# How to Mount Parting Tool



## oskar (Apr 6, 2018)

I bought this parting tool but not sure how to use it. Some sites show the tool located behind the stock and some in front of the stock. Which is the right way to mount the tool?


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## P. Waller (Apr 6, 2018)

Are you asking which side of the tool is Z 0.000 ?
If so use whatever works for you, there is no "correct" way.


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## benmychree (Apr 6, 2018)

Generally, the tool is mounted in front of the stock; on heavier lathes it can be mounted upside down in the back, especially on turret lathes; I'd think, especially on light lathes, backside mounting would not work very well due to the tendency for the tool's cutting forces to lift the carriage.


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## Bill Gruby (Apr 6, 2018)

On a heavy lathe either front or back. As Benny said, the small lathes have aprons that will lift slightly with the pressure of the rear nounted inverted blade. IMHO on light lathes only front mounts will do.

 "Billy G"


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## oskar (Apr 7, 2018)

Thank you all, I will mount it at the front.


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## mikey (Apr 7, 2018)

Sorry guys but I respectfully disagree that a light lathe should only mount parting tools from the front. Parting from the front on a Sherline lathe is problematic at best but I use a rear mounted parting tool post on my Sherline lathe and it will part almost anything from that position. It is mounted directly on the cross slide and I suspect this makes a difference but I can part most materials at 2-3 times normal turning speeds without issues. I haven't had a dig in or chatter in probably 15 years or more and I have parted stuff that is as large as my chuck will hold with a P1-N blade (0.040" thick). Everything from 4140 to plastics have been parted without issues this way.

Not an argument; just an experienced opinion that a light lathe is better off with a rear mounted parting tool if it can be solidly mounted there and the lathe run in the normal direction. If it cannot be mounted in the rear then it will do better with the tool mounted in front with the blade upside down and the lathe run in reverse. For a bigger, more rigid lathe, then do what works.


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## TTD (Apr 7, 2018)

mikey said:


> If it cannot be mounted in the rear then it will do better with *the tool mounted in front with the blade upside down and the lathe run in reverse.*


^^^ That’s exactly how I have to part off with my little 7x12.

The first few times that I parted in the conventional manner (blade out front, chuck spinning forward) was dismal to say the least…not to mention nerve-racking. Wasn’t a matter of “if” the blade digs in, but more “when” is it going do dig. Broke one blade, messed up a couple pieces…I absolutely cringed every time I had to part off. Pucker factor = 11/10

Then I read about the upside down/reverse method. I’ll admit that at first I didn’t understand why this would work any better, but thought I would try it anyways as it surely couldn’t be any worse than my current method. Wow!…the difference was night & day. No more chatter, no more digging in, no more stalling the wee ½ hp motor out & no broken blades since. Now parting off is just another step to do & I don’t give it a second thought. Pucker factor literally dropped to 0/10.

Now, I’m still just a newbie with only a few years under my belt so take it for what it is, but I truly believe that anyone with a small, light lathe who hasn’t tried either the upside down/reverse method or rear mounted method should really give it a try…I think you just might be (pleasantly) surprised with the results.


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## 4ssss (Apr 7, 2018)

A lot of the problems in cutting off on a lathe have to do with the speed of the spindle. As you get closer to the center, the speed of the cut increases, so slowing it down helps quite a bit. That's where a VFD is helpful. I normally keep my motor pulley on the faster side, so my slowest spindle RPM I have is around 550 without the back gears. I'll start at that speed, and around 1/2 way thru I'll re-sharpen the tool, and drop the speed down maybe 30 % with the VFD. Adding an angle to the tool (longer at which side of the cut you need to save) allows the cut off part to be held a little longer so you end up with a reasonably burr free part that you cut off.


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## Ken from ontario (Apr 7, 2018)

TTD said:


> Then I read about the upside down/reverse method. I’ll admit that at first I didn’t understand why this would work any better, but thought I would try it anyways as it surely couldn’t be any worse than my current method. Wow!…the difference was night & day. No more chatter, no more digging in, no more stalling the wee ½ hp motor out & no broken blades since. Now parting off is just another step to do & I don’t give it a second thought. Pucker factor literally dropped to 0/10.


That's how I mount the parting tool also (on a small mini lathe)  and I first learned about it from Mikey,  parting with an inverted blade and the  lathe run in reverse is  just one way of doing the job but to me as a newbie hobbyist  it is an easy (and safe) method .


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## T Bredehoft (Apr 7, 2018)

After I replaced the [plastic] gibs with steel ones on my Atlas/Clausing MK2, I was able to part with the tool behind.  With the plastic gibs I was unable to tighten them enough to keep the compound from lifting.


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## jwmelvin (Apr 7, 2018)

4ssss said:


> As you get closer to the center, the speed of the cut increases...


I believe you have that backwards. Circumference is smaller. Fixed rpm means slower surface speed with smaller diameter.


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## ttabbal (Apr 7, 2018)

With the tool pictured, I can see how one would mount it upside down. 

My HSS parting tool is part of the AXA holder and the angle of the tool is built in. And it would point the wrong way, though I could rotate the tool post to fix that, at the cost of putting the tool further away from the chuck. I would also have to remove the height adjustment to mount it upside down... 

Just curious if there's a way to try it with my setup. I'm guessing it is better to use my carbide parting tool if I want to do this as it's a normal tool I can just flip over. 

