parting tool for small lathes
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  1. #1
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    Default parting tool for small lathes

    how i made this tool:

    https://youtu.be/mUjkuTcNfIc


    greetings from Brazil

    Celso Ari

    parting-tool.jpg

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    At first I thought this was the dumbest thing I'd ever seen but then it occured to me the slit in the holder might work as a spring allowing the tool to flex downwards instead of plunging in to the work piece like is common when parting off on old clapped out machines. I'd have to use it to see if it works.

    I can't see why else that would have slit in it? Probably help if I knew Brazil talk.

    Brent

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    It is a very good way to make the holder, cuts the chatter down by a lot. Same thing is used on planers and shapers for wide surfacing cutters.

    Spring type toolholder. Very old-school device, bit they were not so dumb back them.... lots of old-school things like this work well.

    You set it up so the springiness lets the tool swing away from the work if it tries to dig-in. That cuts the energy input that drives chatter, so the tool will cut smoothly with no troubles.

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    In the 40s these were practically standard equipment. They had shanks to fit the gawd awful lantern tool posts which flexed to dig the tool in. As Jerry says, the spring in the tool holder moved the tool away from the work. Anymore,. with modern inserts, parting is a different story.

    Nice work.

    Bill

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    As others have said, a very old and common approach, one that is especially useful on the floppy lathes of yore. They were often called "gooseneck" tool holders - also commonly used for threading.

    The trick is to arrange things such that when the bit is pushed down, it automatically pulls out of the cut, reducing the force.

    Another approach to achieve the same thing is to put the cutoff tool upside down in a holder that allows that, and run the lathe in reverse. Again, this eliminates any tendency to dig deeper and deeper until something breaks.

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    Quote Originally Posted by Joe Gwinn View Post
    As others have said, a very old and common approach, one that is especially useful on the floppy lathes of yore. They were often called "gooseneck" tool holders - also commonly used for threading.

    The trick is to arrange things such that when the bit is pushed down, it automatically pulls out of the cut, reducing the force.

    Another approach to achieve the same thing is to put the cutoff tool upside down in a holder that allows that, and run the lathe in reverse. Again, this eliminates any tendency to dig deeper and deeper until something breaks.
    Why run the lathe in reverse?

    I routinely use a rear-mounted cutoff tool (that holds the tool upside down at a slight angle) and it works with normal rotation. If the tool starts to dig in it flexes the cross slide and carriage upward, relieving the pressure.

    I may however make one of those spring type tools for my QCTP so I don't have to keep mounting the rear mounted holder.

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    Quote Originally Posted by Scottl View Post
    Why run the lathe in reverse?

    I routinely use a rear-mounted cutoff tool (that holds the tool upside down at a slight angle) and it works with normal rotation. If the tool starts to dig in it flexes the cross slide and carriage upward, relieving the pressure.
    Because I don't have a long enough compound and/or travel for that to work.

    I use a Dorian cutoff blade holder that can be installed upside down, and accepts an ISCAR blade with carbide tooth. Have a big yellow "R" on the holder, to remind me to go into reverse.

    What kind of holder do you use?

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    Please explain how "modern inserts" fix this problem.

    Do they have a spring built in? Are they sharper? Is it geometry? Is the material more slippery so the chip doesn't stick? Oil feed hole to the tip? How?

    I like his tool holder. It looks like a good design. I need to watch the video to see what the dark part is and what it is doing.



    Quote Originally Posted by 9100 View Post
    In the 40s these were practically standard equipment. They had shanks to fit the gawd awful lantern tool posts which flexed to dig the tool in. As Jerry says, the spring in the tool holder moved the tool away from the work. Anymore,. with modern inserts, parting is a different story.

    Nice work.

    Bill

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    Quote Originally Posted by EPAIII View Post
    Please explain how "modern inserts" fix this problem.

    Do they have a spring built in? Are they sharper? Is it geometry? Is the material more slippery so the chip doesn't stick? Oil feed hole to the tip? How?

    I like his tool holder. It looks like a good design. I need to watch the video to see what the dark part is and what it is doing.
    I believe it's more a comment on more modern lathes, the type being "carbide capable", being much more rigid.
    In the spindle, drivetrain, ways, and tool holders.

