Cylinder Boring Techniques for Steam Engines

[Will RobertsonParticipant @willrobertson16447]

I was thinking about something like that – maybe with the milling machine or a final cut using a boring tool or a turning tool with the jaws reversed to face out the way and talking very light cuts (interrupted cut of stainless steel could be tricky) to true the metal plates on the jaws. The snag is that I've never tried to do anything like this before and the chuck doesn't belong to me so if I mess it up it doesn't really bear thinking about…

[Will RobertsonParticipant @willrobertson16447]

Sorry about my silence – work has become a lot heavier over the last few weeks so I haven't been able to spend as much time as I'd like on the engine.

Re. the restoration of the S50: I dismantled two of the jaws on the 4 jaw chuck easily. The other two jaws seem to have some damage to the ends of the threads and so I can't dismantle them completely. At the moment this is preventing me dismantling them and mounting them on the milling machine to true the metal pieces welded onto the ends of the jaws. I'm not sure whet to do now – maybe another try at dismantling these jaws or maybe try to get use of a lathe with an unmodified 4 jaw chuck.

I'm being very cautious about truing the modified 4 jaw chuck – it doesn't belong to me and I've no idea where or whether I could get a replacement so I don't want to make a mess of it.

Re. my own engine: The electrical heating elements arrived to build an electric furnace to braze the cylinder to where it would mate with the valve assembly. I was anticipating something like the coils of nichrome wire used in heaters – which is fairly malleable and easily handled – what arrived were coils of much more springy wire than I was expecting so I need to give some thought to how that can be safely kept in enough tension to prevent it shorting out with disastrous results.

I found an interesting approach to cylinder boring in the hydraulics community – their approach is simply not to bother attempting it – metal stock is bought in 6 metre lengths already precision bored so all that's needed is to cut the required length and fit the other parts needed to make the hydraulic cylinder – much cheaper than buying specialist boring equipment for long cylinders.

[Douglas JohnstonParticipant @douglasjohnston98463]

How on earth do the manufacturers produce 6m lengths of precision bored tubes. Is this possible with extrusion techniques. This material could lend itself to a number of applications if it was easily obtainable in shorter lengths.

Doug

[JasonBModerator @jasonb]

Sound like what the Americans term DOM tubing (drawn over mandrel) smooth enough to use for hydralic rams ets and available in short pieces.

[Will RobertsonParticipant @willrobertson16447]

Apologies for my silence for a while – workload increased a lot towards the end of the year.

I got my paws on a very old, large lathe with a 4 jaw chuck in a farm workshop to re-bore the cylinder of the S50 (the bore was in such a bad state that honing couldn't repair it). Mounting the two largest and two smallest gears in the gear chain and setting the leadscrew gear box to the lowest speed to give the maximum gear ratio for the lead screw gave a leadscrew movement of 0.12mm per revolution of the workpiece – which was a lot faster than I'd like but the best I could do so I went for it.

Using the Ifanger boring bar.

Despite the age of the lathe and it being badly rusted it did a magnificent job of the cylinder bore – says a lot for the quality of the engineering that built the lathe. My only regret was that the fast feed relative to the speed of rotation left a slightly threaded surface on the bore – ideally I'd have used a much lower feed rate but that didn't seem to be possible on this lathe. Although there's a slight thread the bore looks much more dimensionally uniform than it was before re-boring.

[Clive HartlandParticipant @clivehartland94829]

Well done Will, now you can hone it true. By the way, 'Happy new Year to you and family'

Clive

[Ian S CParticipant @iansc]

Will, you could proberbly get a better finish on that old lathe by hand feeding, rather than using the power feed. Nothing wrong with manual opperation of machine tools, or big old lathes. Ian S C

[Will RobertsonParticipant @willrobertson16447]

The machine feed was pushing the apron more slowly than I could have managed by hand – I'd been able to set up a gear chain to give a fairly big gear ratio for the leadscrew. The pitch of the thread on the leadscrew meant that even though the leadscrew was rotating slowly the feed was fairly fast.

What's the slowest rate of fed that it's reasonable to expect to find on a lathe? A friend warned me a while back that on large lathes the minimum rate of feed was often too fast for precision work but I've never been sure what it's reasonable to expect in terms of minimum feed rates in a lathe.

