# Parting Trick



## jschmidling (Jul 29, 2019)

There are numerous videos on tricks for using parting tools but I found one that seems too simple and obvious not to be used universally.

His graphic makes it seem very simple but I don't quite see how it is not dependent upon the position above or below center.

I tried it on a piece of PVC in my mini and it works as advertised.  To me, the most obvious advantage is the way it pushes the chips out the bottom.

Doing it the normal way, I have to stop frequently to remove the tangled mess of chip, including using a scissors to cut it loose.

I am interested in some opinions of this....






js


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## benmychree (Jul 29, 2019)

Cutting off has always been done like this on turret lathes, but on the backside revolving forward, It makes parting off a much more successful operation than the standard method, partly because chips have an easier exit and also coolant/lubricant has easier flow to the cut, and as is pointed out, the tendency to jam up as the model shows, is likely the most important factor of troubles in parting by the standard method.  A great deal of parting problems go away when using heavier industrial rated machinery, and made worse with light hobby style machines.


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## rgray (Jul 29, 2019)

Not a fan myself.
Rotation is trying to lift the tool, compound, and cross slide.
Sure if you have slack in those items the tool will be lifted up away from the cut, but then will be above center also.
Get rid of the slack in those places and you will be able to part off normal.

Plastics are always challenging as far as the cuttings. All strings and no chips.


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## stioc (Jul 29, 2019)

I've never tried this method (though have seen it a few times) so may be I should before I say this but if you're reversing both the tool's orientation and the part's rotation then you're basically doing exactly the same thing just upside down. The graphics are an extreme case scenario. I don't think the tool can dig into work if it's held solid in a tool holder and chips while in this case fall straight down as opposed to spilling over but would that really make that much of a difference? May be a placebo effect?


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## C-Bag (Jul 29, 2019)

Another consideration is you'd not want to do that with a 9x20 because you might unscrew the chuck. I've seen folks with 9x20's mount the cutter on the other side and upside down and then you're still in fwd rotation. They say that it works for parting.  I'm ok with fwd parting now that I've got everything including the headstock bearings adjust correctly.


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## stioc (Jul 29, 2019)

C-Bag said:


> Another consideration is you'd not want to do that with a 9x20 because you might unscrew the chuck. I've seen folks with 9x20's mount the cutter on the other side and upside down and then you're still in fwd rotation. They say that it works for parting.  I'm ok with fwd parting now that I've got everything including the headstock bearings adjust correctly.



Excellent point there, any heavy work in reverse can cause the chuck to unscrew itself from the spindle. I take it you have a 9x20 too? It's a fairly decent machine, way heavier and more rigid than my 7x14 I had years ago. But I think a 12x36 or a 13x40 will be in my future when I retire (and have a bigger shop). I use a carbide insert parting tool and it slices through aluminum like butter, that wasn't the case with my HSS parting tool. Haven't tried steel yet.


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## mikey (Jul 29, 2019)

stioc said:


> I don't think the tool can dig into work if it's held solid in a tool holder and chips while in this case fall straight down as opposed to spilling over but would that really make that much of a difference? May be a placebo effect?



A rear mounted parting tool or an upside down/reverse rotation parting tool works.

This is a P1-N rear-mounted parting tool (0.040" wide tool) cutting a groove in a 1-1/4" OD piece of 12L14 steel at 1200 rpm on a Sherline lathe. Note that the blade is purposely overextended to try to induce chatter. The cut is clean and chatter-free - look at the finish inside the cut. This part was later parted off an inch from the chuck without issues. A Sherline lathe weighs somewhere near 35# soaking wet so it isn't about size; its about how the cutting forces are transferred to the lathe.





This blade, mounted on this lathe, could not make this cut from the front without slowing the speed down really low ... maybe not even then. The rear mounted set up can cut just about any machinable material at high speeds from the rear with no issues whatsoever. I have not had a single issue when parting this way in nearly 20 years so no, not a placebo.


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## stioc (Jul 29, 2019)

Good to know, I'll have to try the rear mounted version. I assume in the rear mounted version the blade isn't held upside down nor is the spindle rotated in reverse?


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## mikey (Jul 29, 2019)

In a rear mounted parting tool holder, the blade is mounted upside down and the rotation of the lathe is normal, not reversed. The cutting forces lift the tool so a dig in is not possible. Moreover, these forces push down on the cross slide, thereby increasing rigidity. This transfer of forces has been controversial because it is difficult to visualize and I won't go into it here because it just leads to arguments. However, I am convinced that this is the reason why a little lathe like a Sherline can part from the rear more effectively than many much larger lathes can from the front.


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## C-Bag (Jul 29, 2019)

stioc said:


> Excellent point there, any heavy work in reverse can cause the chuck to unscrew itself from the spindle. I take it you have a 9x20 too? It's a fairly decent machine, way heavier and more rigid than my 7x14 I had years ago. But I think a 12x36 or a 13x40 will be in my future when I retire (and have a bigger shop). I use a carbide insert parting tool and it slices through aluminum like butter, that wasn't the case with my HSS parting tool. Haven't tried steel yet.


Yes, I've got the despised duo, 9x20&RF30 too. My 9x20 was not used much for anything more than trying to trick it out, but he had no clue about all the QC probs. Being a total noob when I got it I didn't know what was operator error/or mis adjustment. Over time and through the simple projects I found and solved the problems as they came up with the help of other 9x20 users like Savarin. What I've come to is with all the work I've done I understand its shortcomings and have been able to do better and better work. If I ever get to the point I need a larger lathe, I'm going to keep it as a backup as everytime a lathe goes down it is crystal clear I needed a lathe to fix it.


