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Member postings for mgj

Here is a list of all the postings mgj has made in our forums. Click on a thread name to jump to the thread.

Thread: Cylinder Boring Techniques for Steam Engines
02/06/2012 15:27:46

Will - dissimilar metals and precise fits. You can achieve that, but you do have to make sure that the piston never gets to the same size as the bore. The consequence is known a seizure! Simples I'm afraid. What do you do tp prevent it - the arithmetic.

Rings. Smaller engines tend to have packing rings/ O rings. Larger (iron) bores will have rings. In general iron bores will rip graphite packing to bits.

How many piston rings. Usually 2 usually in 2 separate grooves. But some Stuart designs run 2 rings in a single groove. Better/worse I don't know - I'd rather run a narrower ring in 2 grooves and keep themeparate.

Gaps. - for iron rings in an iron bore, you can run at say .001 gap when new. .

Bore dia. Engines will run with their valve gear all over the shop, and bores thous over and undersize with bits made to fit. Probably OK for a single cylinder engine. Not a grand idea on a double or loco with three!. so for me, if the drawing calls for a 2" bore then a 2" bore it will get (+/- .0002". ) Saves pratting about filing rings etc. Its easy enough to achieve - you just approach carefully, and always cut on the in cut and the back cut. Normally, as you get close, twice. It will be dead right.

Piston size --.002/3" Something like that. Not critical if you are fitting rings.

Liners etc I would make of continuous cast meehanite. Its not very expensive, and it should be very consistent (if ringed.)

No experience of unringed bores, but gunmetal/gunmetal is used a lot, with grapjhite/PTFE packing. Lasts well I understand.

May I suggest - you are in danger of wading in a pool that is way too big for the answers. Decide now, how big and the basics. Then you can ask more specific questionsand get targeted answers. At the moment every answer has to cover all the bases from tiny oscillator to 2" bore traction engine, and that would appear to confuse rather than help.

Edited By mgj on 02/06/2012 15:28:46

30/05/2012 23:20:08

Does it matter if you use dissimilar metals for piston and bore? I don't know about this engine, but in general the piston never touches the bore - the rings or packing do. All the piston does is act as a carrier for the rings, and bungs up the rest of the hole. Make it from what you like in principle, so long as it remains small enough never to touch the bore, even at steam temperatures.

Bore finish. Depends on the rings in general? If you are running iron rings in iron bore, then honing is one way. Personally I have never worried about that, and just finish with a decent tool finish. Run in on my Metre Maid, - its done about 4 hours running, its gone from quite tight all round , and now, if you pull the engine back with reverser in neutral, suction on one cylinder will pull the engine forwards half an inch or so. So the seal is pretty darned good. Nice parallel bore, decent finish on a fine feed, and to the size specified by the ring gap is what is needed.

The alternative generally would be a bronze or gunmetal bore, using o rings or other PTFE/graphite packing as rings. In general they like a high polished finish, but I have no great experience of them, and would leave advice on that to others. However, a properly reamed finish should provide a huge pressure seal with O rings on a pump, so that should be Ok for a bore. As always when reaming a round hole, go to about .003" undersize, ream slowly, stacks of coolant to prevent sticking with temp changes and with a floating reamer if possible.

How to bore it. Between centres has the advantage of always producing a parallel bore, but often tooling is not so easy to adjust, and it can chatter horribly. So my choice is always a good stout boring bar and the 4 jaw. But that would depend on the size of the chuck/lathe against the job, and the confidence oyu have in your lather turning parallel. For small work you could use the Keats type angleplate - used to be opular, probalby less so now. The mill is a good way too, as has been suggested. Possibly easier to get bore and portface all in the right place in the mill.

You know your machine, how it cuts on the backcut, and how to remove spring from the tool. At the end of the day have confidence, its just another hole. And, if you don't have that confidence, there is usually enough spare metal to allow you to have a few practise finishing cuts in the bore as you go, before having to hit final dia.

All the best.

 

 

Edited By mgj on 30/05/2012 23:20:45

Thread: Gaskets
29/05/2012 11:50:37

Or you could use Loctite 574. Polly do it.

Quicker easier than cutting out paper, steam and oil proof, gap filling of course, sets in about 3 minutes. Perfect for the job, less messy than Hylomar, and no waiting. On the TE now Metre Maid, I have stopped using paper completely, because 574 is just so quick and easy.

Be a little careful when joining steam flanges, not to use too much - a tiny bit applied with a paint brush is plenty so it doesn't spread into the pipe.

Certainly a very useful alternative.

Thread: Silver solder problems
24/05/2012 19:22:54

Sounds like you are not heating the objects quickly enough, and the flux is then getting exhausted and going black. Further heating has nil effect. Lots of little molten bits, no adhesion and solder that won't flow..

