# Lathe Parting Tool Woes



## kuksul08 (Jan 20, 2013)

I have several parting tools, from 0.03125" to 0.125" width HSS. The top of the blade is flat. When viewed from the side, there is about 20 degrees of relief. When viewed from the top, some are neutral and some have some RH or LH rake. I set the top of the cutting blade to be inline with the center of the material like a turning or facing tool.

The problem is that when parting aluminum, it packs up on top of the blade and stops cutting. It also leaves a very ugly surface finish on the material on each side because it is not cutting well - more like smearing.

What type of blade grind should I be using? Should the surfaces be perfect after parting or is it normal to have to flip and face the piece afterward?


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## gadget_lover (Jan 20, 2013)

Think of a parting tool as any other turning tool. The cutting edge has to be sharp and it has to be at the right height. 

My favorite parting blade for aluminum is .063 HSS blade. I've ground a top rake on it. This provides a chip breaker. I've ground a bit of side clearance on it so that the widest part is the top edge. I hone the top and front edges with a diamond coated nail file. 

I part with a constant drip of tap-magic gold. I back it out to clean up chips frequently. 

I seldom have to clean up a parted surface, assuming that I use the right or left handed one to put the pip where I needed it.

Dan


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## Tiresius (Jan 21, 2013)

center height is key in parting cleanly...i ran into this problem with facing as well and fixed it with a milled plate to compensate for the tools being slightly lower.

Whatever you do, do not engage the feed to auto for parting. You'll break some parts and something will go flying. I've had this problem and the bit went crooked with the aluminum flying away.

Do what Dan mentioned about pulling the parting tool out. When it packs up above the blade, pull it out to clean off the shavings and use it again.


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## kuksul08 (Jan 21, 2013)

Ahh okay, so it's normal to have to back it out? I am going to re-sharpen my blades and try the cutting fluid drip. Thanks for the tips!


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## gadget_lover (Jan 21, 2013)

Also, if not doing it already... 

Lock the carriage so that it does not move. If you do not have a lock, you can engage the half nuts and then push the tailstock up against the carriage so that it's trapped in place. 

Make sure the gibs are tight on the cross-slide as well as the compound. Lock the compound if you have a compound lock.

Make sure the parting blade is EXACTLY perpendicular to the part. The blade should not rub on either side as it advances.

Good luck.

Daniel


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## tylernt (Jan 23, 2013)

Are you using a tapered or "T" shape blade? Is it placed in the holder straight up and down? Some cheap holders will let you put the blade in tilted, which creates rubbing.

If parting large diameters in solid stock (say, 1" or more), I like to step-part. Plunge a couple hundred thou, then back out and move the carriage over (to the _waste _side  ) anywhere from one half to one full parting blade width. Then plunge anew. After another couple hundred thou, back out and step back to the original position. This keeps the slot wider than the blade, for chip evacuation and lubricant application.

...and you do need lubricant. A lot. For aluminum, WD40 works well for me. If you are getting "BUE" or Built-Up-Edge where the Al is melting and sticking to the tool tip, you probably need way more lube. I like to use a chemistry "wash bottle".


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## kuksul08 (Jan 25, 2013)

Thanks for the tips. I actually have both tapered and T shaped blades, but mostly use the T-shaped blades. My holder is actually a modified turning tool holder since I don't have a parting tool specific holder. Probably should get that... but mine is modified to make sure the blade stays vertical.

I'll give this all a shot. Thanks again.


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## P.J (Jan 25, 2013)

I run parting tools a smidge above centre height to compensate for thedownwards flex in the blade while it's working, kerosene is aluminums best friend for cutting. Run the lathe between 1000 & 1500 rpm depending on cnc or manual lathe, the size of the piece the depth of the cut, the quality of the machine and your level of competence. Get rid of the hss tools and convert to tungsten carbide inserts unless you're after tiny width cuts. Like other said make sure your blade is square with the piece and lock the top slide, I typically wouldn't lock the carriage unless you have a particularly light carriage, I've only worked large machines so I can't comment on the small ones. Gentle feed into the piece but doubt let the tool dwel, make it work and if the material stops flowing get the tool out of there.


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## P.J (Jan 25, 2013)

tylernt said:


> Are you using a tapered or "T" shape blade? Is it placed in the holder straight up and down? Some cheap holders will let you put the blade in tilted, which creates rubbing.
> 
> If parting large diameters in solid stock (say, 1" or more), I like to step-part. Plunge a couple hundred thou, then back out and move the carriage over (to the _waste _side  ) anywhere from one half to one full parting blade width. Then plunge anew. After another couple hundred thou, back out and step back to the original position. This keeps the slot wider than the blade, for chip evacuation and lubricant application.
> 
> ...and you do need lubricant. A lot. For aluminum, WD40 works well for me. If you are getting "BUE" or Built-Up-Edge where the Al is melting and sticking to the tool tip, you probably need way more lube. I like to use a chemistry "wash bottle".



If you're Ali is melting your tool is rubbing and the chip is not carrying away the heat. You should be seeing material streaming off the tool, it you're not you're doing it wrong.


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## gadget_lover (Jan 25, 2013)

RE: the speed when parting....

Parting really is a type of turning so surface speed applies just like it does when turning a piece. The speed should be set based on the diameter of part. If you have the capability it's even worthwhile to increase the speed a bit as you get close to the center. In reality, just like most people, I just pick a speed and go for it. 

