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Member postings for Andrew Johnston

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

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Thread: Calculating Feed Rate using Myford G-box
05/09/2011 22:14:39
Posted by JasonB on 05/09/2011 21:00:25:
Thats Julia Not Julie.
 
 
I think not; there's a user with the sobriquet 'Julie' on this site, but not 'Julia'.
 
Andrew
Thread: 3 phase
31/08/2011 21:47:57
Like it or lump it I suspect you'll get a minimum of 60kVA for a three phase supply. As JohnS correctly says the standard single phase supply for a residential plot is 100A. I make that 23kVA rather than 20kVA, but there's probably an allowance for some losses. So, for a three phase supply you'll get 3 phases, each at 100A, ie, 60kVA. I can't imagine the electricity supplier fiddling around with smaller cables.
 
That's what I got when I replaced my single phase supply with a three phase supply. Three phases, each at 100A. Each machine runs off the three phase supply through an individual 16A/phase breaker. The largest motor I run is 5HP, DOL and I've had no problems with breakers tripping.
 
Regards,
 
Andrew
Thread: Reaming a pinion, wall thickness?
31/08/2011 21:27:32
John S:
 
I suspect the motor application is radio control models. So one, the quoted power is likely to be at some fantastical rpm. Second, a quick Google search threw up some motors of a similar size quoting 'peak power' of 3-4kW. However, there is no information about the duration over which this power is quoted. So I think it's basically 'our number is bigger than yours' marketing b******ks. It's a bit like the old audio amplifiers being rating by peak music power; essentially meaningless.
 
Apart from anything else you wouldn't half need a big battery to supply that sort of power for any sustained length of time.
 
Regards,
 
Andrew
 
Edit: Ooops, typing too slowly!

Edited By Andrew Johnston on 31/08/2011 21:28:20

Thread: Proof reading, what proof reading ?
29/08/2011 20:12:05
Sorry, yes an 'iron thermal' relates to the fact my big glider has a small engine in the fuselage, which can be raised up and run if it all goes to worms. Technically it's a self-sustainer, in that the motor is quite small, only a few horsepower, and is intended to keep the glider in the air, but not to allow it to take off under it's own power. Mind you it's pretty marginal at keeping the glider in the air. If everything is going for you, then the climb rate is about 100 feet per minute. The installation is dead simple, two cylinder two stroke, no throttle, and air start. The big advantage of a self-sustainer is that as far as the CAA, and law, is concerned it is still a glider, so no licence required.
 
Terry: I must have been over your place at one point. After I finished getting myself out of the hole at HusBos I was pretty much over the M1, due west of HusBos. I then nipped off to Bruntingthorpe before heading back to Cambridge.
 
Norman: That's too accurate a description of the trials and tribulations of field landings to have been made by a non-participant? At least when one of my gliders had the trailing edge of wing eaten by cows it wasn't me that put it in the field, but my syndicate partner.
 
Regards,
 
Andrew
 
PS: Self-sustainers are all the rage now, despite the extra cost. There are probably several reasons. One, it's a PITA doing retrieves, fuel is expensive, and it means finding people who are prepared to give up many hours of time, as well as debates about who can drive your car. On a more practical note, because of the more unsavoury parts of society, many fields have locked gates or ditches across the entrance that you can't get a car through. The final blow is that with the amalgamation of farms, at least in East Anglia, the farmer might live many miles away. And he's not going to leave his supper and a beer just to unlock a gate! The last field I landed in, just to east of Cambridge, had a farmer who lived near Sudbury, a good 20+ miles away.

Edited By Andrew Johnston on 29/08/2011 20:19:56

Thread: MT3 Standards
29/08/2011 11:14:57
Or they could both be wrong. And we all know two wrongs don't make a right.
 
Andrew

Edited By Andrew Johnston on 29/08/2011 11:15:15

Thread: Proof reading, what proof reading ?
29/08/2011 11:07:22
Hi Robin,
 
Thanks for asking; unfortunately the gliding is competing, and losing, with the great British weather! It is my day in the big glider today. I will be going out to the gliding club soon, but the weather is doing exactly what is forecast, ie, over-developing. So I don't think I will be flying.

I haven't had to use the 'iron thermal' in anger yet, although the thought did cross my mind the last time I flew the big glider. I arrived at HusBos (a gliding site near the M1/M6 junction) at about 1500 feet, after rejecting a few climbs as I didn't think they were good enough. There were then three choices, find some lift PDQ, start the 'iron' thermal', or land and have another launch after a nice cup of tea. I chose to park under the nearest circling glider, only a couple of knots climb, but it gives you thinking time and some height to move on to something better. Took me about 15 minutes to sort myself out and get back to cloud base. After that no more hiccups! Total flight time 4 hours 30 minutes, total distance flown 330 kilometres.
 
Last Monday I did my biennial flight review with an instructor to keep my power licence current. As part of a new CAA initiative the instructor also had to assess, and report on, my English skills. Apparently he rated me 'expert'.
 
