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MEW 182 - Wot no ...

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DerryUK28/09/2011 20:27:32
125 forum posts
... letters page this month?
 
I must write in and complain!!
 
Derry.
PS just joshing folks, I never complain about MEW
David Hanlon29/09/2011 09:07:10
40 forum posts
But a very promising start to a beginners series ... looking forward to using this to move on from my current scrap making activities. I am hoping that this will include some practical exercises and a method for getting feedback/tuition (maybe using this website?).
 
Maybe I should write I letter of encouragement?
 
BTW - No point in suggesting local schools/clubs etc ... I live in the French Alps, cows and ski's only round here (and some very hi-tech manufacturing in semiconductor and nanotech - bit small even for model engineers).
Stub Mandrel30/09/2011 21:24:29
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I think every letter published should win a large lump from the editor's scrap box - if David is moving, it's time for a clearout
 
That would get me writing in!
 
Neil
Robert Dodds01/10/2011 11:14:41
275 forum posts
39 photos
Mick Knight's beginners series certainly fills a need for many but I think there is a slip of the keyboard with respect to Magnesium in steel alloys - isn't it Manganese that is alloyed in steel to produce toughness?
I fear Magnesium is a bit fiery for steel alloys.
Bob Dodds
 
David Clark 101/10/2011 11:21:19
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Hi There
Yes, should have been manganese.
regards David
 
 
Versaboss01/10/2011 11:38:13
461 forum posts
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Posted by Robert Dodds on 01/10/2011 11:14:41:
Mick Knight's beginners series certainly fills a need for many but I think there is a slip of the keyboard with respect to Magnesium in steel alloys - isn't it Manganese that is alloyed in steel to produce toughness?
I fear Magnesium is a bit fiery for steel alloys.
Bob Dodds
 

Aah, I'm glad I'm not alone! I was thinking hard if I should write about that; my fear was a bit to look like a know-it-all. But after searching a lot about Steel constituents I was quite sure my gut feeling was right.

Well I think something like that is not a 'keyboard slip'. Informations given for beginners should be correct. How about giving RPM figures with a resolution of 1 RPM? I already see the letters coming in:

"Help please, Mr Knight says I need 458 RPM to turn 1" BMS, but my lathe only does 420 !!!"

Or to (nit-)pick a bit more:

Steel with carbon content from 0.05 % to 0.6 % is called 'low carbon steel'

Steel with carbon content from 0.3 % to 0.6 % is called 'medium carbon steel' after Mr. Knight.

Question: what now is a steel with 0.5 % carbon??

(a possible answer could be: a 'slip-of-the-keyboard' steel --- )


Greetings, Hansrudolf

mick01/10/2011 16:28:53
398 forum posts
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I thought I'd attract a bit of attention when I poked my head over the parapet by started on this discussion, sorry about the slip of the key board, that was an honset "slip" There are too many grades of steel to describe the carbon content of each. The broad descriptions of a grade of steel has to fall between two set figures, in general terms these may overlap. The object of the carbon percentages was to demonstrate, that only the smallest amounts of carbon can alter the machinability of steel, which I was hoping might encourage the novice machinist, who might feel that the finish and any difficulty experienced in machining was something they were doing wrong, but might have a great deal to do with the material they were using. Still back to the shelter.
Peter G. Shaw01/10/2011 17:14:04
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Mick,
 
What is a "honset" slip please? Is it a new type of slip gauge?
 
Regards,
 
Peter G. Shaw
Andrew Johnston01/10/2011 17:37:27
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Posted by Peter G. Shaw on 01/10/2011 17:14:04:
 
What is a "honset" slip please? Is it a new type of slip gauge?
 
 
I think it's a new type of Chinese banana skin with added magnesium, or should that be manganese?

Regards,

Andrew
Richard Parsons01/10/2011 18:09:15
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Long ago and far away a certain number was dinged into my skull (I can still feel the bump there). The number is the speed for turning mild steel with High Speed/high carbon steel tools. In inches the RPM to use is 288/D where D is the diameter in inches of the billet you are machining. In metric it is 7315/Dmm, where Dmm is the diameter in millimetres.


These figures are guide lines. If you are machining a 1” bar and running at exactly 288 RPM you should increase the speed after every cut. If you are ‘facing’ something and think like that then you have big problems.


If you use the calculated RPM based on 288, and adjust your feed rate to get a suitable cut.


Remember not all lathes have infinitely variable speeds, but the magic number will give you a good feel for the speed to use. So the difference between 420 and 458 RPM is pure nit-picking. I would tend to use a speed around about 300 RPM for a 1" billet.


No two bits of steel are exactly the same even if they came from the same billet.


David I keep well clear of the Alps the Bacco-pipes there are huge. It would cost me a year’s Bacco rations to lend one of them lads a fill !

Stub Mandrel01/10/2011 19:48:28
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4311 forum posts
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Congrats to Mick for taking on a tough task. Being largely self taught, I find articles by tme-served engineers/machinists really useful - there's always something to learn.
 
To paraphrase "You can please some model engineers some of the time, but you can't please any of them all the time!"
 
