Another Parting off Thread

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walterwoj

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Yes, I know it's been answered a million times but I STILL can't figure it out. I can't part off to save my life. I have read several posts on the forum, including on that said to up cross-feed to do it and that helps - to a point. For the latest test I'm using 1 1/4" 1014 Cold Rolled and a HSS T-Style Cutoff tool. What I have done:

  1. Sharped the tool - I might be able to shave with it...
  2. Minimized stick out - Parting off 1 1/4" stock - 1 3/8 Sickout.
  3. Lock down carriage, tighten the gibbs.
  4. Lock down the tool - AXA tool post, specialized tool holder, locked down tight!
  5. Lube - Cutting oil on everything
  6. Reduced speed - I put it in back gear and I'm down to 104 RPM

    Here is where I've tried parting by hand but it scares the living crap out of me so I go too slow and it chatters until i think the lath is going to fall apart! I've also had it stall the lathe and broken 4 carbide cutting tools. Those usually work better... until they don't and brake with a bloodcurdling crunch! :faint: Just thinking about it is causing my blood pressure to rise! :eek: :eek::eek::eek:

  7. Set the cross feed to .038 IPR - LET IT RIDE!

    I set it and let it run. Looks good, chips are curling, kinda long but they curl up tight and break before they seem to jam anything up. This ain't so bad! :cool: I get to about 3/4" diameter (1/2 way ) and :eek: CRUNCH! :eek: WHACK! :eek: :faint: The lathe stalls for a second as the tool digs in, then it breaks loose, launching a chunk of shaving into the ceiling. HOLY F:eek:CK! I need a new pair of pants and a strong drink! I calm down, carefully clear the bur/chip that caused my latest near death experience :ghost: and set up gain. I figure "We are deeper into the part, so the SFPM has dropped... maybe I should increase the DOC to compensate." So I set the cross feed to .048 IPR and try again. Good shaving ... ok this might be good... :eek: CRUNCH! :eek: WHACK! :eek: same ****** ****** thing! I CAN'T TAKE THIS ****!!!! :mad::eek::mad::eek: I finished parting off with a HACK SAW! Way less stress!
I have been working on parting off ever since I got the lathe working.... I can do every other operation but this SCARES THE CRAP OUT OF ME! Someone please tell me what noob stupidity I have that makes this so #$%#$% HARD! :***** slap: It's so frustrating!

Pretty Please! :cry: :dejected:
 
Minimized stick out - Parting off 1 1/4" stock - 1 3/8 Sickout.

- When you say stick-out I hope you mean the length of stock outside the jaws right? (as opposed to parting tool stickout). To make it simple, pre-extend the blade only just enough so it will go over center. Any more extension is unnecessary flex.

- How are you establishing the the center of the cutter is on center with the stock? Newby alert if its the typical blade holder that holds the blade at a rake angle. You set it up to part 1" dia stock with edge on center. Then you need to part 1.5"dia stock so you simply extend the blade. But now the edge is above the center line. therefore you also have to re-establish edge center by dropping the toolholder or however you make your adjustment.

- How are you establishing that the blade is set exactly perpendicular to the stock axis?

- Do you have the edge ground at 90-deg (ie no angle to the edge looking down at the Tee). Some folks grind an angle one way or another so that it will part with no bib on one side or another. I haven't found it makes much difference one way or another if its working right. But I do know that this profile can draw the blade in at an angle during the cut. It then binds up & bad things happen.

- How thick is your T blade & what kind of holder? A lot of problems have been traced to POS import blade holders that do not clamp the blade securely. Tightening actually cants the blade over which is A) now at an angle = bad B) not supported by the tool holder = bad

Feeding by hand should be no different than power feeding, at least to give you a feel for whats going on. You can slow down feed or back off to clear chips... all important things to get established before you let it go autopilot.
 
If you read all the posts regarding parting on this forum you will realize the main criteria is rigidity.
If your holder, cross slide, apron are all tight and the tool post is rigid this will take a lot of variables off the list.
Set your lathe up to part and see if there is any flex no matter how small at the tool tip.
On my lathe you could visible see the flex in the tool post whilst parting until I removed the top slide and replaced it with a solid plinth.
Problem solved. (for me)
 
0.038 IPR? I think that this is one of your problems.

You don't state your lathe or tool specs, so I just have to guess.

My second observation is that you are probably not using enough oil on the cut.

Parting used to give me fits, until I learned the "magic formula" (at least one that worked for me).

My parting blade is a 1/16" wide, "P" type tool. With it, I can part off 1018 that is 1-3/4" in diameter. I use Cool Tool II as my lube, but almost anything that lubes will probably work. I part at the second highest speed on my Heavy 10, which is around 900 RPM and I use power feed (with a fine feed-in rate). Before I start to part, I dip my lubing paint brush into my container of CT2 and start the feed. As the blade is cutting, I continually "paint" the groove with the lube. This is probably the MOST important step, because if my brush needs to be reloaded, I STOP THE IN-FEED AND RECHARGE THE BRUSH! Once reloaded, I re-engage the feed and continue to "paint".

