Trouble turning hot rolled steel!

[gunner312]

Hi, I am attempting to turn a flywheel from 1018 hot rolled steel. The finished dimensions are 4.25" diameter by .750" thick. I bought this grade of steel because it was half the price of cold rolled.

I have never tried turning hot rolled before, and it has been a nightmare. It is chipping the tips on my inserts almost as fast as I can replace them. HSS seems to just wear down rapidly. The finish is terrible and very inconsistent. I have varied the feed rate and depth of cut to no avail.

Is there something I am doing wrong or should I just bite the bullet and buy a blank of cold rolled?

Thanks in advance, John.

John,

You really shouldn't have any problem turning hot rolled. Your first cut should be deep enough to get through the scale on the surface, about .050 at the very most. Also you need to pay attention to speeds and feeds, remember CR X 4 / Diameter of the part = Cutting speed. Cutting speed for hot rolled using high speed steel is 50-60 sfpm (surface feet per minute) So using the formula it is 55X4=220/4.25=51.7 RPM Now that's with High speed steel cutters, with carbide inserts, you can double or even triple the cutting speed of the material so it works out as 2X55=110X4=440/4.25=103.25RPM. or 3X55= 165X4=660/4.25=155.2 RPM.

With carbide you are turning too fast with high speed you are definitely turning too fast.

Try it. Also, feed rate works out as a rough rule as 1/2 the tool tip radius as a starting point. so if your tool has a .015 tip you start at .0075 feed per rev, and go up or down from there.

I was a Machine Shop teacher for a number of years and a machinist for over 30. I owned my own shop for the last 10 of those. Always taught my trainees this.

Jim Wright