# Parting off question



## fishingreg (Jul 8, 2019)

I have just started using my first lathe.  I have played with some 1/2” mild steel rod.  I have turned 20 or so thousands to true up, I faced, drilled it out about 280 thou, beveled some edges, put a 30 degree bevel on it going into the drilled hole.  All that went well considering it was my first attempt at playing.  When I got to parting off, it did not go so well. It was a new blade, it was a Arthur Warner blade and holder, I used a thread cutting lube, kept it wet.  I ran it about 250 rpm.  It did not cut well at all, I applied more pressure, it cut in about 150 thou before the blade broke.  I got another type of blade, it’s 1/2” top to bottom, 4” long and the type that has the kind of “T” contour.  It did not do any better but I stopped before I applied too much pressure.  I forgot to add I only have enough stick out to reach the center of the material.  I have it 90 degrees to the material I’m trying to part off and the cutting edge is centered vertically as close as possible.  Any ideas what I am doing wrong?  How much pressure should I have to apply?

Thanks in advance


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## MarkDavis (Jul 8, 2019)

Parting can be trying.
Square the blade with the work by touching the face  with the side of the blade.
Sharp cutting edge with relief is vital.
Spin the work faster, if it's chattering feed the blade faster.
Mild steel can be gummy, sometimes pulling the parting blade out to lube the sides of it help.
Sometimes letting the work cool will help.


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## fishingreg (Jul 8, 2019)

MarkDavis said:


> Parting can be trying.
> Square the blade with the work by touching the face  with the side of the blade.
> Sharp cutting edge with relief is vital.
> Spin the work faster, if it's chattering feed the blade faster.
> ...



Thanks, Have squared it off to the work.  I don’t think I’ve even gotten to the point of chatter or gummy, I only got 150 thou or so into the first piece I tried to part off.  Today I got the new different blade in and tried it but put as much pressure as I felt comfortable with and it did not cut at all, made a tiny grove.  The blade has a relief angle, it’s not squared off.  It’s a new blade, shouldn’t it come already sharp?  The edge feels good but then again, I’m too new to have a clue what a good edge feels like.


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## MarkDavis (Jul 8, 2019)

Look at the top of the tool with a magnifying glass, the corners should be square.
 I'm guessing you have the tool height correct at the centerline of the work.
I sharpen mine on an inexpensive 8" bench grinder with a green wheel.
Had to scrap the original stamped steel tool rest, and build one that was square to the wheel, took a couple of tries and a couple of weeks.
The height of the AXA quick change holder sliding on the tool rest brings the cutoff blade up the curve of the wheel so the relief is a curve instead of an angle, but its close to 11 degrees at the cutting edge.
It took quite a bit of grinding to bring the cut off tool to the shape of the wheel, but now I can just make a couple of light passes to touch up the edge.


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## fishingreg (Jul 8, 2019)

MarkDavis said:


> Look at the top of the tool with a magnifying glass, the corners should be square.
> I'm guessing you have the tool height correct at the centerline of the work.
> I sharpen mine on an inexpensive 8" bench grinder with a green wheel.
> Had to scrap the original stamped steel tool rest, and build one that was square to the wheel, took a couple of tries and a couple of weeks.
> ...



Thanks, I will check out the blade under a magnifier.  Thanks for the tip on the green wheel.  I have a 8” grinder but just have the stock wheels for auto part/tool work.  I haven’t tried grinding a tool yet.  I will get a green wheel to try.  Should I have to apply any more pressure than say facing 15 thou or so to get the parting tool to cut?  On videos it looks like it should cut fairly easy.  I would think I should be able to let the tool do the cutting and not have to cram it in there.


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## Janderso (Jul 8, 2019)

Parting can be a batch.
My old south bend hated it.
Rigid, rigid is the key.
Make sure all the gibs are tight.
Center the compound over the cross slide.
Sharp cutting tool close to the holder, dead on center of work at 90 degrees.
That’s my two cents.


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## T Bredehoft (Jul 8, 2019)

Cut off as close to the chuck as you can stand. If your 1/2" piece is sticking out three inches and you try to cut off one inch it will not work. It will probably break the tool.


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## benmychree (Jul 8, 2019)

Green wheels are only used to grind carbide, a white, grey or pink wheel will work fine for HSS tools, your problems sound like incorrect tool height (too high) or insufficient front clearance angle.  Jeff's answers are also right on.  Tom's comments, are also right there.


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## MarkDavis (Jul 9, 2019)

Benmychree,
Please elaborate on best wheels for High Speed Steels, best type and grit.
I bought the green wheel because I thought it was good, it's certainly better than the gray wheel that came on the grinder.
Could be, my perceived "better" is in grit size. My green wheel is finer than the old grey wheel.


