# Another Parting off Thread



## walterwoj (May 16, 2020)

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:


Sharped the tool - I might be able to shave with it...
Minimized stick out - Parting off 1 1/4" stock - 1 3/8 Sickout.
Lock down carriage, tighten the gibbs.
Lock down the tool - AXA tool post, specialized tool holder, locked down tight!
Lube - Cutting oil on everything
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!  Just thinking about it is causing my blood pressure to rise!  


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!  I get to about 3/4" diameter (1/2 way ) and  CRUNCH!  WHACK!   The lathe stalls for a second as the tool digs in, then it breaks loose, launching a chunk of shaving into the ceiling. HOLY FCK! 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  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...  CRUNCH!  WHACK!  same ****** ****** thing! I CAN'T TAKE THIS ****!!!!  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!


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## petertha (May 16, 2020)

_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.


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## savarin (May 16, 2020)

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)


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## SLK001 (May 16, 2020)

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.


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## walterwoj (May 16, 2020)

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.
> 
> ...


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!


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## petertha (May 16, 2020)

_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.


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## Nutfarmer (May 17, 2020)

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.


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## Liljoebrshooter (May 17, 2020)

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


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## Grinderman (May 17, 2020)

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
				




This is what I did to improve my China parting tool holder. Made a big difference.


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## Mitch Alsup (May 17, 2020)

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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## deakin (May 17, 2020)

how about using a bandsaw then just a facing cut


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## MrWhoopee (May 17, 2020)

3/16 parting blade is too wide for a less than rigid setup. What lathe do you have?


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## SLK001 (May 17, 2020)

deakin said:


> how about using a bandsaw then just a facing cut



It just takes way too damn long.  Plus, your arm will ache for hours once you're done.


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## Aukai (May 17, 2020)

Try checking your blade against the square face of the piece to be parted after checking it on the chuck to verify. I went to 350 rpm, and my slowest cross feed. The chips are curls, and I use a squirt bottle for constant oiling. My blade is 1/2" x .062 made in China. I do have a very good quality blade that I may start using once I'm confident enough. You just have to see what works for you. I am a complete novice, but I am starting to make washers now.


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## benmychree (May 17, 2020)

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.
> 
> ...


Grinding to end of a parting tool at an angle to reduce the pip at the end of the cut will make the chip wider than the slot that it is trying to escape from, inviting the chips to bind up in the slot and subsequent disaster; this is avoided by insert geometry that tends to narrow the chip with a radius formed in the insert's top edge.  I have seen tools in HSS that have been modified in that manner, how well they work is not known to me, but what is plain to see is that such grinding creates a delicate point on each side of the point of the tool, subject to wear and possible chipping.


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## ttabbal (May 17, 2020)

Rear mounted upside down parting blade holder. Very rigid and works great on my small lathe.


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## deakin (May 17, 2020)

SLK001 said:


> It just takes way too damn long.  Plus, your arm will ache for hours once you're done.



huh?
my bandsaw would cut 1 1/4 in less than a minute with me doing something else

op trying to part that off appears to take hours without success


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## homestead (May 17, 2020)

I solved my cutoff problems using this approach.         



jbarnes


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## Liljoebrshooter (May 17, 2020)

He said hack saw not band saw. I remember using a hack saw to cut stuff down.   I bought a used porta band.  Best $50 I have spent for the shop.

Joe


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## deakin (May 17, 2020)

Liljoebrshooter said:


> He said hack saw not band saw. I remember using a hack saw to cut stuff down.   I bought a used porta band.  Best $50 I have spent for the shop.
> 
> Joe


aaah were was hack saw mentioned?


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## SLK001 (May 17, 2020)

deakin said:


> aaah were was hack saw mentioned?



First post:  "I finished parting off with a HACK SAW! Way less stress! "


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## erikmannie (May 17, 2020)

If I were to start over in learning to part steel, I would experiment and practice on tubing or pipe rather than solid round stock.

I always hand feed on my 10 X 30 lathe.

I thought I saw some pretty high RPM values listed here. What would you guys recommend for parting 2” 1018? I have been using about 170 RPM.


