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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: Rivet snap dimensions
01/01/2012 19:08:15

Pretty handy for strakes - doubt they would ever work loose.
 
Thread: Turning very thin bar
01/01/2012 09:54:54
Sounds like I need to be a bit more determined about using mine.
 
The other option is to build in a bigger scale????
Thread: Rivet snap dimensions
01/01/2012 09:52:40
Well fair enough. I'l try the chisel.
 
Then the press. I'm going for one of Machine Marts economy ones. Clarke is the supplier I think.
 
The economy one looks a bit primitivebecause it uses a bottle jack for the urge, but it has the advantage that the frame bolts together. So if you need to get something really large dia in there, you can. Where you may not be able to with the smarter presses that use a purpose built ram
 
 
31/12/2011 16:25:14
Thank you Jason - tis exactly what I need - and shall make.
 
Tery - yes I can see the advantages of the chisel for smaller/copper rivets, but as indicated, I was thinking more on the lines of 3/16 and 1/4 rivets for TE wheels.
 
Rivet squeezers are excellent tools too, and making one would be good because the commercial ones are expensive. However there comes a point where size, as they say, starts to matter. The 5" loco boys are at one level in the riveting stakes, and possibly in the same or similar pool as the 3" TE gents, but even there I was dealing with a lot of 1/8 iron rivets on the strakes. Once you go up to the 4" engines, then, even for a smaller engine, it becomes a more serious problem.
 
I have seen a thing like a rivet squeezer which did an excellent job for dummy rivets. I suppose you'd call it a dimpler, but the fake heads looked very convincing.
31/12/2011 12:40:12
I thought it would come to that. The only problem with the jig (sawing) is that one has to lock the rivets, or they will rotate (I guess) under the saw?
 
Might come to something like sawing roughly and a burst with an angle grinder and sanding disc for length? Or some grub screws.
 
Food for thought - thanks.
Thread: Help with poor finish when cutting with the side of the cutter
31/12/2011 10:53:09
If its resonance, or flexing , then the other solution might be to change the number of teeth on the cutter. I know most endmills are 4 tooth, but some of the indexable ones have varying numbers of teeth, and you can often find 3 tooth cutters around.
 
One other solution might be to increase depth of cut, so that the helix of tooth A has not left the work before tooth B engages. That cuts down vibration and improves finish, if the size of job permits.(and the shape/helix of the cutter). The small FC3 cutters always seem to produce a very good finish, and that, I think is/may be one of the reasons.
 
I think its also important to realise when milling that the depth of cut is determined by the feed - or more specifically the tooth load per rev, so just because one is taking a deep (long) cut, doesn't mean to say that the cutter is seeing a deep (big) cut. Tooth loads are generally within a couple of thou per tooth per rev - but then if you have a lot of teeth you can feed very fast. What may well be happening is that you are using too low a feed, and the cutter is skidding initially and then digging and engaging, so you end up with peaks and troughs. (and a blunt cutter can do this too - blunt cutters need higher feeds).
 
If you look at Tubal Cains book Milling Operations in The Lathe, the whole business of tooth load and feed rates is explained very well. Its getting a little long in the tooth, since it predated carbide cutters (toothload figures for which should be available from the suppliers, manufacturers web site), but its first calss on the principles one needs to understand, and where to start.
 

Thread: Turning very thin bar
31/12/2011 09:51:50
Tel - yes I have a thing similar to that, but if you'll forgive me saying, I find it a real pain to set up. Because before you can start cutting, if you need an accurate dimension, you need the tool infeed set accurately (and you cant use the cross slide.)
 
And having taken a cut, the old bush won't fit, so you have to make another bush.
 
I'm not criticising particularly, just noting that the whole business of turning slender shafts by whatever means to an accurate dia is just plain awkward. (Perhaps it depends on how accurate)
 
Chris - agreed, but then they always said that there are liars, damned liars and then come statisticians. After that you get model engineers, who seriously reckon you can reverse flow the steam into a boiler without carrying any oil back into said boiler (it comes out the chimney so it should go with the flow?) Yet there is no emulsion in the gauge glasses, no priming, no nasties on blowdown. Clever stuff this oil?
 
