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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: VFD Drives
17/04/2011 22:51:08
Hi Steve,
 
Ah, that may be true, I've only got the one electricity meter, in a domestic environment, it just happens to be a three phase meter. I don't know what you might get charged if you have more than one meter. The single phase supply for the house is split off after the meter, but before the three phase distribution box.
 
Before I had three phase installed I asked the supplier three questions:
 
1) Would I pay extra for a three phase supply/meter? - No
 
2) Would I pay the same domestic rate per kWh? - Yes
 
3) Would the meter cope with an unbalanced input? - Yes
 
Regards,
 
Andrew
17/04/2011 18:47:30
Posted by Steve Garnett on 17/04/2011 17:34:40:
 
Even if you don't use converters at all, and run 3 phase motors from a 3 phase supply, you could get a significant saving by using VFDs, assuming that the machinery is all you have 3-phase for. Simply because by running it from a single phase, the electricity supply company isn't charging you more for the extra metering. Dunno how much that works out to these days, but it's probably significant.
 
Not sure I understand the above comment? As far as I'm aware I don't pay any more for my three phase supply than I would for a single phase one. I also pay a normal domestic tariff for the units used. Units seem to go up and up, but that's another story! My electric bill doesn't mention anything about three phase; just the number of units used and the rate per kWh.
 
Regards,
 
Andrew
Thread: Tool box shadow foam
10/04/2011 22:16:19
I've had no problems buying rigid foams online for delivery to a private address over the last few months.
 
I rather think that H&S and EU regs are sometimes used as an excuse to cover ignorance and/or incompentence on the part of the supplier. Cynical, who me? Never!
 
Regards,
 
Andrew
Thread: Machinability v Mess v Finish.
05/04/2011 11:23:32
Don't know about the small stuff, or using HSS tools, but hot rolled turns fine with carbide, if the surface speed is high enough. As in this picture:
 

The block is 160mm square and was finish turned at 540rpm. This gives a peripheral speed of about 890fpm. The surface finish is about 1.8µmRa; not great but adequate for the job and not too much of a surprise given the tip had a radius of 0.2mm with a feed of 0.1mm/rev.
 
Regards,
 
Andrew
Thread: Junk or what?
04/04/2011 23:34:26
Wot? I didn't know Australia had devalued it's millimetres! Is it part of Ms Gillard's 'moving forward' plan?
 
Andrew
Thread: Machining Strange materials
03/04/2011 11:43:20
Hmmmm, according to Wikepedia dry samarium cobalt powder has a low ignition temperature. If it does catch fire it will be very difficult to control; presumably like most metal fires.
 
In essence both these materials are very hard (mechanically) but also very brittle. As has been stated they can only be machined by grinding. Samarium cobalt is also hard magnetically, while ferrite is usually soft magnetically.
 
Regards,
 
Andrew
Thread: Greenwood Tools - Excellent Service
30/03/2011 11:15:21
Unfortunately there isn't a forum topic for discussing suppliers, so I've put this thread in general questions, even although it isn't!
 
Yesterday evening I lost the screw that holds the insert in my SCLCR toolholder. Actually, I was a butter fingers and I dropped it in amongst two bucket fulls of steel swarf. Since the insert had been running a dull red I was expecting the screw to be hot too, and had a fumble.
 
Having metaphorically kicked the cat and had a sulk, I looked on the Greenwood website, from where I bought the tool, but no spares listed. So I emailed a query. This morning I received an email saying that a spare screw had been put in the post FOC. Excellent service indeed. It's great to know that there are still some companies around that are decent and care about customers.
 
As an aside I've always been very pleased with all the tools I've bought from Greenwood over the years.
 
Regards,
 
Andrew
Thread: Acceptable runout
28/03/2011 23:11:46
Terry,
 
Tut-tut, as both the gnat and midge are members of the smaller Nematocera family they are essentially the same, just the units are different. For all practical purposes we can say that a gnats cock is gnat-urally within a s-midge-n of a midges bull. Hence we can see that the whole thing is a load of imperial cock and bull. Translating to metric that's hen and cow.

