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Member postings for David Littlewood

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

Thread: Horse power and such.......
02/05/2015 19:01:00
Posted by John Haine on 01/05/2015 07:52:55:

David, er, no. For a reactive load the voltage and current are 90 degrees out of phase. The current will be rather low at low load and nearly in quadrature, and build up to the rated current largely in phase as the motor is loaded. And this almost certainly isn't a synchronous motor but an induction motor.

John,

Mea culpa, you are quite right on both points; serves me right for posting so late after sharing a bottle of wine! I was thinking of AC induction motors being (almost) synchronous with the AC frequency, but the term synchronous motor is something else. I do think the underlying point is valid though.

David

01/05/2015 00:21:10

Going back to Rik's original question, no one has mentioned the fact that motors are a mostly reactive load. The current and voltage are not in phase. For a perfectly reactive load, the two are 180 degrees out of phase and no power is consumed, but the current rating is still important as it determines the size of conductor wire required for its connection to the power source. When the motor is at no load, it is nearly purely reactive, but as it is loaded the current and voltage move closer in phase and real power consumption takes place.

Thus, in Rik's example, the specification is 240 V and 2.8 A, which would (for a resistive load) mean a power consumption of 672 W. At no load, the motor would (theoretically) consume no power, but under load the specification suggests it actually consumes 450 W. The efficiency of synchronous AC motors is reasonably high, but I can't say what the mechanical output power is; I believe the power rating quoted for motors is usually the actual power consumption at full load, but I stand to be corrected if someone has more expertise.

David

Thread: Advice on pricing a Myford Super 7 lathe
26/04/2015 13:05:12

Adam,

Condolences about your father.

To assess the lathe, a few questions. Does it have power cross-feed? Are all the gears sound, with no missing teeth? Does the headstock spindle seem to be in good condition? (In the absence of more sophisticated tests, check that there is no disconcerting noise when running, and that if you chuck a stout bar 6-9" long, you can't feel any movement if you push/pull the unsupported end.) Is there any sign of excessive be wear (this will show up be a marked variation in stiffness as you move the carriage from headstock end to tailstock end)? Ditto for the cross-slide. If the answer to all these things is positive, then IMO £750 is much too low a price - by a factor of 2. Even without power cross-feed (and as best I can see from the photos it doesn't have it) it is too low. The gearbox alone would be worth nearly that much (I bought my gearbox new in the early 80's when I upgraded my S7 to S7B and paid over £400 then!).

Of course, that assumes you put in quite a bit of effort to clean it up. For a decent sale price, appearance is important; it suggest the machine has been well looked after. Sorry if I repeat what has been said, but (1) remove all traces of wood dust (if that's what it is); many kinds of wood can be corrosive. (2) Remove any other crud; use a toothbrush if necessary. (3) Go over all parts with an oily rag until nice and polished-looking. (4) Fill the oil cup on the headstock and oil the oiling nipples with the oil gun. (5) Clean up the acessories - many of them (except the 3-jaw chuck) look rather tarnished.

As to what to include and what to sell separately, then by tradition a second-hand lathe would come with 3-jaw s/c chuck, 4-jaw independent chuck, faceplate, tailstock chuck, two 2MT centres, some form of toolholder (the 4-way one on it will be fine, gruesome though they are IMO) and the basic spanners etc. Anything else would be a free gift to the buyer, who probably wouldn't end up paying any extra for them. Thus the swivelling vertical milling table, the tailstock dieholder set, the wood-turning tool rest and any other extras may as well be sold separately. The tailstock offset device looks so disgusting I'd bin it, but you may feel it would clean up.

As for selling, I don't like eBay, except as a buyer (when I have to go where the stuff is to be found). I'd be inclined to put a free ad in ME/MEW and/or on homeworkshop.org.uk. Stuff I have put on there has sold in a day or two. The only advantage of eBay is that you may - occasionally - get lucky if two bidders get carried away.

And finally, As someone else said, don't use WD40 - it's only uses AFAICS are for drying out damp car plug leads, and helping to loose stuck bolts. Use the slideway oil your father probably had somewhere about; Esso Nuto was the traditional one. And absolutely don't use 3-in-1 oil (yuk); it's only useful for garden tools IMO.

David

 

 

Edited By David Littlewood on 26/04/2015 13:06:12

Edited By David Littlewood on 26/04/2015 13:08:40

Thread: acid
04/11/2013 19:35:07
Posted by Russell Eberhardt on 04/11/2013 11:48:40:

Is sulphuric acid really more dangerous than citric.?

