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

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?
4ssss said:
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.
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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.
 
9t8z28 said:
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
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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.
 
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.
BaronJ said:
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.
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Is it better to have the parting tool slightly above center or below?
 
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.
mikey said:
I would put it dead on center, not above or below.
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9t8z28 said:
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°
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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.
 
9t8z28 said:
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.
Click to expand...

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.
 
9t8z28 said:
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?
Click to expand...
A person should realize that putting an angle on the end of the tool that results in not leaving a teat on the cut off part, results in generating a wider chip than one ground straight across, resulting in the chip binding in the cut, and making its exit from the cut more difficult.
I think lack of sufficient lubrication is the biggest cause of parting problems; usually, I use coolant for large parting diameters, it keeps things cool and also helps the chips flow freely.
In the USA, chip are chips, and swarf is such as results from grinding operations; in UK, this may not be true.
 
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