Stringy chip problem

[bmaxwellc33]

We single-point cut a thread in a soft, gummy, low carbon HR steel, and we have a lot of problems with long, stringy chips. The thread is a M95 x 2.0. Any suggestions to improve the process?
High pressure coolant has been suggested, but will it effectively break the chip? What would be the best way to apply it to direct the chips away from the spindle and cutting tool?

[neilw20]

You favourte tool supplier may be able to help with a sutable chip breaker.
You may need a different tool/holder, even though the thread form will not change.

I've machine stringy stuff before. It can be problem.
I found more speed with finer cuts helped to make the chips brittle, but at the expense of tool life.
Push it hard and fast and see if it improves.
When feeding in each cut, do you just plunge further and cut on both sides of the tool, or add a slight z-increment to keep it cutting on one side.
That can help to cause chip to curl, and find a chip breaking surface.
How deep is your cut? How many passes? What speed?

[bmaxwellc33]

This sort of ended up in my lap, so I don't know the entire history. I am pretty sure we've had multiple tool vendors in to try out different chip breakers, and we haven't found one that really fixes the problem. We still have chip problems that cause us to shut down the machine and clean it out.

Also, due to the shape of the part, we are limited on the amount of force we can use to hold it. As a result, we make 8-10 passes including a final 'clean-out' pass. We have tried varying the speed and feed a little bit, but we still have problems with the stringers. We normally run around 1000 rpm, and I'm told we have gone up and down from there by as much as 300 rpm, but we can't get rid of the chip issues.

[ironlung29]

I suspect you cannot get adequate chip control because the lack of rigidity in the setup preventing you getting a sufficent depth of cut.

Please try an infeed angle between 28.5 to 29.5 degrees and keep depth of cut above .005" if your rigity allows. Reduce RPM if it chatters. Use a chipbreaker type insert from the insert manufacturer but theese are more fragile.

I find a zero degree infeed tends to rip the nose off the insert and really hampers chip control. Higher tool force is not what a shakey setup needs. Finer threads it may not matter.

The high pressure coolant might be the only hope as the material and thread are not that tricky.


Last resort would be to setup the tool upside down and change rotation direction for gravity to help get the chips out of your way (with or without coolant).

Good Luck,

Ironlung

[bmaxwellc33]

I verified with some others what I believed to be true. We have tried multiple tools/multiple vendors, with and without chip breakers, etc. and still no luck. We are using a 29 deg. infeed angle.

I'm also told that our current depth of cut is about as far as we think we can cut given our current method of holding the part. We're probably around 3 or 4 thou with each cut. So unless we improve our jaws and can get more force on the part without deforming it, we can't cut any deeper.

Does anyone have any experience using high pressure coolant specifically to break a chip from gummy steel? I generally hear people going to high pressure for deep drilling or something similar, but has anyone used high pressure to help break a chip while turning or threading?

(Thanks for the suggestions so far, I appreciate them)

[Switcher]

We use high pressure coolant on our 4"Acme machines, you still need an insert to break the chips.

We drill every part, so really all the high pressure coolant is doing is washing those chips out of the part after/while drilling.

All our inserts have chipbreakers, makes the chips look like sand in the chip pan (very small).

Did you check the center height on the insert/toolholder?


.

[bmaxwellc33]

We've about come to the same conclusion as you stated. The insert and chipbreaker have to break the chips, and the high pressure coolant probably won't do the job on its own.

We've made some small improvements by switching inserts and finding the best one for the job, but we still can't break the chip.

But just in case, I'll plead for help one last time. Is there anyone who has found any way of dealing with a chip while ID threading a very gummy steel?

[neilw20]

Originally Posted by bmaxwellc33 We've about come to the same conclusion as you stated. The insert and chipbreaker have to break the chips, and the high pressure coolant probably won't do the job on its own. We've made some small improvements by switching inserts and finding the best one for the job, but we still can't break the chip. But just in case, I'll plead for help one last time. Is there anyone who has found any way of dealing with a chip while ID threading a very gummy steel?

You are only taking light cuts. Have you tried to grind a chipbreak hollow into the top of the tool. At light cuts, a lot of top rake should not detract too much from the strength of the tip. Also new tip does not have a perfectly square top edge. Very small radius - free tool wear supplied, so that you can hold a size much longer. Maybe sharpening the top and making it square will work. Try a few licks with diamond file.

[Andre' B]

Live tooling and a thread mill.

[Kiwi]

This method may not give you a thread which meets the required standard.

You could cut some grooves the depth of your thread along the surface the thread is to be cut. This will reduce the turning lengths to the distance between the grooves.