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DoN. Nichols
 
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Default Homemade Carbide Lathe Toolholder

According to Gunner :
On 20 Oct 2005 20:03:35 -0700, "woodworker88"
wrote:

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


You should have none of the bottom of the insert overhanging. It
should be completly supported.


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.)

That being said...try to keep overhang as absolutly small as possible.


Agreed.

Enjoy,
DoN.

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