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A Boring Bar Made from an Allen Key

carrdo

Member
Hi All,

One can, if needed, make a quick boring bar from an any size Allen key. The one shown in the photo is one I made from an 1/8" key.

As usual, there are some limitations as Allen key stock is normally made from high carbon steel which was used as a cutting tool steel before HSS was invented.

It certainly will work on brass, aluminum, soft bronze and soft (leaded) mild steel. But not on hard bronze, drill rod or on any of the tougher alloy or stainless steels. Also, being made from high carbon steel, expect to have to sharpen it more often than with HSS.

One can form something like this quickly freehand with a bench grinder but do not overheat the steel and draw down its hardness. I have a lot of tool holding fixtures and a surface grinder so I can produce any type of nice looking facet/relief I want. As well, correctly honing the finished cutting edge will improve things.

For a small boring bar such as this, if you want to have a nice finish, without chatter, take only a 0.002"" depth of cut per pass at most as you can see how thin the cutting end of the bar has been made in the second photo. Also, as the size of the hole to be bored becomes smaller, the relief angles on the cutting tool have to increase dramatically. I have bored small holes where the relief angles on the cutting tool had to be greater than 30 degrees (which weakens the cutting edge dramatically) to clear the hole and prevent the tool from rubbing so one has to go very easy with the feed and the depth of cut in these situations. The same applies when using HSS and Carbide cutting tools in small bores.
 

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Tom O

Ultra Member
One of the first thing we made in school shop class was making a boring bar in the forge mind you that was around 1967-68 when schools taught you, no-one was special you had the School bully but that was it.
 
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