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## mikey (Jul 29, 2019)

C-Bag said:


> ... everytime a lathe goes down it is crystal clear I needed a lathe to fix it.



Ain't that the truth?


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## C-Bag (Jul 29, 2019)

mikey said:


> Ain't that the truth?


It's one of things that I kept running into as side comments. One of the first things I'd was told about the lathe is its the queen of machine tools, able to reproduce itself! But for some reason I didn't take into account it can't repair itself if it's not working!


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## jschmidling (Jul 29, 2019)

mikey said:


> In a rear mounted parting tool holder, the blade is mounted upside down and the rotation of the lathe is normal, not reversed. The cutting forces lift the tool so a dig in is not possible. Moreover, these forces push down on the cross slide, thereby increasing rigidity. This transfer of forces has been controversial because it is difficult to visualize and I won't go into it here because it just leads to arguments. However, I am convinced that this is the reason why a little lathe like a Sherline can part from the rear more effectively than many much larger lathes can from the front.




Couldn't wait to try it...  Bang!  Show stopper...

How do you get a parting tool on the back side of the work piece in a mini?

js


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## mikey (Jul 29, 2019)

If your cross slide has T-slots along it's length then just make a tool holder and bolt it to the table. If not but the table is machined flat then you can drill and tap a hole to bolt the tool holder in place. Otherwise, you're out of luck.


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## ptsmith (Jul 29, 2019)

mikey said:


> In a rear mounted parting tool holder, the blade is mounted upside down and the rotation of the lathe is normal, not reversed. *The cutting forces lift the tool so a dig in is not possible.* Moreover, these forces push down on the cross slide, thereby increasing rigidity. This transfer of forces has been controversial because it is difficult to visualize and I won't go into it here because it just leads to arguments. However, I am convinced that this is the reason why a little lathe like a Sherline can part from the rear more effectively than many much larger lathes can from the front.



This the reasoning behind upside parting. The video jschmidling posted explains this well. I linked to that point in the video. 

It really works. No reason not to try it if you don't have a screw-on chuck.


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## mikey (Jul 29, 2019)

I'm well aware of how it works. I just don't care to argue about it.


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## ptsmith (Jul 29, 2019)

Okaaaay...I was agreeing with you. How did you read that otherwise?


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## mikey (Jul 30, 2019)

ptsmith said:


> Okaaaay...I was agreeing with you. How did you read that otherwise?



In the past, there have been a lot of guys who argued about how the forces work with a rear mounted tool that have never even tried it. It got to the point where I won't even go there anymore. My apologies for not getting your drift; no offense meant.


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## NortonDommi (Jul 30, 2019)

Upside down parting has so many pros over the accepted as standard that it is a no-brainer.  The usual stuff like making sure the blade is perpendicular to the axis and tight gibbs, locked apron etc still apply though.  There was a comprehensive write-up in Model Engineers Workshop Magazine a few years ago that went into the force reactions in depth.
Joe Pieczynski  shows how to use upside down tooling for thread cutting which is also my preferred technique:
Threading on a manual lathe BEST TECHNIQUE EVER !!!! - YouTube 



Running RH boring bars upside down on the far side is advantageous as well as it is a lot easier to see what is happening.
  As has been noted, if you have a screwed on chuck it might pay to use a rear toolpost but the forces involved are not that great compared to how tight a chuck is.  A friend with a 10" Atlas parts off this way without problem.


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## jschmidling (Jul 30, 2019)

I just bought this but not sure about one detail.









						Cut Off Parting Blade High Speed Steel 3/32 Inch x 1/2 Inch x 4-1/2 Inch  | eBay
					

Find many great new & used options and get the best deals for Cut Off Parting Blade High Speed Steel 3/32 Inch x 1/2 Inch x 4-1/2 Inch at the best online prices at eBay! Free shipping for many products!



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It has been my understanding that the front edge needs some relief, L to R and it's not clear if this has any or just assumes the user will grind in the relief.

Which side the relief is on depends on which side is the keeper part.

If all this is not a figment of my imagination, one would have do something other than just turn the tool upside down, no?

I really wanted a 1/6" tool but the price was too good to quibble.

js


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## mikey (Jul 30, 2019)

jschmidling said:


> I just bought this but not sure about one detail.
> 
> 
> 
> ...



You bought a P2 blade and it will work. All of these blades need to be sharpened and I recommend that you grind it flat across the front instead of at an angle. The reason for this is so you can use it to part, cut grooves with actual flat bottoms and demarcate cuts with it. 

I also recommend a 7 degree relief angle under the cutting edge. This leaves the cutting tip in front, with the area below it angling back at a 7 degree angle. This is a compromise that allows free cutting with good support under the edge for long life.

In order to use a parting tool upside down, you need a tool holder that will allow you to get the tip of the blade at the center height of your lathe. You can make one or buy this one. All of this may seem like a hassle but I assure you that a good parting set up is worth the work.


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## pontiac428 (Jul 30, 2019)

Mikey,
I also grind a 7 degree relief in P-type blades, because it is a good universal clearance angle (5 to 10 degrees, depending on material).  I've experimented with different relief angles, and it makes no difference to the cut as long as there is chip clearance (which on round material should exist regardless).  Not much difference there.  My tool holder is raked up 5 degrees (fixed) so the back rake is always the same.  Do you have any recommendations for ideal back rake angle for parting blades?


