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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: C3 Purchased
07/09/2010 20:43:37
Hi Tigermoth,
 
Wow, big models! I got as far as model gliders and some very simple RC power planes back in the days of 27MHz, before I reverted back to flying full size gliders and then full size power. I've never flown a Jungmeister, or a Spitfire come to that, although it's on my list, along with a P51D and a fast military jet. All I need is a lottery win.
 
Regards,
 
Andrew
07/09/2010 20:16:53
Hi Ian,
 
Hmmm, didn't know that, but I hope the Canadians fitted brakes too! No brakes and a tailwheel would be rather exciting. One would certainly need to be nifty on the rudder pedals. I have seen one Tiger Moth with brakes and a tailwheel; just didn't look right.
 
I wouldn't swear to it but I think most Pawnees in the UK are also used as glider tugs. The one I'm sitting in, in the avatar, is a glider tug. If there is any crop spraying left in the UK it's very low key now. There was a flurry of activity in the 70's and early 80's but then it died equally quickly. Our fields tend to be quite small, are odd shapes and are mixed up with other crops, livestock, houses etc. A few cases of dogs, cats, kids, washing and gardens being sprayed brought a lot of pressure to bear. I did once fly a Pawnee with spray gear fitted, G-BILL, originally owned by Bill Bowker, who was one of crop spraying pioneers in the UK. Nice aeroplane, 260hp, very smooth and two blade prop so good climb rate. The only snag was it being on a Public Transport C of A, so the paperwork took longer than the flying!
 
Regards,
 
Andrew
Thread: What is the ultimate lathe for model engineering
07/09/2010 09:22:36
Brian,
 
Well, there's a golden opportunity for you; why not write an article for ME or MEW utilising your Schaublin and Deckel?
 
By the way I do have a Myford in my workshop, but it's not a lathe, or a mill. I'll leave you to work that one out.
 
Regards,
 
Andrew
Thread: C3 Purchased
06/09/2010 23:05:06
"Next project was to make a pair of alloy wheel hubs for my RC Piper Pawnee"
 
Hi Tigermoth,
 
Given the quote you'll no doubt recognise the aeroplane in my avatar then. The Tiger Moth isn't a bad aeroplane either, apart from the ailerons. It's what I learnt to power fly on, G-AHIZ was my first solo aeroplane. Used to fly G-ANOO from Thurleigh, near Bedford, until we sold it. Was a bit of a challenge operating on a concrete runway though, with only a tailskid and no brakes.
 
Regards,
 
Andrew
Thread: Using a Posilock Chuck
06/09/2010 20:08:33
Can't say I've used a 1mm slot drill in a Clarkson autolock chuck, but using a 1/16" slot drill worked fine with the 'Clarkson' method.
 
Granted the low cutting forces on such a small cutter are unlikely to tighten it much, but at least they are in the tightening direction. But then with such low forces one is unlikely to be worried about the cutter becoming loose either.
 
In general I don't bother using an Autolock style chuck with small cutters now, I use a plain shank cutter and an ER collet chuck.
 
Regards,
 
Andrew
05/09/2010 22:38:36
I prefer the Clarkson method. The only time I left a small gap between the sleeve nut and chuck body I shattered the endmill, at the screwed end. I assume this was because, as the sleeve nut wasn't fully home, the collet was not at the top of the endmill. As the cutter rotated slightly under the cutting loads the centre in the chuck split the top of the endmill as there was no support from the collet to resist the forces.

If the cutter is properly home the depth of cut shouldn't change as the cutter tightens slightly. The sequence as I see it is as follows. If the cutter turns (tightens) slightly under cutting loads it cannot move upwards because of the centre in the chuck. Instead the thread causes the collet to move down slightly into the taper on the sleeve body. Hence the collet grips the cutter more tightly.


As a proviso, and I might be talking nonsense, I've never used the old Clarkson 'C' style chucks, only the newer 'S' types. However I did recently make a new hardened and ground centre for a Clarkson 'C' style chuck for a friend, so I've had a good look at them.