Carbide - yes thank you . Excellent, and I have a green wheel to sharpen it, when the time comes

Edited By mgj on 31/12/2011 09:52:35

Thread: Rivet snap dimensions
31/12/2011 09:38:40
Next problem - if one is cutting rivets to a length - how to do it quickly? Is there an answer.
 
I find if I use cutters and so don't get a nice square end the shank tends to tip leaving an "offset" or malformed head. So its down to hacksawing many rivets - long time slow.
 
Hammering them - work of a second or so with an air hammer, but cutting to length?
 
Any solutions? Or is this just one of the little joys of model engineering?
30/12/2011 23:59:40
Perhaps a lot depends on how much force one has available, and how soft the rivet is. .
 
Certainly you can form the head of a rivet just using a domed snap, but Terrys system is easier, and best is the use of a set up and then a conical snap and finally a domed finisher. The problem being, starting with a domed snap is that its quite easy to offset the head, and once its been knocked off line, its difficult to get all straight again.
 
The bigger presses tend to use guided snaps/dollies, which makes a difference. I shall be doing a 4" TE shortly, with 3/16 and 1/4" rivets. A guided dolly is the way to go there, along with a 10 ton press! The other alternative, where visibility is less of a problem, is to knock the rivet into a countersunk hole, which gets away without forming a second head at all - if that suits the circumstances.
 
There are various charts for head size etc, but snaps do differ, and its probably worth experimenting on a bit of scrap first. Once things are setting right, you know how much to allow.
Thread: Turning very thin bar
30/12/2011 23:23:15
I must admit, I always have an awful job getting something thin truly parallel along its length. Real pain.
 
I've tried the tailstock support bit - even bought one of those nice centres with different sized points. They all help. So do the 55deg tools, as does a pointy bit of tool steel properly Quorned to shape. But at smaller dias, eventually it all gets untidy, and tools and centres tangle. And without a centre it wil probalby flex, and if its long and thin, even multiple runs will cause it to flex.
 
So, being too idle to make hollow endmills, and finding the baby travelling steadies that you drill a hole in for size very awkward, I now leave a length well over size, and overlength. Centre drill, and turn down for a short length to below dia. This gives a clear working area. Then turn what you need down to actual dia, without getting tools and centres tangled. Lop off the excess at the end. A hollow centre is also good. You only need a 1/16 of excess to give working room to get a pointy tool into place with adequate run on.
 
Its not foolproof and if very thin it can still flex, and the other methods have to be used, but mostly it works well.
 
chris S - you have to rember, when seeking common sense, that half the world is of below average intelligence. One of those BGOs that crop up ocasionally, and one has to remember when people expect air to rise at one end of a boiler, but to rise and then descend against a flow at the other - despite being lighter than steam - so it can then get to the other end and then rise again!. Or a changed note from the safeties indicates air in a tilted boiler, when every "musical" intrument in the world will change pitch if the sound box volume is altered. Or someone comes up with the idea of energy neutral brakes.

Edited By mgj on 30/12/2011 23:25:00

Thread: which coal to use
30/12/2011 22:58:42
I have a 3" LS- so I'm not sure if one is comparing apples with apples.
 
Anthracite I am not too fond of. It burns very hot and it seems to like a lot of draught, so its either white hot or dying and nowhere in between.
 
I've used various types of steam coal- seems to burn more red than white, but its not so up and down so I find it rather easier to use. But then I have also had some (theoretically) steam coal which clinkered very badly after hard work, and left the grate clogged.
 
Housecoal they say is pretty good - akin to steam coal. I like the smoke (which you don't get with anthracite). I didn't built a steamer to be all eco.
 
A lot has to do with getting the lumps the right size for the grate in use.
 
Truth is I doubt it matters, so long as you have grate, blast nozzle and coal sizes, and blower nozzle size set for the stuff one is using, but I prefer steam coal, or failing that a mix of anthracite and steam coal, using plum sized lumps.
 