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## mikey (Jul 30, 2019)

I think you're referring to the ubiquitous tool holder that holds a parting tool at an upward angle that are used on many Aloris-type tool posts. I have one of those, too, and I don't really like it because I feel it puts an excessive load on the cutting edge in an area where it has little support. A P-type blade is built like a girder and it relies on that construction for its load bearing abilities. By angling the blade upwards, we eliminate much of the support the body of the blade supplies and I think this adds to the potential for chatter. Moreover, if you do not get the cutting edge dead on center the tool will not work well and I think a lot of the problems folks have with parting is due to the tool holder (and the assumption that close to center is good enough).

I believe a horizontal blade configuration is much stronger and makes better use of the support the body of the blade provides. For example, the rear mounted tool holder I made for my Sherline allows me to use a P1-N blade that is only 0.040" thick to cut material that is double the size that is recommended for this tool. Ordinarily, a P1-N is limited to roughly a 3/4" work piece; I have cut a 2" OD work piece with that blade with no issues at all. I honestly feel this is because the tool holder holds it dead vertical and provides a lot of stiffness to back the cutting edge. My tool holder gets the tip of the blade on the exact centerline of my spindle; it is machined to put the tip there and only there. As a consequence, it works. 

My suggestion is to make a tool holder for your parting blade that holds it dead horizontal and dead vertical. It should allow the body of the blade, the part under the wider top edge, full contact with the tool holder along its length. You can make it from steel or aluminum, both will work. I need to run out for a bit but if you want to discuss this tool holder further, we can.


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## pontiac428 (Jul 30, 2019)

Mikey,

Thank you.  Yes, I am talking about the ChinAloris-type tool holder.  I measured the back rake at 5 degrees because I cut the P-type blade groove in the holder over the weekend.  The blade cut about the same as usual afterward, maybe slightly better, but that may have just been from the fresh hone.  I've been parting with a 0.062 blade lately because the P1-N 0.040 blades have been exploding in my face.  I don't like the lack of full support on that tool holder.  It doesn't hold my tool true against a precision straight edge, and it allows for the parting blade to wag, leading to harmonics that combine with the QCTP's vibes.

Unless I go through with the idea of making a plinth cross slide for my Atlas, I'm stuck using the QCTP.  There is no rigid way to do an inverted parting tool mount.  I could make a base to replace the compound slide using a spare pintle top plate and mount the inverted tool to that.  On the QCTP, I have a 9/16 stud and cone flange nut holding the tool post in place.  I get most of my noise/vibes from the tool post through to the carriage; it's not a very rigid setup.  Oddly, I have the best results parting stainless because of the need to maintain heavy infeed.  With brass, aluminum, and steel, it just leaves room for improvement.

I don't want to crank down my gibs.  I'd rather leave them in adjustment.  I would consider replacing one center-located gib screw per gib (carriage, cross, top) with a thumb screw for quick lockouts.  I need to get some small stock to work from for that.  All in all, my machine is rather tight but it's a (minor) compromise to work around wear areas in the ways.  My babbitt head H-48/10F was one of the first off the line for 1937, so it's a little older than most.  My spindle bearings are adjusted fantastically.  Just background.

So while I consider my mounting options for an inverted tool holder, I am interested in being able to adjust the back rake angle on the parting tool.  I could machine the 5 degree shelf to another angle easily (permanent).  I could shim or angle-block the tool.  I should also double-triple check my center.  I use a planer gauge that serves me well for that.  Aaand, I could buy another lathe... like a 14" machine from the '70s from Japan or Europe.  Yeah, I'll do that later.  But for now, I'd like to get parting to be something I'm successful at in 2 out of 3 attempts, at least.


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## WarrenP (Jul 30, 2019)

Only thing I think of is, if your doing your testing with PVC I dont know that you can really tell a difference. PVC is very easy to cut , should be able to cut it easy both ways. Try your testing with steel to see if whatever your trying really does make a difference....


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## Illinoyance (Jul 30, 2019)

Your animation shows very clearly why parting off running forward tends to jam the tool.  Running in reverse tends to allow the tool to move away from the work, preventing jams.  Well done.


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## jschmidling (Jul 30, 2019)

mikey said:


> You bought a P2 blade and it will work.



I spent the last 20 mins trying to find out what (P2) means or even just the P.  I see that T type is a cross section but can't find any pic of the cross section of P.

>In order to use a parting tool upside down, you need a tool holder that will allow you to get the tip of the blade at the center height of your >lathe. You can make one or buy this one.

I recently bought a low end QCTP and it looks like the half inch blade can be centered either way.

One other thing occurred to me and that is, would not this be a better way to cut threads for all the same reasons?

Thanks,

js


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## NortonDommi (Jul 30, 2019)

mikey said:


> All of these blades need to be sharpened and I recommend that you grind it flat across the front instead of at an angle. The reason for this is so you can use it to part, cut grooves with actual flat bottoms and demarcate cuts with it.


Agree also an angle on the front face introduces a side load which is definitely unwanted on smaller machines.


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## mikey (Jul 30, 2019)

jschmidling said:


> I spent the last 20 mins trying to find out what (P2) means or even just the P.  I see that T type is a cross section but can't find any pic of the cross section of P.
> 
> >In order to use a parting tool upside down, you need a tool holder that will allow you to get the tip of the blade at the center height of your >lathe. You can make one or buy this one.
> 
> ...



