Stuart S50

[WolfieParticipant @wolfie]

OK chaps managed to take some pics tonight. Here is my workshop. As you can see its restricted to a bench with a few bits on and a radio permanently tuned to Planet Rock.

 

The cardboard box at left is my spray booth for my other modelling hobby.

 

 

And my baby lathe, isn’t she cute (not)

 OK my steam engine to date… rear cylinder cover. I have turned the inner part of the inside of it 15 thou too far (radius-wise). Is this likely to be a problem?

 

 

And the rest of it, piston, piston rod and gland thing. Piston rod is 3/32″ too short but I really don’t want to make another one (I’ll have to make a piston too and I’m running out of brass),  is this likely to be crucial??

 

And finally…… my piece of cast iron chuck key for scale

 

 

 

 

 

 

 

[John OlsenParticipant @johnolsen79199]

Hi Wolfie,

 

The slightly smaller register on the cover is not likely to be a very big deal. When you eventually fit it to the cylinder, you will spot through the holes in the cover to start the tapped holes in the cylinder. At that point you can make sure it is lined up nicely on the outside.

 

Speaking of drilling the holes, I don’t suppose you have any dividing equipment as such? If you have access to a good printer and a drawing program you can make a template. Print the template out full size, and you can use it to mark out the holes quite accurately. The best way is to turn a metal template with the register the same as the cover on one side and the cylinder on the other. The holes are drilled through the template in tapping size, and it is used to guide the drill on each part in turn. Another way is to drill the cover, but in tapping size only. Use that to set out the tapping size holes in the cylinder, then enlarge the ones in the cover to a clearance size for the screws. With the second way any mistakes are made on the actual cover….

 

(There are some good free drafting programs available, there is a thread about this on here. An inkjet, or better, a laser printer will give accuracy to about 3 thou or so. )

 

OK, piston rod length. The important thing here is that the piston must not hit either cover at the end of its stroke. There is usually a bit of room for adjustment here, the rod will screw into the crosshead, often with a lock nut. If there is enough length engaged when you have set the piston to clear about equally at each end of the stroke it will be fine. Usually you want a length about equal to the diameter engaged in the crosshead.

 

By the way, it is usually a good idea to make the bore before making the piston, as it is easier to make a piston to fit a bore than it is to make a bore to fit a piston.

 

regards

John

 

[WolfieParticipant @wolfie]

Register?? Whats that?

 

Actually theres a tutorial in the ME mag this last few fortnights making a Stuart engine and they make a steel template with which they drill all cylinder holes at one time

 

Yeah I know I’ve started in an odd spot but I’m restricted to what materials I have handy etc. Can’t afford to buy anything new yet (got made redundant, mkes life difficult).

 

I did look to see if I could buy just the cylinder casting from Stuart and its about £10 so might go for that

[WearyParticipant @weary]

Wolfie,

Don’t know if you are aware of this, but on ‘you tube’  there is a complete series of videos showing construction of an oscilating steam engine to one of Tubal Cain’s designs.

Whilst this is a different engine to the one that you are building many of the procedures are similar. 

Part II deals with machining the cylinder and end-cover (only one in this case of course).

 

If you want to take a look just go to youtube, and search  ‘Building a model steam engine’, or some similar combination of terms. 

 

You will see that there are also quite a few ‘show and tell’ videos of various kinds listed on the side-bar of similar and related vids.

 

There are also videos of dial gauges etc. being used and set-up if you search ‘dial gauges’; though I don’t think that there is anything on that particular topic that answers your questions directly. 

 

Regards, 

Phil

[WolfieParticipant @wolfie]

I wasn’t aware of that but will go look at it. Thanks!

[John OlsenParticipant @johnolsen79199]

A “register” is anything on one part that sticks out so that it can engage with a recess on another part. So the cover has a shallow part that sticks out and engages with the bore, thus locating the cover nicely on the end. This will be more important on the end with the  gland, since you want the bore, the gland, and the crosshead to all nicely line up with each other. But even there, it is possible to get it all to the right position and then nip up the screws. (Perfectionists are free to wince here if they wish.)

One thing you want to be doing is keeping an eye open around the place for bits and pieces of suitable metal. You will need to learn what you can and can’t easily use. Some bits of stuff are hardened and so not so useful. Any brass or bronze you can lay your hands on should be grabbed and treasured. 

