Brand new mill table hardness dilemma. - Page 2
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  1. #21
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    tables are normally soft and normally you dont tighten a hard hold down clamp directly on any precision surface without sticking something soft under to not leave a mark. some old timers use pennies under, as penny is copper or zinc both being soft
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    AND i have seen hand scraped pallets or tables flat to less than .0002 and if fixture left on for many months it will experience rust and corrosion far more than .0002" after only a few months..... new machine builders might want you to only use a hard extra fine arkansas stone of over 1000 grit on their pallets and tables. normally stone so fine you cannot remove rust with the stone

  2. #22
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    Quote Originally Posted by DTM0 View Post
    purchased a new Fortworth csvbm-5vl, and the table is incredibly soft. Our other mill tables test out at about 55-60 rockwell C, but this fortworth shows 20 rockwell C. This is makes it very difficult to not damage as even a single chip caught under a parallel, or a toe clamp bolted directly to the table will cause a large dent.

    The supplier claims that this is actually a feature for superior vibration dampening, and to not mark up the parts youre machining. (hardened parallels and vise jaws seem to go against the "marking up parts" theory.. no?...)
    I’m with Bob being skeptical in post #20, and in no way should you be using the C scale and the diamond point. Most tables will prolly test 60 to 100 on the B scale (with a 1/16” ball braille). Machine tool structures proper are definitely gonna hold to the lower end (better dampening).

    Full out GM-60 type meehanite runs 230Bhn (20RC) with a compression strength of 200Kpsi. You can harden it to 550Bhn (55RC) but it would ring like a tuning fork…

    Don’t know what you mean by “toe clamp” but if you are using something like a gooseneck that’s got the back edge of the clamp on the table it’ll leave a mark. That wouldn't be good practice IMO.

    Good luck,
    Matt

  3. #23
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    Only mention I ve seen is the English Parkanson mill manufacturer claimed all their castings were made of a cast iron/semisteel with a typical hardness of 200 Brinell as cast.

  4. #24
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    my experience is soft cast iron is easier to machine flat.
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    ductile iron and cast steel can have hardness variations which make it harder to machine a large casting flat.
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    my opinion is a hard chrome plating can help table surface last longer cause chrome although thin is relatively hard and it provides some corrosion resistance. dont see much chrome plating any more cause of health concerns where plating is being done.

  5. #25
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    My old Cincinnati mill tested to 90 on the Rockwell B scale. The flame hardened ways on my Monarch only tested at like 50 Rockwell C. I would not expect most mill tables to be that hard.


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