JS, here are the sizes:




The critical thing is that the cutting edge is at the exact centerline of the lathe. If your holder can get it there then you're all good. If not, either buy or make one like the Eccentric Engineering FoR tool holder.

Threading is not usually an issue. However, you can turn the tool upside down and feed toward the tailstock if you prefer. I have done this and it works quite well. I just prefer to feed towards the headstock; been doing it for several decades so it isn't an issue for me. Neither is parting for that matter.


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## mikey (Jul 30, 2019)

@pontiac428, I would take a good look at the Eccentric Engineering FoR tool holder or make one to fit your lathe and tool post that will allow you to mount your parting tool upside down and still get it on the lathe centerline. That way, no need to mess with your lathe or anything else. You do have to be able to run in reverse, though.

I did want to mention the getting on center thing. In my opinion, this is one of the most important things to get right when using lathe tools and parting tool in particular. I suggest making a tool height gauge or you can use your planer gauge if it works for you but you need to measure the exact spindle centerline height with a cut. I'm sure you're capable of it already but for those who may someday read this, let me detail what I'm talking about. 

Determining the lathe's center height is a really important parameter to know. I know many recommend putting a gauge pin in a collet and measure it that way but since we're talking about tenths here, I think the stacking tolerances with this method is excessive. A much more accurate way is to put a piece of rod in your chuck; doesn't matter if it is a 3 jaw, collet chuck or whatever because this is a first order operation so whatever you use will be accurate as long as you don't take it out of the chuck. Take a 0.010" depth of cut, then a 0.002-0.003" deep skim cut to produce a nice finish. Now use a height gauge to measure from the bed or cross slide or back side of a flat compound and measure to the top of the pin you just cut. Then measure the OD of the pin you just cut, subtract 1/2 of that from the height gauge measurement and you have you lathe's centerline height. This is specific to your lathe and very accurate; make sure to write it down where you won't lose it. 

Use this to make a tool height gauge and it will serve you well. 

Parting tools need to be on center height. They do not work well when they are above or below center height. Eyeballing it doesn't work all that well, nor does trying to use a tailstock center to align it. Use a tool height gauge or something like it and you will see a difference when you part.


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## jschmidling (Jul 31, 2019)

mikey said:


> [
> 
> Use this to make a tool height gauge and it will serve you well.



Just before reading this, I turned and faced a 1" piece of brass about 1.5" long.  
I then turned it around in the chuck and faced the other end.  I set the tool height to leave just the tiniest little point remaining.

To set a tool height, I just put this thing in the chuck and adjust the tool until it is "exactly" in the middle of the point.

Anything wrong here?

js


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## mikey (Jul 31, 2019)

You should do whatever you need to do to have a reliable standard. It isn't that you can't do it in other ways but a gauge speeds things up tremendously.

Edit: I suppose I should elaborate a bit more than the above. If you ask a group of experienced machinists how important tool center height is you will likely get all sorts of answers but many will tell you that it isn't all that critical. Some will even tell you to go above or below center slightly. I'm no expert but my personal experience suggests that the closer to center height the better, and this especially applies to parting and turning tools. 

Consider that a parting tool is essentially a form tool with a relatively large contact patch. You are applying a fair amount of force to feed it into the part. If the cutting edge is above center then the tool will rub; if below, it will dig in. If on center then it will cut. It follows that center height means center height, within a half-thou or less. My personal tool height gauge will get me on center within a tenth of so. It takes me maybe 15 seconds to set height or a few seconds to check a tool already installed in a tool post. 

I should write up my tool height gauge when I have some time. It is simple and very nearly foolproof because it has no moving parts. When I have time.


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## ddickey (Jul 31, 2019)

Make sure that parting blade will fit the Eccentric Engineering FoR holder tool before you buy it. The site warns about Chinese blades being 13mm high not .500".


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## brino (Jul 31, 2019)

mikey said:


> I should write up my tool height gauge when I have some time. It is simple and very nearly foolproof because it has no moving parts. When I have time.



Yes, please!
-brino


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## ttabbal (Jul 31, 2019)

I keep thinking about making a parting tool holder. Anyone have drawings before I take the time to make some? I'm leaning towards upside down on the back, held straight. T slot cross slide on my lathe.


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## mikey (Jul 31, 2019)

ttabbal said:


> I keep thinking about making a parting tool holder. Anyone have drawings before I take the time to make some? I'm leaning towards upside down on the back, held straight. T slot cross slide on my lathe.



Here is the prototype I made for my Sherline lathe. Still using the same prototype tool after nearly 20 years because it just works. Meant to make the Mk II version but there hasn't been a need. I still need to make one for my Emco lathe when I have the time but it will be essentially the same thing - ledge that registers to the edge of the cross slide to resist turning forces and to assure perpendicularity to the lathe axis, bolts to the cross slide T-slot, blade slot puts the tip of the blade on the dead centerline of the lathe every single time. Because of these features, this thing can be mounted to the lathe and be in use within 15 seconds or less.

The whole thing is essentially a part of the cross slide when it is bolted down so it is extremely rigid. I can find no fault with this design and it should be easily adaptable to any lathe with a machined cross slide table. If I owned a lathe without T-slots, I would drill and tap a hole to enable this tool to be mounted; it would be worth it to me to be able to use this tool.