Yes, Harold Halls series should be quite useful to you. There are some good ideas there for templates. It is always better to waste time making a template out of cheap material than waste more by spoiling a good part.

Buying the cylinder could be a good  plan, also maybe eventually the flywheel since it is quite hard to make a really nice looking flywheel out of solid material.

regards

John

[WolfieParticipant @wolfie]

Getting on a bit. I bought the cylinder casting (and also the flywheel while I was at it).

 

Its much smaller than I thought it would be, looks like it could be difficult to hold for machining?

 

If you can find the (free) Dockstadter valve gear program and load it on
your machine, you can see live animations of how this all works

 

I downloaded this, looks handy. However I don’t know what my particular valve gear is called??

 

Have made a start on the flywheel. Found it very difficult to get true in chuck. Eventually got more or less true enough to drill although its not perfect. I plan to mount it on a spindle and bolt it on to machine the outside rim.

[John OlsenParticipant @johnolsen79199]

Hi Wolfie,

 

I don’t know if Harold Hall has covered the flywheel or cylinder  yet, but it could be worth checking that series for some ideas.

 

I would usually hold the flywheel in the for jaw chuck, setting it up for the best compromise. You want both the boss and the inside of the rim to be running as true as possible. Since the casting may not be absolutely true, you may have to compromise. That lets you then turn one side of the boss, bore the hole, and turn one side of the rim. Then I would turn it around, mount on the faceplate and clamp through the spoke holes. take care not to put too much pressure on the spokes. Use a piece of plywood to space out from the faceplate and set it true by the bore hole. (using that dial gauge) Now you can turn the other face of the boss, the other edge of the rim, and the rim itself.

 

The cylinder may need some work with a file so that the faces are flat enough to sit nicely against the chuck. Small ones can usually be held OK in the four jaw chuck. One point is to do the bore and the face that will be the bottom cover at the same setting. this is so that face is square to the bore, so that when you put the cover on with the gland it will all be lined up nicely .

 

Your gear will be a single eccentric with no reversing .  None of the setups that Dockstadter shows (in the copy I have anyway) are a match for that since they are all reversing gears. If you look at the STEP_OUT file and set the gear in either full forward or full reverse, what you will see is pretty much what you would get with a single eccentric gear. There is a little icon about the middle of the row which looks like a pipe with steam coming out, this will turn on a display of steam, red for boiler pressure, purple as it expands, and blue for exhaust.

 

regards

John

[Sub MandrelParticipant @submandrel]

I think the S50 has Stephenson valve gear (Yes the same Stephenson as in The Rocket)

 

Neil

[WolfieParticipant @wolfie]

I held the flywheel by its boss. Its difficult when all the surfaces are rough, to start anywhere. Like I said, I drilled the hole first and will try it that way.

 

Whats a faceplate?

[John OlsenParticipant @johnolsen79199]

The S 50 is a horizontal mill engine, it will only have a single eccentric. http://www.stuartmodels.com/inprod_det.cfm/section/casting/mod_id/17

Mill engines were intended for driving factory machines, and as such were very rarely if ever fitted with reverse.  (If I say never someone will come up with an example.)

 

OK, a faceplate is a flat plate with some slots in it that screws or mounts onto the spindle of the lathe. It is a way of holding jobs that are too big or are the wrong shape to easily fit into a chuck. Since it is flat, it does need one side of the job to be at least moderately flat, and it can be a challenge to find ways of clamping the job to it so that the screws don’t get in the way.

 

if you don’t have one, it is something to consider possibly making or buying at some point. Making one can be a bit tricky since ideally you would want to attach the blank to the faceplate to turn it, and since the reason you were making one is because you didn’t have one….

 

in some of the smaller lathes, you will get a drive plate, eg the Unimat provides a little aluminium plate that screws on the mandrel and has three slots in it. This  is intended as a  way to drive a drive dog, which is used when turning between centres. It can be uss a faceplate for light work, but that lathe actually has a much better cast iron T-slotted faceplate available as well.

