# I think I have a parting problem........



## sanddan (Mar 19, 2017)

I think I have a real problem with parting on the lathe. When I got my fist lathe I bought a HHS parting blade and installed it into the holder that came with my QCTP. I started with a thinner parting blade, around .087" thick I think, and watched a bunch of video's before attempting to actually part off a piece on the lathe. It went ok for the first several attempts but then BAM! The tool jammed in the cut and busted about a third of the blade off and left a chunk buried in the part. 

WOW, that got my attention. It was some mystery steel I had for practice so at least I didn't ruin anything important and I wasn't hurt so back to watching video's looking for the cause of my misfortune. I thought, maybe I should get a thicker blade, less likely to break maybe?

Some time goes by (where I avoided the parting tool like a bad dream) and then I needed to make some aluminum washers for a project so I had to break out the parting tool again. No avoiding this time. 

You might see this coming based on the title. Apparently 2 hp can quite easily break a 1/8" parting blade. 

Bummer.

More video's later I decided I needed one of the blade style tools that uses carbide inserts. I got a nice setup from Shars and about the third time I tried it BAM. Actually it broke without the drama that the solid HHS blades displayed, but ruined one of the two ends. This is starting to get expensive.

So I went back to avoiding the parting tool and used the bandsaw instead. I thought my problem might be flexing of the blade so when I saw a cool looking setup that looked very heavy duty I spent more $$ hoping for parting success.

I had to make some plastic washers so thought it was a good time to try out the new tool. After aligning the tool I made several washers without issue (keep in mind this is plastic now) and thought, maybe this is the answer. 

Then I had to make a 1" OD by .100" thick washer with a 1/2" hole in steel. Shouldn't be too bad right? You might see where this is going about now. More carnage.





I think I will go back to the HHS blades as they are a lot cheaper. Ruining a very expensive tool is starting to get old about now.


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## JimDawson (Mar 19, 2017)

If you are doing everything right and are still breaking tools, then something has to be flexing a lot.

On the other hand, this is the only parting tool I own.  It hangs where I can get to it easy.


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## Wreck™Wreck (Mar 19, 2017)

Are you doing this dry?


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## sanddan (Mar 19, 2017)

Wet, cutting fluid for steel and WD-40 for aluminum.

I'll try a hacksaw next. LOL

Tough to make thin washers with that I'll bet.


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## Firestopper (Mar 19, 2017)

Dan,

Are you hand feeding?  What RPM are you turning? last question, is the insert clamp tight on the Kennametal?


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## ronboult (Mar 19, 2017)

Hi Dan
I feel your pain.I went through the same process starting with HSS blade then GTN2 and GTN3 bits in blade holders with similar results. Making relief cuts to stop binding helped a bit. However I think GTN bits are very short which does not help to stabilize the bit in the holder
I finally changed to MEGHR1616-2  holders with Korloy MGMN200-G H01 or NC3020 Inserts. What a difference!
Day before yesterday I was parting 15mm deep (the limit of these holders into 54mm dial steel with no problems. I used the uncoated H01 inserts and they cut the steel like cheese. 460rpm and just hand feed. Didn't seem to matter how fast or slow I fed the cutter the cut just proceeded with no drama. I did take the precaution of making sure the blade was exactly square to the cut, dead on centre and made a clearance cut after entering about 10mm. I'm totally convinced!!!!! I suppose there is a chance with my luck that next time will not go so easily but from my current observations I dont think so.
As mentioned above the only problem with MEGHR1616-2  holders is they are limited to about 30mm diam rod.
Have just ordered some MEGHR1616-3  holders to try and looking for a holder with greater depth of cut. Both holders and Korloy inserts are available on AliExpress very cheap


The next photo compares the inserts. Note the jump in size between MGMN200-G and MGMN300-G and how short the GTN inserts are. I think the MGMN300-G  inserts will be much more robust. I haven't received my MEGHR1616-3  holders yet but I am hoping they will have a greater depth of cut.



Top - MGMN200-G NC3020
Next -MGMN200-G H01
Next - MGMN300-G NC3020
last GTN2 Unknown grade.

Don't give up you will get there
Ron


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## savarin (Mar 19, 2017)

Owning a flexi 9x20 I went through the same woes as your self.
I have cured my problems with parting to the point where I just sling the tool on and go.
A couple of things I had to do to get there.
1, a thin brown paper shim under the axa tool post so it wouldnt turn around the post.
2, tighten the cross slide gibbs. Holding my finger on the join between the cross slide and saddle I could feel the two separate when cutting. A new brass gibb strip cured this.
3, watching the considerable flex in the tool post  when parting I decided to remove the compound replacing it with a solid plinth. I now only replace the compound to cut small tapers.
4, use a continuous supply of cutting fluid to the tip of the parting tool.
The combination of all these has allowed me to part with no worries and to the point where I dont even have to ensure the tool is EXACTLY at 90 degrees to the job.
I've parted a couple of stainless and mild steel parts with a slight cone/curve. (I dont advocate this but it does do it if I'm not exact and works)
With the continuous supply of fluid the swarf just peels out in long tight curls.
I forgot to add I only use high speed steel parting blades.