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## fishingreg (Jul 9, 2019)

benmychree said:


> Green wheels are only used to grind carbide, a white, grey or pink wheel will work fine for HSS tools, your problems sound like incorrect tool height (too high) or insufficient front clearance angle.  Jeff's answers are also right on.  Tom's comments, are also right there.



Thanks for the clarification.  I am using HSS so I will grab a couple different wheels while I am at it so I have a selection as I will end up with some carbide as well I am sure..  

The clearance angle is factory, i have not ground the tool yet, I did not measure it but it is a visible angle, looks like 5 to 7 degrees.  I feel my height is not my issue, I have a tiny spot from facing that I can see is center and I lined it up with that so if I am off center, its only a handful of thousands.  Since I can not seem to part, I can't say for sure and I am brand new to using a lathe but quite used to precision type work and I feel confident I am very close to center.  T Bredehoft mentioned the work being a few inches out of the chuck will cause me issues, that might be an issue.  I do have it probably 2.5 to 3" out where I am trying to part.  I would have thought it would at least cut into the work some but that could be an issue I was not aware of.  I will try chucking it up closer to see what happens.  I just feel like I am trying to cut thick cardboard with a butter knife when I am trying to part, it just kind of makes a shiny ring on the steel but not chips and a minor bit of almost a fine grit it is making from me pushing on it.

Maybe I have a crap parting tool, is there any particular parting tool you recommend?  Not so much a type but like an actual model number so I know I get a decent one?


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## fishingreg (Jul 9, 2019)

T Bredehoft said:


> Cut off as close to the chuck as you can stand. If your 1/2" piece is sticking out three inches and you try to cut off one inch it will not work. It will probably break the tool.



Thanks, I will give that a shot, I am out about 2.5-3" but it had no issues facing or turning so I did not consider it might have issues parting.


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## jdedmon91 (Jul 9, 2019)

fishingreg said:


> I have just started using my first lathe. I have played with some 1/2” mild steel rod. I have turned 20 or so thousands to true up, I faced, drilled it out about 280 thou, beveled some edges, put a 30 degree bevel on it going into the drilled hole. All that went well considering it was my first attempt at playing. When I got to parting off, it did not go so well. It was a new blade, it was a Arthur Warner blade and holder, I used a thread cutting lube, kept it wet. I ran it about 250 rpm. It did not cut well at all, I applied more pressure, it cut in about 150 thou before the blade broke. I got another type of blade, it’s 1/2” top to bottom, 4” long and the type that has the kind of “T” contour. It did not do any better but I stopped before I applied too much pressure. I forgot to add I only have enough stick out to reach the center of the material. I have it 90 degrees to the material I’m trying to part off and the cutting edge is centered vertically as close as possible. Any ideas what I am doing wrong? How much pressure should I have to apply?
> 
> Thanks in advance



All the advice is good. The key thing is rigidity, I have not many parting issues, I do use inserts parting tools, in fact their Banggood on top of that. I don’t part under 1/2 inch diameter because of part flex. Also I use GTN 3 inserts for the same reason rigidity. IHMO the heavier thicker the blade that increases rigidity. So if you need a custom holder to do that you need to do it. I’m attaching two videos one of mine where I made a one piece block fit my insert set up, the second one is a YouTube creator who made a block to hold a large blade to attach to the compound.










Sent from my iPad using Tapatalk


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## Cadillac (Jul 9, 2019)

When parting you should have your blade as close to the chuck as possible to try and elevate any flex. 
For a regular straight parting blade I have good luck with grinding a little hook on the cutting edge. Along with a angle on the cutting edge not a square edge. Pic below. 


 As for a T style which I use on my larger lathe. I use a 6” wheel to put curvature to the business end of the blade slightly. Every time I use the blade I touch up to make sure the blade is sharp. Once you start the plunge do not stop keep the curls coming and lube often. Always lock which ever axis not being used.


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## fishingreg (Jul 9, 2019)

Thanks Jdedmon91, I watched the videos, if rigidity was my issue would I notice some flex, jumping, or something?  It appears to be smooth, no jerking, jumping, shaking or anything, just no cutting at all.  Just a lot of rubbing and making a nice shiny line but thats about it.  Do you notice any movement when it is not rigid or does it just refuse to cut?  The first parting blade I did get to cut some but then it broke.  That one I do think broke due to rigidity, it is a Arthur R Warner and had its own holder which the holder seemed good but the blade was really small and only about 1/4" top to bottom and about 3/32" wide so I don't think the blade itself was very rigid.  The blade I have now is 1/2" top to bottom and 1/8" wide but maybe super dull even though it is new?