 

Anyway, so long as the hole you have made is reasonably true to the rest of the casting, all should be well. So next step is to turn a mandrel to fit the hole on a piece of bar held firmly in the chuck, with a thread on the end (which can be cut with a die) and mount the flywheel on that. You will only be able to take quite light cuts, since it may try to turn on the mandrel. You can use loctite to help too.  If you made your mandrel out of a fairly large diameter piece of bar, you could consider tapping it near the edge for a screw that would engage with one of the spokes to provide a positive drive. The Stuart cast iron is generally excellent, but it is not unknown with any cast iron to find hard patches on the surface. They will usually not be deep, so if you are having trouble, you can consider a little careful grinding to take the skin off the offending patch. Carbide tools are of course good for this job, if you have them.

 

I should stop thinking of possible problems that p[roably won’t happen and let you get on with it.

 

regards

John

 

 

[WolfieParticipant @wolfie]

I watched some of that Tubal Cain video last night where he breaks ot the cylinder cast and faces it and the cylinder covers. I am surprised at how little he seems to worry about accuracy, theres me trying to get it down to the last ten thou….

 

I got some of that glue too. I was advised to get ‘603’, but the best i could find was ‘601’ is there any difference??

Edited By Wolfie on 05/11/2010 09:07:42

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Wolfie, I assume you are talking about Loctite 603, which is an improved 601. I doubt that you will notice much difference. You can get all thier technical info from thier website http://www.loctite.co.uk

 

Regards Nick.

[WolfieParticipant @wolfie]

HELLPP Whats with this flywheel. Its destroying my lathe tools!!!!

[Sub MandrelParticipant @submandrel]

Possibly chill spots on the outside, they can be glass hard.

 

Invest in a cheap set of tungsten carbide tools – I have a pretty basic set and mainly use them for breaking the skin of tough spots on castings.

 

 

Stuart have a reputation for good castings without chill spots (though all four corners of the valve face of my 10V were chilled as was the outsiode of the flywheel), they may change the flywheel if it’s really bad.

 

Neil

[John OlsenParticipant @johnolsen79199]

While I would agree that Stuart do very good castings, I would not agree that they are always without chill spots. However, we also have to remember that Stuart spans a very long period of time, and the ones I have had that were questionable would all be from a long time ago, so should not reflect on current production. They have  had a bit of a habit of providing parts that were pretty well at nominal size even before cleaning up…commendably accurate casting but a little bit of machining allowance is always good to have! I think 10V valve chests may at one stage have been a problem for them, I have seen more than one with a blowhole in the area where teh gland boss meets the chest. They do swap faulty castings I beleive, but from 12,000 miles away it is easier to make another from a piece of bar stock.

 

Where I have seen chill on Stuart castings, it has never been very deep. So a careful sesson on the grinder, taking the surface only from the hard spots will generally get you through it to where the ordinary HSS will cope.  Otherwise as suggested by Neil, a carbide tool may be your best bet.

 

Chilled spots show up when you are turning as having a silvery appearance compared to the rest of the iron, which should be grey. (Hence “grey cast iron” in specifications)

 

Accuracy… well, it is good to try to work to close tolerances, it is good practice for when you really need to. But mostly these parts want to fit each other nicely, they do not need to be a precise size as such. So if the bore comes out a bit bigger than intended, you just make a piston to suit and so on.  This is not how it is (or should be) done in industry, but will be fine for a steam engine.

 

regards

john

[WolfieParticipant @wolfie]

Heres a pic but its not the best. Part of the problem is that the cross slide won't go under the bottom rim of the wheel. So I'm restricted as to what angles of attack I have.

 

Edited By Wolfie on 07/11/2010 10:56:22

Edited By Katy Purvis on 01/06/2015 12:07:57

[TerrydParticipant @terryd72465]

Posted by Wolfie on 25/10/2010 22:32:17:

Thats a superb tutorial. I just wish I understood all of it.

How you get the milling cutters to the thing while its in the lathe chuck?

 Hi Wolfie,

 

The metal isn’t in the lathe chuck on the lathe, the chuck is fitted to a rotary table which in turn is mounted vertically on to the milling table.  This allows the work to be rotated under the milling cutter which allows cylindrical forms to be produced on the miller.

 

Hope that clarifies it a bit,

 

By the way, I find that a traditional straight handled hacksaw ( a bit like a file handle) is easier to use and more efficient than one with the modern pistol grip which I had used for most of my working life, it’s never too late to learn, just keep an open mind,

 

Regards

Terry

[Anonymous]

Hi Wolfie,

 

One thing to consider vis-a-vis machining the flywheel is turning speed. I’m not familiar with the Stuart flywheel, but I assume it’s between 3 and 4 inches in diameter?

