Thread: Chip control in stringy material with HSS

Hi Bryan,

Just adding another dimension to the problem...

I tried a bit of 4140 with a SECO WNMG 060408-M3 TP1500, and also tried SECO WNMG060404-M3 TP2000,

At 950 rpm, and 1mm DOC I get good finish with the 08 NR, but stringy swarf that doesn't break..



By reducing the DOC, to about 0.5 the stringy swarf starts to break (I guess because it's thinner)



The 04 NR insert gives a slightly better finish, but still won't break the chips...

Cranking up the revs to 1500 gives better finish still, but is a bit scary with a continuous razor sharp swarf coming off....

So, I'm no help, just illustrating the problem is not limited to HSS..

Regards
Ray

What feed rates were you using?

Originally Posted by pipeclay

What feed rates were you using?

Hi PC, Apologies for the slow reply, I've been working away for a few days, If I remember correctly it was the slowest feed rate I could get... maybe 0.03 mm/rev.

I seem to recall you were making Hercus parts from 4140, what did you find were the best methods of breaking the chips?

Regards
Ray

Most of what I turn is run at around 800RPM for material around 50 dia and less,occasionally I will increase speed to around 1200RPM for smaller dia stuff but this is usually around 12 dia.
If I am using the Hercus I am limited with standard pulleys to around 800 RPM unless I increase pully size.
With larger material 50 dia plus I run from 400RPM and lower.
I tend to keep my feed rate at the nose radious or under,but not by a lot.
I tend to set my cuts for roughing so as not to stall the lathes.
I dont usually have any problems with chips with High Tensile,when machining 1020 I occasionally have wirey swarf but this is usually eliminated by playing with machining parameters.
I tend to only purchase/use .2/.4 nose radious tips,in ccmt,dcmt,tcmt,wmng.

Thanks PC,

I've been checking the SECO catalog, and they class 4140 as group 4 (that's just their numbering scheme) but for that group (and the inserts I've got) they recommend 300 m/min, that's roughly around 2000 rpm for 50mm diameter, and a feed rate of 0.15 to 0.5 mm/rev.

Nearest I could get to that would be 1500 rpm and crank up the feed rate.. might give it a try later just for interest's sake.

Regards
Ray

Dont forget that most if not all machining parameters covered in the web sites catolouges of manufacturers or suppliers are relating to CNC not manual backyarders.

Originally Posted by pipeclay

Dont forget that most if not all machining parameters covered in the web sites catolouges of manufacturers or suppliers are relating to CNC not manual backyarders.

Exactly the reason why some of us fumble our way through the carbide jungle. I had an orphan Seco CCGT insert, that I'd got from who knows where, and it cut 4140 beautifully. I snapped both corners off in acts off stupidity and then discovered that it was a grade superseded years ago. Most grades sold by the likes of Seco, Kennametal ... are extremely specific in what they are designed to machine and also the conditions that they are to be used in. It's hard work.

BT

Originally Posted by RayG

Thanks PC,

I've been checking the SECO catalog, and they class 4140 as group 4 (that's just their numbering scheme) but for that group (and the inserts I've got) they recommend 300 m/min, that's roughly around 2000 rpm for 50mm diameter, and a feed rate of 0.15 to 0.5 mm/rev.

Nearest I could get to that would be 1500 rpm and crank up the feed rate.. might give it a try later just for interest's sake.

Regards
Ray

Many years ago when I was machining a fair bit of 4140 at TAFE, the basic rule for getting chips to break was, up the speed and up the feed.

PDW

Originally Posted by Anorak Bob

Would you like me to post you some Bruce?

Bob
Thank so much, I recieved the 4140 steel pieces by post today, 36mm dia or 1.425" dia
Set a piece up in the lathe with the same HSS Toolbit with its ground "chipbreaker" on its top face, as shown in previous post, machining mild steel.
The 260 Hercus Lathe speed set at 140 rpm in backgear with a .005" feedrate per rev.
Depth of cut 1/8th inch or 3mm
Coolant Water soluble oil.
Result...Chips came off in short acceptable spirals, I could hear the lathe was "working" but not overloaded. When the coolant was turned off chips became blue & with the HSS toolbit I would say tool life would be short. The coolant was necessary for machining this material with HSS tools.Although I was using a fairly lean oil to water ratio, I believe a ratio of more oil to water would be advantageous.
Photos of the trial are shown including a photo of the chips.
Thanks again for your assistance in providing the trial pieces,
regards
Bruce

Additional to the above I did try increasing speed to 300 rpm.
With the same depth of cut & feed rate.
The lathe did not like it however when depth of cut was reduced to 1/16th all went well.
So perhaps with HSS tools the lesser depth of cut & higher surface speed could be desirable
regards
Bruce

Thanks Bruce. I have some 4140 somewhere. When I get around to using it I'll do some similar tests and post results for comparison. Pretty sure the stuff I first posted about wasn't 4140 though.

Yesterday I made a pair of tee nuts from 1" 4140 to suit some helix clamps I bought for the mill. Using a Kennametal KC 5025 grade insert at 900 rpm with a depth of cut of 0.020" and a feed of 0.003", the results were o.k. Hand feed on the 45 degree bevels resulted in some tearing. The results achieved with the mill were appalling. I should have used a better cutter. The 3/4" slot drill I used works well enough in forgiving cast iron but not so in 4140. Parting off with a no rake HSS tool was effortless.

There is a lot of tearing evident in your test turning Bruce. How about a higher speed and shallower cut?

BT

p.s. Bruce you added another post while I was one finger typing. How about a MUCH higher speed?

Neat idea for the T nuts Bob, and they turned out well.

Bob
I left the piece set up so that I could try other variables like you suggested.
Here is a photo of the finish obtained from the same roughing tool.
The speed was increased to 800rpm & the feed rate reduced to .0025" per rev.
The smaller dia has the 800rpm @.005" per rev feed.
The second larger dia has the 800rpm @ .0025" per rev feed.
However for roughing deep 1/8" cuts & rapid stock removal without finish in mind the slower speed & .005" per rev feed rate gives the best result with the HSS tool & coolant. in terms of metal removal rates
The shallow cuts at high speed do tend to produce the long stringy chips.
I could sharpen a HSS finishing tool to get better finishes on this 4140 steel, if required.
regards
Bruce