# First time parting not too good



## Garyg (Feb 9, 2015)

I tried parting off a 1" piece of  cold rolled steel. Extremely noisy. I cut in about a 1/8 in and it grapped in and stalled then blew the fuse. I was feeding so slow aswell. Its a 10x22 lathe
I had watched you tube video's and read about how difficult it can be.
This is what I was using. It is tapered and the top has a bevel on both sides.


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## great white (Feb 9, 2015)

Worth at least a read: 

http://www.hobby-machinist.com/show...e-About-Holding-Cutting-Tools-On-Small-Lathes


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## NightWing (Feb 9, 2015)

What RPM were you running?  Any cutting oil or fluid?  What grade of cold roll?


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## schor (Feb 9, 2015)

I have found that going too slow when parting can cause chatter.


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## kd4gij (Feb 9, 2015)

The top of the tool needs to be on dead center. And parting verry sharp. and coolant or oil a must.


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## mikey (Feb 9, 2015)

Garyg said:


> I tried parting off a 1" piece of  cold rolled steel. Extremely noisy. I cut in about a 1/8 in and it grapped in and stalled then blew the fuse. I was feeding so slow aswell. Its a 10x22 lathe
> I had watched you tube video's and read about how difficult it can be.
> This is what I was using. It is tapered and the top has a bevel on both sides.



Gary, here are some things to consider:

You are using a 3/16" tool on a 1" piece. This is a huge tool for this cut. I would recommend a T-type tool in size P-1 instead. This tool is only 1/16" wide and will work better in this application. 
Your tool holder holds the cutter in only one small area. It will move. Better tool holders will clamp the entire blade or a good portion of it so that the body of the blade contacts the holder, thereby increasing rigidity. 
Your tool is dull. I'm not sure if this is after it dug in but it also may be why it dug in. Your tool has to be very sharp. 
How rigid is your set up? Any play in your carriage, tool post or tool holder can cause the tool to dig in. Look for ways to improve rigidity. 
Was the tip of your tool on center height? A parting tool is pushed down (tangential cutting forces) when engaging the work. If the set up is not rigid these cutting forces will push the tip of the cutter down and the tool will dig in. One thing to try is to set the tool height a few thou above center height and try again. Also, do you have a height setting gauge for your lathe? Using the tip of a tailstock center is not accurate enough. You might consider making a tool that is set on the exact centerline of your lathe to aid in this sort of thing. 
Was your tool perpendicular to the axis of the lathe? This is a form tool with a square nose and zero rake. Therefore, any deviation from dead square will cause one corner of the tool to take the load and may steer the tool. Best to align the side of the blade with  the end of the work, the face of the chuck or some other reference surface. 
Use lubricant on materials other than cast iron or brass/bronze. 
Feeds need to be positive but don't jam the tool into the cut. You should feel a slight resistance to feed, the emphasis being slight. 
In my opinion, speeds vary with the rigidity of your set up. If you have a good set up you should be able to part at turning speeds. If not, then slow down. You will need to learn how your lathe and tool likes to cut. You might set a speed at say, 1/2 turning speed and see if you can feed smoothly and steadily with a feed that gives you a slight positive feel to the cut. By that I mean you should feel a slight resistance to the feed and the chips should curl continuously out of the cut. Don't rush this; it is a controlled feed and will vary as you go from the faster turning outer diameter to the slower turning inner section. You will notice you need to slow down the feed about 2/3 of the way in. 

If you can figure out how to do it, parting from the rear with a purpose-built tool holder and an inverted parting tool will make all your parting issues go away. It seems that only those of us who use these tools favor them but they work so much better that I wonder sometimes why folks don't try them. I use one on my Sherline lathe and I would walk through the cut you made at about 1200 RPM. It is at the top of my list of things to make for my new Emco lathe. 

Anyway, hope this helps,

Mikey


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## Wreck™Wreck (Feb 9, 2015)

mikey said:


> It seems that only those of us who use these tools favor them but they work so much better that I wonder sometimes why folks don't try them. I use one on my Sherline lathe and I would walk through the cut you made at about 1200 RPM. It is at the top of my list of things to make for my new Emco lathe.
> 
> Mikey



Serious question, what mechanism enables parting off from the backside on a machine that is not constrained by the number of tools on the cross slide or it's travel to perform better?
Chip control, coolant flow? I'm not seeing it.