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## Silverbullet (Mar 19, 2017)

Most if not all small LATHES will never part off a piece of metal. My reason for saying this they lack the strength to keep the parting blade from flexing. First the tool rest moves , compound flexes , the cross slide moves the ways even torque over. If you ever expect to part you will need the tool blocked up from the ways with a roller bearing to support the blades movement up to the point of just touching the piece to be cut . Rigid as possible no flexing at all then the blade still will flex and may break. I'm in the design stage of making a rotating saw blade mounted to the tool post , like a grinder , only mounted in a qctp with air fitting . My thinking with the lathe turning and blade turning no flex of any amount should make much difference. I'm letting the cat out of the bag but I'm sure it works.


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## JimDawson (Mar 19, 2017)

sanddan said:


> I'll try a hacksaw next. LOL
> 
> Tough to make thin washers with that I'll bet.



For that I have a friend named McMaster-Carr


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## woodchucker (Mar 19, 2017)

I am not sure I agree. My small south bend lathe does very well at parting. Admittedly it was learning how to properly part. My problem was being a fraction too low, thinking it would cut better. I learned after a few mistakes that being low was bad , being low often caused a disaster since the piece would lift and all hell would break loose.  Being high by a small amount was acceptable until it stopped cutting, it would not lift.

 Being dead on, would be best. But there might still be a lift danger .. So being high by about .0005 might not be a bad thing.  Being dead on, I still worry .. Being low.. never.


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## mikey (Mar 19, 2017)

Silverbullet said:


> Most if not all small LATHES will never part off a piece of metal. My reason for saying this they lack the strength to keep the parting blade from flexing. First the tool rest moves , compound flexes , the cross slide moves the ways even torque over. If you ever expect to part you will need the tool blocked up from the ways with a roller bearing to support the blades movement up to the point of just touching the piece to be cut . Rigid as possible no flexing at all then the blade still will flex and may break. I'm in the design stage of making a rotating saw blade mounted to the tool post , like a grinder , only mounted in a qctp with air fitting . My thinking with the lathe turning and blade turning no flex of any amount should make much difference. I'm letting the cat out of the bag but I'm sure it works.



With all due respect, I have to disagree, Silverbullet. I have an Emco 11" lathe that parts everything I turn with a HSS P-type blade or an Aloris GTN3 inserted carbide blade. My little Sherline can part anything that will fit in the lathe using a P1-N blade mounted upside down in a rear mounted parting tool post. In fact, the Sherline will part mild steel at 1200-1500 rpm and will cut 303 stainless washers 0.010" thick without any issues at all. 

A sharp blade mounted perpendicular to the work with the tip at center height will part easily on most lathes, small or big. I think the biggest problem for most guys is that what they think is center height is not really center height; a bit high and it won't cut; a bit low and it digs in a snaps the blade. A positive feed is also important.


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## jbolt (Mar 20, 2017)

You should have no trouble parting with your PM-1340GT. What RPM are you parting at? Are you using the power feed? Most problems I see people having are not on center and running the speed/feed too slow. 

Assuming the tool is set at the correct height and is square to the part. Keep the tool length to the minimum required to make the cut and try and keep the tool stick out to max 2x the blade height. For the HSS try 0.003 to 0.004 feed at 100 SFM. For the insert tool try using the power feed at 0.004 to 0.005 at 100 to 200 SFM. Remember your cross feed is 1/2 the chart setting. Parting needs lots of fluid. I use kerosene for aluminum and dark cutting oil for steel, constantly and generously applied with a small brush or squirt bottle. 

Also keep the compound slide retracted and locked. I usually also lock the carriage.


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## sanddan (Mar 20, 2017)

firestopper said:


> Dan,
> 
> Are you hand feeding?  What RPM are you turning? last question, is the insert clamp tight on the Kennametal?



This last time was at 240 rpm and I've only tried hand feeding. The clamp on the Kennametal was tight. After the fact, when I was re-aligning the tool post as it had moved slightly, I noticed that the compound wasn't locked. That might have been the cause.


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## Firestopper (Mar 20, 2017)

Yea, I didn't want to ask basic questions as I know your on it. Rigidness is your friend for this operation. The RPMs are fine even a little higher is ok, but the tool post should be tight and minimal over hang with the compound locked out. I rarely used to lock my compound but always keep the tool post from overhanging and use CXA on the 1440. Another thing I practice after lining thing up square and centered to the work piece is looking or studying the chip produced upon introduction of the cutter. This will reveal any issues with alignment.  I had parting issues off and on but these steps are crucial on smaller machines to include mine. You might also lock out the carriage when parting and use a steady drip of cutting fluid. Your chips should curl nicely and evenly when all is happy. Good luck amigo!


