Stringer Chips

[rake60]

This story goes back a few years and I may have told it before here.

I was running a big vertical boring mill, gouging out a wide groove in the face of an 8 foot diameter
plate with a 60° tool. I'd work if down into the stock 1/4" and feed it to the left. Then gouge in another
1/4" and feed to the right. The resulting chip was a heavy spiral that would grow to about 8 feet in length
then break off. On one of those cuts that spiral chip came straight out and struck me in the center of the
chest. It cut and burnt immediately, then it proceeded to wrap up my shirt and started pulling me into the
machine. I couldn't reach the E-Stop so I just braced up as I could hoping the shirt would rip off. It did.
The whole incident lasted about 5 seconds. You'd be surprised about how much thinking you can do in 5 seconds.

Hobby scale machines are not likely to drag your whole body in but a stringer chip whipping around can catch
a finger. If that happens and your lucky you end up with a few stitches. If the chip pulls your hand into the
chuck the results can change dramatically.

Grind your tools to break the chip and NEVER reach in to clear a stringer chip!

Rick

 

[briankenyn]

Hi Rick,

I have learned to grind my tools to achieve satisfactory finishes on most metals including SS. What I haven't learned to do is to grind the tool geometry to break the string. Your post is timely as I have been thinking about this exactly and i'm wondering if you have an suggestions.

 

[rake60]

A chip breaker is a form that causes the chip to fold back on it's self to a point that will cause it to break.

This is an example of one of my own crude hand ground chip breakers in a brazed carbide bit.

It isn't pretty but it works!

Rick

 

[Tin Falcon]

Harbor freight sells there IIRC diamond life brand tools . I have a few of there dremel sized cutting wheels that would be ideal for the task of a groove in carbide.
Note diamond wheels are not supposed to be used on hss steel . it actually heats the diamond to the point of turning it back to carbon and ruining it. but if it is cheap enough to be considered disposable your tool your choice.
Tin

 

[kvom]

Using power x-feed on a lathe, interrupting the feed every few seconds will break a stringer if the tool doesn't.

 

[shoprat]

I was boring some stainless steel parts at work this last week and was getting some longer strings
and all of a sudden it snatched up a big ball of chips and stringy ss and wrapped around the boring bar
scraping my arm in the process

 

[EE]

Stainless chips are hard to break and the worst to cut you. Another problem is leaving stringy chips on the floor while you are working. If you happen to step on the ends (forming a loop) and the other foot catches in the loop when you take a step they will cut the heck out of your ankle. It takes a little time but its safer to pick them up and put them in the trash as they come off the machine.

 

[doc1955]

Stainless chips are hard to break and the worst to cut you. Another problem is leaving stringy chips on the floor while you are working. If you happen to step on the ends (forming a loop) and the other foot catches in the loop when you take a step they will cut the heck out of your ankle. It takes a little time but its safer to pick them up and put them in the trash as they come off the machine.

You still need to use extrem caution with stringing chips and stainless chips are some of the worse. I've seen a person get a chip caught on his shoe and the other end on the lathe and as he walked away the chip sliced right through his brand new safety shoe. He was just dam lucky they were safety shoes as the steel cap stopped the chip from doing bodily harm. So when you pick chips up be very cautious as if they catch some thing while you are moving them and get pulled through your hand you will get cut.
And never I repeat never pull a or touch a chip with the machine whether lathe mill or what ever running!

 

[mzetati]

recently I was machining a flywheen from a 100mm dia steel rod from the scrapyard: HSS was unusable on that alloy, while the carbide tools I had produced looOOng stringy coils unless I was feeding the tool by hand and volountairily interrupted the cut.
Had the idea of filing a "step" the upper surface of the carbide knife, acting as a chipbreaker: it took only a few minutes, and worked OK.

I've attached a collage of blunt pictures showing the workpiece, the cutting tool, the finished workpiece, the chips I got 'atfer the cure' and a second picture of the tool itself together with the diamond coated needle files I used.

Marcello