It has been stated that citric acid works slowly. This is because the solution is low in acidity (the PH is not very low). If you use a weak solution of sulphuric acid such that the PH is the same it will take equally long to work but should be no more dangerous than citric acid.

Sulphuric acid has a pKa value over 6 below that of citric acid - which means it would have to be diluted enormously (somewhere between 10,000 and one million times) to have the same pH. It would become exhausted very rapidly at this concentration.

In practice, something around 10% should work fine - but be aware it can, even at this concentration, be very irritating to skin and damaging to eyes; it can also destroy fabric over time as it becomes concentrated through evaporation.

I have found sulphuric acid quite easy to buy from jewellers' suppliers - though you may need to sign a book stating the purpose for which you want it ("pickling" should be fine). It was a few years ago though, so it's possible things have changed. I honestly would not recommend anyone to buy/use concentrated sulphuric acid unless you know what you are doing - your point about *always* adding acid to water is bang on, but also bear in mind that so much heat is generated that the solution can boil. Either do it gradually with intervals to cool, or add acid to ice.

Citric acid is readily available through Amazon or eBay.

David

Edited By David Littlewood on 04/11/2013 19:36:55

Thread: drill size for tapping threads...
15/10/2013 22:28:15

John,

I suggest you buy this book, should answer your questions and many more besides.

**LINK**

David

Thread: Picking up where you left off...
09/10/2013 17:57:45

It's a purely personal matter - and it's your model - but I think brass would look entirely wrong for the linkages. OTOH, steel parts with (where appropriate) bronze bearing bushes would look just right; the contrast would create the right effect. Copper, of course, would be totally unsuitable because of its softness and it is horrible to machine.

David

Thread: ML7 Quick Change Tool Holders
09/10/2013 17:50:30

H,

I'm entirely with norman on this; I have a size S00 Dickson set for my S7, with over 25 holders acquired over many years and from a variety of sources. All of them have proved entirely satisfactory, though the ones bought from Myford have a slightly better finish. I also have a size S1 set for my M300, which is equally good, though a lot more expensive.

My personal view is that 4-way tool posts are the spawn of the devil. You can usually only get 3 tools in them if you want one of them for boring, and one of them is always perfectly placed to stab you - but the real problem is the limit of tools ready for instant use. Yes, advocates say that you can keep a piece of shim with every tool - but that still takes many times longer than a QC, and you can't put the tool back in exactly the same place for repeat parts like you can with a QC. I sold the 4-way that came with my S7, after many many years of it gathering dust.

As for tool boats, well frankly you'd have to be desperate.

David

Edited By David Littlewood on 09/10/2013 17:51:52

Thread: Grinding bespoke tools from files, screwdrivers, chisels etc
09/10/2013 12:30:54

On the subject of Phillips and Pozidrive screwdrivers, in my experience there are two common errors which can ruin them. One is using a Pozidrive driver on Pillips screws; these don't have the extra slits of Pozi screws, so they quickly ruin the Pozi driver. I don't think doing it the other way causes damage, so if in doubt use a Phillips (crosspoint) driver. The other is using a driver size smaller than the screw. This was one of my wife's favourite tricks, it took me years to get her out of doing it. Of course this also applies to slotted screws/ drivers, where also using blunt and rounded drivers also ruins many screws and makes them harder to remove and impossible to re-use.

Sure you know this Ian, just that your comment prompted the thought.

David

Edited By David Littlewood on 09/10/2013 12:31:31

Thread: Carbide drill bit stuck in mild steel part.
19/09/2013 18:41:38

Chris,

Three possibilities spring to mind:

(1) Find someone with a spark eroder. Not sure how good they are with carbide, but in theory should work.

(2) If you can drill from the back, do that and punch it out.

(3) Use a core drill to cut around it, then fill the gap with a plug.

David

Thread: Magnetic tool storage
10/09/2013 18:06:27

I tend to agree with the comments against magnietic holders. I use small strips of wood screwed to the wall; for allen keys, and other milling machine bits, this has vertical holes to take each item, and for ring spanners a small screw or pin for each spanner works well. Home made, scrap wood, cost zero.

The bracket to the right of the mill below shows the idea:

http://i980.photobucket.com/albums/ae281/dlittlewood/DRO-Console.jpg

David

Edited By David Littlewood on 10/09/2013 18:13:05

Thread: Emco FB2 oil leak
08/09/2013 23:25:06

My FB2 has leaked oil from the quill for the last 25 years. However, the total amount of oil I've had to put in to top up the level has been about 100 ml over that period, so I decided to live with it. I just need to remember to wipe the base of the head if it hasn't been used for a while, otherwise I get spattered with oil when I turn it on. I have not noticed oil leaking from around the quill lever. Perhaps you should see how much oil is leaking and take your own view on whether it's worth the effort (and risk) of disassembly.