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## mikey (Jul 31, 2019)

Some additional pics to hopefully clarify what this tool looks like. I made this one for one of our HM members without a mill who could not make one himself.





The only critical feature is the bottom of the blade slot; it MUST be on the spindle centerline and it MUST be accurate. You can also see that the top and bottom of the blade slot is relieved. The bottom relief is to clear the wider cutting profile of the blade (EDIT: this allows the blade to be held perfectly vertical by the area of the body where the blade contacts). The top relief is to prevent the blade from being forced out of vertical as the top part of the tool is tightened down; this is important. Otherwise, very simple tool to make. Aluminum is strong enough for almost any hobby class lathe.


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## C-Bag (Jul 31, 2019)

Maybe this isn't the time or place but I have an old General 6 tri square I use for everything not critical. It's always in my apron. So because I'm always wanting to set tool height I put some Dykem on the edge of it and pulled my chuck off and put in the dead center. Making sure my 6" was set flush with the square end, I stood it up on the carriage used the dead center to mark the edge of the Tri square ruler Dykem. Then took my little triangle file and made the scribe more visible. It's always handy so never have to go looking for it.


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## ttabbal (Aug 1, 2019)

Thanks @mikey! That is easy enough and much like what I had in mind, though I had added a bunch of overcomplicated features in my head.  

Is there any reason on a hobby size lathe to use a larger cuttoff blade? If I'm dropping the QCTP holder, I can use any size blade I want, after all.


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## mikey (Aug 1, 2019)

In a rear mounted parting tool holder, I don't think you need to go larger than the P-type blades. Ordinarily, the size of the blade is supposed to increase with the part diameter but when mounted in a tool holder like mine the blade is held so rigidly that you can get away with a much thinner blade.  In addition, the relief angle on an upside down parting tool acts like back rake but on a parting tool, this is essentially side rake. As we know, side rake is the most influential tool angle that affects cutting forces and you will feel the reduced feed requirement when using one like this. Essentially, a thinner P-type blade mounted upside down cuts with lower cutting forces and cutting temperatures so you can easily get away with using a P1 or P2 for almost all work.

An upside down blade also improves oil delivery because the oil gets to the cut first so the cut is cleaner and cooler. In contrast, the chips when using a right side up parting tool carries much of the oil away before it even gets to the cut.

The other advantage when mounting a blade like this is that it allows you to extend the blade however far you need to without worrying about the tip being off center. You will find that blade extension on a rear mounted tool is not critical; I don't even think about it as long as I can reach the center of the part. Sometimes the blade can be 2-4 times the required extension and the blade works just fine, even when I am parting at excessively high speeds.

Speaking of parting speeds, a sharp rear mounted parting tool cuts very fast and easily at higher speeds. You do not need heavy feed pressure with this set up. As long as you can feel a slight resistance to the feed and you can keep up with that, the tool will cut with no issues. I have parted aluminum at 2200 rpm, steel at 1200-1500 rpm and so on. No problems, no dig ins, no chatter.

Make one, Trav. It is worth it.


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## jschmidling (Aug 1, 2019)

mikey said:


> I should write up my tool height gauge when I have some time. It is simple and very nearly foolproof because it has no moving parts. When I have time.



Please do.  I still don't quite follow your description.

I got my P1 parting tool and it's more bad news than good news but mostly the tool holder problems.

First of all, it bottomed out about .010" above or below center, depending on how it was used.  The fix was easy, I just milled about .050" off the top surface and it was good to go.

Second problem was that when I tightened the screws that clamp it in, the tool would shift, sort of a tilt.  Obviously the bottom of the holder was not square with the side so, back to the mill to square that up.

The QCTH is that $30 aluminum job and it's other quirk is that the dovetails are as cast with no machining and are very sloppy.  With a shim on one side, it locks pretty well so I give it a pass at this point.

I spent a good deal of time with a 1.5" aluminum bar cutting fender washers and finally got it to work well enough in the upside down mode but it was pretty tedious feeding it.  I really miss my old lathe with power cross feed.

Next, I tried a 5/8" mild steel bar and it was pretty hopeless at any speed.

I am thinking that 3/32" is just beyond this little machine so I am going to order a P1 tomorrow and hope that's the problem.

What I really do not understand is just what is vibrating when it chatters.  It's as close to the chuck as I can get it and the tool extends no more than half way into the part.

js


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## mikey (Aug 1, 2019)

@jschmidling, what kind of lathe are you using? Is the parting tool held at an upward angle? How precise did you get the tip on center? Did you mount the tool upside down and were you then running in reverse?

A pic of your set up would really help.


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## mickri (Aug 1, 2019)

Parting.  Aaaarg!!!  I am parting challenged.  Most of the time I end up resorting to my hacksaw to finish the part off and then face off the rough edge.  I am ready to make a backside parting tool holder (BPTH).  I have some 2x1.25 1018 bar stock on hand for the base and some round stock that I could turn down for the post.  The cross slide on my craftsman lathe does not have a "T" slot nor any holes to mount anything.  I think that the only way I could make a BPTH is to have it fit in the dovetails on the saddle.  Then how do I connect it to the cross slide to move it.  In looking at Mikey's parting tool holder I thought instead of trying to attach the BPTH to the cross slide why don't I put another cross slide nut on the lead screw and attach the BPTH to that.   Here is what I am thinking.







