[4]

Need help identifying culprit of bad swarf from parting off on lathe (pics inside)

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#1
I rarely have an issue parting on my 8.5x20 Sieg C4 lathe but when I do it’s when I get less than an 1/8” away from the part falling off or right was I first start the cut. The blade either stops cutting or it doesn’t cut at all. If I apply more pressure to make it start cutting this long flat pile of what looks to be microscopic pieces of metal comes off. It slowly builds up and works its way back on the tip of the tool. I have sharpened the parting tool numerous times (I get it razor sharp) and messed around with the height as well. It seems to cut the best when I have it slightly above center.
I am using a Somma Tools T-15 .094” thick T-type blade in an Aloris AXA parting tool holder (I believe its a #71) and a solid tool post and my carriage locked down. Just in case anyone asks, yes I have checked the height after I locked the carriage. Lastly, I made sure that the blade is perfectly straight and not leaning or tilted. The material I seem to have an issue parting is 1018 CRS, 12L14, and general low carbon steel. I do not have this issue with tool steel or aluminum.
My parting speed is usually around 230-350 rpm’s and after the cut is finished the part is not so hot that I cannot touch it. Don’t get me wrong, it’s hot but not to the point that it will burn me. Also the motor does not bog down at all.
Oh, I almost forgot to add that I use a moderate feed. I make sure that the chip keeps rolling off. If I have to stop to put more oil on my brush I back out so that the tool does not rub and potentially work harden the material, or at least I think that is what’s going to happen if I let the tool rub without feeding.

Here is a picture of the swarf that I occasionally get.
4ACCF9E2-C9FA-4716-98F3-9B7F69B76C5A.jpeg
Here is a picture of the part. Can anyone see what’s going on judging by the face of the material? This is the part that falls off. I should probably add that when I face off the part still left in the chuck I do not notice it being concave or convex. A few thou cleans up the face.
23466E0B-AD24-4DA9-9198-FD2F90F97800.jpeg
 

4ssss

Active Member
Registered
Joined
Apr 25, 2017
Messages
440
Likes
252
#2
That 2nd picture shows the tool is rubbing
 

Bob Korves

H-M Supporter - Sustaining Member
H-M Platinum Supporter ($50)
Joined
Jul 2, 2014
Messages
5,520
Likes
5,833
#3
Could you please post a photo of the blade mounted on the lathe in the holder in such a way that we can see the actual clearance angle from vertical it has while in use? From the photos and your description, it seems like the blade might be rubbing on the work below the cutting edge (not enough relief.)
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#4
Does that mean the end relief is rubbing? When I parted off this tool it cut very well until the very end. This tool stays very sharp As well.
That 2nd picture shows the tool is rubbing
 
Last edited:

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#5
Will this work ? F37B75FF-F0DC-4BAB-90D5-87954E989D8B.jpeg
Could you please post a photo of the blade mounted on the lathe in the holder in such a way that we can see the actual clearance angle from vertical it has while in use? From the photos and your description, it seems like the blade might be rubbing on the work below the cutting edge (not enough relief.)
 

4ssss

Active Member
Registered
Joined
Apr 25, 2017
Messages
440
Likes
252
#6
The steel is grabbing the cutoff instead of being cut, which is why you have that chip. (it's not swarf, it's a chip, hence the term "making chips") Your front clearance, and your side clearance is wrong. I always make my front clearance steep and the radius of my grinding wheel. Also put a slight angle on the front, the higher angle on the side that you are cutting off so as not to leave a massive center tit on the finished part. That being said, it wouldn't surprise me also that you're either cutting too slow or your feeding too fast. Contrary to what alot of people here think, crank up your speed. You're only cutting cold roll steel, not magnesium. Look at a youtube video of a B&S or Swiss screw machine running. They sure don't drop down to back gear RPM to do 15 different operations.
 