David

Thread: Parting Tool Feedback
07/08/2013 19:29:56
Posted by Im Indoors. on 07/08/2013 16:24:00:

I note the enthusiasm for the Greenwood tool and have been put off in the past by the price of it and also the cost of replacement inserts at £9.95 each.

Jim

Jim, I understand your concern, but both my Q-cut and its larger brother (like KWIL, S7 and M300) are still on their original tip after 10 years (S7) and 4 years (M300) of admittedly light amateur use, and showing no sign of wearing out.

David

Edited By David Littlewood on 07/08/2013 19:30:15

07/08/2013 13:08:19

I would enthusiastically join those John has heard giving good reports about the Q-Cut. I bought one a few years ago, and now I wouldn't use any other type. I've never had a single problem parting off a variety of materials, never needed to use a rear tool post. I have since acquired a larger one of similar pattern for my larger lathe, and that one happily parts off under power cross feed (to my great regret I don't have pxf on my S7).

Though the blade design provides a good rigidity, I think it is the tip geometry which is the really crucial factor, it curls the swarf inwards do it never jams in the cut.

The only time I use any other type is when I'm parting off or grooving tiny parts like micro tubing for O gauge work, when an Interstate Mini-Thin set is the dog's b******s (though a bit expensive).

Remember, the quality is enjoyed long after the pain of the price is forgotten.

David

Edited By David Littlewood on 07/08/2013 13:10:57

Thread: Ground flat stock supplier ?
02/08/2013 13:53:16
Posted by mike mcdermid on 01/08/2013 23:01:47:

Ken M machines prices are quite ..er shall i put it politely expensive sheffield gauge plate sell entire 18 inch lengths for the same price as the 9 inches m machine are asking

Indeed - and I would be quite uneasy about buying from anyone who seems to think that 1/2 sq ft is the same as 6x6"!

David

Thread: Work holding problem
24/07/2013 15:01:59

Wolfie,

Why is it too long to fit in the vice? If it is a chunky slab it should be rigid enough with say 4" overhang at each end. If not, hold it so one end is close the vice, clean up, move it so the other end is close to the vice, clock the clean end with a centre finder, wind along (ensuring you correct for backlash) and Robert, as they say, is your mother's brother.

If for some reason this won't work, you may be able to clamp it to the bed using toolmakers' clamps, but this may restrict table movement.

Alternatively, if it is to have any holes in it, make the holes first, use them to hold it to the table, and clean up ends to match hole location.

David

Thread: CHROME-VANADIUM STEELS
24/07/2013 00:05:39

I have used EN24T with success for highly-stressed parts. Not sure what its composition is, but it has a UTS many times that of mild steel, but still turns fairly easily. It is readily available from various of our usual retail sources; if they don't have it in stock they will certainly get it for you. I can't remember offhand where I got mine from, but it would have been Mallard Metals or Noggin End Metals.

David

Thread: Workshop comms
20/07/2013 17:04:24

Rik,

Most cordless phone sets have an easy system of internal comms between the handsets (as long as you don't lose the instructions - DAMHIKT). Make very handy phones as well.

David

Thread: Carbide grinding wheel
16/07/2013 23:12:13

Dave,

I got a diamond cup wheel from Arc, as Magpie suggests. It was well balance without any adjustment on my T&C grinder, and it grinds tungsten carbide very well. Also very reasonable price. John S is absolutely spot on, green grit is old hat.

David

Thread: Turning
15/07/2013 00:46:53
Posted by Ady1 on 13/07/2013 13:56:29:

Once I acquired some HSS ability I went back to carbide, those brazed ones, and ground my own tips on a "green grit wheel"

Now green grit really is outdated; it wears away very fast. Diamond impregnated wheels are now so cheap, and orders of magnitude better, I could not imagine why anyone should use the old green grit.

David

15/07/2013 00:44:18
Posted by Steve Withnell on 11/07/2013 19:23:31:

One of the old classics is **LINK**

But it is an old classic. He will have you mixing your own marking out fluid from sulphuric acid + copper sulphate solution, when what you need is a big dobber of a spirit marker from WHS. Nothing wrong with his marking out solution, just not the best option anymore, but still a good book.

Copper plating mild steel with copper sulphate is far more resistant to being erased than the other methods. Engineer's marking blue and felt-tip pen are both quite easy to get wiped off by cutting fluid; I don't know about W H Smith spirit marker.

David

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