The post is the same diameter as my norman style QCTP and I would use the tool holder for the parting blade that I have already made.  Turning the lead screw would move the BPTH in or out and I could use the power feed.

What do you think of this?


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## jschmidling (Aug 1, 2019)

mikey said:


> @jschmidling, what kind of lathe are you using?



7 x 12 Mini, Wen brand

>Is the parting tool held at an upward angle?

No.

>How precise did you get the tip on center?

Within a mil?  Split the tip on my brass tool described up thread.

> Did you mount the tool upside down and were you then running in reverse?

Yes to both.

>A pic of your set up would really help.

Attached two.  Note my last attempt was to experiment R-L relief and it made no difference other than the obvious.

Jack


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## mikey (Aug 1, 2019)

I can think of a few reasons for this set up not working well. Parting depends on a very rigid set up so if the tool post itself is not solid then that causes issues; how rigid is the tool holder held in the post? The tool holder must hold the blade perfectly vertical or the blade will steer; is the body of the blade flat up against the tool holder's blade slot? The tip of the cutting edge must be on the dead center of the lathe centerline, not within a mil; the smaller the lathe, the more important this becomes. I cannot tell if the blade is sharp and deburred but I assume it is, right? Are the gibs properly adjusted?

Another idea is to make a rear mounted parting tool post and mount it at the rear of the cross slide. You would need to drill and tap a hole but that wouldn't be a problem. Might want to consider it if you plan to stay with this lathe. I suspect it will solve a lot of problems for you.


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## ttabbal (Aug 1, 2019)

I'm going to need to root around my stock shelves. I know I have steel that will work, not sure about aluminum.


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## jschmidling (Aug 1, 2019)

mikey said:


> Another idea is to make a rear mounted parting tool post and mount it at the rear of the cross slide. You would need to drill and tap a hole but that wouldn't be a problem. Might want to consider it if you plan to stay with this lathe. I suspect it will solve a lot of problems for you.



I am getting soggy here and think I can summarize by saying I am doing the best that I can with what I have to work with.

I would love to build a rear mounted tool holder but I need some better pics or drawings of such a thing to under stand it and how it would be mounted ........

Just found your blog and when I saw the word "aluminum", you lit my fuse.  My "mill" is not up to machining steel but it works well enough on Al for this project.

I need time to digest this so will get back when I come up for air.

Thanks,

Jack


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## ddickey (Aug 1, 2019)

Rear Tool Posts - hemingwaykits.com
					

Unique projects for the small workshop owner. Please browse our Toolroom and Engine Bay for our latest project kits.



					www.hemingwaykits.com


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## mikey (Aug 1, 2019)

jschmidling said:


> I would love to build a rear mounted tool holder but I need some better pics or drawings of such a thing to under stand it and how it would be mounted ........



Have a look at the design I posted on MachinistsBlog (not my blog, by the way) and make one to fit your lathe's centerline. It would have a ledge that butts up against the side of your cross slide. A hole would need to be drilled and tapped in the bed of your cross slide to accommodate a bolt that goes through the parting tool holder to hold it to your cross slide. Care needs to be taken to ascertain the exact height of your spindle centerline as this determines the height of the blade slot. Otherwise, nothing else is critical.


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## jschmidling (Aug 2, 2019)

mikey said:


> Have a look at the design I posted on MachinistsBlog (not my blog, by the way) and make one to fit your lathe's centerline



You sold me on rear mounting but with my relentless crusade to KISS, I made "a few changes" also in keeping with my now very humble shop facilities.

The attached pic is a model in wood to test the concept.  I ordered a 1/2" x 2" piece of aluminum bar stock and some proper hardware for the real thing.

Although not as rigid as a solid block, I think it will be an improvement over what I have been trying to do in front with the compound slide and marginal tool post.

The only milling required is the shelf for the tool itself and possibly squaring up the cut ends.  If the washers don't work, I will make a proper hold down bar.

Depending on your point of view, it has the "advantage" of being tweaked in all axes.

Thanks for the ideas.  Will report back when made.

Jack


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## mikey (Aug 2, 2019)

Jack, I suspect that configuration my not be rigid enough. I suggest a solid block but go with what you think is best, and good luck.


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## ddickey (Aug 2, 2019)

Is that a screw on chuck? If not mount it in your tool post.


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## ttabbal (Aug 2, 2019)

ddickey said:


> Is that a screw on chuck? If not mount it in your tool post.



Looks like a bolt on. That doesn't mean that the mount plate isn't threaded though. 

Does it matter for this though? With rear mounting, the machine is rotating in the standard direction.


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## ddickey (Aug 2, 2019)

I was saying if it's not a screw on chuck just mount the blade upside down in the tool post. Exact same affect as a rear mounted post.


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## jayman (Aug 2, 2019)

jschmidling said:


> There are numerous videos on tricks for using parting tools but I found one that seems too simple and obvious not to be used universally.
> 
> His graphic makes it seem very simple but I don't quite see how it is not dependent upon the position above or below center.
> 
> ...


I do it this way all the time on my 7x14 Mini-Lathe using P style cutoff blades mounted on my home made quick change turret. I can cut slices from 2" dia. steel bar. Email me at jayman03062@gmail.com for pics. TYPE "CUTOFF" ON THE SUBJECT LINE TO AVOID CONSIGNMENT TO MY SPAM BLACK HOLE.


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## jschmidling (Aug 2, 2019)

ddickey said:


> I was saying if it's not a screw on chuck just mount the blade upside down in the tool post. Exact same affect as a rear mounted post.



