Another steam engine shaped object

[Steamchick]

My text book on balancing is Steam locomotive design data and formulae, by E. A. Phillipson, dated 1936. A new copy available from Camden Miniature Steam Services.
Pages 290 onwards...
Other books, (my Dad's and Grandfather's) are out of print.
K2

 

[Larry G.]

Hi Larry, there is a comprehensive thread on the subject of Balancing Engines by Jorgensen Steam, in the HMEM Break Room, from 2011, elsewhere on this site, so look that one up and see if it covers your query?
I'll try and help properly tomorrow.
K2

I'm off to the Archives!

Thanks

 

[Bentwings]

Hi Doug. I'll be interested to know how you set the valve port sizes and slide valve dimensions. As you'll be aware, lap on valves is quite a critical bit of the design of the engine. I am making a steam pump and the valve timing is adjustable, to compensate for (MY) inaccuracies of machining. But you don't appear to have any adjustment if a port or valve slide is a few thou "off"? I don't want to suggest your machining is as bad as mine, but I have only built engines with some adjustment in the valve train, to tune to balance (centre) the valve when I get to the running stage. That way I do get very smooth and slow running engines, without an odd "kick" or stall at the end of one stroke...
Also, what material are you using in the glands? I always used graphited string, and have put 1 or 2 turns of PTFE tape on the shaft first, but my latest uses silicon O-rings... which I am sure will seal, but hope they will slide smoothly, and not bind. I may be tempted to apply a layer of PTFE tape to reduce friction for when I tighten the glands "just enough" to stop steam leaks.
It looks really good anyway! - Looking forward to seeing it run and make some power!
K2

As far as acting what you did is what I did toot works untill the packing nut gets bottomed out. My shaft happens to be 3 mm so I purchased some Teflon tubing used in 3 d printers that has a 3mm inside diameter I just count an o ring out of this then let the packing gland form it you can make what ever size you need Teflon o rings are a bit hard to find this small but the tubing works fine on compresee air hot steam will probably be even better as it will compress just a little.

I also discovered the need for adjustment in the piston port valves . I just establish top dead center of the piston then set the piston valve some distance down its bore. So it it just barely opens the port to provide the cushion . This can be quite critical as my holes for gas flow are pretty small and you really can’t see where the pist is . I just set it so the enginge runs smoothly . I record the settings then make minor changes and record results . Monitor rpm at given pressures steam could radically change this but I have not tried this yet. I use a split shaft collar that grips both the hub of the eccentric and the crank shaft so it’s relatively easy to adjust . When. Make new eccentrics I’ll incorporate the split collar into the piston valve connecting rod hub so it easier yet to adjust

 

[DJoksch]

I have been loosely following a tandem project at “https://glasgowengineering.com.au/history/steam-engine-restoration” for artistic ideas to soften the bar stock look. He run into problems with balance and added counter weights to the crankshaft. I have been looking up articles but thought I would get it running to see what I am up against.

 

[Steamchick]

Hi Doug,
When you have created the "valve diagram" - as per the explanation, it will be good to see it as a "worked example". I drew one in the dim and distant past for a piston valve (central admission) Stuart SUN engine, but have lost that in the depths of 20-odd years...
I must draw the diagram for the steam pump I am making. (I don't think it considers lap!). I am curious, because the steam pump has a simple link between the piston rod and valve rod, not a crank and eccentric. Therefore there is no lead (advance) on the primary valve. To make the main valve operate, the primary valve has to supply steam to a slave piston valve, that drives the main slide valve. I'll try and make a drawing, as the machining drawings do not do it justice. Ooooh! I feel an Excel spreadsheet coming on.... (my stupid brain!).
K2

 

[Steamchick]

Hi Again Doug,
My experience for silver soldering.
A really nice silver solder for flow and building-up beads is the 55% solder. But to have a couple of different solders for different parts of the assembly I also have stock of 2 others. That way I can make first sub-assemblies in the "hotter grade", build them into "second level" assemblies with the "middle temperature grade" and final assembly with the "coolest" grade.
A quote from a welder: "The most widely used silver solder melting points are 1328° Fahrenheit at 33 percent silver volume, 1247° Fahrenheit at 40 percent silver content, and 1202° Fahrenheit at 55 percent " - I have used Johnson Matthey silver solders if I want something "special",
Silver-flo-filler-metals - matthey.com
(I ordered some "flux-less" silver solder for a Works job for joining wires once - contains Phosphorus - Not the best for a boiler, but good for gas fittings.). But generally, the "cheapest" market quality 55% is OK for most of my final assembly work, and regular "cheapest" is a 33%~35% grade. I guess you'll get ASTM grades in Yuba?