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## fishingreg (Jul 9, 2019)

Cadillac said:


> When parting you should have your blade as close to the chuck as possible to try and elevate any flex.
> For a regular straight parting blade I have good luck with grinding a little hook on the cutting edge. Along with a angle on the cutting edge not a square edge. Pic below.
> View attachment 298091
> 
> As for a T style which I use on my larger lathe. I use a 6” wheel to put curvature to the business end of the blade slightly. Every time I use the blade I touch up to make sure the blade is sharp. Once you start the plunge do not stop keep the curls coming and lube often. Always lock which ever axis not being used.



I am guilty of not pushing too hard so needless to say I have not continued to plunge.  I kind of did on the first blade but it was a smaller blade and broke but at least it did start to cut, this one has not started to cut so I have not felt comfortable cranking down on the wheel, I just can't imagine that would end well.  After all the videos I have watched and its a lot, I suspect maybe my blade is really dull.  I will get a pink or white wheel and attempt to sharpen it and go from there.  There has to be something fundamental wrong since it does not really remove any metal at all.  In every video I watch when the parting blade engages the metal, it makes chips and starts to cut, I am not getting that at this moment.  Now my hacksaw had no problem but it was not very straight...


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## benmychree (Jul 9, 2019)

Another thing is to use the minimum stick out of the tool from its holder, and the closer you can locate the part to the chuck jaws, the better.  If as you say, the tool is on center, the problem likely lies with the front clearance angle.  It would be better to have the tool slightly below center than slightly above center.  You asked about specific grinding wheel specifications, I will get back with that, but buy American, brands such as Norton.


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## markba633csi (Jul 9, 2019)

Your blade is dull;  the blade may be new, but not necessarily ready to use. You should get chips as soon as it touches the work.
What size/type of lathe do you have? On small lathes, parting can be nearly impossible due to rigidity issues and backlash
Try using the slowest speed the lathe will go- use backgears if you have them
Tighten the gibs as much as possible while still allowing movement
You might try mounting the tool upside down at the rear of the carriage and feeding toward you- sometimes this works when all else fails
ps I hate parting off almost as much as I hate running a table saw


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## fishingreg (Jul 9, 2019)

I was watching some more videos and heard Tubalcain mention do not bother trying to part off hot rolled steel.  This could very well be hot rolled.  Could that be my issue and I need to get another piece to play with?


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## mattthemuppet2 (Jul 9, 2019)

turn slow and feed hard - you should be getting nice curls coming off the top of your parting tool. If you're getting shavings, splinters or dust, plus it's making a hell of a racket, you're turning too fast (most likely) or feeding too slow (less likely). If your tool isn't exactly perpendicular or is thin'n'whippy then it can wander and cut at an angle, causing a jam or belt slip. good idea to retract the tool every so often, clean out the slow, apply some more oil. If it cuts on the side as you feed it back in, the blade is cutting at an angle.


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## fishingreg (Jul 9, 2019)

markba633csi said:


> Your blade is dull;  the blade may be new, but not necessarily ready to use. You should get chips as soon as it touches the work.
> What size/type of lathe do you have? On small lathes, parting can be nearly impossible due to rigidity issues and backlash
> Try using the slowest speed the lathe will go- use backgears if you have them
> Tighten the gibs as much as possible while still allowing movement
> ...



It being dull is what I am leaning towards or what I have might be hot rolled steel, I really don't know its just some I had around from an old welding project.  One video said don't bother trying to part off hot rolled steel, just take it to the band saw.  I need to probably make sure of what I am playing around with so I don't confuse myself worse if there is something to trying to part off hot rolled.

As far as the lathe it is a PM 1340GT so it should be able to part off ok I would hope...  I might need to tighten the gibs a little but everything feels really solid minus maybe I need to be closer to the chuck which I will try once I see if I can tell if it is hot rolled or not.


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## homebrewed (Jul 9, 2019)

What kind of cut off blade holder do you have?  Some tilt the blade up, some have the blade flat.  This makes a difference in how much relief the front of your blade needs.  I bring this up because it sounds like the blade is rubbing, not cutting.


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## pontiac428 (Jul 9, 2019)

Parting can be tricky.  The good advice here should get you back on track. I'm not sure if it's been mentioned, but finishing the cutting edge(s) of any tool with a hone is a good idea after the grinder.  I'll echo the above to check that the back rake matches your material, but this isn't usually a big deal with parting.  Lock out your gibs in all but your infeed for rigidity (possibly a big source of chatter).  Parting "likes" a higher surface speed than you may be using for general turning, partly because as you approach center surface speed approaches zero.  Last, align your tool tip on center.  Too high will rub, too low the work will grab and climb your tool.