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## Henrymac (Feb 9, 2015)

I saw a video on youtube where the operator ran the lathe backwards when parting. Instead of pushing down and into the workpiece, the force was away from the spindle. If there were any binding or other undue forces on the workpiece, the tool would be pushed away from the workpiece instead of into it. I believe he ran the tool upside down also. Crashing was near impossible under these conditions. Does this sound like something that should be considered? Just my .02. :makingdecision:


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## Wreck™Wreck (Feb 9, 2015)

Henrymac said:


> Crashing was near impossible under these conditions. Does this sound like something that should be considered? Just my .02. :makingdecision:



Turning on the backside attempts to lift the saddle off of the ways, as far a crashes are concerned, if you crash the tool into the part in either direction it is still a crash. Whomever told you that you can't crash it that way is pulling your leg.

Tell him, as an Englishman might say, to "pull the other one".


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## mikey (Feb 10, 2015)

Wreck™Wreck said:


> Serious question, what mechanism enables parting off from the backside on a machine that is not constrained by the number of tools on the cross slide or it's travel to perform better?
> Chip control, coolant flow? I'm not seeing it.



Yeah, its sort of hard to wrap your head around it but my personal experience suggests that a rear mounted tool improves rigidity. When parting from the front  the cutting forces push the nose of the tool down and causes a lifting force on the tool holder. If there is flex or play in the carriage-holder interface or in the ways then the holder can move and allows the cutter tip to move and cause the tool to dig in. With a rear mounted tool these forces lift the nose of the tool. This lift translates into downforce at the tool holder on the carriage, eliminating play. It works.

In addition, since the tool is mounted upside down the relief angle under the tip now sits above the tip and acts like side rake on a turning tool. This reduces cutting forces and aids in chip ejection, thereby reducing cutting temperatures as well. Furthermore, since the tip is being lifted out of the cut by the cutting forces dig ins just don't happen.

Unlike parting from the front, where much of the cutting fluid is carried off by the chips before it even gets to the cutting tip, the fluid gets to the tip of an inverted tool first. This further reduces cutting temperatures and reduces friction. 

In a shop-made holder that clamps the entire width of the blade such that the body of the blade is in firm contact with the side of the slot it sits in, the blade is held very rigidly. This allows a thin blade to cut much deeper than that blade would be able to cut when parting from the front. How much deeper? I use a P-1-N (0.040" thick) to cut 1-1/2" thick steel at high speeds without chatter so I would guess it doubles the depth capacity of that cutter. 

On a heavy rigid lathe, rear mounting a parting tool may not make a difference but on a light lathe it definitely does. On a Sherline lathe you will have severe chatter when parting large diameter pieces of steel from the front, even at relatively low speeds, but a rear mounted tool will walk right through that same piece without a hint of chatter at much higher speeds. I haven't had a single dig in or any chatter in well over a decade of use so regardless of how it works, it does work.


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## NightWing (Feb 10, 2015)

mikey said:


> Gary, here are some things to consider:
> 
> You are using a 3/16" tool on a 1" piece.
> Mikey



The blade is marked 3/32 (.093).


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## mikey (Feb 10, 2015)

My mistake.


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## stupoty (Feb 10, 2015)

Regarding the rear tool post mount, it might be to do with some smaller lathes having no gib on the bottom of the frount of the sadle, this might alow it to hop up a bit if it grabs and springs ?

i see that most capstan lathes have a rear cut off tool, i always thought it was for speed, but the lever operation looks like you could feel the tool realy well during a parting off.


Stuart


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## mikey (Feb 10, 2015)

Back when I built my rear mounted tool post I wondered why it worked so well. I'd read all the arguments about which way the forces were going and so on but it was really hard for me to see. To resolve this for myself, I put a preloaded dial indicator on the carriage, behind the tool holder, and tried parting from the front; I got a small positive deflection, meaning the carriage was lifted up. When parting from the rear there was no movement of the needle at all, suggesting to me that the forces were indeed pushing the carriage down onto the ways. Not very scientific, I agree, but it was good enough for me.