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## Aukai (Jun 1, 2020)

Did you get to play with this some more? I'm improving on my tries with 12L14 1", and a mystery steel 1.25". I have a 1.25 SS bar that is clean, and as  square as I can tell without getting out the DTI. My 3 biggest improvements were getting center height, squaring the blade, and minimizing stick out before parting. I'm using my "poor" quality parting blade to test with, it says China 1/16 HSS, and is a P ("T") type blade. I am still far from stellar, but there was no drama. I have room for improvement, it took .010 to face the 1.25 square after parting, I dropped the RPM in the mystery bar to 300, it just sounded better, and the cross feed was used at the slowest for now. This is a previous catastrophe, and today's effort on the 1.25. I didn't get the pictures before I cut, sorry.


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## MrWhoopee (Jun 2, 2020)

Aukai said:


> I am still far from stellar, but there was no drama. I have room for improvement, it took .010 to face the 1.25 square after parting, I dropped the RPM in the mystery bar to 300, it just sounded better, and the cross feed was used at the slowest for now.



Parting is like landing an airplane. Any parting operation that ends with the part severed and tool intact is a good one. 

Based on cutting speed of mild steel (80-100 sf/m), 300 rpm is at the upper end of the speed range for 1.25 dia. stock.


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## SLK001 (Jun 2, 2020)

The "bow" in the cut-off usually indicates that your tool is not perpendicular to the work, or that the tool isn't sharp all the way across the cutting edge.  Post a picture of the business end of your cutoff blade.  In your other thread, you said you were feeding it oil - how did you do that?


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## Aukai (Jun 2, 2020)

China blade, p2N, and oil can. Photo quality is not good.


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## Chewy (Jun 2, 2020)

I had all sorts of parting problems when I first started.  Got almost all of the same answers as above. All are correct.  I use a Shars .093 T, 1/2" wide to cut 1018 up to 2" without trouble.  Using it on 2-1/2" 6061 now.  The tool MUST be perpendicular to the piece.  It has no side clearance. Bring up the tool to the face  and eyeball it with a light. Stickout, speed, tool height and lubing the groove is a must.  All pointed out above.

The solution was in an old post.  Some of the guys here I think were in on it.  Good luck finding it, but there was a whole thread on this. 
The tool must be ground to about 5 degrees off of vertical.  Put your bit in the holder. use an angle protractor ruler with a level on it. Get 5 degrees back from plumb and draw a line.  Grind to the line, straight across.  Don't do a Joe Pi trick with a slight angle.  He has years of experience to get just the right amount of angle to eliminate the leftover burr.  It does work, by the way, just not for beginners. Adjust stickout to .060 past center and reset tool height to dead center.

Since I changed the angle, I now cut by eye and ear.  If the chips are right, and there is no vibration or screaming, I don't pay that much attention to speed.  Getting pretty good cutoffs using just hand feed.

If someone can find that old post, it just might solve the problem.

Chewy


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## walterwoj (Jun 2, 2020)

I have not devoted any real time to this recently.  I'm still reluctant after the trouble I've had.  I did part off a piece of 3/8 cold rolled the other day though.  I hand fed, when it started vibrating I pushed harder and it got better.  the chips were terrible... looked like wood shavings, definitely not tight curls, I think they were too thin too curl.  When I get some more time to play with it some more I will let you know.  Thanks for the support so far!


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## Aukai (Jun 2, 2020)

Trying to learn by trying  
Parallel can look close, but if it isn't on, the choir starts up. My eyes are not great, and I'm seeing that my compound zero isn't. I can actually see a film separation if I look real close if there is a touch of oil, and I can feel slight movement while I'm setting Parallel.


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## SLK001 (Jun 2, 2020)

Aukai said:


> Trying to learn by trying
> Parallel can look close, but if it isn't on, the choir starts up. My eyes are not great, and I'm seeing that my compound zero isn't. I can actually see a film separation if I look real close if there is a touch of oil, and I can feel slight movement while I'm setting Parallel.



I hope you mean "perpendicular" instead of parallel.