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## fishingreg (Jul 9, 2019)

homebrewed said:


> What kind of cut off blade holder do you have?  Some tilt the blade up, some have the blade flat.  This makes a difference in how much relief the front of your blade needs.  I bring this up because it sounds like the blade is rubbing, not cutting.



It is one that holds it flat, it has a flat base that the parting blade sits in and a hex screw at that back of the holder that when turned brings down a piece that holds the tool to the bottom and it comes down at kind of an angle to the hex at the back but the tool itself is held level when put in the holder.


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## T Bredehoft (Jul 9, 2019)

One more thought.  You reported that the first tool broke, the second would not cut at all, right away. 

Is there a possiblity that too high a surface feed dulled the second tool before it could cut?  I second the above suggestions, slow your feed way down and crowd the tool into the work. It's scary at first, but you gotta do it. 

Sharpen your blade, verify clearance under the cutting edge, verify on center (level with the center tit from facing), hone the cutting edge to make it as sharp as possible, and give it a try.


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## fishingreg (Jul 9, 2019)

T Bredehoft said:


> One more thought.  You reported that the first tool broke, the second would not cut at all, right away.
> 
> Is there a possiblity that too high a surface feed dulled the second tool before it could cut?  I second the above suggestions, slow your feed way down and crowd the tool into the work. It's scary at first, but you gotta do it.
> 
> Sharpen your blade, verify clearance under the cutting edge, verify on center (level with the center tit from facing), hone the cutting edge to make it as sharp as possible, and give it a try.



Yes, the first tool broke, I think it was way too small, after looking at other parting blades that one did not have much meat to it but it did at least cut into the metal before it broke.

Can you explain what you mean by too high of a surface feed?  I am hand feeding so on the second blade, I just creeped it up to the metal and gently started making contact.  I put cutting fluid on it and I pushed gently but nothing, I pushed a little more and nothing so I threw the towel and and figured I had better ask some questions.  I did not try to use the 2nd blade in the grove the first blade made.   The 2nd blade is 1/8" wide, the first blade was about 3/32.  So I just got my trusty hacksaw out that never fails me and whacked off the first one...  (reverted back to my pre-lathe days) I was on a new section of metal with the 2nd blade but same piece of metal just another inch or two down from the first one.  Are you thinking I am not pushing hard enough at first and dulling it?


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## francist (Jul 9, 2019)

fishingreg said:


> once I see if I can tell if it is hot rolled or not.



Hot rolled material is pretty easy to spot -- it has the rough, blackened finish on the outside as opposed to the smoother, grey finish typical of cold rolled stock. There is nothing really difficult about parting hot rolled steel itself, but that black surface layer is what takes the edge of your tool right away. If you use it, and I do for turning fairly often, it's beneficial to take a decent enough cut to get underneath that rough oxide surface layer. Once you're past it, no different than anything else really.

What sparked my comment now though was, do you know that what you have is indeed "mild steel" and not something else? We could go round and round trying to tell you how to set up a parting tool only to find out later that you're trying on a piece of stainless or 4140 or something, both of which can work harden pretty quickly making any further effort pure hell, regardless of the tool.

Mystery metal is fine if that's what you want to use, but sometimes it really does complicate things by adding yet another unknown to the equation.

-frank


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## T Bredehoft (Jul 9, 2019)

fishingreg said:


> Can you explain what you mean by too high of a surface feed?



Most cut off blades are High Speed Steel , at best, 90  to  100 surface feet per minute is as fast as High Speed Steel can tolerate. Faster, generates too much heat that dulls the tool. 600 RPM is about as fast as as you can turn 1/2" steel without burning the tool. 

Did you perhaps touch the surface of the spinning steel at a faster RPM? That would be a  too high surface speed.


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## fishingreg (Jul 9, 2019)

francist said:


> Hot rolled material is pretty easy to spot -- it has the rough, blackened finish on the outside as opposed to the smoother, grey finish typical of cold rolled stock. There is nothing really difficult about parting hot rolled steel itself, but that black surface layer is what takes the edge of your tool right away. If you use it, and I do for turning fairly often, it's beneficial to take a decent enough cut to get underneath that rough oxide surface layer. Once you're past it, no different than anything else really.
> 
> What sparked my comment now though was, do you know that what you have is indeed "mild steel" and not something else? We could go round and round trying to tell you how to set up a parting tool only to find out later that you're trying on a piece of stainless or 4140 or something, both of which can work harden pretty quickly making any further effort pure hell, regardless of the tool.
> 
> ...




Thanks Frank, that is a good question, I really don't buy anything other than mild steel for my projects so I assume it is mild steel.  I buy some AR500 plate from time to time but this is not plate and I have no reason to buy AR rod.  I think this piece actually came just from Home Depot if memory serves, I think I was in a bind one weekend and needed some 1/2" round for something and picked it up there.  I can't imagine they have anything other than mild steel unless they have some strange alloy but it welds like normal steel.

