# Grinding parting tools



## pkastagehand (Mar 13, 2012)

I see a few threads on parting and the setup on the lathe but only found 1 on grinding the tool and it looked different than the tool I am trying to use.

I have one the QC tool posts with the tool holder and blade (imports). The top surface of the blade has that bevel along one edge to help hold it in the tool holder.  It is about 1/8" wide. I am finding nothing in my books or online that shows the geometry for these. Anyone point me to some pictures?

Paul


----------



## n4zou (Mar 13, 2012)

This video will show you how and why.
[ame]http://youtu.be/82LtUTBmxwQ[/ame]


----------



## pkastagehand (Mar 13, 2012)

Thanks for that link. I've looked at some other Tubal Cain videos but hadn't thought of him for this. Very useful and informative.

But he still didn't address the issue of that beveled corner and how that affects the cut. Maybe it acts like the carbide tool he showed that causes the chip to curl a bit so it clears the slot better? Or does the one with the bevel on one top corner need to be ground with a back rake or something to get rid of the bevel?

Paul


----------



## Tin Falcon (Mar 15, 2012)

parting tools for holders are pretty basic. there is a the T style and the taper style . they are flat on the top and only ground on the end. the end should favor the right hand side so the right and side cuts first this keeps the nip on the parent metal instead of on the part. A trick you will not see anywhere else is you can grind a thin slot in the end make it look like a snake tongue. this can dampen vibration. a cutting disk on a dremel tool works well for this. 
Tin


----------



## lensman57 (Mar 17, 2012)

pkastagehand  said:
			
		

> Thanks for that link. I've looked at some other Tubal Cain videos but hadn't thought of him for this. Very useful and informative.
> 
> But he still didn't address the issue of that beveled corner and how that affects the cut. Maybe it acts like the carbide tool he showed that causes the chip to curl a bit so it clears the slot better? Or does the one with the bevel on one top corner need to be ground with a back rake or something to get rid of the bevel?
> 
> Paul



Hi Paul,

If by bevel on one edge you mean that the tip of the cutting tool in ground to a 5 degree angle to the right then the purpose is to be able to part off the piece and then continue to advance the tool to get rid of the nib that otherwise would be left on the remaining stock. Think of it as a facing tool. Other than this I have no idea, you could also try and grind a little groove on the top tip of the tool to help the swarf curl away from the cutting surfaces, almost all of the carbide indexible tool tips have either one or both of these features. If you wish to grind the groove it is best achieved with a dremel and a carbide grinding wheel, the depth of the groove is quite shallow. See the link below for the tool geometry.
http://www.aloris.com/index.php/pages/Carbide Insert Cut-Off & Grooving.html


----------



## rkepler (Mar 17, 2012)

I like the "P type" parting tools, they're T shaped and the middle of the top has a little dip and the sides are relieved from the vertical a couple of degrees. You usually present them to the work with about 4-5 degrees rake and I grind about 6-7 degrees relief in the front. That makes it that only the cutting edge touches the work so there's no friction to eventually jam things. The dip in the top helps to 'crunch' the chip a bit so it's narrower than the cut and so clears well. 

Generally, if I'm not using the GT type carbide I'm using a .093 P type parting tool (if I'm cutting small brass tubing I'm likely to use either a Kaiser Thinbit or a Nikole tool, they both go down to razor blade thickness). If I think I need a really sharp tool I'll use the P type and hone it right be using it - it's needed on aluminum bronze and works well on other bronzes.


----------



## pkastagehand (Mar 21, 2012)

Here is a section view of my tool. Note the bevel across the top. Do I have to sharpen that flat and provide back rake? This bevel runs the length of the tool and I presume is for helping anchor it in the holder.





parting tool by stagetech56, on Flickr


----------



## lensman57 (Mar 21, 2012)

pkastagehand  said:
			
		

> Here is a section view of my tool. Note the bevel across the top. Do I have to sharpen that flat and provide back rake? This bevel runs the length of the tool and I presume is for helping anchor it in the holder.
> 
> 
> 
> ...



Hi,

I am no expert at grinding tools but if the cross section shown is the front of the tool as presented to the stock then I think you might have an issue with placing the tool on the center line. The parting tools sre usually only sharpened at the cutting edge.


----------



## Tin Falcon (Mar 21, 2012)

I have never seen one made like that. when it comes to paring tools only buy good ones like from LMS Warner or a name brand from MSC,enco etc. I bought one from harbor freight there was no real geometry cut into it. where di yours come from??
Tin


----------



## Ramon (Mar 21, 2012)

Hi Paul 
I have just seen your request and feel I may be able to help. 

