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[4]

Live Center

January Project of the Month [3]
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benmychree

John York
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#2
I have used them, although not from Shars; sorry fact is that I had to leave the set at my shop when I sold the business, but I did very much like them, the one that I had was made in Poland, I think.
In reading the description in Shars catalog page, I took notice of the following statement; "Hardened body and taper shank for extra strength, rigidity and long life", all correct, I suppose, except for the word RIDIGIDTY; the fact is that heat treatment has no effect on ridigidty, it does not change the modulus of elasticity, thus no change in deflection under load; this I learned when I was a young machinist, from the book "Tool Steel Simplified"
 

mmcmdl

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#3
Yes , use them all the time but at the MT5 levels . They are nice . That looks like a winner for an MT2 .
 

mikey

Active User
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#7
I use a Royal changeable tip live center. Good center, very versatile. Nowhere near as economical as the Shars, though. On the other hand, it does guarantee 0.00005" run out.
 

mmcmdl

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#8
You know my feelings about tools , but I'm not going to preach it ! ;) Royals , Hardinges , Shodas etc . here .
 

Ray C

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#9
I have used them, although not from Shars; sorry fact is that I had to leave the set at my shop when I sold the business, but I did very much like them, the one that I had was made in Poland, I think.
In reading the description in Shars catalog page, I took notice of the following statement; "Hardened body and taper shank for extra strength, rigidity and long life", all correct, I suppose, except for the word RIDIGIDTY; the fact is that heat treatment has no effect on ridigidty, it does not change the modulus of elasticity, thus no change in deflection under load; this I learned when I was a young machinist, from the book "Tool Steel Simplified"

John, it's a difficult concept to fathom but, when all is said and done, I want my live center components to be heat treated :grin big:.

This is way off topic but, here's a pictorial view of what you correctly stated. I added a red line to show the same piece of material that's been heat treated. The modulus of elasticity ratio is the same for the black line (untreated) but the heat treated part (red line) has increased yield strength. Basically, the ratio of stress to strain remains the same but, heat treated part can take more stress before it permanently deforms. If for example, the heat treated part starts to deform at the green star and that point happens to be 330MPa then the strain would be 0.0016. The ratio would still be 207kMPa.


Stress_strain.jpg

Now back to regular programming...

I do not have a live center with changeable tips but it makes a lot of sense. I have about 5 different live centers and the one I use the most is the medium duty, long nose type. I don't remember what brand it is. Anyhow, for hobby purposes where the typical part is probably under 20 pounds and DoCs are under 0.050", I suspect an interchangeable type in medium duty would be perfectly adequate.


Ray
 
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