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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: Artillery
21/09/2009 18:24:12
You could also cut it with a shaper or slotter from head on. One of the Hemingway slotters and a dividing head would do that.
What was the ignition system on the originals - a vent tube presumably?
I'm just wondering whether we really are into FACs? I cannot believe that every yacht club in the country with its little signalling gun has an FAC? And this isn't a gun - its a model. And there are collectors exemptions. What about all the museum models - they all have FACs?
There is an awful lot of unsubstantiated rubbish spouted in the deer world about FACs, especially on the DSC courses by people who really don't have a full command of the facts, and things pass into lore. It might be worth talking to a real expert on the matter.(Speaking as someone who stalked commercially for 15 years - and mercifully got out!)
And no I'm not qualified to give an opinion on the legalities - but I do for example remember the tiswas that BASC got into about the Hunting bill, and there was a many paged article about how it was going to affect all the many game shooters who weren't going to be able to use their dogs and the effect it would have on owners and field triallers, and the cruelty of not recovering birds. Except that the Bill was about hunting mammals, and so far as I know, birds are not mammals, and using a dog to recover a wounded bird is not the prmary means of catching. Nor even is using tracking dogs for deer.
Talk to the experts if you want a "working" version.
Thread: Milling collet arbor jammed in milling machine
20/09/2009 21:29:15
Not that near Bristol- Sturminster Newton - but not a million miles if you are pressed and need access to a machine for a specific job. PM me if necessary.
You are quite safe -  my mill has an R8 taper so you won't jam anything in it. .
Thread: O Ring Groves
20/09/2009 19:46:00
Are we not in danger of getting in a tiswas over actual and nominal.
Jason is quite right- actual should be.139 +/- whatever the tolerance is.. However the groove size quoted is for 1/8 nominal. (.139 actual)
Thus the .132 depth is giving the pinch/stretch and the .160 the ability to roll slightly?
Geoffrey - you want that MEH - its just so useful.
I'm doing piston rings - same chapter. So it has all that sort of useful guff in it.(I'm delighted to say that, having solved that horrendous equation in there, my answer came out to within .003 of the graphical solution plotted in ME a little while ago.  Thankyou Casio.

Edited By meyrick griffith-jones on 20/09/2009 19:46:30

20/09/2009 13:41:50
The figure for groove width that you are using is the SAE figure.
For model engineering (low pressure) applications, a groove width for a 1/8 cord ring is .160"(Model engineers handbook).
Depth should be .132. (MEH).
The SAE figures which you quote,  should seal to 1500 psi, but at the cost of increased pinch and hence friction.
So says Tubal Cain. And he'm pretty well always right!