4ssss

Active Member
Registered
Joined
Apr 25, 2017
Messages
440
Likes
252
#7
I just saw your pic. Put more angle on the front
 

Bob Korves

H-M Supporter - Sustaining Member
H-M Platinum Supporter ($50)
Joined
Jul 2, 2014
Messages
5,520
Likes
5,833
#8
Yes, more relief angle on the blade. The slope of how it is mounted to the tool holder reduces the clearance by that angle. I use the same style holder that you are using, and it has 3.5 degrees of upward angle, which needs to be put into the blade so it is vertical, zero clearance angle to the work. From there you probably want perhaps 7 degrees more (depending on what you are cutting), which would require a 10.5 degree total clearance angle on the blade itself. It is difficult to read the protractor in your photo, looks like maybe 8 degrees to the work. Try 2 or 3 degrees more angle and see what happens.

Also make quite sure the cutting edge is not above the center of the work. Match it up with the concentric rings of a facing cut on some stock.
 
Last edited:

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#9
Here is a pic of the swarf or chip when it is cutting good. The other pic that I posted earlier of the single chip is what I get when it stops cutting.
I tried to unroll the one roll of chips to open it up but it wasnt happening lol. Do these chips or swarf look normal ? I thought they did. I took the picture with my iphone looking theough a magnifying glass. My iPhone takes s***ty close up pictures by itself
0168722C-7A99-4D73-9D41-8F1EBA4F77DB.jpeg
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#10
I know it’s kind of hard to see but the Square head protractor is reading 8.5° . I had it at 7° which is what I thought was recommended and it didn’t want to cut so I added a little more (not a lot more) to 8.5° and it started to cut so I left it at that and figured the problem lied somewheres else. So you are recommending an additional 3° so that should put me at about 11.5°- 12°
Yes, more relief angle on the blade. The slope of how it is mounted to the tool holder reduces the clearance by that angle. I use the same style holder that you are using, and it has 3.5 degrees of upward angle, which needs to be put into the blade so it is vertical, zero clearance angle to the work. From there you probably want perhaps 7 degrees more (depending on what you are cutting), which would require a 10.5 degree total clearance angle on the blade itself. It is difficult to read the protractor in your photo, looks like maybe 8 degrees to the work. Try 2 or 3 degrees more angle and see what happens.

Also make quite sure the cutting edge is not above the center of the work. Match it up with the concentric rings of a facing cut on some stock.
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#11
I just posted a photo showing the normal chip or swarf that I get when it is cutting. They are curls, not straight pieces like my first photo show when it stops cutting.
I tried putting an angle on the blade so it left the part being cut off cleaner but it seem to reduce its ability to cut after I did that. I don’t think I’ve mastered that yet. I think I need to get it to cut first and then I will work on that.
What end relief angle do you recommend?
The steel is grabbing the cutoff instead of being cut, which is why you have that chip. (it's not swarf, it's a chip, hence the term "making chips") Your front clearance, and your side clearance is wrong. I always make my front clearance steep and the radius of my grinding wheel. Also put a slight angle on the front, the higher angle on the side that you are cutting off so as not to leave a massive center tit on the finished part. That being said, it wouldn't surprise me also that you're either cutting too slow or your feeding too fast. Contrary to what alot of people here think, crank up your speed. You're only cutting cold roll steel, not magnesium. Look at a youtube video of a B&S or Swiss screw machine running. They sure don't drop down to back gear RPM to do 15 different operations.
 

mikey

Active User
H-M Supporter - Gold Member ($25)
Joined
Dec 20, 2012
Messages
4,241
Likes
4,585
#12
I own one of those holders and use a P-type blade with a 7degree relief angle and have no issues parting with it. If I had to guess, I would say your tool is not on center. I mean exactly on center.

The only other thing I can think of that will affect the cut as you approach the middle is your cutting speed, which slows down significantly in the inner third of the cut.

You might try recentering the tool and pick up your speed as the tool gets into the problem area.
 

BaronJ

Brass
Registered
Joined
Aug 7, 2018
Messages
508
Likes
256
#13
Here is a pic of the swarf or chip when it is cutting good. The other pic that I posted earlier of the single chip is what I get when it stops cutting.
I tried to unroll the one roll of chips to open it up but it wasnt happening lol. Do these chips or swarf look normal ? I thought they did. I took the picture with my iphone looking theough a magnifying glass. My iPhone takes s***ty close up pictures by itself
View attachment 276959
From looking at those chips, I would guess that too slow a spindle speed and too hard a cut.

