Thread: Parting Off Blade/Tool Advice

Yep. Parting off is one thing I really struggled with when I first started playing on my lathe. Got to the stage I wanted to part with my eyes closed because I knew what was coming...... Ping! and a piece of part off blade bouncing off the roof.

As usual, it was my fault. Wrong tool geometry etc. Now I seem to get it right more often than wrong and when I get it wrong I can tell straight away by how the tool cuts/feeds and stop and re-adjust. If the tool does not cut like butter then something is wrong. For larger diameters I will often cut two blade widths to give the blade clearance. I also generally err on a slower speed too. As pointed out above, I can't come up with a reason to purchase a TC parting tool. Well, not for my circumstances anyway. I part off blade cost me $20 and lasts many years. I guess if I have to part off a harder type steel then I may look at purchasing an indexed part off tool holder. But for now, parting off is one of those little jobs like screw cutting..... A skill that used to haunt me and now I can do, which makes it so much more enjoyable when I do it.

Simon

Originally Posted by BobL

I just use my EE inverted parting tool as a regular mounted parting tool and I found it works really well.

Do you use their tool holder and T Blade or just their T Blade in a generic tool holder? I'm thinking of buying the Ausee HSS tool holder and blade and see how that goes and maybe down the track buy the T Blade from EE.

Hi BaronJ,

A short explanation of how Ecentric Engineering's FoR Inverted Parting Tool is used should clear up the confusion.
When the EE FoR IPT holder in used in the front tool post, the parting blade is mounted upside down, so the lathe needs to be run in reverse for the tool to cut. Hence it could potentially screw off a screw mounted chuck. It achieves the same thing as using a parting tool in a rear mounted tool post for those of us who don't have the option of a rear mounted tool post.
Hope this helps.
Alan

Even neutral geometry TC parting inserts are generally dished or have other geometry on their top face to curl the chip in on itself so it clears the parting groove. That can be especially useful if parting larger diameter parts. HSS blades are either flat or ground left or right. Clearing the chip is essential, if it doesn't clear it's very likely to cause issues.

Parting blades are generally set at or below centre. Tailstock support can normally be used and then just withdrawn for the final parting off. Parting is typically a lot more aggressive than many people realise, and the natural reaction is to take it very gingerly. In fact if you're having issues more often than not they can be overcome by feeding harder. Try playing with the speed, easier with a VFD. The ideal speed will vary with diameter. A narrow blade is generally preferred for smaller lathes, as it will put less demand on the lathe's rigidity, however it may limit the DOC available.

Hi Alan,

Thank you for that info !
I didn't know about the Ecentric Engineering parting tool set up. I agree, if I did that on the Myford the chuck would definitely unscrew.

I just had a quick look at Eccentric Engineering's site on this parting blade, and it looks ok to me. I think people could do worse than equip their small lathe with that tool. It is very thin however. I didn't go through all the information provided, but grinding the one face of a parting tool isn't a big deal, that's how the blades are normally sharpened anyway. The EE blades are however hollow ground, and for a thin blade like that I think that would be good as I haven't seen that in regular parting blanks.

One thing that was emphasised is the lack of overhang, and that's something that shouldn't be ignored. Here's a blade holder I made a while back with that in mind, the normal blade holders go in an AXA holder, then the whole stack goes onto the toolpost. It's a bit of a recipe for disaster and incorporating the dovetail in tool body helps a lot. They're not especially difficult to make.

P1010739.jpgP1010741.jpgP1010742.jpgP1010743.jpgP1010745.jpg

Here's a tool I made to, err, make the other tool

Dovetail tool.jpg

Originally Posted by Pete F

Parting is typically a lot more aggressive than many people realise, and the natural reaction is to take it very gingerly. In fact if you're having issues more often than not they can be overcome by feeding harder.

Pete F
Man Oh man! Isn't that the truth.

Once you have experienced that bump,bump, grrrrind, crunch, and then shattering CRAAAACK of a breaking parting tool it is then very hard to then disregard that psychological impulse to gently sneak up on any subsequent cut you are brave enough to attempt.

I have had good results from hand feeding the cross slide in and feeling that constant firm load against the tool.
On some materials, you can observe the chip comes off in little curly C shapes and one face of the chip is often looking like it is polished.
To me, that's the indicator that the cut is progressing well.