Thread: Milling collet arbor jammed in milling machine
19/09/2009 22:48:05
Ah well - when I did my young officers course, a very few (the Berlin Squadron and the gunner OPRA) were still on Centurion, though us Chieftain regiments still had Cent recovery vehicles.
So we got our V12 fix daily - though it wasn't supercharged, and it wasn't actually a Merlin - it was a Meteor and although it had Rolls Royce on the rocker boxes they were actually built by Rover.
Later I ran the Trials Section at Chertsey, and we had a tug with a Gryphon in it for pulling the early Challengers. (After the war many Gryphons ended up in MTBs which is where this one came ftrm. 1100 horse with little armour and no turret is still quite fun - esecially with a genuine crash box - double declutch up and down. And about 5-6 gallons per mile x country. Now thats what you call ecologically friendly driving. (The Cents were a bit more economical at about 3-5 GPM)
Still the sound of a real Merlin or Gryphon is just fabulous. We were later stationed at Saffron Walden, (Debden) just down the road from Duxford, and a lot of the piston engined fighters used hold over us quite regularly. Lovely to watch - brings a lump to your throat.
19/09/2009 15:09:27
With respect - I credit the remainder on this forum with a degree of common. It would be audacious to assume that they did not have it.
Else every post would be more caveat than useful information.
Anyway, it's too nice a day to have a squabble - over something that is outside our control. Hopefully this chuck has dropped out with just the wedges, and more extreme meaures are not necessary.
Thread: Lapping valve tapered plug
19/09/2009 11:13:20
I had the same thought on a boiler feed pump tapered valve. Not on an Allchin, but same idea.
I turned the taper on the plug, and the taper for the body reamer at the same setting using a nose radiused cutter - so the finish was pretty glossy. Then I just added a dab of silicone grease.
I havent tried it in service with water, only air, but that holds air without leaking at 150psi.  If it won't hold water properly I shall just add a small O ring this side of the hole in the taper.
Thread: Ball screws
18/09/2009 18:09:41
Some of these precision ball screws can be tolerably expensive.
RHP/SKF standard type brgs for the back of a Myford. £5 each +vat. (7205 or whatever).
Precision version, dimensionally interchangeable etc - £50 + vat. (each)
I just mention it in passing!!!!!
Thread: Milling collet arbor jammed in milling machine
18/09/2009 17:53:30
Bits - of flying HSS - So whats happening on an ordinary milling cutter?  Or a 2" tipped facemillat 500rpm? Or a gear cutter?  They are all going round - on an interrupted cut, and I don't see that we'd all be assessing the risk (Oh god!!) as high .And on the very rare occasions when one of those breaks, one doesn't notice bits flying over far.
Maybe I haven't done enough milling, but such things do not seem dangerous to me. Start putting fingers in there to see if its hot, or peering into rotating machinery without safety glasses, go mixing cloths and clothing with rotating machinery, or trying to hold jobs down by hand,  etc different story.
So lets be realistic.
If someone goes at it at warp speed on max power feed and generally behaves like a complete fxxxwit..........Clearly they are getting down on bended knee and begging for trouble, in which case they should hardly be surprised if it is visited upon them in full measure.
At the end of the day the individual is responsible for his own actions,  and will presumably consider the problem slightly before  doing something so spectacularly stupid. (Such as playing conkers without a face mask!!!!)
Last 2 points
1. We aint at work, so we can do as we please, subject to the above.
2 H&S doesn't stop people from doing things. All it actually says is that if one is going to do something, you do it in a considered way, such  that the risk is minimised.
So if one is going to use Chris system which might well work, take precautions, don't go at in a stupid way, ensure bits are retained and keep clear.
 I can light a gallon of petrol safely, and I can equaly half blow my head off. The difference is the degree of brain engagement?

Edited By meyrick griffith-jones on 18/09/2009 17:54:30

18/09/2009 12:57:50
Large cutters spinning out of spindles?
Team we've had drill chicks come loose - all that happens is the taper releases and the chuck stops turning.  Its not as if we are going to select maximum revs are we.
Low speed, start with a fairly light contact,short distance to top of block of wood. Its just going to drop onto the drawbar, or top of block of wood and stop. If there is only a small gap between bottom of cutter and wood/table it cant go anywhere because the lenght of the taper is going to stop it . It won't have eanough spce to go walkabout.
If the chuck does tighten on a loose drawbar - I'm afraid I don't see the physics of that possibility because there is nothing to hold the drawbar against rotation - to the point of no release. Lift head of machine, cut drawbar, turn spigot on lathe to fit collet or whatever, centre drill and drill out. Chuck recovered. Make new drawbar for working milling machine. 
If in doubt, stand well clear - like near the mains switch on the wall.
We are getting a bit over H&S?
18/09/2009 04:53:24
Personally I think it an excellent idea, along with wiping all tapers (chucks, reamers etc) with an oily rag after use to prevent rust.
Oiled or dry I've never had one jam up - but then I suspect I have never been quite so anxious about locking it in place either! 
To go along with Chris above - that could well work. I think I might tip some Plus Gas down from the top of the spindle and leave it overnight, before trying.
Thread: Ball screws
18/09/2009 04:34:56
If you look in the Nachi catalogue, which covers most of the standard bearings. They make bearings like every other manufacturer. You'll find single nut ball screws, double nut screws, precision screws, etc etc from 14mm dia up to 80mm, in various leads, plus the support bearings etc.
There is also an entirely separate ball screw catalogue which will I imagine list tech specs and installation requirements.  (And possibly a wider range of products?)
I should google Nachi, Hoffman, SKF etc.See what the makers recommend for their bearings as a first port of call. Then when you have found something reasonable, ring the makers tech services dept. You cannot beat talking to the makers of these things - they have a habit of knowing what the thing was built to do.