Regards,
 
Andrew
 
PS: Completely overcast in Cambridge now, wouldn't be surprised if it rained later. Ah well, at least it means workshop time this afternoon.
Thread: MT3 Standards
29/08/2011 10:23:41
In my newest Machinery's Handbook the depth of Morse taper in a socket is defined, as is the length of Morse taper tooling with a tang. Hence by implication the length of a Morse taper without tang should also be known. It shouldn't be longer than the depth of taper in the socket.
 
Regards,
 
Andrew
Thread: Proof reading, what proof reading ?
28/08/2011 19:54:54
Martin; looks like you've quacked it!
 
For anybody who doesn't see the connection, technically the small winglets at the front of the fuselage are called canards. Colloquially, canard is also used to describe the generic arrangement of main wing at the rear and small wings for stability at the front. Canard is also the French word for duck, hence........
 
I will now duck, in another sense of the word, in case there are any incoming brickbats.
 
Regards,
 
Andrew
28/08/2011 14:31:37
In response to Ady's picture all I can say is 'quack quack'. I'll leave it to others to work out why that is appropriate.
 
Regards,
 
Andrew
Thread: Info wanted on making use of ex aircraft 'Trim Servo'
27/08/2011 10:47:34
The 28V DC system on aircraft is still based on 24V. It is just that the alternator voltage is used. That's the same as your 12V car system. When it is running it will not be at 12V, but is more likely to be nearer 14V.
 
Larger aircraft also have an AC electrical distribution system. Normally 115V, 400Hz, three phase.
 
Regards,
 
Andrew
Thread: So, now i have removed the Clarkson chuck should i stick with it?
27/08/2011 10:41:29
Posted by John Stevenson on 25/08/2011 16:18:28:
 
However fast forward to nowadays and the use of CNC's and experienced users of CNC will use the former method, the reason being if you use the correct factory method you will tighten the cutter, set the tool off set and once in use it self tightens and your offsets go all to pot.
 
 
I don't understand this; surely if the cutter rotates slightly under cutting forces it doesn't move axially, as it is constrained by the centre. Instead the collet moves down slightly against the taper on the sleeve, thus tightening the grip.
 
The only time I tried the method of leaving a small gap between sleeve and body the centre broke the end of the cutter.
 
Regards,
 
Andrew
Thread: Time for reflection
27/08/2011 10:35:02
Posted by Steve Withnell on 27/08/2011 08:23:29:
 
....... and another 547 bits to make for my Whittle V8, which will probably result about 5470 questions on here!
 
 
Errrr, 547 bits? But a V8 has an even number of cylinders. Oh, of course, you're taking into account the bit that will inevitably be left over once the engine is assembled.
 
Regards,
 
Andrew
Thread: So, now i have removed the Clarkson chuck should i stick with it?
25/08/2011 15:22:39
Posted by John McNamara on 25/08/2011 13:44:21:

To set a cutter in the Clarkson is so simple. First insert the correct collet to match the cutter shank, Then Screw in tightening collar on the chuck by hand until it is fully screwed in without the cutter. Then screw the cutter in until it hits the centering pin. Now the important bit; unscrew the tightening collar about a third of a turn and screw the cutter in a little more while keeping the tightening collar from moving. Finally tighten the tightening collar it should almost but not quite stop against the main chuck. It only needs to be moderately tight, there is no need to apply great force.


 
Interesting, but not what my Clarkson instructions say:

Does the chuck use C or S collets?
 
Regards,
 
Andrew
Thread: end mills, how many flutes?
24/08/2011 22:57:52
Posted by Stub Mandrel on 24/08/2011 21:39:42:
A two flute cutter can never have more than one flute cutting at a time.
 
Straight plunge cut?
 
Regards,
 
Andrew
 
PS: In theory, theory and practice are the same, but in practice theory and practice are completely different.
Thread: Electronic Speed Controller
24/08/2011 09:58:46
As far as I'm aware the C5 motor is a permanent magnet DC motor, so speed control is just a case of varying the amature voltage. Two quick ways spring to mind.
 
One just use a large power device, a MOSFET is probably better than an IGBT at low voltage, and turn it on slowly. While turning on there will be quite a lot of dissipation in the power device; put it on a bigger heatsink! It would be simple enough to generate a linear ramp to drive the power device. However since the turn on characteristics of the device are not linear you may not get a linear increase in voltage at the output.
 
The second method uses a PWM signal increasing linearly from 0% to 100% to turn the power device on and off. To a first approximation this takes the switching characteristics of the power device out of the equation, as it is either on or off. The output voltage then becomes solely a function of the PWM.
 
Regards,
 
Andrew
Thread: Old Oxygen Bottles Use
23/08/2011 21:32:06
Posted by Jon on 23/08/2011 15:11:32:
Andrew wouldnt that be classed as breathing air?
 
 
Probably, but not breathing air can be a problem!
 