That is good to know about the surface of hot rolled.  The first cut where I used the smaller blade, I had taken quite a bit more off the outside before parting, I was just playing and getting a little lathe time in.  This cut I did not take but a few thou to make sure it was taking a cut all the way around.  

I will try to hit a steel supply this weekend and see if I can get some cold rolled mild steel so I know for sure what I am working with.


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## fishingreg (Jul 9, 2019)

T Bredehoft said:


> Most cut off blades are High Speed Steel , at best, 90  to  100 surface feet per minute is as fast as High Speed Steel can tolerate. Faster, generates too much heat that dulls the tool. 600 RPM is about as fast as as you can turn 1/2" steel without burning the tool.
> 
> Did you perhaps touch the surface of the spinning steel at a faster RPM? That would be a  too high surface speed.




I was running slow, I tried 205 and 335 RPM and both netted the same results.  The tool does not have any off color but I did not jam in it very hard either.  As little as it was cutting I am sure the heat would have come on quick if I had pushed it hard.


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## mikey (Jul 9, 2019)

pontiac428 said:


> Last, align your tool tip on center.  Too high will rub, too low the work will grab and climb your tool.



Greg, look hard at what @pontiac428 says here. Others have said it, too. If the tip of the tool is not dead on center, it will not cut. I know you said you're a precision kind of guy and got it close by eye but I am going to guess that your tool tip is high and it is rubbing. I say its high because if it was low, it would dig in. If it was on center, it would cut. If it is high, it will rub on the relief angle below the cutting edge and it will not cut; it will leave a bright line on the work but it won't cut. 

Parting is not rocket science. You need enough relief angle on a tool to allow the edge to cut. The edge needs to be sharp. The tool needs to be perpendicular to the work, and the tip of the tool must be on center. Do all of this and the tool will cut. Your lathe is more than rigid enough to part a 1/2" piece of steel easily. 

Make yourself a good height setting gauge that reflects the true centerline of your spindle and use it. It will save you a lot of grief.


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## markba633csi (Jul 9, 2019)

Your lathe is quite capable,  it has to be the tool or the material.  You'll get it eventually, or, like me you'll swear off parting for the rest of eternity LOL
Just kidding
Did I mention I hate parting off?


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## pontiac428 (Jul 9, 2019)

mikey said:


> Make yourself a good height setting gauge that reflects the true centerline of your spindle and use it. It will save you a lot of grief.


This is sage advice.  I keep a planer gage on my lathe bench that is set to center height.  It's so much more precise than eyeballing off of a live center, which has a couple extra elements of uncertainty in addition to a blunted point.

I don't like parting off either.  It lets me know how flexy my lathe is.  It is counterintuitive to feed into the noise.  1/2" Hot rolled steel bar should be a walk in the park, though, and if you find what's wrong and fix it, you should be parting and grooving your way to funkytown.


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## fishingreg (Jul 9, 2019)

mikey said:


> Greg, look hard at what @pontiac428 says here. Others have said it, too. If the tip of the tool is not dead on center, it will not cut. I know you said you're a precision kind of guy and got it close by eye but I am going to guess that your tool tip is high and it is rubbing. I say its high because if it was low, it would dig in. If it was on center, it would cut. If it is high, it will rub on the relief angle below the cutting edge and it will not cut; it will leave a bright line on the work but it won't cut.
> 
> Parting is not rocket science. You need enough relief angle on a tool to allow the edge to cut. The edge needs to be sharp. The tool needs to be perpendicular to the work, and the tip of the tool must be on center. Do all of this and the tool will cut. Your lathe is more than rigid enough to part a 1/2" piece of steel easily.
> 
> Make yourself a good height setting gauge that reflects the true centerline of your spindle and use it. It will save you a lot of grief.



I did see that and have made notes on all the suggestions.  It could be I am 10 or 20 thousands high but I faced the end off so I can see center pretty clear and I am very close but I can see how if I am even just a little above center maybe the cutting edge is not touching the material.  I can try adjusting that and see what happens.

I will have to youtube a height setting gauge, that is not in my vocabulary yet...  It will be now, another note written down...  

That's exactly how I feel, this should not be rocket science, people talk about using the same tool for years and if it were this tough, they would not keep a tool in one piece for years...  I'll get it, there is something wrong and I have just not found it yet.  I might play again tonight when I get home to see if maybe I am a hair high.  Thanks for all the help.


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## benmychree (Jul 9, 2019)

a number of wheel that is pink and does nice work on HSS is made by A.P. DeSanno Co (an American brand, the number is RA 80 12 VOS, that is an 80 grit wheel, for rough grinding you'd want a coarser grit, such as 46 or 60.