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## jbolt (Mar 20, 2017)

Definitely use the power feed. Hand feeding is difficult to get the feed rate correct and consistant. Its okay for smaller work. 

Sent from my SAMSUNG-SM-G900A using Tapatalk


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## woodchucker (Mar 20, 2017)

I don't power feed, always afraid it might dig in, by hand feeding I get feedback.  Just my opinion


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## Randall Marx (Mar 23, 2017)

I always hand feed when parting because I don't have power cross-feed capability.


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## markba633csi (Mar 23, 2017)

Hacksaw here too.  I hate farting off.  I mean parting off. 
Mark S.


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## HBilly1022 (Mar 23, 2017)

I recently got a bigger lathe 12 x 36 and was very pleased at how easily it parted until the other day when I was having a nightmare trying to part a 1/2" diameter piece of steel. So I checked out some parting videos on Youtube and in one of TubalCain's vid's I noticed he said to never part hot rolled steel, _"it's a nightmare"._ I checked and sure enough that is what I was trying to part. The next few pieces of steel I parted went fine. But I usually don't know what I'm working with since most of it comes from the scrap yard. I did however know these pieces were hot rolled since I got them from the local hardware store. No place near me to get steel and it seems that any project I want to start needs a selection of shapes and sizes and material types I don't have. So I make due with what is on hand. Sometimes it doesn't produce the best product but I'm still learning.


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## unioncreek (Mar 23, 2017)

Turn the tool upside down and reverse the lathe.

Bob


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## HBilly1022 (Mar 23, 2017)

unioncreek said:


> Turn the tool upside down and reverse the lathe.
> 
> Bob



I've got to try this. The nice thing about is that, is I would be able part off small machine screws without them unscrewing themselves from the bolts that are used to hold them in the chuck. Thanks for the suggestion.


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## unioncreek (Mar 23, 2017)

I have a Harbor Freight 8x12, my starter lathe.  I couldn't part for nothing, speed didn't make a difference it would chatter constantly.   I don't know which forum I read it on, but someone else was having the same problem.  Another forum member recommended this, so I can't say it was my idea.  I can now part at just about any speed regardless of the material.  I do slow the lathe to around 140 rpm, but have parted small pieces off at 600.

Bob


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## ebolton (Mar 23, 2017)

unioncreek said:


> Turn the tool upside down and reverse the lathe.
> 
> Bob



I don't think this is adviseable if your lathe has a threaded-on chuck, as mine does.

-Ed


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## TheGoodLordCalvert (Mar 24, 2017)

I had the same problem/fear with my lathe. Parting would either break the tool or stall the machine. I found a youtube video that mentioned turning the tool upside down and running the lathe backwards, as Bob mentioned above, and now I'm able to part without any problems. 

You could also try using a rear-mounted tool post if you don't want to run in reverse.


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## Sblack (Mar 25, 2017)

The best book on machining on small lathes is, IMHO, The Model Engineer's Workshop Manual by George H Thomas. It is sold by Tee Publishing in the UK. In it there is a chapter called On Parting Off. He used a Myford Lathe, which is pretty small and he used an upside down tool in a purpose built holder which cut from the far side of the work. Hemmingway sells castings for it. The tool post stayed on the cross slide but the blade could be rotated out of the way when not in use. Because it was running upside down, when the loads got high the tool would flex away from the work rather than digging in.

http://www.hemingwaykits.com/acatalog/Retracting_Tool_Holder.html

I don't need such a holder on my super 11 because with an MT5 sized spindle it is pretty rigid. It is all about rigidity. I always hand feed because I can feel when it is cutting well and I can vary the pressure to get the cutting action that I want, which is chips rolling up into curls. You need a good firm oressure, not too light and not too heavy. If the cutter is just plowing or ripping off material I stop and investigate, sharpening or realigning the tool if necessary. Obviously it has to be at center height. If the groove is getting filled with curls I stop and brush them out. I apply cutting oil continuously.

A lot of cheap chinese lathes and older worn machines won't have good contact on their moving slides. This will make them prone to flexing and chatter. I have seen some where the carriage casting, when sitting on the bed ways, will teeter back and forth due to a the casting having warped after being machined, orobably because it was never stress relieved or seasoned. Good luck parting off with that!


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## Rockytime (Mar 25, 2017)

I have a MaxiMat7 which is a light lathe. I part in a conventional way with a standard parting blade. I just use lots of ATF fluid. But then I use ATF for everything, cutting, tapping, drilling, etc. I have a Sherline in which I use a parting tool mounted upside down at the back of the lathe.


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## NortonDommi (Mar 26, 2017)

I agree with above comments on upside down tools, I also like to do threading upside down and in reverse. Magic. If a screwed chuck make a rear toolpost and fit a chamfer tool as well, you won't regret it.
  Could I also suggest locking the compound AND the sasddle and making absolutley certain that the blade is at 90 degrees.
I'll post a pic of toolholder from scrap that works for me this evening. 
  In the meantime have a look at this vid.






