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Stuart S50

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Wolfie07/11/2010 10:54:55
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502 forum posts
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

Terryd07/11/2010 11:29:13
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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
Andrew Johnston07/11/2010 11:56:35
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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
Weary07/11/2010 13:40:40
421 forum posts
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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
Wolfie07/11/2010 16:44:32
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502 forum posts
"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?
Stub Mandrel07/11/2010 17:45:41
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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.
Andrew Johnston07/11/2010 20:05:28
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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 Olsen07/11/2010 21:23:15
1294 forum posts
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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
Terryd07/11/2010 21:42:35
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1946 forum posts
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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
Wolfie23/02/2011 22:06:26
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502 forum posts
Hi chaps, now that North Yorkshires winter has finally let me back into the workshop, I've done a bit more. And I'm dead chuffed with this even if it is small stuff to you lot, so be gentle.
 
I was worried about tackling the cylinder casting as I really wasn't sure how to hold it to begin with, but after talking to someone at PEEMS (http://www.nrmodeltruck.co.uk/peems.html) at the Feb meeting I bit the bullet and went for it.
 
Using lathe tools and a reamer I reckon this is a success! The piston fits beautifully (although there doesn't seem to be much in the way of compression) and it moves up and down spot on even with the covers attached. It does bind slightly when I tighten the gland up, but I can open up the hole in the top of the gland a dab as there will be an O ring in the bottom.
 
I have to tell you its great when things like this come off, I have new confidence and all sorts!
 
Be gentle
 


 

 



 
 

Edited By Wolfie on 23/02/2011 22:09:07

Edited By Wolfie on 23/02/2011 22:10:28

Edited By Wolfie on 23/02/2011 22:12:58

John Olsen24/02/2011 09:21:46
1294 forum posts
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Hi Wolfie,
 
Looking good there. Don't worry about the compression, you are not trying to make one of those model aeroplane engines where the fit of the piston is all that seals the compression pressure. Stream engines will run fine with steam leaking past the piston, they just get even less efficient. You can groove the piston for some soft packing, or for an O ring and get a good seal that way, but if it is a nice sliding fit it would probably run fine without. You may notice that the Mamod style of engine has no attempt at sealing on the piston. (You can also make proper piston rings, but that would probably be a bit ambitious at this stage of things.)
 
regards
John
Ian S C24/02/2011 13:18:24
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Your problem with compression may be because you reamed the cylinderuntil the piston fitted, with a reamer the cylinder will be parallel, but may have corrigations. You should stop say.ooo5 before the piston dia is reached, then lap it the rest of the way (well thats what I would do, except I would not be using a reamer, but boring in the lathe), my expiriance is with hot air engines, not steam so I'm not sure what sort of fit is required. Ian S C
Wolfie24/02/2011 15:01:57
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502 forum posts
Whats lapping??
 
I made the piston first as it happens and then made the cylinder bore to the plan as I only had the one reamer (5/8")
 
I may yet make another piston as the rod is a tad short too.

Edited By Wolfie on 24/02/2011 15:03:35

Terryd24/02/2011 16:05:26
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1946 forum posts
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Hi Wolfie,
 
'Lapping' is done using an abrasive to finish the bore of the cylinder. It is done with a lapping tool which is a simple piece of softer material e.g. in this case, brass or aluminium or even plastic or wood, which fits quite tightly into the bore. It is made so that it can be expanded with a simple wedge device or similar and is loaded with abrasive such as grinding paste and then introduced into the bore of the cylinder which is rotating slowly in the lathe chuck. the 'lap' is fed in and out rhythmically so that the whole bore is lapped evenly. This is continued, renewing the abrasive and expanding the lap as needed from time to time, until the piston is a close sliding fit in the bore. It can also be done on a drilling machine by holding the cylinder in a vice and the lap in the chuck and move the quill up and down. Far quicker to do than describe.
 
Finer abrasives are used as the bore gets to a close fit similar to lapping valves in an i.c. engine. I often end with Brasso on the piston to get a good sliding finish. It is quite rewarding to see a piston and it's rod slowly slide down a finished bore under it's own weight.
 
I do hope that is clear,
 
Best regards
 
Terry
 
By the way it is usual in engineering to make a hole first and then make the other component (in this case a piston) to fit. This is because it is easier to turn a piston to a high degree of accuracy than it is a hole, especially a deep one.

Edited By Terryd on 24/02/2011 16:06:31

Richard Parsons24/02/2011 17:35:55
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Wolfi Terry missed out some things when lapping. They are these: -

1. Always try to use a different pattern of lapping. This will let you see when the finer grit has rubbed out the scratches left by the coarser grit.

2. Never proceed to a finer grit than the one you are using until you have removed All the scratches from the previous grit.

3 Never let the lap become dry. In the UK I used a mixture of oil and paraffin (the stuff you buy for stoves (NOT liquid paraffin which is very moving). In Hungary I cannot get paraffin I use either very thin oil or a mixture of cooking oil with a little meths added to thin it.

4 I charge my lap by mixing the grit with the oil on a bit of glass then quite firmly roll the lap in the mixture. I use thrown away ice popsicle/lolly sticks to mix the grit. (I used to live near a several schools so I have a huge box of them). Watch out SWAMBO may nick them for her plants.

5 This is the first bigee before start lapping, cover your machine over with disposable plastic sheeting (Black dustbin bags are just right for the Myford and you can turn then inside out for SWAMBO to use.

6 Finally for success always scrub every trace of the previous grit from everything, every nook and cranny (except the machine cover) - the lap, the work piece, the glass, and your hands before starting to use a new finer grit. Use washing up liquid, suitable brushes (in your case old tooth brushes) and lots of running water. You must even wash the brushes before you use them to remove the next grit. 

It is a good idea to run the lap slowly holding it in the chuck and hold the work piece in your (gloved) hand. You can then ‘feel’ how the job is going and when to add more lubricant etc.
 
Watch out with brasso it often contains quit large grains. 

Edited By Richard Parsons on 24/02/2011 17:38:02

Edited By Richard Parsons on 24/02/2011 17:42:36

John Olsen24/02/2011 18:12:23
1294 forum posts
108 photos
1 articles
While this is all excellent advice on lapping, let us remember that this is a steam engine, not an IC engine, and further it is his first attempt, so we don't want to make things too hard.
 
My Dad, as a young fellow in a rural village in depression era New Zealand made a few small steam engines without access to a lathe or any power tools. He made pistons for them by casting lead into the well greased bore.
 
regards
John
Terryd24/02/2011 21:42:43
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1946 forum posts
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Hi John,
 
I agree with you wholeheartedly. Wolfie simply asked what 'Lapping' was, not how to do it with loads of inconsequential detail. I tried to inform him in as simple a way as I could avoiding excess detail and complications which can be found on the internet or in countless books.
 
If you want to see a simple steam engine I suggest you look here. It is eye opening for those who insist that toolmakers lathes and super accurate micrometers and dust free environments etc are essential for simple working models.
 
Best regards
 
Terry

Edited By Terryd on 24/02/2011 21:47:08

Ian S C24/02/2011 22:52:11
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7468 forum posts
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Back in the 1930s and before, lead was used quite a bit for making pistons, and flywhels.
I should have explained lapping, but thats been covered better than I could have done. also the point of making the hole first, then making the piston to fit.
For a lead flywheel, it may be cast in a wooden mold, and a brass bush can be cast into the center. Heat and pour the lead out side, if you can find lead these days. I'm OK for it I'v got about 200kg of clean lead. Ian S C
 
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