(I know of one individual who, in desperation, declutched the leadscrew from his lathe and drove it from a custom gear chain and the DC motor and speed control from an old MIG welder!)

The cross-slide was rusted badly with a big variation in friction over its travel so moving it at a constant speed by hand would have been very difficult.

[JasonBModerator @jasonb]

My finest longditudal feed is 0.0025" (0.06mm) per rev so about half what you have. Its half that on the cross feed at 0.00125"

One way to compensate for a fast feed is when you get to the end and take several passes at the same setting to work the spring out of the tool is to fractionally move the topslide (provided it is set parallel to teh lathe axis). If you were to move it say 0.04mm twice that would give you three fine Vs instead of one large V. A slightly rounded end to the tool will also halp by leaving a U rather than a V

Will, some time back in this thread I mentioned I would be fabricating a large cylinder, well I got it done over the christmas, have a look at this post and the one after

J

[Will RobertsonParticipant @willrobertson16447]

Thank you very much. Using the cross slide in this way seems a great way of handling this situation. Is it OK simply to put the lathe into reverse to bring the boring tool out, adjust the cross slide than run forwards to take another cut? (I'd normally want to move the tool out of contact with the workpiece before reversing but there's almost a complete revolution of play on the transverse feed so I'm guessing that it's very worn and I'm not sure whether it would accurately get the tool back into exactly the same position.)

Unfortunately I left all my tool steel at home and the lathe I'm using is on a farm in Arctic Norway so I don't have any with me to make a u-shaped tool. Hoping to get a fine diamond grinding disk to help finish home-made precision tools.

Thank you very much for the detailed photographs of your engine – it's good of you to take the time to photograph each step in detail and a big help to folk like me who're learning.

[Will RobertsonParticipant @willrobertson16447]

I just realised that anyone reading the above post would think that I was fairly dense. Obviously, I want to keep the direction of rotation the same and reverse the direction of feed so that the boring tool will cut on the way out as well as on the way in and leave a good cross-hatch pattern. I'm blocked from doing this unfortunately because the pin that holds in place the lever that engages and disengages reverse gear for the power drive is rusted in position and penetrating oil for several days followed by persistent use of a small hammer couldn't move it.

[JasonBModerator @jasonb]

You won't get a cross hatch by feeding out unless you also alter the direction of rotation but then the tool will be the wrong way up, on a worn lathe like you are using you will likely just get another helix that is offset from the first by the amount of play in the lathe.

Best to just stop the lathe and wind the carrige back by hand on all but the last spring cut as the tool will leave a line on the bore where it is dragged back across the finished surface, this will be machined away with subsequent cut sbut obviously not the last.

rather than rely on a sloppy hand wheel dial if you have a DTI set that to measure the cross slide travel and you should be able to return to the same point.

J

[Sub MandrelParticipant @submandrel]

rusted in position and penetrating oil for several days followed by persistent use of a small hammer couldn't move it.

You deserve an award for model wengineering in the face of adversity! next you will tell us the difficulties of being distracted by a polar bear in teh shop…

Neil

[Will RobertsonParticipant @willrobertson16447]

D'oh – sorry – yes – you're right – I wouldn't have got a cross-hatch pattern that way. I'd have had to take the workpiece out and turn it around.

Thanks for your advice about using the DTI – I hadn't thought about using it in these circumstances thought I should have – a significant help since parts of the readout on the handles are too rusted to be easily readable.

Thanks very much for all your advice and taking the time to teach me these things.

[Gordon WParticipant @gordonw]

I often cut in both directions when boring, this can give a very good finish, especially on a spring cut. But be aware- a worn lathe or badly adjusted one can cut deeper on the back cut, or not at all, depending on the wear. I've just ruined a small bore in aluminium with an extra 10 thou' or so cut.

[Will RobertsonParticipant @willrobertson16447]

I've got more machining done for the restoration of the S50 – I'll try to post some photos. Every step of the way I've been guided by advice from people on this forum – I'm very grateful.

For my own engine I'm thinking more about the problem of heating the stock for the cylinder and the mounting flange for the valve assembly to 600 C to solder them. The high temperature heating wire I got turned out to be much springier than I was expecting so I looked again at the idea of a paraffin or diesel fuelled furnace.