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    img_0735.jpg


    y'all know this is a standard type holder right?

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    Yes, I have seen this type before. But not with that black "button" part. I watched the video, but still don't know what it is made of or what it's function may be. Anybody know?

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    Some of that type holder had a place to "gag" it so it would not move, and one could put stiff rubber in there to give more return force, etc.

    That button might be a similar thing, I seem to recall that some were made with a thing like that, and no actual "gag".

    I've never used one that had the extra stuff, gags, etc, on it.

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    Quote Originally Posted by JST View Post
    Some of that type holder had a place to "gag" it so it would not move, and one could put stiff rubber in there to give more return force, etc.

    That button might be a similar thing, I seem to recall that some were made with a thing like that, and no actual "gag".

    I've never used one that had the extra stuff, gags, etc, on it.
    I suspect that the purpose of the black button (whose clamping force could be adjusted, it appears) was to damp vibration to reduce remaining chatter (versus digging in).

    Some also had a feature to prevent the spring action, probably for increased precision of cutting.

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    [QUOTE=EPAIII;3681197]Please explain how "modern inserts" fix this problem.

    One source of trouble is the chip binding on the walls of the cut preventing free exit. Material builds up and chokes. Inserts have a configuration that folds the chip, making it narrower. There are numerous shapes that accomplish it. I do the same thing on HSS blades by grinding a notch in the middle of the cutting edge so it makes three narrow chips.

    Bill

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    the black boton is to give extra strength in the return

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    so if you want to stiffen the holder you put in the button?

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    Quote Originally Posted by celsoari View Post
    the black boton is to give extra strength in the return
    What does Extra Strength mean exactly? Increased spring stiffness by shortening the effective lengths of the spring arms?

    How does it work? Are there conical seats?

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    Quote Originally Posted by digger doug View Post
    I believe it's more a comment on more modern lathes, the type being "carbide capable", being much more rigid.
    In the spindle, drivetrain, ways, and tool holders.
    Actually no. It is the design of the insert that is key. Insert cutoff/grooving blades can be used on small hobby lathes and work very well. Once sized down for height.
    The key is that the insert folds the chip away from the walls of the cut so they exit without jamming in or rubbing on the walls. Of course rigidity is a factor but considering this works in non rigid lathes the insert geometry is most important.

    This approach of folding the chip can easily be accomplished with a hss straight blade. Grind a shallow grove ~0.015” on the top of the blade along its length. Leave a little land at either edge about .015” wide. Geometry doesn’t matter too much. This results in a lightly folded and continuously rolled chip. Cutoff speed will normally be 1/2 the turning speed of the particular material. Soft materials even faster.

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    Quote Originally Posted by Rickyb View Post
    Actually no. It is the design of the insert that is key. Insert cutoff/grooving blades can be used on small hobby lathes and work very well. Once sized down for height.
    The key is that the insert folds the chip away from the walls of the cut so they exit without jamming in or rubbing on the walls. Of course rigidity is a factor but considering this works in non rigid lathes the insert geometry is most important.

    This approach of folding the chip can easily be accomplished with a hss straight blade. Grind a shallow grove ~0.015” on the top of the blade along its length. Leave a little land at either edge about .015” wide. Geometry doesn’t matter too much. This results in a lightly folded and continuously rolled chip. Cutoff speed will normally be 1/2 the turning speed of the particular material. Soft materials even faster.
    As a "Hobbyist Machinist" how many cut off tools have you ground ?
    And how long did they hold up in production ?
    And how many inserted carbide types have you tried ?

    I suggest you try over at one of the hobby machining forums.

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    Quote Originally Posted by digger doug View Post
    As a "Hobbyist Machinist" how many cut off tools have you ground ?
    And how long did they hold up in production ?
    And how many inserted carbide types have you tried ?

    I suggest you try over at one of the hobby machining forums.
    Sorry. I do realize this is a production forum. However this thread had the appearance of a non production discussion. Aside from 9100 bill there seemed to be a lack of understanding of some of the physics behind cut offs. The premise of solving a rigidity problem by adding more compliance and using machines lacking rigidity didn’t sound like high production with worries about tool life.


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