There used to be two types of oxygen system for gliders, the constant flow and diluter demand. The constant flow is what it says, 2 litres or 4 litres a minute. The diluter demand system adds oxygen to the surrounding air as required to maintain an adequate supply of oxygen. The diluter demand system is much more expensive and much bulkier, but much more economical with the oxygen. The rule of thumb is to use oxygen above 10000 feet, with a constant flow system set at 2 litres/min, switching to about 4 litres/min above 17000 feet, where the air pressure is about half that at sea level. Above 35000 feet or so you really need a pressure system, as at those heights the ambient air pressure is lower than the partial pressure of oxygen at lower altitudes. In other words, even if you're breathing pure oxygen you will still not get enough.
 
There is now a third system available from the US, which uses a canula, identical to those seen in hospitals, and an electronic meter systems. I have flown with these as we have said system in one of my two seat gliders, but if you don't have your own personal canula it can be a bit yukky!
 
Since I don't smoke and am moderately fit I find no problem up to about 14000 feet without oxygen, but it does vary widely from person to person. If you look in my odds 'n' sods album you'll see a photo of Mt. Pelvoux taken at about 13500 feet; I didn't bother with oxygen during that flight.
 
Regards,
 
Andrew
23/08/2011 11:05:17
There are companies that will test gas cylinders, but they are few and far between. I have two oxygen cylinders, one is part of an oxy-acelylene set and the other is in my glider.
 
I own the cylinder in my glider. It needs testing every five years. I take it to a place at Oxford airport, who then send it on to a specialist supplier. It comes back tested, stamped and filled with aviation oxygen, which is supposed to be specially dried. The cost 3 years ago was about £80.
 
The oxy-acelylene cylinder is owned by the gas company, and testing is their responsibility. I think this is pretty common for industrial gas cylinders, in the UK at least. I pay a rental for the cylinder, and a fee when I exchange it for a full cylinder.
 
When I bought the glider cylinder it came with an on/off valve fitted, and I also purchased a constant flow regulator and mask. I'm not sure that the valves are generally available, as they normally come fitted to the bottles. I have bought a new regulator for the oxy-acelylene set, about £60 if I remember correctly. When I started renting an argon cylinder it came with the valve and regulator all built in. I believe this is quite common in the EU, so you can bet your pants it'll be forced on us here too. The rental for the argon cylinder is a bit less than the plain bottle, the refill cost is a bit more, but the bottle runs at 3000psi rather than 2000psi, so you get more gas for the money.
 
In short I think you'll have problems trying to sort your own bottle. Many years ago we did get some old military oxygen bottles checked and modified for use in gliders, but it was difficult then, probably damn near impossible now!
 
Regards,
 
Andrew
Thread: end mills, how many flutes?
21/08/2011 22:17:11
I wouldn't have thought that the number of flutes would have much affect on the finish, assuming of course that you're using a constant chip loading. The helix of the flutes may have more of an effect.
 
I have read about slot drills (traditionally two flute) cutting oversize slots, although I've never really noticed the problem. Keys are made to fit anyway; I think keysteel is normally supplied slightly oversize.
 
There is supposed to be a theory that cutters with odd numbers of flutes are less prone to chatter. I suspect that within the amateur workshop machine rigidity would be the over-riding factor.
 
On the manual vertical mill I tend to use a mix of HSS and carbide, two, three and four flute, depending upon what comes to hand at the time!
 
On the CNC mill I've standardised on 6mm and 10mm three flute uncoated carbide and 12mm three flute HSS rippa mills. Smaller cutters, special forms, different numbers of flutes and special coatings are used as required.
 
The vast majority of cutters I buy these days are centre cutting, whether they be two, three or four flute. I suspect this trend is driven by commercial use of CNC where the same cutter is used for all operations where possible and hence needs to the ability to cut on the sides and end.
 
All things being equal a cutter with more flutes should allow more material to be removed per unit time. However, the gullets (space between the teeth) are smaller and more prone to get jammed with swarf, so as in all things it's a compromise.
 
Personally I think that three flutes is a good compromise between metal removal, swarf clearance and tool strength. And it's what my local tool store sells!
 
Regards,
 
Andrew
 
Addendum: Here's my take on Steve's question. I think the distinction between end mills and slot drills is becoming blurred, and traditional endmills are dying out. For carbide cutters I use Garr, as they are stocked by the local tool shop. In their catalogue they only list endmills. I had a quick flick through the 90 odd pages of endmills, 2, 3 and four flute, and as far as I can see they are all centre cutting.
 

Edited By Andrew Johnston on 21/08/2011 22:23:30

Thread: digital tv switchover
18/08/2011 22:19:09
Bizarre, one 'complaint' and the thread gets deleted. Not only that but the complainer has contributed nothing to this forum except sarcasm and whining about free subscription gifts not being available to him.
 
Andrew
Thread: Turning
18/08/2011 12:56:15
It's not a case of whether you can grip the material, it's more a case of whether it is possible to turn it at all. Trying to turn long thin shafts almost inevitably leads to breakage.
 
You'd be better off re-designing it, or making it from stock 0.5mm, 1mm and 2mm rod silver soldered together.
 
Regards,
 
Andrew
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