Regards,

Andrew
Thread: What is the ultimate lathe for model engineering
05/09/2010 11:14:52
I knew I'd made a mistake when I bought my lathe; now I know why. It hasn't got T-slots on the cross slide, dooooh! There are two triangular slots along the length which can be used for bolting accessories onto the cross slide, but I guess that doesn't count. Mind you it will turn stainless at speeds and feeds appropriate to carbide tooling.
 
I have to make up for my deprivation by resorting to plenty of tea slots during the day. The kettle is always on for a brew.
 
Regards,
 
Andrew
03/09/2010 16:41:28
Think carefully before asking questions! 
 
Before deciding upon the 'ultimate' lathe and mill you would need to define those criteria by which each machine will be judged, otherwise the choice is just somebody's opinion. But, since those criteria will be different for each person the OP's original question is meaningless. Some of the things by which an individual may make a choice are:
 
1) What is being made; size, materials, complexity
 
2) Other machines available, which will dictate how versatile each machine needs to be
 
3) Space available
 
4) Electrical supply available
 
5) Depth of one's pocket
 
6) Skill of the operator
 
7) What yer mate has, and sings the praises of same
 
8) What you used as an apprentice
 
9) How much time you have available
 
And a whole load of other things.........
 
The only real way to find out is to buy a lathe and a mill, use them, and then you'll realise what you should have bought!
 
Regards,
 
Andrew
Thread: Phase Converter Which Type?
03/09/2010 09:37:24
My experience in the UK mirrors that mentioned by Alan and John above. I simply rang the electricity company, they sent a man out to do a survey, they quoted a price and you either agree or otherwise. However, the cost is highly dependent upon the location of the existing three phase supply. The total cost to me was £2500. The existing street supply is on the far side of the road to me, and I'm told by a friend in the house building trade that this probably accounted for £1000 of the bill. The reason being that if the electricity companies dig up the road, then they have to gaurantee the repairs for a year. Consequently they bump up the price, just in case their sub-sub-contractors make a mess of it.
 
Although expensive, I think that having the three phase supply installed was worthwhile in comparison to the time wasted in mucking about converting motors from star to delta, buying inverters (this was 10 years ago, so the electronics wasn't as cheap then) and sorting out the contactors, wiring etc. The other factor was that the existing single phase supply was below par, and needed replacing according to the survey report done before I bought the property.
 
I can categorically state that no license is needed, and it is nothing to do with the council. I've never had a visit from revaluation people or aliens. I pay exactly the same per kWh as I would if it was a single phase domestic supply. The house runs on a single phase anyway!
 
Regards,
 
Andrew
Thread: Lathe lub oil
01/09/2010 20:23:10
I would concur with KWIL that the page in your manual is misprinted.  As stated the top three icons should point to the top line and the bottom icon to the bottom line.
 
In my M300 I use the following:
 
Main gearbox: HYD68AW - equivalent to Shell Tellus 68
 
Powerfeed gearbox: MO220 - equivalent to Vitrea 220
 
In the apron and other slideway areas: SL68 - equivalent of Shell TX68
 
I buy all of the above from Hallett Oils in Wolverhampton.
 
www.hallettoil.co.uk
 
The people there are friendly and helpful. They made a special very thin oil for my surface grinder spindle a few years back. I also use their Biokool14 coolant; it seems to last very well with no nasty smells.
 
Regards,
 
Andrew

Edited By Andrew Johnston on 01/09/2010 20:23:58

Thread: Phase Converter Which Type?
31/08/2010 21:09:02
Indeed an active PFC boost converter is a type of switch-mode power supply. The problem with a passive voltage doubler is that it doesn't provide quite enough headroom on the DC bus to generate a three phase supply from a single phase supply, if you want to maintain the same phase to neutral voltages from input to output. Hence the need for an active boost converter.
 