Edited By meyrick griffith-jones on 18/09/2009 04:36:02

Thread: Mini-lathe question
17/09/2009 15:25:29
And/or a dimple to stop the ball wandering. Or a little crushable copper slug in front of the screw.
Or since one puts a wipe of vaseline between strip and body to hold it during assembly anyway,  why not shove dob of it, (or grease) in the screwhole and pop the ball in. That'll hold it - just like getting a nut to stick on screwdriver long enough to get a thread to take  in confined spaces.

Edited By meyrick griffith-jones on 17/09/2009 15:30:25

Thread: Milling collet arbor jammed in milling machine
17/09/2009 15:21:27
True - and if you can't get it out directly with the wedges, tap them in firmly to put tension on, and then tap the end of the chuck or whatever between two hammers (from two sides) to induce a shock. Just like freeing any jammed taper - car swivel bearings spring to mind.

Then were I you, I'd be looking in my parts list to find out what the bearing numbers are - because they are screwed. No question - change them.Others may disagree, but I wouldn't even think about keeping them if they have been beasted like that. I might also look at the downfeed rack and worm, and just make sure that doesn't bear any witness marks.
I doubt the oil hurt - the taper was just doing what it was designed to do. To support Circlip, but in principle its the angle in the taper that does the holding and provides the self locking effect. All the drawbar does is to stop it pulling FORWARDS - it doesn't lock the taper in place, so it doesn't need more than nipping up.
This is the advantage of the R8 and Int tapers. They are too steep to self lock. The taper locates, and drive is provided by a dowell or peg.
Thread: Stent Tool Grinder
17/09/2009 06:17:11
Blackgates stock all the castings, and have done so for years. So they should be able to help.
Set of 4 drawings £18,  Full set of castings listed at £205,  motor, various accessories and bearings also stocked.
construction series ME Dec 91 - June 92.
Details form their catalogue which I picked up at the last MEX.
Thread: Engine building without power tools
16/09/2009 16:56:54
If I might suggest it - a little centre drill and a centre punch might be wise. (apologies to grannies)
All drills skid, even in a megabucks milling machine!.  A quick centre pop is a useful cure for premature baldness, as suggested. Using a centre drill means you don't need much of a pop - you can almost get away with nothing more than a scribed cross, so for a couple of quid its a very good investment.
Thread: Novice beginner
16/09/2009 06:37:21
Well then that would explain why I have an invoice for £1819.90, including vat and delivery? I did check the 3 listed suppliers and all were about the same. I went to Bell Boilers in the end, and I will say that it was spot on to drawing,  delivered when he said it would be, at the original quoted price. (Normal disclaimer)
The Foster is about £2k +vat., and I'll get Wayne Bell to knock up the boiler.
But I do agree that probably a 4" engine is best value. The castings are not much more expensive - I looked at LSM for 3 and 4" Fosters, and there is about £400 or so in it (from memory) And you do get a much more chunky machine - MUCH more, like 4CWT more which may be a consideration in the transport and in manipulation while building.
If I'd had the 6" lathe when I started, I would have gone for the 4", but starting with a Myford the smaller engine seemed wiser.  Actually a 3" engine would be a bit of a stretch for a Myford. Possible certainly, but one would have had to farm quite a lot out.

