Sunday, September 8, 2013

Boring Bar Holder

Since my tool post has no way to put my boring tools on centerline (let alone holding them), I built this holder for them.  Since all my boring tools have the cutting edge aligned with the center of the shank, all I had to do was raise the center of the shank .5" off the tool post.  The hole is .75" and the smaller tools fit with adapter sleeves.
Using the same 2"X1" hot rolled steel, I milled off a piece 1.5" long.  I really should get a saw.

Facing the piece.  I think the finish looks cooler when using a small end mill to face rather than a fly cutter.  Also notice my makeshift parallels, just a couple of 1/2" high speed lathe tools.
Milling the step to fit in the tool post.
I started drilling the hole with a center drill, then a 5/16" drill.
Then a 15/32"
Since I'm ill equipped for this operation and 15/32" is my biggest drill bit, I used an endmill to widen the hole.  This one was about 5/8".  Since I'm widening an existing hole, I can get away with holding the endmill in a drill chuck.  I don't recommend doing this for starting holes or side milling.
To get the hole to the final .750" size I used the last option, the boring head.  This was a bit of a bear to do with my machine since it doesn't have the most rigid spindle setup.
Eventually I did get the hole to finished size and the boring bar fit right in.
Afterwards, I drilled and tapped the screw holes with a #10-24 tap.  This thread seems ideal opposed to the #10-32 I used on the previous holder.
To fit different sized boring bars, I turned, drilled, and bored some adaptor sleeves.  The outside is .750" to fit in the holder, and the inside diameters are 5/8" 1/2" and 3/8" to fit my entire range of boring bars.
Different boring bar shanks: 3/4" 5/8" 1/2" 3/8"
I had to mill little windows in the side of the sleeves for the securing screws to fit through.
All done, here is the holder with a 1/2" shank boring tool and sleeve.  Notice there is a shim between the top of the tool post and the holder.  This is to prevent the holder from being smashed by the tool post screws like what happened to the knurling tool holder.

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