Wright writes.....

[jamie92208]

With LSGC off the exhibition circuit next year (unless anything new is booked in) I may take the opportunity to learn how to produce my own brass etchings. In todays climate it makes sense a lot of sense to get control over what you require.

At least at Shipley you have several very able people to help you with your ambition. I wish you luck with the etching. I found that mastering CAD was the first skill. That was solved with tutorials on YouTube. The second was to try to work out how to turn a drawing into a set of etches that you are able to assemble. A warped mind certainly helps there.

 

 

Jamie

[Jol Wilkinson]

At least at Shipley you have several very able people to help you with your ambition. I wish you luck with the etching. I found that mastering CAD was the first skill. That was solved with tutorials on YouTube. The second was to try to work out how to turn a drawing into a set of etches that you are able to assemble. A warped mind certainly helps there.

 

 

Jamie

I didn't find it too difficult. Firstly I use a 2D CAD package (CorelDraw) that I found quite easy. I read up several articles on "traditional" hand drawn kit artwork and, together with the information given on various etches sites, was able to quite quickly get the hang of things. Latterly I discovered the Hollywood Foundry Tutorial site and would recommend that as a good source of information:

 

http://www.hollywoodfoundry.com/HowToPapers.shtm

[Headstock]

At least at Shipley you have several very able people to help you with your ambition. I wish you luck with the etching. I found that mastering CAD was the first skill. That was solved with tutorials on YouTube. The second was to try to work out how to turn a drawing into a set of etches that you are able to assemble. A warped mind certainly helps there.

 

 

Jamie

 

Thanks Jamie,

 

I think that Frank is doing some CAD demonstrations at an exhibition in the future. Fortunately, I'm pretty familiar with 3D and drawing packages so the migration to CAD soudn't be the worst thing in the world.

Edited October 28, 2018 by Headstock

[Lecorbusier]

As far as I know the Victorians abandoned singles and went to 2-4-0's as locos got larger and more power needed transmitting. I believe that it was the invention of steam sanding that brought back the beautiful Midland and GN singles (I'm sure there were others as well). Also by that time rails had got stronger and higher axle loadings were allowed.

 

Jamie

I always understood that this was all about the diameter of the wheel and thus the relative gearing. Big wheel, high velocity at the circumference hence tendency to slip ... smaller wheel diameter, the opposite. So smaller wheels for goods as top speed not an issue but grip pretty important.

[Chuffer Davies]

I always understood that this was all about the diameter of the wheel and thus the relative gearing. Big wheel, high velocity at the circumference hence tendency to slip ... smaller wheel diameter, the opposite. So smaller wheels for goods as top speed not an issue but grip pretty important.

 

This is another misnomer. Grip is not influenced by diameter as this is neither a function of weight or coefficient of friction.

 

What is happening here is that the smaller diameter of the driven wheels will increase the mechanical advantage of the pistons just as happens with a lever. Hence there will be an increase in the tractive potential but at the cost of speed.

 

Regards,

 

Frank

[Lecorbusier]

This is another misnomer. Grip is not influenced by diameter as this is neither a function of weight or coefficient of friction.

 

What is happening here is that the smaller diameter of the driven wheels will increase the mechanical advantage of the pistons just as happens with a lever. Hence there will be an increase in the tractive potential but at the cost of speed.

 

Regards,

 

Frank

I may be misunderstanding this ... but here goes (I can only look a fool after all).

 

Steam as a power source is I believe very high in torque particularly at low revs. At the same time, because there is no gearing in a steam engine, maximum speed is limited by the diameter of the wheel? So if you have very high torque put through a small diameter wheel the speed at which the wheel can rotate is limited. By the same reasoning if you have a large diameter wheel, then the speed of rotation at the circumference will be far greater?

 

If this reasoning is correct, then with the high torque wouldn't greater force/acceleration occur with the larger wheel for the same amount of regulator? Hence the spectacular wheel slip seen on the big Pacifics on film .... but not as far as I am aware shown when heavy goods trains are filmed? Or did heavy goods trains suffer just as badly?

[stewartingram]

Wouldn't you need five of 'em for that?

 

+ spares!

 

Stewart

[jamie92208]

I may be misunderstanding this ... but here goes (I can only look a fool after all).

 

Steam as a power source is I believe very high in torque particularly at low revs. At the same time, because there is no gearing in a steam engine, maximum speed is limited by the diameter of the wheel? So if you have very high torque put through a small diameter wheel the speed at which the wheel can rotate is limited. By the same reasoning if you have a large diameter wheel, then the speed of rotation at the circumference will be far greater?

