What lcoo could these 5" wheel casting be for?

[ettingtonliam]

Thats what I thought originally, but Ajax has Walscherts valve gear, so a shorter stroke will affect the position of the return crank for the valve gear. Not a deal breaker, though, IMHO.
I'd go for a thicker piston, thicker end covers will impinge on the valve ports at the ends of the cylinders.

[stevep]

The shorter stroke will have two effects. First, the combination lever, which provides 2x(lap + lead) movement to the valve, would have to be re-proportioned. But this is simple arithmetic.

Then, as you say, the size and position of the return crank will have to be changed to give you the same movement, but starting from a different position of the crank.

Neither is a deal breaker.

[VGC]

@greg and @davewoo :
People do so much work building a steam loco looking like the original. And still have to pay lots of money for castings. And then they shall have a result looking dilettantic for engineers, only because the supplier of wheels do not do their work correctly? (If this is the case here.)
I would really get angry if I would find out that I got such parts after machining them and building a loco with them.
And if I build a freelance model, I really would not want to make it look dilettantic either. It is not the perfect angular offset that physically counts in these small size with minimized mass effects at scaled-down speed, it is the fact that everybody can see that I do not even take into account the basic physics of general original designs and therefore only have a loco that could not be copied to original size even where this should be possible without any material extra efforts. I see no reason for building a freelance model today based on the lack of knowledge from 150 years ago. Except for lack of personal competence.
Just my personal opinion and my personal claim.

[mbrown]

I've just finished re-reading Eric Langridge's book, "Under 10 CMEs", and he says at one point that the benefit of offsetting balance weights in the wheel is uncertain and the extra cost in pattern making etc may not always be worth it.

An interesting view from a hugely experienced loco designer. Of course, if you are modelling a specific prototype you should have weights where the real loco has them, but for a freelance...?

Malcolm

[Greg]

Dec 29, 2023 22:23:50 GMT VGC said:

@greg and @davewoo :
 I see no reason for building a freelance model today based on the lack of knowledge from 150 years ago. Except for lack of personal competence.
Just my personal opinion and my personal claim.

Yes information is certainly available to build scale models, but building a non scale loco certainly does not mean someone has a '"lack of competence".

I'm currently finishing off a 3 1/2"  264T Stanier tank, so I don't feel that I lack "personal competence". It's not why I'm for thinking of doing a freelance loco for my next build. My choice is based more on giving myself freedom to do what I want and not needing to add scale detail. For me it should be a more enjoyable and efficient build.

I also own a 3 1/2" 440 County and a 5" V2, so I have enough scale locos. 

Yes we are all entitled to our personal opinions, but those being provided, unlike others on this thread, have not helped me with my original query. If I build a loco using these wheels, the quality of the castings won't bother me and that's all that matters.   

[lesstoneuk]

Dec 29, 2023 8:04:09 GMT lesstoneuk said:

Surely you can use the motion designed for the loco you are building. The only difference is the piston stroke. There will be 1/8th of an inch extra clearance at each end of the cylinder. Either machine a wider piston or let in the piston covers. Drilling and fitting eccentric crank pins is complicating things too much.

If you can manage an extra 1/16th on the cylinder diameter, that'll bring the TE up closer to the original specs

[Greg]

Dec 30, 2023 10:45:18 GMT lesstoneuk said:

Dec 29, 2023 8:04:09 GMT lesstoneuk said:

Surely you can use the motion designed for the loco you are building. The only difference is the piston stroke. There will be 1/8th of an inch extra clearance at each end of the cylinder. Either machine a wider piston or let in the piston covers. Drilling and fitting eccentric crank pins is complicating things too much.

If you can manage an extra 1/16th on the cylinder diameter, that'll bring the TE up closer to the original specs

Yes I could do that, but it would only be used for light running, so I could go with original bore size. Although as it is freelance and more about aesthetics, no issue varying some dimensions to suit. Being flexible on sizes might make it easier for me to find some castings suitable for cylinders.

[VGC]

Dec 29, 2023 22:37:24 GMT mbrown said:

I've just finished re-reading Eric Langridge's book, "Under 10 CMEs", and he says at one point that the benefit of offsetting balance weights in the wheel is uncertain and the extra cost in pattern making etc may not always be worth it.

An interesting view from a hugely experienced loco designer. Of course, if you are modelling a specific prototype you should have weights where the real loco has them, but for a freelance...?

Malcolm

The "benefit" can easily be calculated, at least in current 3D CAD programs. Set a ring element on the bolts of the axle which represent the according part of rotating masses (and further masses to be compensated by dynamic balancing) of the rods, then you can let the program calculate the inertia parameters, also the dynamical ones.

I do not see where a ballast position for cross balancing increases the efforts for manufacturing, as there is the same amount of patterns needed like without cross balancing, at least if one does not exaggerate diversity of patterns by the way independently from cross balancing needs.
But perhaps I do not know enough about the background of practical manufacturing there.

[ettingtonliam]

Dec 30, 2023 12:25:45 GMT VGC said:

Dec 29, 2023 22:37:24 GMT mbrown said:

I've just finished re-reading Eric Langridge's book, "Under 10 CMEs", and he says at one point that the benefit of offsetting balance weights in the wheel is uncertain and the extra cost in pattern making etc may not always be worth it.

An interesting view from a hugely experienced loco designer. Of course, if you are modelling a specific prototype you should have weights where the real loco has them, but for a freelance...?

Malcolm

The "benefit" can easily be calculated, at least in current 3D CAD programs. Set a ring element on the bolts of the axle which represent the according part of rotating masses (and further masses to be compensated by dynamic balancing) of the rods, then you can let the program calculate the inertia parameters, also the dynamical ones.

I do not see where a ballast position for cross balancing increases the efforts for manufacturing, as there is the same amount of patterns needed like without cross balancing, at least if one does not exaggerate diversity of patterns by the way independently from cross balancing needs.
But perhaps I do not know enough about the background of practical manufacturing there.

I don't think you are being very helpful to the OP.

[Greg]

Thanks to all those that helped with their comments and suggestions. I got some helpful advice.

I'll use the wheels with reduced the stroke that they were made for. A thicker piston was a good suggestion if I decide to keep everything else the same.

If others want to keep posting here about other stuff, then feel free, although I feel if you want to talk about things that are not closely related to the original post it's always better to create your own separate post.