Boring a deep hole with a Forstner bit requires a bit extension. I made this Fostner bit extension at the TechShop San Jose, http://www.techshop.ws, using the Jet Metal Lathe and Jet Vertical Mill.It is turned from a piece of 3/4 inch diameter X 8 inch long cold rolled steel, the type available at HD, Lowes or your local hardware store.

Step 1:

Start by mounting the stock in the three jaw chuck on the Jet metal lathe and face off the end. Proceed to turn the diameter to approximately .45 inches dia. X 1.25 inches long. The jacobs chuck I will be using this extension in has a nominal .5 inch maximum opening and I want to keep the end of the shaft as large as possible, so I turned the shaft to .45 inches diameter.
Do the set screws hold it well? I imagine since the fostner bit is round rather than having a hex shaft that the screws would allow it to slip if you were going through really hard wood.
That depends on the size bit you are using and the wood you are working with. Most often I will drill progressively larger holes when deep boring, but grinding a flat on the shank is a reasonable approach, also.

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