  Cheers,
  - Barry.


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## Sblack (Mar 26, 2017)

Yes lock everything down. In the book I describe above George Thomas (GHT) shows a locking cross slide and compound. Anything that helps reduce flexing. A sharp tool on center is also essential. GHT used to demonstrate parting off 1" cold rolled steel at 300rpm at the Model Engineer expo in England just for "showmanship". He does admit yhat on his furst lathe, which was foot powered (!) he was reduced to using a hack saw. As his lathes grew in spindle size his success at parting improved as well.


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## firbikrhd1 (Mar 26, 2017)

Parting seems to be difficult for almost everyone, including me, until you learn the "secrets" (which are really simple steps that must be followed to a "T" in order to be successful.) I respectfully disagree with those that say parting cannot be accomplished on a small lathe. I have successfully performed parting on my 1943 Logan 10" lathe as well as my dad's old worn Atlas 10" bench lathe, a model which many say is not very rigid.  On both lathes I have been able to reliably part by both hand and power feed. I am an amateur machinist with no claim to expertise, however these are the keys to success for me:

#1 Rigidity of the work.  The cut should be made as close to the chuck jaws as possible. Certainly no more than two diameters of the work away from the chuck jaws. Closer is preferable. DO NOT attempt to part between centers in an attempt to achieve rigidity. You will likely break your parting tool toward the end of the cut or damage the work..

#2 Rigidity: If the chuck's jaws are bell mouthed you cannot maintain rigidity of the work, no matter who much you tighten the chuck jaws. If you are using a lathe with a threaded spindle be certain there are no chips in the threads of the spindle or the back plate and of proper fit between the spindle shoulder and the chuck back plate. There should be full contact at those points if the backplate is properly fitted. Blue those areas and install the chuck then remove and look for blue that has not been removed. Those are areas with no contact, correct the fit. The portion of the spindle shoulder I speak of is the one that the back plate butts against, not area that enters the backplate bore. (Without getting into a huge debate about how back plate bores should fit the spindle I'll say that I subscribe to the belief that the threads, due to their 60 degree form, center the chuck on the spindle to prevent runout and that the shoulder the backplate butts against holds the chuck true to the axis of the lathe ways. Others may disagree, and that is fine, but that debate is like debates on which oil is best, circular and without end.)

#3 Rigidity: The tooling must be set up as rigidly as possible. If you are using a Lantern tool post ditch the rocker and make a solid steel ring of a thickness that puts the tip of the parting tool on center. With a QC tool post be certain there are no chips under the tool post and that it fits the compound flat without rocking. Compounds can have worn surfaces from years of use that will not allow tool posts to be rigidly mounted. Dings from dropped tooling will cause raised areas that allow minute rocking and ultimately chatter. Be certain that the parting tool does not extend any further from the holder than is necessary regardless of what tool post you use. If using a Lantern tool post choke up on the tool holder as much as possible. Keep overhang to a bare minimum.

#4 Rigidity: Think about every possible way for movement to creep into your setup and eliminate it as much as possible. Properly adjusted machine gibs, small tool overhang, tight tool posts, holders etc. Be certain your headstock bearings are properly adjusted if they are plain type or have proper preload if of ball type. 

Up to this point most of what has been said is appropriate for accurate chatter free plain turning and boring as well as cutting off. Much is just general good practice for machine maintenance. 

#5 Parting tool alignment. The parting blade must be perfectly perpendicular to the work and on center. Take great care in assuring this. I usually use the lathe chuck as my guide and put the parting bit right up against it. I use a white piece of paper or a light shined from below to adjust the tool holder/post until the light coming through shows an equal space at the blade tip and where it meets the holder at the outer perimeter of the chuck.  I use the same care I would when I set up a threading tool for a threading operation using a Center Gauge. The parting tool must also be perfectly vertical. If it leans one way or the other it will rub on one side and track to the other.

#6 No back rake on the parting blade itself. It should be on centerline of the work and level. Be certain there is adequate front clearance or the tool will rub rather than cut and of course there should be side clearance on both sides of the blade. If the cross feed requires much pressure when attempting to part be certain to check front clearance, the tool is most likely rubbing due to lack of front clearance or is adjusted above center. The blade should be sharp and honed to a fine edge at the tip and sides. Some advise grinding the tip at a slight angle to eliminate the tit left on the work. I do not do this as it seems to make the narrow parting blades I use try to wander to one side. I grind my tip so it is perfectly parallel to the work.

#7 Once you have the cutoff tool position where you want the cut lock the carriage to the ways.

#8 Speed. I generally use speeds of about 1/2 to 2/3 that recommended for turning whatever material I am parting. Don't be afraid to try a faster or slower speed if chatter develops. Note that chatter is a sign of lack of rigidity. Check again to assure you have done all you can to assure a rigid setup.