I have used the QC type parting tool holder with blades as you show sectioned for many years. Indeed I currently have three holders containing similar blades set up.

It appears to me that the bevel you are refering to is that for the clamp that holds the blade into the holder to register against and apply a certain amount of down as well as inwards force.

To use the blade needs grinding back on the top surface for as long as you desire (in front of the clamping area) removing the top surface to below the bevel. You can apply a degree of back rake at the same time too if you desire. Grinding down too far will have the effect of reducing the blade width and so limits the depth the tool can be plunged. The same applies to too much top rake - as you grind the front to re-sharpen the height of the blade gradually diminishes. 

This is the reason I have aquired three tool holders over the years - all ground to suit differing widths/lengths using the same blade sizes.

Hope I'm reading your question correctly and that that that helps some 

Regards - Ramon


----------



## Tin Falcon (Mar 21, 2012)

looks like your bit is of the armsrong type . look here
http://www.arwarnerco.com/warner_products_cut-off-tools_specs.html
Tin


----------



## Omnimill (Mar 21, 2012)

I have blades like that as well, Ramon has it right. Just grind it flat with a bit of rake.

Vic.


----------



## lensman57 (Mar 21, 2012)

Ramon  said:
			
		

> Hi Paul
> I have just seen your request and feel I may be able to help.
> 
> I have used the QC type parting tool holder with blades as you show sectioned for many years. Indeed I currently have three holders containing similar blades set up.
> ...



Hi Ramon,

I am sure that your advice is correct, what I don't understand is how an advantage is gained from manufacturing a blade with such profile if it has to be ground flat again?

Regards,

A.G


----------



## Ramon (Mar 22, 2012)

Hi A.G.

I don't think it is intened for any advantages as such merely a manufacturing process. Unlike an inserted tip blade or some other types of HSS blades they are not bought as 'ready to use'.

I have just been out to the workshop and took these which may be of help....






The left and centre holders have blades as described by Paul. The broken, central one was ground to 1/16th width back about 3/4" which, with a little side rake on each side made it rather thin. As you see a momentary lack of concentration lead to it's disappearance 





This is the most recent holder bought with blade as supplied. This has only been ground on the top and front faces and is, for all intents and puposes, 'full width'.





This is the original holder bought circa late seventies and still has the original but now very short blade. As you can see this has the bevel ground all the way across the top face as is the spare blade.

Hope this helps explain a little more - if nothing else it's motivated me to regrind that broken blade 

Regards - Ramon


----------



## lensman57 (Mar 22, 2012)

Hi Ramon,

Thanks for taking the trouble to post the photos.

Regards,

A.G


----------



## tomfilery (Mar 22, 2012)

Lensman,

My parting tool is slightly different from pkstagehand's diagram, in that where his shows a horizontal element on the top (and only one bevel), mine has a pair of bevels rising, to a peak (though not dead central on the blade). I don't grind it flat when sharpening the tool and it works fine! Ramon's is different to mine in that his only appears to have a single bevel.

My blade came as part of a SOBA set.

Regards Tom


----------



## Blogwitch (Mar 22, 2012)

As Ramon has shown, there are no such things as 'magic' parting off tools that will do every job.

The longer you are in this game, the more you collect, and you will soon find that you need specific grinds for specific jobs and materials. Just doing one type of grind will only get you through the job you are doing at the time. Parting off say a larger diameter or different material, you will most probably have to regrind the tool to a different shape.

I must have at least a dozen knocking about my shop, all geared to certain types of job and materials, no one is a favourite as such, just a couple are more 'universal' than others, and so tend to get used a little more often.

A good example is just by putting a tiny "chip breaker" groove at the back of the cutting edge can sometimes transform the way a tool will cut certain materials.

There is a lot of experimentation and experience required to get your head around parting off, and getting good results most of the time, so don't worry too much in the early stages of your learning curve. It is only like any other machining regime, where you have to get the 'feel' for the job in hand. Some people struggle all their lives with parting off, whereas most mainstream machinists, it is nothing that needs to be concerned over. 
Eventually things will 'click', and all of a sudden, parting won't be such a thing to be feared. 
I personally never had any problems with parting, because in my early learning days, I was so naive, I didn't realise that it could be a problem. I just did it to how I thought it should be done. 

