Tuesday, November 6, 2012

Metalworking: Boring Bar Holder

Okay - Here is another metalworking project I did at Xerocraft.  This one was done on the milling machine.

One of the tools that we were missing for the metal lathe was a boring tool that could be used to make precision holes, tapered holes, or holes that are larger than available drills.  Tool holders that fit the KDK quick change tool post on our lathe are hard to find and pretty expensive, so I decided I would make my own.

Rather than go all out and create a holder that fits the dovetail on the tool post, I decided to go the easy route and create a holder that would fit into the 1/2" slot on one of the KDK tool holders and hold a 1/2" round boring bar.

The design is very simple.  Its a block of aluminium (because that is what I had on hand, and its easy to work with).  One side is drilled through with a 1/2" hole, and the other is milled to a 1/2" width to fit in the slot of the tool holder.  The part that fits into the toolholder is slit to allow the setscrews that hold it in the toolholder to compress the hole in order to hold the boring bar.  The photo above shows the boring tool as it is mounted for use.  The shiny part is what I built.

I started by cutting a chunk of 6061 aluminium to the approximate size, then squaring it in the mill.  Next I marked and drilled the hole for the boring tool, first with a center drill, then a small bit to establish a guide hole, and finally the 1/2" drill to fit the boring bar.  I did not ream the hole to size because the precision is not needed for this purpose.

Next I mounted the block directly to the mill table using a 1-2-3 block and some strap/step clamps.  I aligned the block to the axis of the mill with a dial indicator, then cut the steps for the part that mounts into the holder.  I used successive passes to get to the desired depth.  If I were to do it again, I would likely side mill at approximately the same depth to use more of the milling cutter.

I flipped the piece and aligned and cut the other side in the same way.

The final step was to mount a slitting saw with the same clamping setup, and cut a slit on the center line of the 1/2" width slot to the boring bar hole to provide a method for holding the boring bar.

When completed, the boring bar would slide into the hole at the appropriate depth and the 1/2" part would fit into the slot of the tool holder and get clamped into place.  This holds both the block in place, and by compressing the slit in the center, holds the boring bar in place.

The photo below shows an example of the boring bar holder mounted to bore a hole on the lathe.

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