#9 Feed. Start with hand feeding, feed slowly but steadily and with enough feed to produce a thin continuous chip (in steel or aluminum). Be aware of tool pressure. The tool should feed in easily if there is enough front clearance. The chip should come off as a curl when everything is right and will roll up on itself. When conditions are right I get a curl that looks much like what the curl of metal that is produced when using a key to open a can of sardines. There is a distinct sound when all is well. To me it sounds like a hissing or tearing sound.

#10 Lubrication. Continuous lubrication should be applied while parting. If you don't have coolant pumped (I don't) use a brush and flood the cut. I find that I can usually work the hairs of an acid brush deeply enough into the kerf to keep things lubed adequately. I use dark cutting oil on steel and stainless and WD 40 on aluminum although the dark oil will work on aluminum as well. 

#11 Once you have gotten the hang of feeding by hand and knowing what RPM to use you can mimic the feed rate with your power cross feed.

#12 RIGIDITY! Truthfully that is 70% 0f success so it bears repeating. Do all you can to make everything as rigid as possible. The other 30% is tool alignment and front clearance.


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## NortonDommi (Mar 26, 2017)

WOW! Firbikrhd1 you have said everything that needs saying. Great stuff.

  Hear's those photo's I said I'd post, please excuse the state of the lathe, it does actually get cleaned on a regular basis.
The toolholder needs to have countersink screws but it was knocked op in an hour with what came to hand from the scrap bin.
P.S. Scrap machinery like computers, washing machines, old microwaves are a good source for odd screws ect.
  I hope this will be of help.

  -Barry.


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## unioncreek (Mar 27, 2017)

NortonDommi said:


> I agree with above comments on upside down tools, I also like to do threading upside down and in reverse. Magic. If a screwed chuck make a rear toolpost and fit a chamfer tool as well, you won't regret it.
> Could I also suggest locking the compound AND the sasddle and making absolutley certain that the blade is at 90 degrees.
> I'll post a pic of toolholder from scrap that works for me this evening.
> In the meantime have a look at this vid.
> ...



I've seen the YouTube video that Barry posted and I'm going to try it as soon as I get a little break in spring work.

Bob


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## markso125 (Mar 27, 2017)

jbolt said:


> Definitely use the power feed. Hand feeding is difficult to get the feed rate correct and consistant. Its okay for smaller work.
> 
> Sent from my SAMSUNG-SM-G900A using Tapatalk



Woah you should never power feed on the x axis when parting on a manual lathe. The reason for this you ask, the surface speed decreases on the tool the smaller the diameter gets, that is a quick way to kill a tool.

But in all honesty I usually don't recommend to any of my students on using the power feed on the x axis at all on a manual lathe for that same reason. A lot of the time you will set your feeds and speeds to the outer diameter and the outer 1/4 of the part has a great finish but as you get closer to the center you end up with galling on the face of the part, and just a crappy finish overall. That is because of the different surface speed with the center running slower then the larger OD. If you have ever watched NC machines run you would be able to see they make up for this by speeding up the spindle the closer you get to the center of the part, this creates a constant surface finish on the part. I have found I can get a smoother surface finish about everything I run on a lathe by feeding the x axis in by hand and I can usually do it a lot quicker then messing around with the feed levers.


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## davidpbest (Mar 28, 2017)

Keep your hand on the speed control potentiometer and turn it as you watch the Tach readout on SFM to keep the SFM constant.


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## markso125 (Mar 28, 2017)

davidpbest said:


> Keep your hand on the speed control potentiometer and turn it as you watch the Tach readout on SFM to keep the SFM constant.



That only works if you have a potentiometer, geared head lathes cant do that. Most of the lathes larger then benchtop lathes and a good amount of benchtop lathes are geared heads and don't have any speed variation other then the gearing available.


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## davidpbest (Mar 28, 2017)

Sounds like you have yet to enjoy the benefits of a VFD conversion on a geared head lathe.


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## markso125 (Mar 28, 2017)

Actually I have, I have even run Clausing lathes that came with potentiometers from the factory. The one flaw with your argument you have is that the feed on all the geared head lathes is run in relation to the rpm. You can run 100 rpm or 10,000 rpm but if you set your feed rate at .001 on the gearbox of a geared head lathe it will move that much regardless of how fast the spindle is moving so you still have the same problem with finish if you are feeding with the x axis power feed.


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## davidpbest (Mar 28, 2017)

I think we should just agree to disagree.  In practice, I have found that keeping the SFM constant (by varying the RPM) makes powered parting-off a breeze compared to hand feeding, and results in a lot fewer broken tools, inserts and mishaps - on the same lathe as the OP.