Ask at the club, see what they suggest for such a loco and then give that  a go - see whatt happens? At the end of the day its a steam engine - ain't that critical and ain't exactly rocket science.

Edited By mgj on 30/12/2011 23:00:55

Thread: Fly-cutting flat surfaces
28/12/2011 18:17:40
What Ramon has raised is a very interesting point - the difference between smooth and flat.
 
Which is more useful - a smooth but slightly dished surface, or one which is a series of very small dogs teeth. It may not be (quite) so smooth, but it may actually be flatter. (CLA)
28/12/2011 18:04:48
It mans that the head is tilted along the line of traverse.
 
If you are traversing on the x axis and you have a tilting head then you'l need to check that. If its on the y axis you may need to reset the column or shim it a smidge.
 
If those things check out, another possible culprit would be the vice or whatever packing you are using, but theoretically that should not be so, because the only way to get a dished, as opposed to an inclined, surface is for the disc to be tilted with respect to the line of travel.
 
There is a sneaky one which allows the disc to deflect under load. ie your checks pan out, but the disc effectively tilts under load - flexing or in the bearings?
 
Theoretically, flycutting does generate a truly flat surface. In fact its very difficult, and you may find that you need to rub it on a plate to get it genuinely flat. (I use the term flat meaning truly flat)

Edited By mgj on 28/12/2011 18:08:53

Thread: Here we go - parting off
24/12/2011 16:40:31
Well I certainly won't suggest a rear toolpost. Most commercial lathes can't be set up to use them, and for me the rear toolpost on a small lathe is just plain inconvenient and cramped.
 
I could jam up anything with ease, and going wider doesn't solve the problem.
 
Mostly its down to rake angle (because you can get jam up on rear tollposts too (I know!!))
 
Basically if you have a lot of rake, which looks "sharp", then the download on the top of the tool generates an inwards vector, pulling the tool into the work. If you then don't feed fast enough to keep the x slide pressed up against the back of the leadscrew, the tool can jump forwards into the job - indeed its pulled forwards into the job.
 
This geometry also applies on a rear toolpost too.
 
Most of us who are having parting problems tend, from all I have spoken to, to increase rake, and feed gently - with care, because you think its about to jam up. Which is exactly what one should not do
 
So the tricks are to get rid of the top rake and part with a minimal degree of rake - you have been given this advice already in a different form, because the Glanze tools are fitited with ISCAR GTN2 negative rake tips, or clones thereof.
 
And feed positively so you keep the load on the cross- slide. If you are feeding fast enough, you keep the pressure on the x slide, and it can't pull forwards into the work. As soon as you relieve the feed, you unload the feednut, and it can pull forwards into the backlash, and you are in trouble. Mostly my  jam ups occurred not as you I was feeding, but just as I backed off, ready to take another handful of handwheel,  - and thats why.
 
Since that penny dropped, I have not had a single jam up, and I used to dread parting off. Now its the proverbial piece of p... . Same blades, same holders etc etc.
 
Rotational speed - of no great concern I reckon. If you slow down, your hand feed rate per rev (thickness of chip) goes up - which is not what you want if you are in jam up country. So now I part off at whatever sped I was last using, and more or less never in back gear. If it chatters a bit I slow down. 
 
I do have tipped parting tools, and they are excellent as Coalburner says, but actually I don't use them very much any more, because a decently ground Eclipse blade is better, and it doesn't jam! More useful too, because the front faces are ground handed so they drop the job off
 
You will see people producing drawings showing how a rear mounted tool is suposed to throw the tool out of the work. But actually they are too simplified to be of use, and take no account of the efffects of rake - the angle at which the force is being generated, or the difference between having a tool mounted, front or back toolpost, above or below centre (by a small amount) .

Edited By mgj on 24/12/2011 16:47:48

Thread: Radiant Superheater Types.
18/12/2011 17:01:54
Flue diameter is just over 5/8 - its 3/4 od tube.
 
This is new territory for me, but I was wondering if the spearpoint design could cause losses by that very sharp return bend.
 