If you can't turn the wick up any more, try more effective shielding/heat retention, and reflect heat back into the work.

What should happen is the flux will melt, keep the heat on, the flux goes runny, move hte torch a bit sideways but keep the job hot, touch the rod dipped in flux to the job, and the rod melts and flashes round the whole joint in one. Job done - so long as you heat the work and get it hot enough quick enough. If you cannot do that try Tenacity flux or get a torch with enough thermal capacity. .

Thread: Injectors Full Time?
28/04/2012 09:14:02

A lot might depend on hte size of hte boiler- or more precisely demmand from it.

If you know approximate revs of the engine, you can easily work out how many ounces per minute the injector should supply. The trouble is that for many applications its difficult to get a good injector small enough, and making one can be a little awkward (in the smallest sizes)

A 12oz injector easily maintains level on both a 3" Little Samson Traction engine, and a Metre Maid. With both of them I tend to run on the injector, because is easyy, painless and supplies very hot water. You don't flatten the boiler. For my money, and injector is a much better bet, if you can get a reliable one of the right size. tehy also tend, if one is buying one, to be a lot less work to make (of course. Just plumb it in and off you go)

The Chivertons, available from Polly seem to light first time every time.

Pumps work well too! All you need is a controllable by pass circuit and you can adjust delivery to the boiler very easily.

Pays your money and takes your choice

Thread: 5" Britannia Injector
17/04/2012 19:06:24

Ianmac. If I could sugest a couple of other things.

As Michael Williams suggests the injector must be kept cool - up to a point. The logic is that the presure drop in an injector is very great, which means that warm injectors will cause boiling. Or more precisely warm water will boil  in hte injector, to the detriment of all!

I'm less convinced about keeping the injector rather than the feed cool. My experience (not great ) is that if you have a decent water supply, then it doesn't matter if you start steam first or water first. (ie with a red hot injector) mostly on the TE I actually open the steam valve first - less mess. The suction draws the water, and bang , she lights first time. The point being that steam first establishes a decent suction jet. People will argue., but thats how mine work. Anyway, heat is a point to watch. Small heat shield if necessary?

Pipes - a pipe is only as big as its smallest dia, so I am careful about fittings olives and bends.

You need a filter in the line. Being a tender loco I imagine you have one, but if not, it might be wise to fit one.(of sufficient capacity)

DAGs book is I think very good. If it has a weakness, he is less positive on the need for a good steam supply. If you look at the flow factors for various fittings, its horrendous the equivalent line size drop they create. One is losing pressure all the time. Good smooth run, and I wouldn't ever use a globe valve for a steam control again. The injector ones impose far less restriction.

 

all the best.

Edited By mgj on 17/04/2012 19:10:01

16/04/2012 23:40:00

40oz is a bit steep isn't it.?

A 12 oz would easily keep up with a Britannia at full chat. If you need the calculations see DAG Browns book on injectors.24 oz maximum I'd suggest, but a 12 won't cool off the boiler - but you might need a bit more forethought and planning using it. I just run with the injector on most of the time, because its sized quite well and one can largely forget about the pump. Its a lot more efficient than the pump too.

Clack - you don't need to restrict the lift to 30 odd thou, since the ball is not trying to be caught up by the pump frequency. You can afford to let it lift 1/8" or a touch less to allow it to get out of the way and minimise restriction.

Having been through injector woes, I can tell you what I did. First I tested the injector on anohter model. It worked.

Next step was to look along the lines for a blockage - I used Locktite 574 in the joints. There weren't any. Then I checked the water lines were big enough to keep water velocity down. They were (3/16 pipe foir a 12 oz injector.) See DAG browns book about sizing lines.

So it had to be the steam supply. (since it wasn't water and boiler feed lines) Sure enough, making sure the steam feed was properly straight, and removing a nice scale elbow sorted all- because by then the penny had dropped. Its a pressure recovery device, and if one is inducing pressure drops in the plumbing then its not available for pumping water.

Exit all injector woes, and it lights first time everytime.

I don't think there is anyhtng magic about injectors, or the diagnosis of basic problems - one just has to plod logically through the steps to sort the problem. (borrrow a working injector etc) Personally I was convinced there was a blockage, because the injector would strike but then almost immediately vent steam . Well there was - the ball wouldn't lift becase the pressure had been lost in the line. (Just not the normal type of blockage!) So the injector was seeing a blocked line.

Thread: Steel boiler problems
08/04/2012 08:45:02

How big is the boiler in terms of volume. A lot of things will affect how long it takes to raise steam, but if its any consolation, my 3" Little Samson takes about 40 minutes to raise steam to the full 125 psi. About 30 minutes to get 25 psi on the clock ready to switch over to the steam blower. The electric blower is one of those very common 12/24 volt ones, run at 24 volts. At 12 volts life is very slow.