When parting, I always start with a freshly sharpened tool, which is not hard to do, just 2 or 3 seconds at the grinding wheel is all it takes. Also, I start with the tool advanced for only a depth of 1/2", even though the actual part is much deeper. Once I reach the 1/2" mark, I stop and reposition the tool for 1" depth, then continue. This goes on until I have parted as deep as I dare. Once I chicken out with the parting tool, I grab the hacksaw and finish the part.

I also NEVER (at least very seldom) part manually. The power feed can feed-in far more consistently than I can by hand.
 
petertha said:
Minimized stick out - Parting off 1 1/4" stock - 1 3/8 Sickout.

- When you say stick-out I hope you mean the length of stock outside the jaws right? (as opposed to parting tool stickout). To make it simple, pre-extend the blade only just enough so it will go over center. Any more extension is unnecessary flex.

- How are you establishing the the center of the cutter is on center with the stock? Newby alert if its the typical blade holder that holds the blade at a rake angle. You set it up to part 1" dia stock with edge on center. Then you need to part 1.5"dia stock so you simply extend the blade. But now the edge is above the center line. therefore you also have to re-establish edge center by dropping the toolholder or however you make your adjustment.

- How are you establishing that the blade is set exactly perpendicular to the stock axis?

- Do you have the edge ground at 90-deg (ie no angle to the edge looking down at the Tee). Some folks grind an angle one way or another so that it will part with no bib on one side or another. I haven't found it makes much difference one way or another if its working right. But I do know that this profile can draw the blade in at an angle during the cut. It then binds up & bad things happen.

- How thick is your T blade & what kind of holder? A lot of problems have been traced to POS import blade holders that do not clamp the blade securely. Tightening actually cants the blade over which is A) now at an angle = bad B) not supported by the tool holder = bad

Feeding by hand should be no different than power feeding, at least to give you a feel for whats going on. You can slow down feed or back off to clear chips... all important things to get established before you let it go autopilot.
Click to expand...
By stick out I meant tool stick out. Only enough to get the job done. Also the material cut off point was less than an inch from the check jaws. I set this up as an experiment so I didn't have any project requirements in the way.

I'll triple check my blade height, but I pretty sure the tip was on center for the length of tool stick out.

I ran the blade up against the chuck face to ensure it was perfectly straight. I'm confident it is strait.

Yes, 90-degree cutting edge, not gonna get fancy until I can do the basics....

3/16 Blade (Chinese) in a Chinese axa holder. I noticed the blade will cant if I pressed it up against the side so I held it a little away from the side at the bottom but tight at the top is it is straight when clamped down. I looked down the blade/holder at a good light to make sure it was making contact across both faces (top and bottom).

I suspect there is a speed and feed related issue here because the first half of the cut went beautifully, then it all went south.

I was using the power cross feed to compensate for my total lack of confidence at this point. This is one of the few things I can say I'm terrified of in my entire life.. Once I get SOME method working reliable I'll work on the other method.

Thanks for the reply!
 
Minimized stick out - Parting off 1 1/4" stock - 1 3/8 Sickout.
By stick out I meant tool stick out. Only enough to get the job done.

If your stock diameter is 1.25, then half of that (=the radius to get to the center of the stock & part off) is only 0.625". If your parting blade is extended 1.375 now you have an extra 0.75" hanging out there for no purpose. The longer it is, the more the same cutting force will torque against your tool post. Bending, flex & vibration can all increase as a result.
 
90% is have a machine that is ridid enough to part off with. If it's a light machine you are better off taking the part out of the lathe and cutting it off with a saw. I can part off with a Warner and Swasey lathe all day long,but ask me to do the same on my Atlus is a lost cause. Quit beating yourself up over something that is marginal for your machine to accomplish.
 
Get a good quality blade. When I first bought my lathe I could not part to save my life. All the same issues that you are having.
I bought a new Empire brand HSS blade and it made a huge difference. I can part 304ss no problems.

Joe
 
www.hobby-machinist.com

Import parting tool holder

If you guys own one of these it’s probably not one your most prized possessions. They do have some problems. I had three choices: Use it as is (not really an option) Throw it out (too cheap to do that) Try and fix it I tried to fix it. The first thing was to mill a grove in the upper portion of...
www.hobby-machinist.com www.hobby-machinist.com

This is what I did to improve my China parting tool holder. Made a big difference.
 
Quit autofeeding the parting tool--you feed by hand listening to the machine and watching the chips while brushing on lube.
Continuous lube while parting, back off parting tool when dipping brush in more lube.
 
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