Stock slipping back in the chuck.
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  1. #1
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    Default Stock slipping back in the chuck.

    Mazak lathe
    Kitagawa BB208 chuck with OE hard jaws
    Hot rolled 4140 HT 1.5" and smaller
    Max recommended hydraulic pressure set
    Chuck is free moving and free of junk inside

    The only way I can get this to not slip back in the jaws is cutting the feed down to 0,2mm/rev (8 thou) and DOC down to 2mm (78thou). I would like to run almost double the feed and DOC. I also tried putting wet&dry paper between the bar and the chuck but it did not help much.
    Is this just how it is for everyone or is there anything else to change ?
    Are there hard jaws available from somewhere that has a sharp diamond knurl ? Marking the stock is not an issue.

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    Serrated hard jaws. I have also heard them called claw jaws. They work very well. What kind of cutting insert are you using? A smaller nose radius anf a positive rake insert will also reduce cutting forces.

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    You could try boring soft jaws close to the OD size for more contact area.
    Also make sure you minimize any bar whip inside the spindle.

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    ^^ This! Bar whip will make your stock move! So will holding bar stock in non-concentric chuck jaws.

    Also could be from using Hot Rolled material . . .

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    Some thoughts

    Is there plenty of movement of the chuck jaws after they grip the given diameter - as in you're not at the end of their travel.

    Id the chuck actually generating the holding pressure, ...pressure gauges can be misleading.

    What insert and tool holder are you using? .....if you've got a ''bad match '' or worse still wrong insert it will push back rather than cut.

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    Tool geometry such as rake angle and side cutting edge angle along with sharpness of cutting and size of wear land.
    Serations or groves might be cut into a set of chuck jaws..or the jaws might be relieved so the contact area be less. for a repeat job a screw tight collar might be added the the part.part design might include leaving a shoulder step fro first turn ,then nip that shoulder when part is turned.
    Extra set of jaws can be sharp diamond knurled or just releaving some ID jaw surface with using surface grinder.
    We had machine clamp jaws (not lathe chuck jaws) coated with with hard steel and even carbide with an electric discharge to the jaw surface..cant remember the company but it was a simple process..High amp DC current with polarity going the way of the discharge of material.
    Easy to grind groves long way in chuck face ..so the center would not change but the contact decreased so much like hold-downs in a shaper vise the contact area decreased so PSI of contact would go up higher. Such groves need not be highly accurate because the original ID surface would be retained.

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    Quote Originally Posted by Panza View Post
    Mazak lathe
    Kitagawa BB208 chuck with OE hard jaws
    Hot rolled 4140 HT 1.5" and smaller
    Max recommended hydraulic pressure set
    Chuck is free moving and free of junk inside

    The only way I can get this to not slip back in the jaws is cutting the feed down to 0,2mm/rev (8 thou) and DOC down to 2mm (78thou). I would like to run almost double the feed and DOC. I also tried putting wet&dry paper between the bar and the chuck but it did not help much.
    Is this just how it is for everyone or is there anything else to change ?
    Are there hard jaws available from somewhere that has a sharp diamond knurl ? Marking the stock is not an issue.
    So your goal is 16 thou feed and 160 thou DOC? HSS tools in OEM-jawed 4-J on old manuals can do that to 4XXX HRS all day long on far larger diameters.

    Tooling issue IMNSHO.

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    As others have said, insert geometry can really make or break the overall process rigidity. That being said I have had jobs where the parts moved regardless so I coated the ID of the spindle collet with "carbinite" and the parts stopped slipping. It was like $50 or something and they did it in like 2 days. Check it out -> Carbinite Metal Coatings - Workholding Solutions
    Last edited by Nerdlinger; 12-28-2017 at 01:42 PM.

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    I would try the serrated jaws in your case. Strangely enough 4140 HT is the only stock I have push back issues with. Fortunately on the sizes around what you are dealing with I can make them out of slugs with a dead stop 16C collet and not add much time. On the smaller sizes using a different machine I just went 20% over max pressure (taking a gamble) and got away with it. Not sure about your stock but what I get is badly out of round, pretty sure that causes the clamping issues. In my case I am sure sending the stock out for grind would cure the problems, unfortunately there aren't any local centerless grinding shops here.

