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YJ_Jeff
11-17-2004, 08:52 PM
Hi all,

What is causing me to create big long springs instead of those nice little chips on my lathe? I'm turning a piece of 2.25" steel at 208 rpm. I've tried speeding up to 325 rpm and slowing down to 120. I started out with the bit height right at center. When that wasn't working like I thought it should I tried moving it slightly above and below center. No matter what I've tried I seem to always get these big long stringy springs.

I remember my machining teacher telling me that you don't want chips like those.

So what am I doing wrong? The chips are all purple and black too. I don't remember seeing chips get so hot. I'm not sure what grade of metal I am working with. I picked it up at the local scrap yard.

Thanks,
-Jeff

torker
11-17-2004, 09:08 PM
Are you using carbide or HHS bits?

dsergison
11-17-2004, 09:26 PM
I picked it up at the local scrap yard.
http://bbs.homeshopmachinist.net//smile.gif http://bbs.homeshopmachinist.net//smile.gif http://bbs.homeshopmachinist.net//smile.gif


[This message has been edited by dsergison (edited 11-17-2004).]

nheng
11-17-2004, 09:37 PM
You need chip breaking actions, commonly supplied by a chipbreaker. This is usually a physical obstruction to the chip located a short distance from and parallel to the cutting edge. On HSS bits, you've got to grind a groove in to create one, on carbide it can be molded in or if a flat topped insert, you need an external chipbreaker (looks like a small plow shaped piece behind the edge).

When the chip curls and hits the chipbreaker, it should break off and when all is perfect, the broken curls look like little "6"s and "9"s.

Even with a chipbreaker, you won't get chipbreaking action unless the feed (not the depth of cut) is rapid enough. From your description of the chips, it sounds like you're probably there.

Some metals (and other materials) will not break well but I don't have much experience there (except for Delrin http://bbs.homeshopmachinist.net//smile.gif ).

Den

[This message has been edited by nheng (edited 11-17-2004).]

Lynn Standish
11-18-2004, 02:16 PM
I am not an accomplished machinist so take it FWIW, but I have never been able to get chips to break well on 1018 CRS. Like you, I've tried different speeds and feeds, HSS and Carbide with a chipbreaker groove in the insert, and I hardly ever get 6's and 9's with that stuff. I even tried cutting .125 at a pass, and the finish was good but the insert was soon eroded at the tip. I'd guess you are working with something similar.

jmcmullan
11-18-2004, 03:27 PM
I've had similar results even using a coated carbide tool with a chipbreaker. The material I was turning was A36 HRS - pretty crappy structural steel from what I gather. I even saved one of the curls about 4 feet long as a "what you don't want souvenir". I got better results taking less aggressive cuts, but the best improvement was when I used just a light flow of WD40 as a cutting fluid. BTW, did you say what kind of surface finish you are getting? Before using the WD40 my surface finish was ROUGH!

JeffG
11-18-2004, 04:26 PM
Pardon a newbie question, but if the finish is OK, what's the problem with "springs"?

Lynn Standish
11-18-2004, 04:55 PM
JeffG --

When you get about 3 feet of hot, razor sharp chip hanging out there with a risk of having the chuck grab it and whip it around to slit your throat, it's kind of nerve-wracking.

HTRN
11-18-2004, 06:07 PM
I have a friend how used to like the long stringers of chips. He also thought brass would be "real nice" to machine. Oh how I laughed...

HTRN

Spin Doctor
11-18-2004, 06:08 PM
Some materials just have atendency to cut stringy. P6 or Carpenter 158 mold steel is a good example when cut with HSS. The grinding of chip breakers in HSS tool bits is almost becoming a lost art as the use of carbide explodes even in the HSM field. If you have a material that is cutting stringy with HSS cut the surface feet down (50 to 60 ft per minute)and increase the feed per revolution (.007 to .010). Also use adequate coolant to decrease frction in the cutting action and keep the tool from losing its temper. One way to get a chip breaker in HSS with out having to be an artist at the pedestal grinder is to place a piece of material that is higher than the tool on the tailstock side of the tool bit that the chip has to run into as it flows along the top of the tool away from the cut. This of course only works in the square type or QC tool posts. Another option is to grind the tool so that instead of being at basically a right angle to the centerline you grind the cutting edge on the end of the tool bit and place it in the tool post similiar to the set up as a boring bar. Not the thing for use with centers but it does give more tool for the buck in some ways. You then can place a chip breaker piece on top of the tool. One thing I don't like about grinding the chip breaker into the tool is that if the tool becomes sufficently worn from use and goes through numerous regrindings you are right back where you started from.

hoffman
11-18-2004, 07:40 PM
I used to just drop the feed lever every so often on rough cuts when I had those big scary springs. Let em run off 8-10 inches and stop the feed for a second. Maybe not the best way but it lessened the chance of one of those big chips snagging on the chuck and whipping around.

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Hoffman in Warner Robins Ga