My reasoning is that the tool post and lock down bolt act as a fulcrum. A lifting force at the nose of the tool will attempt to lift the front edge of the tool holder but since the tool holder is firmly bolted to the carriage it pushes the rear of the tool holder down. This takes up any play in the works and increases the apparent rigidity of the lathe. 

Perhaps just as important as which way the forces are running is the fact that the tool is lifted out of the cut when parting from the rear so dig ins are essentially eliminated. Couple that with a rigid tool holder and the girder-like construction of a T-type parting tool and you have a set up that works.

Again, if you have a lathe that is large and rigid enough to resist the cutting forces developed by a parting tool then this sort of work around is not necessary but on a small lathe it is a very big deal. 

Stu, on a capstan lathe (turret lathe here in the States) ALL the tools are mounted on the same turret. I suspect these lathes part from the rear due to the design of the turret rather than to resist cutting forces. They are all CNC lathes as well so feel is a non-issue. They do work really well, though, don't they?

To the OP, I didn't mean for this to go off on a tangent. My apologies.

Mikey


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## Henrymac (Feb 10, 2015)

I found the video of the guy parting using the lathe in reverse with the tool holder upside down.  The video explains it better than I could. Enjoy!

https://www.youtube.com/watch?v=-RZRq0olsxM


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## Garyg (Feb 11, 2015)

Not sure what grade of cold rolled it was. It is just some practice metal I bought at Princess auto. I was turning about 300 rpm or maybe less. I tried some oil also.


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## higgite (Feb 11, 2015)

A video in the thread that 'great white' linked to in post #2 explains it in terms of the relationship of the pivot point to the tool/work piece interface. I found it very enlightening. And a neat tool, also.
https://www.youtube.com/watch?v=KETVR9qtEmY

Tom


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## mikey (Feb 11, 2015)

Garyg said:


> Not sure what grade of cold rolled it was. It is just some practice metal I bought at Princess auto. I was turning about 300 rpm or maybe less. I tried some oil also.



Gary, it might be better to practice on some Aluminum until you get the hang of this. Parting steel is not difficult with a good set up but you need to learn how to do it first. I would suggest 1" 6061 or something that won't deflect too much and part off close to the chuck. Use WD-40 as a lube.

Sharpen your tool. A 7 degree angle at the front is good. Hone any burrs off the top of the tool. Keep your parting tools sharp.

Be sure your tool height is as close to on center as you can get it or a few thou above center. You can check your tool height with a 6" rule. Trap the rule between the tip of the tool and the work and adjust the height of your tool until the rule is vertical.

Be sure your tool is precisely perpendicular to the work. The easiest way is to move the tool up to the chuck and align it with the face of the chuck. 

Lock all gibs except your cross slide feed. You want everything as solid and rigid as you can make it.

Aluminum will part at higher speeds than steel but will also part at lower speeds and I would suggest about 300-400 rpm to start. Move the tool in until is just starts to cut and lube the little groove that you just made, then start to feed the tool into the work. You want to feed so that you can feel the tip cutting and watch for a continuous chip coming off the tool tip. Keep the cut lubed; you don't have to soak it but try not to let it run dry. You will hear the tool whine or squeal when it gets dry so lube it before it makes that noise. As you feed in about 2/3 of the way through you will need to slow down a little because the surface speed of your work is lower as you cut into the center. Just keep feeding so you can feel the tip in firm contact with the work until you cut through. 

Give us some feedback on how things are going. Parting is not difficult and you will be doing this for as long as you do lathe work. It pays to find a set up that works for you and stick with it. Just come back here if things are not going right and we can try to trouble shoot along with you.


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## ICanBreakIt (Feb 13, 2015)

Is this the video you were referring to?  I found it interesting as well.

[video=youtube;-RZRq0olsxM]https://www.youtube.com/watch?v=-RZRq0olsxM#t=12[/video]





Henrymac said:


> I saw a video on youtube where the operator ran the lathe backwards when parting. Instead of pushing down and into the workpiece, the force was away from the spindle. If there were any binding or other undue forces on the workpiece, the tool would be pushed away from the workpiece instead of into it. I believe he ran the tool upside down also. Crashing was near impossible under these conditions. Does this sound like something that should be considered? Just my .02. :makingdecision:


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## Henrymac (Feb 14, 2015)

ICanBreakIt said:


> Is this the video you were referring to?  I found it interesting as well.
> 
> [video=youtube;-RZRq0olsxM]



Yes, I posted it in an earlier post, but thanks. Would this technique work on a larger lathe? I would think so.


