Homemade Carbide Lathe Toolholder

I just made my own lathe toolholder for indexable carbide inserts out of a perfectly sized piece of aluminum I had lying around. I matched
the height of the cutter to a regular toolholder I have. I filed the recess for the carbide and drilled and tapped the 4-40 hole for the screw that secures the carbide. I copied the rough dimensions off of some other tools I have seen and a carbide tooholder for a Amaco brake lathe. My main question is what is the acceptable overhang of the carbide over the toolholder. I know the carbide is brittle, and as I was generously given the carbide inserts I really don't want to break them. The current overhang is about 3/32" of an inch, but the one I was copying from had less than 1/16" The brake lathe is designed for ultimate rigidity, and I don't need quite that much accuracy, but I don't want to be snapping carbides either. Thanks, Woodworker88 and the Los Altos High School Robotics Team #114 www.lahsrobotics.org
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wrote:

You should have none of the bottom of the insert overhanging. It should be completly supported.
That being said...try to keep overhang as absolutly small as possible.
Gunner
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
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Different inserts have different properties. Some are much tougher than others by a factor of 2, 3 or more. Some work very well on one material but not others. Do a web search and see what you have.
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Also there's an old machinist's trick. Put piece of soft material (0.010" soft copper works well) between the shim and the steel tool holder.
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    O.K. That would be an alternative to the carbide anvil which I just suggested in another branch of this thread. It would deform easily enough to bed into any imperfections in the pocket in the holder, and provide better support than a tough steel would, and is easy to replace when you replace the insert.
    Enjoy,         DoN.
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Sounds good, guys. Since the overhang is slight now but I don't want to redrill and tap the screw, I think I'll put a small sheet aluminum or brass shim under the insert that will support it to the edge. This won't be much of a height problem because I made the toolholder just a tad too short to be centered when in the lathe.
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    And in particular, the better insert toolholders (both turning and threading) tend to have an anvil of carbide to offer better support than the unhardened steel can offer. If you want to make a really *good* toolholder, but a couple of spare anvils, and the hardware for attaching it (sometimes a screw with a cylindrical post for orienting the insert properly -- if the insert has a center hole, or sometimes a flat-head screw designed to be flush with the top of the anvil, if the insert has no center hole, and is designed to be supported purely by being clamped in place -- often with a chipbreaker on top of it.
    The cheap toolholders will often distort when an overloaded insert breaks, and this offers less support for the next insert, making it break at a lesser load than the previous one broke at.
    I think that the anvils are a tougher (less brittle) form of the carbide than some of the inserts (depending on what the inserts were made to cut.)

    Agreed.
    Enjoy,         DoN.
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woodworker88 wrote:

Nice site. I see LAHS has assumed ownership of the MVHS Eagle as mascot. Does that make me an Alumni for LAHS? <G> (MVHS, class of '75)
Seriously, it's nice to see your robotics program in a school in this day and age. Sure wish there'd been something like that when I was in HS.
Jon
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Thanks for checking out our site. We try to create a robotics experience in which people become better educated in the skills that are important in the world right now. These skills help people get jobs and have training they might not otherwise have. As the student in charge of our machinery and the shop, I help the team with the maintainence and operation of an Excello mill, a craftsman lathe, a clausing drill press, and many other large and small tools. In addition to routine maintainence and operation, we have worked on everything from calibration and adjustment to fabricating replacement parts. I hope that we will continue to get the funding we need to maintain our team and continue to acquire new tools and skills.
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all carbide tool holders I have support the carbide with a second piece of carbide below it - this second piece of carbide is not sharp and doesn't cut, it's only job is to support the cutter.

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