I noted that you don't have the cutter exactly on center ! It needs to be close, within a couple of thou. For mild steels I run at around 600 rpm and two thou per turn. The blade I use has a tapered cross section and is 2 mm wide at the top and 1.4 mm wide at the bottom. It was also made in the USA. I also use it upside down from the rear of the crosslide.
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#14
I just faced off a 1” part and then put the parting tool in the holder and verified that it is on center with a magnifying glass and my opti visor. The method I use to set my tool height is with a stack of Pratt & Whitney gauge blocks. My gauge block set came with these precision ground accessories that allow you to measure OD’s. I put this accessory on top of my gauge block stack. I then put the stack on top of the lathe bed and bring the tool up under it. I rotate the gauge block stack until the tip of the tool just clears the tip. Of course this is all done after I have faced off with 3 tools and then used the height of these tools to set my stack height. I know it’s not good to keep Gauge blocks together like this as they can stick together but I check it often and they have never welded together,
image.jpg
If I run faster, like 500 to 600 rpm’s it screams and chatters. There’s no feed that I can get that will stop it from chattering.
From looking at those chips, I would guess that too slow a spindle speed and too hard a cut.

I noted that you don't have the cutter exactly on center ! It needs to be close, within a couple of thou. For mild steels I run at around 600 rpm and two thou per turn. The blade I use has a tapered cross section and is 2 mm wide at the top and 1.4 mm wide at the bottom. It was also made in the USA. I also use it upside down from the rear of the crosslide.
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#15
Is it better to have the parting tool slightly above center or below?
 

mikey

Active User
H-M Supporter - Gold Member ($25)
Joined
Dec 20, 2012
Messages
4,241
Likes
4,585
#16
I would put it dead on center, not above or below.
 

9t8z28

Active Member
Registered
Joined
Aug 16, 2016
Messages
213
Likes
82
#17
That is my intention but I would like to know what others think. I have heard that is better to be slightly above center than below.
I would put it dead on center, not above or below.
 

Bob Korves

H-M Supporter - Sustaining Member
H-M Platinum Supporter ($50)
Joined
Jul 2, 2014
Messages
5,520
Likes
5,833
#18
I know it’s kind of hard to see but the Square head protractor is reading 8.5° . I had it at 7° which is what I thought was recommended and it didn’t want to cut so I added a little more (not a lot more) to 8.5° and it started to cut so I left it at that and figured the problem lied somewheres else. So you are recommending an additional 3° so that should put me at about 11.5°- 12°
It depends on the material and the feed rate. Softer metals and high feed rates want larger relief angles, and vice versa. If it is cutting well at the angle you have it with the materials you use, then go for it. If not, adjust.

Aim for a sharp tool, good sharp edges and corners, and mount it as close as you reasonably can to on center and square to the work, and rigid. Both too high and too low (and too flexible) cause problems.
 

BaronJ

Brass
Registered
Joined
Aug 7, 2018
Messages
508
Likes
256
#19
I just faced off a 1” part and then put the parting tool in the holder and verified that it is on center with a magnifying glass and my opti visor. The method I use to set my tool height is with a stack of Pratt & Whitney gauge blocks. My gauge block set came with these precision ground accessories that allow you to measure OD’s. I put this accessory on top of my gauge block stack. I then put the stack on top of the lathe bed and bring the tool up under it. I rotate the gauge block stack until the tip of the tool just clears the tip. Of course this is all done after I have faced off with 3 tools and then used the height of these tools to set my stack height. I know it’s not good to keep Gauge blocks together like this as they can stick together but I check it often and they have never welded together,
View attachment 276975
If I run faster, like 500 to 600 rpm’s it screams and chatters. There’s no feed that I can get that will stop it from chattering.
I must confess that all I use to set tool hight is a scrap of "L" shaped alloy with a line scribed across it from a hard center placed in the lathe
spindle. I just sit it on the crosslide and adjust the tool to suit.

I've just checked the parting off blade and it is very fractionally below center, about the thickness of the scribe line. Remember I'm parting off from the rear of the top slide.
 
[6]
[5] [7]
Top