be a strip of paper. Use a sharp pin to pick out the axle centres. Transfer this to a strip of plastikard or scrap brass and drill 1mm. Back to the frames and see if the centres line up. This might take a few attempts. When happy, use the template to make a second one. These can now be tried on the crank pins. If successful, use them to drill out the solid blank.

This was my approach when replacing the brittle plastic rods on my 85A ,Hunslet.

[melmerby]

 

9 hours ago, OFFTHE RAILS said:

They are not connecting rods. They are coupling rods.

That's what comes from posting late at night!

Now corrected

[melmerby]

Thanks for the replies.

This is an ancient kit that I part built 30+ years ago and have come back to. M&L haven't existed for years.

(There are several discrepancies in the body fittings as well, the 633 is much better)

 

The chassis has snug fitting bushes (soldered in) for 1/8" axles

 

You can see both rods in the picture, they are N/S and extremely fine,   the frames are brass

(There is a M&L 850 kit on e-bay right now and the rods fret is different, it's chunkier!)

The holes in the current rods are too small even to get Alan Gibson crank pin bushes into!

Opening them out would probably destroy them, so another reason to replace the rods.

 

I'm not going to be building any more kits, I just want to finish this one as best I can, so investing in special jigs would be pointless.

[t-b-g]

I made some new rods for one of the locos on Buckingham by simply setting dividers to as near as I could get to the wheel centres and then marking that dimension on a sheet of nickel silver. I scribed a straight line first and then marked the centres along that line.

 

I was a bit surprised when I drilled the holes, cut out the rods and they fitted perfectly first time but even I get lucky sometimes.

[DLT]

28 minutes ago, t-b-g said:

I made some new rods for one of the locos on Buckingham by simply setting dividers to as near as I could get to the wheel centres and then marking that dimension on a sheet of nickel silver. I scribed a straight line first and then marked the centres along that line.

I was a bit surprised when I drilled the holes, cut out the rods and they fitted perfectly first time but even I get lucky sometimes.

 

Agreed, that's the sort of method I use, its very effective.

 

For Mr. Melmerby's issue, I would consign the kit coupling rods to the spares box and replace them Alan Gibson "Universal" etched rods (as per Mark C's suggestion). 

These are fairly straightforward to assemble, they don't need a jig, and will look very good.

I've used them successfully in the past.  

 

Cheers, Dave

Edited April 6, 2019 by DLT

[Jeff Smith]

It looks as though you have not fitted the crank pins yet, if Gibson the wheels will have to come off for fitment.  There may be two things to do.

 

1 . make some jigs from 1/8" dowel sharpened both ends in a pencil sharpener.

2.  If the crank pins are fitted align all the wheels so the crank pins are all at 3 (or 9) o'clock.  Use a six inch rule to check they are in line and horizontal.

 

Check possibility of using the existing rods or make new ones.  It may be possible to use half a rod and make a new one for the other end hinged on the centre wheel crank.

[34theletterbetweenB&D]

Visually, the rods look right for the centre to right spacing in the photograph. If that is confirmed by running them on crankpins on just these two wheels then  a cheap and simple solution offers in my opinion, and there's nothing to lose in trying it, and a potential benefit.

 

On any loco with more than two driven axles a jointed rod is preferable. Hopefully there is some scrap on the etch from which two slightly shorter rods can be cut correct for the centre to left spacing. Drill first, then cut roughly to shape and fit and try, if there's enough scrap you can have several goes at it. Once you have a fully proven working set for all three axles both sides, take the DIY rods and file carefully to finish shape.

[N15class]

Making a pair of coupling rods identical with hand tools is very hard. Change your crank pins to suit. Adjust the frames. It will work far better.

[Jeff Smith]

Sorry, can't agree with that.  When soldered back to back, drilled through and filed to shape they will be identical!

[Denbridge]

As suggested,  get a set of A.Gibson universal rods plus a set of London road alignment jigs. I've used this method several times and it works a treat.

[DLT]

My Finecast E1/R chassis used Gibson universal rods:  https://www.rmweb.co.uk/community/index.php?/topic/2359-dlts-sr-locos-n15x-finishing-for-jack/&do=findComment&comment=28355

Initially I had them in two sections, but thats really only necessary with a compensated chassis.  You don't need this extra complication with a rigid chassis, and I soldered mine together in one piece.

Cheers, Dave.

[Jeff Smith]

This is something I really don't understand.  The Bachmann 57xx I bought some years ago had one piece coupling rods but the centre axle was sprung down....  I used drop-in P4 wheels and Gibson two-piece coupling rods to allow some centre axle movement.

 

Maybe the original configuration relies on sloppy crank pin holes.....

[N15class]

3 hours ago, Jeff Smith said:

Sorry, can't agree with that.  When soldered back to back, drilled through and filed to shape they will be identical!

Yes they can be made I've made numerous. But you still need to set the bearings to the rods. If the rods are the right wheelbase why make more. Then there's only then you only need to set the bushes. As Dave said no need for hinged rods on a fixed set of frames.

[Izzy]

Like others I would suggest the Gibson universal rods as I designed them for exactly this kind of problem, which was quite common in the past, as well as odd wheelbases that fixed sets didn’t cover. 

 

Izzy

[N15class]

I don't understand the need to change the bit that's right, and try and match the part the wrong. 

If the rods are to thin beef them up.

At the end of the day to get a reliably running set of frames the rods and the frame bushes need to match. This needs to be done whether you make new rods or use the old ones. I know that the etched parts on M&L kits is hand drawn, I would not guarantee the bush holes in either side of the frames match. There was good advice posted above about using stub axles to achieve this. 

[melmerby]

Thanks again for the various suggestions.

 

As I said, I was not going to invest in any gauges or suchlike or a new chassis so I have made a start on fabricating new rods.

Using some suitable brass strip and measuring and re-measuring the axle spacings, I drilled three 1.7mm holes.

I then fitted some Romford stub axles, complete with nuts:

 

Then I offered the axles up to the frame

Left hand side, which were a nice fit:

 

Then tried in the right side, which were a little tight, so I might need to adjust the bush positions in the frame slightly:

 

So far so good, I'll sweat a second piece of brass to the first and drill through.

Looks like It might be go.

Edited April 8, 2019 by melmerby