My First Stationary Engine

I am taking a couple of weeks off the class 22, I need a machining fix I havnt done any work on the lathe or mill since before Christmas. I was going to make some tooling but then came across a number of online drawings for stationary engines.

I didnt want anything complex or long winded so looked for something simple and found a Julius de Waal drawing of the Muncaster Simple Oscillating Engine, which although quite simple I do like the look of it .

So I thought I would have a go and try and get it out of the material I have on the shelf, it will be 95% as per the drawing but maybe one or two cosmetic changes.

Having gone through the drawing I am ok with the detail but I have a question re the cylinder/piston. The cylinder is brass with a bore of 16mm (reamed) and the piston is 16mm close fit but what does close fit equate to with a piston/cylinder..? Also I dont have bronze for the piston, I was thinking brass..?

The piston has a 1.5mm O ring fitted into a 13.5mm diameter groove which leaves the ring protruding 0.25mm which seems a lot but will the ring compress enough to be ok..? Also there is no detail on the O ring material would it be silicone..?

Thanks Ron

Brass will work. The Muncaster engine published in ME even had an aluminium piston. Aluminium is often used for the piston in full size engines to reduce the mass. Heavy pistons cause the engines to rock as they move back and forward. Brass is OK in steam applications but will corrode (de zincify) when in water.

Paul

Are you sure the o-ring is 1.5 mm cross section? The nearest UK standard size would be 1.6 mm. Tubal Cain recommends (in his Model Engineer's Handbook) a groove width of 2.3 to 2.5 mm and depth of 1.18 to 1.25 mm. The width is greater than the ring cross section to allow for the compression of the ring. I would start at the tighter end of the tolerances, try it, and adjust to get a good feel for the fit. Yes, silicone is good.

Russell

Hi Russell

Looking at the drawing again the 1.5mm is actually the groove width with a depth of 1,25mm but there is no detail of the O ring size. Even if 1.5mm was available I can now see it would be too tight.

p.s. Looking on Ebay Silicone 1.5mm rings are listed but I wonder if they are actually 1.6mm..?

Thanks

Ron

Edited By Ron Laden on 23/01/2020 09:31:09

I've just used cotton kitchen string dredged in LM3 moly/graphite grease in some of my engines, when I couldn't get o-rings or nylon 66 to work smoothly. I also think brass will do fine unless you're expecting to run it for hundreds of hours at high temperature.

Edited By Mick B1 on 23/01/2020 10:05:56

That looks really good! I'm REALLY NOT looking for yet another project but that looks nice.

Please let us know how you get on with it Ron.

Brian

HI Ron,

Piston fits for team engines don't need to be airtight, as you usually use packing or an o-ring.

Personally I would bore the bore rather than ream it, then turn the piston down very slowly so that it passes through the bore without any binding, but don't panic if there's a thou or more clearance as long as it isn't 'rattling'.

With a small engine like this that won't be doing any work, aim for the piston (with ring) to be able to move pretty easily, as this will help slow running (especially on air) which is more important than getting maximum efficiency in a display model.

Neil

Thanks guys for the advice.

Neil, I did wonder about the reamed finish for the cylinder but it is what the drawing listed, I can quite easily bore it.

Ron

Ron' I'll work out the correct groove width and depth for you this evening, on site now

Thanks Jason, appreciated.

Ron

I thought a brass piston in a brass cylinder would cause galling ?

Hi Ron,

I made that engine but mine was to the original sizes in the Muncaster book.

J.D.W. has scaled it up.

I used cast iron throughout apart from a bronze main bearing, a bronze liner in the big end and a gun metal piston.

I have a Muncaster photo album which may be of interest

Geoff

Geoff, I had a look at your album some nice work there, did the engine run well..?

I also see that J.D.W has changed the design of the flywheel, assuming yours was as per the book.

Ron

Hi Ron,

Yes it ran ok. It's on youtube, search "mini muncaster oscillating engine"

No ring just a plain gun metal piston.

The flywheel is a stuart casting the smallest one they have 2 1/2" diameter used on the progress engine. The muncaster drawing was just a plain wheel.

I like stuart castings, they always machine really well, the 3" wheel may be around the right size for your engine?

Geoff

As geoff says you could get away without a ring and maybe just cut a couple of shallow oil grooves with a Vee pointed too, if it is good enough for all those Stuart 10 series and smaller engines it will be fine for this one and the reduced friction will also help with slow speed running on low pressures. Or cut the ring groove and run it without a ring for display and fit the ring if you ever want it to do light work.

I like to use aluminium pistons which again help with smoother running and as this engine has no counterbalance weight on the crank every bit of weight saved helps. Aluminium would work both grooved or with a ring 6082 will be OK.

Fit will be as per that video I posted the other day and hardly measurable but if I had to put a figure on it -0.01 to 0.02mm, a little more if running on steam rather than air.

I tend to use 2.4 cross section rings so for that size cylinder a 11.6mm ID x 2.4mm ring will work well. Groove 2.6mm wide and 2.3mm deep giving a diameter at the base of the groove of 11.4mm. I'd also suggest Viton as it is not sensative to oils.

Stuart 10 series flywheel would be fine and look nicer or you could make one like my Preston's oscillator.

Thanks Jason that is really helpful.

Think I will go with an aluminium piston and try a pair of shallow V oil grooves.

The drawing gives an option of either steel or aluminium for the flywheel as shown on the drawing, I was surprised as I thought it would be steel/cast iron and not aluminium or is alu easier to drive on a small engine.

Regarding running I am about to get a new airbrush which comes as a set with a compressor (reservoir type) which is rated up to 30 psi, I am hoping that will be ok for driving the engine.

Ron

Aluminium for any flywheel is a bit light unless the diameter is increased but it is easier to machine. I'd stick with steel or iron particularly as it is only single acting and the energy stored in the flywheel is what drives the non power stroke.

An alternative to the Stuart casting would be this one from the same guy that does the one I used on my Muncaster

Thanks Jason,

Assuming the Stuart castings are like their pictures they do look to be nice castings though the one you linked is a good shape and a bit different. I may even have a go at making my own but we will see.

Ron

Hi Geoff

Watched your video it did run well, well done.

Did you make your cylinder as a one piece, the J.D.W drawing shows it as a one piece in brass but must admit I havnt quite got my head around how to make that yet, I was thinking of possibly 2 parts.

Ron.

You could cut it from a single piece of 35mm dia or use 32mm dia and solder the valve block to it or if you want to keep the swarf down then make with a soldered on top flange too then you only need 7/8" stock for the cylinder.

The original muncaster drawing shows the end cap soldered on which makes it easier to bore straight through, though loctite would do.