I'm not sure where 100kHz gets fed to a three phase rectifier. The PFC converter runs at, say 100kHz, creating a DC bus which then feeds the three phase half bridges that generates the AC output.  The newer styles of PFC converter do away with the input rectifiers, thus saving the energy lost in the diode drops.
 
The informal group I work with designed what is essentially an AC to DC boost converter last year. It turned out to be quite a design challenge mechanically, as the unit is only 300x300x120mm and is rated at 30kW in an ambient temperature of 100°C. Liquid cooled of course. The unit takes the three phase output from a generator on a diesel engine and outputs 600VDC. Of course once the hardware is in place it is trivial (software changes) to run the converter in reverse and use the 600VDC to generate a three phase supply which uses the generator as a motor and starts the engine.
 
Regards,
 
Andrew
 
Thread: Scale model Economy hit & miss engine builders wanted
28/08/2010 11:29:57
Interesting information, thanks guys, which I have no doubt will help me when I get my Economy engine finished. Just need to make a few more bits, weld up a stainless steel fuel tank,  finish the design of my own ignition system, and design and build the spark plug.
 
I was planning to try running the engine on Colmans stove fuel. Not that easy to get in the UK, but the bigger camping shops seem to stock it. No idea what the fuel is, but I assume it's a mix of the lighter hydrocarbons. Anybody tried this fuel?
 
Regards,
 
Andrew
 

 
 
 
 

Thread: Chipped corners on milling cutters
27/08/2010 14:52:14
A Newell Microsyn 2-axis DRO for my vertical mill is the best thing I ever bought for the workshop. Spent some of my redundancy money on it, and it has more than paid for itself, enabling me to win jobs that I wouldn't have been competitive on without it.
 
Only had one wobbly with it in ten years. It got itself into an odd state that made no sense to me. A friendly tech support guy at Newell talked me through some hidden codes and setup functions that are not in the manual to fix the problem. In essence the unit had reconfigured itself as a lathe version. He mentioned that this could happen if there was a power glitch at power up. Oddly enough I HAD just noticed an electrical funny on a power up sequence just beforehand.
 
Best Regards,
 
Andrew
 
Thread: Phase Converter Which Type?
26/08/2010 10:09:52
As I understand it the traditional way to get 415V three phase from 240V single phase via an inverter is to put a three phase step-up transformer on the output of the inverter. Like some of the other respondents I did a quick internet search and didn't find anybody else selling 240V single phase in, 415V three phase out inverters. Seems slightly odd, apart from the obvious point, already made, about a limited market.
 
One would assume that any half decent inverter should be using active PFC (power factor correction) in the initial AC to DC stage. Assuming that one wanted to build the said inverter I would have thought that the simplest way would be to adapt the active PFC to a incorporate a boost converter. This would be fairly efficient and since it should be switching in the 100kHz region and the inductors will be fairly small. After that just use the standard three phase half bridge, rated for the appropriate voltage.
 
Regards,
 
Andrew
 
 
 
 
 
 

Thread: Undersize Taps
26/08/2010 09:41:19
Interesting, I had read somewhere that the bottom tap in a hand set was slightly larger than the taper and 2nd. Can't find anything about it in Machinerys Handbook though, but my older copies do mention the serial tap sets already discussed. However, for my metric hand tap sets it doesn't seem to be the case.Commercial screws fit fine in a thread using the taper tap only. I only use the bottom tap if I need a few more threads at the bottom of the hole, and I never use the 2nd tap. All the metric tap sets are by Dormer. It will be interesting to experiment with some of my older BSW/UNC sets to see what happens.
 
If the tap cuts a bit oversize you can always tighten up the thread a bit by putting a tapered rod in to the hole and hitting it with a hammer. This will distort the top few threads and tighten the fit. Similarly a ball bearing on the top thread and hit with a hammer achieves something similar.
 