Grahame

I found HSS is nothing but problems unless you use an oil lubricant constantly dripped onto the workpiece.

Once I moved to carbide inserts I never looked back.

Originally Posted by .RC.

I found HSS is nothing but problems unless you use an oil lubricant constantly dripped onto the workpiece.

Quite true!

I use a 20 mml syringe with a empty metal pen ink refill tube substituted for the needle.

The tube allows me to deposit just enough lube so a big mess is avoided.

It is the dark sulphur based lube and quite thick.Its thick enough not to be flicked off by the job rotation.

Probably cancer laden but since I don't eat it I will probably get away with it.

Originally Posted by Pete F

... HSS blades are either flat or ground left or right. Clearing the chip is essential, if it doesn't clear it's very likely to cause issues.

Not 100% sure so don't quote me, but I believe that the right or left grinds are to cut off the little nub that gets left. However, I find that for anything except the shortest length of parting blade protruding, that bias is enough to pull the tool off to one side. As well as then making the end concave (or convex), that can also lead to chip clearance issues. I would suggest sticking to a straight grind to start with.

Originally Posted by Grahame Collins

Once you have experienced that bump,bump, grrrrind, crunch, and then shattering CRAAAACK of a breaking parting tool it is then very hard to then disregard that psychological impulse to gently sneak up on any subsequent cut you are brave enough to attempt.

If you are fortunate enough to have power feed on your cross slide, I would suggest using that - provides a lot more constant pressure on the tool.

Another thing that people do is slow down for parting. Sometimes you have to, but it should not be necessary. HSS will cope but carbide will not like it very much. The material being turned does not recognise that the tool you are using is a parting blade and so it should adopt a different optimum cutting speed. A typical industrial carbide tip in particular does not like running slow or lightly loaded (there are probably some designed for doing that, but the trade off would be a short life if run at anything other than optimal conditions.

Michael

[QUOTE=M



If you are fortunate enough to have power feed on your cross slide, I would suggest using that - provides a lot more constant pressure on the tool.

[/QUOTE]

I've never had the balls to part off with power feed, even on the work lathes. Definitely not on the Hercus.

Originally Posted by Michael G

I would suggest sticking to a straight grind to start with.

Agreed.

Originally Posted by bwal74

I've never had the balls to part off with power feed, even on the work lathes. Definitely not on the Hercus.

Me either!

I solved most of the parting-off problems on my Hercus with an AXA parting tool holder that holds a T shaped blade at 7 degrees to horizontal. The VFD helps a lot too. As does a frequent touch-up of the blade on the CBN wheel. And lube- lots of lube.

Originally Posted by Briangoldcoast

I have an Eccentric Engineering FoR Inverted parting tool, and for my money its unbeatable.

I also have the Eccentric Engineering FoR Inverted parting tool, Works VERY WELL, Makes Parting off easy,

Check it out: https://www.eccentricengineering.com...chk=1&Itemid=3

Regards
Ray

I did so parting off in the lathe today.

First I switched the blade around and put a new insert in. It seems to work ok on brass and aluminium, I didn't try it on MS or harder.

I then got out an old parting off HSS tool holder (I had to mill couple a couple off mm to make it fit in the AXA tool holder) and gave that a crack on some brass. It cut really well.

I had a another HSS parting off blade in another Lock tool holder which I had been using in my old shaper. It's geometry was way out so I re-ground it and had a go with it on brass as well. It worked really so I gave it a go on some MS (about 20 mm dia) and it well too. Then I re-ground it again and pretty much stuffed it. Played around some more and got it back to reasonable results. There's tearing marks on the face of the work but it'll do for now.

I do admit using the HSS blade seems much easier and less frightening than the insert blade.

I wouldn't mind getting the EE parting off blade as I have the EE turning tool and it works really well. Or I may just get the Ausee one.

Ben.

Originally Posted by bwal74

I've never had the balls to part off with power feed, even on the work lathes. Definitely not on the Hercus.

Yes I agree, on a heavy machine I think it's possibly worthwhile, I don't know I have no experience there. I guess a squillion CNC machines can't be wrong however But on a noodle like I have the feel of how much pressure you're putting in and ability to change the rate of cut is pretty important.