Super Simplex 0-6-0

[Builder01]

I am beginning the build of a freelance steam locomotive design by Martin Evans, Super Simplex. I am re-gauging it to run on 4-3/4" track. Two things that will have to be squeezed to fit between the frames are the saddle and the bottom of the fire box. Since the bottom of the fire box and grate will be 1/4" narrower than originally designed, should I consider reducing the bore of the cylinders? As designed, the cylinder bores are 1-9/16".

Thanks,
David

[WJH]

I have those plans somewhere... If you reduce the bores, I still doubt that there will be a lack of power, surely the wheels would slip before they would stall. Just my thoughts on the matter. I would be more concerned about the firebox / grate area.

[Builder01]

How do you calculate the grate area? Length times width? If so, the grate area as designed is 15.453 inches. If the width is reduced by 1/4", the grate area will be 14.015". About 1.5 inches smaller than designed. What are typical grate areas for successful 4-3/4" gauge locomotives?

The fire box, at least above the frame, will not be reduced. So, the heating area inside the firebox will not really change.

David

[Harold_V]

I am beginning the build of a freelance steam locomotive design by Martin Evans, Super Simplex. I am re-gauging it to run on 4-3/4" track. Two things that will have to be squeezed to fit between the frames are the saddle and the bottom of the fire box. Since the bottom of the fire box and grate will be 1/4" narrower than originally designed, should I consider reducing the bore of the cylinders? As designed, the cylinder bores are 1-9/16".

Thanks,
David

I'm curious about your inquiry in regards to reducing the bore of the cylinders. That wouldn't be a requirement for re-gauging, as bore diameter plays no role in cylinder center distance. Did I miss something?

Harold

[Builder01]

Yes, you are correct, re-gauging has nothing to do with bore size. The reason I brought up cylinder diameter was because of the slight reduction of the grate size. I guess my first question should have been, is there any sort of relationship between grate size and cylinder? If there is not, then perhaps this should not be a worry. I guess a different question might be, is there a relationship between the grate size and any other part of the boiler or steam system in general? Perhaps I am concerned about something that with this small modification, will not make any difference anyway.

[Glenn Brooks]

I am certainly no expert, but yes, I understand there is a direct relationship between grate size and cylinder size, and these are tied to type of fuel, and steam making capacity of the boiler. there are some interesting formulas in Meyer's 1896 Locmotive Construction, that enable builders to select the correct cylinder size, grate area, etc, including driver diameter and other things relating to delivery of steam. Unfortunately, I don't have a clue what reduction of 1/4" or so might mean for a 1" or 3/4" scale locomotive. you can probably overcome any slight loss of capacity by tweaking the draft in the smoke box or improving combustion capacity in the firebox. I talked to one master locomotive mechanic recently who dramatically increased his steaming capacity by reducing his firebox by 15% and concentrated same combustion in a smaller space - thereby increasing his heat generation by reducing cold air intake through his grates ( at the front end of the firebox). Now he always popping his values, sometimes whilst running. Perhaps some knowledgable 3/4" scale builders can advise further.

[Harold_V]

Thanks. I see your point clearly now. Fact is, if the boiler was not good at steaming, I expect any reduction of the grate area would contribute to the problem. You're wise to consider every possible issue.

Harold

[Builder01]

Hi Glenn,

Thank you for your comments. Very interesting indeed. I had a feeling there is some relation between these parts of a locomotive.

Decreasing the firebox, as in your example, is exactly opposite of what one would expect. But, after thinking about it, it does make sense. I hope others may have experienced comments or suggestions for my situation.

Thanks,
David

[Pontiacguy1]

I don't think it would hurt you at all power-wise to make the cylinders 1.500" instead of 1.563". In fact, It might be easier to come up with a set of iron steam service piston rings. This would reduce the piston area by approximately 8%, which is pretty close to your reduction in grate area (9%).

[Builder01]

Hi Pontiacguy,

Thanks for the input. I have posed the same question on another forum and have been given a similar suggestion. That is, to reduce the pistons to 1-1/2". Thanks for taking the time.

David

[Andy R]

Glenn Brooks wrote: "Perhaps some knowledgable 3/4" scale builders can advise further."
I have four locomotives that run on 3.5-in track with another under construction, so will masquerade as knowledgable and offer the folowing comments.

Glenn's suggestion "...improving combustion capacity in the firebox..." should be priority one. Add a combustion chamber. That will allow the hot gases to more completely burn and heat up the crownsheet where the heat is needed.

Second, Glenn's observation regarding "...reducing cold air intake through [the] grates... " should be effected by careful placement, rather than size, of the grates. Keep the cold air from flowing between the firebox wall and the first grate bar. You may also have to modify the ashpan to direct air toward the center of the grates.

Third, Place the grates low. You want to have a deep enough bed of coal to burn effectively but not so shallow that the coal blocks the lowest row of tubes.

Fourth, Design the firebox door to be closed tightly when not shoveling in coal. That cold air above the fire is not helpful. You want a lot of air flowing through the grates and coal bed, not above.

Fifth, Adjust the nozzle and stack dimensions. There is a tremendous amount of discussion on this bulletin board to provide guidance.

Now you can select the correct cylinder size.

Regards,
Andy

[Builder01]

Hi Andy,

Thanks so much for your comments.

Let me be clear, I am not designing a locomotive, I am modifying one. The locomotive in question is the "Super Simplex" designed by Martin Evans. As this is a British design, it was designed for 5" gauge track. I am going to build it to run on 4-3/4" track. One of the few things that will have to change is the bottom width of the fire box in order to get it to fit between the frames. This will squeeze the width of the grate by 1/4". The fire box itself will be left pretty much unchanged otherwise.

The question is, will this reduction of the grate width effect the performance of this locomotive significantly? Can I compensate in other ways?

It has been suggested to reduce the cylinder bore from 1-9/16" to 1-1/2".

All of the items you have mentioned are already designed and I will build them as drawn on the blueprints.

I do have a question for you though, and I hope this is not a dumb question. What is the "combustion chamber"? Is this the same thing as the firebox? Or, is this something else that can be added to an existing design?

Thanks,
David