A couple of engines for GreenTwin

[Jasonb]

I know Greentwin has said he does not like making small engines and when I saw these yesterday on the Stuart stand I thought of him, start saving now💲💲💲💲 About a 14" flywheel

Also a double size Otto on another stand

 

[GreenTwin]

LOL, das what i'm talkin about !!
Big ole working-class engines, and you can get a free workout carrying them into the show, without even going to the gym.

I really like the larger models, and the machining work is so much more forgiving.
When I try to machine tiny parts, it seems like I can blink and ruin a part.

The advent of the larger format 3D printers like the Prusa XL is helping a lot with these grand-scale engines.

Very nice engines indeed !

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[Jasonb]

I thought the opposite. Simply scaling up the very basic 10 V & H designs does not really work you end up with a chunky and clumsy engine. For example they still have the "extruded" profile bearings and simple one piece eccentric strap. At the very least on an engine of that size you want split bearings and a split eccentric with more than the end of a screw running in a slot to locate it sideways. Modern BZP nuts don't do it any favors either.

In this case big is not beautiful, at least in my eyes

 

[GreenTwin]

Myers had some nice sized engines and castings at the 2019 NAMES show.
Some significantly larger than I would attempt, but most impressive castings.

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[GreenTwin]

I thought the opposite. Simply scaling up the very basic 10 V & H designs does not really work you end up with a chunky and clumsy engine. For example they still have the "extruded" profile bearings and simple one piece eccentric strap. At the very least on an engine of that size you want split bearings and a split eccentric with more than the end of a screw running in a slot to locate it sideways. Modern BZP nuts don't do it any favors either.

In this case big is not beautiful, at least in my eyes

They took a few shortcuts, but I will forgive them, since they made the effort, and made the engines.
3D printing of patterns could easily add the find detail back into their design.

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[GreenTwin]

I like machining hardware (nuts and bolts) that are large enough to easily see and feel, like this one.

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[GreenTwin]

You can get into some pretty chunky risers when making larger castings.
A large enough casting could require either a large crucible, or a double-pour.
Quite a bit of metal is required in addition to the casting itself.

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[Jasonb]

The difference is that the large Myers offerings look right. That is due to them having been scaled down from real full size engines. The Stuarts have been scaled up from small freelance engines were originally designed for ease of casting and machining.

I'm almost certain those large Stuarts were from 3D printed patterns. It is not the type of pattern that will "easily add back detail". That stems from whoever is doing the enlarging be it with pen, paper and wood or a Cad package then 3D printing etc

A double size Stuart No1 would have come out around the same size and not looked so bad but I suppose saying it is a 5 times No10 sounds more impressive than a 2 times No1

Given the basic bed, frame, cylinder and valve chest castings a sympathetic build could be done that looked a lot more appropriate for the size of castings.

 

[GreenTwin]

With 3D modeling and 3D printing, there is no reason to lose any detail, from say scaling down the O-S shown below.
It is not very hard to just model it exactly like it is built.

In this day and age, I am excited to see anyone doing any type of modeling.

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[minh-thanh]

you end up with a chunky and clumsy engine.

I quite agree.
For me, a model engine needs to be relatively easy to move, I can take it anywhere, I can put it on shelves, cabinets, tables... I see quite a few engines from 1 to V12... they are quite small and I can lift it with just one arm
A cylinder diameter of about 25 mm is fine (30 mm is also not a problem) but if it is smaller, it is more interesting, because it is a model engine
Why ???, Because the purpose of a model engine is: to reduce the size of the engine
If someone only makes one for himself, how big or how small is not important to me
But if to cast few sets at the same time and sell few castings with each set weighing a few dozen kg, 30, 50, 70 kg... then it will be a problem for him.

 

[GreenTwin]

The large format model engines make for an eye-catching display at a show, and I think that is part of the purpose of displaying them; to draw attention to the booth, and sell more reasonably sized kits.
You can see a large-format engine all the way across the room/arena.

And if you don't have a gym membership, then you can just power lift your engines, and save a lot of monthly fees.
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[Jasonb]

Well if you have seen the guy who owns Bridport (Stuarts) then he would be quite happy to tuck one of those large ones under each arm and not break into a sweat!

The other downside of big engines for many is the size of machines needed. I had quite a long chat with one of the other supplier who had the double size Otto 3D print. he said he had just cast and built four of them as a special order but the main downside of putting it out as a kit was the 16" flywheel and very few would have the machines to handle that or the main large casting as shown in the earler photo. He was OK as he has a faceplate lathe that can swing 54" dia.

This is why most kits tend to be smaller, in the UK a 9" flywheel is quite common a sit will fit in the gap of the popular Myford lathes. Similar sizes or a bit bigger in the US to fit Atlas etc lathes

And the final killer is cost, double the size of an engine and the cost goes up by the cube so 8 times as much for raw material. Though buying barstock is often considerably cheaper than buying kits. Homecasting probably similar.

 

[GreenTwin]

Machining flywheels larger than 12" diameter is a problem for me.
I am planning on farming out the 14" flywheel for the 1/2 scale Ball Hopper Monitor, and I know someone who can do it.

I have not totally ruled out machining a 14" flywheel on my mill, using a tool-and-die grinder with some sort of bit in it, assuming I can take very light cuts, and the flywheel is cast close to net, and so is almost at its final size before machining (with bound sand, I can make near-net castings).

I have seen some line-boring machines for boring large equipment, and have considered adapting that for oversized boring/machining.

While casting grand scale parts is more expensive, from the standpoint of 3D printing, bound sand usage, metal usage, cruible size, etc., I have invested in 3D printing and foundry equipment to accommodate some larger castings, or for making multiple small castings.

There are many downsides to building grand-scale model engines, and this discourages most from attempting them.

The upsides to building grand scale engines is the potential to use them to power things on a fractional horsepower level, so they are working engines, and not just model engines (ie: think the Cretors line of steam engines that powered peanut and popcorn roasters, and were built with babbitt bearings for long life).
And if you walk into an engine show with a 1/2 scale Ball Hopper monitor, or other grand scale engine, chances are you are not going to see another engine like it, at least not at that size.
I don't necessarily want to build an engine that is just like multiple other engines at the same show; I like unique and differently sized engines.

And I like to try things that nobody has tried before, because .......... why not ?
Sort of like climbing Everest; how do you know what you really are capable of achieving if you don't attempt some difficult things.

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