Author Topic: Small Flash Single  (Read 10506 times)

Offline vtsteam

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Re: Small Flash Single
« Reply #45 on: December 07, 2022, 02:19:33 PM »
Thanks kindly, Ron!  :cheers:

I'm at the stage now where I'm trying to decide what to do next.....I could start on the crankshaft, but I think I need the piston and con rod done first so I can weigh them to figure out what the balance weight should be sized and shaped like. The con rod aluminum is on order, I don't think it probably should be cast -- though that would be much easiest for me to do. The ally I've ordered is a short cutoff of 2014 hex bar.

I could start on the crankcase back plate, but I want to incorporate the water pump gears in a housing there. Steel spur gears are on order. Not sure if I'm going to cast a housing, and if iron or aluminum. I'd like to have the gears in hand before deciding on the exact arrangement.

I could start on the piston, I have plenty of home cast iron stock, but the cylinder bore isn't at finished size yet. Been holding off on that until the other block work is done. I'd like to fit the piston to the bore, rather than the other way around.  Maybe I should finish the bore now, then I could start on the piston. Kinda look forward to that....

Wondering what the bore finish should be like for a flash steam engine of this type? Honed cross-hatched, like an IC engine? or polished with a lap?

I do know in either case I need big clearance, and planning on a dykes ring...

Steve

Offline vtsteam

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Re: Small Flash Single
« Reply #46 on: December 09, 2022, 05:59:11 PM »
I realized that to start making the piston, I should first hone the cylinder to get the final diameter, but to do that, I remembered, the uniflow ports ought to be milled so the honing could clean them up. So, we're two steps back. Time to mill ports. Hmmmm, how to do that......

I don't have a rotary table or dividing head for the mill. I do have a 5C collet spinner, but holding the rectangular crankcase in that and also hand rotating it while milling just didn't seem promising. Instead, I decided to try using the lathe.

I have my 4 jaw chuck presently mounted to my lathe's face plate, and it seemed well suited to holding the square crankcase.To get the lathe ready for for dividing, I first disconnected the drive belt and power, and then I taped a paper strip around the edge of the faceplate, slicing through the paper overlap with a razor blade to make an exact length strip.

Removing it, I divided the strip into 12 equal lengths using dividers, and then drew lines across with a square so I could index 6 equal ports and 6 equal solid lands, shorter by a tool width. I colored in the port spaces with black marker line so I would be less likely to make a mistake when cutting. Then with some removable contact adhesive, I re-attached the strip to the edge of the face plate. I made a pointer from a length of brazing rod which I sharpened to a point. I attached that to a magnetic gauge base post. This was my dividing rig.

For a mill, I used my small rotary grinder as a tool post attachment with a .125" rotary metal cutting bit. To test, I made very gradual cuts in order not to overstress this admittedly delicate makeshift. I turned the faceplate by hand to make the cut. Comfortable depth of cut worked out only to about .003"/pass, so it was going to be a looong way through the .250" cylinder wall thickness.

The carbide bit I'm using also isn't ideal for the purpose, intended for aluminum. But is doing the job. I just have to go slowly. I do have proper 1/8" endmills for cast iron ordered, and they may arrive today. Maybe at the slow rate I'm going, they will be here in time to get used!

« Last Edit: December 09, 2022, 08:22:55 PM by vtsteam »
Steve

Offline vtsteam

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Re: Small Flash Single
« Reply #47 on: December 09, 2022, 09:58:08 PM »
...Maybe at the slow rate I'm going, they will be here in time to get used!
In fact, yup they did. The new end mills let me cut at .010" depth per pass, making things go 3 times as fast! It was still about 100 passes to finish. But finish I did by dark.


Steve

Offline Admiral_dk

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Re: Small Flash Single
« Reply #48 on: December 10, 2022, 12:52:16 PM »
Great Ports - I'll say that you succeded very well with those  :ThumbsUp:    :cheers:

Per

Offline vtsteam

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Re: Small Flash Single
« Reply #49 on: December 10, 2022, 05:20:07 PM »
Thanks Per!

Now that I look at my engine in the metal, I think I ought to change a couple things. The first is a mistake I hadn't noticed before, which is that one screw hole is out of position -- I thought it was just camera distortion in the pic above, but when I looked at the block it was obvious. I don't know how I missed that before. :facepalm:  :facepalm2:

I think it's 0.1" off - I must have misread the coordinate when drilling. Darn! It's okay structurally, but it's going to bother me.

The other is I'd like to cut the exhaust space recess further down towards the main block. There's no reason it has to be tangent to those ports. And I think that space looks restrictive.

When I drew it, I was going by the examples of K.B.C's and Bob Kirtley's engines. But they have separate cylinders, and need to allow room for studs and nuts under a flange (see K.B.C' engine for sv OOYAH below). Since my engine is one piece, the exhaust expansion space can be deeper.

Also I think I was being too stingy with the depth of the groove for fitting the outer exhaust ring. No reason not to make that deeper, as well.

K.B.C's engine block:
Steve

Offline vtsteam

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Re: Small Flash Single
« Reply #50 on: December 10, 2022, 10:44:21 PM »
Exhaust space widened:

Steve

Offline Zephyrin

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Re: Small Flash Single
« Reply #51 on: December 11, 2022, 08:31:35 AM »
nice progress with the build...
this kind of very large port can catch piston rings during its stroke...it happened to me on a tiny 2 stroke of my design, which of course did not survive !

