axle & crankpin clearance - Comet 14XX chassis

[ozthedog]

Good Morning All

 

Below is my first attempt at building the Comet 14XX chassis with Romford wheelset.  So far so good.  It runs freely when pushed along on track.  At this stage I have 3 questions that previous builders may be able to help me with:

 

1) There is a lot of sideplay on the wheels.  Presumably this is taken up by using spacers.  Problem is I cannot find what final clearance I should aim to achieve. 

 

2) Ditto crankpins

 

3) As can be seen from the photo the threaded crankpins are too long and stick out of the nut.  I assume the crankpin is cut to size after assembly.  Is there any particular technique for doing a tidy job on this?

 

Any advise would be gratefully received.

 

Thanks

 

Keith

 

[drduncan]

Hi Keith,

To answer your questions:

1. It depends on the radius if the tightest curve on your layout. Push it through the curve and see what sideplay there is and add washers to take up the play. You should not normally have sideplay on the driven axle.

2. If you mean between the boss, the pin and then the securing washer, not much. Try a piece of fag paper on either side of the rod when you solder the washer in place. Use oil on the faces of the rod to make sure solder doesn't get where it shouldn't.

3. Side cutters and then fine files.

 

You should get Iain Rice's book on etched chassis construction - its full of useful stuff.

 

drduncan

[ozthedog]

Thanks for your comments drduncan.  I have Iain Rice's book but was just seeking reassurance.  I tend to move carefully when stepping into uncharted territory.  I am really enjoying making etched brass kits.  This is my first chassis but my first kit was the Comet B Set coach which went together well and is awaiting painting.  The chassis is different in that it has working components.

 

Cheers

 

Keith

[drduncan]

0 4 2s are notorious for balance problems. I'd think about putting the 14xx on hold and build an 0 6 0 like a 57xx first. If this idea appeals I'd buy a High Level Kits chassis kit - they are simply the best designed chassis I've come across and the instructions are exceptional. That said, once you've built a High Level chassis your patience with the shortcomings of other brands might get rather limited!

drduncan

[N15class]

It looks good for your first attempt.

 

As above for the crank pins, If this is OO gauge I would ave no side play in either of the driving axles. The rear axle looks like it is in bushes in the frames? if so very little side play.  There is lots of slop in the wheels and track. It is surprising how little side play is needed despite what the RTR manufacturers do.

 

If it does not go around your curves etc more side play on the trailing axle first. If your motor is mounted on a gearbox and there is no side play between your gearbox and the gear that goes on the ale the driven axle can move around without any problems. I nearly always mount my motors on a compensated axle that will move up and down and twist without a problem

 

As for weight get the ballast in the smoke box and boiler. You should be able to get it to stand on the four drivers, there is also space between the frames.

[Grovenor]

 

Push it through the curve and see what sideplay there is and add washers to take up the play.

Do this excercise with the rear wheelset also in place, its only the existence of the rear wheelset that brings the need for sideplay.

Regards

[DCB]

I agree with drduncan Try an easy one first

 

The 14XX is a nightmare to make work decently and pull a realistic load. I have seen a 14XX pull out of Winchcombe station station with at least 5 if not 6 MKis up hill without a trace of slip.  14XX have also been timed at over 80 mph so it is a tricky beast.

 

I still have not made a successful 14XX. I have made Dapol/ Hornby ones better but a scrap box containing the remains of 6 locos tells its own story.

 

The crankpin question, Use end nippers for cutting the crank pins not side cutters.  End nippers cut square, from the middle whereas side cutters by definition cut from one side.  I grind cheap and hasty Chinese 50p nippers to a nice sharp point using a sanding disc in a electric drill. They work well for track cutting too, and when thinned down, extracting track pins.

 

Sideplay, tricky, depends on which axle is driven. I would fit the trailing axle and check it around a curve 2" less than your minimum 3rd radius if you use 2ft etc. It is best to shim the leading and trailing axles pretty tight and concentrate sideplay on the centre axle if you want good high speed stability.  However this means the centre axle has the sideplay, but the centre axle is the best axle to drive from a weight distribution perspective.

