# Fly cutter = Boring bar ?



## Tin Falcon (Aug 14, 2007)

Guys:
     I have not been making many chips in the shop lately . Lots of distractions with life. I have a project on the shelf I decided to move forward on . It had a hole 2" diameter by .600 deep I needed to open it up to 2 -11/64
I did not feel like changing the setup on the lathe to use the face plate. And my boring head for the mini mill only goes to 1 1/2. So says I lets try the fly cutter . So I ground up a cutting tool for the 2" fly cutter. It took a few cuts and a little treaking of the cutter. It was rubbing at first then digging in and stalling the  machine. By the time I took the final cut I had it cutting nice . Now why couldn't I get it cutting good on the first cut arrgg!!
Anyway I was hoping to get a tolerance of +.005 -000.  well it was more like plus .010. The Inspector and supervisor both approved it.  They are both easy folks to get along with. This is the home shop after  all. I would not try this on a cylinder bore or press fit but if you just need a basic clearance fit it works great. the tool advance was a small soft face hammer and I used the digital calipers to measure movement. 
Caution: The but end of the cutter can cause problems trim to keep inside the tool holder if needed. 
Curious has anyone else tried this. ??

Tin


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## 1Kenny (Aug 14, 2007)

Tin,

Most of my experance is with 3.5 to 4.125 cylinders, cast and steel lined, but it may apply on this.

The tool bit may be out too far from the fly cutter head. When starting the first cut the bit can flex untill it finds its groove. A very slow feed at the start will keep the bit stable. Sometimes with the bit out too far it will retain heat and grow in length. The bits in a boring bar machine stick out very little and that acts as a heat sink keeping the bit cooler.

The bit can flex back away from the cutting side and can in-large the hole. The chips will start to look smoother or ruffer depending on how the bit angle was at the start.

The cylinder tempature during the machine process has the greatest 
effect on a cylinder bore. Too little assertion on the first cut will cause hot spots and the cylinder will expand more it that area. Before the second cut let the cylinder rest and heat soak. That can take an hour on a large cylinder. Before you make the final cut let everything sit one or two hours to come back to room tempature.

If anyone is interested I can post an infrared image of a cylinder being honed. 

Kenny


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## Hilmar (Aug 15, 2007)

Tin

go look in my post under Stuart Triple Expansion. I posted two more Pictures 
of boring the Cylinders.
Hilmar


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