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## firbikrhd1 (Mar 28, 2017)

I am going to disagree with not using power feed for parting as well. In truth there is no need to even have a variable speed as diameter of the cut decreases. Regardless of surface feet per minute changes the rate of feed per revolution remains the same because the power crossfeed is directly dependent upon the gearing of the feed screw. Most materials have a wide range of SFPM at which they can be cut. The published recommendations are mostly for efficiency and to prevent premature tool wear. If the rate of cross feed is set to remove "x" thousandths of material per revolution that feed remains the same regardless of diameter. The only thing that changes is the surface feet per minute and that actually gets lower as diameter decreases. Regarding finish of the parted surface, if finish of that surface is critical, reliance on a parting tool is fallacy to begin with in 99% of cases. Parting tools, even when properly set up, do not necessarily produce a truly flat surface without dish or crown, precisely 90 degrees to the axis of the work. Parting blades tend to be thin in cross section and will flex minutely even under the best conditions. In nearly all situations a parted surface should be faced to final dimension and finish to assure proper dimension, flatness, finish and assure a perpendicular surface. The only exceptions to this I can imagine are when a further operation will eventually be performed on the parted surface or that surface will be welded to something else.


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## Rockytime (Mar 29, 2017)

I just parted off a piece of leaded steel today on my MaxiMat7. I presume everyone already knows this but I took a couple of photos showing how I make sure the blade is perfectly perpendicular to the piece in the chuck. I place the blade up tight against the face of the chuck which is perfectly perpendicular to the piece in the chuck.


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## Glenn Brooks (Mar 30, 2017)

So, after many epic, nay legendary, parting disasters I finally discovered a couple of things that actually allow me to part just like those  guys on You Tube.   Tried out my knew found knowledge whilst parting with quick change tool posts on both small and large lathes with QCTP holders having a parting tool holder (0xa and BXA size)

#1:  Parting blades are beveled on top - -apparently for a reason.  All my blades are beveled. The high edge sits up against the inner edge of the tool holder, and contacts the upper clamp portion of the holder. But it can And does rock over to the side if not installed correctly. If not careful, when you tighten the holder down, the blade will kick out a little bit at the bottom of the holder, and then cant's sideways a hair -due to the beveled top edge.  So it's basically not straight up and down, like it's supposed to be. The work then will impart twist in the blade after one cuts into the work over 1/2", because of sideways pressure on the edge of the tool caused by the slot in the work.  The work essentially turns the blade into a pretzel - until it decides to explode, implode, break, or shatter.  OR in my case, the last time, jumped  right out the holder and flipped across the shop, with a very loud bang. Very surprising. Even more so, when it came up intack.  That's when I noticed the beveled top edge and possibility of cant  in the mounting bracket.

  My fix is to now hold steady finger pressure on the blade when I install  the blade in the holder.  If held flat against the machined inner surface, it seats nicely and cuts perfectly.  So apparently I wasn't been  paying sufficient attention to how I mounted the blades.   Not so, anyone!  Easy Steven parting with the blade mounted properly - except for #2 below...

# 2:  skinny little blades are no good.    I kept  breaking and jamming smallish, thin cutting blades on my 14" lathe.  Even after checking mounting per lesson # 1 above.  So Switched out to an old Armstrong parting blade, maybe 1/8" thick.  Cut like butter.  I will henceforth only use skinny little blades only on my little  precision 7" Dalton Lathe - with small parts, say under 1" OD.

Iam a happy camper now- until my supply of ancient dull grey Armstrong blades gets used up.

Glenn


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## markba633csi (Mar 30, 2017)

Good thing the blade didn't park itself in your hide Glenn! You dodged a blade-bullet 
Mark S.
ps I hate parting off


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## buster (Apr 1, 2017)

not sure where I saw this but I have made several parting tools from a carbide tipped table saw blade - yup that's right. you can get a bunch of them from one 10" C-T'd blade. Just go easy on the feed and use a diamond wheel to reshape the cutting 'point' to suit your fancy.


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## AMDtrucking (Jan 31, 2018)

Guys, parting is a royal pain and we all agree on that. But I have a different question: Where do I get a stubby (Short) Morse-3 dead center to insert into my headstock, attach a lathe dog, when it's "leg" can actually reach a hole in a faceplate? My standard length MT3 dead center is too long for that.


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## NortonDommi (Feb 1, 2018)

markso125 said:


> Woah you should never power feed on the x axis when parting on a manual lathe. The reason for this you ask, the surface speed decreases on the tool the smaller the diameter gets, that is a quick way to kill a tool.
> 
> But in all honesty I usually don't recommend to any of my students on using the power feed on the x axis at all on a manual lathe for that same reason. A lot of the time you will set your feeds and speeds to the outer diameter and the outer 1/4 of the part has a great finish but as you get closer to the center you end up with galling on the face of the part, and just a crappy finish overall. That is because of the different surface speed with the center running slower then the larger OD. If you have ever watched NC machines run you would be able to see they make up for this by speeding up the spindle the closer you get to the center of the part, this creates a constant surface finish on the part. I have found I can get a smoother surface finish about everything I run on a lathe by feeding the x axis in by hand and I can usually do it a lot quicker then messing around with the feed levers.


  Why I love variable speed, change on the fly, only thing better would be constant surface speed like on some of the Harrisons and a few others.