I think you may find some who would argue with that point.

To me, the more stuff you can get rid of between the tool and the carriage, the better.
Rear mounting eliminates both the do everythig tool holder and the compound slide.

js


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## ddickey (Aug 2, 2019)

I meant as far as the cutting action they're the same. Of course a solid post mounted in the rear (rigidity) is probably better than a tool post mounted to the compound unless you use a solid post in the front then once again equal. Convenience is another thing. I used a rear mounted post for a long time and they're quite convenient.


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## jschmidling (Aug 3, 2019)

Patience not being one of my strong points, I came up with something to try while waiting for the bar stock.

One of the "souvenirs" salvaged from our fire was a pattern for cranks used in our "Maltmill" which the fire turned back into an aluminum blob shown in the attached pic.

After a few hours of cutting and milling, I came up with the two pieces needed for the rear mounted parting tool holder.

A few more hours and I had a finished prototype that works better than anything I have tried so far on my mini.

I was able to cut off a a 5/8" steel bar with no problems at all at speeds faster than I would have used if I still had my South Bend doing it the usual way.

There are a few changes I need to make but basically, it works as advertised.

Thanks for all the ideas,

Jack


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## mikey (Aug 3, 2019)

Glad it's working better. I wanted to tell you to strongly consider using a ledge under the tool holder. It anchors the tool solidly and makes any off-axis movement impossible. This matters a lot because of the very high cutting forces experienced with parting. 

The other thing I need to mention is that the thing that makes the parting blade so solid is the way it is held in the tool holder. You are using two bolts with washers and that may be enough but maybe not. If you do have issues with this design, consider a design that captures/traps the entire body of the blade like mine does. I found that this greatly increases rigidity.


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## jschmidling (Aug 4, 2019)

mikey said:


> Glad it's working better. I wanted to tell you to strongly consider using a ledge under the tool holder. It anchors the tool solidly and makes any off-axis movement impossible.



I noted that on your design and didn't quite understand what purpose it served.  By the time I figured it out, the vertical piece was too short to do the ledge.  If I re-do it when I get the bar stock, I will add that.  The way it is now, it is real easy to square up with a small square but with only one screw, it is not as stable as the ledge would be.

>The other thing I need to mention is that the thing that makes the parting blade so solid is the way it is held in the tool holder. You are using two bolts with washers and that may be enough but maybe not. If you do have issues with this design, consider a design that captures/traps the entire body of the blade like mine does.

Well, here is how that went....

After getting it to work, the first "improvement" I made was to make a full length strap with 1/8" steel.  It hopelessly cocked the tool when the screws were tightened.  I was able to get it to work once with a single washer as a shim on the non tool side.  I was never able to find that sweet spot again so I went back to the washers.

A little ledge on the non-tool side would be the way to do it but again, I was out of altitude.  As it is, I have about .020" of shim under the base to get it on center.

Will be interesting to see how the 1/16" blade works.

Thanks again,

Jack


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## jschmidling (Aug 5, 2019)

jschmidling said:


> Will be interesting to see how the 1/16" blade works.



Actually, it doesn't work.

First of all, I didn't read the description through and missed the fact that it is a "T" profile and I see no way this could be mounted in my rear mounted  holder or in the QCTP.  It can't stand vertical just by tightening the hold down screws and it squeels like a Banshee in use.

Secondly, it is bowed and there is no way to square it with the part.

Third, it is not really a T.  It is quite lopsided.  Almost no relief on one side and all the rest on the other.  It works a little better on the low relief side but still can not be square without shimming or some other bandaid.

In the information it states that P type implies or defines a T profile.

My P2 blade is perfectly flat and parallel and sits square in the holder when the screws are tightened.

What am I missing here?

Jack


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## ddickey (Aug 5, 2019)

Pics or a link?


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## mikey (Aug 6, 2019)

jschmidling said:


> What am I missing here?



What you're missing is that it sounds like you did not buy a P-type blade. Instead, you bought a "beveled-type" blade; a common source for these is China. Note that the side of the tool are simply beveled from top to bottom; there is no wider cutting edge




A P-type tool has a distinct top profile. It originally had a flat top but many also have a concave scoop on top nowadays. Patented by Luers, the P-type design had a 5 degree side bevel ground into the cutting insert material. 




The T-type blades are very similar to the P-type; I am not clear on their side bevel angle. You can essentially consider the P- and T-type blades functionally the same.


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## NortonDommi (Aug 6, 2019)

Yep, bevelled blade and they only go one way in the holder and that is with the flat square to the top side against the holder, thick bit,top, at the top.


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## ddickey (Aug 6, 2019)

These are T types.




__





						T-Type Cut-Off Blades H.S.S. | Somma Tool Company
					

View our line of T-Type Cut-Off Blades H.S.S.



					www.sommatool.com


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## jschmidling (Aug 6, 2019)

mikey said:


> What you're missing is that it sounds like you did not buy a P-type blade. Instead, you bought a "beveled-type" blade; a common source for these is




It's not beveled.  The thickness of the non-cutting part is constant.  Looks like a surface grinder step.  Problem is that the step is much deeper on one side than the other.  More like an "L" than a "T".  If it were flat on one side, it would work if that side is pressed against the holder but there is still a small step there forcing it out of square.

I gave up trying to get a better pic, but you can get the idea from this...







I called LMS and all I could learn was that he would send another one out.

