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In this video, I make an adjustable drill bit. I start by using the metal I cut from the M12 bolt. Then I am cutting a Spade Drill Bit. Then I combine the two.
Making Video :
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Did you see this ? Countersink Drill Bit making
You can use it both to drill 90 degree holes and to drill holes in the depth you want. It also works for joining two woods together, you can see in the video.

In this video, I am making a tablesaw crosscut sled. It is simple and useful. Watch this video and learn making a table saw sled. You can download a PDF plan, see below.