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## Aukai (Jun 3, 2020)

I guess I'm confused with terminology, I was thinking the blade and the part had to be exactly parallel on the face, as in no tangents. to cut straight. That would make them perpendicular.


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## AGCB97 (Jun 3, 2020)

Until now I've had trouble parting (100 year old lathe!) and mostly just used the bandsaw. Saw this vid, which was referenced above and ordered the tool and some inserts. Made a adjustable support plate (surface ground) that rests on the bed and an adjustable rod that slides along it that supports the tool at the clamping point. Works great and I'll be parting off in the lathe from now on!
Thanks for your interest
Aaron


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## SLK001 (Jun 3, 2020)

Aukai said:


> I guess I'm confused with terminology, I was thinking the blade and the part had to be exactly parallel on the face, as in no tangents. to cut straight. That would make them perpendicular.



Okay, the blade has to be perpendicular to the rotational axis,  You're saying that you are setting the blade parallel to the work face.  That's okay, as long as the work face is flat (it's not always - what if you had just turned a radius?).  What I do is set the angle by sighting down the edge of the parting blade and aligning it with the front of the carriage.  The blade I use (cheap Chinese HSS 0.0625" P1 blank) has enough flexibility that small perpendicularity errors are not a problem (it just cuts a slight radius in the work).


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## walterwoj (Jun 12, 2020)

I did some parting-like operations today on my power feed project.  I had to cut a groove .200" wide by .200" deep in a piece of 3 1/4" 12L14.  I resisted my urge to be gentle and turned it in a lot faster than I wanted to and it cut pretty good.  Still had some chatter but nothing as bad as the past.  I think that it is just a matter of me gaining enough confidence to feed it in fast enough.  Every time I feel a little more confidence and it goes a little better.  I'll keep posting as I do more.


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## Aukai (Jun 12, 2020)

It's pretty much all in the setup, sometimes if I hear or feel something not right, I'll double check. Thanks for posting it up, bigger diameters, I play with RPM too.


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## walterwoj (Mar 22, 2021)

Just a follow up for everyone who offered me some guidance:  I think I found the issue,  I noticed the parting tool would almost swivel when it was mounted in the tool holder.  I checked the bottom of the tool holder (where the tool mounts in the holder) against a straight edge and realized it was bowed (crowned) in the middle.  I took my finest diamond sharpening stone (flattest surface I have) to the crown and it seems much flatter.  I have since done 5 or 6 parting operations with almost no chatter while running in back-gear, It still wants to chatter at normal speeds, but now I am confident enough to part instead of sawing it off.

THANKS TO ALL WHO HELPED WITH THIS!


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## erikmannie (Mar 23, 2021)

walterwoj said:


> Just a follow up for everyone who offered me some guidance:  I think I found the issue,  I noticed the parting tool would almost swivel when it was mounted in the tool holder.  I checked the bottom of the tool holder (where the tool mounts in the holder) against a straight edge and realized it was bowed (crowned) in the middle.  I took my finest diamond sharpening stone (flattest surface I have) to the crown and it seems much flatter.  I have since done 5 or 6 parting operations with almost no chatter while running in back-gear, It still wants to chatter at normal speeds, but now I am confident enough to part instead of sawing it off.
> 
> THANKS TO ALL WHO HELPED WITH THIS!



I have been having fantastic luck parting at 36 RPM spindle speed.


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## Aukai (Mar 23, 2021)

I did my 2nd part today with 4130 on the new lathe, the first one with a P2 blade was a little concave. The 2nd one I used the 1/8" Iscar at 90 RPM, on slow feed it started complaining, I hand fed it, and increased the feed, it started curling. Changed the feed rate on the Norton box and it sliced right through.


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## erikmannie (Mar 23, 2021)

Aukai said:


> I did my 2nd part today with 4130 on the new lathe, the first one with a P2 blade was a little concave. The 2nd one I used the 1/8" Iscar at 90 RPM, on slow feed it started complaining, I hand fed it, and increased the feed, it started curling. Changed the feed rate on the Norton box and it sliced right through.



You have more courage than me if you are using the power feed for parting.