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## savarin (Jul 9, 2019)

Parting on my 9x20 generic asian lathe was a nightmare and like you I broke many blades.
I could actually see the tool post flex under some cuts so I removed the compound slide and replaced it with a solid plinth.
WOW, parting became a breeze after that. 
I use the "T" section blades now  in a qctp and also use a diamond hone to touch up the cutting edge before every use.
Just in case you want to go down the solid plinth route heres how I made mine.








						Plinth For Qctp On 9 X 20 Lathe
					

In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp. In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit) After seeing Bill G's plinth I felt it was time to go. I forgot to take...




					www.hobby-machinist.com


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## mikey (Jul 9, 2019)

fishingreg said:


> That's exactly how I feel, this should not be rocket science, people talk about using the same tool for years and if it were this tough, they would not keep a tool in one piece for years...  I'll get it, there is something wrong and I have just not found it yet.  I might play again tonight when I get home to see if maybe I am a hair high.  Thanks for all the help.



It is not hard to part on a lathe. While it is true that some lathes are a  bit flexy and parting is difficult, that is not the case with a PM1340. The issue is set up or a poorly ground tool. 

Grind your tool with a 7 degree relief angle under the edge. Try to grind it square across the front. You will know you have it when you raise an even burr across the front of the tool. Then use a diamond stone to gently knock the burr off. You do this by laying the top of the tool, the flat part, on the stone and pulling back, away from the edge. If you use a good tool, like that AR Warner P2 tool you had, it will last a long time before you need to sharpen it. I re-grind my tool maybe once a year or so and I may re-hone it once every few months. It cuts just fine.

Not to belabor this but you also need to be careful when you install the blade in the tool holder. The blade must be precisely vertical in the tool holder and flush up against the inside of the slot. Many tool holders do not allow this because the top of the blade is wider than the body. The easiest way around this is to use some shims between the body of the blade and the tool holder to space it evenly away so the top of the blade clears. Check this carefully; it makes a big difference.

Contrary to popular belief, you do not need to run at really low speeds to part. You just need to feed fast enough so the tool cuts continuously. This is true of almost all cutting tools - the feed must keep up with the speed or you ruin the tool's edge. If you cannot keep up with the feed then you need to lower the speed ... simple. 

I also do not agree that you have to apply a lot of feed pressure to part. A good tool, set correctly, will cut easily. You are looking for a positive resistance to the feed. I mean that you should feel a slight resistance at the hand wheel as you feed in. There should be a nicely curled chip forming and you will feel that push back. Once you get a good chip forming, just maintain that feel of slight resistance and the tool will cut well. Note that a wider blade will cut with more resistance, which is why I personally use the thinnest parting blade that is appropriate for the work. For a 1/2" piece of steel, a P1 or even a P1-N would work fine. The larger the diameter of the work, the wider the tool is supposed to be but I've parted stock up to 1-1/2" OD with a P1-N blade that is only 0.040" thick. 

Parting is a routine operation and an important one. You will use it to cut grooves, demarcate cuts and part stuff off. You need to figure out how to do it well on your lathe so don't give up.


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## jdedmon91 (Jul 9, 2019)

fishingreg said:


> Thanks Jdedmon91, I watched the videos, if rigidity was my issue would I notice some flex, jumping, or something? It appears to be smooth, no jerking, jumping, shaking or anything, just no cutting at all. Just a lot of rubbing and making a nice shiny line but thats about it. Do you notice any movement when it is not rigid or does it just refuse to cut? The first parting blade I did get to cut some but then it broke. That one I do think broke due to rigidity, it is a Arthur R Warner and had its own holder which the holder seemed good but the blade was really small and only about 1/4" top to bottom and about 3/32" wide so I don't think the blade itself was very rigid. The blade I have now is 1/2" top to bottom and 1/8" wide but maybe super dull even though it is new?



This sounds like a center hight issue, or a relief on the blade issue. Like I said the only time I have any parting issues is with small diameter stock like 1/4 inch or so. Today I’m working on a spade drill holder and parted 1 1/4 stock with no problem. 


Sent from my iPhone using Tapatalk


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## fishingreg (Jul 9, 2019)

Thank you to everyone, I appreciate all the detail.  It’s really hard for someone who has never parted a piece off to explain or comprehend pressure and feel type items like that.  so thank you all for helping and pointing me in the right direction.  I got home today, chucked the piece up closer to the chuck, centered my tool post, and double checked the height.  I dropped it down a hair to make sure It was not above center line.  I tried it, applied a good bit of pressure and nothing but a shiny line and a lot of squinting from me.  So I took the tool down to my pink wheeled chain saw sharpener ( the only non automotive stock grinding wheel I have and I have no stones yet).  I ground an edge, went back, put it in and with minimal pressure got a nice rolling chip coming off.  I parted several more without any issues.  I do not know if it came dull or if I dulled it but it must have been horribly dull.  Thanks again to everyone and I have some more homework to do on centering the tool and making something to help me with that.  I’m sure I’ll be asking something else basic soon, I’m really enjoying learning and getting some hands on time.


