CONWAY 0-4-0 3 1/2" GAUGE LOCO

[Firebird]

Hi

I spent the best part of a day fettling the axle boxes and horns until the axles were a nice easy sliding fit. They need to be a little on the loose side so that the axle can rock a little.

With that done I tried the coupling rods. The first one went on easily but when I tried to fit the other side it was clearly too tight. I managed eventually to get the con rod on but when I tried to rotate the wheels they were clearly binding.

 

Take the con rods off again for a closer inspection. Join the rods together with a 5/16" pin through one end

Just eye balling the other end it is clear there is something wrong. I turned and drilled and reamed the bushes in the lathe very carefully 

I set up a bit of scrap ally bar in the mill, drilled and reamed a 5/16" hole and loctited a 5/16" pin in.

Then using the DRO moved the table exactly 8" and fitted another 5/16" pin

I pressed the bush out of one end on each rod and dropped them over the pins

Once again it can be clearly seen something is wrong.

I pressed out the other 2 bushes and checked each one

<a href="https://www.youtube.com/watch?v=J0J4miI5nxM" target="_blank">http://www.youtube.com/watch?v=J0J4miI5nxM</a>

The problem is the bushes are eccentric, the worst one by 15 thou!!!

I might be able to solve the problem by rotating the eccentric bushes and aligning them on the jig.

I tried making another bush on a test piece in the lathe and although I centre drilled then drilled the drill could be seen  wobbling. The reamer then followed the drill hole. The bush ended up eccentric. I think it would be better where accuracy is required to use a boring bar instead of a drill and reamer

Well at least I have found the problem.

Cheers

Rich

[cnr6400]

Great job on those rods! Another approach or idea you might try is to fit bushings drilled well undersize on purpose, then bore the bushings in place in the rod on the mill. That way they will be as accurate as the mill / DRO is. With this method or with "clocking" eccentric bushes to the correct fit, it is important to pin the bushings in place so they can not rotate or move after being made to correct centres. Hope these ideas help.

[Firebird]

Hi

Thanks cnr6400 

I had an idea along those lines 

If I can't position the existing bushes accurately enough I will make 2 more bushes but leave them solid. Drop the 2 con rods onto a pin and clamp in place then drill and ream the solid bushes. Doing it as a pair should make them identical.

Cheers

Rich

[Florian Eberhard]

Hi Rich

Well drilling is more or less accurate for things like bushings. I would rather bore those bushes out before reaming. This way you can make sure the bore is absolutely concentrical to the outside diameter.

If you can't reach a good enough surface with boring (or have difficulties to get the right diameter) there is a trick to help the reamer staying in center and not wobbling around:
Support the reamer with a piece of material you clamp into the tool holder (instead of a lathe bit).
You have to be careful though not to bend the reamer out of the center, otherwise you will increase the diameter of the bore. (Better check that with an indicator!)
However, if you do so, you will restrict the wobbling in one direction and that usually is already enough to get the drill / reamer / spot drill centered.

Another possible way would be to first finish the inside diameter of your bushes, then make a lost mandrel and finish the oudside of your bushes on that lost mandrel. This should also result in a minimal runout.

Cheers Florian

[Firebird]

Hi Florian

Thanks 

Cheers

Rich

[Firebird]

Hi

Along the lines of Florians suggestion.

Turn a mandrel to a very accurate 5/16"

Drop on a new bush that has been drilled and reamed and turn the outside

<a href="https://www.youtube.com/watch?v=7aCA_ooyUZs" target="_blank">http://www.youtube.com/watch?v=7aCA_ooyUZs</a>

Thats better

Cheers

Rich

[Florian Eberhard]

Hey Rich
Well done!   

Florian

[Firebird]

Hi

Thanks Florian 

Just one small correction, they are the coupling rods not the con rods 

Cheers

Rich

[cnr6400]

Great job on the new bushings!

[Firebird]

hi

Thanks cnr6400

I figure its time to fit the axles permanently so I stripped them out and spent a few more hours fettling to get things nice and smooth.

Cut some felt pads and fit them into the recess in the axle box

Drill the cranks right through and ream the hole with a tapered reamer and tap in some 3/32" taper pins

With the axles fitted into the frames the connecting rods are fitted

<a href="https://www.youtube.com/watch?v=bykiQzvjYGY" target="_blank">http://www.youtube.com/watch?v=bykiQzvjYGY</a>

There is a little resistance but nothing to worry about I don't think. Hopefully when I run it in on air it will bed down

Cheers

Rich

[NickG]

Looks like a lovely fit on all that Rich.


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[Firebird]

Hi

Thanks Nick

I have been fitting some of the parts. A great deal of fettling to get them to fit nicely. Too much to list in detail so I'll just show a few of the items.

The piston rod was a little too tight in the rear cover so I made up a steel bush that is a good fit in the cylinder, reamed to take my 1/4" reamer and reamed it through in situ.

The motion plate is attached to its bracket and is fitted to the guide rods. The guide rods have had their rear ends drilled and tapped M2.5

The holes are spotted in the frames then the motion plate removed and the frames drilled

The motion plate needs a shim behind it

Attached with stainless steel button head screws and self locking nuts

A couple of progress shots

Cheers

Rich

[Kim]

Looking good, Rich!
Making all that motiony stuff fit together right is fiddly work.  Looks like you're just making it happen! 
Kim

[Firebird]

Hi

Thanks Kim

I am spending hours getting things to move correctly. I am glad I opted to bolt most things together instead of rivets. Had I riveted I would have had some serious problems by now. I have the option to take it apart and fettle

Cheers

Rich

[Firebird]

Hi

I spotted this on Fleabay

In the description the guy says it is a scan from an old 1950's Model Engineer magazine. At our club we have all the old magazines.

Doe's anyone have any idea as to the Date??? to save me a lot of searching

Cheers

Rich