Edited By meyrick griffith-jones on 16/09/2009 06:38:25

15/09/2009 15:26:02
Little over 1K Jason! Unless prices havee dropped a bit recently. Promise. Still it makes the point that boiler costs are not a huge influence either way.
4" Foster is about £2k, and 8 months delivers. LS was about a year - thank God!

Edited By meyrick griffith-jones on 15/09/2009 15:26:22

15/09/2009 12:42:21
Jason you are right - I think the 6"GMT that was highlighted in ME a month or so ago is Edwards.
I had just though in my own mind that 6" was a bit big, but then I suppose it depends on the size of the prototype. Also most firms supplying castings offer machining., which can get one out of a hole.
Perhaps also for Kerbtrawler,  - you might satisfy your family interest by making any TE, and then naming it (various firms do custom nameplates) after which ever family member seems to offer the best advantage? This could offer a good balance between cost, convenience and personal survival?
Edward is cheap (very) on castings and (most important) P&P. Also drawings, and the drawings are sound.
The Little Samsons in  any scale are very simple engines, and with the cast wheels, and cast differential and bevel gears (cheap!!) they are not difficult to build.
The down side is that once you get into 3" engines really you are looking at a steel boiler, and you have to start to manipulate 10mm/1/2" plate. Which means for most of us getting a boiler built.  Which is going to cost £1500 plus the vodka and tonic. The advantage is that someone is making a bit for you over the 1 year delivery so you can save while tackling other castings and fabrications, and it is all properly EU certified and made to drawing so it all fits. (Bell boilers usual disclaimer) That's what I did.
On the smaller engines, yes you can make your own (satisfaction) boiler, but there is the fiddle factor, and the horsepower factor when built. Boiler cost - I'd doubt, if you bought a copper flanged kit, and took in the cost of the rods and gas, that there would be as much in it as you might think. 
I can say for sure that a 3" LS can be made on a 1237 spinning 17" in the gap. All of it, including machining the cast rear wheels. I did all my milling, including cutting all the drive gears on a Dore Westbury mill and a GHT versatile dividing head. (The setup doing a 9" 8DP final drive pinion was a bit creative but it worked and its accurate)  You could do a 4" LS on a 12xx lathe, but you would have to get the rear wheels machined (18" dia) or make spoked versions which are in the drawings.Flywheel will fit. Smallest thread - probably 4mm. I've used 3mm extensively on the 3"LS.
And a 2" sized engine in a 6" lathe. You don't think that might be a little brave. Some of those bits could be a little tiny compared with an 8" chuck. You might have a little difficulty actually finding the bits after parting off.
So there is a quite a lot of cogitation in there. Look at the Little Samson site, and also Live Steam Models, and Brunel and Blackgates. MJ of course. Bridport Castings (Foundries?) - they do the Plastow Burrells. A lot of them have been made
Be nice to know what you finally decide.

Edited By meyrick griffith-jones on 15/09/2009 12:45:18

Edited By meyrick griffith-jones on 15/09/2009 12:52:06

Edited By meyrick griffith-jones on 15/09/2009 12:53:18

15/09/2009 06:30:41
Gawd, with a 1224 gap bed. You could build a 4" engine if you wanted!!!! (Flywheel you'd have to get done outside. My next engine is a 4" Foster, and that will be built on a 1237 gap bed, though the 37 bit isn't important, and a reasonable mill)
Why, if I may ask, go to 2". The smaller it is the more difficult, simply because things flex, and are more difficult and fiddly to hold, screws and threads are smaller. 
You'll recover the cost difference if any, in unbroken taps.  
Go for a 3" if you can? Pull you along fine, and easier to make for my money. There are several 3" Burrells around, (but the Little Samson is very cheap for castings and has cast wheels which saves a lot of time)
For me, the most important thing is good drawings - ones that are error free. I know nothing about MJ, and wouldn't presume to criticise or suggest anything in that direction, but do make sure that whoever's engine you go for, the darn drawings are fully swept up
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