You could consider using a gearbox, shimming the worm wheel to the gearbox and allowing the gearbox and motor to float sideways.  Otherwise the worm wheel will just push sideways depending on the direction of travel.  The old front drive Airfix 14XX was terrible for this.

 

If you want a working model you need as much weight in front of the centre axle as possible and as little behind. I did wonder about a lead filled K's smokebox and front end with a plastic Airfix cab at one stage. Trailing wheels need to pick up through the axle to minimise drag.

 

I have considered a double chassis, almost a single Fairlie with an 0-4-0 power bogie in effect pivoted to the rest of the chassis, but seeing your brass chassis I thought hang on. either A) power the trailing wheels as well. maybe an N gauge motor?  and B) drive the trailing wheels from the centre wheels through a layshaft, C) or a driveshaft from the back of a double ended motor, 40:1 and 50:1 gears should do it.  Come to think of it, there is one of those brass chassis in my scrap box.  I shall go and play.

[6892 Oakhill Grange]

Hi Keith

 

I built one of these as my first chassis and it was beginners luck. It works beautifully, Subsequent chassis attempts have not been so successful.

 

For trimming the crank pins and side play, the advice given is all valid.

 

For weighting and balance, everyone is identifying a problem that definitely exists and was an issue with the original airfix chassis. I have read of people springing the trailing axle to allow the drivers to remain on the track at all times. Comet actually provide the solution in the form of the pivoting subframe. However you have soldered a spacer between the wheels so that is ruled out.

 

Unless you are after the massive haulage feats of the prototype then just carry on and see what happens. There is plenty of space for weight in the body, mine weighs 240g.

 

Perform some haulage trials before painting and brake gear assembly and if haulage and pickup is not satisfactory then look at that subframe again.

 

Oakhill

[Isambard Kingdom Brunel]

I have a 14xx Comet Chassis which runs well at 2/3 to full speed, but, slower it seems to be rubbing.

I can't find the problem, do you think that if I keep running it in, it will improve? Or is there something else I should be looking for?

[Gordon A]

Ozthedog, 

As already stated before making adjustments fit the trailing wheels first.

 

I would minimise the side play on the middle (Rear driven) axle leaving some side play in the leading and trailing axles.

 

A practical method is to draw a section of curve that matches the inside rail of your tightest curve.

 

Take a straight length of card and mark the axle positions on the ledge.

Place the middle axle on outside of curve with outer axle positions an equal distance from the curve.

That distance is the minimum amount of side play needed.

 

Gordon A

Bristol

[N15class]

You say it rubs. But you need to show us how the side play is set up. As we do not know if it rubbing on the frames the track or the gearset. If you post a picture or two there might be some more accurate answers.

[Isambard Kingdom Brunel]

Will try to post some photos later currently in Clatterbridge whilst wife has chemo all day. If she feels ok tomorrow will get out to shed. England tonight if we get home in time

[Isambard Kingdom Brunel]

 

 

 

Managed to get out and have a play today with the chassis.

 

The three photos above were taken o my mobile, and are not very good. I have dismantled the coupling rods and tested the chassis and it ran well, so the problem is related to the Coupling rods

 

As the driving wheel does not move the front wheels have some slop, a couple of mm in either direction,  meaning there is  slop in the coupling rods on the crankpins

 

How much would you expect this to move? I think one of the crank pins is also a very loose fit.

 

I think I need to get some new wheels and coupling rods,  fit new crankpins and work from there, any other ideas?

[5050]

After you have nipped off the surplus ends of the crank pins and filed them flat try a drop of nail varnish on the end.  It helps to stop the possibilty of it all unscrewing in use and is easy to remove if you need do perform some maintenance etc.

[N15class]

Looking at your photos, there looks to be a lot of side play on the wheels. If it is the case I would add somewashers to stop the drivers from moving side to side. The trailing axlecould avea littleside to side movement. Also check the centres of the driving axles is the same as the coupling rods. It looks like you have rocking front axle do the boxes slide easily without any side play?