I think that boiler takes about a gallon

The red - might that not be anti scale colouring the water? Tannins that is.

Edited By mgj on 08/04/2012 08:46:13

Thread: Dore Westbury Milling machine
30/03/2012 21:49:43

I have a noise/vibration finish problem now. As mentioned its caused by wear in hte drive casting. when I can be bothered I shall replace that casting with a turned steel top hat and a pair of inserted bronze driving pegs. Better, if I get really excited, I will remove the main shaft extension, and replace it with one with 4 drive slots, and alter the top hat accordingly.

 

Vibration generally - when I built mine the whole gearbox assy was out of balance - not surprisingly since it contains several castings. I made a holder and mounted it in the Quorn spindle, (which is very finely set up) and kept drilling holes in the edge of the housing rim, until it balanced. Exit all vibration till the drive casting wore, 20 years on!

 

Oh and you need to balance the drive pulley as well - it should be turned on all surfaces, but it was still slightly out of balance, so thats one to check.

Belt tension?

Edited By mgj on 30/03/2012 21:51:06

Edited By mgj on 30/03/2012 21:51:35

30/03/2012 16:40:42

Sorry - forgot to say.

When you put the pins in to the holes on the side of the gearbox when engaging low gear, they must engage in corresponding holes in the non rotating section. What one is doing is locking the bottom half of the box (the body) - the pulley will then totate independently. The fixed holes are likely to be aligned with the table centreline.

Likewise when engaging direct drive. There are two holes on the underside of the drive pulley, and you are locking the drive pulley to the gearbox body when you push the pins in from underneath.

30/03/2012 08:39:50

To check the oil level you have to take the top off the gearbox. Start undoing bits at the top of the machine - its mostly small allen screws. There is one circlip. Self explanatory - just follow your nose downwards.

Once you have have got to the gearbox, the top comes off - six IIRC countersunk screws. Might be worth marking the lid because the assembly should have been balanced with the lid in place.

To operate. You have 2 pins, which normally live under the gearbox - near the outer rim. You take themout, and put them into the two holes in the side of the gearbox along thete bottom edge. They are about 1/4" dia, and there is an o ring for retaining purposes.

Good machine. I have had one for nearly 30 years - the top drive plate casting needs new dogs, but other than that its done me very well indeed.

Thread: Steam pipe olives
16/03/2012 03:26:31

Yes it will work - for a little while if my experience is anything to go by.

I built a 3" traction engine and soft soldered all the joints. And after they failed in less than a month, I had to replumb the whole thing. I don't think I have a single original joint remaing.

So I would stronly advise you to forget the soft solder - unless you enjoy plumbing.

Comsol might be OK - no exerience, but personally, I have no intention of putting soft solder anywhere near a steam pipe again!

Thread: Slot milling speeds
22/02/2012 17:39:32

Well..... the FC 3 cutters are all 3 flute cutters and they are excellent for slots. Use them exclusively for all small sized slotting. Tend to give a better finish due to lower levels of vibration by reducing springback in the tool.

The trick is to have a rigid mill, and a decently held bit of work, and to cut at the correct speed AND toothload. A 1/4 " FC 3 (which is not far off a 6.5 mm cutter - .264) will cut very well at 2000 rpm though 1500 RPM is about 100fpm. Thats more or less what I cut at all the time, simply because its a recommendation for a general purpose steel, and it happens to be the H2 ratio on the mill.

If the stuff is EN3b, it is common or garden free cutting mild, with a direct equivalent of 070M20 in new money. Nothing special - just lovely soft stuff specifically for machining.

So Andrew has to be right - its either the feed rate, which shouldn't be more than a couple of thou per tooth per rev, or the cooling is up the duff. Might not be enough, or it could be neat that should be dilute so one is not getting the flow removing chips, or heat transfer out of the work. As Andrew suggested, 2k RPM might be trotting on a bit, but it is not outrageous - but the 600s as suggested are probably way too slow, because the likelihood is that one will have far too high a tooth load which leads to tool bending and breaking. Still, if one has a blunt cutter, the wise thing to do is to maintain revs, and increase tooth load slifghtly to prevent rubbing.

Edited By mgj on 22/02/2012 17:40:54

Thread: DRO Linear correction
19/02/2012 13:05:51

I don't know about all of them, but on mine there is a set up menu, (you press 9 longtime to get in but others makes will be similarish )and you add corrections in millionths of a metre (.001mm) or parts per million. ie 100 is .1mm and 1000 would be !!! 1mm.

I think the ppm system is fairly common. Remember to work out which way is + and - depending on which way you have the sign on that axis set, .

Technically one should work out the distance applied - I used 1"" off a long travel DTI, and then you work out the error as a %, convert that into .001ths of a mm. and that gives the correction.