Offline vtsteam

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Re: Small Flash Single
« Reply #52 on: December 11, 2022, 03:30:16 PM »
Thanks Zephyrin.  :cheers:

Well we'll just have to see what happens. This engine is a close approximation of K.B.C's and Bob Kirtley's, so I have some hope that it won't self destruct, but it's a first for me, so it is a total experiment with no backing experience.

I wonder if the number of ports might have some bearing (pardon the pun) on it? This has 6, how many did yours have? Well maybe the number is unrelated, as the old Cox .049's had only two and they didn't catch.

What might make things even riskier is that these engines of this size typically have a 3 thou piston clearance, and Dykes rings right at the crown. They tend to press outwards on the upstroke. Seems like that's a combination that would catch if anything would.  :zap:

ps. Kirtley mentions pinning the ring gap in line with one of the port lands so it won't rotate. Could your ring gap have rotated into a port position?
« Last Edit: December 11, 2022, 03:37:30 PM by vtsteam »
Steve

Online Michael S.

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Re: Small Flash Single
« Reply #53 on: December 11, 2022, 06:22:23 PM »
There was a company in my town that built large stationary boiler steam engines and in the variant with two cylinders as a compound steam engine, the low-pressure cylinder was a direct current cylinder with the exhaust in the middle. As with you.
So that the ends of the piston rings do not jump into the doors and then break, screws were installed to prevent them from twisting.
The picture shows an example. Even with normal single-cylinder steam engines, they built the pistons with the locking screws. Maybe you can do it like this?

Michael

Offline vtsteam

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Re: Small Flash Single
« Reply #54 on: December 11, 2022, 07:01:00 PM »
Michael thanks for the interesting piston and ring idea. I think that might be more suitable for a larger engine, And some day I might build one, so I will remember that. This little one has only 1" bore. Kirtley used a pin on his engine. Also there will be only one ring on this engine.

My engine is modeled on K.B.C's and Kirtley's racing engines, which were featured here on this forum ten years ago, and in Model Engineer 33 years ago respectively. Kirtley at the time of the ME article had broken the 100 mph model steam racing hydroplane record. K.B.C did a great job photographing and describing his own engine for his 40 mph R/C sports boat: https://www.modelenginemaker.com/index.php?topic=2760.0.

I'm closely following their examples, in all the design elements, except for the solid CI block and cylinder. My version is not going into a racing boat. It's just an experimental stationary utility engine, and it will see much lower speeds and pressures.
Steve

Offline Admiral_dk

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Re: Small Flash Single
« Reply #55 on: December 11, 2022, 07:35:45 PM »
I'm pretty sure that the Cox Model Engines didn't use pistonrings - but that the piston where Lapped to the Cylinder ....

Every Two-Stroke above a certain cc size using Rings, have some kind of control pins that prevents the rings from turning (resulting in an end going 'Out the [Port] Window').

On the other hand - if the openings aren't vide enough (and have the right shape) it's not very likely that you will have any problems .... then again - safe and sorry are a few words that spring to mind  ;)

Per

Offline vtsteam

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Re: Small Flash Single
« Reply #56 on: December 11, 2022, 07:49:06 PM »
You're right Per, they didn't have rings.  :facepalm: I was thinking the corner of the crown itself catching. But I'm sure that wasn't a hard corner.

I'm wondering how, with a single Dykes ("L" shaped) ring, is that pin located in the ring gap? It must be at the bottom of the cylinder groove, in the lower leg of the ring.......  :thinking:

Also with a single Dykes ring, how is compression maintained across a ring gap? Isn't there leakage through that gap?

Steve

Offline vtsteam

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Re: Small Flash Single
« Reply #57 on: December 11, 2022, 08:05:28 PM »
Here are a couple of Dykes ring photos I've found. These seem to have a cutback in the lower leg -- which maybe is there to suit a pin -- other photos I've seen don't show that, though.

Also the second ring has a chamfered upper edge, which would seem to be less likely to catch on a port. But that would actually change exhaust timing in a Uniflow engine, I think......
Steve

Offline john mills

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Re: Small Flash Single
« Reply #58 on: December 11, 2022, 08:58:18 PM »
did that ring have another ring with a lip which fitted in that gap and the join on the other side so the gap is covered.
when i was machining rings mainly for processing compressors , i made every form you could think off  including ones  with steps with room for pins   one set that was made was in three pieces with steps and room to have pins.
a two piece ring that was made had a part sitting up which fitted in a gap on the second part covering the gap the gaps were on opposite
sides.
john

Offline vtsteam

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Re: Small Flash Single
« Reply #59 on: December 12, 2022, 03:18:49 AM »
John, thanks for that really interesting info  :cheers:
I'm afraid I don't know exactly how the pin and gap were done, as I haven't seen a photo or explanation. Kirtley's pin does seem to fit the bottom of the "L" as drawn in the ME article. He shows only a one piece ring. I think K.B.C did as well, but there are no pics of his piston with a ring in place.

I'm thinking now that the gap in the upper leg might close up at operating heat. The racing engines operate at very high temperature and an estimated 1500 psi and 15,000 rpm, and are designed to run at top speed only.

I might need to reduce the ring gap slightly (and maybe the piston clearance?) for a lower speed engine intended for 400 psi and lower operating temperatures in order to maintain compression. So it's going to be guess work for me.  :thinking:
Steve

 

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