Newbie Question - Finish on CI

[Stuart B]

I bought a part finished Cast Iron chuck backplate which I am planning to use as a face plate. I mounted it up and took a very fine (both in depth and feed) skimming cut. I used a new HSS tool with a sharp point. What resulted was what appeared to be be a fine finish. In reality though it was very rough. Wiping it off with a paper towel, left bits of the towel on the surface. I am thinking that I need a bigger radius on the tool? Apologies if this seems a "machining for dummies" question, but this is the first time I have taken a tool to CI. Also I remember from college(some 25 years ago) that you didn't need coolant or lubricant for CI due to the carbon content. However I decided to put coolant on half way through the cut to keep the CI dust out of the air and clear of the tool. The finish was much better on the 2nd half.

Any tips on tool forms, speed & feeds would be appreciated

Regards

Stuart

 

[Mainer]

Yes, a small radius ought to help. Speed depends on diameter. If you were facing off the backplate, did you notice any improvement or deterioration in finish close to the center vs. out at the edge? Maybe you can use that as a guide to a "good" average speed.

Personally, I avoid coolant with CI because it makes such a sludge all over the place, but whatever works...

 

[rake60]

Cast iron is extremely abrasive on the tooling.
It will take the edge off of the contact point very quickly.

The best way to cut it with a Grade C2 Brazed Bit.
The C2 carbide is made for cast iron and can save a lot
of headaches.

Scroll down on THIS PAGE to see
Enco's listings for them.

Rick

 

[tel]

the first cut on CI should be reasonably deep, to get under the hard skin. Once you get down to the soft inner metal you will find it machines like a dream.

 

[rake60]

The video I had posted in this thread shows
why cast is more challenging.

Surface Finish Challenging?

Rick

 

[Stuart B]

Thanks for the tips, I had assumed that the skin had already been removed as it did already have a rough turned finish. I defintely got a better finish on the outer diameter of the plate, so I must have been running too slow at the start. I will give it another go with a radius on the tool.

 

[Stuart B]

Quick update, with a very positive result.
I ground my first HSS tool from a piece of 1/4 tool stock. Nice generous radius.
I took a generous cut with a low spindle speed appropriate for 80FPM for CI.
Result was a lovely finish. I am well pleased
Stuart