Freesteel Blog » Corner grindings over the edge

Corner grindings over the edge

Tuesday, October 1st, 2013 at 6:30 pm Written by:

This has got to be an old idea. But I don’t know if it’s been done yet.

The issue is when a ball-nosed cutter of radius r goes over the edge of a part it spends a long time (between points a and b) in contact with the same point on the corner, grinding it away as it follows the green circular path (if it crosses the corner at right angles; otherwise it’s an elliptical path).

If you wanted nice crisp knife-edge corners, you aren’t going to get it.

(At least that’s my guess. I don’t actually know as I am not a machinist and don’t have access to a machine on which to conduct experiments.)

I have recently been doing a lot of curve fitting, which gave me an idea.

How about if I detected these outer circular motions and bulged them out slightly by a small factor e. Then the tool would leave the corner at the top surface when it is at point a, and rejoin the corner when it is at point b — and not grind it down smooth on its way over.

If we did this everywhere, would it make the whole part that little bit sharper and nicer?

Who knows? But I’m not going to spend my time programming it for the general case until I see some evidence that it does make a difference. It would be easy enough for a Process Engineer to directly design some special paths that only work on a test corner and do a set of experiments that involve scientifically quantifying the sharpness of the corners that results from this strategy — and then product tests the feature for desirability.

Now, who do I know who works in a large company that ought to be well enough organized to deploy resources to check up on an idea like this? Never mind. I can’t think of one off the top of my head.

There’s an 80% chance that this idea is garbage. It’s necessary feature of progress that there are many failed experiments along the way, because you don’t know what you are doing. Of course, if you did know what you were doing, you wouldn’t be doing anything new, would you?

If we did do these experiments and they didn’t work out, it would be very important to publish the results accurately so that the next people can either (a) avoid going down this dead end, or (b) spot something in our procedure that we didn’t quite get right.

(Let’s set aside the evil capitalist logic that intends to promote damage and waste external to the organization by ownership control, lying and deliberately withholding technical information.)

I believe I have recognized the hallmark of an innovative system — it’s one that is capable of funding these failures. It might seem efficient to direct all your programmers to work only on “real” projects. But if you do you won’t encounter the sequence of failures, abandoned experiments and learning opportunities that are an utterly essential part of the innovative process. Or worse, you’ll continue to push through on a serious “real” project long after it should have been declared a failure and learnt from.

This critique works on the pharmaceuticals system. New drugs require a great deal of innovation to develop. But we only reward the successes through a government-granted patent monopoly long after the work is fully complete. Who is paying for all the necessary failed drugs along the way? This crucial part of the system is overlooked. It is real work, and it has to be paid for. The official story is that the drugs companies recycle the profits from the successes into future failed experiments. But there’s very little quantified evidence of that.

So here’s to failure. We need more of it. And we need not to be frightened of it.


  • 1. Graeme Nisbet replies at 3rd October 2013, 7:02 am :

    The machines I use (HAAS) deliberately cut the corner to keep the cutting feed up. you can tweek this amount using a G187 if you require sharper corners.

    When I am faced with intersecting surfaces I want to machine and I need a sharp edge I will create multiple paths 1 for each face.

    Whenever I do any surface machining I get more wear on the nose of the cutter than the edges. I could if I was using a 5-axis machine tilt the cutter to stop this happening but I’m only using vertical milling machines.

  • 2. Matt replies at 12th December 2013, 6:28 pm :

    I’d be willing to test this out for you. In my experience (I own a very small job shop), my customers typically want edges to be not sharp (up to 0.3mm is normal).


Leave a comment

XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <blockquote cite=""> <code> <em> <strong>