 

If this reasoning is correct, then with the high torque wouldn't greater force/acceleration occur with the larger wheel for the same amount of regulator? Hence the spectacular wheel slip seen on the big Pacifics on film .... but not as far as I am aware shown when heavy goods trains are filmed? Or did heavy goods trains suffer just as badly?

That's about right. One of the limiting factors in loco speed is piston speed due to potential lubrication problems. Another is balance, which was always a set of compromises, usually worked out for a particular speed range. Freight locos usually had smaller wheels to give the good starting torque with the ability to apply it without slipping. Express passenger locos were always lighter on their feet when starting for the reasons you've outlined. However 4-6-0's were usually more sure footed than pacifics as when starting weight tends to be transferred to the rear of the loco and in a 4-6-0 it comes to the rear driving wheel rather than a pony truck. It pains me to say this but GWR locos had a reputation for being sure footed.

 

Another factor was the design of the steam passages which in many earlier locos were tortuous and in effect throttled the loco at higher speeds. Thus when internal streamlining was introduced, particularly in the BR standards you had the 9F's which were recorded doing over 90mph on several occasions and Evening star was used on the Red Dragon a few times until high ups found out and were frightened of piston speeds of 8 revs per second.

 

Jamie

[Chuffer Davies]

I may be misunderstanding this ... but here goes (I can only look a fool after all).

 

Steam as a power source is I believe very high in torque particularly at low revs. At the same time, because there is no gearing in a steam engine, maximum speed is limited by the diameter of the wheel? So if you have very high torque put through a small diameter wheel the speed at which the wheel can rotate is limited. By the same reasoning if you have a large diameter wheel, then the speed of rotation at the circumference will be far greater?

 

If this reasoning is correct, then with the high torque wouldn't greater force/acceleration occur with the larger wheel for the same amount of regulator? Hence the spectacular wheel slip seen on the big Pacifics on film .... but not as far as I am aware shown when heavy goods trains are filmed? Or did heavy goods trains suffer just as badly?

I agree with your first paragraph but not the second.

 

If we assume the cylinders and piston throw are the same in both examples then the tractive force available at the rim of a large wheel is less than that available on a small wheel. Imagine the mechanism as a 3ft lever pivoted at one end ( the equivalent of the wheel hub). If a force of 1 ton is exerted 1 ft from the pivot (the equivalent of a typical crank pin position) this will translate as 1/3rd ton at the 3ft end (equivalent to a 6ft diameter wheel). In contrast at 2ft from the pivot (I.e. equivalent to a 4ft wheel) the available force will be 1/2 ton. This is why smaller wheeled locomotives have greater power at the draw bar but only as long as the wheels remain in grip with the track.

 

I therefore would deduce that without good regulator management that a small wheeled loco is more likely to slip than a large wheeled loco of the same weight (the number of axles being irrelevant as previously explained).

 

Hope that makes sense.

 

Frank

Edited October 28, 2018 by Chuffer Davies

[AndyID]

 

Steam as a power source is I believe very high in torque particularly at low revs. At the same time, because there is no gearing in a steam engine, maximum speed is limited by the diameter of the wheel? So if you have very high torque put through a small diameter wheel the speed at which the wheel can rotate is limited. By the same reasoning if you have a large diameter wheel, then the speed of rotation at the circumference will be far greater?

 

If this reasoning is correct, then with the high torque wouldn't greater force/acceleration occur with the larger wheel for the same amount of regulator? Hence the spectacular wheel slip seen on the big Pacifics on film .... but not as far as I am aware shown when heavy goods trains are filmed? Or did heavy goods trains suffer just as badly?

 

 Hi Tim,

 

You certainly won't look like a fool. It's quite a tricky subject.

 

It might be better to think about it in terms of the force produced by the pistons on the crank. For a particular steam pressure, cylinder bore and piston stroke, the force produced that tends to turn the wheel is independent of the diameter of the wheel. For larger wheels the maximum force that can be exerted at the wheel's rim on the rail (assuming it is not slipping) is smaller than that produced by smaller wheels. Larger wheels are "higher geared" which means they can run faster than smaller wheels for a given piston velocity.

 

One of the reasons Pacifics can be a bit light-footed when starting (more so than 4-6-0s) is due the trailing wheels under the cab. When a locomotive starts to pull a heavy train there is a significant weight transfer towards the rear of the locomotive. On a Pacific that puts more weight on the non-powered trailing wheels and less on the driven wheels.

 

Cheers!

Andy

[chris p bacon]

Very interesting....but what happens when you turn the controller to . . .11. 

[Headstock]

Very interesting....but what happens when you turn the controller to . . .11. 

Blue Peter.

[AndyID]

Snap!

 

EDIT: By the way, the other reason goods locomotives were less likely to slip when starting is 3-link couplings. The buffers bunched up when the train stopped. When the locomotive started it gradually connected to the full load of the train as the couplings tightened up.