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    Quote Originally Posted by Dualkit View Post
    I would try the serrated jaws in your case. Strangely enough 4140 HT is the only stock I have push back issues with. Fortunately on the sizes around what you are dealing with I can make them out of slugs with a dead stop 16C collet and not add much time. On the smaller sizes using a different machine I just went 20% over max pressure (taking a gamble) and got away with it. Not sure about your stock but what I get is badly out of round, pretty sure that causes the clamping issues. In my case I am sure sending the stock out for grind would cure the problems, unfortunately there aren't any local centerless grinding shops here.
    The chuck he is using is a wedge - not scroll - operated power 3-Jaw:

    Kitagawa BB28 Large Thru-Hole Power Chuck | Kitagawa

    Reasonably righteous bit of kit as to grip. Out-of-round stock won't repeat for a second-grasp, second-op worth a damn, but he isn't doing that. It should grip well-enough for a first-go-is-last-go op.

    Different jaws or surface treatment of them will surely help, but he is having the problem on 1.5"-minus stock and at a feed rate and DOC that are not really all that aggressive.

    SHOULD be a pizzacake.

    Tooling. Tooling. Tooling.

    Have we failed to mention "tooling?"


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    The stock shouldn't be whipping around as the bar is supported with a liner that fits with little clearance. And the stock still slips when the bar is almost used up.
    Tooling: CNMG 120408 in a DCLNR holder. I would rather not use a smaller nose radius as inserts are not lasting long as it is.
    Did anyone have a supplier of those serrated hard jaws ? Maybe just as easy to buy another set of the standard jaws ones and modify them to suit.

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    Stock degreased? I was looking I see here: http://www.usshoptools.com/prod_page...de=%20101030_3
    They do sell jaws that are more pointed but they are expensive. I think I would try some bored soft jaws first.

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    Most effective and efficient way is to use/create a back stop. Could be something like a collet stop or soft jaws bored to have a end stop. Soft jaws by themselves have better gripping in my experience than hard smooth jaws.

    Tom

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    Quote Originally Posted by Panza View Post
    Did anyone have a supplier of those serrated hard jaws ?
    With you in Norway?

    Ladner in France, others in Spain & Italy. Has to be a German source and probably Polish as well. Use the local-languages for search rather than Google in English. I was practically tripping over them a while back whilst looking for Cazeneuve chuck backplates.
    Maybe just as easy to buy another set of the standard jaws ones and modify them to suit.
    Your chuck has a common standard so No Fine Way it's "easier". DIY may not even be cheaper, depending on how you cost yer time.

    At 1.5"-and down, I have the options of collets, stops, and a Kasto saw to turn bar into slugs...

    IF a change of tooling didn't fix it.

    Tooling should be a pretty cheap thing to chase for improvement, no?

    I mean.. you have a problem.

    "I'd rather not use..." has to at least be set aside long enough to TRY something else. Even if it wants more than one alternative tested, you will know more.
    Last edited by Monarchist; 12-29-2017 at 09:18 AM.

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    Quote Originally Posted by Panza View Post
    Max recommended hydraulic pressure set
    Max recommend pressure on our machine is something like 18bar witch figures out to be less than 300psi. I sometimes do go higher. if it ain't wiping around, your not using the T/S then your shoving it back. It adds time but to completely eliminate this I turn a step to push against. Obviously your running bar stock so I'd crank up the pressure. At your own risk of course. But I do go over Max what they say sometimes, oddly enough it's when i have push back issues. Lol...

    Brent

    20140919_155036.jpg

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    I don't have hard jaws for my chuck. I bore the soft jaws undersize for hot rolled (I think .005" to .010"). This gives six points of contact and bites into the bar. I don't need to take cuts as heavy as the OP though.

    I grease the chuck regularly which makes a difference.

    Bill

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    Quote Originally Posted by Panza View Post
    Mazak lathe
    Kitagawa BB208 chuck with OE hard jaws
    Hot rolled 4140 HT 1.5" and smaller
    Max recommended hydraulic pressure set
    Chuck is free moving and free of junk inside

    The only way I can get this to not slip back in the jaws is cutting the feed down to 0,2mm/rev (8 thou) and DOC down to 2mm (78thou). I would like to run almost double the feed and DOC. I also tried putting wet&dry paper between the bar and the chuck but it did not help much.
    Is this just how it is for everyone or is there anything else to change ?
    Are there hard jaws available from somewhere that has a sharp diamond knurl ? Marking the stock is not an issue.
    .
    4140 HT is moderately hard
    figure 0.3 cubic inch per hp per minute
    1.5 dia
    .008 ipt doc .078 (radius .039)
    824 lbs of force
    tool going dull force can increase 200 to 10000%

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    Quote Originally Posted by jyd12f View Post
    Rocklinizer
    How the fuck did you make it to 12 posts? SpamBot

    If its not "Rocklinizer" It EDM centre,
    Jerry piss off.

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