Or you could just work carefully against the DTI a bit at a time, and then when its all about right, fine tune off the micrometer as you go along. I find that works well and is a great deal less stressful!

Edited By mgj on 19/02/2012 13:06:06

Edited By mgj on 19/02/2012 13:06:38

Thread: Brazing copper
14/02/2012 20:23:37
V8 - that is a very dangerous route where boilers are concerned. Its a well known technique, and very good in its place, but somehere in the presence of sulphur is not one of them.
 
It becomes very brittle, and is useless for our purposes, in our environment. Avoid like the plague in boilers using coal as a fuel.
 
Dezincification - thats why I feel it has been somewhat overstated as a risk, but its best avoided, at least in the structure of a boiler where an item can't be replaced easily. Fittings, I think brass is fine. For my money, if after many years something goes brittle, you just take it out and change it.
13/02/2012 22:54:51
Well one thing is for sure, is that you don't want to go using brass spelter inside a boiler.I think the risks of dezincification have been very much overstated, but even so, in a joint subjected to HP steam for some time, it would be unwise.
 
Which leaves you with what we all know as silver solder. - whether its brazing or soldering is a matter of semantics (other than brazing tends to use brass and the rest of the world talks about silver soldering?) - its the temperature range and suitablitiy of the alloys which matters.Any of the silver based eutectics recommended above will be fine. If this component actually sees the firebox temperatures, then you'll need the high temp alloys.(though I'd prefer to weld) Otherwise the 620C stuff will be fine.
 
I have used 55. i've heard people say it doesn't flow so well. Can't say I have noticed much difference personally. More expensive though. Might buy some CD bearing stuff claiming its for electrical connections if it comes to it. Its still legit for that I understand.
12/02/2012 23:08:48
With silver solder these days.
 
If you are just starting out like that, I fear there isn't enough space on this forum to give you a good compete answer, but everyone has to start somewhere. .
 
Strongly recommend Tubal Cains Soldering and Brazing, and Alec Farmers Book - Model Loco Boilers.(or similar, but Alec Farmer is the author.) Might also be a good idea to go down to the local club and ask those who have doen it before.
 
It isn't difficult, but you do just need to have it properly worked out, with access to the right kit, to avoid disappointment and/or very expensive mistakes.
Thread: Stroke
12/02/2012 08:42:12
I would suspect that somewhere a compromise is being made, possibly to do with space available.
 
Because what has not been mentioned is torque. By having uneven throws (without a corresponding correction in cylinder area), or not having them identical, for any given chest pressure, the deliverered torque is uneven. Thats not desirable since it tends to lead to vibration and whip in the crank axle/shaft.
 
Con rods don't have to be identical length, because they just connect two points, but longer is generally better, at the cost of rigidity. You'll get differences in accelerations and  angular velocity in the bearings, and extreme differences will cause vibration, (none of which are good things) and losses because of angularity, but in principle, but as long as you connect the bit that pushes with the bit that turns it should work.

Edited By mgj on 12/02/2012 08:42:56

Edited By mgj on 12/02/2012 08:48:47

Thread: Fine Finish on Crankshaft
11/02/2012 22:30:33
The way that got me a very nice highly polished surface on a TE crank was as follows.
 
1. Make spacers or braces so that you can stiffen or block any bits that are not being machined. Tubal Cains book Workholding in the lathe shows this very well. Rigidity is key, especially as one is likely to be turning between centres.
 
2. Then with a nice deep and narrow parting tool, ground with a radius on each side and with a face truly flat, I machined each section down to about .002 oversize, but a little bigger wouldn't harm.
 
3. Make up a dummy split bearing, and attach to a dummy conrod. coat each journal in turn with valve grinding paste, and jsut lap in with the lathe at low speed. You just keep tightening the "bearing" until it is exactly to size.You don't even need to hold the end of the dummy conrod. I rested it on a bit of wood on the top of the compound slide. Better than holding it.,
 
4. Finish/polish with fine emery and oil.
 
Lovely and shiny, dead parallel.
Thread: What size do i drill a brass cylinder in order to ream it 5/16 "
11/02/2012 13:27:53
Depends on the reamer tolerance, but the standard H5 should cut about .0005 oversize. Nominal bar should be a touch undersize.
 
As for getting reamers to cut to size, I always understood it depended a bit on the reamer. A machine reamer tends to be more tolerant of being asked to take a bit of chunk.
 
The problem is howerver, less one of cutting to size, but if any length is involved, cutting straight. Where that is important, I'd be inclined to bore to within about .005 of finished diameter, and then I know that either kind of reamer will cut both straight and to size - because by the nature of the beast, its difficult to guarantee that a drill will do either.
 
OTOH, if its not critical, then I'd drill 1/64 or so undersize and put a reamer though.
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