When using the gnats anatomical measurement system I alway design using double elephant, but usual reduce it to elephant for workshop use, as the workshop is too full to get a double elephant in.
 
Regards,
 
Andrew
Thread: The boat that Guy built
27/03/2011 20:11:12
Oh dear, if it was then I expect the iron was actually dis-t-rought at being wrongly identified.
 
Andrew
Thread: Acceptable runout
27/03/2011 16:14:43
And for the toolmaker it's a specific part of a gnats anatomy. If all goes according to plan and the part is to a gnats anatomical part then it is promoted to the dogs tackle. If however if it should not go according to plan then it becomes part of a pig.
 
Andrew
Thread: Things we should not do
27/03/2011 12:35:16
Do not wear gloves when operating machinery - if it gets caught, it'll drag your hand in.
 
Do wear gloves when welding - they protect against burns.
 
Regards,
 
Andrew
Thread: t.i.r.?
23/03/2011 17:21:02
Total Indicated Runout, ie, what you actually measure. It doesn't, on its own, tell you whether the runout is axial or radial, or a combination of both.
 
Regards,
 
Andrew
Thread: The boat that Guy built
18/03/2011 18:40:41
Posted by Mike on 18/03/2011 16:44:16:
When "The boat that Guy Built" series first started, I asked my wife to record all the episodes for me. I have now asked her to erase them. I find the programme dumbed down and amateurish - an insult to engineers both professional and amateur. There does seem to be a certain element within the BBC with a philosophy of "if you don't understand a subject, take the mickey out of it."
 
It's worse than that; it only seems to apply to engineering, and to some extent science. I don't suppose that everybody in the BBC speaks German, but can you imagine them taking the mickey out of the Ring Cycle because they don't understand the language?
 
Regards,
 
Andrew
Thread: The mis-conception round bar is round
16/03/2011 20:18:47
Surely silver steel is supposed to be ground to a specific diameter? Plus or minus a tolerance of course; the piece I have is well outside of that tolerance and thus no use to me.
 
GordonW: I still have piece. After a run in with J&L about a different issue with the same order I decided it was going to cost me more mucking about on the 'phone for 15 minutes than the steel was worth. If you want it for cost of the postage PM me and I'll work out the postage.
 
Regards,
 
Andrew
16/03/2011 11:36:41
Posted by Gordon W on 16/03/2011 11:03:30:
 
Somebody throwing out steel because it's a gnats thingy under some arbitrary size, wish I lived nearer.
 
 
Each to his own; by its very nature silver steel is supposed to be a precision product, but this silver steel is well outside the normal tolerance. It should be better than +/-0.00025". Assuming a Gaussian distribution any errors would probably normally be undectable in the home workshop, as was the case with the replacement silver steel.
 
If the manufacturers of this steel are prepared to take such a cavalier approach to size control what else is wrong, the composition may be?
 
Time is precious to me, and I'm not going to waste it working with inferior materials!
 
Regards,
 
Andrew
Thread: Tony Jeffree's Grinder letter in MEW175
15/03/2011 21:45:00
Posted by NJH on 14/03/2011 23:40:44:
You guys must have big sheds!
(Please note funny little yellow thingy Andrew - I've never used one before! )
 
 
Hi Norman,
 
Errr, there seems to be a funny yellow thing in your posting!
 
I don't have a big shed, just a double garage, and it is very crowded, but it's a bit like the Tardis! It is also a great incentive to lose weight; if I drink too much beer then I get too fat to fit between the machines. Inevitably though the garage has spread into the house with the dining room being used for cutter and measuring tool storage and the kitchen acting as an assembly hall and casting storage area for my traction engines.
 
What I really need is a large warehouse with a kitchen, bathroom and bedroom attached.
 
Regards,
 
Andrew
Thread: The mis-conception round bar is round
15/03/2011 21:37:34
Graham,
 
Seems to me that it was a perfectly reasonable thing to do; starting another thread to discuss an interesting topic that nevertheless had deviated from the subject in the original post. That way the new topic should get more exposure.
 