I built a diesel burner with a simple atomiser and fan fed air supply but the atomiser produced droplets of diesel which were too large and had far too high a flow rate, resulting in a large, yellow low-temperature flame – useless. One hint of hope did come as the diesel in the pressure tank ran out and a mixture of diesel and air passed through the atomiser – that gave a very fine colloidal diesel mist which looked almost like smoke and burned beautifully with an intense hot, blue flame. If I could only create that reliably… That gave the idea of using a compressed air to make something similar to those perfume bottles with a rubber bulb and air tube attached that you see in 1930s films but I don't know if this would give the very fine droplets of diesel that I'm looking for.

Now I'm thinking about vaporising the fuel instead. Does anyone have any advice about how to make the orifice that the vaporised diesel passes through in the Venturi effect mixer of the burner? I made this sort of burner often when I was a child but the fuel was ways LPG – I made the orifice by gently hammering a piece of copper brake pipe until the right diameter of hole was made and I got the right sort of flame. If I burn vaporise diesel, I need to be more aware of the need to prick the jet to clean it and keep it free of the deposits that tend to build up in this sort of burner.

[Gordon WParticipant @gordonw]

I don't know what facilities you have, or really what you are trying to do, but – I once saw a home made furnace ,made of bricks, the burner was rescued from an old central heater boiler, the owner used it to melt aluminium scrap by feeding old engines etc. in at the top and molten alloy out the bottom, might be worth a thought.

[Will RobertsonParticipant @willrobertson16447]

Hi Gordon,

This sounds very similar to what I'm planning – I've got heat resistant bricks and my furnace will be much smaller than your friend's (only for soldering at 600C – not for foundray work). I'd love to get my paws on the burner from an old central heating boiler but so-far I haven't managed.

Will

[Will RobertsonParticipant @willrobertson16447]

Back to the cylinder bore for a moment – I think I've got a supplier for Veritas lapping grit (silicon carbide). After boring should I hone the cylinder bore with the 600 grit or should I use a coarser grit (e.g. 400 grit) first then the 600 grit? I don't mind if using the 600 grin means that the honing will take a little longer – washing everything to change grit would take a lot of time as well.

I'd like to use 1000 grit or paste but the 1000 grit always seems to be diamond, not carbide.

Will

[JasonBModerator @jasonb]

Lap with the coarsest grit then the next finer and work through them all to the finest you can get.

If you start straight away will the 600 it will take you forever particularly as you said the finish off the tool was not that fine.

[HomeUseParticipant @homeuse]

This is a good supply of polishing/grinding media – Its used in lapidary (polishing stones) http://www.ukge.co.uk/uk/grits.asp

[Will RobertsonParticipant @willrobertson16447]

Hi Jason,

Thanks – I'll take different grade of sandpaper and make scratches on some scrap steel sheet with it then I'll compare the visual appearance and feel of each 'grade' of scratches with the visual appearance and feel of the bore and that should give me an idea which grade to start at (hopefully…). Veritas go all the way to 90 but I suspect that that might be too coarse. I'm guessing from the feel and appearance of different grades of sandpaper compared to the bore that I should maybe start at somewhere round 300 – does that seem reasonable? I'll try it out as described above and let you know how I get on.

Hi HomeUse,

Thank you very much – this is the only place I've seen 1000 grit carbide for sale. I might also order some more stuff from them and get around to polishing some of the stones I find on the mountains some day (or some of the stones that find me in the case of rock falls…)

Will

[HomeUseParticipant @homeuse]

Hi Will R – I think they still do the 1600 grit – I use this mixed to a thickish paste with veg oil (Usually Linseed) and find that it is a good polishing compound for all metals

[Will RobertsonParticipant @willrobertson16447]

Thanks – I think I need to be a bit cautious though – there seems to be agreement that the cylinder should be ground to a finish that still has microscopic scratches because these microscopic scratches help to hold some oil to lubricate it and that a polished surface with none of these scratches wouldn't hold the lubricating oil so well – I might be wrong in this though.

I've found someone who carries stock of "Steel 50" and "Steel 51" now – unfortunately I'm having difficulty working out what Steel 50 or Steel 51 means – can anyone suggest what it's machining properties are like or what the equivalent BS number would be?

[Will RobertsonParticipant @willrobertson16447]

Sorry – one more question – if I get a diamond grinding wheel for honing my HSS (or carbide) lathe tools should I get the "hard bonded" or "soft bonded" type?

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