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## British Steel (Feb 1, 2018)

NortonDommi said:


> Why I love variable speed, change on the fly, only thing better would be constant surface speed like on some of the Harrisons and a few others.



If running from a VFD, install a slide potentiometer to carriage and cross-slide, its slider goes to the VFD speed input as normal, its ends go to the wipers of a pair of rotary pots each across the VFD 10v analogue supply - hey Presto, (nearly) constant surface speed with max/min settings 

Dave H. (the other one)


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## Ray C (Feb 1, 2018)

Hmmmm, it seems that Parting is causing a lot of people "separation anxiety"... 

... Sorry, sorry, sorry...  I had to get that out of my system.

Ray

PS:  Rigid setup, proper feed/speed, blade alignment, positioning, practice and luck is all it takes.   Other than that, it's really easy


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## vocatexas (Feb 1, 2018)

I posted a thread about this a few days ago, but if you have one of the little 9x20 lathes with the two-bolt compound base, do yourself a HUGE favor and make a four-bolt base. It really makes a difference when you are parting. You also get over-all better performance turning and facing.


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## dlane (Feb 1, 2018)

On My SB 10L I set a thin blade on center and straight with the chuck hand feed with cutting oil , haven’t had a problem Don’t know what I’m doing rite.


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## ericc (Feb 1, 2018)

buster said:


> not sure where I saw this but I have made several parting tools from a carbide tipped table saw blade - yup that's right. you can get a bunch of them from one 10" C-T'd blade. Just go easy on the feed and use a diamond wheel to reshape the cutting 'point' to suit your fancy.



I tried something like this.  It worked just great on my Craftsman AA 109 lathe, as well as the Jet 1440 at the now defunct Techshop.  It did not work on my South Bend 9.  I am not sure why, but I suspect backlash in the cross slide.  The parting blades are free, but they require a lot of labor to cut out.  After I break 2 in a row (bang problem again), I start to compute effective hourly wages, which is what I usually do when I am not having fun.  Eventually, I am afraid that I'll break something on that lathe if I don't figure out how to get it right.


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## T Bredehoft (Feb 1, 2018)

I'm running an Atlas/Clausing 618 or MK2 lathe. 
I replaced  the plastic gibs on the cross slide and compound with steel gibs. Actually I've replaced the compound with a new non-adjustable tool block.  Anyway, for parting, I put a little pressure on the gib (which is on the wrong side of the cross slide to have the right effect).  I recently needed 6 pieces of 6160, 1 3/8 diameter by .500 long. I chucked up a piece in the lathe, put a center in the end, and cut all but .400 off all at one time, then cut them off with  the manual hack saw. Not a problem at all. I kept the tool wet with A-9.


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## SSage (Feb 1, 2018)

I've recently tried a cheap MGEHR1212-2 insert carbide parting tool off eBay and it actually works good with 1" rounds of tool steel on my 12x36. Better than my usual M42 parting blade set up. I can only imagine that the name brand insert parting tools are even better, but the $16 tool is surprisingly a great value. Its cheaper than a single Shars parting blade shipped. I can power through hard and get a decent parting, the inserts are lasting better than expected.


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## NortonDommi (Feb 1, 2018)

British Steel said:


> If running from a VFD, install a slide potentiometer to carriage and cross-slide, its slider goes to the VFD speed input as normal, its ends go to the wipers of a pair of rotary pots each across the VFD 10v analogue supply - hey Presto, (nearly) constant surface speed with max/min settings
> 
> Dave H. (the other one)


Dave H, Thank you very much for that I'll have a very good look at it.


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## NortonDommi (Feb 1, 2018)

Here's the photo I said I'd post of part-off block. Upside down 32 mm blade. It is as close to center of the tool holder  as I can make it, wish I had a wedge type though. Also for those interested an article by G. Thomas on parting. Again rigidity is the single biggest influence.


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## Ray C (Feb 1, 2018)

LOL:  I just had a "parting moment"...  piece of 4140 and hardened to RC38.   It was parting just fine and all the sudden, its not cutting.  I push a little more, no go.  I push even more... no go.  What? am I losing my mind???   Take a close look... should be fine.  Push a little more -Nothing, no curls coming off.

Time for a cup of coffee -which solved the problem very quickly.   The blade was not sticking-out far enough.  -Duh!

