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Axle sideplay for 0-4-0T


dpgibbons
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I'm building the Connoisseur 0-4-0T starter loco, which has a 47mm wheelbase and a simple fixed worm gear drive.

 

Following the instructions on spacing out the bearings gives me ~1.5mm sideplay on the driven axle, which seems a little excessive for optimum gear engagement. So should I reduce this to say 0.5mm and leave more sideplay on the other axle? And if I do, what sideplay would I need on the latter to accommodate say a 36" radius curve?   

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Fully agree with Pete, the only side play in an 0-4-0 should be bearing clearance.  A “fag paper”, really, nearly nothing.
 

If you have 1.5mm of side play on the driven axle, your gearbox will last about 5 minutes. There must be similarly, almost zero sideplay between worm and worm wheel.

 

Even on an 0-6-0 & 36” curves, you’ll not need much with 32mm gauge, and then only on the middle axle.
 

if in doubt, post up a photo.

 

hth

Simon

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Although 1.5mm seems perhaps excessive up to around 1mm should be quite okay without causing crabbing actions so long as the chassis is square and true, which with Jim’s kits is easy to ensure. I doubt there would be a gearing issue as most worm gear sets have straight cut teeth just cut at the helix angle to match the worm, so sideways movement is not a problem. Just make sure the fold-up gearbox is square in all planes.

 

Izzy

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I would strongly recommend re-reading the instructions. 

 

I'm sure Jim knows what he's takling about, and his kits have an excellent reputation, but you don't need any play apart from running clearance in an 0-4-0 chassis, and the same in the gearbox.

 

To illustrate the point this is a sectional view of one of my 0-4-4-0 Garratt's engines (7' wheelbase, very short) at railhead level, on a curve whose outside rail gauge face is on 900mm diameter.  Ie, 18 inch radius.  You can see that the flanges on the inside wheels are not jamming on the track. 

 

image.png.b47fe2168977fe42877f2bec7cb926c4.png

 

and just so you can make some sense of it

 

image.png.0cd47d3b06ea8b925988facc6d2445cd.png

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Guest Isambarduk
On 30/09/2020 at 14:16, doilum said:

If Jim recommends 1.5mm I would be tempted to follow the instructions

As Simon says, I would recommend re-reading the instructions.

 

If Jim really does suggest 1.5mm slop, I would definitely ignore that part of the instructions.

 

David

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11 minutes ago, Isambarduk said:

As Simon says, I would recommend re-reading the instructions.

 

If Jim really does suggest 1.5mm slop, I would definitely ignore that part of the instructions.

 

David

I haven't seen the instructions, just admired the final outcome from a first time builder well into his seventies. At the budget end, Jim's kits are second to none and his instructions first rate.( I built the J39) .

It is easier to add a thin shim than to start trying to create clearance where it doesn't exist. This was deliberately designed as a first time kit to encourage new builders. Whilst experienced builders will have their own views, newbies might be advised to follow the instructions provided.

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Nowhere in these instructions http://www.jimmcgeown.com/0 Gauge Starter Loco pdf print off.pdf  does Jim recommend 1.5mm of slop.  The instructions state that the chassis has been designed narrow for coarse scale wheel sets to be used,  and go on to say that the bearings should be eased out for finescale wheels.   Jim reckons that a distance of 28-28.5mm over the faces of the bearings is just about right.

 

Charlie

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1 minute ago, Lochgorm said:

Nowhere in these instructions http://www.jimmcgeown.com/0 Gauge Starter Loco pdf print off.pdf  does Jim recommend 1.5mm of slop.  The instructions state that the chassis has been designed narrow for coarse scale wheel sets to be used,  and go on to say that the bearings should be eased out for finescale wheels.   Jim reckons that a distance of 28-28.5mm over the faces of the bearings is just about right.

 

Charlie

Thanks for clearing that up. Look

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Slater's website states: 

All locomotive wheels are to Fine Standard ("Finescale") profile with a back-to-back of 29.2mm. We also make and can supply axles for Scale7 b-b.

30mm is clearly more than it should be.

Dave

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I’d go for Rizla blue...  they’re thinner than green  :)

 

Notwithstanding the comments about Jim’s kits, the whole point of asking “experienced builders” is to find out what works.  And a few of us have pretty much unanimously said “minimal clearance”.  Physics really doesn’t care if you’ve built one loco or a thousand, it only cares if you built them in a way that facilitates them working properly, or not.

 

Simon

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3 hours ago, daifly said:

30mm is clearly more than it should be.

 

Depends where its measured. 30mm at the bosses, which is what matters for bearings, would be perfectly fine, in that the critical b-t-b for pointwork only applies from flange-tip up to rail-head level.

 

I'm entirely with Simon on this: measure the b-t-b at the wheel boss, and set the bearings to give bare running clearance inside that.

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This is getting far more complicated than it needs to be!

 

The is big red herring here is not which part of a Slaters wheel the back to back is measured from.  Back to back is determined by the length of the round part of the axle between the squared off facings which secure the wheels.  This dimension is 29.2mm.  The exercise then becomes a matter of measuring the distance over the faces of the wheel bearings and comparing this to 29.2mm.  It should be shorter!  It is then a matter of using packing washers to minimise slop whilst maintaining running clearance.  Slaters supply these washers as does Jim.  I would advise both suppliers to get a suitable combination of thicknesses to do the job.

 

Charlie 

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31 minutes ago, PenrithBeacon said:

I have always thought that B2B was the dimension between the inner faces of the tyres

Correct.  Slaters wheels achieve the correct B2B by the machining of the axle and moulding the wheel so that the surface of the brass centre and the inside of the steel tyre are in the same plane./

 

Charlie

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