Damn it, I'm seeing spirals everywhere now! I had to move a 1m length of 1/2" silver steel this evening to get to my small stuff stock rack, and blow me down it's got spirals on it. Quite unlike the normal uniform slightly dull finish on silver steel. Funnily enough this particular length has been rejected by me, as it is consistently 0.0007" undersize. It was bought from a professional source (J&L), but as they'd already boo-boo'd over the order I couldn't be bothered to sort this out as well. I bought some 13" lengths of 1/2" silver steel from a different supplier and it's bang on size, as best I can tell.
 
Regards,
 
Andrew
 
PS: If anybody wants a 1m length of nominally 1/2" silver steel PM me and you can have it, if you collect it, otherwise it'll get recycled next time I go to the council tip.
14/03/2011 23:21:14
Ok, to pick up on some points. I've dug out the original invoice for the stainless steel. Turns out it is grade 1.4307, ie, 304L. It certainly isn't 'coppery' in appearance, more kitchen sink! I'll have to stamp 304L on it tomorrow evening before I put it back on the rack.

It definitely isn't an offcut; I bought the standard 3m length from Parkersteel, based in Canterbury, but they have a big warehouse near Cambridge. Probably a bit late to complain now if it isn't up to scratch, as I bought it in 2008. I've got two 1m lengths on the rack, so I must have used the other 1m. I haven't got any recollection of what I made with it though.

While having a bit of a re-arrangement in the kitchen this evening to move the boilers for my traction engines I noticed, for the first time, that the material I've used for the rear axles has a very faint helix, just like Grahams picture. Any out of roundness is better than 0.01mm though, ie, I can't for certain detect it with an ordinary 25-50mm micrometer. Strangely, in view of Ramon's comment, the axle material is EN8.

Regards,

Andrew

Edited By Andrew Johnston on 14/03/2011 23:21:38

Thread: Tony Jeffree's Grinder letter in MEW175
14/03/2011 21:28:33
Definitely an interesting letter. I will admit to having, and having read, the book on the Quorn, but I've never had a desire to build one. I've always been mystified by the comments on the ball handles though. I can't imagine that the functionality of the machine is affected by the handles, so if I did build one I'd re-design to use much simpler handles. No need to waste hours making ball handles.
 
As no-one else has owned up to having any grinders for an informal poll, I'll stick my head above the parapet with my collection; here goes:
 
1. Cheap B&Q angle grinder: used for weld preparation, sorting out the welds after I've had a go at welding, and for DIY jobs where the 'ammer is not suitable
 
2. Small bench grinder, one aluminium oxide wheel and one green grit wheel: used for offhand grinding of drills, HSS lathe tools and sharpening TIG electrodes
 
3. Old Clarkson T&C grinder with centres, bits of a universal head, a radius attachment and a swivelling vice: sharpening milling cutters and HSS lathe tools, not yet set up to sharpen drills or taps
 
4. Brown & Sharpe surface grinder: making things flat and parallel to better than I can achieve on the mill and for sharpening Coventry die sets
 
5. Myford cylindrical grinder: making jigs and mandrels, accurate tapered items and things like cylinder liners that need to be parallel and accurate to size to better than I can achieve on the lathe
 
Quack, quack - that'll be me ducking the flak!
 
Regards,
 
Andrew
Thread: The mis-conception round bar is round
14/03/2011 19:09:35
To pick up on a post I made earlier in the thread on 'Travelling Steady', I've dug out the material that has a helical finish on it:
 

Rather stupidly I've stamped it only with 'SS', so I don't know exactly what grade of stainless steel. However I suspect it would be 303, as that is the grade I normally buy for general turning. Interestingly the pitch of the helix is quite fine. It is the only material on which I've seen such a finish.
 
Measurements around the circumference show a maximum variation in diameter of 0.02mm, a bit under 1 thou in old money.
 
Regards,
 
Andrew
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