Regards,
 
Andrew
 
 

Thread: Doris LMS Black 5 by LBSC
25/08/2010 16:31:58
I can confirm that UK car brake pads do not use asbestos any more. Most medium performance pads use a mix of iron, copper, steel and graphite to form the pad. The snag is that the pads tend to be harder than the old asbestos based ones and hence tend to wear the brake discs more quickly. I know this because I recently had to have changed both the pads and discs on the front wheels of my car at great expense. I asked lots of questions first, including demanding to have a look for myself before agreeing. Both pads and discs were well worn, so not much choice in the end.
 
Regards,
 
Andrew
 
Thread: Chipped corners on milling cutters
23/08/2010 23:53:08
Just as important as feed and rpm is the tooth load. Nornally one would start with an estimate of the tooth load, times that by the number of flutes and, via the recommended surface speed and hence rpm, you can calcualate the feed rate. As a conservative estimate for tooth load assume 1% of the cutter diameter. So, for a 10mm diameter cutter that would be 0.1mm, or 4thou per tooth per revolution. A sure way to damage cutter edges is to allow them to rub rather than cut.
 
Another way to damage edges, particularly for carbide, is allowing the cutter to recut the swarf, sounds horrible too.
 
As JasonB says carbide is unforgiving because while it is very stiff, that stiffness comes at a price, which is brittleness. For instance if you lower a cutter gently on to the workpiece to set a reference, but over do it by a couple of tenths then HSS will just dent the workpiece slightly. Carbide will chip instantly, even if the workpiece is relatively soft, like aluminium alloy. I learnt that the hard way (no pun intended!) using plain carbide cutters on a CNC mill. Overshoot the zero by a tiddly amount and the corners of the mill are chipped. If you rotate the cutter by hand at the same time as jogging down until you see a witness mark the sharp corners are fine.
 
Might any of this be a possibility to explain the chipping?
 
Regards,
 
Andrew
 
Thread: Where to buy indexable tool tips
22/08/2010 14:38:11
I would whole heartedly endorse the statement by KWIL. I was going to buy a set of insert lathe tools from a well-known ME supplier. Having pushed the sales person they eventually admitted that the inserts were non-standard, so I didn't buy.
 
On another note regarding insert tooling I have found that the Glanze boring bars (Indian made) from RDG are of reasonable quality, but the supplied inserts are hopeless. Fortunately they take standard ISO inserts, which I get from either Greenwood or industrial suppliers.
 
Regards,
 
Andrew
 
Thread: Which Milling Machine?
22/08/2010 09:37:34
My experience has been that since getting a vertical mill, and fitting it with a DRO, I almost never use my drill press. Can't remember the last time I used it, but it is probably more than a year ago. If I need to whip a small hole through something for the garden or house I use the portable electric drill and if it's for the workshop it usually needs to be precise.
 
Of course your mileage might vary, depending upon what it is you're making.
 
Regards,
 
Andrew
 
 

Thread: advice on purchasing a small mill
21/08/2010 10:35:21
Just to be clear, the 1 cubic inch per HP guide is independent of the cutting tool type. It is based on the energy needed to shear away and deform the material in a given time. The type of tooling will dictate the surface speed of the cut and the depth of cut. Thus there are two different calculations here. One, which is dependent upon tooling type, will dictate the rate at which metal could be removed. The second, which is independent of tooling type, will determine whether the machine has sufficient power to achieve that rate.
 
I tend not to use flood coolant with carbide tooling, especially on the lathe. On the CNC mill I do use flood cooling, but this is mainly to wash away the swarf, not to cool the tool. Carbide doesn't mind running hot; for some of the newer coatings it's a requirement to run hot for them to work properly.
 
While the ME doesn't need to achieve 'industrial' levels of metal removal I susepct that a lot of reported machining issues might go away if more attention was paid to cutting speeds, feed rates and chip loading.
 
As has been stated above the size of mill you need will be dictated by the size and type of parts that need to be machined.
 
Regards,
 
Andrew
 
 
 
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