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## MarkDavis (Jul 9, 2019)

Thanks benmychree, made a note of mfg and part number. My little stable of HSS tools has been growing slowly and getting better thanks to many posters on this site.
Thanks to Mikey too! I spend some time lurking on the HSS sharpening thread.


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## fishingreg (Jul 9, 2019)

mikey said:


> It is not hard to part on a lathe. While it is true that some lathes are a  bit flexy and parting is difficult, that is not the case with a PM1340. The issue is set up or a poorly ground tool.
> 
> Grind your tool with a 7 degree relief angle under the edge. Try to grind it square across the front. You will know you have it when you raise an even burr across the front of the tool. Then use a diamond stone to gently knock the burr off. You do this by laying the top of the tool, the flat part, on the stone and pulling back, away from the edge. If you use a good tool, like that AR Warner P2 tool you had, it will last a long time before you need to sharpen it. I re-grind my tool maybe once a year or so and I may re-hone it once every few months. It cuts just fine.
> 
> ...



Thanks Mikey for the details on sharpening.  I need to go shopping and get a stone.  I did order a good wheel today for my bench grinder but sounds like the stone will be the finishing touch.


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## Cadillac (Jul 9, 2019)

[QUOTE="fishingreg, post:   So I took the tool down to my pink wheeled chain saw sharpener ( the only non automotive stock grinding wheel I have and I have no stones yet).  I ground an edge, went back, put it in and with minimal pressure got a nice rolling chip coming off. 
[/QUOTE]

Sounds like you found your “stones”. Good job on finding the problem keep it lubed you should be good to go.


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## mattthemuppet2 (Jul 9, 2019)

no need for fancy height gauges and the like to set tool height, just use a piece of flat steel (I used my fishtail gauge) and pinch it between the tool and the work. Adjust heing until the piece of steel is vertical. Done. Did this last night with a poly-V groove tool, took me about 30s of fiddling with the tool holder height screw. Not saying a height gauge would not be a nice and useful thing to have, but it's far from a necessity for setting tool height.


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## mikey (Jul 9, 2019)

fishingreg said:


> Thanks Mikey for the details on sharpening.  I need to go shopping and get a stone.  I did order a good wheel today for my bench grinder but sounds like the stone will be the finishing touch.



HSS parting tools do not come pre-sharpened. You have to sharpen them yourself. I highly recommend a 7 degree relief angle on parting tools. 7 degrees allows for a very sharp cutting edge with decent edge life that works with almost any material we part on a lathe. 5 degrees requires too much feed pressure, 10 degrees cuts well but the edge doesn't last.

Get this set. You will use the fine and extra-fine stones to hone your tools and DMT makes good ones.

Glad you got it worked out.


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## fishingreg (Jul 10, 2019)

mikey said:


> HSS parting tools do not come pre-sharpened. You have to sharpen them yourself. I highly recommend a 7 degree relief angle on parting tools. 7 degrees allows for a very sharp cutting edge with decent edge life that works with almost any material we part on a lathe. 5 degrees requires too much feed pressure, 10 degrees cuts well but the edge doesn't last.
> 
> Get this set. You will use the fine and extra-fine stones to hone your tools and DMT makes good ones.
> 
> Glad you got it worked out.



Thank you for the suggestion on the stones, I have looked at stones but had no idea which ones were good.  I have ordered those and looking forward to probably even a much better finish than I got just making an edge on my chain saw grinder in haste...  And I had no idea the HSS tools don't come pre-sharpened, that alone probably would have saved me a good bit of heartache...  Live and learn, every day is a learning experience for me.

Thanks again,
Greg


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## mikey (Jul 10, 2019)

I may as well give you the whole enchilada so you have enough info to feel comfortable with this subject.

Parting tools come in HSS, HSS-cobalt, inserted carbide and home made tools. For most hobby applications, HSS or cobalt tools suffice. Inserts work, too, but tend to require a more rigid lathe and set up. Depending on the configuration of the insert holder, it may be limited in depth of cut or may be on the wider side compared to HSS tooling.