Here is a link to it...





__





						Cut-Off Blade, P1 1929 - LittleMachineShop.com
					

Cut-Off Tools 1929 This blade is size P1.; High Speed Steel; Width: 1/16", Height: 1/2", Length: 4-1/2"; 1/16" x 1/2" x 4-1/2" M2 HSS cut-off blade. T...




					littlemachineshop.com
				




Seems to me that one needs a special holder for a T profile.

Jack


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## mikey (Aug 6, 2019)

Why not buy a decent blade from AR Warner or Somma? A parting blade can last a quarter century or more if cared for - spend the money on a good blade.


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## jschmidling (Aug 6, 2019)

mikey said:


> Why not buy a decent blade from AR Warner or Somma? A parting blade can last a quarter century or more if cared for -



Several very good reasons:

1. I will be 105 about that time and I figured that $7 worth is about all I would need.

2. I lost shop, business and 50 years of treasure in a recent fire and replacing everything with the highest quality just is not within my budget.

3.  Most of the companies I grew up with and respected no longer exist and the ones that do make everything in China and we have no way of sorting Chinese Junk from quality anymore.

4.  I gathered that LMS was highly respected by this group and thought I would get what they advertised.

5.  Until someone like you comes along and recommends a quality product, I am just groping in the dark and go for bargains assuming no great loss if junk.

Other than that, thanks for your help. 

Jack


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## mikey (Aug 6, 2019)

Jack, I understand being on a budget, which is why buying good stuff matters - buy the right thing once and take care of it and it will outlast you. I have an Eclipse P1-N parting blade that has been in use for nearly 30 years and it is still going strong; it was my first parting blade ever and I still reach for it whenever I part on my Sherline lathe. If you cannot afford a decent blade, PM me your personal address and I'll send you a good one.


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## royesses (Aug 6, 2019)

jschmidling said:


> It's not beveled.  The thickness of the non-cutting part is constant.  Looks like a surface grinder step.  Problem is that the step is much deeper on one side than the other.  More like an "L" than a "T".  If it were flat on one side, it would work if that side is pressed against the holder but there is still a small step there forcing it out of square.
> 
> I gave up trying to get a better pic, but you can get the idea from this...
> 
> ...



I have 2 P1 blades from LMS and they are symmetrical, unlike yours. Looks like you got a factory defect.
My holder for my 0XA QCTP is this:



Roy


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## jschmidling (Aug 7, 2019)

mikey said:


> Jack, I understand being on a budget, which is why buying good stuff matters - buy the right thing once and take care of it and it will outlast you. I have an Eclipse P1-N parting blade that has been in use for nearly 30 years and it is still going strong; it was my first parting blade ever and I still reach for it whenever I part on my Sherline lathe. If you cannot afford a decent blade, PM me your personal address and I'll send you a good one.



Thanks for your kind offer but it's not quite that bad.

When one has nothing but a few screwdrivers left, one has to assign priorities about what to replace and how much to spend on each item. In general, my strategy is to buy the least expensive thing that should do the job.  I buy almost everything through EBAY and PayPal because of the no hassle, nearly automatic refund if not happy.

I have had a few regrets (bench grinders, table saw, Mickey Mouse drill press to name a few) but in general I am getting back to being able to do many of the things I used to do.  I will probably never have a real milling machine or a foundry again but I am having a lot of fun.

A mini lathe isn't much of a lathe but it is infinitely better than no lathe.

I think I have the parting business under control now.  Strangely enough, the thin blade actually works pretty well upside down in the $30 CQTH as long as I make sure the flatter side faces to tool holder.

It didn't work at all in the rear mounted one but I think it's the washer business we discussed before.  The QC holder has a step on the back side that keeps the hold down level.

BTW, I was reading the thread on tool grinding samples that were to be passed around and wonder if that ever got off the ground.  I have a hard time understanding some of the views in the books and a model to work to would be worth a thousand pics.

Anyway, thanks again,

BTW  my email addy is no secret and my prefered way to communicate  jack@schmidling.com

Jack


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## mikey (Aug 7, 2019)

I'm sorry for the loss of your property; I'm sure it was really devastating and I hope you get back on your feet soon. Tough time in life to have to do that. If you change your mind about that blade, do let me know.

As for the model tools, contact @Z2V and he should be able to hook you up.


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## Nutfarmer (Aug 7, 2019)

jschmidling said:


> Several very good reasons:
> 
> 1. I will be 105 about that time and I figured that $7 worth is about all I would need.
> 
> ...


Sorry for your loss. Replacement is hard. The China thing is hit and miss. Mostly miss. Bought a 5C chuck that was was supposed to be with in .0002 .  It was so far out of wouldn't even mount on the spindle . Stay away from CME.


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## ttabbal (Aug 8, 2019)

Figured I would do some practice cuts with the toolpost. Not bad at all. Very stable, good finish, though I suspect I can do better with practice and honing my blade. 12L14, hand feed. It's very smooth to the touch. I also had the blade extended much too far. Good test though. 

I think it might be a tiny bit high still, milling off a little on the base to bring it into alignment. Doesn't look like it in the photo due to parallax.


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## mikey (Aug 9, 2019)

Yup, looks a bit high but the cut looks clean. When you get the tool height correct the tool will cut with very little resistance. It will cut accurately and much faster than you think.

As you found, the extension of a rear mounted tool is non-critical in this application, as is the speed. 

Good for you, Travis!


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