At times, just too much theory can be pushed at a subject, and so cloud over what is trying to actually be achieved.

Do I do this, or that? Should I have top rake or not? etc etc. Whereas really, you should be looking at your material and diameter, and set the tip up as you would for normal turning, say no top rake if cutting brass etc, and as experienced is gained, you will automatically know how to grind your parting blade to do the job. No more, no less.

Then you only have to get over the fear of plunging in almost as fast as you can go. Once you can do that, you've got it cracked.

Just as a side note, anything over 1/2" diameter, I just part off using my power cross feed, without even thinking about it, and that is not boasting, I'm just trying to let you know that it really is that simple, nothing to worry about at all.


John


----------



## lensman57 (Mar 22, 2012)

tomfilery  said:
			
		

> Lensman,
> 
> My parting tool is slightly different from pkstagehand's diagram, in that where his shows a horizontal element on the top (and only one bevel), mine has a pair of bevels rising, to a peak (though not dead central on the blade). I don't grind it flat when sharpening the tool and it works fine! Ramon's is different to mine in that his only appears to have a single bevel.
> 
> ...



Hi Tom,
This is very inyteresting as I have not seen one of those, is there any chance that you could post a photo of it, I am just curious.

Regards,

A.G


----------



## tomfilery (Mar 23, 2012)

Lensman,

Photos as requested:-

End-on showing the "peak" running along the top of the tool.

Regards Tom


----------



## tomfilery (Mar 23, 2012)

Lensman,

And side view - pretty much as per Ramon's (but without the shaped tip).

Regards Tom


----------



## lensman57 (Mar 24, 2012)

tomfilery  said:
			
		

> Lensman,
> 
> And side view - pretty much as per Ramon's (but without the shaped tip).
> 
> Regards Tom



Thanks a lot Tom for posting the photos, that is one hell of a well designed tool in its correct holder.

Thanks for sharing this,

Regards,

A.G


----------



## pkastagehand (Mar 28, 2012)

Thanks for all the input. Lots of info there and I didn't realize there were so many variations.

So, Tom, as regards your double beveled top profile do you just grind the front relief and you're good to go or do you do as others suggest and grind a back rake to get a flat cutting edge?

If you don't grind off that double top bevel do you think I could get away with not grinding my single top bevel? In some ways it seems like a way to have it remove the tit from the parted off piece if the flat side is set at center. But it may also mean I have some slight side thrust that may cause problems and the beveled side would be below center which may also change the dynamics.

Paul


----------



## Ramon (Mar 28, 2012)

Paul, double or single bevel, the blade is not shaped as a 'cutting edge' as bought, they are just HSS blanks. 
If you consider it - presenting this to the work as is presents a tool with negative side rake on both sides with the double and an unbalanced profile with the single. I'm not saying it doesn't work (I can say I've never tried it) but I think you will find it will cut much better with a slight amount of top rake ground on and a lot less inward cutting force required too.

Without wishing to labour a point heres that broken tool from the previous pics as reground






If you are not convinced then try grinding just a short piece back - say 2-3mm and see how the cutting improves. If you're still not convinced then all you need do is grind it back.

BTW you do not have to grind the side faces as shown above. This was done simply to reduce the width of the tool for my personal situation but the top angle is about right for most save brass where it is better to have zero top rake.

As John says - many do find parting off a real stumbling block compared to the rest of the turning operations - giving yourself a head start with sharp tooling will be a big help.

Regards - Ramon


----------



## tomfilery (Mar 29, 2012)

Paul,

No - I just leave the double-bevel top of the blade as it comes. I know that what Ramon says (about them just being blanks which need grinding) is correct, but I didn't bother and it works for me (I have an ancient Myford Super 7).

I rarely have parting problems (but tend to only work on stock less than an inch diameter). 

Regards Tom


----------



## pkastagehand (Mar 30, 2012)

Thanks everybody for the input.

Ramon, what you're saying is what I've always done in the past. I just hated that I end up with something less than full blade with with that top rake and so needing to grind off and start over (or grind some side relief farther back on the tool) for a longer reach. I suppose I could do like many of you and have several parting tools for different purposes/materials/depths of cut, etc. Just hate spending money if I don't need to. 

Tom,

I have tried parting CRS with an unground top with that funny (Armstrong) profile and it worked but I wasn't pleased with it overall. Might work OK in other materials, especially brass?

I will possibly buy a couple more tools and have some different shapes eventually but for now will probably just go back to putting the top rake on it.

Paul


----------