If running the tool behind the work, don't you need to run in reverse or upside down?


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## Bill Gruby (Apr 7, 2018)

You mount the tool  upside down.

 "Billy G"


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## Robert LaLonde (Apr 7, 2018)

4ssss said:


> A lot of the problems in cutting off on a lathe have to do with the speed of the spindle. As you get closer to the center, the speed of the cut increases, so slowing it down helps quite a bit. That's where a VFD is helpful. I normally keep my motor pulley on the faster side, so my slowest spindle RPM I have is around 550 without the back gears. I'll start at that speed, and around 1/2 way thru I'll re-sharpen the tool, and drop the speed down maybe 30 % with the VFD. Adding an angle to the tool (longer at which side of the cut you need to save) allows the cut off part to be held a little longer so you end up with a reasonably burr free part that you cut off.



Huh?  As you approach the center (smaller diameter same time per revolution) the surface speed decreases.  For simplicity sake: On a 3in diameter part at 1000 RPM you have a surface speed of about 785.4 SFM.  At the same 1000 RPM with a 1in diameter part you have a surface speed of about 261.8 SFM.  

(Pi(D") X 1000) / 12 = SFM

If D1 > D2 then SFM1 > SFM2

I'm not great with a lathe so I don't always know how to apply that to the feed for the best cuts, but the math is pretty simple.


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## mikey (Apr 7, 2018)

ttabbal said:


> With the tool pictured, I can see how one would mount it upside down.
> 
> My HSS parting tool is part of the AXA holder and the angle of the tool is built in. And it would point the wrong way, though I could rotate the tool post to fix that, at the cost of putting the tool further away from the chuck. I would also have to remove the height adjustment to mount it upside down...
> 
> ...



You can make or buy one like this: https://www.eccentricengineering.com.au/index.php?option=com_content&view=article&id=31&Itemid=45. I think @ddickey has one and @Ken from ontario made one.

If you rear mount the tool then yes, it has to be mounted upside down and you use it with the lathe running in the normal direction. Unfortunately, most lathes do not have a T-slotted cross slide that would allow you to mount a separate tool holder to the bed of the cross slide. My Sherline and Emco lathes do and a stand-alone parting tool holder mounted to the back side of the cross slide is the way to go on these lathes. It  makes parting a routine non-event. 

If it is of any interest, I wrote my Sherline tool up here: http://www.machinistblog.com/rear-mounted-parting-tool-holder-for-sherline-lathe/


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## ttabbal (Apr 7, 2018)

Interesting. Thanks Mike! I do have T-slots on the cross slide, so I could try something like that. Though it would be a lot easier to make with a mill.. 

I did try flipping my carbide parting tool over and run in reverse. It does seem to part smoother in aluminum. That tool limits depth to about 1", but it shows that the idea could work well for an HSS blade as well. Not that I do a lot of parting on thicker material.


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## British Steel (Apr 7, 2018)

Bob La Londe said:


> Huh?  As you approach the center (smaller diameter same time per revolution) the surface speed decreases.  For simplicity sake: On a 3in diameter part at 1000 RPM you have a surface speed of about 785.4 SFM.  At the same 1000 RPM with a 1in diameter part you have a surface speed of about 261.8 SFM.
> 
> (Pi(D") X 1000) / 12 = SFM
> 
> ...




Agreed, I have my VFD set up with a slider potentiometer on the cross slide to increase the RPM as it approaches centre - right at the centre it should be infinite, but my lathe will only go up to 2500  

It parts just fine with power feed and either HSS or inserted-carbide tools, but it's a heavy, rigid lathe*, and the "near constant" surface speed makes facing a lot better, more consistent surface finish, and turning different diameters is quicker not having speed changes.

Dave H. (the other one)

*13x30 but well over 4000 pounds


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## mikey (Apr 7, 2018)

ttabbal said:


> Interesting. Thanks Mike! I do have T-slots on the cross slide, so I could try something like that. Though it would be a lot easier to make with a mill..
> 
> I did try flipping my carbide parting tool over and run in reverse. It does seem to part smoother in aluminum. That tool limits depth to about 1", but it shows that the idea could work well for an HSS blade as well. Not that I do a lot of parting on thicker material.



I meant T-slots that run the length of the cross slide like this. It makes mounting accessory tool posts simple:







Have a good look at that ForR parting tool holder. You can make that with your milling attachment and a drill press. Or buy it - not that expensive.


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## ddickey (Apr 7, 2018)

I have pics if you want them of the FoR holder and the one I made.


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## ttabbal (Apr 7, 2018)

ddickey said:


> I have pics if you want them of the FoR holder and the one I made.



I would like to see what you have. It is always helpful to see what people have done.


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## ddickey (Apr 8, 2018)

If you have a T-slot I could make you one. Free of charge.


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## ttabbal (Apr 8, 2018)

ddickey said:


> If you have a T-slot I could make you one. Free of charge.



Thanks! My lathe cross slide looks like the one @mikey posted a picture of, but with only 2 slots.


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## The_Apprentice (Apr 8, 2018)

In case I missed it... when parting off on a mini-lathe, don't forget the 2mm rule.

As you advance the cutting tool into the work, back it out every so often and re-cut 2mm to the left (or right). This creates a little gap to save you from BIG problems when binding occurs.

I always cringe when parting off on my machine too for a very good reason...


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