Edited October 28, 2018 by AndyID

[Headstock]

I agree with your first paragraph but not the second.

 

If we assume the cylinders and piston throw are the same in both examples then the tractive force available at the rim of a large wheel is less than that available on a small wheel. Imagine the mechanism as a 3ft lever pivoted at one end ( the equivalent of the wheel hub). If a force of 1 ton is exerted 1 ft from the pivot (the equivalent of a typical crank pin position) this will translate as 1/3rd ton at the 3ft end (equivalent to a 6ft diameter wheel). In contrast at 2ft from the pivot (I.e. equivalent to a 4ft wheel) the available force will be 1/2 ton. This is why smaller wheeled locomotives have greater power at the draw bar but only as long as the wheels remain in grip with the track.

 

I therefore would deduce that without good regulator management that a small wheeled loco is more likely to slip than a large wheeled loco of the same weight (the number of axles being irrelevant as previously explained).

 

Hope that makes sense.

 

Frank

 

The other way about, because a large wheeled locomotive is far more sensitive to mishandling or the regulator.

[Headstock]

Adhesive ratio is what makes the difference, The P2 locomotives could generate massive amounts of torque and had a high adhesive ratio, due to large amount of adhesive weight available over the four coupled axles, so much so that they would break a crank axle rather than slip.

Edited October 28, 2018 by Headstock

[AndyID]

The other way about, because a large wheeled locomotive is far more sensitive to mishandling or the regulator.

 

I think that's because, if it does start to slip, the "high gearing" results in a much higher velocity at the rim than would be the case with a small wheel. Also, when a large wheel does get going it's got a lot more kinetic energy which tends to keep it slipping longer.

[Headstock]

A2 Blue Peter is basically a P2 without the fourth driving axle and a better design of crank axle. Without the fourth axle it has lost a significant amount of adhesive weight compared to the P2. However it still has the highest starting attractive effort of any conventional British steam locomotive, discounting the likes of the U1 etc. As a result it has a lower adhesive ratio and becomes more likely to slip if you give it full welly.

Edited October 28, 2018 by Headstock

[thegreenhowards]

 

no plans at present, with the layout under constant threat of scraping I'm trying to do as much as I can before the axe falls.

Andrew,

 

Are you seriously suggesting that LSGC is facing the axe? That would be a terrible shame as it’s one of, if not THE best on the circuit. If so, I may have to make the effort to get to Spalding on Saturday.

 

Good luck with the exhibition either way.

 

Andy

[Chuffer Davies]

I think that's because, if it does start to slip, the "high gearing" results in a much higher velocity at the rim than would be the case with a small wheel. Also, when a large wheel does get going it's got a lot more kinetic energy which tends to keep it slipping longer.

I’m struggling to get my head around this last question. The video evidence tends to relate to express engines slipping their wheels because few bothered to video goods trains pulling away.

 

I still think the physics indicates that a smaller wheel will be more likely to lose traction because the tractive force exerted at the rim is greater than that on a larger wheel for the same cylinder pressure whilst the coefficient of friction remains the same irrespective of diameter. That assumes everything else remains the same I.e. the same number of driven axles. Remember that an 8 coupled goods loco is distributing the forces exerted through the connecting rod across 8 wheels rather than 6 as in a typical express loco and so this will reduce the tendency for a goods locomotive to slip.

 

Of course in reality there are many variables at work including actual weight on each driven axle, the crank throw, the steam pressure as well as the wheel diameter and the number of driven axles, all of which will have an influence on the risk of wheel slip.

 

Frank

[Tony Wright]

Just returned from visiting the excellent Leeds Show.

 

May I thank the organisers for selecting such excellent layouts, please? The only disappointment was the trade - a bit 'samey' in that most on sale was RTR, new or second-hand. Not much for the likes of me. 

 

May I also thank those who've been so elucidating on the mechanics of the steam loco, with lots of hard sums and physics? In both categories, count me out ( I taught art!). I'm only interested in the effects, not the science behind it with regard to model locos' haulage capabilities. In that respect, I was delighted that my A4 SIR NIGEL GRESLEY easily took its train up Shap time after time, with no signs of slipping at all. How? A very heavy loco and a big motor/gearbox combination.

 

 

 

These were taken at Warley last year. It was rather nice to go to a show today, just as a punter. No camera and no notebook!

 

My other two locos seemed to run well as well, but they were on Up trains (going downhill, though they must have been able to climb back up in the fiddle yard). 

 

 

Here's my DJH Standard Five drifting down from the summit. This was built originally by Roy Jackson and painted/weathered by Geoff Kent. I rebuilt the chassis.

