# Inserted Boring Bar Fly Cutter



## bac1972 (Aug 18, 2020)

A few months ago I was needing to mill a 12” wide piece of steel. I noticed these cool fly cutter sets made by Suburban Tool but couldn’t justify purchasing the set. So, I made my own version....it uses a .750 diameter inserted boring bar. It works great!


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## Flyinfool (Aug 18, 2020)

Nice.
What is your max cutting diameter with that. And what diameter did you use on the test piece?


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## rwm (Aug 18, 2020)

Wow 12"! That would mean 6" stick out of the tool? How does that work out? How do you balance that? 
Beautiful execution BTW.
Robert


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## bac1972 (Aug 18, 2020)

Flyinfool said:


> Nice.
> What is your max cutting diameter with that. And what diameter did you use on the test piece?


Max diameter is around 17”, but I haven’t tried it! The test piece in the picture is approximately 4”x7” but I’ve done 12”x12”


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## bac1972 (Aug 18, 2020)

rwm said:


> Wow 12"! That would mean 6" stick out of the tool? How does that work out? How do you balance that?
> Beautiful execution BTW.
> Robert


Thanks! You can’t clearly see in the picture, but the bar isn’t perpendicular to the spindle axis. It’s about 87.5 degrees and it is out of balance somewhat but not too bad. I slowed my machine down but thought about experimenting with a counterweight. I was mostly experimenting with the angle because of the geometry of the boring bar insert location itself. The insert leading edge came out close to 90 degrees this way. I also used a different bar (a TPG 322 insert style) other than the one pictured. It had a little more mass at the insert end. It was really all about trial and error and I got lucky !


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## benmychree (Aug 18, 2020)

That could be an excessive load it impose on a lightly built milling machine, noting the R8 shank, the back gears are likely not designed for high loads and intermittent cuts such as those that the tool could impose, the spindle key is especially at risk of shearing off.


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## rwm (Aug 18, 2020)

I'm going to put that on my Sherline mill!


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## tjb (Aug 18, 2020)

rwm said:


> I'm going to put that on my Sherline mill!


Make sure you video it.


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## benmychree (Aug 18, 2020)

rwm said:


> I'm going to put that on my Sherline mill!


Would the tail walk the dog, or what?


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