 

For a soft, as cast,  grey cast iron Machinery’s handbook gives a cutting speed of 90 feet per minute with a HSS tool. If the flywheel is between 3 and 4 inches, then the circumference will be about a foot. So, you need to be revolving the flywheel at 90rpm. Given that the casting might have hard spots, and taking into account a smaller style lathe, a bit slower than 90rpm might be appropriate.

 

Regards,

 

Andrew

[WearyParticipant @weary]

Go to approx. 1min 40 secs and 4 mins on this youtube vid’ and it will show how another guy held the cutting tool (and style of tool – like a ‘reversed’ boring tool) when turning a flywheel that would not fit under his ‘slide.

You also get a good visual idea of the rotational speed that he is using on alloy & subsequently steel..

You can also see a ‘backplate’ made from ply.

 

(The flywheel is significantly larger than yours, and he has adopted a few other ‘tricks’, but the general principles may be of use to you)

 

Regards, etc., Phil

[WolfieParticipant @wolfie]

“a bit slower than 90rpm might be appropriate”

 

Hmmm this might explain quite a lot

I thought cast iron was one of the softer metals which is why someone thought of adding chrome to it?

[Sub MandrelParticipant @submandrel]

The bright steely cleam of your flywheel rim does look suspiciously like ‘white’ chilled cast iron. If so, the little dappled patches of a grey colour are where you have got beneath teh chilled layer.

 

Neil.

[Anonymous]

Hi Wolfie,

 

Correct, some, but by no means all, cast irons are soft. But then again copper is soft, but the recommended cutting speeds are only just above cast iron. The best advice for machining copper is to get somebody else to do it. It’s ‘orrible!

 

Once you get your book on hardening and tempering you’ll be able to read all about the complex chemistry of iron and carbon, and why cast iron can have hard spots.

 

If you don’t have one, I’d also recommend getting a copy of ‘Machinery’s Handbook’. Don’t buy new, a secondhand one from decades ago is just as useful to model engineer.

 

Regards,

 

Andrew

[John OlsenParticipant @johnolsen79199]

Apart from the chilled spots, iron that is cast in a sand mould will tend to have a bit of sand fused into the surface.So the surface is harder than the bulk metal. So where the machine and the method of holding the work is up to it, it is actually good to make the first cut a reasonably generous one to get under the skin. On small machines this is not always possible.

 

Even though cast iron is generally soft, the cutting speed does not want to be too high. The cutting speed is mostly what determines the peak temperature at the cutting tip. Above a maximum, even high speed steel will go soft and blunt easily. I experimented with this once with a large bore that needed a fair amount of material taken out on my Myford…it was a three inch bore five inches long for my compound launch engine.  There is a temptation to try to go faster to get the job done quicker, but there is a certain point above which the edge of the tool goes very quickly. If I went at the right speed the tool would last for many passes through the job, but if I went half as fast again it would not last through one cut.

 

For the situation you show, you need the opposite hand of turning tool. Put it in the tool post so that it is along the axis of the lathe and overhang the side of the cross slide so that it can reach along face of the flywheel. With a really small lathe like my Unimat, sometimes the toolpost needs to be turned around so that the tool is on the side towards you, to get it out far enough to work around the job. Actually I just did the same on the Myford to clean up some 7 inch diameter by 35mm thick steel disks. Actually  one of them was tougher than the other, and I had to run the lathe at half speed on the controller, while in the lowest belt speed and in back gear.

 

regards

John

[TerrydParticipant @terryd72465]

Posted by John Olsen on 07/11/2010 21:23:15:

Apart from the chilled spots, iron that is cast in a sand mould will tend to have a bit of sand fused into the surface.So the surface is harder than the bulk metal. So where the machine and the method of holding the work is up to it, it is actually good to make the first cut a reasonably generous one to get under the skin. On small machines this is not always possible.

 

Even though cast iron is generally soft, the cutting speed does not want to be too high. The cutting speed is mostly what determines the peak temperature at the cutting tip. Above a maximum, even high speed steel will go soft and blunt easily. …………………

 

regards

John

 

Hi John,

 

I was always led to believe that HSS was hardened at a very high temperature (around 1250 deg C) and also tempered at a temperature of around 840 deg C (which is above cherry red heat).  Therefore it could be run at a very high temperature without losing hardness.  Even red heat.

 

Terry

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