 

Thanks for giving them all a run, Graham. 

[Headstock]

Just returned from visiting the excellent Leeds Show.

 

May I thank the organisers for selecting such excellent layouts, please? The only disappointment was the trade - a bit 'samey' in that most on sale was RTR, new or second-hand. Not much for the likes of me. 

 

May I also thank those who've been so elucidating on the mechanics of the steam loco, with lots of hard sums and physics? In both categories, count me out ( I taught art!). I'm only interested in the effects, not the science behind it with regard to model locos' haulage capabilities. In that respect, I was delighted that my A4 SIR NIGEL GRESLEY easily took its train up Shap time after time, with no signs of slipping at all. How? A very heavy loco and a big motor/gearbox combination.

 

Shap 09.jpg

 

Shap 10. A4.jpg

 

These were taken at Warley last year. It was rather nice to go to a show today, just as a punter. No camera and no notebook!

 

My other two locos seemed to run well as well, but they were on Up trains (going downhill, though they must have been able to climb back up in the fiddle yard). 

 

Shap 15.jpg

 

Here's my DJH Standard Five drifting down from the summit. This was built originally by Roy Jackson and painted/weathered by Geoff Kent. I rebuilt the chassis.

 

Thanks for giving them all a run, Graham. 

 

Torque + adhesive weight = ultimate power WHA HA HA, at least in model railway land. The real things also require an effective steam producer as well.

 

Andrew,

 

Are you seriously suggesting that LSGC is facing the axe? That would be a terrible shame as it’s one of, if not THE best on the circuit. If so, I may have to make the effort to get to Spalding on Saturday.

 

Good luck with the exhibition either way.

 

Andy

 

I like it too.

 

Thank you, I shall enjoy the exhibition very much.

[Woodcock29]

Hello Tony

 

On the subject of J11s I post photos of my two Bachmann models - both significantly modified with cut down tenders for the 3250 gallon variant with which most were coupled. Also 5311 has been fitted with an original GC chimney and dome. I may have posted photos of these before? 

 

In addition, I have posted a photo of my latest kit built loco - a J3, which has been made from a very cheap Ks kit but with a Mainly Trains scale J52 chassis, and a LRM Stirling tender. The chimney, dome and safety valve came from my spares box as the none of the Ks items were correct. It also has a Graeme King J6 smokebox front which very significantly enhances it over the Ks part supplied. I had originally intended to use Graeme's resin J6 boiler as I understood the Ks boiler to be significantly undersize but upon measuring this and comparing it with the Ks boiler the difference was less than 0.5 mm in diameter so I used the heavier Ks boiler which was quite a good casting even if the washout plugs are not totally correct.

 

Andrew   

[Barry O]

Lovely to see you and Mo yesterday Tony.

Biggest problem is to find and invite traders who sell things other than RTR.

There were plenty of bargains though. I am now the proud owner of about 14 Scalecraft roadrailers obtained cheaply as they need work to refresh them.

 

Baz

Edited October 29, 2018 by Barry O

[t-b-g]

Hello Tony

 

On the subject of J11s I post photos of my two Bachmann models - both significantly modified with cut down tenders for the 3250 gallon variant with which most were coupled. Also 5311 has been fitted with an original GC chimney and dome. I may have posted photos of these before? 

 

In addition, I have posted a photo of my latest kit built loco - a J3, which has been made from a very cheap Ks kit but with a Mainly Trains scale J52 chassis, and a LRM Stirling tender. The chimney, dome and safety valve came from my spares box as the none of the Ks items were correct. It also has a Graeme King J6 smokebox front which very significantly enhances it over the Ks part supplied. I had originally intended to use Graeme's resin J6 boiler as I understood the Ks boiler to be significantly undersize but upon measuring this and comparing it with the Ks boiler the difference was less than 0.5 mm in diameter so I used the heavier Ks boiler which was quite a good casting even if the washout plugs are not totally correct.

 

Andrew

 

Very nice. I love the fact that the J3 gives no clue to its origins as the old Ks kit. It is the sort of kit building I like. Take one fairly grotty kit and give it a work over until it looks like what it was intended to be. My rule of thumb is that if you can still see whose kit it was, then you haven't done enough to it. If you can't tell whose kit it was, either it was a very good kit or all the faults have been corrected.

[St Enodoc]

Lovely to see you and Mo yesterday Tony.

Biggest problem is to find and invite traders who sell things other than RTF.

There were plenty of bargains though. I am now the proud owner of about 14 Scalecraft roadrailers obtained cheaply as they need work to refresh them.

 

Baz

Ha! I've got about a dozen too. No idea what I'm going to do with them. Do you need an adaptor bogie? I might have a spare.