Mind you, the concentric type with a "chamber" at the far end is hardly the "super flow" set up either.
 
Could be a case of any (effective) superheat is better than none?
17/12/2011 23:09:08
I was going to take the quick solutiuon and buy from Blackgates the welded spearpoint superheaters for Metre Maid. However, they don't do them any longer, and I am having a lot of trouble getting some made - its actually quite difficult to get them to the right dia, and still get enough swerve at the far end to achieve a decent weld, and still have them fit down the flues.
 
The alternative is to use the concentric type which I can get welded very easily, and will be far easier to get down the superheater flues - and I can keep the areas constant quite easily..
 
Is there any advantage with the welded spearpoint type, that anyone knows of, or are concentrics OK. Or when designing them, is there anything I should watch out for particularly.
 
Essentially I was going to pass the wet steam down the centre of a 5/16 tube, turn it round at the far end and bring it back round the outside in a bit of 1/2". Put holes in the 5/16 tube - x150% area to minimise losses at the firebox end turning through 180 deg, and bring it back down the outside. The cap at the far end would be finned of course, and I'll get it as far as possible into the firebox to maximise radiant area.
 
Anything else needed, since I have no drawings. .
Thread: Dore-Westbury info?
10/12/2011 17:58:47
For the Mk 2 version there was no specific belt tension, beyond tightening it till it didn't slip.
 
The 1/4" round belts are no longer available, but the 7mm transparent round poly belting from Hemingway works well, at the recommended tension for that. There is a cutting length - I forget the detail now, but the belt is so much short for every foot of run. Its on his website.
 
Works well for (5 years!)and hasn't upset the bearings in any way., so I doubt its that critical.
 
The other way to find out is to look at typical loads for motors, and see what they recommend.
Thread: Spur Gear Diff
09/12/2011 21:20:44
It is a very simple mechansim. The second half of your question was - is it worth it?
 
Probably not, unless you want to make it. It might even be a bad idea. Could a 1" Minnie pull you - probably on a very smooth surface, but its going to need every bit of traction available - and if you want traction, locked (no) diffs are good things to have, because the slightest bump and one wheel will spin.
 
People will say a diff will help steering. Well yes, particularly on vehicles whose l/w ratio is relatively high. You can get round that problem without a diff by removing a driving pin, but then you lose traction.
 
If you want to build a bigger one with a proper diff that comes in the form of cast gears and bevels, and which will most certainly pull you and others (at the same time), and is pretty compact and doesn't have lunatic prices for castings, look at littlesamson.co.uk (Little Samson models). The 3" Little Samson is a simple economic choice with plenty of grunt and is still family car transportable.(its a tiny bit bigger than a 2" Minnie at a sane price)
 


Thread: Speedy axle boxes
08/12/2011 20:29:33
Ah - yes. electricity that makes a difference.
 
Why did I use bronze - because I had it, and because if it wears out then I have an easily split - able axle box - the centres of the axles are relievd. If it ever came to it I'd use split shell bearings in a split axlebox. Steel or cast iron makes no difference. .
 
If i hadn't had bronze, I wouldn't have bothered. If I'd had some ball bearings of the right size I'd have used those, and if I'd thought about it enough, I'd have sent off to someone for some needle rollers or oilite. As it was drawn bronze was there, and if kept lubricated it will see me out - but then so would oilite or rollers.
 
Take your pick - does it it matter as long as its kept lubricated..
06/12/2011 22:48:53
Yes - why not. We run cast pistons in cast bores - though the heat etc does have some metalurgical effects that means that though it sounds similar, actually one is comparing apples and pears.
 
Grease will solve the problem!
 
Stub mandrell - Sweet Pea uses gunmetal hornblocks with cast iron axleboxes as standard. I added bronze bushes for the axles, and just pressed them in. Sweet Pea /Metre Maid is not known for having undue wear on the axle assemblies. Depending a bit on the ashpan arrangements, it might be worth rigging some sort of cover or deflector to keep the grit away from rotating bits?

Edited By mgj on 06/12/2011 22:49:44

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