Neil
Robert Dodds01/10/2011 20:17:57
275 forum posts
39 photos
What a hyperactive lot you are!
Mick,
The reader always sees more errors than the writer but someone has to do the writing. Good on yer.
In a more serious vein it would be good to get some ideas for home checking what comes out of the stock box.
If its 2ft long, shiny grey it probably is free cutting mild steel but that 80mm noggin end and covered in rust would just be long enough if I knew what it was.
Do I put it on the grinder and guess the spark type? Stick it in the lathe and attack it with a 1/2" drill to see the swarf coming off?
I recently spent a couple of hours making 2 shafts to be hardened. Got the bright shiny steel noggin end out of the stock box thinking silver steel, and set about turning it up. The swarf coming off told me it was tough by its colour so I happily finished the machining and proceeded to get up to cherry red for quenching.
All went well until I did a file test after quenching on an inconspicuous bit and found it still soft. Then I remembered I had some stainless bar of the same dia left over from another job. A magnet confirmed my worst fears and the scrap box got a bit heavier!
Lots of folk out there on a Saturday afternoon could benefit from a few tips on how to sort the wheat from the chaff! Life is too short to wait until a week on Wednesday for new stock bar!
I hope it's not too late to add something in you series.
Bob Dodds
 

Andrew Johnston01/10/2011 23:19:17
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5828 forum posts
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Posted by Stub Mandrel on 01/10/2011 19:48:28:
Congrats to Mick for taking on a tough task. Being largely self taught, I find articles by tme-served engineers/machinists really useful - there's always something to learn.
 
 
Quite so, but it's also interesting to read articles by non-professionals. Sometimes the trouble with professionals is that they 'know' it can't be done, but the amateur has no such knowledge or training, so he goes and does it anyway.
 
Regards,
 
Andrew
Terryd02/10/2011 12:09:33
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1935 forum posts
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Posted by Stub Mandrel on 01/10/2011 19:48:28:
Congrats to Mick for taking on a tough task. Being largely self taught, I find articles by tme-served engineers/machinists really useful - there's always something to learn.
 
To paraphrase "You can please some model engineers some of the time, but you can't please any of them all the time!"
 
Neil
 
Hi Neil,
 
Such articles are only useful if accurate. If not they should be challenged (see my comment below re. 'peer reviews'). If one mistake occurs how do you know there aren't more unless corrected?  Which do you prefer, accuracy or 'no comment'.  It's not about 'pleasing' anyone, but about accuracy.
 
With all respect to Mick's article perhaps it should also be pointed out that white and grey cast irons are brittle full stop, while malleable cast iron is not. Also cast iron is very good in compression, hence all of those cast iron columns in Victorian buildings and steam engines etc (not to mention the Ironbridge) while it is very poor in tension, hence no cast iron ties or bolts!
 
To be even more pedantic, it is not the 'molecules which are aligned to give the properties mentioned rather it is the crystal structure.
 
After reading the bit of Mick's article on cast iron, I couldn't bring myself to read the rest, I didn't wish to find other errors. Surely articles should be accurate, especially those aimed at novices, otherwise mistakes are perpetuated.
 
 
Posted by Robert Dodds on 01/10/2011 20:17:57:
What a hyperactive lot you are!
Mick,
The reader always sees more errors than the writer but someone has to do the writing. Good on yer.

 
Hi Robert,
 
Pointing out mistakes in published work is long established in all sorts of professions, especially so in medical, scientific and engineering papers where 'peer reviews' are essential to weeding out errors. It should not be seen as as criticism but as an established and valuable process helping to ensure accuracy. It ensures that the mistakes and errors we are all capable of are not established as fact by allowing them to pass unchallenged.
 
Regards
 
Terry

Edited By Terryd on 02/10/2011 12:11:09

mick02/10/2011 13:00:17
398 forum posts
44 photos
Hi. Peter.
Its not a new kind of slip gauge, rather one of the oldest still in every day use!
Still in the shelter, as I expect some more incoming, but its nice to hear a bit of friendly fire as well.
Regards.
Mick
Versaboss02/10/2011 15:12:46
461 forum posts
51 photos
Posted by Terryd on 02/10/2011 12:09:33
 
Such articles are only useful if accurate. If not they should be challenged (see my comment below re. 'peer reviews'). If one mistake occurs how do you know there aren't more unless corrected? Which do you prefer, accuracy or 'no comment'. It's not about 'pleasing' anyone, but about accuracy.

[snip]

After reading the bit of Mick's article on cast iron, I couldn't bring myself to read the rest, I didn't wish to find other errors. Surely articles should be accurate, especially those aimed at novices, otherwise mistakes are perpetuated.
 
[snip]
 
Pointing out mistakes in published work is long established in all sorts of professions, especially so in medical, scientific and engineering papers where 'peer reviews' are essential to weeding out errors. It should not be seen as as criticism but as an established and valuable process helping to ensure accuracy. It ensures that the mistakes and errors we are all capable of are not established as fact by allowing them to pass unchallenged.
 
Regards
 
Terry

Thank you very much, Terry, for that above. It describes exactly the point(s) I wanted to make, partially unsuccessful as it seems. Well maybe I have a bad understanding of British humour...

Glad also that you commented about the 'cast iron is brittle in compression' claim.

I did not want to add insult to injury to bring this forward also.

Going back in shelter also (without bacco pipe, though ),

Hansrudolf

mick02/10/2011 16:46:41
398 forum posts
44 photos
OK, I don't have a copy of MEW but I supplied a diagram of two identicial components with a through bore, I said that it would be brittle if squeezed. Put that component in a vice and squeeze it and see what happens, it will break. Put the other one in the vice and squeeze with the same amount of pressure, the likely hood that it might distort are quite high, but it won't break. The point being don't clamp castings across thin sections as they will snap, because they are brittle.

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