Daniel


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## precisionworks (Jan 26, 2013)

kuksul08 said:


> ... but mostly use the T-shaped blades.


Those were state of the art during WWII 



> ... I don't have a parting tool specific holder.


That needs to be your next purchase. Small machines do well with something in a GTx insert that's between 1.5mm & 2mm wide. 

My 14" machine is pretty heavy & that allows using a huge 2.4mm GTN insert (.093" wide). Smaller & lighter machines do better with narrower inserts but don't go too small like a 1.0mm, they are fragile. A 1.5mm is a good width for a smaller machine.



> You should be seeing material streaming off the tool, it you're not you're doing it wrong.


+1

A narrow carbide parting insert will throw off ribbons of aluminum.


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## wquiles (Jan 26, 2013)

gadget_lover said:


> Lock the carriage so that it does not move. If you do not have a lock, you can engage the half nuts and then push the tailstock up against the carriage so that it's trapped in place.
> 
> Make sure the gibs are tight on the cross-slide as well as the compound. Lock the compound if you have a compound lock.
> 
> Make sure the parting blade is EXACTLY perpendicular to the part. The blade should not rub on either side as it advances.



+1

Excellent tips. Each one of those tips is very important, and each one helps a little. When you do them all, you got the best chance at success


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## kuksul08 (Feb 1, 2013)

Daniel, awesome help.

Might as well go carbide indexable since I'm already using them for steel and aluminum turning & boring.


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## PCC (Feb 3, 2013)

Make sure your parting tool is sharp. I know, this seems like an obvious thing, but, it happens. The other day I was parting a piece of 5/8" diameter 7075 T6 and it seemed like I was driving my parting tool in with a lot of force. At first I thought it was because I had not worked 7075 before and that it must be tougher to cut. After struggling with it for a few minutes I decided to see if sharpening would help. Three seconds on the grinding wheel was enough to make the parting tool cut that 7075 like butter! It took about the same amount of time to cut the remaining 90% of the way as the first 10% did with the dull tool.


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## kuksul08 (Feb 3, 2013)

Do you sharpen the blade simply by grinding the front back a bit, or do you also grind on the top of the blade? some of the blades I have were ground in all sorts of weird ways.


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## gadget_lover (Feb 3, 2013)

I grind the front and the top, so there's a little top rake. 

In between grinding I touch up with a diamond hone tool. It's like a nail file but with diamond dust. I also use the diamond hone to put a better edge on carbide inserts.

Daniel


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## FlashKat (Feb 3, 2013)

Some cutting oils do not work well with aluminum. 
Try slowing down your RPM, and use WD-40.


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## PCC (Feb 3, 2013)

My parting blade already has the top cut, u just needed to touch it up and get the edge on it.


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## Clark (Feb 10, 2013)

Parting is a lot of woes for me.
Maybe I need to get past WWII.


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## richief (Feb 14, 2013)

yes all tips pretty much as I have good experience with too, I especially agree with Dan on honing tool bits for aluminium, as some alloys are gummier than others and grinding and honing with finer stones, really helps bits from friction, and loading up with aluminium.
Summary
Center height, tool square to work, toolbit ground square, with clearances and chip breaker, honed smooth, speed not too fast, keep tool plunging, or retract immediately to avoid dwelling toolbit, cutting fluid. 
I also have insert type parting tools, but find HSS is just fine for aluminium.
Glad to be here this site is very interesting.
New guy
Rich


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## Lathedog (Feb 14, 2013)

Need lube as stated on aluminum.make a huge difference.steady feed rate is also important.


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## precisionworks (Feb 15, 2013)

gadget_lover said:


> I also use the diamond hone to put a better edge on carbide inserts.
> 
> Daniel


Tooling engineers spend hundreds of hours designing inserts for specific applications. How do you improve on a design that is already optimized? Also, the majority of inserts today are coated & that means the carbide substrate never touches the material - all cutting is done with the coating. Honing a coated insert removes the coating & makes it perform the way inserts did in 1990.


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## gadget_lover (Feb 15, 2013)

precisionworks said:


> Tooling engineers spend hundreds of hours designing inserts for specific applications. How do you improve on a design that is already optimized? Also, the majority of inserts today are coated & that means the carbide substrate never touches the material - all cutting is done with the coating. Honing a coated insert removes the coating & makes it perform the way inserts did in 1990.



 Well, it all depends on your starting point. You get the right tooling for the alloys you are working on. You have some really nice coated inserts. I have inserts that I bought when I was still trying to figure out what "center height" meant. Some are pressed, some are coated, some are new and some are used.

The cheap ones are not ground, they are pressed and have a decidedly rounded edge. They cut better on a small lathe with a well defined edge. Once worn I can get a bit more use by touching up the edge.

To be honest, I have only one parting blade that uses carbide inserts and have not used it much. I don't recall needing to do anything to it. My old HSS blade works well for just about all my work. 

Daniel


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## caveBob (Feb 17, 2013)

I'm still learning the ropes with my lathe and don't know what type/size you have, but maybe this will help... coming at it from the back side & upside down:

Rear-mounted Parting Tool Holder for Sherline Lathe
http://www.machinistblog.com/rear-mounted-parting-tool-holder-for-sherline-lathe/

Rear Tool Post
http://www.hemingwaykits.com/acatalog/Rear_Tool_Post.html

REAR MOUNTING TOOL POST (MLA-6)
http://www.statecollegecentral.com/metallathe/MLA-6.html

I haven't made one of these yet... it's on the list of todos...


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