How do I know a cutter is still sharp?

[Downunder Bob]

It's definitely economy, but has cobalt. This is the exact cutter

I am pretty sure this is not a rigidity issue, but I suppose I could be reading things wrong.

Is it normal for cutters to wear out this fast? Is there a guide to 'extending cutter life' somewhere? Or a list of 'things that contribute to cutter wear'? I use brushed-on motor oil when cutting steel, and have a different cutter for aluminum.

Rigidity is always an issue on smaller lighter machines, have you been running the cutter at the correct speed or perhaps a little too fast. running aHSS cutter a little overspeed will dramatically shorten its life, and conversely run at 10% underspeed will extend it's life.

Also are you using the correct depth of cut and feed rates, making cuts too light will cause the cutter to rub rater than cut, quickly dulling it. Examine the cutter under a decent magnifying glass for wear marks, even feel the cutter edges, a HSS cutter should feel sharp.

I would question why don't you just use the fly cutter from scratch. Finally motor oil is not an ideal cutting fluid, I guess anything is better than nothing, but get a proper cutting fluid, it's purpose is to keep the cutter cool.

A final question has the steel you are cutting been oxycut or welded, machining oxycut surfaces is particularly hard on cutters also some welded surfaces can be a problem because of local hardening.

Give us all the information and we can help solve your problem.

The picture of the cutter is a new one not the one you have used and therefore is of no use in diagnosing this problem. Post a picture of your actual cutter and we will know what is happening.

 

[mickri]

I can't give you a technical answer to this. I'm just a newbie. What do I know about machining. Squat to be honest. But I can give you an analogy. I have tens of thousands of miles of open ocean sailing experience in all kinds of weather. A question that often comes up is when should you reef down your sails. The answer is always the same. The instant that you think about reefing down is the time to do it. Don't wait and think more about it. Just do it. Conditions will only get worse.

I apply the same principle in determining when to sharpen a tool. The moment I think about needing to sharpen a tool I do it. I might sharpen a tool before it needs to be done but I eliminate the problems of trying to cut with a dull tool. Some day I might gain enough experience to actually know when a tool needs to be sharpened. Until then I will sharpen as soon as I think about.

 

[T Bredehoft]

I found online a chart giving rpm/diameter vs surface feet, printed it out, hung it behind my milling machine. I can match diameter of the tool with effective rpm. I have another that I developed, giving amount of feed per tooth at a number of rpms. I try to keep between 1/2 and 1 1/2 thou per tooth. I had to time my travel and establish rate of feed at various points on the dial.