In theory, you should only use certified material for Boiler-work. Talk to your BOILER TESTER/INSPECTOR, in case he wants to know what solder grades you are using, and he may want to see prepared but unassembled parts, and drawings for the boiler. I have never needed to present calculations to the Boiler Tester (they just do a visual exam to be sure all joints look OK, before doing the pressure testing), but (now) always do those FIRST, as it is easier to increase a material thickness or change a design before making anything! But I have had to De-Rate some boilers (even one I designed and made) following a more comprehensive study of ASME, some university papers and "industrial practice" papers. But your Yarrow is relatively simple and we have already discussed sizes and strengths of tubes.
There is a curious effect when silver soldering: (A metallurgist should be able to explain?). When the pool of silver solder is molten, some of the adjacent copper diffuses into the solder, changing the metal composition, so it moves to a different place of the "liquidus" curve, and later needs a higher temperature to melt the joint. Too much heat (prolonged or too high?) can increase this diffusion, but what it does for joint strength I cannot say.
Cheers!
K2

 

[Bentwings]

I have been loosely following a tandem project at “https://glasgowengineering.com.au/history/steam-engine-restoration” for artistic ideas to soften the bar stock look. He run into problems with balance and added counter weights to the crankshaft. I have been looking up articles but thought I would get it running to see what I am up against.

I’d suggest reading articles on automotive crank balancing. There are ways to come up with what is at called bob weights which are based on some percentage of parts that rotate and those that swing like connecting rods the weighs are then added to the crank and it is balanced as an assembly . It’s been a long time since I was in the automotive machine shop it’s something like all of the rotating weight and some percentage of reciprocating weight . It’s quite involved if you have many cylinders and connecting rods . The balancing machine itself is complex.

 

[DJoksch]

Thanks. I’m still at the deciding how to do the counter weight calculations for weights. I knew I had to address this and I am at the point where it will be an issue. I will ask about the silver solder to make sure I’m following the requirement. I’m hoping to run it on air next week.

 

[Steamchick]

Doug, an easy way to balance primary....
Set the engine so the piston rods are vertical. Set the engine at half stroke. If "no friction" the imbalance will cause pistons to drop. Add some weight opposite to the crank pin, until it is almost balanced.
Then set the engine on the bench and run slowly.
The primary balance weights will then cause a secondary imbalance, partly negated with the weight of con-rods plus big end, as when at TDC, The balance weight will drop that side of the flywheel, but at BDC will have to raise the balance weight. Watch study and work it out. For slow running, the secondary imbalance is not significant. You'll see when it runs. You can reduce the balance weight by 1/3rd to get a good compromise.
Enjoy the balancing act!

K2

 

[DJoksch]

Just made a temporary steam inlet pipe and am about ready for a test run. I acquired this little mechanical oiler and was planing to use it, but it seems to just crank to its limit and binds. Unless I’m missing something, you have to stop the engine, load more oil, then manually crank to its upper limit and start over or risk damage.

 

[Steamchick]

No idea about your oiler, but it does look to have a simple displacement oiler in the pipe-line... So maybe you can just use that? Usually quite adequate for models.
I use them as intended for steam, or inverted (reservoir above the line) for running on air. But you must also use the appropriate lube, depending on steam or air: Proprietary steam oil, of Air-tool oil, are my options. Hope my 1-minute sketch helps?

K2

 

[Steamchick]

Awaiting the first run with bated breath....
K2

 

[DJoksch]

Update: Finishing up the base. I decided on a planked floor. I saw a similar floor with same sized planks. I didn’t like the even pattered result so I cut random sizes and thicknesses then picked and matched at random. While I’m varnishing, I’ll mill the sides of the cylinders so I can clad them. That leaves the split main bearing modification and the cross slide.