My personal bias is for the P-type blades with a flat top. These tools are typically ground with a 5 degree side relief on both sides and, as mentioned, a 7 degree front relief angle works really well. I grind these flat across the front; done well, the tool will not steer. If you are concerned about keeping the blade perfectly vertical while grinding it, simply install it in the tool holder and use that to keep it flat and stable on your tool rest while you grind. I do it this way.

Sharpening these tools requires a light touch because they cut very fast and it is easy to turn the tip red hot if you go too aggressively. Grind a little, cool it in water, grind some more until you grind the whole front. Again, you want to grind until you have an even 7 degree bevel under the front edge and raise a little burr across the top of the tool. Then hone it gently, keeping the top of the tool flat on your diamond stone. You are trying to get rid of the burr, that's all. Done well, you will not see any light reflecting off the edge of the tool. In use, if you see light reflecting off the edge, hone it. If the edge is beat up or chipped, regrind it. You can typically go for months in a hobby shop without having to regrind the tool. My current P1-N blade is now well over 25 years old and is very nearly its stock length; it cuts with no issues whatsoever.

You will see these tools called P-type or T-type blades. They are functionally the same but the cutting element may be shaped a little differently. Some come with flat tops, some with V's and some with a scoop or concave shape on top. Personally, I much prefer a flat topped tool as it cuts predictably for me.

Parting tools are form tools and the bigger/wider it is, the more cutting force it generates. P-type tools are built like a girder or T-beam and are very rigid. I don't worry too much about how far I extend the blade from the holder because it isn't that critical; just get it out far enough to reach center or more. Supposedly, the bigger the work piece, the bigger the parting tool you should be using. This is because the bigger the work, the more extension you need to reach center so the thinking is that you need a bigger tool to reach out that far. There is some logic to this because we know that greater overhang results in greater deflection. However, as I said, a P-type tool is built like a girder and can extend farther than you might expect. For work up to about 1", a P1 or P1-N works well. From 1-2", a P2 is good. From 2-3", go to at least a P3 or 4. They are all ground and used the same way.

Using form tools, including parting tools, is a high pressure situation so lubrication is important. On soft stuff like aluminum, WD-40 works fine. On mild and medium carbon steels, cutting oils works well. For stainless or higher carbon steels, I prefer to use sulfur bearing oils because I am using more feed pressure to maintain a continuous cut and reduce work hardening. On Delrin, nylon, brass, bronze or cast iron, no lubricant is needed.

For speeds, I don't get all that fussy. I usually run at about half the typical turning speed for the material. As long as I can feed fast enough to keep up with the speed and produce a continuous chip, I'm happy. This applies when parting from the front. If you part in reverse with the tool mounted upside down in front of the work or with the tool mounted upside down in a rear mounted parting tool holder, you can go much, much faster and part much, much easier without any digging in or chattering.

That should give you enough info, I hope. Look into a height gauge for your tools. Lots of folks believe that tool height is not a big deal but IMHO, it is. Lathe tools are meant to work best when the tool tip is on center. A height gauge simply allows you to do this very quickly and precisely every time.


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## Jimsehr (Jul 10, 2019)

mikey said:


> Greg, look hard at what @pontiac428 says here. Others have said it, too. If the tip of the tool is not dead on center, it will not cut. I know you said you're a precision kind of guy and got it close by eye but I am going to guess that your tool tip is high and it is rubbing. I say its high because if it was low, it would dig in. If it was on center, it would cut. If it is high, it will rub on the relief angle below the cutting edge and it will not cut; it will leave a bright line on the work but it won't cut.
> 
> Parting is not rocket science. You need enough relief angle on a tool to allow the edge to cut. The edge needs to be sharp. The tool needs to be perpendicular to the work, and the tip of the tool must be on center. Do all of this and the tool will cut. Your lathe is more than rigid enough to part a 1/2" piece of steel easily.
> 
> Make yourself a good height setting gauge that reflects the true centerline of your spindle and use it. It will save you a lot of grief.


Search this forum for     One way to find center.      Shows how to use a depth micrometer to find center of stock.


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## fishingreg (Jul 11, 2019)

mikey said:


> I may as well give you the whole enchilada so you have enough info to feel comfortable with this subject.
> 
> Parting tools come in HSS, HSS-cobalt, inserted carbide and home made tools. For most hobby applications, HSS or cobalt tools suffice. Inserts work, too, but tend to require a more rigid lathe and set up. Depending on the configuration of the insert holder, it may be limited in depth of cut or may be on the wider side compared to HSS tooling.
> 
> ...



Thank you for taking the time to explain all of this in great detail.  It is very helpful.


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## MrWhoopee (Jul 11, 2019)

My first (and last) impression is the primary problem is height of the cutting edge. A few thousandths below center will not hurt, a few above will not cut. If it rubs and doesn't cut when you first touch the stock, it's too high.


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