Totally Screwed Machine Shop

TNMT indexable tool holder

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Updated January 25, 2013 10:40


TNMT Insert holder

My buddy Paul offered up a couple TNMT inserts and having none I took a couple even though I had no holders for them. In the past I never really liked to use them as I couldn't seem to get the desired finish, which I blamed on not having a clearance angle made into them. Thoroughly board one Sat. the plan to make a tool for TNMT inserts was set into motion. The 1st version was made to be flat but the finish from it was enough to require a remake with 5° clearance as seen below.

inboard inboard inboard inboard inboard

1st picture is the 1/2" key stock set in the low vice on the rotary table with a 5° incline.     2nd pic, Using the rotab we cut in the angles pretty much 30°.  I prefer a little angle on the tool which helps give some room between QCTP and chuck.    3rd pic, The seat for the insert is cut and the hole for the bolt was drilled. Simply by taking .250" (half of the .5" end mill) from .375" (included circle of the insert) thus moving the drill out .125" to its proper location from the shoulder.    4th pic, The hole was tapped 4mm and a bolt was lightly filed in the lathe for a slip fit into the insert. Parts were assembled and inspected. Looks like it's set too far back but it isn't.     5th pic, Shows a test. Still not pleased! I gave the tool to Paul who likes to rough with carbide and finish with HSS shear tool. Note the triangle on the top of the tool (same on bottom) is the only flat part of the tool so the holder was made to only touch that section thus making it look like the tool overhangs to far.

It's a nice simple little project that doesn't require a rotab but if you got it use it ehh? If it don't work out chop off 1" and try again, nothing about the clearance angles is critical.


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