 

[Steamchick]

Beautiful! I used thick "planks" of balsa wood on boilers for insulation. Very effective! But on the (plywood) deck of a boat I cheated. Instead of planking, used 2mm thick 3-ply, with drawn planks (random lengths) using a fine ball pen (pencil did not work for me). When varnished it looked real enough.
I like your proper job!
K2

 

[Steamchick]

Doug, do you want a design for a ceramic gas burner to suit this boiler? If so, send me sizes and I'll do you a design. I'll probably need to have the enclosure sizes as well. (I once made a burner to someone's sizes, but it didn't fit the access hole). Needs >1/2" clearance between the bottom of the lowest tube and the ceramic.
K2

 

[DJoksch]

That would be terrific. I will get that to you. I’m on my Summer beak after tomorrow which will speed up the engine and boiler project.

 

[Steamchick]

I am retired, so every day is a beak!
K2

 

[DJoksch]

Work definitely gets in the way. I keep getting asked to teach Summer classes. I respond by saying if I wanted to work year around, I would have stayed at Lockheed. This is a sketch of the boiler. I also have a 5-1/4 X 3-5/8” piece of ceramic I did not use on the last burner project. I was not sure if this would work. The overall size of the engine and boiler still fits on my glass to backyard table.

 

[Steamchick]

Work definitely gets in the way. I keep getting asked to teach Summer classes. I respond by saying if I wanted to work year around, I would have stayed at Lockheed. This is a sketch of the boiler. I also have a 5-1/4 X 3-5/8” piece of ceramic I did not use on the last burner project. I was not sure if this would work. The overall size of the engine and boiler still fits on my glass to backyard table.

Excellent Doug. If you want to stick to the single ceramic, it should be rated around 2kW. (I'll check properly later). But if you want to fully exploit the full capacity of the boiler's steaming ability, I suggest a burner about 7" long and 4" wide between the 2 bottom tanks. You could even go full width of the bottom tanks if you wanted to mount a burner beneath those?
The fun is working out how to join panels of ceramic to the size you want. I join them with firebrick cement, and cut to size using a fine hacksaw, or junior hacksaw on smaller burners. But you need to fully support the ceramic on a flat board, up against a bench stop, when cutting. Follow the holes so the swarf (dust) drops through. Gently and carefully cut with long smooth strokes and very little down pressure. I'll send picture of a similar large burner I made - using an appropriately sized biscuit (cookey) tin.
Cheers,
K2

 

[Steamchick]

Hi Doug. Now on my proper PC...
This picture shows a large burner, made from 2 ceramic slabs. It is about 5" x 7 1/2". Using a 0.022" jet, in a 16mm ID mixer tube, with Propane gas at around 15psi (It would take 20psi but was roaring! - I suspect too hot and the ceramic could fail after >10 mins.). Note the zoning, due to some weird pressure variations beneath the ceramic. Hardly perceived "By eye" - by the camera is more sensitive and clearly shows the non-uniformity of the combustion, which could lead to differential expansion and early life failures. I should do a better job next time! (The mixer tube needed more tuning!). The diagonal line was a stainless steel wire support beneath the ceramics.

This fitted beneath a 9" diameter vertical boiler:
as seen in
The International Toy and Model Steam Hospital

Gas jet was providing gas for over 7kW of heating.
I estimate that you could use a 7" x 7" square burner, which should manage about kw: using a No 72 or 71 jet (0.65mm or 0.025" or 0.026" diameter hole) to give around 9kW of heating. The mixing tube should probably be 19mm - you may get away with 16mm? The air holes should be 3 off x about 12mm diam. - maybe as big as 14mm? (Start smaller!). You'll need about 140mm from air-hole to end of mixer tube: - I'll have to sit down later and design a diffuser tube, as I can't do that "off-the cuff". I'll do some drawings later as well, with a "proper" set of sizes.
Hope this gives you an idea about the largest burner you could have to fire that boiler?
When you design the enclosure, please consider how the heat can radiate from the burner - e.g. between gaps in the water tubes - and arrange that the inside surface is shiny (stainless steel?) to reflect the heat back onto copper tubing. Very effective! I have incorporated internal reflectors in fireboxes on some boilers to improve efficiency (reduce lost-heat that only heats the casing!).
Cheers!
K2