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## Aukai (Mar 23, 2021)

Try it, you'll like it. Keep up with cutting fluid. It works, you have the rigidity, make it square, and on center. 36 is a little slow, depending on diameter, you've been doing some big stuff.


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## erikmannie (Mar 23, 2021)

Aukai said:


> Try it, you'll like it. Keep up with cutting fluid. It works, you have the rigidity, make it square, and on center. 36 is a little slow, depending on diameter, you've been doing some big stuff.



I will try it. I am going to start with the slowest feed available.

36 RPM was for 8-10” pipe. I should have probably mentioned that.


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## Aukai (Mar 23, 2021)

That will give you the surface speed. If your hand feeding, if it grumbles at real slow feed, feed faster until it starts shaking. You can see if slow, or fast makes a difference. I was surprised at the difference with the hand feed, slow was chattering, I cranked on it hard, and it started curling. The 1228 did not like that at all, the tool post would rattle so bad it would release.


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## mikey (Mar 23, 2021)

It might help to consider what a parting tool is. All parting tools are form tools. Some are sharp, like HSS tools, and some are not so sharp, like inserts. Some have zero rake, some have scoops on top, some inserts have complex shapes. Regardless, they are all form tools SO all else being equal (enough power and rigidity, perpendicular orientation to the work, tip on center height) you have to feed the tool into the work at a rate that is commensurate with the speed. Unlike many form tools, a parting tool's cutting area does not change as you feed in so feed rate is simpler to manage. About the only complication to this is that when you reach the inner 1/3 or so, you have to slow the feed a bit because surface speed drops significantly that far in. 

Like all form tools, surface area matters. The wider the tool, the greater the tangential cutting forces will be and the slower you will be able to feed. For me, a P1-N or P-1 blade is sufficient for almost all the parting I have to do on either of my lathes for most materials. For me at least, the wider the blade the more problems it creates. I have carbide parting tools but rarely use them, mostly because they tend to be too wide and therefore require more feed force and that takes away from me being able to feel the tool cutting.

I have read that you have to use a lot of force when feeding a parting tool. This has not been my experience parting from the front or the rear. Rather, I have found that feeding so there is a slight resistance to the feed is sufficient to keep the tool cutting continuously. Yes, this is when feeding manually and is how I prefer to part. This same positive resistance to feed is the same resistance I am looking for with any cutting tool when I feed it manually, be it a lathe tool or an end mill. I'm sure older hands than I know exactly what I'm talking about here. 

Sure, power feed works but you will break more tools with it.

I also think that too slow a speed is detrimental to parting. For me, parting speeds are determined by how well I can keep up with the feed. As long as I can feel that positive push back from the tool, I don't worry much about the specific speed I'm at. When parting from the rear on my Sherline lathe, I am often turning at 2-3 times normal turning speeds; somewhere in the 1100-1200 rpm range in mild steel and maybe a bit faster in softer materials. On my Super 11 when parting from the front, I am going somewhere near 800-1,000 rpm for the same materials. I may slow things down a little with larger work pieces but I never have chatter or a dig in on my Sherline and can recall maybe once having chatter on my Super 11.

I think sharp tools in general are important but I think my parting tools get sharpened maybe once or twice per year. I may take a few honing strokes across the top once in a while but the blade is taken to the grinder only occasionally. 

I guess what I'm saying is to worry less about speeds and focus more on feel. If it chatters, do the usual thing by slowing the speed or even better, increase the feed rate to keep up with the cut. Once you develop that feel for a tool that is cutting efficiently you will be fine. That feel will be the same when turning, boring, drilling, reaming, feeding an end mill and so on.


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## Mitch Alsup (Mar 23, 2021)

walterwoj said:


> Just a follow up for everyone who offered me some guidance:  I think I found the issue,  I noticed the parting tool would almost swivel when it was mounted in the tool holder.  I checked the bottom of the tool holder (where the tool mounts in the holder) against a straight edge and realized it was bowed (crowned) in the middle.



Perhaps this gets to the point of why I haven't had any parting off problems. My parting blade is a few thou smaller than what the holder can grasp, so to solve this problem I made a short shim and placed it at the front of the holder......


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