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## janvanruth (Feb 14, 2015)

higgite said:


> A video in the thread that 'great white' linked to in post #2 explains it in terms of the relationship of the pivot point to the tool/work piece interface. I found it very enlightening. And a neat tool, also.
> 
> 
> 
> ...


the video, especially the animation sucks
watch the animation in regard to centerhight


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## randyc (Feb 14, 2015)

Tapping a hole in the cross-slide allows installing a 1/2 diameter steel rod directly under the toolpost.  The cutting forces are then transmitted directly to the cross-slide and the carriage.  There is no "rocking" and "tipping" of compound or cross-slide.  The capability of thelittle 8 x 18 lathe when working hard-to-machine materials went up by 100%.








The shortcoming of this "fix" is that movement of the compound is limited, although it's simple enough to unscrew/remove the support rod and restore full compound travel.  With the support removed, rigidity is diminished and chatter returns during heavy cuts using the compound.


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## janvanruth (Feb 14, 2015)

draw a circle 
draw a line going from the centre out and beyond the circle
that is a centreline
now draw a line perpendicular to the centreline outside the circle
that is the line of force
now explain why the force would change with the changing of the turning movement  of the circle 

you wont be able because there is no difference

the reason for having the cutoff tool on the back is speed of working
in stead of having to change the tool for a  cutting off tool and reversing the lathe all you do is crank the backtool towards you
offcourse the tool will be upside down otherwise it wouldnt cut
and as the cuttingtool holder only serves one purpose it will be much more rigid than the compound that has to serve more purposes

a cuttingtool with no top rake will never be drawn into the piece be it high or low
only a cuttingtool with a positive rake on the top can be drawn into the workpiece

rigidity is the key to parting off


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## janvanruth (Feb 14, 2015)

Garyg said:


> I tried parting off a 1" piece of  cold rolled steel. Extremely noisy. I cut in about a 1/8 in and it grapped in and stalled then blew the fuse. I was feeding so slow aswell. Its a 10x22 lathe
> I had watched you tube video's and read about how difficult it can be.
> This is what I was using. It is tapered and the top has a bevel on both sides.
> 
> View attachment 94564


how do you mean a bevel on both sides?


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## higgite (Feb 15, 2015)

janvanruth said:


> the video, especially the animation sucks
> watch the animation in regard to centerhight


The video that I referenced doesn't have any animation. It's not the same video that Henrymac referred to earlier.



janvanruth said:


> draw a circle
> draw a line going from the centre out and beyond the circle
> that is a centreline
> now draw a line perpendicular to the centreline outside the circle
> ...


In your example, the pivot point would have to be on the center line of the spindle for the force and the reaction to that force to be the same in both directions of rotation. The pivot point on a tool post/cross slide combo is below the center line of the spindle. Direction of rotation and tool orientation do make a difference in that case. The video that I referenced does a good job of explaining it.

Tom


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## coolidge (Feb 15, 2015)

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356


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## mikey (Feb 15, 2015)

Deleted


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## janvanruth (Feb 16, 2015)

higgite said:


> The video that I referenced doesn't have any animation. It's not the same video that Henrymac referred to earlier.
> 
> 
> In your example, the pivot point would have to be on the center line of the spindle for the force and the reaction to that force to be the same in both directions of rotation. The pivot point on a tool post/cross slide combo is below the center line of the spindle. Direction of rotation and tool orientation do make a difference in that case. The video that I referenced does a good job of explaining it.
> ...



the pivot point could indeed be beneath the centre line, it  depends upon the setup whether it is or not
but in turning upside down it would be exactly the same distance above the centre line using the same kind of setup
so no difference at all


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## higgite (Feb 16, 2015)

janvanruth said:


> the pivot point could indeed be beneath the centre line, it  depends upon the setup whether it is or not
> but in turning upside down it would be exactly the same distance above the centre line using the same kind of setup
> so no difference at all


As much as I hate the cliche', I'm afraid we will have to agree to disagree. I'm done.

Tom


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## janvanruth (Feb 17, 2015)




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