Ray


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## cg285 (Feb 1, 2018)

back some time ago i had a job to part a couple hundred heads off of 3/8 rivets (for an industrial look on metal furniture frames) using "separator" carbide inserts. had trouble damaging the tooling so being self taught all my life i assumed i needed to slow things down. the slower i went the worse it was. put the question to a friend who was shocked at my speeds/feeds. ended up running at my max speed (2000) @ .002ipr and it was like pushing through crisco. sometimes you need not to be scared. (my modest lathe and tooling are relatively rigid with flood coolant)


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## cg285 (Feb 1, 2018)

[QUOTE="

Time for a cup of coffee -which solved the problem very quickly.   [/QUOTE]

coffee is not good for you this week. wait a month and it'll be approved again


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## benmychree (Feb 1, 2018)

I have no problem parting with my 19" Regal Leblond lathe with carbide or HSS, but do have trouble on my 10" Monarch, which is in excellent condition so far as ANY wear is concerned; I have come to the conclusion that the root of the trouble is the QC tool holder, which tends to lean over towards the chuck when the cut is made, causing the blade to bind; the reason being that the tool is overhung past the front side of the cross slide; I think, a Armstrong type holder in the original tool post would solve the problem by centering the tool over the cross slide.  I have broken many HSS parting tools because the rocker wedge can slip under the cut, causing the blade to bind in the cut;  This I solved on an older American lathe by replacing the rocker with a solid washer of such a height to bring the tool on center; many less broken tools after that ---


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## 682bear (Feb 1, 2018)

cg285 said:


> [QUOTE="
> 
> Time for a cup of coffee -which solved the problem very quickly.



coffee is not good for you this week. wait a month and it'll be approved again[/QUOTE]

Coffee only causes cancer if you live in California...

-Bear


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## NortonDommi (Feb 2, 2018)

I was looking at 1-cyl wooden boats on You Tube and this popped up:





  I couldn't resist posting.


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## Ray C (Feb 2, 2018)

cg285 said:


> [QUOTE="
> 
> Time for a cup of coffee -which solved the problem very quickly.



coffee is not good for you this week. wait a month and it'll be approved again[/QUOTE]

I would not survive a month without a cup of coffee.  -That's a fact.

Ray


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## Fabrickator (Feb 2, 2018)

woodchucker said:


> I am not sure I agree. My small south bend lathe does very well at parting. Admittedly it was learning how to properly part. My problem was being a fraction too low, thinking it would cut better. I learned after a few mistakes that being low was bad , being low often caused a disaster since the piece would lift and all hell would break loose.  Being high by a small amount was acceptable until it stopped cutting, it would not lift.
> 
> Being dead on, would be best. But there might still be a lift danger .. So being high by about .0005 might not be a bad thing.  Being dead on, I still worry .. Being low.. never.




I agree that you never want the cutting tip to be anywhere near "low" of center.  I run mine a bit just above.  Also, I disagree that smaller, hobby lathes are not capable of parting???  I suggest that you look at my 4" Hollow Vessel project and see how the tool post is set up on the carriage/cross slide, and how I cut an 1/8" pass through a 4" ball of 6061 aluminum.  Granted, it had to be finished afterward, but it does cut it and I just allow a bit extra material to clean it up.

I use an Aloris (kind of expensive) with replaceable tool bits, like yours. Align the tool, post, compound and cross-slide directly over the carriage and under the tool for maximum support.  Use a live center to prevent flexing. Always try to keep the part being cut as short to the chuck as possible.  Some say no more than 1" extension for every 1" of diameter (or something like that) to minimize deflection.  When I cut the 4" ball, I only chucked a 1 1/2" L  X 5/8" Diameter tenon on the drive end.  I took my time with a couple of thou at a time, ran the spindle as slow as the machine allowed and used cutting oil to keep the tool happy. It took about 30-40 minutes and was still pistol hot when I got done.


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## pstemari (Feb 2, 2018)

The one thing that made the biggest difference for my parting success was using a square to align the tool every time. One other thing is that you can't be shy about it—hit the power feed and drizzle on oil until you're through.

I have a Dorian insert blade w block, an insert tool for smaller diameters from latheinserts.com, and a bunch of hss cobalt blades. They all work just fine.

One other thing to note is that the side rake on the cutting edge determines which side gets the little pip. You can save yourself some finishing work by choosing the insert or blade orientation to match your work setup.

Sent from my Pixel XL using Tapatalk


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## Grumpy Gator (Feb 2, 2018)

_ I agree with all of the above. But if you only make a one pass part off then you run the risk of chips loading up in the cut.Never a good thing. If your cut off tool is 1/8 thick back off 3/16 and make a relief channel halfway down to the center. Then advance the tool and cut off on your mark.
Old school is still cool
**G**_


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## Fabrickator (Feb 2, 2018)

grumpygator said:


> _ I agree with all of the above. But if you only make a one pass part off then you run the risk of chips loading up in the cut.Never a good thing. If your cut off tool is 1/8 thick back off 3/16 and make a relief channel halfway down to the center. Then advance the tool and cut off on your mark.
> Old school is still cool
> **G**_



I'm with you on that and forgot to mention it regarding my Sphere project.  That was a very deep cut, having to actually stop and avdvance the blade to complete it.  A lot of the time it took was to back up, clear the chips, oil and continue. I did, and always open up the cut for chip clearance.


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## pstemari (Nov 22, 2018)

My little Taig has a rear tool post for parting that holds an inverted blade, which really helps with chips. The big lathe doesn't have any issues with chip clearance: the Dorian inserts and parting blade pop out nice tight little coils that look like watch springs.

Sent from my Pixel XL using Tapatalk


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